摘要:

Atmospheric pressure capacitively coupled plasma source for the direct analysis of non-conductive solid samples† Sorin D. Anghel,a Tiberiu Frentiu,b Emil A. Cordos,*b Alpar Simonc and Adrian Popescuc aDepartment of Physics, Babes-Bolyai University, M. Kogalniceanu 1, 3400 Cluj, Romania bDepartment of Chemistry, Babes-Bolyai University, Arany J 11, 3400 Cluj, Romania cResearch Institute for Analytical Instrumentation, P.O. Box 717, PO 5, 3400 Cluj, Romania Received 8th September 1998, Accepted 4th January 1999 An atmospheric pressure capacitively coupled device for the rf sputtering and direct analysis by AES of nonconductive solid samples was developed.It operates at 13.56 MHz, with Ar flow rates lower than 1 l min-1 and rf input powers between 20 and 50 W. With the aim of studying the expulsion mechanism and determining the analytical performance, the following materials were used: ZnO with known content of trace elements (Si, Pb, Cd and Na); four andesite standards with certified contents of Pb, Cu and Cr; and a synthetic ( laboratory made) andesite standard.The expulsion mechanism depends on the rf power. Below 38 W, the sputtering rate is nearly constant and the atomisation is produced only by sputtering. At powers higher than 38 W, thermal evaporation will be present in addition to rf sputtering. All measurements for evaluating the analytical performance were made at optimum working parameters (rf power=36 W, Ar flow rate=0.5 l min-1).The detection limits are 0.3, 0.7, 1.0 and 0.9 mg g-1 for Na, Pb, Si and Cd, respectively, in the ZnO matrix and 0.8, 1.0 and 0.5 mg g-1 for Pb, Cr and Cu, respectively, in the andesite matrix. The dynamic range for Pb is about three orders of magnitude. The relative standard deviations for Pb in the certified standards are between 1.7 and 12.7% and the recoveries compared with the certified values are between 95 and 104% for the concentration range 5.8–35.1 mg g-1.and its most challenging problems are related to non- Introduction conductive samples. Over the last few decades, plasma excitation sources for Low pressure plasmas have become sampling systems; in analytical atomic emission spectrometry (AES) have been well the 1980s, glow discharge (GD) techniques experienced rapid characterised as sensitive spectral sources. After considering growth.2,3 The increased interest in this technique is attributed all of the characteristics of plasma sources that make this almost totally to its performance in the analysis of solid technique very popular, one problem area still remains unre- samples. One of the most exciting areas of GD development solved: sample introduction process versus sample state.is the coupling of radiofrequency powered GD with various Therefore, sample introduction is one of the most fertile spectrometric techniques.4 In this way, rf sputtering has research areas in AES. become a sample introduction method and the analyses are As emphasised by Blades et al.,1 the sample must be no longer limited to conductive samples.presented to the spectral source in a form that the source can Capacitively coupled plasmas, sustained at atmospheric accommodate easily using a method that ensures good trans- pressure, have been used for direct solid sampling in a relatively port eYciency towards the spectral source, is optimum for the few cases. Pless et al.5 used a capacitively coupled microwave particular sample and provides the best opportunity for plasma for sampling and excitation of solid samples, placed obtaining the required information.in W cups and introduced into the plasma. This type of plasma For samples in the solid state, there are basically two routes. has also been used for the direct analysis of steel samples.6 The first consists in dissolving the solid with a suitable solvent Radiofrequency capacitively coupled plasmas (rf CCPs), susand presenting it to the spectral source in liquid form, using tained at atmospheric pressure, were used by Liang and the specific techniques for liquid sample introduction.In some Blades7 and Anghel et al.8 to analyse conductive samples (low particular cases (when the geometry and the mode of operation or medium alloyed steel ) by the AES technique. In these of the source permit), the sample atoms and ions can be sources, rf coupling was achieved in diVerent electrode geoliberated directly from the matrix through thermal evapo- metries, but in both cases the sample was one of the discharge ration, sputtering or ablation.The idea of solid sampling is electrodes in direct contact with the plasma. The possibility of based on the fact that in devices where the discharge is in easy adaptability to solid sampling requirements and direct contact with the electrodes (or with the sample), material analysis of conductive solid samples was highlighted.The rf expulsion could take place. For this situation, the vaporised CCP discharge also has the advantage that it could be mainmaterial is entrained in a flow of gas and transported to the tained at low powers (from 300 down to 10W), at atmospheric plasma spectral source. pressure and with low gas consumption (usually1 l min-1).9 Without any doubt, direct solid sampling provides a good In previous publications from our laboratory, the developopportunity to avoid lengthy sample preparation procedures ment and characterisation of atmospheric pressure rf CCP torches for AES in various electrode configurations (tip–ring, tube–single ring, tube–double ring) were described.10–15 These torches have been used mainly for the analysis of liquid †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998.samples. The rf CCP achieved with these torches could be J. Anal. At. Spectrom., 1999, 14, 541–545 541Fig. 1 Experimental set-up.modified in order to carry out atmospheric pressure rf Fig. 2 The sputtering chamber. 1=Tungsten electrode, diameter sputtering of non-conductive solid samples. 4 mm, 45° (connected to rf ); 2=upper PTFE lid; 3=PTFE electrode In this paper, we present results obtained by applying an rf holder, 12 concentric holes, 1 mm id; 4=quartz chamber, 14 mm id, CCP discharge for solid sampling and direct analysis of non- 100 mm length; 5=PTFE sample pellet holder cup; 6=brass counter conductive samples, viz., oxides and silicates.The original electrode; 7=lower PTFE lid; 8=Ar inlet; 9=Ar outlet; 10=lateral tip–ring rf CCP design11 has been modified to provide the port, 5 mm id, 50 mm length. sampling and excitation conditions. This modified rf CCP torch allows both solid sampling of non-conductive samples electrode holder (12 concentric 1 mm id holes). The sample and direct analysis of such samples by AES. pellet was placed inside a PTFE sample holder cup on a plate brass counter electrode.The rf electrode and the sample holder were placed at the opposite sides of the quartz tube and fixed Experimental with two PTFE lids. The plasma viewing is ensured by the Instrumentation lateral port. The experimental set-up is shown schematically in Fig. 1 and Standards and sample pellet preparation details of the equipment used and the operating conditions are provided in Table 1. The experimental measurements were carried out on cylindrical sample pellets of two representative matrices: oxides (ZnO) The capacitively coupled plasma used for rf sputtering of non-conductive solid samples was obtained inside a tubular and silicates (andesite).For studying the analytical performance, the following quartz chamber (14 mm id, 100 mm length, with a lateral port of 5 mm id, 50 mm length) on a sharp tungsten electrode materials were used: ZnO powder (puriss. 99+%, from Research Institute for Semiconductor Materials, Bucharest, (4 mm diameter, 45°) (see Fig. 2). The plasma gas (Ar) was introduced inside the chamber via a gas inlet and a PTFE Romania) with trace elements (Si, Pb, Cd and Na) and as certified reference materials four andesite standards (Japanese, JA-1, JA-2, JA-3; and American, AGV-1) with certified con- Table 1 Instrumentation and operating conditions tents of Pb, Cu and Cr. Also, synthetic (laboratory made) Plasma generation Rf oscillator with inductive reaction and andesite matrices (57% SiO2, 18% Al2O3, 3% MgO, 7% CaO, grid tuned circuit: 13.56 MHz; 10–80 W. 3% K2O, 3% Na2O and 9% Fe2O3) were prepared with known Laboratory constructed contents of Pb (3, 10, 30, 100, 300 and 1000 mg g-1). Using Stabilised power supply BS 452 E type these synthetic and certified standards, calibration curves for (2×500 V; max. 400 mA). TESLA, Brno, Pb were constructed to establish the dynamic range and verify Czech Republic the analytical method.Stabilised power supply I 4104 type (40 V; 5 A). IEMI, Bucharest, Romania All the oxides were of high purity (Johnson Matthey Sputtering chamber and Laboratory constructed (Fig. 2) Chemicals, Royston, Herts., UK). plasma support gas High purity Ar, 0.1–1 l min-1. Azo-Mures, The raw materials necessary for pellet preparation were Tg. Mures, Romania mixed with 30 ml of ethanol in a mortar and stirred until Optics 110 mm focal length, 30 mm diameter homogeneous. This procedure was continued until the whole fused silica lens amount of the added alcohol had evaporated, and this pro- Monochromator Computer driven scanning type (1 step= 0.002 nm), 1 m focal length, Czerny– cedure was repeated twice.Drying at 105 °C was followed by Turner mount, with 2400 grooves mm-1 7 h of sintering in a furnace at 1000–1100 °C. After a new set diVraction grating and 20 mm slits (internal of grinding and sifting steps, the sample was homogenised wavelength calibration with an Si hollow again.Some powder obtained in this way was pressed in a cathode lamp). Research Institute for steel press at a pressure of 87×105 Pa for 10 min. The resulting Analytical Instrumentation, Cluj-Napoca, analytical sample pellets had a cylindrical shape, with a Romania Detector 9781 R photomultiplier tube operated at diameter of 11 mm, and were used for analytical 700 V. Thorn EMI, Ruislip, Middlesex, determinations. UK Driving, data acquisition Digital data acquisition and monochroma- Results and discussion and processing tor driving carried out by an IBM PC equipped with a laboratory constructed Atomisation mechanism of the sample pellets. Parameter interface (64 ms data acquisition time); optimisation data processing with appropriate in-house software.Research Institute for Analytical The main characteristic of our capacitively coupled plasma is Instrumentation, Cluj-Napoca, Romania that it is an intrinsic part of the tuned circuit of the rf generator 542 J.Anal. At. Spectrom., 1999, 14, 541–545Fig. 3 The plasma and the tuned circuit of the rf oscillator. Rg, Cg= automatic negative group; L=adjustable coupling coils; C=condenser of the oscillating circuit. (Fig. 3). The oscillator is of the inductive reaction type having the tuned circuit placed in the control grid network of the active element (pentode tube) and it is presented in detail elsewhere.16 The presence of the adjustable inductive coupling in the reaction circuit oVers the possibility of maximisation of the rf power transferred to the plasma.The automatic grid bias network (RgCg) develops a negative voltage on the grid in the range 150–200 V. Its value is a function of the anode positive bias. Over this negative dc component the rf component is superimposed, the amplitude of oscillation being 15–20% greater than the dc potential of the control grid. Because the oscillator works under resonant conditions, the amplitude of the rf oscillations on the sustaining electrode of the plasma is in the range 2000–3000 V.Owing Fig. 5 EVect of rf power on the emission intensities at an Ar flow rate to the dc component, the rf wave is translated towards negative of 0.5 l min-1 for (a) 20 mg g-1 Na (588.99 nm) from ZnO matrix and values, its form being asymmetric with respect to ground. (b) 35.1 mg g-1 Pb (405.78 nm) from AGV-1 andesite standard. During a full cycle of the rf wave, the plasma sustaining electrode has at negative potential a time interval longer than ation.At suYciently high rf powers (38 W in the case of an a half-cycle. This fact, combined with the lower mobility of argon plasma), the heating of the sample is so great that it the positive ions relative to the electrons, causes an accumutends to show incandescence. We assume that the increase in lation of positive charge greater than the negative charge close the sample temperature causes thermal evaporation on its to the sustaining plasma electrode.This accumulation of surface. This can be a supplementary atomisation mechanism positive charge has two consequences: (a) an excess of negative which will cause an increase in the number of sample atoms charge that appears toward the free end of the plasma where in the plasma. These observations are supported by the plots the sample is placed and (b) electrostatic shielding of the in Fig. 4 and 5. sustaining electrode of the plasma.Consequently, an internal Fig. 4 shows the dependence of the expulsion rate on the rf dc electric field appears in the plasma. When the distance power absorbed by the plasma. The expulsion rate was calcu- between the plasma electrode and the sample is 2–4 mm, this lated as the diVerence between the ZnO sample mass before field is suYciently intense to accelerate the positive ions and after exposure to collisions with ions. Nine replicate towards the sample and to induce sputtering of the sample, sample pellets were used.At powers lower than 25 W, the causing sample atomisation. Sputtered atoms are then availsputtering rate is low since the intensity of the dc internal field able to enter the plasma for subsequent excitation and ionis- Fig. 6 EVect of Ar flow rate on the Pb (405.78 nm) emission intensity Fig. 4 Expulsion rate (mass loss per minute) as a function of rf power for a ZnO sample pellet. for the AGV-1 andesite standard (35.1 mg g-1) at an rf power of 36 W.J. Anal. At. Spectrom., 1999, 14, 541–545 543Table 4 Concentrations and statistics for Pb in standard andesite Table 2 BEC and LODs for trace elements in ZnO and andesite matrices matrices Pb concentration/mg g-1 Statistics Element l/nm BEC/mg g-1 LOD/mg g-1 Matrix Na 588.99 11.4 0.3 ZnO Andesite Certified Determined standard value value c: ±sc tcalculated ttabulated (n; 95%) Pb 405.78 21.4 0.7 ZnO Si 251.61 33.3 1.0 ZnO Cd 228.81 28.1 0.9 ZnO JA-1 5.8 5.5±0.7 0.96 2.78 JA-2 19.3 19.9±0.6 2.23 2.78 Pb 405.78 23.1 0.8 Andesite Cr 425.43 31.5 1.0 Andesite JA-3 6.7 7.0±0.7 0.96 2.78 AGV-1 35.1 34.8±0.6 1.12 2.78 Cu 324.75 14.5 0.5 Andesite Student factor |tcalculated|=(c: -m)Óm/sc.c: =Average concentration of m=5 successive measurements; sc=standard deviation for m=5; m= certified concentration; n=m-1 degrees of freedom. is low. In the range of 25–38W, the sputtering rate is nearly constant, which means that the intensity of the accelerating field remains nearly constant.An explanation of this phenomenon could be the complementary eVects of the increases in ology, respectively, both elaborated by Boumans et al.17,18 the rf voltage amplitude and in the electrostatic shielding. In The relative standard deviation of the background (RSDB) this power range the sample atomisation is produced only by was calculated for 10 successive measurements of the the sputtering process. At powers higher than 38 W, thermal background.evaporation will be present because of heating of the sample As can be seen in Table 2, the detection limits are1 mg g-1. by energised ions. Hence an increase in the atomisation These results are similar to other results obtained for the direct rate occurs. analysis of solid samples.4 In Fig. 5 the eVect of rf power on the emission intensities The dynamic range was determined for Pb from andesite of Na (588.99 nm) from a ZnO matrix and Pb (405.78 nm) matrices.It is about three orders of magnitude. The correlation from AGV-1 andesite is shown. coeYcient for the calibration curve is about 0.999 for this As can be seen, each plot is composed of two straight lines dynamic range and the standard deviation of its slope is 2.8%. with diVerent slopes. The first line corresponds to the For the statistical comparison of the two calibration curves sputtering mechanism and the second to the combination of (F-test and t-test), the null hypothesis was used.19 The statistics sputtering and thermal evaporation.Observing that the of the calibration curves for Pb in andesite matrices are increase in the slope takes place at an rf power of 37–38W, presented in Table 3. which is the same as when the atomisation rate begins to As shown in Table 3, the calculated values for F and t are increase, the thermal evaporation assumptions seem to be smaller than those tabulated, so there are no significant plausible. diVerences between the two curves for a probability of 95%.In Fig. 6, the eVect of the gas flow rate on the Pb Therefore, the Pb concentrations in the certified standards (405.78 nm) emission line intensity from AGV-1 andesite at were determined using the calibration curve obtained with an rf power of 36W is shown. The plot has a maximum at a the synthetic standards. Subsequently, the recoveries and the gas flow rate that can be considered optimum (0.5 l min-1).RSDs of concentrations were also calculated. In Table 4, the At this gas flow rate, the number of sputtered atoms entering results and statistics for Pb determination (five successive the plasma, where the excitation and atomisation processes measurements) in certified standards are given. take place, is maximum. At gas flow rates greater than the Table 4 shows that for each standard, tcalculated<ttabulated. optimum, the residence time of atoms in the plasma decreases Therefore, for a probability of retaining 95% and n=4 degrees and, as a result, the net intensities of the emission line of freedom, the null hypothesis is valid and there are no also decrease.systematic errors between the certified and determined values of the concentration using the plotted calibration curve. Analytical performance The RSDs for Pb in andesite are 12.7% for JA-1, 3.1% for JA-2, 10% for JA-3 and 1.7% for AGV-1. The recoveries for All measurements for evaluating the analytical performances were made at an rf power of 36W and an Ar flow rate of Pb compared with the certified values are 95±12% for JA-1, 103±3% for JA-2, 104±10% for JA-3 and 99±2% for AGV-1. 0.5 l min-1. In Table 2, the background equivalent concentration (BEC) The determination errors are much higher at lower concentrations, but for concentrations higher than 10 mg g-1 Pb, they and the limits of detection (LODs) are presented. They were calculated with the 3s method and the BEC–RSDB method- are very good, being around 2–3%.Table 3 Statistics for calibration curves for Pb in andesite matrices Intercept Slope Andesite No of Calibration curve equationa matrix points Fcalc Ftab b ttab d Fcalc Ftab b ttab d y=(a±sa)+(b±sb)c type plotted s12/s22 F(n1; n2) tcalc c (n; 95%) s22/s12 F(n2; n1) tcalc c (n; 95%) -4×10-3 ± 28.5+(7.1±0.2)c (r=0.999) Synthetic n1=6 5.74 F5;3=14.88 6×10-5 2.31 6.250 F3;5=7.764 0.45 2.31 -5×10-3 ± 11.9+(7.2±0.5)c (r=0.997) Certified n2=4 standard aa=Intercept; sa=standard deviation of the intercept; b=slope; sb=standard deviation of the slope; r=correlation coeYcient.bn1=n1-1, n2= n2-1 degrees of freedom. ct=(x: 1-x: 2)/sÓ(1/n1+1/n2); s=Ó[(n1-1)s12+(n2-1)s22]/(n1+n2-2) where x: 1 and x: 2=intercepts and slopes of the calibration curves (a1; a2; b1; b2); s1 and s2=standard deviations of the intercepts and slopes of the calibration curves. dn=n1+n2-2 degrees of freedom. 544 J. Anal. At. Spectrom., 1999, 14, 541–54511 E.A. Cordos�, S. D. Anghel, T. Frent�iu and A. Popescu, J. Anal. References At. Spectrom., 1994, 9, 635. 12 T. Frent�iu, S. D. Anghel, A. M. Rusu, M. Ponta and E. A. Cordos�, 1 M. W. Blades, P. Banks, C. Gill, D. Huang, Ch. LeBlanc and Fresenius’ J. Anal. Chem., 1996, 355, 254. D. Liang, IEEE Trans. Plasma Sci., 1090, 19, 1991. 13 E. A. Cordos�, T. Frent�iu, A. Fodor, M. Ponta, A. M. Rusu and 2 W. W. Harrison, C. M. Barshick, J. A. Klinger, P. H. RatliV and S. Negoescu, ACH Models Chem., 1995, 132, 313. Y. Mei, Anal. Chem., 1990, 62, 943A. 14 T. Frent�iu, S. D. Anghel, A. Simon, A. Popescu, A. M. Rusu, 3 D. C. Duckworth and R. K. Marcus, Anal. Chem., 1989, 61, 1879. S. Negoescu and E. A. Cordos�, ACH Models Chem., in the press. 4 R. K. Marcus, T. R. Harville, Y. Mei and Ch. R. Shick, Anal. 15 T. Frent�iu, S. D. Anghel, A. Simon, A. Popescu and E. A. Cordos�, Chem., 1994, 66, 902A. ACH Models Chem., in the press. 5 A. M. Pless, A. Croslyn, M. J. Gordon, B. W. Smith and 16 E. Ta¢ taru, S. D. Anghel and I. I. Popescu, Rev. Roum. Phys., 1991, J. D. Winefordner, Talanta, 1997, 44, 39. 36, 29. 6 W. R. L. Masamba, B. W. Smith and J. D. Winefordner, Appl. 17 P. W. J. M. Boumans, Spectrochim. Acta, Part B, 1991, 46, 431. Spectrosc.., 1992, 46, 1741. 18 P. W. J. M. Boumans, J. C. Ivaldi and W. Slavin, Spectrochim. 7 D. Liang and M. W. Blades, Spectrochim. Acta, Part B, 1989, Acta, Part B, 1991, 46, 641. 44, 1049. 19 J. C. Miller and J. N. Miller, Statistics for Analytical Chemistry, 8 S. D. Anghel, T. Frent�iu, A. M. Rusu, L. Bese and E. A. Cordos�, Wiley, New York, 2nd edn., 1988, ch. 3, pp. 53–62 and ch. 5, Fresenius’ J. Anal. Chem., 1996, 355, 252. pp. 101–115. 9 M.W. Blades, Spectrochim. Acta, Part B, 1994, 49, 47. 10 S. D. Anghel, T. Frent�iu, A. Simon, E. Darvasi, A. M. Rusu and E. A. Cordos�, Fresenius’ J. Anal. Chem., 1996, 355, 250. Paper 8/07036I J. Anal. At. Spectrom.,

ISSN:0267-9477    

DOI:10.1039/a807036i

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Theoretical evaluation of solid sampling–electrothermal atomic absorption spectrometry for screening purposes† Miguel A. Belarra,* Martý�n Resano and Juan R. Castillo Department of Analytical Chemistry, University of Zaragoza, E-50009 Zaragoza, Spain Received 30th October 1998, Accepted 25th January 1999 Obtaining results in the determination of metals by electrothermal atomic absorption spectrometry is conditioned by the non-homogeneity of the sample and the possible appearance of outliers, which make it diYcult to obtain reliable results with only a few measurements.In order to establish the optimum conditions for using the technique as a screening method, 18 000 results corresponding to diVerent possible situations were simulated by computer and subsequently analysed using information theory. In view of the results obtained, it can generally be claimed that the median can be used to better eVect than the mean value as the former is less aVected by the potential presence of outliers.Using the median and with normal working conditions, the minimum number of measurements that need to be carried out to guarantee a recall of over 0.95 in a screening method ranges from 5 to 20, involving between 15 min and 1 h work. One of the main reasons why the determination of metals by analyte distribution is of great importance. Furthermore, under these conditions the appearance of potential outliers is particu- electrothermal atomic absorption spectrometry with direct introduction of solid samples (SS-ETAAS) is not more widely larly problematic for two reasons.First, if a small number of measurements are carried out the influence of potential outliers used is that the relative standard deviation (RSD) values obtained are high, in most cases between 10 and 30%. In a is greater, and second, it is more diYcult to reject them statistically. previous paper it was shown that, in general, with samples of an organic nature these values cannot be attributed to The purpose of this work was to study the influence of sample non-homogeneity and the appearance of potential deficiencies of the technique but are caused by the nonhomogeneity of the small sample masses introduced into the outliers on the results in order to establish the optimum working conditions and to evaluate the possibilities of the atomizer (normally around 1 mg), and also that this problem is diYcult to solve.1 technique in a screening system.Since the median was sometimes found to provide better results than the mean,7 an A second cause of imprecision and bias is the possible appearance of outliers. Despite its importance, this subject has important part of our work consisted in comparing them. In order to do this, 18 000 results were generated with a only been dealt with in depth by Kurfu� rst when overestimated results are obtained, which he classified as either endogenous computer using the empirically observed type of variation and frequency of outliers in SS-ETAAS as input parameters.In (appearance of ‘nuggets’, small particles with an unusually high analyte content) or exogenous (essentially contami- this study the presence of potential outliers of an endogenous nature, which are diYcult to detect and require special treat- nation)2 and developed a method for treating the former.3 In our experience, the appearance of potential outliers should ment, was not considered, so all the outliers were treated as exogenous. The conclusions reached using this simulation are always be taken into account when using SS-ETAAS, since they can considerably aVect the treatment of results even if contrasted with the real experimentally obtained results.few in percentage terms. Moreover, we have found results that provide underestimated values, probably owing to an Simulation design occasional incorrect atomization process, although this is much less frequent.Nine populations of diVerent characteristics with 2000 values The characteristics of SS-ETAAS are well suited to the each were generated to simulate the results obtained by study of the homogeneity of CRMs4 in which the diVerent SS-ETAAS. The procedure given in Table 1 was used for the analyte distributions in the sample pose no problem but are, generation and treatment of results for all the populations. in fact, the object of study and the problem of potential Three of the populations correspond to normal distributions outliers can be overcome by carrying out a large number of with m=100 and three diVerent RSD values (RSDs=10, 20 measurements.2 and 30% representing diVerent degrees of sample non- Apart from this special application, the SS-ETAAS homogeneity); higher RSDs values, which seem improbable, technique seems useful when the aim is to obtain reasonably were not considered. reliable results economically and rapidly.SS-ETAAS is poten- The other six populations take into account the appearance tially useful as a screening method5 since it is possible to take of potential outliers, which was simulated by replacing at advantage of the high throughput of the technique to filter random 100 and 200 values in the former populations (correout the majority of the samples in a two-stage control system.6 sponding to 5 and 10% of the total values) with random results In this situation, sample handling should be minimal and obtained between 0 and 300, so that the appearance of the smallest number of measurements possible should be unusually overestimated results is more probable.carried out, so the influence of an insuYciently homogeneous The mean value (x: p), the median (mp) and the relative standard deviation (RSDp) of the final nine populations are given in Table 2 and the distribution of results of two popu- †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998.lations can be seen in Fig. 1. It can easily be appreciated that J. Anal. At. Spectrom., 1999, 14, 547–552 547Table 1 Generation of the populations and calculation of results 1. Three series of 2000 values were generated with a normal distribution with m=100 and a variable RSDs (RSDs=10, 20 and 30%) which represents the non-homogeneity of the sample 2. q values were generated at random ranging from 0 to 300 (q=0, 100, 200), which represent potential outliers 3.q values of each of the normal distributions obtained in (1) were randomly replaced by the q random results obtained in (2) 4. The mean value (X9 p), the median (mp) and the RSD (RSDp) of the final populations were calculated 5. The 2000 values (x1, …, x2000) of each population were grouped into 100 series of 20 correlative values (x1 to x20, x21 to x40, etc.) 6. The mean value [X9 1(n) to X9 100(n)] and the median [m1(n) to m100(n)] of each series were calculated using only the first n values of the series (n= 5, 7, 10, 15, 20) 7.The average value and RSD of the mean values [X9 x: (n) and RSDx: (n)] and the medians [X9 m(n) and RSDm(n)] were calculated n=20 n=15 n=10 n=7 n=5 x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 x16 x17 x18 x19 x20 X9 1(n) m1(n) x21 … x40 X9 2(n) m2(n) e e x1981 … x2000 X9 100(n) m100(n) X9 p mp RSDp X9 x: (n) X9 m(n) RSDx: (n) RSDm(n) the mean value moves away from 100 when the number of Table 2 Characteristic values of the nine populations generated outliers increases with a deviation of up to almost 7%, whereas RSDs (%) Outliers (%) x: p mp RSDp (%) its influence on the median is much less marked ( less than 2%).The presence of outliers clearly increases the RSDp values 10 0 100.3 99.7 10.0 (between 25 and 200%). 10 5 103.6 100.2 24.0 In order to simulate the influence of the number of 10 10 105.4 100.4 30.9 measurements carried out to obtain a result, the 2000 values 20 0 100.8 100.9 20.2 for each population were grouped in series of 20 so that 100 20 5 103.9 101.5 30.4 20 10 106.6 101.9 35.6 determinations were simulated for each of the nine cases.For 30 0 100.0 99.6 29.2 each of the 100 series the mean value [ x: 1(n) to x: 100(n)] and the 30 5 103.2 100.2 36.2 median [m1(n) to m100(n)] were calculated in several situations: 30 10 104.9 100.4 40.1 using only the first five, seven, 15 and 20 values (n=5, 7, 10, 15 and 20).Finally, the average value and the RSD of the mean values [ x: x: (n) and RSDx: (n)], and the average value and the RSD of the medians [ x: m(n) and RSDm(n)] were calculated. The results are given in Table 3. Results and discussion Analysis of results using information theory Given the large number of results available, their analysis is complex mainly because the diVerent variables considered (RSDs, number of outliers, use of the mean value or median and number of measurements) may aVect the precision and bias diVerently.Information theory simplifies the study as it makes it possible to calculate a single parameter (total information content, TIC) which includes both precision and bias. The TIC value was therefore calculated for all results using the expression proposed by Eckschlager and Danzer:8 TIC=lb x2-x1 sÓ2p -0.72 d2+sr2 s2 (1) where x2-x1 are the limits of the a priori information, d is the bias, that is, the diVerence between the value of x: x: (n) or of x: m(n) (depending on whether the mean values or medians were used in each series) and 100, s is the standard deviation of the 100 results and sr is the standard deviation of the true value, which was considered to be zero.In view of eqn. (1), the TIC values obtained clearly depend to a great extent on the amount of previous information [ lb (x2-x1)]. This poses no problem for a general treatment since Fig. 1 Distribution of the results of the populations with RSDs=20%: (a) without outliers; (b) with 10% of outliers.the TIC is only used in this study for the purpose of comparison 548 J. Anal. At. Spectrom., 1999, 14, 547–552Table 3 Results of the mean value, relative standard deviation and total information content of each population in function of the number of measurements RSDs (%) Outliers (%) X9 x: (5) X9 m(5) X9 x: (7) X9 m(7) X9 x: (10) X9 m(10) X9 x: (15) X9 m(15) X9 x: (20) X9 m(20) 10 0 101.2 100.9 101.1 100.8 100.7 100.1 100.2 99.8 100.3 99.8 10 5 103.8 100.9 104.5 101.0 104.4 100.6 103.8 100.3 103.6 100.3 10 10 106.9 101.1 107.0 100.9 106.6 100.9 105.6 100.4 105.4 100.4 20 0 101.6 102.1 101.1 102.0 100.9 102.0 100.8 100.6 100.8 100.8 20 5 105.5 102.4 105.7 102.5 104.6 102.4 103.8 100.8 103.9 101.5 20 10 107.1 102.5 108.5 103.0 107.6 103.1 106.5 101.5 106.6 102.0 30 0 100.3 100.5 100.5 100.7 100.3 101.2 99.9 99.6 100.0 100.2 30 5 102.9 101.1 103.1 101.5 103.2 102.2 102.5 100.1 103.2 100.9 30 10 104.4 101.7 104.5 102.0 105.2 103.0 104.2 101.2 104.9 101.2 RSDx: (5) RSDm(5) RSDx: (7) RSDm(7) RSDx: (10) RSDm(10) RSDx: (15) RSDm(15) RSDx: (20) RSDm(20) 10 0 4.2 4.9 3.9 4.6 2.8 3.1 2.4 2.8 2.0 2.4 10 5 11.2 5.6 10.6 4.8 8.3 3.5 6.7 2.9 5.8 2.5 10 10 14.7 6.5 12.1 5.4 10.2 4.1 8.6 3.4 7.1 2.8 20 0 9.0 9.7 7.8 9.1 6.8 7.6 5.4 6.1 4.6 5.5 20 5 14.7 10.0 12.7 9.7 10.8 8.0 8.4 6.6 7.3 5.9 20 10 14.5 9.9 13.6 9.2 11.1 8.0 9.2 6.7 8.5 6.2 30 0 13.0 15.5 11.3 13.5 9.5 10.6 7.3 9.1 6.3 7.3 30 5 16.0 15.6 14.0 14.0 10.9 10.9 9.1 9.0 7.4 7.5 30 10 17.9 16.3 15.8 15.2 12.2 12.1 9.5 9.6 7.8 7.6 TICx: (5) TICm(5) TICx: (7) TICm(7) TICx: (10) TICm(10) TICx: (15) TICm(15) TICx: (20) TICm(20) 10 0 6.5 6.3 6.6 6.3 7.1 6.9 7.3 7.1 7.6 7.3 10 5 5.0 6.1 5.1 6.3 5.3 6.7 5.6 7.0 5.8 7.2 10 10 4.6 5.9 4.8 6.1 5.0 6.5 5.2 6.8 5.4 7.1 20 0 5.4 5.3 5.6 5.4 5.8 5.6 6.2 6.0 6.4 6.1 20 5 4.6 5.2 4.8 5.3 5.1 5.6 5.4 5.9 5.6 6.0 20 10 4.6 5.3 4.6 5.3 4.8 5.5 5.1 5.8 5.2 5.9 30 0 4.9 4.6 5.1 4.8 5.3 5.2 5.7 5.4 5.9 5.7 30 5 4.5 4.6 4.7 4.8 5.1 5.1 5.3 5.4 5.5 5.7 30 10 4.4 4.4 4.5 4.6 4.8 4.9 5.2 5.3 5.3 5.6 and no attempt is made to reach conclusions about absolute cases and diVerent percentages of outliers present) when 10 measurements were carried out to obtain the result (n=10).values with regard to the total amount of information gained. The discontinuous central line represents the situation in which Consequently, for this study values x1=10 and x2=1000 were the mean value and the median provide the same total amount used.The TIC results thus obtained are given in Table 3. of information and the points above the line indicate that better results were obtained when the mean value was used Comparison between the use of mean value and median (the further away from the line the better) while the points Fig. 2 shows the TIC values obtained using the mean value below the line indicate the opposite.against those obtained using the median (for diVerent RSDs In the graph it can clearly be seen that the diVerent behaviours of the mean value and the median depend on the presence of outliers to such an extent that the mean only gives TIC values which are slightly higher than those of the median when outliers are absent. The presence of 5% of outliers causes a marked decrease in the TIC obtained when the mean value is used and this drop increases, although less markedly, when the outliers exceed 10%.It can be observed that when outliers are present the TIC values obtained using the mean value hardly improve when the RSDs value decreases. However, the TIC values obtained when the median is used, which depend to a considerable extent on the RSDs value, depend very little on the presence of outliers. This can be deduced from the verticality of the lines joining points of equal RSDs value. Although the median always gives higher TIC results than the mean value when outliers are present, the diVerence between the two is less noticeable when the RSDs value increases so that when it reaches 30% the diVerences between using the mean and the median, both in the presence and in the absence of outliers, are almost insignificant.The results obtained when the number of measurements carried to obtain the result is 5, 7, 15 or 20 are similar to those previously mentioned for 10 measurements, with the diVerent lines in a slightly diVerent position from those given Fig. 2 Comparison between the TIC values obtained for the diVerent populations using the mean value and the median with n=10. in Fig. 2. J. Anal. At. Spectrom., 1999, 14, 547–552 549Table 5 Percentage variance ascribable to each factor using the mean value and the median Variance (%) Factor Using the mean value Using the median No. of measurements (n) 14.2 13.8 RSDs 21.1 85.1 Percentage of outliers 64.7 1.1 the mean or the median. The cases when outliers are present or absent are studied separately.With regard to the use of either the mean or the median, it can be observed in Table 4 that this has little influence when there are no outliers, but in the presence of outliers it becomes the main source of variance and the results are better with the median. Taking into account this conclusion, the small contribution of the percentage of outliers to the total variance (approximately 4%) could be considered surprising.It is mainly due to the fact that in this analysis only an increase in potential Fig. 3 Comparison between the TIC values obtained using the mean outliers from 5 to 10% was considered which, as can be seen value and the median in function of the number of measurements for in Fig. 2, has a much less marked eVect than an increase from the three populations with RSDs=20%. 0 to 5%. The percentage variances abscribable to each of the first three factors, using the mean value or the median, are Influence of number of measurements presented in Table 5, studying all the populations (with and without outliers). One can now clearly observe the influence In a similar way as in the previous study, Fig. 3 shows the TIC values obtained using the mean and the median when a of the percentage of outliers, which becomes the main source of variance when working with the mean whereas it is almost diVerent number of measurements were carried out to obtain the result for the intermediate case where RSDs=20%. The insignificant when working with the median.The RSDs value, however, is the main contributor to the other two distributions display identical behaviour. As expected, an increase in the number of measurements variance when the median is used while its contribution is less important with the mean. The number of measurements carried leads to improved TIC values but, unlike in the study of the mean and the median, no diVerences can be established out to obtain a result is the least dependent variable of the other factors, given that its variation ranges in all cases from between the diVerent conditions.In fact, the improvement is the same using the mean or the median ( lines with a slope 12.6 to 14.2%. close to unity) and, in proportion, the TIC gain with increase in the number of measurements is almost independent of the Results as a screening method number of outliers. The discussion in the previous sections is based on a very As there is no criterion which makes it possible to relate large number of results (100 per population, each of which is the absolute values of TIC to conventional analytical paramthe mean or median of 5, 7, 10, 15 or 20 values). Consequently, eters, it is impossible to decide with these results which is the general tendencies can be seen but it is impossible to reach most suitable number of measurements to obtain a result, concrete conclusions regarding the number of measurements.taking into account that 20 measurements involve a fourfold Given that the use of SS-ETAAS as a method of screening increase in time to obtain a result compared with five measureinvolves the minimum number of measurements possible, ments. Consequently, the influence of the number of measurestudying this parameter is of fundamental importance. ments will be studied later when the procedure is applied as a Consequently, the recall (the characteristic screening param- screening method.eter) was calculated using the values x: 1(n) to x: 100(n) and m1(n) to m100(n) for each of the nine cases studied: Results of analysis of variance The conclusions drawn from the variance analysis of all the recall= No. of correct identification No. of attempted identifications (2) TIC values obtained coincide perfectly with those reached in individual cases. Table 4 shows the percentage variance ascrib- where correct identifications are considered to be those in able to RSDs, the percentage of outliers, the number of which the value of x: i(n) or mi(n) (i=1, 2, …, 100) is within a measurements carried out to obtain each result and the use of pre-established margin.The results for the case when the margin is ±20% are given in Fig. 4. Logically, the results Table 4 Percentage variance ascribable to each factor with and without depend on the RSDs values and the percentage of outliers, outliers data which can hardly be considered as previously known in the case of a rapid screening method.However, if we consider Variance (%) a recall value 0.95 to be acceptable, it can be seen that when the median was used seven measurements provided correct Populations without Populations with results in all cases unless the RSDs value was 30%, in which Factor outliers outliers case 15 measurements were necessary. No. of measurements (n) 12.6 12.7 In our experience in the field of SS-ETAAS, we have found RSDs (%) 82.7 28.7 RSDs values higher than 30% on only one occasion (for a rice Percentage of outliers 4.0 sample, not previously homogenized, which decreased to less Mean/median 4.7 54.6 than 20% after reduction of the particle size1) and the most 550 J.Anal. At. Spectrom., 1999, 14, 547–552Fig. 5 Distribution of results for the determination of (a) cadmium in sewage sludge and (b) copper in a vitamin complex. Table 6 Characteristic values for the determination of cadmium in sewage sludge and copper in a vitamin complex Cadmium Parameter With outliers Without outliers Copper No.of results 105 96 157 x: p 6.8 6.4 107.1 mp 6.4 6.4 106.4 RSDp (%) 30.7 15.5 18.7 sample dissolution are not statistically significant at the 95% level. Consequently, the data seem similar to those of the Fig. 4 Predicted results of a screening system with a tolerance margin model with RSDs=20% when outliers are absent. of±20%: (a) RSDs=10% ( lines corresponding to the mean and the However, the distribution of the results obtained in the median without outliers overlay); (b) RSDs=20%; (c) RSDs=30%.determination of cadmium in sewage sludge indicates the presence of outliers; the diVerence between the mean and the frequent values are in the 15–25% range. In these conditions, median is statistically significant at the 95% level and and in view of the previous results, it can be said that in the median result is closer to that obtained after sample practice 10 measurements (approximately 30 min work) should dissolution (6.3±0.2 mg kg-1).After eliminating the results guarantee a recall higher than 0.95 for a tolerance margin of outside the interval x:±ts, a normal distribution is obtained ±20% and that frequently (RSDs value lower than 20%) five with the characteristics shown in Table 6. The situation is measurements may be suYcient. therefore similar to the model with RSDs=15% and 10% Clearly, if the tolerance margin desired is smaller, the of outliers.number of measurements should be increased. Hence, for a If the 105 results obtained in the determination of cadmium margin of ±15%, 20 measurements should be carried out and and the 157 obtained in the determination of copper are it does not seem generally possible to guarantee a margin grouped in series of five (21 determinations for cadmium and of ±10%. 31 for copper) and the same calculations are carried out as with the model [calculation of, x: x: (5), x: m(5), RSDx: (5), RSDm(5) Comparison between the model and the results with real samples and the recall of a screening method with a tolerance margin of ±20%, the results of which are given in Fig. 6], the data The eYciency of the model proposed and the validity of the results obtained by its application were compared with the in Table 7 are obtained. The predicted values are also given (in the case of cadmium, intermediate values between RSDs= results obtained experimentally in the determination of cadmium in sewage sludge9 and copper in a vitamin complex,10 10 and 20%) according to the model proposed.The bias percentage was calculated in comparison with that obtained using the results obtained with optimum sample masses in both cases. Their distribution is shown in Fig. 5 and their after sample dissolution. No predicted result is given for copper because the distribution is normal. population data are given in Table 6. The determination of copper in the vitamin complex appears As can be observed in Table 7, the agreement between the experimental results and the model is generally very satisfac- to have a normal distribution, which was confirmed by applying the Kolgomorov–Smirnov test, and the diVerences between tory, supporting the conclusions reached previously with the model.The most significant diVerence is in the cadmium recall the mean value and the median and the value obtained after J.Anal. At. Spectrom., 1999, 14, 547–552 551nations) after rejecting potential outliers by the Dixon Q test with a 95% level (Fig. 6, determinations 3 and 12 would no longer be erroneous, 7 and 18 would still be erroneous and 10 would then become erroneous), a recall of 0.86 is obtained, which despite the additional work for the treatment of results is still clearly lower than that obtained with the median, even if the latter were close to the predicted value (0.95). Conclusions The results obtained in the determination of metals by SS-ETAAS can be compared with a model with two variables: the lack of homogeneity of the small subsamples introduced into the atomizer and the presence of potential outliers.Information theory, which combines bias and imprecision in a single parameter, proved to be very suitable for the analysis of 18 000 results created according to the model proposed and corresponding to diVerent situations of both variables (RSDs= 10, 20 and 30% with 0, 5 and 10% of outliers). Although this data set has been generated according to our experience working with SS-ETAAS, the conclusions drawn might also be applied to other methods that present a similar pattern.The results obtained using the mean value or median with a small number of measurements (5–20) show that the mean value depends greatly on the presence of outliers. Outliers have hardly any incidence on the results obtained using the median, which are only influenced by the RSDs value.Consequently, if screening tests are carried out by SS-ETAAS when the sample characteristics are unknown, the median Fig. 6 Results of a screening system with a tolerance margin of ±20% should be used. If no outliers are present the results are (upper and lower lines) for (a) cadmium in sewage sludge and comparable to those obtained with the mean value and with (b) copper in a vitamin complex. outliers the results are clearly better. If the median is used, with or without outliers, 10 Table 7 Comparison between the predicted values and the results measurements (which involves around 30 min work) are obtained experimentally in the determination of cadmium in sewage suYcient to guarantee a recall higher than 0.95 in a screening sludge and copper in a vitamin complex with n=5 method with a tolerance margin of ±20%, provided RSDs Cadmiuma Coppera values lower than 30% are used, which is usually the case.Mean value Median Mean value Median The authors acknowledge the financial support by the Direccio�n General de Investigacio�n Cientý�fica y Cultura Bias (%) 7.6 (7) 2.2b (2) 4.3b 3.6b (DGICYT, PB 97–0995) RSD (%) 13.8 (15) 7.6 (8) 9.9 (9) 11.1 (10) Recall 0.81 (0.79) 1.00 (0.95) 0.94 (0.96) 0.94 (0.94) aThe predicted values are given in parentheses.bThe bias is not References statistically significant at the 95% level. 1 M. A. Belarra, M. Resano and J. R. Castillo, J. Anal. At. Spectrom., 1998, 13, 489. 2 U. Kurfu� rst, Fresenius’ J. Anal. Chem., 1993, 346, 556. when the median is used, but it should be taken into account 3 U. Kurfu� rst, Pure Appl. Chem., 1991, 63, 1205. that going from 1.00 to 0.95 involves the appearance of a 4 Th.-M. Sonntag and M. Rossbach, Analyst, 1997, 122, 27. single erroneous result. 5 Draft Commission Decision, OV. J. Eur. Commun., 1993, L118, These results show the possibilities of the SS-ETAAS 64. technique as a screening method within the margins previously 6 M. A. Belarra, I. Belategui, I. Lavilla, J. M. Anzano and mentioned, as it makes it possible to obtain a recall of the J. R. Castillo, Talanta, 1998, 46, 1265. 7 M. A. Belarra, I. Lavilla and J. R. Castillo, Analyst, 1995, 120, order of 0.95 in 15 min. If potential outliers are absent 2813. (copper), using the median rather than the mean value does 8 K. Eckschlager and K. Danzer, Information Theory in Analytical not lead to worse results, but with outliers (cadmium) the Chemistry, Wiley, New York, 1994. median is clearly superior. 9 M. A. Belarra, M. Resano, S. Rodrý�guez, J. Urchaga and In the determination of cadmium, the treatment of possible J. R. Castillo, Spectrochim. Acta, Part B, in the press. outliers needs an additional comment. As seen previously, 10 M. A. Belarra, C. Crespo, M. P. Martý�nez-Garbayo and J. R. Castillo, Spectrochim. Acta, Part B, 1997, 52, 1855. obtaining 105 results enables us to eliminate nine outliers after which correct results are obtained. However, if only five results Paper 8/08432G are available (which is the case with any of the 21 determi- 552 J. Anal. At. Spectrom., 1999, 14,

ISSN:0267-9477    

DOI:10.1039/a808432g

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Study of cross-sectional and longitudinal distribution of some major and minor elements in the hair samples of haemodialysed patients with micro-PIXE† Ja�nos Dombova�ri,*a Lajos Papp,a Imre Uzonyi,b Ildiko� Borbe�ly-Kiss,b Zolta�n Elekes,b Zsuzsa Varga,c Ja�nos Ma�tyusc and Gyo�rgy Kakukc aLajos Kossuth University, Debrecen, P.O.B. 21, H-4010 Hungary bInstitute of Nuclear Research of the Hugarian Academy of Sciences, Debrecen, Bem Square 18/c, H-4026 Hungary c1st Department of Medicine, University Medical School, Debrecen, P.O.B. 19, H-4012 Hungary Received 8th September 1998, Accepted 27th January 1999 The concentration of Zn, K, Ca, Fe and Cl was determined in the hair samples of haemodialysed patients and healthy controls. Cross-sectional and longitudinal measurements were performed using the micro-PIXE method. The concentration changes of the above mentioned elements along the length of the hair and their cross-sectional distribution were studied. The eVect of the washing procedure on the concentration of these elements has also been determined.The ability of the PIXE method was examined using Human Hair certified reference material (NCS DC 73347), and the results show that this method can be used to determine the concentration of the selected elements in the hair samples. We compared the results of the PIXE method with the results obtained from microwave digested reference material with the ICP-OES method. The concentration ranges of Ca, Fe and Zn were similar in the patients and controls while the concentration ranges of Cl and K were diVerent (controls: Ca, 135–1598; Cl, 394– 2382; Fe, 6–51; K, 54–1055; Zn, 102–183 mg g-1; versus patients: Ca, 298–559; Cl, 2476–7821; Fe, 15–58; K, 327– 2031; Zn, 96–163 mg g-1).The washing procedure highly aVected the concentration of K and Cl (unwashed: K, 1164±846; Cl, 6107±1714 mg g-1; versus washed: K, 497±552; Cl, 3470±1446 mg g-1). There were no diVerences between controls and patients in the cross-sectional distribution of the selected elements; the distribution of Cl was homogeneous, the Ca was concentrated in the outer layer of the hair while the distribution of K was nearly homogeneous with a slight increase at the outer layer.(3) to validate the micro-PIXE and ICP-OES methods used Introduction using a certified reference material. Elementary composition of blood and plasma samples involv- It has to be noted that hair analysis does not replace the ing micro- and macro-elements is altered by some diseases conventional clinical methods for elementary analysis.such as chronic renal failure (CRF). The main alterations in However, it gives useful additional information about the laboratory parameters of these patients are the increased levels excretion and long-term distribution of the elements. of K, P and Mg, and the decreased levels of Fe, Ca, and Cl. During the last decade, human hair has been extensively Experimental studied in clinical practice as a noninvasive tool for determination of trace elements in the body.The advantage of the In these studies three haemodialysed (HD) patients (mean age 57±1 a) and three healthy subjects (mean age 47±1 a) were hair analysis is that besides noninvasivity it gives an average concentration of trace elements over a longer period of time. involved. Samples were collected from the same place on the head, In this respect, Al is one of the most interesting ions causing intoxication in CRF patients.It is due to the altered metab- namely from the occipital region. In the case of each person some hair strands were removed from the scalp by pulling olism of Al in these patients.1–4 However, the average concentration of macro-elements such as Ca, Mg, Fe, Cl and P, and them out, preferably together with the hair root (because in this way the identification of the proximal end is easy). the eVect of preparation and washing procedures on the concentration and distribution of these elements in the hair, Hair strands were washed with diethyl ether–acetone (3+1) mixture, nonionic detergent solution (1% Decon-90 in triply is not yet known.Preparation and digestion of hair samples prior to analysis requires special care involving several washing distilled water) and triply distilled water, respectively. After washing the hair samples they were dried at 105 °C for 90 min. procedures5–7 and digestion methods.7–9 Therefore, the aims of our present work were: (1) to study the eVect of the washing For cross-sectional studies samples were embedded into Araldite resin (Eporapid, Budapest, Hungary) as follows: a procedure on the concentration of some elements in the surface and the cross-sectioned part of hair samples using micro- single hair was placed in the axis of a plastic tube (10 mm internal diameter, 30 mm length) and then the tube was filled PIXE; (2) to compare the concentration of these elements in the hair of CRF patients with that of healthy controls; and with resin.After hardening, sections were cut at 5, 10 and 15 mm from the proximal end, respectively. Samples were polished, washed with triply distilled water and dried at room †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998. temperature. In longitudinal studies hair strands were streched J. Anal. At. Spectrom., 1999, 14, 553–557 553onto an aluminium frame and their ends were fixed with from the sample, excluding the radiation from the resin.This method was applied in the longitudinal experiments, too. cyanoacrylate glue (Heurel KGaA, Du� sseldorf, Germany). On the frame three parallel single hairs were fixed at a distance of Because of the limited scan length (2.5 mm) the full length of the hair samples (25 mm) was examined in 10 segments and 3 mm from each other. To eliminate the X-ray radiation from the mountings of the equipment, a high purity Teflon plate the total concentration of the selected elements was determined in each segment.(3 mm thickness) was placed behind the frame. The study of the certified reference material (NCS DC 73347 Human Hair, purchased from: National Research Centre for Results and discussion CRMs, No. 7 District 11, Hiepjinge 100013, Beijing, China) was performed by both PIXE and ICP-OES methods. For The applicability of the micro-PIXE method was studied using the certified reference material and the results obtained were PIXE measurement pellets of about 1 mm thickness and 8 mm diameter were made from the powdered reference hair. The compared with the results of the ICP-OES measurement of the same reference hair.These results are shown in Table 3. concentrations of major elements which cannot be determined by PIXE (C, O, H and N) and the concentration of sulfur In the case of Ca, K and Zn the ICP-OES method produced better recoveries, while for Fe 80% (ICP-OES) and 120% which had to be used as an internal standard were determined with independent analytical methods, or the certified values (PIXE) of the certified concentration was measured.The concentration of Cl was not measurable using the direct ICP- were used. In ICP-OES measurements #0.5 g reference hair was digested in a Milestone MLS 1200 Mega high pressure OES method, and the results obtained with PIXE could not be explained with the lack of a certified value.microwave digestion unit (Microwave Laboratory Systems, Italy) in Teflon vessels, by the addition of 3 cm3 of 65% high The comparison of the measured values of HD patients, healthy controls and the concentrations taken from the litera- purity nitric acid (Merck, Darmstadt, Germany) and 0.5 cm3 of 30% high purity hydrogen peroxide (Merck). Samples were ture12 are shown in Table 4. Comparing the results of the HD patients with the controls we found that the concentrations of filled to 10 cm3 and the concentration of the selected elements was determined.ICP-OES experiments were carried out using Zn, Ca and Fe were in the same order of magnitude, if the error of the method and the biological variability was taken a Spectroflame (Spectro GmbH, Germaupled plasma optical emission spectrometer; the experimental param- into account. The concentrations of Cl and K were greater in the case of HD patients than that of the controls.It is also eters are shown in Table 1. In PIXE experiments the samples were analysed with the micro-PIXE technique using the scan- seen that the measured concentration values in HD patients were at the lower part of the reference range in the case of Ca ning proton microprobe facility at the Institute of Nuclear Research of the Hungarian Academy of Sciences in Debrecen. and Zn and higher than the reference for Cl and Ca; and in the case of Fe the two ranges were almost identical.It is Instrumental conditions are shown in Table 2, further details on the experimental setup can be found elsewhere.10 The known in clinical practice13 that the K concentration in the plasma of HD patients is higher than the normal values, while Si(Li) detector was protected from the backscattered protons by a hostaphan absorber of 12 mm thickness. Characteristic Fe, Ca and Cl concentrations are lower than the normal values.In the hair of HD patients this tendency was true only X-ray spectra and the elemental composition of the samples were evaluated by using the PIXYKLM program package.11 for Ca and Zn. The cross-sectional distribution of the selected elements is Because of the lack of a suitable current integrator we used S as an internal standard in the evaluation of Micro PIXE shown in Fig. 1. The concentrations of Ca, K and Cl in the human hair is high enough to obtain adequately evaluable spectra supposing 4.5% for its concentration. Besides S the detection limits were low enough to evaluate the concentration distribution maps.We found that the distribution of Cl was homogeneous in the cross-sections. In the case of K its of Cl, K, Ca, Fe and Zn but they were not satisfactory for P and Cu in many cases. During the cross-sectional study a distribution was also nearly homogeneous. However, the conshort scan was made on the surface of each sample to determine the exact location and shape of the hair section.Table 3 Intercomparison of the certified reference material (NCS DC The long data acquisition (Tm=60 min) was performed only 73347 Human Hair) Concentration/mg g-1±standard deviation Table 1 Instrumental and analytical conditions of ICP-OES Instrument Spectroflame ICP-OES Element Certified ICP-OES PIXE Frequency 27.1 MHz Nebulizer Spectro concentric nebulizer Ca 2900±200 2768±110 3700±200 Cl — — 100±40 Spray chamber Scott-type Flow rate of plasma gas 1.5 L min-1 Fe 54±6 43± 7 65± 5 K 20* 19±2 17± 5 Flow rate of cooler gas 15 L min-1 Flow rate of nebulizer gas 1 L min-1 Zn 190±5 195±8 210±15 Rate of sample 1 cm3 min-1 *Not certified, for reference only.introduction Integration time 25 s on the line, 25 s at the background Applied software Spectro EPC3 for Windows Detection lines/nm Ca, 31.9; Fe, 259.9; K, 766.5; Zn, 213.9 Table 4 Comparison of the measured concentration ranges of diVerent subjects (washed samples, longitudinal experiments, micro-PIXE) Concentration ranges/mg g-1 Table 2 Micro-PIXE experimental setup and analytical conditions Scanning Nuclear Microprobe Haemodialysed Control Element Literature12 (n=3) (n=3) Instrument Oxford, Microbeams type Proton beam energy 2 MeV Ca 146–3190 298–559 135–1598 Cl 950–4805 2746–7821 394–2382 Beam current #50 pA Collected charge #0.2 mC Fe 5–45 15–58 6–51 K 150–663 327–2031 54–1055 Integration time 60 min Beam spot-size #2×2 mm Zn 99–450 96–163 102–183 554 J.Anal. At. Spectrom., 1999, 14, 553–557Ca Cl Fe Zn 50 mm 50 mm 50 mm concentration low high 50 mm 50 mm K Fig. 1 The typical cross sectional distribution of the selected elements (selected maps, haemodialysed patient, micro-PIXE). J. Anal. At. Spectrom., 1999, 14, 553–557 555Fig. 2 Typical results of the longitudinal experiments: 1 segment=2.5 mm (haemodialysed patient, micro-PIXE). centration of K was higher in the outer layer than inside the tendency was observed.The Cl concentration was the lowest in the first segment, and there was a maximum in the second medulla, suggesting that an inadequate washing procedure might aVect its concentration in the outer layer. We found segment. The tendency was the same in the case of K. We found that Fe concentration increased in the cross-sections as small segregations in the case of Ca in the outer layer of the hair, in contrast with the more homogeneous distribution of a function of distance from the proximal end.The Zn concentration in the cross-sections does not change considerably at K. Because of their lower concentration, the distribution maps of Fe and Zn are less valuable, but it is observable that the diVerent distances. Fig. 2 shows the results of the longitudinal studies. The distribution of Zn was nearly homogeneous and the Fe was segregated in the outer layer. concentration of Zn was practically constant on the surface along the length of the hair sample.The concentration maxi- The diVerence in the concentration before and after the washing procedure in the case of K was the highest among mum at the distal end of the hair sample was probably of exogenous origin, which was proved by the fact that the the examined elements (see Table 5), which suggests that K can easily be extracted from the outer layer of the hair by the washing procedure removed this maximum, and the Zn level of the hair became nearly constant. After the washing pro- washing procedure because of its mobility.14 The identification of the exogenous or endogenous origin of the extracted K cedure the Zn concentration of the hair decreased #15%, except for the proximal end. In the case of unwashed hair requires further experiments.The change in concentration of Cl during washing was also high, although its distribution was samples K and Cl concentrations increased from the proximal to distal end.After washing this tendency was eliminated, and homogeneous in the cross section of the hair. The concentration of Ca, Fe and Zn remained nearly unchanged during the K concentration became constant along the length of the hair. In the middle of the hair the K level is higher than at washing. In Table 6 the typical concentrations of the selected elements the ends. The possible reason for this might be that the washing procedure did not completely remove the exogenous measured in the cross-sections of a single hair taken from diVerent distances from the proximal end (5 mm, 10 mm, K or the endogenous K is distributed inhomogeneously in the hair.It is discernible that the concentration of K was almost 15 mm, respectively) are shown. In the case of Ca decreasing the same at the proximal end of the single hair before and Table 5 Changes in concentration during the washing procedure (average of all measured values in the longitudinal experiments, micro- Table 6 Typical results of cross-sectional experiments (washed samples, haemodialysed patient, micro-PIXE) PIXE, n=6) Mean concentration/mg g-1±standard Concentration at diVerent distances (l) from the hair root/mg g-1±standard deviation deviation Element Before washing After washing Element l=5 mm l=10 mm l=15 mm Ca 1130±14 629±7 713±8 Ca 408±150 384±112 Cl 6107±1714 3470±1446 Cl 1474±72 3362±40 2162±49 Fe 57±11 6±4 49± 6 Fe 32±20 31±22 K 1164±846 497±552 K 179±9 420±6 239±6 Zn 202±30 175±16 186±20 Zn 142±24 121±42 556 J.Anal. At. Spectrom., 1999, 14, 553–557after washing. At this region the exogenous K concentration In clinical practice the monitoring of the trace element content of the body during a longer life period could be which can be removed by washing was smaller than at the other segments of the hair. The K concentration increased important (except for acute problems like poisoning). Such examinations require analytical methods in which small from the proximal to the distal end of the hair when unwashed, while it was nearly constant after washing, because the exogen- amounts (0.5–0.01 g) of hair are used, and prior to analysis homogenisation, dissolution or digestion is applied to avoid ous contamination was proportional to the exposure time, and this period was the shortest in the case of the proximal hair the sample inhomogenity and concentration fluctuations.However, the distribution of the elements inside the hair, segment.The concentration of Ca slightly increased along the hair before washing because of the accumulation of exogenous along the hair strands, can be determined by using PIXE or micro-PIXE methods. These are nondestructive and have high Ca. After performing a washing procedure the Ca level fluctuated. In the middle of the washed hair sample, similarly to K, resolution, but are slow and expensive methods, which cannot be applied routinely in clinical practice. the Ca level was high, possibly because of the increased K and Ca uptake at that period.The concentration of Cl increased on the surface of the hair, although the tendency is not as Acknowledgements clear as in the case of Ca or K. After washing, the Cl level This research was granted by the National Research greatly decreased, the change in concentration was higher at Foundation (OTKA) under project number T22739. the distal end where the exogenous contamination was higher.We observed that the concentration of Fe on the surface References fluctuated before washing. After washing we found that the Fe concentration decreased from the proximal to the distal 1 T. D. Lyon, C. Cunningham, D. J. Halls, J. Gibbons, A. Keating end. The iron concentrations at the distal and proximal ends and G. S. Fell, Ann. Clin. Biochem., 1995, 32, (2), 160. of the washed sample were higher than in the case of unwashed 2 L. Scarpino, A. Confessore, A. Bruno, A.Bonifati, M. Gatti, I. sample. This decrease is in good agreement with former results Maimone, M. P. Minella, C. Sapio, F. Smilari and G. Attademo, Minerva Urol. Nefrol., 1994, 46, 89. found in the literature,15 which show that the iron is not 3 U. Vogelsang, Schweiz Rundsch. Med. Prax., 1994, 83, 738. incorporated into the hair at the hair bulb but it is incorporated 4 J. E. Jervis, B. T. Kua and G. Hercz, Biol. Trace Elem. Res., 1994, from other sources close to the skin surface.Hence its concen- 43–45, 335. tration is high in the outer layer, and along the hair the highest 5 J.S¡ tupar and F. Dolnis¡ek, Spectrochim. Acta, Part B, 1996, 51, values are measured not in the hair bulb, but close to the skin 665. at the proximal end. Therefore the decrease of the Fe level 6 J. Bacso� , P. Kova�cs and S. Horva�th, Radiochem. Radioanal. Lett., 1978, 33(4), 273. can be explained by the dissolution of the iron from the hair 7 D. E. Ryan, J. Holzbecker and D.C. Stuart, Clin. Chem., 1978, by environmental eVects. 24, 1996. 8 J. Dombova�ri and L. Papp, Microchem. J., 1998, 59, 187. 9 P. Senofonte, N. Violante, L. Fornarelli, E. Beccaloni, A. Powar Conclusions and S. Caroli, Ann. Ist. Super. Sanita, 1989, 25, 385. 10 I. Rajta, I. Borbe�ly-Kiss, Gy. Mo� rik, L. Bartha, E. Koltay and Our results show that there are considerable diVerences A. Z. Kiss, Nucl. Instrum. Methods Phys. Res., Sect. B, 1996, 109– between the concentrations of Ca, Cl and K in the hair of HD 110, 148. 11 Gy. Szabo� and I. Borbe�ly-Kiss, Nucl. Instrum.Methods Phys. Res., patients, healthy controls and the results found in the literature. Sect. B, 1993, 75, 123. However, sample treatment has a major eVect on the measured 12 G. V. Iyengar, W. E. Kollmer and H. J. M. Bowen, The Elemental values; the applied washing procedure influences the element Composition of Human Tissues and Body Fluids, Verlag Chemie, content of the sample. Our general observation is that the Weinheim, New York, 1978, pp. 7–13, 51–54. measured values and the tendencies along the length of a 13 F. Fischbach, A Manual of Laboratory Diagnostic Tests, third single hair were more variable prior to the washing procedure. edition, ed. D. Inteno, J.B. Lippincott Co., Philadelphia, 3rd edn., 1988, pp. 41, 46, 66, 97, 159. A possible reason is the inhomogeneous endogenous trace 14 F. Watt and J. P. Landsberg, Nucl. Instrum. Methods Phys. Res., element distribution (which is due to the irregular uptake). Sect. B, 1993, 77, 249. This endogenous distribution is covered by the more fluctuat- 15 A. J. J. Bos, C. C. A. H. Van Der Stap, V. Valkovic, R. D. Vis and ing exogenous contamination of the external layer. Another H. Verkenl, Nucl. Instrum. Methods in Phys. Res., Sect. B, 1984, reason could be the insuYciency of the applied washing 3, 654. procedure which cannot completely remove the contamination from the surface of the sample. Paper 8/07030J J. Anal. At. Spectrom., 1999, 14, 5

ISSN:0267-9477    

DOI:10.1039/a807030j

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Dc arc spectrometry of solids: some new aspects of an old method† Karol Flo�ria�n,*ab Ju�rgen Haßlerc and Eva Surova�a aDepartment of Chemistry, Faculty of Metallurgy, Technical University of Kos¡ice, Letna� 9, SK-042 00 Kos¡ice, Slovakia bDepartment of Physical and Analytical Chemistry, Faculty of Sciences, P.J. S¡ afa�rik University, Moyzesova 11, SK-041 54 Kos¡ice, Slovakia cElektroschmelzwerk GmbH, P.O. Box 1526, D-87405 Kempten, Germany Received 10th September 1998, Accepted 24 November 1998 The critical evaluation of old-fashioned dc arc excitation under modern conditions and in connection with a multichannel spectrometer is reported.As typical solid samples in all evaluation steps, various kinds of SiC powders were used; as analyte elements, the most important impurities (Al, Fe, Ni, Ti and V) were chosen. The broad use of the method is also demonstrated in the ecologically relevant analysis of sediments, where the main toxic and essential elements (Cr, Cu, Ni, Pb, V and Zn) were analysed. Contrary to our earlier investigations, in this case, neither a special working atmosphere nor the dilution of samples with spectrochemical additives was applied. The main figures of merit of the method were determined (precision of the method, calibration characteristics, limit of determination, etc.).Their values confirmed the applicability of the modernized dc-arc-OES method as a rapid alternative to existing solid sampling (SS)-OES and SS-AAS methods.For a long period of spectroscopic history, direct current (dc) enables the destruction of such complicated ceramic matrices as SiC or B4C and, at the same time, the total evaporation of arc excitation was the leading technique for the direct analysis of powdered samples, especially in the specific area of geo- impurities from the powder sample. These aspects of the forgotten dc arc technique were reported in the last Solid chemical analyses. This initially semi-quantitative method, after much optimization and quantification1 (internal Sampling Colloquium.9 If the disadvantages of old-fashioned dc arc spectrography, the non-controlled free burning of the standard method, Lomakin–Scheibe equation, blackeningtransformation procedures, etc.), became a rapid, widely used arc and the photographic registration of spectra, are avoided, a new modernized dc arc connected with quartz-fibre optics multi-element quantitative method.The latter optimization, in the evaluation of photographically registered spectra1 (modern to a multichannel spectrometer will give a good alternative spectrochemical method to the existing ICP-ETV and/or densitometers), led to an average precision of about 15% with relatively low detection limits.Some modifications of the dc SS-ETV-AAS techniques in the routine analysis of complicated powder samples. These statements are underlined with the arc itself were also developed, e.g.the use of stationary magnetic fields,2 inhomogeneous magnetic fields3 and the availability of commercial dc arc sources from ARL Fisons (Crawley, W. Sussex, UK) or Thermo Jarrel Ash (Franklin, double-plasma method.4 Also, continuous sample introduction techniques were successfully evaluated and used in the practical MA, USA). The research reported in this paper confirms the statements analysis of powdered samples. The intensive development of new excitation sources in given above.As a model for all evaluation steps, SiC powder was chosen—a typical sample in solid sampling. The use of atomic spectroscopy and the commercial use of modern spectrometric techniques halted the evaluation of dc arc excitation, the proposed dc arc-OES method is evaluated on the basis of the analysis of sediment samples of environmental importance. and research in the field of the direct analysis of solids was consequently directed in both atomic emission and atomic Special attention was paid to the calibration procedure: calibration with diVerent weights of a single reference material absorption spectrometry towards the use of various models of electrothermal vaporization (ETV).5 In connection with the (RM) was preferred and evaluated in detail. most successful excitation source of the last three decades, the ICP, other sample introduction techniques were evaluated Experimental (slurry nebulization, direct sample insertion, laser ablation, etc.), but ICP-ETV and ETV-AAS seem to be the most Instrumentation widespread.The experiments were carried out using an LECO-750 (St The use of the ETV technique has certain disadvantages, in Joseph, MI, USA) simultaneous spectrometer with quartz- particular the upper temperature limit of about 2900 °C. fibre optics and a computer-controlled dc arc excitation source Therefore, in special cases of solid sampling (SS) analysis with optimized ramping (see Table 1) of the arc current.The (ceramic powders, sediments), the use of either working atmosconnection between the dc arc light source and the LECO-750 pheres6 of special gas mixtures or of spectrochemical additives7 spectrometer was realized by two vertically oriented quartz is necessary. fibres with collecting lenses (double optics, DO arrangement); The dc arc excitation source in connection with highresistance carbon auxiliary electrodes achieves on the top of the carrier electrode, a temperature8 of about 4000 °C, which Table 1 The arc current–time programme of the dc arc source Burning time/s 0–5 5–8 8–16 16–29 29–65 65 †Presented at the 8th Solid Sampling Spectrometry Colloquium, Arc current/A 2.7 6.9 3.9 8.4 13.5 0 Budapest, Hungary, September 1–4, 1998.J. Anal. At. Spectrom., 1999, 14, 559–564 559Table 2 The characterization of the reference samples of SiC used Reference sample SiC-2495 SiC-3757 SiC-628 SiC NMP-6 d50/mm 54–59 10.8–13.3 1.5 80–90 Al/mg g-1 825 350 265 458 B/mg g-1 — — 40 19.5 Ca/mg g-1 60 19 23 74.4 Cu/mg g-1 — — 3 5.1 Fe/mg g-1 520 140 415 702 Ni/mg g-1 135 — 100 134 Ti/mg g-1 290 140 90 183 V/mg g-1 780 380 410 217 Usually, the calculation of the straight line of the calibration is based on the least-squares method, but the fulfilment Fig. 1 The arrangement of the quartz-fibre optics.of predicted conditions is rarely reported. First of all, the normality of repeated measurements (signals) should be checked with the David test, in which the value in the special case of arc stability testing, a single (SO) quartz fibre was used (see Fig. 1). D� =Ri/si for each data set of repeated signal measurements for given Evaluation procedure calibration concentrations is calculated (Ri is the range and si the standard deviation of the given data set) and compared Testing of instrumental parameters with the table data. If the calculated value lies inside the range In the first step, the optimum observation position of the (2.21<D<2.71 for K=5 repetitions, and statistical signifi- collecting lens of the quartz fibre was determined (see Fig. 2). cance level a=0.10), the normality of the data set is confirmed In the following steps, the influence of the sample homogeneity, (denoted as + in Tables 9–13). sample amount weighed into the cavity of the carrier electrode In the second evaluation step, the homoscedasticity (homoand slit width of the spectrometer was investigated.In all of geneity of variances si2) should be checked;10 when K1=K2= these experiments, the influence on both the integrated intensity .....KN=K=const., the value (Cochran test) means and the RSD values was followed, using SiC powders of variable grain size as model samples. G� =smax2/ S N i=1 si2 Calibration and its characteristics is calculated and compared with the table data. If The analytical calibration using SiC standards (see Table 2) G� <Gtab and eight sediment RMs (see Table 3) was based on the linear the homoscedasticity is confirmed (denoted as + in Tables calibration function: 9–13).integrated intensity=f [concentration] The goodness of fit (test of the linearity, test of the adequacy of the linear model ) can be evaluated on the basis of two The integration coen for each element. The variances:10 the residual variance experimental conditions varied as a function of the number of RMs used, caused by the non-linearity of the calibration line in some cases.Besides the classical calibration with a set of sres.2= 1 N-2 S N i=1 (yi-y� i)2 RMs, calibration with diVerent weights of a single RM was used. and the variance of repeated measurements sw2= S N i=1 S K j=1 ( yi,j-yi)2 N(K-1) with the linear calibration function y=A+Bc and N calibration samples (concentrations c), each with K repetitions. If, for the calculated value FLIN= sres.2 sw2 FLIN<FTAB is true (FTAB of the Fisher distribution; degrees of freedom n1=N-2; n2=N(K-1); and statistical level of significance a=0.05), then the goodness of fit is confirmed (denoted as + in Tables 9–13).The figures of merit Besides the mentioned characteristics of calibration (the residual variance is the most important characteristic), other figures of merit were calculated: Fig. 2 The experimental arrangement of various observation positions of the quartz-fibre optics. (i) the average relative standard deviation RSDa6 [the RSDi 560 J.Anal. At. Spectrom., 1999, 14, 559–564Table 3 The characterization of reference materials (RMs) of sediments used Element/mg g-1 RM Cu Zn Cd Pb Cr Co Ni V B BCR-277 101.7 547 11.8 146 192 43.4 BCR-280 70.5 291 1.6 80.2 114 73.6 BCR-320 44.1 142 0.53 42.3 138 75.2 GWB-07305 137 243 0.82 112 70 18.9 34 109 51 GWB-07309 32 78 0.26 23 85 14.4 32 97 54 GWB-07312 1230 498 4.0 285 35 8.8 12.8 46.6 NIST-2704 98.6 438 3.45 161 135 14 44.1 95 SL-1 30 223 0.26 37.7 104 19.8 44.9 170 (39) Table 4 The dependence of the integrated intensity means and RSDs obtained using the position in the middle of the electrode gap, on the observation position (six repeated measurements, each of them but with lower signal values.As the precision of the measuretwice, see Fig. 2) ments is most important, the observation position 4 was chosen for future experiments. Position Homogenization of the SiC sample is of greater importance Element Parameter 1 2 3 4 5 6 when powders of larger grain size are examined (Table 5), but a homogenization time above 25 min had a negative influence Al SI/a.u. 67.7 23.3 22.6 26.7 40.1 37.5 on the RSD values. The distribution of grain size changed RSD (%) 11.9 7.8 10.3 7.2 10.0 11.6 from a typical normal distribution to a skewed one in the Fe SI/a.u. 39.3 22.5 20.6 21.3 35.0 48.5 direction of smaller particles. This fact can explain the worsen- RSD (%) 9.1 5.6 7.0 7.1 13.6 10.0 ing of the RSD values, especially after the second homogeniz- Ni SI/a.u. 24.8 15.5 15.1 18.5 34.2 65 RSD (%) 13.7 4.2 5.7 6.3 16.9 12.1 ation, due to the inhomogeneity of the sample. These Ti SI/a.u. 72.7 34.6 37 41.7 63.4 79.8 conclusions are in good agreement with the calculated data of RSD (%) 17 4.0 9.4 7.2 9.9 9.9 the so-called span:13 V SI/a.u. 41.4 20.2 21.6 27.2 46.4 47.2 RSD (%) 19.9 10.2 10.9 5.6 10.8 8.5 span= d90-d10 d50 (i=1-N) data of K=5 repeated measurements were averaged which are 1.30–1.46–1.92 for the sample with larger grain size for the series of measurements of calibration samples]; (SiC-2495) and 0.38–0.73 for the sample with smaller grain (ii) the relative precision of the method (RSDMETHOD) size (SiC-3757).The signal values did not show any dependence calculated according to the German norm;11 on the homogenization, with the exception of Ti, where the (iii) the detection limit (LOD), calculated12 as the upper doubling of the signal can be explained only by the release of limit of the expected range of the intercept (A) of the calibration Ti from the large grains of the SiC skeleton (in the case of line (y=A+Bc).fine SiC powder, this increase was not observed). The dependence of the signal values on the amount of Results and discussion sample weighed into the electrode cavity is, as expected almost linear; the diVerent evaporation rates of the diVerent amounts Optimization of instrumental parameters of SiC samples is the basis of the diVerent RSD values.These are better when samples with smaller grain size or samples The optimum observation position is element dependent (Table 4) and the two chosen parameters (signal/RSD) contra- after homogenization are used (Table 6). The slit width of the spectrometer can also have an influence dict each other. The maximum signal values were obtained at the observation position near to the counter-electrode (cath- on the tested parameters, e.g. the signal value and its reproducibility. A decrease in the slit width led, for some elements, to ode), due to the well known cathode-layer eVect, but they are associated with the highest RSDs. The optimal RSDs were typical minimum RSD values at a slit width of 1.5 mm Table 5 The dependence of the integrated intensity means and RSDs on the homogeneity of the SiC samples with various grain sizes (sample weight=6 mg) Homogenization of the sample 0 min 25 min 2×25 min SiC sample Element SI/a.u.RSD (%) SI/a.u. RSD (%) SI/a.u. RSD (%) 2495 Al 42.6 8.3 47.0 5.3 48.4 4.3 Fe 48.3 10.0 52.1 6.6 51.0 12.0 Ni 36.1 19.0 41.5 5.9 39.7 15.0 Ti 37.4 16.0 71.7 5.7 64.3 14.0 V 40.9 22.0 47.0 7.8 45.7 23.0 d50/mm 54–59 36.5 25.1 3757 Al 20.4 4.3 22.2 5.4 Fe 18.5 5.3 19.7 3.5 Ni 12.6 4.7 13.4 4.7 Ti 36.5 8.5 32.2 4.3 V 25.6 7.5 22.7 5.9 d50/mm 10.8–13.3 10.6 J. Anal. At. Spectrom., 1999, 14, 559–564 561Table 6 The dependence of the integrated intensity means and RSDs on the amount of SiC sample weighed into the cavity of the carrier electrode Amount of sample 9 mg 6 mg 3 mg 1.5 mg SiC sample Element SI/a.u.RSD SI/a.u. RSD SI/a.u. RSD SI/a.u. RSD (%) (%) (%) (%) 3757 Al 37.7 8.1 20.4 4.3 11.5 14.0 6.2 13.0 (10.8–13.3 mm) Fe 26.3 7.1 18.5 5.3 14.0 13.0 11.2 8.9 Ni 17.5 5.4 12.6 4.7 9.7 12.0 7.2 10.0 Ti 47.7 3.6 36.5 8.5 20.9 9.7 14.0 9.8 V 39.2 7.5 25.6 7.5 12.6 8.7 6.6 15.0 2495 Al 73.0 11.2 42.6 8.3 20.7 3.6 (54–59 mm) Fe 76.9 13.1 48.3 10.0 26.4 13.3 Ni 56.5 19.5 36.1 18.5 21.2 12.0 Ti 95.9 30.3 37.4 15.5 37.3 27.5 V 72.4 21.0 40.9 21.9 18.6 18.9 2495 Al 80.8 2.3 47.0 5.3 22.8 8.3 (25 min homog.) Fe 79.1 6.0 52.1 6.6 28.2 13.0 (36.5 mm) Ni 62.2 8.0 41.5 5.9 22.1 17.0 Ti 95.4 10.0 71.7 5.7 35.9 19.0 V 80.6 6.8 47.0 7.8 15.6 46.0 Table 7 The dependence of the integrated intensity means and RSDs on the slit width of the spectrometer (SiC-3757, 6 mg, n=5) Slit width/mm 2.5 2.0 1.5 1.0 Element SI/a.u.RSD SI/a.u.RSD SI/a.u. RSD SI/a.u. RSD (%) (%) (%) (%) Al 46.6 4.7 27.3 5.7 38.4 5.7 12.5 15.1 Fe 40.7 5.6 26.3 3.5 28.3 3.9 8.2 8.3 Ni 33.6 5.4 22.1 1.7 20.2 5.3 5.3 42.0 Ti 78.5 5.7 52.1 3.1 52.0 2.9 16.9 11.0 V 50.8 9.0 33.9 10.0 34.9 4.3 12.1 20.0 Table 8 The dependence of the integrated intensity means and RSDs on the observation mode used (10 repeated measurements; SO, single optics=only one glass fibre optic; DO, double optics=two, 90° oriented, fibre optics; see also Fig. 1) SiC Sediment SO (m=8 mg) DO (m=8 mg) SO (m=6 mg) DO (m=3 mg) Element SI/a.u.RSD SI/a.u. RSD SI/a.u. RSD SI/a.u. RSD (%) (%) (%) (%) Al 12.4 12.0 18.2 12.0 B 23.0 7.1 45.9 7.8 Ca 9.5 11.0 14.9 9.5 Cr 72.0 3.2 89.7 4.7 Cu 5.1 9.5 8.6 8.5 72.0 4.5 79.0 6.1 Fe 23.2 7.8 37.1 7.3 Mg 3.7 8.2 6.6 7.0 Ni 16.9 7.0 31.9 7.6 53.8 7.9 49.9 6.8 Pb 14.9 8.5 19.5 9.9 Ti 17.7 11.0 30.2 11.0 V 30.2 15.0 48.6 14.0 68.6 8.7 80.0 8.1 Zn 21.5 11.0 21.1 6.7 (Table 7), but without a common trend. The highest signals about a factor of 1.5–2.0, but there were no significant diVerences in the RSDs.This allows the conclusion to be were obtained at a slit width of 2.5 mm with, on average, acceptable values of RSD. Therefore this value was used in drawn that the stability of arc is high and the so-called ‘dancing of arc’ is totally eliminated in the electronically all subsequent experiments. The arrangement used for optical signal processing allows controlled dc arc. In the second part of the experiment, in order to obtain similar signal values in the single optic the signal dependence and arc stability to be studied.When the same amount of SiC sample was excited and the signals arrangement, two fold higher amounts of the sediment sample werepplied. Similar signal values were characterized in this were detected first using only one (SO) quartz fibre and then using both (DO) quartz fibres, the following results were case with no significant diVerences in RSDs.These experiments confirm the perfect function of the quartz fibre coupling. obtained (Table 8): the signal values increased, on average, by 562 J. Anal. At. Spectrom., 1999, 14, 559–564Table 9 The figures of merit for calibration with a single calibration sample (SiC-628: concentration of elements, see Table 2) at diVerent weights (12, 8, 4, 2 and 1 mg) in the carrier electrode cavity Element Parameter Al B Ca Cu Fe Ni Ti V RSDa (%) 12.7 8.1 14.6 12.9 9.9 11.3 14.8 14.1 Norm./homosc.(+/-) +/- +/+ +/- +/+ +/+ +/+ +/+ +/- r 0.989 0.998 0.976 0.994 0.998 0.995 0.991 0.991 A -0.44 4.80 4.30 1.99 6.90 10.2 8.60 -3.90 B 0.118 1.48 0.780 3.10 0.112 0.327 0.394 0.220 RSDMETHOD (%) 9.4 5.8 19 9.6 5.1 8.1 12 11 FLIN (a=0.01) + + + + + + + + LOD/mg g-1 39 3.6 6.7 0.5 33 13 16 72 Table 10 The figures of merit for calibration with a single calibration sample (SiC NMP-6: concentration of elements, see Table 2) at diVerent weights (12, 8, 4, 2 and 1 mg) in the carrier electrode cavity Element Parameter Al B Ca Cu Fe Ni Ti V RSDa(%) 11 12 13 13 13 14 16 15 Norm./homosc.(+/-) +/+ +/+ +/+ +/- +/+ +/+ +/- +/- r 0.997 0.999 0.980 0.998 0.999 0.999 0.995 0.995 A -0.11 2.15 10.7 1.77 4.53 10.3 8.21 0.52 B 0.138 1.52 0.420 2.91 0.119 0.309 0.391 0.179 RSDMETHOD (%) 6.9 3.0 17 5.2 4.5 2.3 8.5 8.6 FLIN (a=0.01) + + + + + + + + LOD/mg g-1 62 0.9 20 0.4 49 4.7 24 29 Table 13 The figures of merit for calibration with a single sediment Table 11 The figures of merit for calibration with four sediment RMs (GBW-07305, -07309, -07312, BCR-277: concentration of elements, RM (SL-1: concentration of elements, see Table 3) at diVerent weights of the sample (12, 8, 6, 4, 2 and 1 mg) in the carrier electrode cavity see Table 3) at two diVerent weights (4 and 2 mg) in the carrier electrode cavity Element Element Parameter Cu Cr Ni Pb V Zn Parameter Cu Cr Ni V Zn RSDa (%) 7.0 10 11 10 10 11 Norm./homosc.+/+ +/+ +/+ +/+ +/+ +/+ RSDa (%) 7.8 7.3 5.9 6.8 6.0 Norm./homosc.(+/-) +/+ +/- +/- +/+ +/+ (+/-) r 0.962 0.986 0.976 0.969 0.983 0.996 r 0.975 0.997 0.978 0.966 0.959 A 19.9 0.946 12.7 1.20 4.82 A 10.6 6.2 30.9 9.1 7.5 9.3 B 0.90 0.67 0.70 0.22 0.58 0.07 B 0.722 0.976 0.484 0.535 0.026 RSDMETHOD (%) 14 4.0 13 14 15 RSDMETHOD (%) 20 11 15 17 14 6.8 FLIN (a=0.01) + + + + + + FLIN (a=0.01) + + + + + LOD/mg g-1 23 5.3 7.4 28 261 LOD/mg g-1 8.2 15 13 10 30 19 Table 12 The figures of merit for calibration with eight sediment RMs preparation of calibration sets.With the exception of two (concentration of elements, see Table 3) and a weight of 6 mg in the analytes (Ca and V), no significant diVerences in the main carrier electrode cavity figures of merit were observed (Tables 9 and 10) in some cases, the homogeneity of variance was not confirmed and a Element revision of the data sets or the use of the weighted least- Parameter Cu Cr Ni V Zn squares method in future optimization is needed.Both the RSDa and RSDMETHOD values, defining the precision, are RSDa (%) 13 16 12 10 8.5 acceptable for the direct solid sampling method, but the values Norm./homosc. +/- +/+ +/+ +/+ +/+ obtained for analytes Ca, Ti and V need some optimization. (+/-) The adequacy of the linear model used was confirmed in all r 0.996 0.959 0.962 0.992 0.993 cases, with the exception of Ca and V, there are no significant A 16.7 10.3 27.3 6.5 23.1 B 0.340 0.470 0.460 0.130 0.220 diVerences in the parameters of the calculated straight lines.RSDMETHOD (%) 5.0 12 13 11 5.5 The LOD values are, with the exception of Al, also acceptable, FLIN (a=0.01) + + + + + because the concentrations of the elements lie above these LOD/mg g-1 10 33 15 30 18 limits in commercial SiC products which should be controlled. For the calibration of sediments, three diVerent kinds of calibration process were used. Firstly (Table 11), a calibration Calibration and method validation with four diVerent RMs at two diVerent weights in the carrier electrode; secondly, a calibration with eight diVerent RMs (see As mentioned, the analytical calibration was carried out using two typical samples: SiC and sediments.For SiC calibration, Table 12); thirdly, only a single RM (SL-1) at six diVerent weights (Table 13). In most of these cases, all three basic tests only the method using diVerent weights of a single calibration sample was employed because of a lack of suitable RMs.Two (normality of data sets, homoscedasticity and linearity) were confirmed, but there are significant diVerences in the param- SiC samples with diVerent grain sizes were used for the J. Anal. At. Spectrom., 1999, 14, 559–564 563eters (A and B) of the straight lines. These diVerences could Acknowledgements be caused by classical matrix eVects, due to the diVerent origin This work was supported by the Slovak Grant Agency VEGA, of the RMs having SiO2 as the main component, but also the Grant.No 1/4365/97, and by common Slovak–German coop- type of species in which the elements are present can have eration project SLAX 262.8. some eVect. Future experiments are needed to answer these questions. The RSD values above 10% should also be revised, but values of about 5% (Cr, Cu, V) are fully acceptable. The References LOD values depend partially on the ‘goodness of fit’ of the 1 K. Zimmer, K. Flo� ria�n and Gy. Heltai, Prog.Anal. Atom. calibration lines; on average they are acceptable, because the Spectrosc., 1982, 5, 341 (and references cited therein). lowest concentrations of the elements in sediments from 2 D. Lummerzheim and H. Nickel, Z. Anal. Chem., 1969, 245, 267. Slovakia are: 26 mg g-1 for Zn, 2.2 mg g-1 for Cr, 5.8 mg g-1 3 M. Todorovic�, V. Vukanovic� and V. Georgijevic�, Spectrochim. for Pb and 5.2 mg g-1 for Cu. Acta, 1969, 24B, 571. 4 D. Vukanovic�, V. Simic�, V. Vukanovic�, H. Nickel and M. Mazurkiewicz, Spectrochim. Acta, 1977, 32B, 305. 5 D. C. Baxter and W. Frech, Spectrochim. Acta, 1995, 50B, 655. 6 Gy.Za� ray and T. Ka�ntor, Spectrochim. Acta, 1995, 50B, 489. Conclusions 7 H. Nickel and Z. Zadgorska, Spectrochim. Acta, 1995, 50B, 527. Using typical samples for solid sampling spectrometry, a 8 H. Muller, M. Mazurkiewicz and H. Nickel, Ber. Kernforschungsanlage Ju�lich, Nr. 1449, 1977. complex methodical evaluation of dc arc spectrometry was 9 K. D. Ohls, Spectrochim. Acta, 1996, 51B, 245. made. Dc arc OES is a possible alternative to the modern, but 10 K. Danzer and L. A. Currie, Pure Appl. Chem., 1998, 70, 993. more complicated, methods of solid sampling analysis, because 11 DIN 32645, 1994. of its simple handling and lack of need for sample preparation 12 V. Damman, G. Donnevert and W. Funk, Quality Assurance in or the use of special working atmospheres to achieve complete Analytical Chemistry, Verlag Chemie,Weinheim, 1995. evaporation of the analytes. The figures of merit obtained 13 W. Mutter, Int. Lab. News, 1993, 12, 26. show the need for further optimization steps, directed in particular to the special problems of classical matrix eVects. Paper 8/07088A 564 J. Anal. At. Spectrom., 1

ISSN:0267-9477    

DOI:10.1039/a807088a

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Elemental analysis of micro-samples of liquids or slurries by coiled- filament in-torch vaporization-inductively coupled plasma atomic emission spectrometry (ITV-ICP-AES)† Vassili Karanassios,* Victor Grishko and Gregory G. Reynolds Guelph-Waterloo Center for Graduate Work in Chemistry, University ofWaterloo, Department of Chemistry, Waterloo, Ontario, Canada N2L 3G1 Received 8th September 1998, Accepted 17th December 1998 In coiled-filament in-torch vaporization (ITV) sample introduction for inductively coupled plasma atomic emission spectrometry (ICP-AES), a sample is placed onto a coiled filament (e.g., a Re wire) and the sample carrying filament is inserted into a vaporization chamber which is attached to an ICP torch.In this study, six vaporization chambers were tested using in-situ generated smoke. Of these, a 6.5 cm3 (internal volume) chamber was chosen. An Ar–H2 (#3% v/v) carrier gas was used and the eVect of flow rate and filament insertion position was determined for several elements (e.g., Zn, Pb, Cd, Mn, Mg, V, Be and Sr) that covered a range of wavelengths and vaporization characteristics.Analytical performance characteristics were also obtained and calibration graphs were linear over several orders of magnitude. Detection limits were in the pg to sub-pg range. Coiled-filament ITV-ICP-AES was also briefly tested with powdered solids as slurries using a biological standard reference material and Mn and Zn as test elements.photodiode array spectrometer1,2,19 and was briefly evaluated Introduction with a photomultiplier tube (PMT)-based direct reading spec- In-torch vaporization (ITV)1–3 is an attractive alternative to trometer and with ICP-MS using Pb, Cd, Zn and Sr as test electrothermal vaporization (ETV)4–6 and to direct sample elements.3 In these feasibility studies, the vaporization chamber insertion (DSI)7–9 sample introduction for the analysis of was part of a de-mountable torch and, overall, ITV sample limited size samples by inductively coupled plasma atomic introduction was largely un-optimized.In this work, several emission spectrometry (ICP-AES) or ICP mass spectrometry vaporization chambers were designed and tested. In addition, (ICP-MS). In coiled-filament ITV, a metallic filament is the ITV was further characterized with liquid micro-samples and sample carrying probe. A sample is pipetted onto the probe was briefly tested with slurries of a powdered sample.which is inserted into a vaporization chamber and is positioned about 10 cm from the plasma. Electrical power is applied to the probe for drying, charring/ashing and vaporization and Instrumentation the vaporized sample is carried to the plasma with the aid of The ITV sample introduction system (Fig. 1) consists of a a carrier gas. In a way, ITV can be thought of as an in-situ, vaporization chamber, an electrically heated filament (e.g., Re mini-electrothermal vaporization device which is positioned wire) attached to a thermocouple ceramic insulator1 and a close to the plasma and is driven by a modified DSImechanism.modified drive mechanism which has been used for direct Unlike DSI-ICP, ITV uses an external power supply and sample insertion.8 Initial focus was on the design of a vaporiz- this facilitates independent optimization of vaporization and ation chamber. The objective was to maintain the relatively plasma operating conditions.In addition, rapid heating of the small volume of the previous chamber1–3 but with some sample carrying probe, the relatively small volume of consideration to gas flow dynamics. the vaporization chamber and the short distance analyte vapor Six chambers with diVerent volumes, shapes and carrier gas travels to reach the plasma result in a fast, transient atomic inlet configurations and inlet diameters were designed empiri- population with a high concentration of analyte vapor per cally.For example, the internal volume ranged from 3.4 to unit time. Also, the short distance analyte vapor travels to 18.0 cm3, the shape from conical to oval, the carrier gas inlet reach the plasma reduces or eliminates transport eVects10–18 from single- to dual-tangential and the internal diameter of and the short duration of analyte emission (e.g., tens to the carrier gas inlet from 4.0 to 1.5 mm. Volume is an important hundreds of milliseconds of full-width at half-maximum3) consideration because larger volumes tend to increase disper- results in sharp and narrow signals. In ITV-ICP-AES, such sion and dilution of vaporized samples whereas smaller vol- signals typically translate to improved detection limits.3 umes are thought to give rise to condensation and to analyte Furthermore, owing to the use of metallic rather than graphite loss on the cold walls of the transport system4,5,11–13,20–22 (in sample carrying probes, carbide formation (a key chemical this case, the vaporization chamber and the central tube of limitation of graphite tubes or cups used with the typical the torch).In addition, tangential introduction of the carrier ETV-ICP4–6 or DSI-ICP7,8 systems) is no longer an issue. gas with a high linear velocity was expected to help form a ITV-ICP was developed and characterized with a centralized vortex on top of the filament. The vortex was expected to provide thorough mixing of the hot sample vapors with the carrier gas, to keep the gas containing the vaporized †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998.sample away from the walls of the vaporization chamber and J. Anal. At. Spectrom., 1999, 14, 565–570 565Fig. 1 Cross-section of ITV sample introduction (only the vaporization chamber is shown to scale). to rapidly cool them by the time they reached the central tube of the torch. Rapid mixing and cooling have been reported to Fig. 2 Photographs of ITV sample introduction. (a) Vaporization help vaporized samples condense into aggregates or micro- chamber as attached to an ICP torch, (b) ceramic and seal mechanism and (c) ITV and seal as mounted on the DSI-drive mechanism. particles that can be transported to the ICP with high eYciency.4,11,13,22 To obtain an indication of gas flow dynamics inside the vaporization chambers and to help visualize gas flow patterns, Light emission from the ICP was monitored using a direct reading spectrometer (JY-48, Instruments SA, Edison, NJ, the chambers were tested using in-situ generated smoke by placing mineral oil mixed with an inert binder onto the filament USA) with 32 PMT channels.Current from the photomultiplier tubes was amplified using a low noise current amplifier/ and by applying power to the filament. Each chamber was evaluated visually for smoke-generated black deposits on the low-pass filter (SR570, Stanford Research Systems, Sunnyvale, CA, USA) and the resultant voltage was digitized using a chamber, on the ceramic or both and by examining videotaped recordings of smoke distribution under diVerent gas 12-bit analog-to-digital converter, a data acquisition rate of 500 Hz, LabView software and an Apple Macintosh microcom- flow rates and filament insertion positions (Fig. 1). When the top of the filament was positioned at about 15 mm into the puter.3 This data acquisition sub-system allowed the fast, transient emission signals of ITV sample introduction to be chamber shown in Fig. 1 and the carrier gas flow rate was set at 0.6 l min-1, a swirling stream of smoke which was confined measured.within the center of the chamber was observed. Also, black deposits on the ceramic were not noticed. As a consequence, Experimental this chamber was used throughout and the 15 mm insertion position and 0.6 l min-1 flow rate provided an initial starting For system characterization with liquids, Zn (I, 213.856 nm), Pb (II, 220.353 nm), Cd (I, 228.802 nm), Mn (II, 257.610 nm), point for optimization.An additional advantage of this chamber is that it clips onto any ICP torch with a ball joint, Mg (II, 279.079 nm), V (II, 292.402 nm), Be (II, 313.042 nm) and Sr (II, 407.771 nm) were used. These elements were chosen thus facilitating rapid sample introduction system changeover. Photographs of the vaporization chamber, the seal and part because they cover a wide range of wavelengths and have diVerent vaporization characteristics. Standards were pur- of the drive mechanism are shown in Fig. 2. The 0.25 mm diameter Re filament was 6 cm long and it chased from Leco (St. Joseph, MI, USA) and single element solutions were prepared by serial dilution with distilled, formed a three-coil loop with a diameter of 3 mm. Microliter volumes of a liquid sample or slurry were deposited onto the de-ionized water (18MV) of the respective 1000 mg ml-1 stock standard solution.The system was also briefly tested with filament, the coiled filament attached to the ceramic was manually driven into the vaporization chamber, a seal was slurries. These were prepared by accurately weighing up to 1 g of a powder, adding 10–100 ml of distilled, de-ionized water formed, the sample was dried, ashed/charred (if necessary) and vaporized by applying progressively higher power levels. (18MV) to the powder, adding a thixotropic agent (TritonA X-100, 0.05%) and magnetically stirring the resultant suspen- Power applied to the filament was supplied by a laboratory variac.sion. Unless otherwise stated, 10 ml volumes were placed onto 566 J. Anal. At. Spectrom., 1999, 14, 565–570the Re filament (Iso-Mass Scientific, Calgary, Alberta, Canada) using an Eppendorf micropipette (Cole-Parmer, Vernon Hills, IL, USA). To reduce the potential for contamination from particles landing on the filament,1 solutions were dried and slurries were dried and ashed/charred inside the vaporization chamber.The dried/ashed residues on the filament were vaporized by applying about 35 W. At this power level, the filament was glowing white hot. The vaporized sample was carried to the ICP using an Ar or an Ar–H2 carrier gas. Argon and hydrogen were purchased from Linde (Toronto, Ontario, Canada). Argon was mixed with H2 using a rotameter (Linde) and the carrier gas flow rate was controlled using a mass flow controller (Brooks Instruments, Hatfield, PA, USA).Plasma observation height was set at 14.5 mm above the load coil and, with the exception of Sr (900 W) and Mn (1200 W), a 1.5 kW forward power was used throughout. Results and discussion Similar to ETV-ICP-AES23 and DSI-ICP-AES7,8 sharper signals in ITV-ICP-AES generally translate to improved detection limits. Sharper signals were expected by increasing the heating rate and, depending on elemental volatility, the final temperature of the filament.To use the fastest possible heating rate once the desired power level was set, power was applied to the filament using the on/oV switch of the variac. However, as power increased over that used previously,3 a pressure pulse became more evident, in particular, at longer wavelengths. In addition, a spectral interference from Re (II, 213.904 nm line) on Zn (I, 213.856 nm line) was observed [Fig. 3(a) and (b)] Fig. 4 Rhenium emission observed by monitoring the Re 213.904 nm line.(a) Regular power (#35 W, insert: scale expansion 10 times) and and a black deposit was noted on the top part of the (b) high power (#70 W, insert: scale expansion 20 times). vaporization chamber. A possible explanation is that the hot Re filament is attacked by O2 and H2O which are present in the Ar carrier gas, to form black hydrated oxide(s).24 either at the onset of the rise in background [Fig. 3(b)] due to Re emission from vaporizing Re oxide(s) in the plasma Depending on power levels, analyte emission was observed (thus complicating background correction) or on top of it (thus also causing a carrier eVect).14,23 The problem of spectral interference was solved by mixing #3% v/v of H2 with the carrier gas and examples are shown in Fig. 3(c) and (d). Most likely, H2 acted as an oxygen scavenger. The small rise in background and the diVerence in the amplitude of the signals shown in Fig. 3(b) and (d) is attributed to a beneficial eVect of mixing hydrogen through the central channel.25 The amount of Re vaporizing from the filament at diVerent power levels was tested by monitoring the Re 213.904 nm spectral line and examples are shown in Fig. 4. Even at high power levels, for example 70 W, only a low intensity signal was observed by monitoring the Re line, thus indicating that Re vaporizing from the filament is not a problem. With power fixed at about 35 W, optimization of insertion position and carrier gas flow rate was attempted.The eVect of carrier gas flow rate was examined with the insertion position initially set by smoke experiments (i.e., using in-situ generated smoke as described under Instrumentation) and the results are shown in Fig. 5. The signal-to-background ratio (SBR) was used to establish optimum flow rates because plasma background was also reduced as the carrier gas flow rate increased. These results indicate that compromise conditions would be required for simultaneous, multi-element determinations.With the carrier gas flow rate set to the optimum for each element (Fig. 5), the eVect of insertion position was studied next. Significant loss of signal intensity was observed when the top of the filament was positioned below the zero insertion position (Fig. 1); signals became broad and, in some instances, Fig. 3 Interference of the Re 213.904 nm spectral line on the Zn nearly disappeared. In addition, loss of signal intensity was 213.856 nm line.(a) Water blank obtained using Ar carrier gas, observed when the filament was inserted above the top inser- (b) dried solution residue of a stock standard solution of Zn, (c) water tion position (Fig. 1). As a consequence, the insertion position blank obtained using Ar–H2 carrier gas and (d) dried solution residue of a stock standard solution of Zn. was varied between 0 and 22 mm or zero and top insertion J. Anal. At. Spectrom., 1999, 14, 565–570 567Fig. 7 Reproducibility for (a) Cd (300 pg) and (b) Be (3 pg). and 20 mm (Fig. 6), compromise conditions would be required for simultaneous, multi-element determinations. With the insertion position set to the optimum for each element, the eVect of carrier gas was tested again using the optimum insertion position for each element (Fig. 6) and SBRs did not vary by more than about 15% of those shown Fig. 5 EVect of carrier gas flow rate. in Fig. 5. As a consequence, the ‘optimum’ flow rates (Fig. 5) and insertion position values (Fig. 6) were maintained throughout detection limit and precision determinations. position in Fig. 1. Analyte signal intensities increased with an The relative standard deviation (%RSD) obtained for peak increase in insertion position, passed through a maximum and height and peak area measurements (ten replicates) was 4.2% then decreased (Fig. 6). The reduced peak heights at low and (2.1% peak area) for Cd and 6.1% (2.5% peak area) for Be.high insertion positions are attributed to a destruction of the Examples are shown in Fig. 7. All other elements had %RSDs vortex that caused analyte loss either on the ceramic and/or between these two values. These %RSDs reflect not only the the cold walls of the vaporization chamber. Although there is precision of the technique but also that of manually pipetting relatively little loss of signal intensity in the region between 15 a sample onto the filament. Automation should further improve the overall precision of ITV-ICP.Calibration graphs (not shown for brevity) were linear over several orders of magnitude. To further increase their dynamic range and to improve concentration detection limits of environmentally important elements, such as Pb, Cd and Zn, preconcentration using multiple drops was tested. For example, 10 ml of a sub-ppb stock standard solution of Zn were deposited onto the filament, the solution was dried and the experiment was repeated ten times.Although the approach allowed subppb (or low pg level ) determinations of Zn, it also proved to be time consuming. Is there a way of increasing the capacity of the filament and thus reducing drying time? This question was addressed using a 16 cm long filament that was coiled into five loops with a diameter of 4.1 mm and a maximum capacity of 50 ml. Solution residues were vaporized by applying 50W to the filament and examples are shown in Fig. 8. The approach may find applicability, in particular, in relatively clean water samples.Detection limits (3s) were obtained using 10 ml of single element standards and were estimated by setting one-fifth of the peak-to-peak value for the noise between 1 and 3 s equal to 1s. The values were: Zn (10 pg), Pb (15 pg), Cd (10 pg), Mn (0.3 pg), Mg (3 pg), V (10 pg), Be (0.1 pg) and Sr (0.08 pg). These values compare favorably with those obtained by ETV sample introduction,4,26 with ITV oVering significant improvements, especially for carbide-forming elements.In addition, detection limits improved over those reported previously,1,3 for example, for Be by one order of magnitude. Can ITV be used for the analysis of solid micro-samples as well? This question was briefly addressed using slurries27 of a Fig. 6 EVect of insertion position (as per Fig. 1) on signal intensity. powdered biological standard reference material (NIST SRM 568 J. Anal. At. Spectrom., 1999, 14, 565–570Fig. 8 Water blanks and emission signals for Zn for coiled filaments with 10 and 50 ml capacities. obtained with this chamber and liquid micro-samples is superior to that reported previously.1,3 Also, Ar–H2 carrier gas mixtures reduced or eliminated spectral interference and carrier eVects from Re vaporizing from the filament, and allowed the use of higher ITV power levels, thus helping to improve detection limits. In addition, the feasibility of direct elemental analysis of powders as slurries has been demonstrated.A new holder that replaces the ceramic and allows either coiled filaments or metal cups to be used with ITV has been designed and tested,27,28 thus further expanding the scope and application of ITV-ICP. It is clear from the results reported here and elsewhere1–3,19,28,29 that ITV has the potential to become a useful sample introduction system for the ICP, in particular, when only micro-samples are available for analysis. Examples include samples of clinical, biological or forensic origin.Also, the short duration of ITV signals may prove to be beneficial to ICP-AES with area sensor detectors and to ICP-TOF-MS (ICP-time-of-flight-mass spectrometry)30 for simultaneous elemental determinations from micro-samples. Acknowledgements Financial assistance from the National Science and Engineering Council of Canada (NSERC) is gratefully acknowledged. References 1 V. Karanassios, K. P. Bateman and G. A.Spiers, Spectrochim. Fig. 9 Slurry of NIST SRM 1577a Bovine Liver. (a) Calibration graph Acta, Part B, 1994, 49, 847. for Mn (slope: 0.98) and Zn (slope: 0.93) and (b) reproducibility for 2 V. Karanassios, K. P. Bateman and G. A. Spiers, Spectrochim. Mn (100 pg in 10 ml of slurry). Acta, Part B, 1994, 49, 867. 3 V. Karanassios, P. Drouin and G. G. Reynolds, Spectrochim. Acta, Part B, 1995, 50, 415. 1577a, Bovine Liver). Examples of calibration graphs are 4 J. M. Carey and J.A. Caruso, Crit. Rev. Anal. Chem., 1992, shown in Fig. 9(a). Reproducibility (peak height) was 6.2% 23, 397. for Mn and 7.3% for Zn and examples are shown in Fig. 9(b). 5 J. M. Carey, F. A. Byrdy and J. A. Caruso, J. Chromatogr. Sci., These results indicate that ITV has the potential to be used 1993, 31, 330. 6 D.C.Gre� goire, Can. J. Anal. Sci. Spectrosc., 1997, 42, 1. for the analysis of powders (as slurries). To accommodate 7 V. Karanassios and G. Horlick, Spectrochim. Acta Rev., 1990, solid micro-samples that cannot be converted easily to a 13, 89.powder or to permit analytical determinations when only solid 8 V. Karanassios and T. J.Wood, Appl. Spectrosc., 1999, 53, 197. micro-samples are available for analysis, the coiled filament 9 C. D. Skinner and E. D. Salin, J. Anal. At. Spectrom., 1997, was replaced by a Re cup; an application of Re-cup ITV-ICP- 12, 1131. AES for direct elemental analysis of solid micro-samples is 10 D. L. Millard, H.C. Shan and G. F. Kirkbright, Analyst, 1980, 105, 502. described elsewhere.28 11 S. E. Long, R. D. Snook and R. F. Browner, Spectrochim. Acta, Part B, 1985, 40, 553. Conclusions 12 S. M. Schmertmann, S. E. Long and R. F. Browner, J. Anal. At. Spectrom., 1987, 2, 687. A new vaporization chamber that clips onto an ICP torch has 13 T. Kantor, Spectrochim. Acta, Part B, 1988, 43, 1299. been designed and tested. The chamber facilitates rapid sample 14 R. D. Ediger and S. A. Beres, Spectrochim.Acta, Part B, 1992, 47, 907. introduction system changeover and, overall, the sensitivity J. Anal. At. Spectrom., 1999, 14, 565–570 56915 D. C. Gregoire, S. Al-Maawali and C. L. Chakrabarti, 25 A. Montaser, K. D. Ohls and D. W. Golightly, in Inductively Spectrochim. Acta, Part B, 1992, 47, 1123. Coupled Plasmas in Analytical Atomic Spectrometry, ed. 16 C. M. Sparks, J. Holcombe and T. L. Pinkston, Spectrochim. Acta, A. Montaser and D. W. Golightly, VCH, New York, 1992, ch. 19. Part B, 1993, 48, 1607. 26 H. Matusiewicz, J. Anal. At. Spectrom., 1986, 1, 171. 17 G. Zaray and T. Kantor, Spectrochim. Acta, Part B, 1995, 50, 489. 27 L. Ebdon, M. Foulkes and K. Sutton, J. Anal. At. Spectrom., 18 R. W. Fonseca and N. J. Miller-Ihli, Appl. Spectrosc., 1995, 49, 1997, 12, 213. 1403. 28 H. R. Badiei and V. Karanassios, J. Anal. At. Spectrom., 1999, 19 V. Karanassios, K. P. Bateman and G. A. Spiers, Spectrochim. 14, 603. Acta, Part B, 1994, 49, 989. 29 V. Grishko and V. Karanassios, in Proceedings, Second Biennial 20 H. Matusiewicz and R. M. Barnes, Appl. Spectrosc., 1984, 38, 745. International Conference on Chemical Measurement and 21 H. Matusiewicz and R. M. Barnes, Spectrochim. Acta, Part B, Monitoring of the Environment, ed. R. Clement and B. Burke, 1985, 40, 29. Ottawa, ON, Canada, 1998, vol. 2, p. 507. 22 C. J. Park, J. C. Van Loon, P. Arrowsmith and J. B. French, Can. 30 P. P. Mahoney, S. J. Ray and G. M. Hieftje, Appl. Spectrosc., J. Spectrosc., 1987, 32, 29. 1997, 51, 16A. 23 D. C. Gregoire, M. Lamoureux, C. L. Chakrabarti, S. Al-Maawali and J. P. Byrne, J. Anal. At. Spectrom., 1992, 7, 579. 24 F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, Interscience, New York, 3rd edn., 1972. Paper 8/07032F 570 J. Anal. At. Spectrom., 1999, 14, 565–5

ISSN:0267-9477    

DOI:10.1039/a807032f

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Survey of sampling techniques for solids suitable for microanalysis by total-reflection X-ray fluorescence spectrometry† Reinhold Klockenka�mper* and Alex von Bohlen Institut fu�r Spektrochemie und Angewandte Spektroskopie (ISAS), Bunsen-KirchhoV-Str. 11, D-44139 Dortmund, Germany Received 5th October 1998, Accepted 16th December 1998 A survey of solid sampling techniques is given, suitable for microanalysis or even ultramicroanalysis by totalreflection X-ray fluorescence (TXRF). A sample amount of 1 ng to 100 mg is placed on a clean, flat carrier usually made of quartz glass or PlexiglasA.For quantification, a drop is added to the sample with a known amount of a single element serving as internal standard. Solid samples can be applied as small particles, fine powders, thin sections or deposits. Several techniques of solid sampling have been examined and one example of each technique is given demonstrating its suitability: direct placing of individual particles, suspension of powdered materials, collection of air dust by impaction, the touchstone technique for metals, laser ablation for local analysis, the Q-tip technique for paints and inks, freeze-cutting of organic materials and direct contamination control of wafers.Total-reflection X-ray fluorescence (TXRF) is a special variant of the sample is recorded by a spectrometer or a semiconductor detector. In comparison, TXRF uses an X-ray tube with a of energy-dispersive X-ray fluorescence (EDXRF) analysis which, today, is widely known.It was first proposed by two narrow or ‘line focus’, emitting a primary beam which is shaped like a strip of paper. The high energy part of its Japanese scientists, Y. Yoneda and T. Horiuchi, in 1971. TXRF has achieved remarkable importance in atomic spec- spectrum may be cut oV by a low-pass filter. In any case, the primary beam strikes a flat glass carrier at a very small angle trometry, and a critical evaluation of recent developments places this method in a leading position.1 Today there are and, consequently, it is totally reflected at the carrier.The sample has to be placed on the carrier in a small amount so three major and three minor suppliers of TXRF instruments, and nearly 300 pieces of equipment are in use worldwide. that total reflection is scarcely hindered. The fluorescence radiation of the sample is recorded by an energy-dispersive Several reviews have been published recently,2–5 and also one monograph6 is available, which is entirely devoted to TXRF. detector, mostly by an Si(Li) detector.The equipment in Figs. 1(a) and 1(b) mainly diVers in geometry: XRFA uses a An inherent feature of conventional X-ray fluorescence analysis (XRFA) is the investigation of any sample in its combination of about 45°/45° for incident and take-oV angle, while TXRF uses a combination of 0.1°/90° (nearly a 0°/90° original phase, i.e. of a sample ‘as is’. Solids can be analysed as solids, liquids as liquids and gases as gases.In contrast with combination). The analytical examples in this paper were carried out on most analytical methods, XRFA is a non-consumptive and, in several cases, a non-destructive method. Vaporisation or even an EXTRA II instrument (Rich. Seifert & Co, Ahrensburg, Germany), equipped with an Mo and a W tube (visible line atomisation of sample material is not necessary. TXRF is a modification of conventional XRFA, but is preferably applied to liquid samples and solutions after an easy preconcentration step: an aliquot is pipetted and dried on a sample carrier, since only the dry residue can be analysed by TXRF.Solid samples are favourably analysed after ashing and/or digestion. This preparation step is carried out for the purpose of homogenisation and possibly preconcentration before a small part of the sample is chosen for analysis. Nevertheless, TXRF can be applied directly to solid samples, which is recommended if microanalysis is needed, i.e.if only a small or minute amount of a sample is present or available. DiVerent solid sampling techniques have been developed for microanalysis by TXRF, and a survey of these techniques is given in this paper after a short review of fundamentals. Fundamentals Instrumental peculiarities of TXRF The essential diVerences between conventional XRFA and the variant TXRF are demonstrated in Figs. 1(a) and 1(b), respectively.XRFA uses an X-ray tube with a broad focus, emitting a cylindrical primary beam. The fluorescence radiation Fig. 1 Simplified instrumental set-up: (a) for conventional XRFA; (b) †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998. for the variant TXRF. J. Anal. At. Spectrom., 1999, 14, 571–576 571focus of 40 mm×8 mm), operated at 50 kV and <40 mA. For used. For direct analysis of organic samples, the lower mg g-1 range can be reached if 100 mg are applied.For inorganic energy-dispersive analysis and data processing, a Link System QX 2000 with Si(Li) detector (Oxford Instruments, High samples, e.g. oxides or metals, only traces of some 100 mg g-1 can be detected if microgram amounts are applied. Major and Wycombe, UK) was used. The total counting time for analysis was mostly set to 100 s. minor constituents can still be detected if only nanogram amounts are available for analysis.Prerequisites of TXRF Quantification by internal standard. Quantification is gener- Sample carriers. Sample carriers are mostly made of quartz ally carried out by an internal standard element added to the glass, but also silicon, glassy carbon, boron nitride and sample in a known amount. TXRF primarily determines the PlexiglasA can be used. They have to be optically flat and unknown mass of an analyte element: extremely clean at their surface. The cleanliness can be checked by a blank spectrum taken in advance of the unloaded carrier.mx= Nx/Sx Nis/Sis mis (1) If spectral peaks of any contaminants appear, the carrier has to be cleaned again. The cheap Plexiglas carriers are usually where m is the mass, N is the net intensity and S is the relative delivered in a suYciently clean condition. sensitivity, either of the analyte (x) or of the internal standard Clean carriers can be used directly for the deposition of (is). The S values are usually known since they were measured solid samples.For the deposition of liquid samples or suspen- by means of standard solutions. This kind of simple calibration sions, they have to be hydrophobic, otherwise the drops are needs to be carried out only once or very seldom. dispersed over the surface. Plexiglas, silicon, glassy carbon Relative mass fractions or concentrations can be determined and boron nitride are hydrophobic by nature, but quartz glass if the total sample mass mtot or the total sample volume Vtot is hydrophilic.It has first to be covered by a silicone solution is measurable: which, after drying, leaves a thin hydrophobic film on the surface. cx= mx mtot or mx Vtot (2) Presentation of solid samples. Conventional XRFA uses a If the total amounts cannot be determined, relative mass sample amount of 1 mg to 10 g or 0.1–50 ml, so that XRFA fractions can at least be calculated (relative in relation to the is more a macro- than a micro-method.In contrast, TXRF sum of all detected elements call): only uses a sample amount of 1 ng to 100 mg of solids or 1–100 ml of liquids yielding micrograms of a dry residue. crx= Nx/Sx SNj/Sj call (3) TXRF, consequently, is a micro- or even an ultramicromethod. This restriction is necessary since the capacity of the This sum may be 100% or simply be set to 100%. For this detector would be exceeded and the total reflection at the simple case, not even an internal standard is needed.carrier would be disturbed if a larger amount of sample This method of easy quantification was applied many times material was applied. The appropriate amount of sample mass and proved reliable. The prerequisite is a minute amount of can easily be adjusted by means of the detector, keeping its sample placed as a thin layer or a thin-film-like sample on a dead time below 50%. clean carrier so that matrix eVecte negligible. This condition Solid samples can be applied as one or several individual is usually not fulfilled for macro-samples of conventional particles, as a suspension or slurry of finely powdered mate- XRFA, but fortunately it is met for the micro-samples of rials, as a thin section of organic materials, as a thin foil of TXRF.The internal standard added via a drop should evenly metals or polymers or as a deposit of metals or non-metals. wet the sample, but it need not be homogeneously distributed In any case, the samples have to be placed in the centre of a within the small or minute sample.carrier as a thin-film-like sample with a thickness of some 0.1–10 mm. For quantification, a drop of an aqueous standard solution has to be added which usually is pipetted onto the Examples of solid sampling deposited sample. Only in the case of suspensions is it rec- General survey of techniques ommended to add a standard solution previously. This solution should contain a single element initially not present in the Numerous solid samples of diVerent kinds and shapes have sample, but afterwards serving as internal standard for all been investigated and diVerent sampling techniques have been other elements in the sample.Generally, rare elements are applied. Individual particles can easily be taken and placed chosen, e.g. Ga, Ge, Se or Y. Drying by evaporation and onto a carrier for TXRF analysis. Fine powders can be recording of the TXRF spectrum follows. suspended, and the suspensions can be pipetted onto a carrier and dried.Air dust or aerosols can be collected by adhesives Features of TXRF covering a carrier. Solid materials, such as metals, can be rubbed on a hard quartz glass carrier so that they are rubbed Detection limits. All elements with atomic numbers Z14 oV. Micro-regions of metals or non-metals can be removed by (silicon) can easily be detected by TXRF. The detection of laser ablation, and some material can be emitted and deposited lighter elements is hampered by several obstacles which are on a glass carrier.Colours or inks can be wiped oV the surface inherent to energy-dispersive XRFA, although some of them of paintings or manuscripts by means of a cotton-wool tip, can be overcome by specifically designed instrumentation.7,8 often called Q-tip, and the loaded Q-tip can be dabbed onto While detection limits of conventional XRFA are at the a carrier. Tissues or polycarbons, generally organic materials, migrogram level, those of TXRF go down to the low picogram can be freeze-cut and the sections can be placed on carriers.level. The improvement is caused by the extremely reduced Wafers can directly be applied and the contaminants on them spectral background according to the minimum portion of the analysed. One example of each technique is chosen in order impinging photon flux that penetrates into the carrier. It is to demonstrate its suitability. proportional to the low transmissivity and to the small glancing angle of incidence.Direct placing of individual particles Relative detection limits are dependent on the sample matrix and sample mass or volume being applied. For high purity Individual particles, such as grains or crumbs of several nanograms or single pieces of hair or textile fibres of several waters or acids, the ng l-1 region can be reached if 100 ml are 572 J. Anal. At. Spectrom., 1999, 14, 571–576micrograms,4,9 can simply be placed onto a carrier.A wooden or repeatability of ten determinations was 3%; the accuracy of the mean or the trueness was 4%. toothpick is recommended for this manipulation. Fig. 2 shows conglomerates of several grains of a pigment powder. The edge length is between 0.1 and 2 mm; the total mass is about Collection of air dust by impaction 1 ng. This is the lower limit of sample amount needed for Airborne particles can be fractionated according to size and TXRF analysis. collected by a cascade impactor with several stages stacked on top of each other, e.g.a Battelle- or Anderson-type impactor. Suspension of powdered materials Air is pumped through one nozzle per stage and dust particles are deposited onto an impaction plate behind the nozzle Fine powders or pulverised materials can be applied as individual particles, but also via a suspension.10,11 Natural suspen- according to their inertia or size. Larger particles are deposited behind a coarser nozzle in an upper stage, smaller particles sions, e.g.river water with a certain portion of suspended particulate matter, can be applied directly.12 For powdered behind a finer nozzle in a lower stage. Simple Plexiglas discs fitted for TXRF devices can be used as impaction plates.14–16 materials, an aliquot can be taken up by a pure solvent; usually several milligrams of the powder are suspended in 5 Particles of wet air stick to the flat discs which can be directly applied to TXRF.Particles of dry air, however, are bounced or 10 ml of water. The aqueous suspension is thoroughly homogenised with a magnetic stirrer or by ultrasonication, or blown oV.14 To avoid this eVect, the discs must first be coated, for example with a medical petrolatum,14 i.e. and a small drop of 10 or 20 ml is pipetted onto a carrier. Afterwards, the single drop is dried by evaporation leaving a VaselineA, or be sprayed, for instance with a medical plaster.17 Dust particles from a total volume of 1 m3 of ambient air dry residue of about 10 mg.A synthetic mixture of three diVerent pigments (titanium were collected in a Battelle-type impactor within 1 h. Fig. 3 shows a spectrum of particles with a diameter of 1–4 mm white, zinc white and strontium yellow) was suspended in petroleum ether with a mixing ratio of 15151. Aliquots of collected on stage no. 4. Ge (100 ng) was added as internal standard. Detection limits are about 0.1 ng m-3, so that 100 ng of the powder were used for TXRF analysis.An internal standard was not needed. First, relative mass fractions pollution during the course of a day can be observed. However, care must be taken to avoid contamination. This can be caused of the four elements Ti, Zn, Sr and Cr were determined after eqn. (3). Since oxygen could not be detected, the relative mass by erosion of the impactor walls or nozzles if made of stainless steel. For that reason, the impactor in use was reconstructed fractions of the respective oxides TiO2, ZnO and SrCrO4 were calculated according to stoichiometry.Finally, the mixing with Plexiglas; even better is an antistatic polymer.17 proportions of these oxides or pigments were determined by normalisation to 33.3%. Table 1 gives the results. The nominal Touchstone technique for metals proportion of 15151 was confirmed by TXRF. The precision When only a survey analysis is required, an old famous technique can be applied: the touchstone technique18,19 explained in Fig. 4. Usually, black jasper is used as the touchstone and the test needles as well as a piece of a precious metal are rubbed on it. The coloured strokes provide a hint of the composition of the metal. This technique was already known in antiquity. The touchstone for TXRF is a quartz glass carrier.6 Solid objects with lower hardness can be rubbed on it in a single stroke; or a quartz glass carrier can be rubbed on a fixed object. In both cases, a small amount of sample material will be smeared onto the carrier, which can be analysed by TXRF.A gold ring may serve as an analytical example: 20 ng were rubbed oV altogether and Mn (5 ng) was added as internal standard. The TXRF spectrum showed the major components Au, Cu, Ni and Zn. The quantitative results are given in Table 2. The gold value of 574 mg g-1 corresponds quite well with the hallmark 585. However, this is a favourable case; it Fig. 2 Conglomerates of several pigment grains placed on a Plexiglas carrier by a wooden toothpick and photographed by a scanning electron microscope. Numerous small, irregularly shaped grains are mixed with larger cubic grains of 2–3 mm edge length.The total mass of ca. 1 ng is suYcient for TXRF analysis. Table 1 Determination of the mixing proportions of three diVerent pigments, titanium white (TiO2), zinc white (ZnO) and strontium yellow (SrCrO4), in a suspension (after Klockenka�mper et al.13). The mean values and standard deviations are given for ten samplings of the suspension and TXRF analysis.The nominal proportion was given by 15151 Relative mass Pigment Relative mass Mixing Element fraction (%) or oxide fraction (%) proportion Fig. 3 TXRF spectrum of air dust collected from ambient air near Dortmund city. Dust particles of 1–4 mm in diameter were deposited Ti 27.0±0.8 TiO2 31.4±0.9 0.94±0.03 on stage no. 4 of a Battelle-type impactor made of Plexiglas. Ge was Zn 39.8±1.6 ZnO 34.6±1.4 1.04±0.04 added as internal standard.The spectrum gives the counts of photons Sr+Cr 33.3±1.0 SrCrO4 33.9±1.0 1.02±0.03 recorded within 100 s as a function of their respective energy. J. Anal. At. Spectrom., 1999, 14, 571–576 573of diVerent elements can be recorded. The lateral resolution may be 10 mm. Q-tip technique for paints and inks Valuable works of art, such as oil paintings or book illustrations, should be analysed only non-destructively. A very gentle method of micro-sampling has been developed for this purpose: the Q-tip method.13 By means of a dry and clean cotton-wool tip, often called a Q-tip, a minute amount of paint or ink can be removed from the surface of paintings or manuscripts.DiVerent Q-tips can be applied to diVerent spots. This technique can be regarded as non-destructive since only a microgram amount is removed. It has to be presupposed that the paintings are not covered with a varnish layer, unless this layer is to be removed for the purpose of restoration. The Q-tips can be locked in bottle caps and transported.For analysis, they are dabbed onto a glass carrier once and less Fig. 4 Woodcut of Lazarus Ercker, Prague 1574, demonstrating the touchstone technique.19 A and B are two sets of test needles; C is a than 100 ng are transferred. This technique was applied to cylindrical or a cubical touchstone made of black jasper. samples of some 20 oil paintings and book illustrations from 12 museums, in Europe, and many questions of restoration, conservation and dating have been answered.21–23 Table 2 Quantitative results for a gold ring after sampling by the One example was presented by Moens et al.23 Paintings of touchstone technique and TXRF analysis. Nearly 20 ng were rubbed the old masters often suVer from so-called ultramarine disease oV altogether; 5 ng of Mn were added as internal standard which turns parts of a glowing blue into a greyish green.Element Mass/ng Mass fraction/mg g-1 Pigments from blue spots and from green spots of the cloak of a Madonna were taken and identified. The pigments of the Ni 2.3 118 blue spots obviously contain ultramarine; those of the green Cu 4.6 234 spots, however, showed the element pattern of a totally Zn 1.5 74 diVerent pigment as demonstrated in Fig. 5. This pigment, Au 11.4 574 Sum 19.8 1000 containing K, Co and As, is called smalt; it is also a blue pigment and is based on cobalt glass.However, it is less valuable than ultramarine and changes colour over the centuries. Thus, so-called ultramarine disease is actually a smalt should be mentioned that deviations occur when preferential disease. abrasion of a soft component occurs. Freeze-cutting of organic materials Laser ablation for local analysis Organic materials, such as plant or animal tissues, and also A targeted or local analysis of solids can be carried out if a food, can be ashed or digested prior to analysis, but can also laser beam is used.The laser beam, e.g. of a Nd-YAG laser, be analysed as solid materials. As known from histology, such is focused by an objective of a long focal length onto the organic materials can be frozen and cut by a freezing micro- sample. Material is ejected from a small crater and partly tome. By means of a plastic stretcher, a thin section of deposited on a Plexiglas carrier, which can afterwards be 10–20 mm can be slid onto the scalpel of the microtome.This analysed. section can be placed on a glass carrier by gently touching it. This sampling technique was applied by Bredendiek-Ka�mper Subsequently, it has to be spiked with an internal standard, et al.20 to a ceramic superconductor Y1Ba2Cu3O6.9. A crater dried by evaporation and analysed by TXRF.24–26 of ca. 100 mm in diameter and 20 mm in depth was shot by a Table 4 shows the results for a section of lung tissue obtained single laser pulse and 22 ng of material were deposited on a from a foundry worker.Quantification was carried out after Plexiglas carrier. For quantitative analysis, Ge was used as diVerence weighing of the carrier with and without the dried internal standard. Table 3 gives the results. The small devisection on a microbalance. The total dry mass was determined ations between stoichiometry and TXRF analysis are about to be nearly 80 mg. The mass fractions of heavy metals given 5%, demonstrating a good accuracy.By successive ablations from neighbouring spots, material can be deposited side by side on a carrier and a total line scan Table 3 Quantitative results for a ceramic superconductor Y1Ba2Cu3O6.9 obtained by laser ablation and TXRF analysis of the deposit.20 Ge (5 ng) was used as internal standard. Mass fractions were normalised to the sum of the detected elements of 834 mg g-1 (besides oxygen) Mass fraction/mg g-1 Relative Element Mass/ng TXRF Stoichiometry deviation (%) Y 3.3 125 134 -6.7 Ba 11.6 435 413 +5.2 Cu 7.3 274 287 -4.5 Sum 22.2 834 834 5.5a Fig. 5 Element pattern of the blue pigment smalt showing its main aQuadratic mean. constituents besides oxygen. 574 J. Anal. At. Spectrom., 1999, 14, 571–576Table 4 Quantitative TXRF results for lung tissue obtained from a foundry worker. Sampling was carried out by a freezing microtome and a section of 14 mm in thickness with a dry mass of 80 mg was analysed. Ga (2 ng) was applied as internal standard.The values for the normal range and the upper limit of a population of 125 people have been determined by Baumgardt27 Normal range/mg g-1 Upper limit/mg g-1 Element Mass fraction/mg g-1 (95% of a population) (99.9% of a population) Ti 1400 Cr 17 0.1–10 34 Fe 5460 100–2500 4000 Ni 5.3 0.1–50 500 Cu 13 2.5–40 49 Zn 85 Up to 100 Zr 83 Pb 7.4 0.1–3.0 3.7 in mg g-1 are very high, and those of Cr, Fe and Pb are deposited in thin layers on the surface of wafers. These contaminants are called bulk type, particulate type and thin significantly above the normal range assessed for 95% of a population; Fe and Pb are above an upper limit exceeded by layer type.4,6 Thin layered structures of nanometre thickness covering a silicon substrate can also be examined.The com- only 0.1% of the population. This heavy metal contamination was probably caused by the occupational exposure of the position, thickness and density of individual layers can be determined.34–38 For this purpose, a tilting device is needed in foundry worker.order to carry out an angle scan and to record intensity profiles of the respective elements as a function of the angle Direct contamination control of wafers of incidence. The last example is taken from the field of semiconductor technology. Large but thin discs of silicon, so-called wafers, Conclusions are a basic material of semiconductors. The wafers are initially polished so that they are optically flat and they themselves Several advantages of solid sampling for TXRF can be enumercan serve as totally reflecting carriers for TXRF. ated, but some prerequisites must be observed.Only extremely Contamination at or in the surface of a wafer can be analysed small amounts (ng or mg) are needed for analysis which directly.28,29 Fig. 6 shows a spectrum of a wafer strongly therefore is nearly non-consumptive or non-destructive. contaminated by several elements. Quantitative results are Several techniques of solid sampling have been developed and usually given in numbers of atoms per cm2.For the internal can be applied to a large variety of sample materials: inorganic standard Se, 1011 atoms are equal to 13 pg. This value is still as well as biogenic solid materials. On the other hand, the abohe detection limit. taking and handling of micro-samples is not easy and represen- Even lower detection limits can be obtained after a so-called tative sampling can be a problem.Extreme cleanliness must vapour-phase decomposition.30–33 In a special reactor, a solu- be observed; clean bench working is a must. tion of HF is heated and evaporated. The vapour condenses Simultaneous multi-element detection is advantageous, and on the cold wafer and its native oxide layer of nanometre a simple and reliable quantification by an internal standard thickness is decomposed. Simultaneously, the contaminants ensures a good precision and high accuracy.On the other on the surface are dissolved. Afterwards, the film of aqueous hand, the exclusion of light elements with atomic numbers fine droplets wetting the wafer is collected over its entire area below 14 is regrettable. Light elements can be analysed only as a drop of water and this drop is placed on a carrier for with special detectors and excitation sources in a vacuum TXRF analysis. Detection limits are improved by a factor of chamber. Nevertheless, TXRF is widely applicable to the 100, so that the level of 108 atoms cm-2 is now accessible at microanalysis of solids.the expense of information on the spatial distribution of the elements. This study was financially supported by the German Further techniques have been developed for surface and Bundesministerium fu� r Bildung, Wissenschaft, Forschung und thin layer analysis. TXRF is capable of distinguishing between Technologie and the Ministerium fu� r Schule und diVerent types of contaminants: impurities distributed homo- Weiterbildung, Wissenschaft und Forschung des Landes geneously in a wafer, located in granular particles or evenly Nordrhein-Westfalen.References 1 G.To� lg and R. Klockenka�mper, Spectrochim. Acta, Part B, 1993, 48, 111. 2 R. Klockenka�mper and A. von Bohlen, J. Anal. At. Spectrom., 1992, 7, 273. 3 R. Klockenka�mper and A. von Bohlen, X-Ray Spectrom., 1996, 25, 156. 4 A. Prange and H. Schwenke, Adv. X-Ray Anal., 1992, 35, 899. 5 H. Aiginger and C. Streli, Spectrosc. Eur., 1997, 9, 16. 6 R. Klockenka�mper, Total-Reflection X-Ray Fluorescence Analysis, Wiley, New York, 1997. 7 C. Streli, H. Aiginger and P. Wobrauschek, Spectrochim. Acta, Part B, 1993, 48, 163. 8 C. Streli, P. Wobrauschek, W. Ladisich, R. Rieder and H. Aiginger, X-Ray Spectrom., 1995, 24, 137. Fig. 6 TXRF spectrum of a silicon wafer strongly contaminated by 9 A. Prange, U. Reus, H. Bo�ddeker, R. Fischer and F.-P. Adolf, Adv. X-Ray Chem. Anal.Jpn., 1995, 26s, 1. Cl, Ca, Fe, Zn and some minor pollutants. Se was added as internal standard; counting time, 500 s. All numbers are given in 1011 10 A. von Bohlen, R. Eller, R. Klockenka�mper and G. To� lg, Anal. Chem., 1987, 59, 2551. atoms cm-2. J. Anal. At. Spectrom., 1999, 14, 571–576 57511 T. Graule, A. von Bohlen, J. A. C. Broekaert, E. Grallath, R. 24 A. von Bohlen, R. Klockenka�mper, H. Otto, G. To� lg and B. Klockenka�mper, P. Tscho� pel and G. To� lg, Fresenius’ J.Anal. Wiecken, Int. Arch. Occup. Environ. Health, 1987, 59, 403. Chem., 1989, 335, 637. 25 A. von Bohlen, R. Klockenka�mper, G. To� lg and B. Wiecken, 12 U. Reus, B. Markert, C. HoVmeister, D. Spott and H. Guhr, Fresenius’ J. Anal. Chem., 1988, 331, 454. Fresenius’ J. Anal. Chem., 1993, 347, 430. 26 R. Klockenka�mper, A. von Bohlen and B. Wiecken, Spectrochim. 13 R. Klockenka�mper, A. von Bohlen, L. Moens and W. Devos, Acta, Part B, 1989, 44, 511. Spectrochim. Acta, Part B, 1993, 48, 239. 27 B. Baumgardt, PhD Thesis, Ruhr-Universita�t Bochum, 1985. 14 A. Salva`, A. von Bohlen, R. Klockenka�mper and D. Klockow, 28 W. Berneike, Spectrochim. Acta, Part B, 1993, 48, 269. Quim. Anal., 1993, 12, 57. 29 V. Penka and W. Hub, Spectrochim. Acta, Part B, 1989, 44, 483. 15 R. Klockenka�mper, H. Bayer and A. von Bohlen, Adv. X-Ray 30 C. Neumann and P. Eichinger, Spectrochim. Acta, Part B, 1991, Chem. Anal. Jpn., 1995, 26s, 41. 46, 1369. 16 B. Schneider, Spectrochim. Acta, Part B, 1989, 44, 519. 31 R. S. Hockett, Adv. X-Ray Anal., 1994, 37, 565. 17 M. Schmeling and D. Klockow, Anal. Chim. Acta, 1997, 346, 121. 32 L. Fabry, S. Pahlke and L. Kotz, Adv. X-Ray Chem. Anal. Jpn., 18 G. Agricola, De re Metallica. Libri XII, Froben-Verlag, Basel, 1996, 27, 354. 1556. 33 L. Fabry, S. Pahlke and L. Kotz, Fresenius’ J. Anal. Chem., 1996, 19 Lazarus Ercker’s Treatise on Ores and Essaying.—Facsimile 1580, 354, 266. translators A. G. Sisko and X. Y. Smith, University of Chicago 34 U. Weisbrod, R. Gutschke, J. Knoth and H. Schwenke, Fresenius’ Press, Chicago, 1951. J. Anal. Chem., 1991, 341, 341. 20 S. Bredendiek-Ka�mper, A. von Bohlen, R. Klockenka�mper, A. 35 J. Knoth, R. Bormann, R. Gutschke, C. Michaelsen and H. Quentmeier and D. Klockow, J. Anal. At. Spectrom., 1996, 11, Schwenke, Spectrochim. Acta, Part B, 1993, 48, 285. 537. 36 H. Schwenke and J. Knoth, Anal. Sci., 1995, 11, 533. 21 W. Devos, L. Moens, A. von Bohlen and R. Klockenka�mper, 37 D. K. G. de Boer and W. W. van den Hoogenhof, Spectrochim. Studies in Conservation, 1994, 40, 153. Acta, Part B, 1991, 46, 1323. 22 B. Wehling, P. Vandenabeele, L. Moens, R. Klockenka�mper, A. 38 D. K. G. de Boer, Phys. Rev. B, 1991, 44, 498. von Bohlen, G. Van Hooydonk and M. de Reu, Mikrochim. Acta, in the press. 23 L. Moens, W. Devos, R. Klockenka�mper and A. von Bohlen, J. Trace Microprobe Techniques, 1995, 13, 119. Paper 8/0769

ISSN:0267-9477    

DOI:10.1039/a807693f

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Direct determination of metal concentrations in freshwater algae by total reflection X-ray fluorescence spectrometry† Katalin Barka�cs,a Anita Varga,b Kamilla Ga�l-Solymosc and Gyula Za�ray*b aDepartment of Chemical Technology and Environmental Chemistry, L . Eo�tvo�s University, P. O. Box 32, H-1518 Budapest 112, Hungary bDepartment of Petrology and Geochemistry, L . Eo�tvo�s University, P.O. Box 330, H-1445 Budapest, Hungary cResearch Group of Environmental and Macromolecular Chemistry, Hungarian Academy of Sciences, L.Eo�tvo�s University, P.O. Box 32, H-1518 Budapest 112, Hungary Received 11th October 1998, Accepted 15th February 1999 A direct TXRF method for the determination of metal impurities by applying three diVerent freshwater algae, viz., Chlorella keslerii, Synehococcus sp. and Cylindrospermopsis raciborskii, was developed. The applicability of the slurry sampling technique was confirmed by comparing the analytical results obtained with those obtained by total digestion of the algae.The concentration data showed an acceptable agreement for Cu, Fe, Mn and Zn. The calculated accumulation factors for the metals detected were highest for Chlorella keslerii. The problems caused by the increasing number of pollutants cants in biomass needs multi-elemental analytical techniques having also low detection limits. In practice, inductively from diVerent sources, and their eVects on the quality of the environment, also on aquatic life—from cellular to ecosystem coupled plasma atomic emission-,17 and mass spectrometry10 and also total reflection X-ray fluorescence spectrometry levels—are well known and have been widely investigated.1–4 Research published on the eVects of pollutants on water (TXRF)22–24 have been successfully used.These methods have generally been applied to the analysis of periphyton samples organisms has covered the testing of many diVerent species, as applicable organisms for alternative methods in aquatic previously digested with nitric acid,3,15–18 nitric acid–sulfuric or perchloric acid14 and also nitric acid–hydrogen peroxide biomonitoring and toxicology.4–9 These test organisms vary from aquatic animals: bacteria (bacterial bioluminescence mixtures.9,24,25 Pettersson and co-workers25–27 have developed a direct assays), Daphnia species (Daphnia magna), mussels, fish cells and fishes to plants; and among the most recent from hyacinths TXRF method for the investigation of periphyton communities.During their experiments, marine periphytons were to algae species.4,10–14 Much of the research work on toxic eVects has dealt with phototrophic algae and cyanobacteria, colonized on soda glass discs used as both benthic sample holders and TXRF carrier plates. They established that the as the primary producers in the hydrosphere.3,5,14 For monitoring pollutant inputs into the ecosystem and for evaluating analytical data of the wet digestion and direct methods for K, Ca, Mn, Fe, Ni, Cu, Zn, As, Rb and Sr were in good toxic eVects, the use of algae and algal communities, has some particular advantages.They easily meet the requirements of agreement. With all of the methods applied, the heterogeneity of the intensive toxicity screening by ensuring a considerable number of test animals. On the basis of high pollutant accumulation samples, and also the sample preparation procedure, including the eVective removal of the water medium, were found to be capacities compared with other species related to specific morphological and physiological properties, algae have been important.14,16,20 In this work, on the basis of the data obtained for sea-water found to be highly sensitive detectors of micropollutants, making them suitable biomonitors to quantify environmental periphytons, a direct TXRF method was developed for the analysis of freshwater algae. Three diVerent algae species were quality.15–17 The calculated accumulation factors (AF), i.e., the concentration ratio expressed as the concentration of a investigated, by applying slurry sampling or microwaveassisted vapour-phase acid digestion procedures.pollutant in dried algae relative to its ambient concentration in water, are on average within the interval 102–105.3,10,14–20 These high accumulation factors and also high tolerance to pollutants enable the algae to create a time integrated accumu- Experimental lation (the LD50 values, characterizing their tolerance, for Algae samples most of the metals are generally around several thousand mg g-1).3,15,21 Algal communities might provide Three diVerent freshwater algae species were investigated: more complex information on water quality than the direct Cylindrospermopsis raciborskii (filamentous green algae), water qualification carried out by chemical tests at defined Synehococcus sp.(unicellular, ellipsoidal, blue–green algae of times and locations. 5 mm length), and Chlorella keslerii (unicellular green algae, The various environmental stresses result in changes in the round or ellipsoidal of 2–10 mm length). These species were metabolism of the algal communities, which are reflected in chosen as test materials because of their diVerent morphologithe content of trace elements and also nutrients in algae. The cal and physiological characteristics and also their widespread determination of concentrations of micro-nutrients and toxi- occurrence in surface waters, such as the River Danube and Lake Balaton.The selection of a suitable sample preparation procedure, †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998. combined with metal content determinations carried out by J. Anal. At. Spectrom., 1999, 14, 577–581 577TXRF, required a large number of well defined, homogeneous samples. For this purpose, the algae species were grown in ‘Allen-nutrient solution’ under controlled conditions (sterility during aeration, artificial UV lighting, temperature).The concentrations of chemical compounds in this culture medium are shown in Table 1. In order to determine the metal impurities in these biological materials, the sampling of the tested algae species was carried out in the logarithmic-phase of algal growth. Homogeneous suspensions of algae samples were handled during a multi-step sample preparation procedure preceding their metal content determination by TXRF.Sample preparation The multi-step algae sample preparation method is demonstrated in Fig. 1. The first step was the separation of the suspended algae cells from the nutrient solution. This separation was carried out by using a laboratory centrifuge (2000 rpm, 5 min) or by filtration. Sartorius membrane filters of 0.2 mm pore size were applied and the filtration speed was enhanced by means of a vacuum pump.During this mechanical separation process, deionized water was applied as a washing medium according to the suggestions of other workers. 14,16,19,20,23 The eYciency of media removal was controlled by measuring the specific conductivity, and metal and nitrate ion concentrations of the filtrates. The calculation of metal concentrations in algae samples requires the exact determination of their dry mass. Therefore, the washed algae samples were freezedried,5 and the powder samples were divided into two portions. One portion of the samples was used for direct measurements by preparing slurries from known weights (2–10 mg) of dry algae samples suspended in 1 ml of deionized water by ultrasonic treatment (Branson – 3200 E1 ultrasonic cleaner working at 47 kHz for 10 min).The other portion of the samples was digested by applying a microwave-assisted vapour-phase acid digestion procedure (2–10 mg of dry algae were decomposed in the vapour of 9 ml of concentrated nitric acid and 1 ml of hydrogen peroxide) based on the CEM-2100 (Matthews, NC, USA) pressure controlled microwave digestion system.28 Fig. 1 Sample preparation procedure. The digestion program used for decomposing the algae samples consisted of the following steps: (1) 1 min at 25% thoroughly cleaned and siliconized (silicone swer (pressure, 138 kPa); (2) 4 min at 66% power (pressure, Feinbiochemica, Heidelberg, Germany), and dried in a clean- 689 kPa); and (3) 30 min at 33% power (pressure, 689 kPa) box at 80 °C for 30 min on a ceramic-coated hot-plate.The (100% power=950±50 W). amount of the Ga was 100 ng in the 25 ml droplets. The surface After digestion, the liquid samples were made up to 1 ml densities of the algae samples on the carrier plates were with deionized water. The pre-treated samples (slurries, calculated, assuming that the droplets had a homogeneous digested sample solutions) were mixed with a Ga standard distribution regarding their dry residues and covered a surface solution (as internal standard).After homogenization, a 25 ml of 20 mm2. The data varied between 2 and 10 mg mm-2 dry aliquot was dropped onto a quartz-glass carrier, previously algae. The surface densities of the digested samples shown in Fig. 2 are not the true surface densities; they were calculated Table 1 Concentrations of chemical compounds in the ‘Allen’ for comparative evaluations, assuming that the original, nonnutrient solution digested dry algae content of the samples was still present.Component c/mg l-1 Instrumentation NaNO3 1500 The analysis of the algae samples, nutrient solutions, filtrates, K2HPO4 39 deionized water, reagents (nitric acid and hydrogen peroxide) MgSO4·7H2O 75 Na2CO3 20 and digested blank solutions was carried out with an EXTRA CaCl2 27 IIA total reflection X-ray fluorescence spectrometer (produced Na2SiO3·9H2O 58by ATOMIKA Instruments, Oberschleissheim, Germany).EDTA 1.0 The specific analytical parameters were as follows: Mo Citric acid 6.0 micro-focus X-ray tube (50 kV, 38 mA); high energy cut-oV Iron(III) citrate 6.0 filter (quartz glass mirror); attenuation filter (200 mm Mo, Boric acid 2.9 MnCl2 1.8 240 mm Al ); Si(Li) detector (80 mm2 area); integration time ZnSO4·7H2O 0.2 500 s; energy of applied analytical lines: K (Ka) 3.312 keV; Na2MoO4 0.4 Ca (Ka) 3.690 keV; Mn (Ka) 5.894 keV; Fe (Ka) 6.398 keV; Co(NO3)2·6H2O 0.08 Cu (Ka) 8.040 keV; Zn (Ka) 8.630 keV.CuSO4·5H2O 0.05 In order to check the influence of the inhomogeneous 578 J. Anal. At. Spectrom., 1999, 14, 577–581be a more beneficial tool in handling very small sample amounts. Filtration was carried out in several (4–5) steps, so that the residue of the nutrient solution was first removed, then the algae were resuspended in deionized water on the surface of the filter and filtration was repeated. The metal concentrations of the subsequent filtrates were measured by TXRF.As Fig. 3 demonstrates, for Synehococcus sp., the element concentrations of the filtrates decreased stepwise during the washing procedure. The fourth filtrate was virtually a metal-free solution. However, the specific conductivity and metal concentrations (mainly Ca) increased in the next washing step, possibly because the use of deionized water caused the algae cells to rupture on osmotic shock. There is a risk, therefore, of metal content loss with increasing time or water volumes applied during separation. Similar results were Fig. 2 EVect of surface densities of the digested and suspended observed for each algae sample; no variations were experienced Synehococcus sp. samples on the Fe concentrations measured by in the eYciency of the washing procedure owing to the TXRF. Surface density data are expressed in mg dry algae per mm2 diVerences in algae species. In summary, the application of and calculated also for the digested samples, assuming that the original four washing steps, and a total volume of deionized water no dry algae mass was present. greater than twice the original volume of the algae medium, resulted in the eVective separation of interstitial water and hence the eVective removal of the disturbing metals originating from the sample medium.In order to check the eYciency of the digestion procedure, chemical oxygen demand (COD) tests were applied.29 (COD of the organic materials expressed in milligrams of O2, determined according to international standards by a rapid, microscale Merck-test. The method is analogous to ISO 6060.) The algae samples were tested both in slurries (without digestion), and also after the digestion procedure.The data measured by the COD method showed that, after digestion, the samples generally contained less than 5% of the organic materials originally present. In order to select the appropriate concentration of algae slurries, the influence of the total algae mass on the carrier plate on the determined element concentrations was measured.It should be emphasized that the amount of Ga added in the Fig. 3 Element concentrations of the filtrates measured by TXRF as droplets was in all cases 100 ng. Typical data of these experi- a function of the washing steps; amount of Synehococcus sp. algae on ments are demonstrated in Fig. 2, which summarizes the iron the filter: 13 mg (dry mass); washing medium: deionized water, 4 ml per washing step.concentrations of the digested samples and of the directly measured Synehococcus sp. slurries as a function of the algae surface densities. It can be seen that the measured concen- distribution of the dried slurry droplets, the TXRF measuretration values show the lowest deviation at a surface density ments were carried out at three diVerent orientations (0°, 120°, of 5 mg mm-2. The RSD values of these measurements also 240°) of the carrier plates.For the investigation of dried slurry demonstrate that, at low surface densities, an increased uncer- droplets, a scanning electron microscope (Amray 1830 I/T6) tainty of the measurements was observed. However, a surface equipped with an EDAX PV9800 ED spectrometer (20 kV density higher than 5 mg mm-2 created less homogeneous acceleration voltage, 2 nA beam current) was used. samples having a relatively high thickness. Hence, a surface density of 5 mg mm-2 is appropriate for both sample types.Results and discussion Since during drying of the slurry droplets thin layers having a relatively rough surface are formed, the analytical data are During the algae sample preparation process—as an important expected to be influenced by the surface properties. In order and determining step in the correct measurement of the metal to study this phenomenon, digested and non-digested Chlorella content of the cells—the removal of interstitial water was keslerii samples (surface density 5 mg mm-2) were investigated tested first.For a proper separation of algae cells and their in three diVerent positions of the carrier plates. The data in medium, the filtration procedure proved to be more eVective Table 2 suggest the existence of slight diVerences measured as and less time consuming than the use of a centrifuge. Filtration required smaller volumes of washing water and was found to a function of the carrier position and hence a relatively uniform Table 2 Mean metal concentration values in Chlorella keslerii determined by TXRF at three diVerent orientations of the carrier plates (0°, 120°, 240°) containing the same sample and relative standard deviations calculated from the data obtained at diVerent positions Sample type Mn Fe Cu Zn K Ca Slurry— Mean value/mg g-1 4510 15 400 118 646 4170 35 600 RSD (%) 7.1 6.6 5.7 7.3 4.7 6.2 Digested— Mean value/mg g-1 4530 13 600 125 728 3270 29 400 RSD (%) 2.7 0.3 3.6 1.5 4.4 4.4 J. Anal.At. Spectrom., 1999, 14, 577–581 579Fig. 5 Calculated accumulation factors (AF) of metals for the three diVerent algae species. concentrations were measured in the slurries of Chlorella keslerii and Cylindrospermopsis raciborskii. Similar Cu concentrations were determined in both sample types for all the algae species, whereas lower Zn concentrations were found in each Fig. 4 Back-scattered electron image of the slurry sample of case when slurries of algae were applied.The RSD values of Synehococcus sp. (a) and X-ray image of Ga Ka (b) showing the the determined metal concentrations were higher for direct distribution of the internal standard element at the border of the measurements than those for the digested samples for almost sample droplet; total amount of Ga added: 1000 ng; average surface all the metals. The lowest deviations in the mean concen- density of the algae sample in the dried droplet: 5 mg mm-2; image magnification: ×15 (a), ×113 (b).trations determined by the slurry and digestion techniques were found for Synehococcus sp. The algae species grown under the same conditions can be thin layer structure. Comparing the data obtained with and compared regarding their metal accumulation capacities without digestion, slightly lower RSD values, as a function of (accumulation factors). The calculated accumulation factors the carrier position, for almost all the metal concentrations of for the diVerent elements (see Fig. 5) emphasize the diVerences the digested samples were found. However, all the RSD values depending on the metal qualities regarding a particular species, for the non-digested algae slurries were also less than 10%. and also the variations in a given element accumulation ratio The investigation of the structure of droplets of algae slurries for the diVerent species. Among the algae species tested—on having diVerent concentrations and the distribution of the Ga the basis of the highest accumulation factors determined— internal standard in the dry thin layer was carried out with a Chlorella keslerii appears to be the best species for scanning electron microscope.In this case the amount of Ga biomonitoring. added was higher (1000 ng) than during TXRF measurements, to ensure the detection of Ga by the EDAX system. Independently of the slurry concentration, Ga shows a similar Conclusion distribution profile in the droplets of all the samples. A homogeneous distribution of the Ga internal standard did not A solid sampling algae preparation technique has been developed and modified as a multi-step sample preparation pro- occur on the total surface of the droplets; instead, the Ga was concentrated in the outer parts of the droplets, as the X-ray cedure. The main steps included the eVective removal of the nutrient solution, and hence the removal of the disturbing image of Ga Ka shows in Fig. 4. The photograph, of a dried Synehococcus sp. sample slurry having a 5 mg mm-2 surface metal content, by filtration and washing with deionized water. Freezedrying of the algae after washing ensured the homogen- density, demonstrates the characteristic Ga enrichment ‘ring’ found for the algae slurry droplets. eity of the samples. Slurries were prepared from the dried algae and deionized water by using ultrasonic treatment. In The element concentrations of the dried algae formed from freshly cultivated algae communities were measured by TXRF order to compare the analytical results, acid-digested algae samples were also analyzed.and are summarized in Table 3. The average concentrations of the elements (mean values calculated from three repeated The deviations of the metal concentration values determined by TXRF investigation of slurry and digested algae samples measurements) determined using both slurries and digested solutions of the same algae samples and the RSD values are lowest for Synehococcus sp.Since Chlorella keslerii shows only slightly higher deviations and its accumulation factors calculated from these measurements are also compared in Table 3. The data generally show higher mean values for Mn are considerably higher than those of the other algae, this species seems to be the most promising for biomonitoring. measured in slurries than in digested samples. Also, higher Fe Table 3 Element concentrations of dry algae mass measured for the diVerent species and sample types by TXRF (surface density: 5 mg mm-2) Sample Mn/ RSD Fe/ RSD Cu/ RSD Zn/ RSD K/ RSD Ca/ RSD Algae type mg g-1 (%) mg g-1 (%) mg g-1 (%) mg g-1 (%) mg g-1 (%) mg g-1 (%) Cylindrospermopsis Slurry 243 2.9 1155 7.4 72.8 1.7 36.3 8.0 6240 6.6 2175 4.5 raciborskii Digested 208 2.4 1090 7.4 72.8 0.6 41.4 1.3 6100 5.6 1440 3.9 Chlorella Slurry 4300 9.9 14 940 12.4 113 9.1 633 10.4 118 22.3 1085 10.3 keslerii Digested 3865 9.4 12 490 3.1 114 2.9 680 1.9 116 46.6 642 70.3 Synehococcus Slurry 77.8 5.8 1210 10.4 15.4 17.3 54.7 12.6 1470 2.9 614 7.1 sp.Digested 75.1 6.2 1285 6.1 15.0 12.3 60.5 7.5 1385 9.7 479 6.5 580 J. Anal. At. Spectrom., 1999, 14, 577–58113 J. M. C. Geuns, A. J. F. Cuypers, T. Michiels, J. V. Colpaert, A. Acknowledgements Van Larere, K. A. O. Van der Broeck and C. H. A. Vandecasteele, Sci. Total Environ., 1997, 203, 183. The authors are grateful to Dr. T. K. Kiss, Dr.A. Kozma, 14 M. D. K. Abo-Radey, Arch. Hydrobiol., 1980, 89, 387. Dr. E� . A� cs and Mr. I. Grigorszki for their valuable instructions 15 M. G. Kelly and B. A. Whitton, Interspecific diVerences in Zn, Cd and for the algal cultures. This research program was sup- and Pb accumulation by freshwater algae and biophytes, Durham, ported by grants T 014861 and T 023726 from the National UK, 1987. Scientific Research Foundation (Hungary). 16 B. A. Whitton, I. G. Burrows and M. G. Kelly, J.Appl. Phycol., 1989, 1, 293. 17 C. A. Mahan, V. Majidi and J. A. Holcombe, Anal. Chem., 1994, 66, 624. References 18 B. M. McHardy and J. J. George, presented at the Series of 1 S. Hall, J. Chamberlain and E. Godwin-Saad, Water Environ. Symposia Biologica Hungarica, Hungarian Academy of Sciences, Res., 1995, 67, 713. Budapest, Hungary, 1985, vol. 29, p. 37. 2 Gy. Lakatos, E� . A� cs, K. Buczko� and Cs. Cserha�ti, presented at 19 P. T. S. Wong, Y. K. Chau and J. L. Yaromich, Can.J. Fish. the 10th International Svedala Symposium on Ecological Design, Aquat. Sci., 1987, 44, 1257. Budapest, Hungary, 1992. 20 P. L. Foster, Nature (London), 1977, 269, 322. 21 J. W. Rijstenbil, A. Sandee, J. Van Drie and J. A. Wijnholds, 3 P. L. Foster, Freshwater Biol., 1982, 12, 17. FEMSMicrobiol. Rev., 1994, 14, 387. 4 E. Nusch, Z. Umveltschem. O� kotox., 1993, 5, 155. 22 K. Gu� nther, A. von Bohlen, G. Paprott and R. Klockenka�mper, 5 P. J. Say and B. A. Whitton, Hydrobiologia, 1980, 76, 255.Fresenius’ J. Anal. Chem., 1992, 342, 444. 6 L. S. Clesceri, A. E. Greenberg and R. R. Trussell, Standard 23 T. Bistriczki and M. Munwar, Can. J. Fish. Aquat. Sci., 1983, Methods for Examining Water and Wastewater, American Public 39, 506. Health Association, Port City Press, Baltimore, Maryland, USA, 24 J. Bohman, H. Blanck, P. Standzenieks, R. P. Pettersson and N. T. 17th Edition, 1989. Hong, X-ray Spectrom., 1993, 22, 260. 7 S. A. Badr and H. F. Abou-Waly, Bull. Environ. Contam. Toxicol., 25 R. P. Pettersson, Doctoral Thesis, Chalmers University of 1997, 59, 298. Technology, Go�teborg, Sweden, 1997. 8 M. A. El-Dib, H. F. Abou-Waly and A. M. H. El-Naby, Bull. 26 R. P. Pettersson and M. Olson, Proceedings of the EDXRS-96 Environ. Contam. Toxicol., 1997, 59, 438. Conference, Lisbon, Portugal, 1996, p. 32. 9 S. C. Gardner, C. E. Grue, J. M. Grassley, L. A. Lenz, J. M. 27 R. P. Pettersson, Proceedings of the 6th Conference on TXRF and Lindenauer and M. E. Seeley, Bull. Environ. Contam. Toxicol., Related Methods, Dortmund, Germany, 1996, p. 69. 1997, 59, 492. 28 Zs. Cze�ge�ny, B. Berente, M. O� va�ri, M. Garcý�a Tapia and Gy. 10 I. Bruns, K. Friese, B. Markert and G. J. Krauss, Sci. Total Za�ray, Microchem. J., 1998, 59, 100. Environ., 1997, 204, 161. 29 Validation of Merck Spectroquant COD Cell Test, Quality 11 Th. Braunbeck, Eco-Informa ’97, 1997, 12, 446. Assurance Group,Water Research Institute, Budapest, 1998. 12 R. Altenburger, U. Ensenbach, K. Jung, M. Knops, P. Popp, H. Segner, H. Weiss and G. Schu�u� rmann, Eco-Informa ’97, 1997, 12, 452. Paper 8/08806C J. Anal. At. Sp

ISSN:0267-9477    

DOI:10.1039/a808806c

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Direct solid sampling ETAAS determination of cadmium in equine muscle† Ernst Lu�cker Institute of Veterinary Food Science, Justus-Liebig University, Frankfurter Strasse 92, D-35392 Giessen, Germany. E-mail: ernst.h.luecker@vetmed.uni-giessen.de Received 10th November 1998, Accepted 22nd December 1998 Direct solid sampling by means of electrothermal atomic absorption spectrometry (ETAAS) was evaluated as a rapid procedure for the determination of Cd in equine muscle tissue with respect to the introduction of a legal limit for Cd in equine muscle tissue in Germany.Analysis of the distribution of Cd within individual muscles of horses showed the variance component ‘heterogeneity’ (relative standard deviation, RSD: 16%)to be clearly dominated by residual analytical variance (RSD 24%). Error of mean value estimation can be reduced by increasing the number of samples—each taken from diVerent sampling sites—from approximately 30% (n=1) to 11% (n=6) . In a comparison between solid sampling ETAAS and a conventional compound procedure as reference (regression analysis, n=394), the Cd content ranged from 0.01 to 0.9 mg g-1 fresh substance.Results were found to be closely correlated (r=0.98) and proved to be analytically and statistically (P>0.10) of no relevant diVerence. Ranges of erroneous classification were calculated, which allow the identification of transgressing samples. For the legal limit of 0.2 mg g-1 fresh substance, erroneous classification (false positive and false negative) ranged from 0.14 to 0.27 mg g-1 fresh substance.Limits for the 1% range of erroneous classification were calculated to range from 0.13 to 0.32 mg g-1 fresh substance. Based on these results, a model strategy is proposed for the application of direct solid sampling analysis as a rapid in-process screening procedure within the scope of meat hygiene regulations. Musculus longissimus dorsi is given in the literature as ranging Introduction from 0.001 to 0.01 mg g-1 fresh substance.13–17 However, for Residues of heavy metals in food are oYcially controlled equine muscle tissue a distinctly higher Cd content is reported almost exclusively by means of electrothermal atomic absorp- as shown in Table 1.tion spectrometry (ETAAS) as part of compound procedures. In addition, the meat hygiene legislation in Germany has These procedures are nationally standardized1 or prescribed2 recently introduced limits for heavy metals for all slaughtered and internationally recommended as reference.3 Compound animals.23 These limits are based on the recommended control procedures include homogenization and transformation of the values for specified tissues of pigs and cattle.24 Thus, the solid sample into solution prior to instrumental analysis.higher Cd content of equine muscle tissue will lead to a However, compound procedures are not only expensive and distinctly increased probability for the transgression of the time consuming but also markedly prone to errors.The main legal limit (0.2 mg g-1 fresh substance). Consequently, the Cd source of analytical error is known to be caused by pre- content of the muscle tissue of all of the horses which are analytical contamination due to the omnipresence of heavy slaughtered in Germany should be determined. However, there metals at relevant concentrations.4 As an alternative, solid is no analytical procedure at hand which allows a rapid and sampling ETAAS was introduced5 and later characterized as inexpensive determination of Cd within the process of a rapid and low-cost analytical procedure in numerous studies.6 slaughtering. Even so, a serious drawback of solid sampling ETAAS was and still is seen in the very low sample masses (microgram to milligram range) which are needed for analysis.Thus, solid Table 1 Cd (mg g-1 fresh substance) in equine muscle tissue as reported sampling ETAAS has been predominantly applied to homoin the literature genized samples.Some workers, however, have studied the matrix-dependent distribution of analytes by means of solid Muscle n x: x� Min. Max. Ref. sampling and the eVect on analytical precision in fresh and Ba 68 0.13 —b 0 1.5 18 untreated samples. They reported a relatively low degree of Ba 40 0.15 —b 0.02 0.69 18 heterogeneity for elements such as Cd, Zn, Pb and Hg in some —b 142 0.17 0.13 0.01 1.7 19 animal tissues—such as porcine and bovine liver7–10 and renal Diaphragm 109 0.13 0.12 0.01 0.47 20 cortices11 as well as avian kidney.12 Thus, they have shown M.rectus abdominis 100 0.06 0.0 0.007 0.26 20 that a true ‘direct’ solid sampling is not only possible but also Diaphragm 17 —b 0.11c 0.01c —b 21 is totally error-free with regard to sample preparation. M. rectus abdominis 17 —b 0.05c 0.005c —b 21 M. longissimus 17 —b 0.05c 0.005c —b 21 Within the scope of oYcial heavy metal control in food, Musclesd 17 0.11 0.06 0.005c 1.5 21 muscle tissue is usually of minor concern, as its heavy metal M.longissimus 209 0.08 0.05 0.03 0.62 22 burden is very low. The Cd content of porcine and bovine M. semitendinosus 209 0.07 0.05 0.03 0.54 22 aB: Muscle samples from bacteriological examination. bNo data given. †Presented at the 8th Solid Sampling Spectrometry Colloquium, cValues taken from graphs. d12 diVerent muscles. Budapest, Hungary, September 1–4, 1998. J. Anal.At. Spectrom., 1999, 14, 583–587 583Therefore, the present study was performed in order to Analytical quality assurance evaluate the applicability of direct solid sampling as a rapid The certified and in-house standardized reference materials in-process procedure for the determination of Cd in equine used were: bovine liver (NIST SRM 1577a, LIS-G01, LISG10), muscle tissue within the scope of meat hygiene regulations. porcine kidney (BCR CRM 186), and bovine muscle (BCR Furthermore, the determination of Cd in equine muscle tissue CRM 184).presents a suitable model for the general characterization of Compound as well as solid sampling procedures as used in representativity of both direct solid sampling and conventional this study were evaluated in several national and international compound procedures. For this purpose, (i) information about round-robin exercises.26,29–31 the distribution of Cd between and within individual muscles is obtained by applying a multifactorial hierarchic analysis of Analytical models variance, (ii) a suitable sampling strategy is developed, (iii) the correctness of direct solid sampling ETAAS results is Analysis of Cd distribution in equine muscle tissue was evaluated with regard to the oYcially prescribed reference performed using three muscles (MLC: M.longus capitis, MG: method, (iv) limits of erroneous classification are established M. gastrocnemius and MD: M. diaphragmaticus) taken from and (v) the performance of direct solid sampling analysis is two horses.evaluated with respect to analytical time and cost. Within each muscle, six sampling sites were chosen in a totally randomized way. From each sampling site six microsamples were taken from an area—which was circumscribed Experimental as closely as possible—and analyzed. Additionally, the material taken from a sampling site was homogenized during Material microsampling. Thus, multifactorial analysis of variance of Muscle tissue samples (459) were taken during regular the mixed model (ANOVA) gave estimations of betweenslaughtering of horses.The main sampling sites were: M. sampling site variance (heterogeneity, sh) and within-sampling longissimus thoracis (n=154), M. semitendinosus (n=153) and site variance (residual analytical variance, sa). Prior to M. diaphragmaticus (n=99). Additionally, muscle samples ANOVA, data were logarithmically transformed in order to (n=53) of the distal extremities taken for bacteriological achieve homogeneity of variance.The resulting dispersion investigation were used. If necessary, samples were stored in factor (df ) around the geometric mean is dimensionless and close-fitting polyethylene foil at -21 °C. can be expressed as relative standard deviation (e.g. df= x·1.23±1lusmn;23%)32 in a simplified albeit more illustrative manner. Direct solid sampling ETAAS Comparison of methods consisted of the analysis of 394 The analyses were carried out using solid sampling samples: first, by means of solid sampling ETAAS and second, spectrometers (SM1 and SM20) with Zeeman-eVect back- by means of the compound procedure after sample homogenizground correction (Gruen AMS, Ehringshausen, Germany).ation and decomposition. Note that virtually the same sample In addition, a conventional high energy deuterium background was thus analyzed following solid sampling analysis, as the corrected atomic absorption spectrometer (PU9100x, TJA mass of the six microsamples taken was about 2–4 orders of Unicam, OVenbach, Germany) was used with a modified magnitude lower than that of the field sample.graphite system for solid sampling.25 Calibration was eVected Results were analyzed by means of regression analysis by means of working standard solutions (5, 10, 20 and ( least-squares method), t-test and Wilcoxon test. Logarithmic 30 mg l-1) derived from a 1000 mg l-1 stock standard solution transformation of data was used in order to normalize and ( Titrisol, Merck, Darmstadt, Germany) and checked by at standardize the standard deviation of the y-values for given least one certified and one in-house standardized reference x-values.The resulting standard deviation sy.x facilitated the material. The reference material was also used to optimize the estimation of limits for erroneous classification with respect basic optical and thermal conditions (Table 2) prior to the to legal limits according to Lu� cker.33,34 Calculations were analyses of field samples.Field samples of equine muscle tissue performed with the help of the following software packages: (5–100 g) were analyzed without any pre-treatment. During MS-Excel 97 (Microsoft, Redmond, WA, USA), Limit33 and microsampling, these field samples were kept at +2 °C and BMDP.35 99% relative humidity. The actual analytical sample (‘microsample’) was plugged from the field sample with the help of Results two Inox micro-tweezers (Kretschmer, Giessen, Germany) and rapidly transferred to the tared platform on a M500P or Distribution analyses 4503MP6 microbalance (Sartorius, Go� ttingen, Germany).The distribution of Cd within and between sampling sites of Typical sample masses were 0.1–5 mg. The instrumental analythe analyzed equine muscles is depicted in Fig. 2. The Cd sis was started after the platform had been introduced into content ranges around 0.02 mg g-1 in muscles of horse A and the graphite cuvette of the spectrometer (Fig. 1). Instrumental around 0.2 mg g-1 fresh substance in horse B. The mean parameters are listed in Table 2. Quantification was achieved relative standard deviations (RSDs) of the sampling sites are using peak height measurement with the SM1 spectrometer 22 and 15%, respectively. Reference material and working and using peak area integration with the SM20 and PU9100x standard solutions were analyzed alternately after each analysis spectrometers.Further details are given elsewhere.9–12,26–28 of three field samples. The respective mean RSD of the reference material ranges from 3.2 to 13.2% (4–8 micros- Reference procedure amples) and that of the working standard solutions from 2.4 to 8.9% (n=4, manual pipetting). Thus, in direct solid sam- Field samples were homogenized by means of a noncontaminating kitchen mixer (Moulinette, Moulinex, Solingen, pling analysis the observed variance of non-homogenized equine muscle tissue is somewhat higher than in homogenized Germany).Then, 5 g of the homogenized material were decomposed with purified HNO3 in an open system (Tecator, reference material and distinctly higher than in liquid standards. Frankfurt, Germany).26 Instrumental analysis was performed using a PU9100x atomic absorption spectrometer with high Results of the four-factorial hierarchic analysis of variance of the mixed model ( logarithmically transformed data, 2 energy deuterium background correction (D2-ETAAS). 584 J.Anal. At. Spectrom., 1999, 14, 583–587Table 2 Instrumental parameters for the determination of Cd in fresh and untreated equine muscles by means of direct solid sampling ETAAS SM1 SM20 PU9100x Optical parameters: Emission source Electrodeless Electrodeless Hollow cathode low frequency low frequency Resonance line l/nm 228.8 228.8 228.8 Bandpass/mm 0.25 0.25 0.20 Background correction Direct Zeeman Direct Zeeman High energy deuterium Graphite system: Cuvette Pyrolytically coated Uncoated Pyrolytically coated Carrier (platform) Boat-like Boat-like Drawer-like pyrographite graphite pyrographite Chemical modifier NH4H2PO4 — NH4 H2PO4 Cut-oV value (%) 25 25 — Argon/l min-1 0.4 0.4 2.8 Program: Temperature/time: °C s °C s °C °C/s s Phase 1 (Dry 1) 100 15–20 200 25 120 5 30 Phase 2 (Dry 1) — — — — 300 10 40 Phase 3 (Ash) 200 15–100 600 15–100 500 50 50 Phase 4 (Atomize) 2200 3–7 2400 3–7 1550 >2000 5 Phase 4 (Clean)a 3000 0–5 3000 0–5 2400 >2000 5 Phase 6 (Cool ) 5 0–5 5 0–5 5 — 25 aOptional for SM1 and SM20.muscles of each horse (P>0.1). Within all muscles, no positive eVects are obtained for the ‘sampling site’ (P>0.6), or for the possible interactions. In this model of direct solid sampling a total error of mean value estimation of about 30% (dft=1.30±1) is obtained for the analysis of one microsample. The estimate of the variance components shows that residual analytical variance (dfa= 1.24±1) clearly dominates heterogeneity induced variance (dfh=1.16±1).Comparison of methods The Cd contents of the 394 equine muscle samples range from Fig. 1 Flow scheme of analytical steps in direct solid sampling ETAAS 0.01 to 0.9 mg g-1 fresh substance (Fig. 3). The control value analysis of fresh and untreated equine muscle tissue. of 0.1 mg g-1 fresh substance (as recommended by the German Ministry of Health) is exceeded by 133 samples (33.8%) as analyzed by direct solid sampling ETAAS, whereas only 111 samples (28.2%) exceed the control value when applying the compound procedure. For the legal limit of 0.2 mg g-1 fresh substance, the respective figures are 41 (10.4%) for solid Fig. 2 Distribution of Cd (mg g-1 fresh substance, FS) in muscles of two horses (A and B): total mean values of muscles (dotted lines), mean values and standard deviation of sampling sites within the muscles (sampling scheme: 2×3×6×6, MLC: M.longus colli, MG: M. gastrocnemius, MD: M. diaphragmaticus). animals ×3 muscles ×6 sampling sites ×6 microsamples, n= 216) indicate an influence on total variance for the error sources ‘animals’ (P<0.001) and ‘muscles’ (P<0.05). When Fig. 3 Histogram of the analytical results of direct solid sampling regarding the muscles as a whole, the increased (P<0.01) Cd ETAAS and compound ETAAS with sample decomposition and content of the diaphragmatic muscle (MD) becomes apparent frequency of transgression of Cd contents in equine muscles with respect to the German legal limit of 0.2 mg g-1 fresh substance (FS).(Fig. 2), whereas no positive eVects are found for the other J. Anal. At. Spectrom., 1999, 14, 583–587 585the significant increase in Cd in the diaphragmatic muscle— was shown.20,21 This demonstrates that representativity36 of sampling is not easily achieved, when only one muscle is sampled. Homogenization of a sample usually leads to decreased analytical variances.However, the observed variance does not correspond with analytical imprecision as (i) information about native variance is lost, (ii) no additional information is obtained regarding the Cd content of the total muscle mass of the respective animal, (iii) the probability of secondary contamination is increased and (iv) information about such a contamination may be lost after homogenization. All of this may lead to a false kind of security as regards analytical quality.Still, a wealth of information is needed rder to correctly assess representativity when estimating the Cd burden of all muscles of an individual animal on the basis of only one sample. The carcass of a slaughtered animal is Fig. 4 Comparison of Cd contents of 394 equine muscle sample as composed of more than 200 individual muscles. In equines analyzed by direct solid sampling (x) and after homogenization and digestion of the respective samples ( y).The probability function and (and bovines) the mass of these muscles may exceed 400 kg. 5% range of erroneous classification is given for the German legal The analysis of one muscle sample being 3–4 orders of limit of 0.2 mg g-1 fresh substance (FS). magnitude lower in mass, however, is a standard procedure in oYcial meat hygiene residue control. Representativity has been tacitly taken as given. Interestingly, the same problem is sampling and 36 (9.1%) for the compound procedure.Comparison of the corresponding results obtained with direct inherent in solid sampling ETAAS where microsamples are usually several orders of magnitude lower than the total sample solid sampling ETAAS (x) and after sample homogenization and decomposition ( y) yields the equation of y=0.97x for the mass. Thus, much might still be learned from solid sampling distribution analyses. non-normalized data (r=0.983) and y=0.87x0.96 for the logarithmically transformed data (r=0.981).In the latter case, the Another result of the present distribution analysis is the low degree of heterogeneity within individual muscles. Previous standard deviation of the y-values for given x-values is about 20% (sy.x=1.21). On average, the Cd content as obtained by studies have demonstrated corresponding results for the distribution of Pb, Cd and Hg in fresh and untreated porcine,7 direct solid sampling ETAAS is expected to be about 4% above the corresponding Cd content as obtained by use of the bovine8 and equine liver,10 bovine renal cortices11 and avian kidneys.12 compound procedure.The noted diVerences are, however, not significant for both normalized and non-normalized data The total error of mean value estimation can be reduced by increasing the number of microsamples analyzed.37 As shown (P>0.01, t-test, Wilcoxon test). Erroneous classification of samples as analyzed by direct in Table 3, the maximum reduction of total variance is achieved when each microsample is taken from a diVerent sampling solid sampling can be characterized by means of a probability function using the legal limit, the standard deviation of the y- site.Corresponding results were found in a variety of solid sampling ETAAS distribution studies (e.g. Hg in avian kidney, values for given x-values (sy.x=1.21) and the t-distribution. An example is given in Fig. 4 for a significance level of 95%. Cd in equine liver) and in a study of the distribution of Fe in rabbit muscle tissue using a compound procedure.38 When For the legal limit of 0.2 mg g-1 fresh substance, erroneous classification (false positive and false negative) ranges from using this sampling strategy in the determination of Cd in equine muscles by means of solid sampling ETAAS, the 0.14 to 0.27 mg g-1 fresh substance.Limits for the 1% range of erroneous classification are calculated to range from 0.13 reduction of heterogeneity induced variance is impressive (Table 3), even though heterogeneity was found to be only a to 0.32 mg g-1 fresh substance.When applying the solid sampling spectrometer with direct minor component of total analytical variance. In solid sampling analyses, results (mean value, standard Zeeman-eVect background correction, the analysis of six microsamples takes about 10 min. Thus, in one hour 40–60 results deviation) are acquired continuously with the analysis of each microsample.Taking advantage of this analytical in-process can be obtained. This is equivalent to 4–7 samples, including analysis of reference material and working standards. The information, the number of microsamples to be analyzed can be chosen according to the observed mean value: After analyz- average analytical cost with respect to argon, graphite and reference material in the analysis of one sample (six microsamples) is calculated to be approximately $0.4–0.7. Analytical Table 3 Error of mean value estimation in the determination of Cd expenditure is found to be increased when using the convenin fresh and untreated equine muscles by means of solid sampling tional atomic absorption spectrometer with high energy deu- ETAAS with respect to number of microsamples analyzed and terium background correction and modified graphite system.sampling strategy applied Respective factors for average analytical time and cost are Error of mean Number of value estimation 1.5–2.0.This is directly correlated with the need for a prolonged furnace program (Table 2). However, with both syssampling sites microsamples per tems as used in this study, analytical time and cost range far per field sample sampling site df a RSD (%)b below the limits as given by the circumstances of horse slaughtering. 1 1 1.299 30 1 6 1.188 19 3 1 1.163 16 Discussion 2 3 1.147 15 6 1 1.113 11 In this study the analysis of the distribution of Cd in equine 9 1 1.091 9 muscle tissue indicates analytically and legally relevant diVer- 20 1 1.060 6 ences between muscles within individual animals.This finding aDistribution factor around geometric mean. bApproximation for corresponds with previous studies where heterogeneity of Cd relative standard deviation for arithmetic mean. between diVerent muscles of individual animals—especially 586 J. Anal. At. Spectrom., 1999, 14, 583–5873 Commission of the European Communities, Commission ing, e.g.three microsamples, we can observe a mean Cd Decision 90/515/EEC, ABl, EC 1990, L 286, 33. content which does not exceed the lower 1% limit of erroneous 4 P. Tscho� pel, in Hazardous Elements in the Environment. classification (0.13 mg g-1), the field sample can then be classi- Techniques and Instrumentation in Analytical Chemistry, fied as non-suspect (with respect to the 5% limit) and analysis ed. M. Stoeppler, Elsevier, Amsterdam, vol. 12, 1992, pp. 73–95.is stopped. Samples exceeding the range of the lower 1% limit 5 U. Kurfu� rst, Nachr. Chem. Tech. Lab., 1981, 29, 854. 6 U. Kurfu� rst, in Solid Sample Analysis. Direct and Slurry Analysis have to be analyzed further. After increasing the number of Using GF-AAS and ETV-ICP, ed. U. Kurfu� rst, Springer-Verlag, microsamples analyzed to, e.g. n=6, samples can be finally Berlin, Heidelberg, 1998, pp. 1–127. classified as suspect or non-suspect with respect to the 5% 7 B.Klu� ßendorf, A.Rosopulo and W. Kreuzer, Fresenius’ Z. Anal. limit of erroneous classification. The number of microsamples Chem., 1985, 322, 721. analysed with regard to the 1 and 5% limits should be chosen 8 A. Besse, PhD Thesis, University of Gießen, 1987. according to the observed variances and with respect to 9 E.Lu� cker, C. Gerbig and W. Kreuzer, Fresenius’ Z. Anal. Chem., 1993, 346, 1062. variances obtained for working standard solutions, reference 10 E. Lu�cker, J. Meuthen and W.Kreuzer, Fresenius’ Z. Anal. Chem., material and previously analyzed samples. Maximum tolerable 1993, 346, 1068. observed variances were recorded in the literature.34 11 E. Lu� cker, A. Rosopulo and W. Kreuzer, Fresenius’ Z. Anal. Samples suspected of exceeding the legal limit can be verified Chem., 1987, 328, 370. either by using a compound reference procedure or by further 12 E. Lu�cker, Fresenius’ Z. Anal. Chem., 1997, 358, 848. increasing the number of microsamples analyzed.This latter 13 H. Hecht, Ber. Landwirtschaftswiss. 1978, 55, 828. 14 H. Hecht, Fleischwirtschaft, 1979, 59, 1621. step, however, depends on the legal acceptance of solid 15 L. Jorhem, S. Slorach, B. Sandstro�m and B. Ohlin, Food Addit. sampling ETAAS. Contam., 1991, 8, 201. As shown by the comparison of methods, results of direct 16 A. Niemi, E.-R. Vena�lainen, T. Hirvi and E. Karppanen, Z. solid sampling do not deviate from the respective results as Lebensm. Unters.Forsch., 1991, 192, 4nventional compound procedure applied in 17 J. Falandysz, Sci. Total Environ., 1993, 136, 193. this study. The slight increase in Cd content as observed in 18 J. Holm, Fleischwirtschaft, 1979, 59, 737. 19 A. Salmi and J. Hirn, Fleischwirtschaft, 1981, 61, 1199. solid sampling can be related to a loss of mass due to 20 H. Hecht, Fleischwirtschaft, 1984, 64, 1113. evaporation during preparation and mass determination of 21 P. Geppert and B.Brunner, in Tagung des Arbeitsgebietes the microsamples.12,27,28 Accordingly, the number of samples Lebensmittelhygiene, ed. German Veterinary Society, Gießen, exceeding the legal limit was slightly increased. With respect 1995, vol. 36, pt. 2, pp. 243–250. to a modified sampling strategy, however, the frequency of 22 F. Weyermann and E. Lu� cker, Fleischwirtschaft, 1998, 78, 251. erroneous classification can be expected to be extremely low. 23 Ministry of Health, Germany, Fleischhygiene-Verordnung, Bundesgesetzblatt, 1996, pt. 1, p. 1678. With respect to the conditions of horse-slaughtering and the 24 Zentrale Erfassungs- und Bewertungsstelle fu� r Umweltche- given legal situation, both analytical time and cost of direct mikalien (ZEBS), Bundesgesundheitsblatt, 1996, 39, 193. solid sampling ETAAS are suYciently low to characterize it 25 A. Besse, A. Rosopulo, C. Busche and G. Ku� llmer, Labor Praxis, as a rapid procedure. In addition, a further 90% reduction of 1986, 1/2, 64.analytical time and cost can be expected when applying the 26 A. Rosopulo, Fresenius’ Z. Anal. Chem., 1985, 322, 669. sampling strategy outlined above. 27 A. Rosopulo and W. Kreuzer, in Fortschritte in der atomspektrometrischen Spurenanalytik, ed. B.Welz, Verlag Chemie,Weinheim, This study shows that direct solid sampling ETAAS can be vol. 2, 1986, pp. 455–463. applied as a rapid screening procedure in oYcial meat inspec- 28 E. Lu�cker and O. Schuierer, Spectrochim.Acta, Part B, 1996, tion ad hoc. The present situation in meat hygiene is rather 51, 201. exotic, initiated by certain—probably transient—legal pre- 29 E. Lu� cker, A. Rosopulo and W. Kreuzer, Fresenius’ Z. Anal. scriptions. However, direct solid sampling is the first analytical Chem., 1991, 340, 234. procedure suitable for in-process analysis within the scope of 30 E. Lu�cker, H. Ko� nig, W. Gabriel and A. Rosopulo, Fresenius’ Z. Anal. Chem., 1992. 342, 941. meat hygiene control of heavy metals. It will certainly serve 31 R. F. M. Herber and K.-H. Grobecker, Fresenius’ Z. Anal. Chem., to further our understanding of analytical imprecision and 1995, 351, 577. could give an impetus towards the development of new rapid 32 L. Sachs, Applied Statistics, Springer-Verlag, New York, 1984, procedures. Furthermore, there might be other interesting pp. 105–110. fields in meat hygiene—such as non-oYcial meat quality 33 E. Lu� cker, LIMIT—Program for the calculation of erroneous programs—for applying direct solid sampling ETAAS. classification, University of Gießen, 1997. 34 E. Lu� cker, in Tagung des Arbeitsgebietes Lebensmittelhygiene, ed. German Veterinary Society, Gießen, 1995, vol. 37, pp. 129–134. References 35 W. J. Dixon, BMDP Statistical Software Manual, University of California Press, Berkeley, 1992. 1 Amtliche Sammlung von Untersuchungsverfahren nach § 35 des 36 R. Klockenka�mpfer, Fresenius’ Z. Anal. Chem., 1977, 285, 345. Lebensmittel- und Bedarfsgegensta�ndegesetzes, Federal Institute of 37 E. Lu�cker, Appl. Spectrosc., 1997, 51, 1031. Consumer Health Protection and Veterinary Medicine, Beuth 38 E. Lu� cker, K. Failing, K. Lange, G. Walker and M. Bu� lte, Food Verlag, Berlin, 1995, p. 31. Sci. Technol., 1998, 31, 150. 2 Allgemeine Verwaltungsvorschrift zur Durchfu�hrung der amtlichen Untersuchungen nach dem Fleischhygienegesetz vom 11.12.1986 (VwVFlHG), Ministry of Health, Germany, BAnz Nr. 238 a. Paper 8/08804G J. Anal. At. Spectrom

ISSN:0267-9477    

DOI:10.1039/a808804g

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Determination of ruthenium in photographic materials using solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry† Yi Hu,a Frank Vanhaecke,a Luc Moens,*a and Richard Damsa and Ingrid Geuensb aLaboratory of Analytical Chemistry, University of Ghent, Proeftuinstraat 86, B-9000 Ghent, Belgium bR&D Analytic Research, Agfa-Gevaert N. V., Septestraat 27, B-2640 Mortsel, Belgium Received 9th November 1998, Accepted 11th January 1999 Ru was determined in photographic emulsions and films using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) after minimal sample pre-treatment (no separation or preconcentration required).The emulsion samples were either (i) converted into a colloidal solution by dissolution in warm water or dilute HNO3 ( liquid sampling) or (ii) dried at 105 °C (solid sampling) prior to analysis. For the analysis of photographic films, only solid sampling, requiring no sample pre-treatment, was used.By optimization of the ETV heating programme, on-line separation of Ru (analyte) and Ir (internal standard) from the Ag matrix was accomplished: #90% of the Ag present was removed prior to the vaporization of Ru and Ir. Quantification of Ru was accomplished by single standard addition, whereby Ir was used as an internal standard. The absolute limit of detection was found to be#1 pg. The results obtained showed a good agreement with those obtained by pneumatic nebulization ICP-MS and/or electrothermal atomic absorption spectrometry after sample dissolution. sampling, sample preparation can be reduced to a minimum, Introduction which significantly reduces the risk of sample contamination During the production of photographic emulsions, trace or analyte losses.Moreover, since the samples are not diluted, amounts of precious metals (e.g., Au, Rh, Ru or Ir) are the detection limits may be improved. In our laboratory, purposely added in order to obtain desirable characteristics in research has been carried out concerning direct solid sampling terms of light sensitivity.1–4 In order to assess the quality of with ETV-ICP-MS.As, Se, Cd, Sb and Hg have been deterthe photographic materials thus produced, accurate quantitat- mined successfully in samples of diVerent origin.12–16 Also, for ive determination of these elements is important. However, liquid samples, the use of ETV as a sample introduction the often low concentrations of these dopants and the heavy technique21–25 oVers some distinct advantages over pneumatic Ag matrix make this analysis diYcult.In addition, separation nebulization: (i) the limit of detection can be significantly of the precious metals from the Ag-containing matrix prior to improved owing to the enhanced sample transport eYciency their determination is often not self-evident. (#80%), (ii) small sample volumes (5 ml ) can be analyzed Inductively coupled plasma mass spectrometry (ICP-MS) is and (iii) on-line matrix removal is sometimes possible when a powerful analytical technique, showing extremely low limits using an appropriate heating programme.Since ETV has of detection, multi-element capabilities, a wide linear dynamic already been extensively used for many years in combination range and a high sample throughput. Originally, ICP-MS was with AAS and ICP-OES, valuable information (e.g., temperamainly intended for the analysis of aqueous samples and ture programming, the use of chemical modifiers) is available hence, pneumatic nebulization is the most widely used method in the literature.for sample introduction. Pneumatic nebulizers owe their suc- In this work, the determination of Ru in photographic cess to their low cost, instrumental simplicity, high sample emulsions was carried out using liquid and solid sampling throughput and good stability. However, pneumatic nebuliz- ETV-ICP-MS after minimal sample pre-treatment (no separaation also shows important drawbacks.The sample transport tion or preconcentration required). Ru in photographic films eYciency is very low (in combination with a spray chamber, was determined using direct solid sampling ETV-ICP-MS. typically 1–2%), while the sample must be dissolved and a relatively large volume of solution is required. Hence, eVorts have been made to couple alternative sample introduction systems to ICP-MS in order to extend its application range. Experimental At present, solid samples can be directly analyzed using laser Instrumentation ablation (LA)5–10 or in some cases also using electrothermal vaporization (ETV)11–20 for sample introduction.The poten- The present study was carried out using a commercially tial of ETV-ICP-MS for ‘solid sampling’ has been recognized available graphite furnace of the ‘boat-in-tube’ type (SM-30 for some years and some publications on the subject have Gru�n Analytische Mess-Systeme, Ehringhausen, Germany), appeared, but most of these papers are concerned with analys- originally developed for ETAAS.This graphite furnace was ing slurries17–20 rather than (dry) solid samples. With solid modified for coupling with ICP-based instruments (ICP-OES, ICP-MS). The description of this modification has been published elsewhere.26 The heating programme of the furnace was †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998.controlled by an in-house developed computer program. The J. Anal. At. Spectrom., 1999, 14, 589–592 589Table 2 ICP mass spectrometer: instrument settings and acquisition Table 1 Graphite furnace temperature programme parameters Step Duration/s Temperature/°C ICP-MS PE SCIEX Elan 5000 ‘Drying’ step 10 100–120 ‘Ashing’ step Ia (for matrix removal ) 30 800 Rf power 1 kW Plasma gas flow rate 12 l min-1 ‘Ashing’ step IIb (for matrix removal ) 60 1400 ‘Intermediate’ step 10 200 Auxiliary gas flow rate 1.2 l min-1 Carrier gas flow rate 0.75 l min-1 (to switch the valve to the ‘measuring’ position and allow the plasma Scanning mode Peak hop transient Acquisition points per peak 1 to stabilize) ‘Vaporization’ step 15 1900 Sweeps per reading 1 Readings per replicate 300 ‘Intermediate’ step 40 No heating (to switch the valve to the ‘venting’ Dwell time 30 ms Total measuring time 30 s position after the data acquisition has been completed) ‘Cleaning’ steps 2×5 2400 into the sample holder for subsequent analysis.An advantage aThis pre-treatment step is aimed at removing the film base (PET) of this approach is that the analytes of interest are enriched when analyzing a sample of photographic film. bThis pre-treatment by a factor of approximately five. Photographic emulsion step is intended to remove Ag to the largest possible extent. normally contains #100 mg of Ag per gram of emulsion.Photographic films. For film samples, first the weight per furnace temperature was monitored using an optical pyrometer square centimetre was determined. This was accomplished by (PY20, Gru�n Optik, Ehringhausen, Germany). taking 9 cm2 of film and accurately determining the corre- The ETV system was coupled to a Perkin-Elmer SCIEX sponding weight. In order to determine the Ru content, the Elan 5000 ICP mass spectrometer (Perkin-Elmer, OVenbach, film was cut into small pieces (of about 1.5 mg each) using a Germany) via a 10 mm id silicone rubber tubing.A three-way ceramic knife. These film samples were loaded into a sample valve was used to vent vapours generated during the drying, holder and accurately weighed. Thereafter, the sample holder ashing and cleaning steps. As a result, only vapours generated was inserted into the graphite furnace for subsequent analysis. during the vaporization step of the heating programme were An additional ashing step was used for the film in order to allowed to reach the plasma, so that deposition of vaporized remove the film base (polyethyleneterephthalate or PET), matrix material (on the torch, interface and lens stack), before the vaporization of the analyte, see Table 1.contamination of the inace pump oil and plasma over- Photographic film normally contains #2 gm-2 Ag. loading could be reduced to a minimum. The flow rate of the Ar carrier gas was controlled by means of a mass flow Calibration and internal standardization controller (Model 5876, Brooks Instruments, Veenendaal, The In previous work carried out in our laboratory,12 it was shown Netherlands).that in solid sampling ETV-ICP-MS, single standard addition The settings for the ETV system and the ICP mass specis an accurate, fast and practical calibration strategy. Three trometer are listed in Tables 1 and 2, respectively. The following measurements of the blank, five measurements of the sample isotopes (abundances given in parentheses) were monitored and five measurements of the sample to which an analyte spike since they are free from inter-element isobaric interference: of appropriate concentration is added are suYcient to obtain 99Ru (12.7%), 101Ru (17.0%), 103Rh (100%) and 193Ir (62.7%). an accurate and precise concentration value.Hence, in this work, single standard addition was used for calibration. Standards and reagents In solid sampling ETV-ICP-MS, the use of an internal All reagents used were of analytical-reagent grade or higher standard is often imperative.12 In contrast to pneumatic nebulpurity.Water was de-ionised and further purified using a ization ICP-MS, for which a close match in mass number Milli-Q water purification system (Millipore, Bedford, MA, between the analyte elements and the internal standard is the USA). Ru, Rh and Ir standard solutions were prepared from most important selection criterion,27 similar volatility of the commercially available 1 g l-1 single-element standards, by analyte element and the internal standard is a more important appropriate dilution with 20% HCl for Ru and with 1% HNO3 issue in solid sampling ETV-ICP-MS.In this work, Ir and Rh for Rh and Ir. HNO3 (65%) and HCl (32%) were purified by were tested as potential internal standards, as their volatility sub-boiling distillation in quartz equipment. is similar to that of Ru. The experiments showed that biased results were obtained when Rh was used as an internal Sample preparation standard, probably because of a spectral interference at m/z 103, the origin of which could not be identified. Consequently, Photographic emulsions.Two ways of sample pre-treatment Ir was chosen as an internal standard to correct for signal were used: suppression due to residual matrix eVects (matrix-induced For ‘liquid sampling’ ETV-ICP-MS, approximately 500 mg signal suppression or enhancement) and to improve the pre- of emulsion were first dissolved in 100 ml of warm (#40 °C) cision of repeated measurements (repeatability).The signal of water (or 0.14M HNO3) to form a colloidal solution. the argon dimer (Ar2+), which is always present during plasma Thereafter, a micropipette was used to transfer an appropriate operation, was always monitored as an indicator of residual amount of this solution (10 ml ) into a sample holder, which matrix eVects.28 was inserted into the graphite furnace for subsequent measurement.Although a pure AgCl emulsion can be dissolved in Analysis procedure concentrated ammonia very easily, this dissolution method was not used in this work, because photographic emulsions An appropriate amount of standard solution (Ru) and/or internal standard (Ir) was pipetted into the sample holder and often contain AgI or AgBr, which cannot be dissolved in an ammonia solution. subsequently dried under an infrared lamp prior to sample loading.This preliminary drying facilitates solid sample load- For ‘solid sampling’ ETV-ICP-MS, a solid sample, which is easy to handle, was obtained by drying the emulsion (overnight ing and it has been shown in earlier work12 that—at least for some elements—an identical behaviour of the analyte (i) in at 105 °C). About 0.5 mg of dried sample was directly loaded 590 J. Anal. At. Spectrom., 1999, 14, 589–592the solid sample and (ii) in the standard solution can only be guaranteed under these conditions.When liquid sampling is used, 10 ml of sample solution are inserted into the sample holder by means of a micropipette and dried under an infrared lamp before introduction into the furnace. For solid sampling, the sample holder was first tared using a microbalance (readability of 1 mg; M3P, Sartorius, Go� ttingen, Germany) and subsequently the solid sample was loaded and weighed. Finally, the sample holder was inserted into the graphite furnace with the aid of a pair of tweezers, which can slide on a rail (rigidly mounted in front of the furnace), allowing reproducible loading.Results and discussion Fig. 2 Vaporization curves for Rh and Ir (no ashing step was applied, the heating time is 15 s for each corresponding temperature). In photographic emulsions and films, Ag is present at a high concentration: #100 mg g-1 in emulsion and #2 gm-2 in film, while precious metals, such as Ru, are added at trace or ultratrace levels (usually around 1 mg g-1 Ag).Owing to its high mass number and relatively low ionization potential, Ag gives rise to severe matrix eVects in ICP-MS. Strong suppression of the analyte signals by a 1 g l-1 Ag matrix was observed when pneumatic nebulization ICP-MS was used for the multielement analysis of photographic materials, carried out previously at our laboratory.29 On the other hand, separation of Ag from Ru is diYcult owing to the low concentration of the latter and the complex matrix involved (predominantly AgX and gelatin).One of the advantages of ETV as a means of sample introduction is that on-line separation of the analyte(s) of interest from the matrix element becomes possible if an appropriate heating programme is used, provided that the Fig. 3 Separation of Ru and Ir from the Ag matrix obtained by elements of interest and the matrix elements show a suYciently heating a sample of film II (about 0.1 mg). A 10 ml volume of diVerent volatility. 500 mg l-1 Ru and 50 mg l-1 Ir standard solution was added and an OmniRange setting of 30 was used for the Ag+ signal in order to In order to investigate the possibility of separating Ag from prevent overloading of the detector. Ru and to select an appropriate internal standard, the vaporization curves of Ag, Ru, Ir and Rh were recorded using a 50 mg l-1 standard solution of these elements. The results obtained are given in Fig. 1 and 2. As can be seen from these vaporization curves, Ag starts to volatilize at a temperature of about 1000 °C while Ru, Rh and Ir are volatilized at temperatures of about 1500 °C or higher.Hence, on-line separation of Ag from Ru, Rh and Ir is possible. The vaporization curves of Ru, Rh and Ir agree well with those obtained by Byrne et al.,30 who studied the vaporization mechanism of the platinum group elements (PGEs, e.g., Ru, Rh, Pd, Os, Ir and Pt) in the graphite furnace in detail. They suggest that, except for Os, all PGEs are vaporized as metal vapour sublimed from metal deposited on the graphite surface after oxide decomposition. Next, the ETV heating programme Fig. 4 Signal profiles for Ru, Ir and Ar2+ observed for a sample of was further optimized, with the aim of maximizing the volatiliz- film II (vaporization step). ation of Ag in the ashing step, while minimizing the losses of Ru, Rh and Ir during this step. As a result, the heating programme shown in Table 1 was used in all further work.For both film and emulsion samples, this multi-step heating programme allowed #90% of the Ag matrix to be removed prior to the vaporization of Ru and Ir. The separation of Ru and Ir (used as an internal standard) from the Ag matrix is clearly visible from Fig. 3, which was obtained by heating a ‘real-life’ film sample using the heating programme listed in Table 1. Two peaks are observed for Ag. It is tempting to attribute this behaviour to the occurrence of two diVerent Ag species in the film sample.However, a similar signal profile was observed for an AgNO3 solution. Hence, it is more likely that Ag previously condensed on cooler parts of the furnace and/or migrated to some extent into the graphite the sample Fig. 1 Vaporization curves for Ag and Ru (no ashing step was applied; the heating time is 15 s for each temperature). holder is released at the higher temperature of the vaporization. J. Anal. At. Spectrom., 1999, 14, 589–592 591Table 3 Results in ppm (mg Ru per g Ag); standard deviations are given in parenthesesa Emulsion I Emulsion II Film I Film II Ru added 1 ppm 10 ppm 10 ppm 50 ppm Liquid sampling — 11.0 (0.4, n=5) — — ETV-ICP-MS Solid sampling 1.36 (0.12, n=5) 11.0 (0.8, n=5) 13.3 (0.9, n=5) 52.1 (1.6, n=5) ETV-ICP-MS ETAAS 1.06 (0.09, n=3) 11.1 (0.2, n=3) 12.6, 12.6 45, 49.1 Pneumatic 1.34 (0.03, n=4) 11.4 (0.7, n=4) — — nebulization ICP-MS aThe Ag concentrations for emulsions I and II are 88.8 and 88.6 mg g-1, respectively.Films I and II contain 1.94 and 2.07 g m-2 Ag, respectively. Two samples consisting of a pure AgCl emulsion, provided References by Agfa-Gevaert and doped with diVerent amounts of Ru, 1 T. H. James, The Theory of the Photographic Process, Macmillan, were measured using both liquid and solid sampling ETVLondon, 4th edn., 1977. ICP-MS. Two film samples which were coated with Ru-doped 2 R. S. Eachus and M. T. Olm, Cryst. Lattice Defects Amorphous AgCl emulsions provided by Agfa-Gevaert were also measured.Mater., 1989, 18, 297. Signal profiles for Ru, Ir and Ar2+ obtained during analysis 3 R. S. Eachus and M. T. Olm, Nippon Shashin Gakkaishi, 1991, of a sample of film II are given in Fig. 4. The almost unsup- 54, 294. 4 D. Volman, G. Hammond and D. Neckers, Advances in pressed smooth curve of the argon dimer signal indicates that Photochemistry, Wiley, New York, 1992, vol. 17. the removal of the matrix during the ashing step is eVective 5 P.Arrowsmith, Anal. Chem., 1987, 59, 1437. and that only a minimum amount of matrix is left after this 6 E. R. Denoyer, K. J. Fredeen and J. Hager, Anal. Chem., 1991, step. Both 99Ru and 101Ru were monitored and the total Ru 63, 445A. contents calculated using both signal intensities were in excel- 7 J. S. Crains and D. L. Gallimore, J. Anal. At. Spectrom., 1992, lent agreement, indicating that no significant spectral inter- 7, 605. 8 N. J. G. Pearce, W. T. Perkins and R. Fuge, J. Anal. At. Spectrom., ferences occurred. Hence, either of these two isotopes can be 1992, 7, 595. used for the determination of the Ru content by ETV-ICP-MS. 9 S. F. Durrant and N. I. Ward, Fresenius’ J. Anal. Chem., 1993, The results for both the emulsion and film samples are listed 345, 512. in Table 3. For comparison, the results obtained by ETAAS 10 E. H. De Carlo and E. Pruszkowski, At. Spectrosc., 1995, 16, 65. (Agfa-Gevaert) and by pneumatic nebulization ICP-MS 11 J.Wang, J.M. Carey and J. A. Caruso, Spectrochim. Acta, Part B, (University of Ghent), after taking the sample into solution, 1994, 49, 193. 12 F. Vanhaecke, S. Boonen, L. Moens and R. Dams, J. Anal. At. have also been included. Spectrom., 1995, 10, 81. As can be seen from Table 3, the agreement between the 13 S. Boonen, F. Vanhaecke, L. Moens and R. Dams, Spectrochim. ETV-ICP-MS results and the results obtained by ETAAS and Acta, Part B, 1996, 51, 271. pneumatic nebulization ICP-MS is very good.On each 14 G. Galba�cs, F. Vanhaecke, L. Moens and R. Dams, Microchem. occasion, the diVerence between the average ETV-ICP-MS J., 1996, 54, 272. result and the corresponding reference value (ETAAS result 15 F. Vanhaecke, S. Boonen, L. Moens and R. Dams, J. Anal. At. Spectrom., 1997, 12, 125. or pneumatic neulization ICP-MS results) is <10%. In 16 F. Vanhaecke, I. Gelaude, L. Moens, and R. Dams, Anal. Chim. addition, the precision of the results obtained (average RSD Acta, in the press.<10% for n=5) is also satisfactory. It is important to mention 17 U. Voellkopf, M. Paul and R. E. Denoyer, Fresenius’ J. Anal. that sample inhomogeneity may deteriorate the results Chem., 1992, 342, 917. obtained.31 Hence, in each case a suYcient number of sub- 18 D. C. Gre�goire, N. J. Miller-Ihli and R. E. Sturgeon, J. Anal. At. samples should be analysed to obtain a reliable result. Spectrom., 1994, 9, 605. 19 S. Hauptkorn, V. Krivan, B. Gerken and J. Pavel, J. Anal. At. The limit of detection was determined using an empty Spectrom., 1997, 12, 421. sample holder as a blank and was calculated according to the 20 M. J. Liaw, S. J. Jiang and Y. C. Li, Spectrochim. Acta, Part B, 3s criterion (IUPAC). The absolute limit of detection was 1997, 52, 779. found to be approximately 1 pg. When liquid sampling is used, 21 J. M. Carey and J. A. Caruso, Crit. Rev. Anal. Chem., 1992, this corresponds to a relative value of 0.1 mg l-1, taking 10 ml 23, 397.as a typical sample volume. For solid sampling, this is equival- 22 R. W. Fonseca. and N. J. Miller-Ihli, Spectrochim. Acta, Part B, 1996, 51, 1591. ent to 1 ng g-1, taking 1 mg as a typical sample mass. 23 H. Naka and D. C. Gre�goire, J. Anal. At. Spectrom., 1996, 11, 359. From the results obtained, it is clear that ETV-ICP-MS can 24 C. C. Chang and S. J. Jiang, J. Anal. At. Spectrom., 1997, 12, 75. be considered as a promising technique for the determination 25 L. Yu, S. R. Koirtyohann, M. L. Rueppel, A. K. Skipor and of trace and ultratrace amounts of Ru in photographic emul- J. J. Jacobs, J. Anal. At. Spectrom., 1997, 12, 69. sion and film samples. 26 P. Verrept, R. Dams and U. Kurfurst, Fresenius’ J. Anal. Chem., 1993, 346, 1035. 27 F. Vanhaecke, H. Vanhoe, R. Dams and C. Vandecasteele, Talanta, 1992, 39, 737. Conclusion 28 F. Vanhaecke, G. Galba�cs, S. Boonen, L. Moens and R. Dams, Solid sampling ETV-ICP-MS is a fast and accurate analytical J. Anal. At. Spectrom., 1995, 10, 1047. 29 Y. Hu, F. Vanhaecke, L. Moens and R. Dams, Anal. Chim. Acta, technique for determining trace amounts of Ru in photo- 1997, 355, 105. graphic materials. Since only single precious metals are nor- 30 J. P. Byrne, D. C. Gre�goire, M. E. Benyounes and C. L. mally added to the photographic emulsion as a dopant, it can Chakrabarti, Spectrochim. Acta, Part B, 1997, 52, 1575. be predicted that the content of Ir in photographic materials 31 F. Vanhaecke, J. Diemer, K. G. Heumann, L. Moens and R. can also be determined in the same way, but using Ru as an Dams, Fresenius’ J. Anal. Chem., 1998, 362, 553. internal standard. Furthermore, it is also to be expected that this analytical method can be applied to the determination of the other precious metals. Paper 8/08751B 592 J. Anal. At. Spectrom., 1999, 14, 589

ISSN:0267-9477    

DOI:10.1039/a808751b

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Investigation of impurities in thermoluminescent Al2O3 materials by prompt-gamma activation analysis† Zs. Kasztovszky,*a Zs. Re�vay,a T. Belgya,a B. Fazekas,a J. O� sto�r,a G. L. Molna�r,a G. Molna�rb and J. Borossayb aDepartment of Nuclear Research, Institute of Isotope and Surface Chemistry, Chemical Research Center, POB 77, H-1525 Budapest, Hungary. E-mail: kzsolt@alpha0.iki.kfki.hu bDepartment of General and Inorganic Chemistry, Eo�tvo�s Lora� nd University, POB 32, H-1518 Budapest 112, Hungary Received 11th December 1998, Accepted 21st January 1999 a-Al2O3 is one of the most important materials for thermoluminescence dosimetry.The thermoluminescent features are strongly aVected by impurities, which were investigated with the non-destructive method of prompt-gamma activation analysis (PGAA). Impurities in four samples of thermoluminescent alumina materials were investigated. The precision and reproducibility of the PGAA method were also tested on standard samples spiked with B, Na, S, Cl, Fe, Cu and Ag.low thermal eVective flux (2.5×106 cm-2 s-1), destruction Introduction eVects on the crystal lattice are negligible; thus, the PGAA High-purity aluminium oxide powders are widely used for the method preserves the original physical and chemical form even production of diVerent ceramics. Impurities, even in trace of single crystal samples. Moreover, one avoids any sample amounts, can aVect the quality (i.e. optical, electrical, mechan- preparation problems arising from the chemical and mechanical ical and other properties) of these ceramics.Recently, specially resistance of aluminium oxide. prepared alumina ceramics (and single crystals also) have been Because only mass ratios of the elements in a sample are increasingly applied in the field of thermoluminescence (TL) determined, matrix eVects due to self-absorption and scattering dosimetry. Since impurities can be directly involved in the TL of neutrons are cancelled.10 Moreover, aluminium oxide is an mechanism, they can determine basic dosimetric properties ideal matrix for PGAA because aluminium and oxygen have such as sensitivity and fading.Therefore, the determination of medium and low neutron capture cross-sections, respectively, impurities in these materials is important. so trace elements are well distinguished on the low spectral Chemical analysis of Al2O3 powders can be performed by background. This is in contrast to INAA where a high level direct or solution-based methods.Among the direct methods, of short-lived activity is produced due to the high thermal flux optical emission spectrometry is the most widespread.1 This and the presence of fast neutrons.7 method, especially when alkali halides are employed as thermo- The aim of this work was to demonstrate the performance chemical reagents, is sensitive to many important elements, of the PGAA method for the analysis of thermoluminescent but suVers from poor reproducibility and requires solid refer- alumina materials.These measurements—among other ence materials for calibration. Other methods such as slurry parallel analytical experiments—serve as test cases for the sampling, direct sample insertion and electrothermal vapori- applicability of PGAA with guided neutrons. zation techniques, combined with ICP-AES/MS, generally oVer better detection limits, but they have several limitations Experimental (e.g.calibration problems, grain size limitations).2,3 When solution-based methods, such as ICP-AES/MS and AAS, are PGAA method applied, a complete dissolution of the solid sample is manda- Prompt-gamma activation analysis is based on the detection tory.4,5 This results in higher detection limits and lower of prompt gamma rays originating from neutron radiative precision because of the dilution and contamination of the capture or (n, c) reaction. By the spectral analysis of prompt sample.6 Moreover, owing to the high melting-point as well gamma rays, according to their energies and intensities, it is as the hardness and chemical inertness of alumina, the dissolupossible to determine the chemical composition of a given tion is tedious and time-consuming. sample.The nuclear reaction is independent of the physical Although instrumental neutron activation analysis (INAA) is and chemical form of the samples. a well-established technique and has been widely applied to the analysis of alumina,7 prompt-gamma activation analysis (PGAA) is a relatively new technique, which can be performed Experimental apparatus.The measurements were carried out best with cold neutron beams of nuclear reactors.8,9 PGAA at the Budapest Research Reactor, Hungary. This is a waterenables, in principle, the detection of all elements of the Periodic cooled, water-moderated research reactor with a thermal power Table — many of them with remarkable sensitivity.Since the of 10MW. A beam of low energy neutrons is transported to a neutrons used for PGAA are of low energy (<25 meV) and of distance of approximately 35 m from the reactor core by a slightly curved neutron guide, made of glass coated with a nickel reflector. At the end of the guide—where the prompt-gamma †Presented at the 8th Solid Sampling Spectrometry Colloquium, Budapest, Hungary, September 1–4, 1998. experimental apparatus is situated—the energy of the neutrons J.Anal. At. Spectrom., 1999, 14, 593–596 593is less than that of thermal neutrons, because the higher energy the quality factor (Q), which is derived from the diVerence between the measured and literature energies. The closer the neutrons are not reflected. The thermal-equivalent eVective flux is approximately 2.5×106 cm-2 s-1 at the target position. The value of Q is to unity, the more reliable is the element identification. One must also consider the intensity ratios system has been described elsewhere.11,12 The samples are usually sealed in thin FEP Teflon bags or between the diVerent gamma peaks of an element. The possible background lines are also examined.The background gamma Teflon capsules, and placed directly in the beam, which is collimated to an area of about 2×2 cm. Because the sample is rays mostly originate from the (n, c) reactions in the surrounding material. The most important sources are H and N in the virtually transparent to neutrons, the determined chemical composition is an average value for the whole irradiated volume.air, Fe and Al in the equipment’s material and F in the Teflon packaging of the samples. Natural background radiation can The emitted prompt gamma rays are observed with a complex detector system. The main part of this system is a also be observed in the spectra from members of the U and Th series. Canberra high-purity germanium detector. The detector is surrounded by a bismuth germanate (BGO) scintillator annulus in order to reject the Compton-scattered photons.With Determination of chemical composition. The detected gammaray intensity, represented by the peak area (AE), is directly the present set-up, a baseline suppression ratio of about six can be achieved for the 1332 keV energy peak of 60Co. This proportional to the mass of a given chemical element, and the measuring time, t. Hence ratio becomes much higher for higher energy c-rays.9 The whole detector system is shielded against neutron- and gammaradiation background.m= 1 S · AE t (1) The spectra are collected into 16 000 channels by a Canberra S100 MCA multichannel analyzer. The energy and eYciency where calibrations of the measuring system are performed using precisely known c-lines emitted by radioactive sources and S= NA M ·h·s0·Ic·W0·e(Ec) (2) (n, c) reactions. The collected spectra are evaluated by ‘Hypermet PC’, a complex c-spectrum evaluation program, is the analytical sensitivity, expressed in units of developed in our laboratory.13 counts s-1 mg-1.It is proportional to the neutron capture cross-section of the nucleus s0, the isotopic abundance h and Element identification. The element identification is based the gamma yield Ic, which are nuclear constants, as well as to on our own nuclear data ler compilation of the neutron flux W0 and the detector eYciency e(Ec), which (n, c) data, compiled by Lone et al.,14 is being replaced by new are characteristics of the measuring system. The sensitivity for experimental data measured with higher precision in our an element can be related to that of a comparator element: laboratory for each stable element.The elements are identified according to the energy values of their most intense prompt- Sx SC = (h·s0·Ic/M)x (h·s0·Ic/M)C · ex(Ec) eC(Ec) = k0,C(x)· ex(Ec) eC(Ec) (3) gamma peaks. The reliability of the element identification is controlled through diVerent statistical parameters, which are This ratio is independent of the neutron flux; it depends only derived from the deviations of measured energy and intensity on nuclear constants and the detector eYciency.The latter are values from the literature values.15 One of these parameters is known with good accuracy. The k0-factors were determined by internal standardization measurements. The mass ratio for Table 1 Interference-free prompt-gamma lines used for determination an element ‘x’ can be determined according to the following of mass fractions.k0-factors are related to the 1950.955 keV promptequation: gamma line of Cl Element Energy/keV k0 Uncertainty of k0 (%) mx mR = AE,x AE,R · k0,C(R) k0,C(x) · eR(Ec) ex(Ec) (4) H 2223.182 1.801 0.65 where R is an arbitrary reference element contained in the B 478.000 3.597×10-2 0.93 sample. The comparator elements were typically H and Cl in Na 869.160 1.424×10-2 1.1 samples with precisely known compositions.10,16 874.369 9.946×10-3 1.28 Al 1778.888 8.297×10-2 2.27 The masses were calculated according to eqn.(1)–(4). The 2271.617 1.414×10-3 4.14 gamma lines used and the corresponding k0-factors are listed 2282.705 3.179×10-3 2.96 7723.645 2.286×10-2 2.5 Table 2 Sensitivities and detection limits for the present PGAA system S 840.928 3.212×10-2 1.57 3220.468 1.113×10-2 2.59 4869.297 5.632×10-3 3.28 Sensitivity/ Detection limit/ Element counts s-1 mg-1 mg g-1 Cl 1164.740 1.38 0.86 1950.955 1 1959.146 6.428×10-1 1.46 H 6.49×10-2 13 B 4.02×101 0.8 2863.750 2.899×10-1 0.92 6110.692 1.063 1.25 N 2.37×10-4 6100 F 1.38×10-4 17 600 Fe 352.326 2.641×10-2 2.44 691.876 1.357×10-2 2.51 Na 1.78×10-2 570 Al 2.22×10-3 520 1612.682 1.542×10-2 2.83 5920.323 2.340×10-2 3.06 S 4.28×10-3 290 Cl 8.10×10-2 15 7631.123 6.903×10-2 2.83 7645.580 5.805×10-2 2.90 Ca 1.75×10-3 520 Fe 3.84×10-3 315 Cu 203.000 1.568×10-2 1.68 278.273 7.222×10-2 1.33 Cu 1.18×10-2 150 Zn 1.88×10-3 680 7306.598 1.970×10-2 2.29 7915.419 7.013×10-2 2.17 Ga 1.73×10-3 1070 Ag 6.86×10-2 29 Ag 237.100 8.774×10-2 2.08 360.632 7.013×10-2 2.97 Eu 1.16×101 0.18 Gd 1.35×101 0.15 657.911 1.004×10-1 1.83 594 J.Anal. At. Spectrom., 1999, 14, 593–596Table 3 Mass fractions of elements in four Al2O3 samples measured by PGAA. The values and the 1s uncertainty are given in mg g-1 TLD-800 CA-600 Pure 0223 CA-320 Sample c±uncertainty Q c±uncertainty Q c±uncertainty Q c±uncertainty Q H <13 — 125±5.5 0.80 <13 — 300±9 0.97 B 1.76±0.05 0.46 <0.8 — 1.1±0.4 0.93 <0.8 — Na <500 — 1530±72 0.80 <570 — 4380±80 0.93 Cl 52±3.1 0.75 <15 — <15 — <15 — Fe <300 — 525±79 0.73 <315 — 590±94 0.65 Cu <150 — <150 — <150 — <150 — Zn <680 — <680 — <680 — <680 — Ga <1070 — <1070 — <1070 — <1070 — Ag <30 0.47 <30 — <30 — 220±33 0.62 Eu <0.1 — <0.1 — 0.1±0.06 0.82 <0.1 — Table 4 Mass fraction (%) and 1s uncertainties of spiked impurities measured by PGAA PGAA PGAA PGAA PGAA Element Compound Nominal measurement 1 measurement 2 measurement 3 average B H3BO3 0.034 0.0328±0.0006 0.0339±0.0006 0.0353±0.0006 0.0340±0.0006 Na NaCl 0.617 0.55±0.08 0.64±0.05 0.68±0.03 0.62±0.08 S Fe2 (SO4)3 0.519 0.54±0.02 0.59±0.02 0.57±0.02 0.57±0.02 Cl NaCl 1.026 0.98±0.02 1.01±0.02 1.07±0.02 1.02±0.02 Fe Fe2(SO4)3 0.490 0.49±0.02 0.58±0.02 0.52±0.02 0.53±0.02 Cu CuCl2 0.373 0.37±0.01 0.38±0.01 0.41±0.009 0.39±0.01 Ag AgNO3 0.326 0.330±0.009 0.324±0.009 0.336±0.009 0.330±0.009 in Table 1.The possible interferences between diVerent gamma and height 5 mm were pressed from the same homogeneous powder with a hydraulic press. These discs were sealed in peaks were individually examined, and the peaks aVected by spectral interference neglected. The elemental masses were Teflon bags in groups of three. The three diVerent samples with a mass of about 3 g each were measured individually for related to the mass of Al2O3, which was determined from the detected mass of Al by a calculation according to stoichi- 85 000–230 000 s.The analytical purity of the Al2O3 was checked by a PGAA measurement of a 4 g ‘pure’ Al2O3 ometry. Because of the poor detectability of oxygen, this procedure gives more precise mass values than the direct sample. Unexpectedly, it was found to be contaminated with Na (mass fraction 0.216%) and S (mass fraction 0.095%).measurement of the oxide. The total uncertainties (standard deviations) were calculated from the statistical (counting) During the calculations of nominal mass fractions, these values were taken into account. uncertainties of the peak areas, the uncertainties of the k0- factors and the uncertainties of the detector eYciencies. As the last two typically have standard deviations of a few per Results and discussion cent, the total uncertainty is mainly determined by the counting statistics reflected in the analytical sensitivities.Four alumina samples with previously unknown contaminants were investigated with PGAA. The mass fractions of the identified elements are shown in Table 3. The Q-factors show Detection limits. For the undetected elements, detection limits (CL) were calculated from the spectra themselves the reliability of element identification in PGAA. It is a remarkable feature of PGAA that the detection limit for some light elements, such as B, is much lower than that of ICP.CL= 3·sB S (5) Moreover, H cannot even be detected by ICP. For the samples with known contaminants, the nominal where sB is the standard deviation of the baseline and S is the mass fractions and the results of PGAA measurements for sensitivity for a given element. The baseline is a complex some elements are compared in Table 4. The elements investi- function, calculated by Hypermet PC automatically for each region.sB is the constant part of the function. Table 2 contains the sensitivity values and the calculated detection limits of the elements investigated. Measurements. The elemental compositions of three commercial alumina TLD powders, namely TLD-800 (VICTOREEN), CA-600 and CA-320 (DESMARQUEST, France) were investigated by means of PGAA. The masses of the individual samples were between 1 and 3 g. The samples were sealed in thin Teflon bags and irradiated for 17 000–63 000 s.In order to check the reliability of the PGAA results for some elements, a nominally pure aluminium oxide powder sample with a known amount of contaminants was prepared in our laboratory. It was spiked with B, Na, S, Fe, Cu and Ag in the form of NaCl, Fe2(SO4)3·9H2O, CuCl2·2H2O, 6 B. Zs. Varga, M. Ballo� k, G. Molna�r and A. Bartha, unpublished gated were B, Na, S, Cl, Fe, Cu and Ag. Three measurements work. were performed. It was found that the three measurements 7 H.Rausch, S. To� ro�k and A. Simonits, Isotopenpraxis, , show good reproducibility, and the agreement between nom- 229. inal and measured mass fractions is good (see Fig. 1). 8 R. M. Lindstrom and C. Yonezawa, in Prompt Gamma Neutron Activation Analysis, ed. Z. B. Alfassi and Ch. Chung, CRC Press, Boca Raton, FL, 1995, p. 93. Conclusion 9 G. L. Molna�r and R. M. Lindstrom, in Nuclear Methods in Mineralogy and Geology, ed. A. Ve� rtes, S. Nagy and K. Su� vegh, Prompt-gamma activation analysis without the use of stan- Plenum Press, New York, 1998, p. 145. dards is a valuable analytical tool. It should be emphasized 10 G. L. Molna�r, Zs. Re�vay, R. L. Paul and R. M. Lindstrom, that the method is non-destructive and no sample preparation J. Radioanal. Nucl. Chem., 1998, 234, 21. is necessary. Although at present the detection limits for many 11 G. L. Molna�r, T. Belgya, L. Dabolczi, B. Fazekas, A� . Veres, I. elements are higher than those characteristic of other well- Bikit, Z.Kis and J. O� sto� r, J. Radioanal. Nucl. Chem., 1997, 215, established techniques (e.g. ICP-AES, INAA), some elements, 111. 12 T. Belgya, Zs. Re�vay, B. Fazekas, I. He�jja, L. Dabolczi, G. L. viz., H, B, Cl, Gd and Eu, can be detected at very low levels, Molna�r, Z. Kis, J. O� sto� r and Gy. Kasza�s, in Proceedings of the 9th which are diYcult to attain by other methods. International Symposium on Capture Gamma-ray Spectroscopy, ed. PGAA has been shown to be a useful complementary G.L. Molna�r, T. Belgya and Zs. Re�vay, Springer Hungarica, method for the determination of impurities in thermoluminesc- Budapest, 1997, p. 826. ent alumina materials. The analytical sensitivity should be 13 B. Fazekas, G. L. Molna�r, T. Belgya, L. Dabolczi and improved by the installation of a cold neutron source, as A. Simonits, J. Radioanal. Nucl. Chem., 1997, 215, 271. 14 M. A. Lone, R. A. Leavitt and D. A. Harrison, Atomic Data Nucl. expected from the experiences at the cold-neutron based PGAA Data Tables, 1981, 26, 511. facilities of NIST, USA,17 and JAERI, Japan.18 15 J. O� sto� r, Z. Kis, B. Fazekas, G. L. Molna�r and A. Simonits, in Proceedings of the 9th International Symposium on Capture References Gamma-ray Spectroscopy, ed. G. L. Molna�r, T. Belgya and Zs. Re� vay, Springer Hungarica, Budapest, 1997, p. 788. 1 W. Schro� n, M. Krieg, D. Wienke, M. Wagner and K. Danzer, 16 M. Heurtebise and J. A. Lubkowitz, J. Radioanal. Chem., 1976, Spectrochim. Acta, Part B, 1992, 47, 189. 31, 503. 2 Gy. Zaray, G. Konya, J. A. C. Broekaert and F. Leis, Chem. Anal. 17 R. L. Paul, R. M. Lindstrom and A. Heald, J. Radioanal. Nucl. (Warsaw), 1990, 35, 311. Chem., 1997, 215, 63. 3 Z. Slova�k and B. Docekal, Anal. Chim. Acta, 1981, 129, 263. 18 C. Yonezawa, Anal. Sci., 1993, 9, 185. 4 T. Ishizuka, Y. Uwamino, A. Tsuge and T. Kamiyanagi, Anal. Chim. Acta, 1984, 161, 285. 5 E. Tata�r, I. Varga and Gy. Za� ray, Mikrochim. Acta, 1993, 111, 45. Paper 8/0885

ISSN:0267-9477    

DOI:10.1039/a808857h

出版商:RSC    

年代:1999

数据来源: RSC