摘要:

Determination of Rare Earth Elements in Precambrian Sediments at lsua by Inductively Coupled Plasma Mass Spectrometry Journal of Analytical Atomic Spectrometry TOMONORI UCHINO AND MITSURU EBIHARA Department of Chemistry Faculty of Science Tokyo Metropolitan University Hachioji Tokyo 192-03 Japan NAOKI FURUTA* Department of Environmental Chemistry National Institute for Environmental Studies 16-2 Onogawa Tsukuba Ibaraki 305 Japan Inductively coupled plasma mass spectrometry (ICP-MS ) was applied to the determination of rare earth elements (REEs) in Precambrian sediments which contain high concentrations of iron [ 1.5-62% measured by instrumental neutron activation analysis (INAA)]. Although a large suppression effect was observed owing to a huge amount of iron the suppression effect was corrected for by using both In and Bi as internal standards and reliable analytical results could be obtained.It was found that the interference of oxide ions was not so significant for the determination of REEs. The REE data obtained by ICP-MS are in relatively good agreement (within 10%) with those by INAA. The precision of the analytical results obtained by ICP-MS was 1-14% when using internal standards. Keywords Inductively coupled plasma mass spectrometry; rare earth elements; ion suppression; Precambrian sediment; geochemical analysis Studies of the 14 rare earth elements (REEs) in sedimentary rocks have provided much information for understanding their petrogenetic histories. Because of their unique chemical behav- iours REEs can be used as indicators or tracers for particular geochemical processes.Thus accurate measurement of REEs in geochemical materials such as sedimentary rocks gives us very important information about the geological environment of the earth when they were formed. There are several analytical methods available for the determination of the REEs in geological materials. Among them the methods commonly used are instrumental neutron activation analysis (INAA) inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Particularly since the introduction of ICP-MS trace element analysis of geological materials has shown remarkable progress because ICP-MS has the following abili- ties to determine trace elements including the REEs; low detection limits high sensitivity large dynamic range and simplified sample preparation.Several researchers have applied the ICP-MS method to the determination of trace metals in geological Lichte et al.' applied ICP-MS for the determination of REEs in certified reference rocks [BCR-1 (US Geological Survey) etc.] using Cd as an internal standard for the correction of sensitivity changes. They chose Cd as an internal standard because of its low normal abundance in igneous rock samples. The data * To whom correspondence should be addressed at Department of Applied Chemistry Faculty of Science and Engineering Chuo University 1-13-27 Kasuga Bunkyo-ku Tokyo 112 Japan. Journal obtained from ICP-MS were compared with those from ICP- AES and INAA. Hirata et al.' applied ICP-MS to the determi- nation of the REE contents of geological reference rocks [JA-1 JB-1 JB-2 and JB-3 (Geological Survey of Japan)].Tin was chosen as an internal standard element. Doherty3 obtained REE abundances for geological certified reference materials using ICP-MS with Ru and Re as internal standard elements. The Ru-Re internal standardization scheme was shown to be capable of compensating for errors in the determination of Y and REEs in rock samples. The samples used in this work show clear black and white layers of banded iron formation (BIF) which are mainly composed of magnetite and quartz respectively. These samples were collected from Isua situated some 150 km northeast of Godthaab West Greenland. The area is known to contain the most extensive and well-preserved 3800-3600 Ma old rocks which are the best samples available of the oldest-known crust.The BIF from the area has yielded a Pb:Pb whole-rock isochron age of 3760 f 70 Ma.4 The geology and mineralogy of the Isua iron-formation have been described in detail previously.5i6 Studies of REE in the Isua iron-formation have also been Shimizu et a1.' recently reported iso- topic ratios of Ce and Nd in BIF from Isua in addition to the abundances of REEs and Ba. In this work we have analysed Precambrian sedimentary rocks by using INAA and ICP-MS and compared the REE abundance data obtained by ICP-MS with those by INAA. Prior to the analysis of REEs in BIF the suppression effect due to abundant iron and the degree of interference due to oxide ion were examined.The major purpose of this paper is to present and discuss the usefulness of ICP-MS in its application to geological samples such as BIF. Table 1 Instrumental operating conditions Parameter Spectrometer Forward power Argon gas flow rate/l min-' Coolant Intermediate Injector Sample uptake rate/ml min-' Load coil-aperture spacing/mm Quadrapole mass analyser Data aquisition mode Total acquisition time/s Value VG PlasmaQuad I1 1.4 kW at 27 MHz 13.0 0.60 0.76 0.60 11 Model 12-12s developed by Range-scanning mode 120 VG Masslab (5.5-239.5 u) of Analytical Atomic Spectrometry January 1995 Vol. 10 25EXPERIMENTAL Instrumentation The ICP-MS instrument used in this study was a VG PlasmaQuad I1 (Fisons Instruments). The operating conditions of the ICP-MS spectrometer are listed in Table 1.Samples were introduced using a concentric pneumatic nebulizer with a standard Scott-type spray chamber. The ICP conditions were optimized by using the "'In ion signal. The sensitivity of the instrument was in the range 2 x 106-5 x lo6 counts per pg ml-'. Sample Preparation As the BIF sample has a layered structure composed mainly of silicate and iron oxide several layers were cut off with a diamond wire saw. A total of 15 samples were finally prepared which are referred to as Sample 1-Sample 15. All of the BIF samples were washed with 6.6 moll-' HF-HN03 in an ultra- sonic cleaning bath for about 10 min to clean the surface and then in C,H50H to remove organic matter. After drying all the samples were crushed in an agate mortar.About 100-500mg of the powdered BIF samples were digested using mineral acids in a clean room (less than 1000 particles per cubic foot). De-ionized water was obtained from a Milli-Q system (Millipore) and the water collected was further purified by sub-boiling distillation. The digestion pro- cedure is described in Fig. 1. The REEs in each digested sample I Sample (0.1-0.5 g) In a Teflon beaker covered with a watch glass 4 I HNO (5 ml) 150 "C 4 h HNO (3 ml) HCIO (5 ml) 160 "C 2 h 170°C2 h 1 1 8 0 T 5 h 200 "C 3 h HN03 (2-3 ml) HCIO (2-3 ml) should be transparent Watch glass was removed White fumes due to HCIO HF (4 ml) 200 "C 3 h HN03 (4 ml) 200 "C 3 h I Diluteto50ml I Fig. 1 Digestion procedures for BIF samples Table 2 Some nuclear data for seven REEs and Fe determined by INAA were measured by using a mixed standard solution of 14 REEs.In both the digested samples and the standard solutions known amounts of In and Bi were added for internal stan- dardization; both the In and Bi concentrations in the final solution were 100 ng ml-'. For INAA about 40-60mg of each powdered sample was precisely weighed and heat-sealed into a clean plastic bag (1 x 1 cm). The JB-1 sample (a basaltic reference rock) and the Allende reference sample (powdered meteorite) prepared by the Geological Survey of Japan and the Smithsonian Institution respectively were used as reference standards. Neutron activation was carried out in a TRIGA I1 reactor at the Institute for Atomic Energy Rikkyo University Japan. All the samples including reference materials were irradiated for 6 h.After activation gamma ray measurements were repeated three times in succession at different cooling intervals of 7-8 12-17 and 30-51 d with counting times of 3 x lo3 1 x lo4 and (4-8) x lo4 s respectively using a HP-Ge (ORTEC GEM 15180) and a planar-type pure Ge detector (ORTEC GLP 16220). As a result 16 elements including seven REEs (La Ce Sm Eu Tb Yb Lu) and iron were determined. Some nuclear data for REEs and Fe are shown in Table 2. RESULTS AND DISCUSSION Effect of Ion Suppression As Fe is a major element in the sample solution its effect on the quantitative analysis by ICP-MS was examined first. Because of the high concentration of Fe in the sedimentary rocks a matrix effect may arise. The concentration of Fe in the samples was determined by INAA to be in the range 1.5-62%.These samples were diluted by a factor of lo2 approximately (see Fig. 1). Then the final concentration of ion introduced into the ICP was 0.6% at most. Before ICP-MS was applied to the sedimentary rock samples a preliminary examination was performed. Mixed standard solutions of Pr Tb Ho Tm In and Bi (100 ngml-I) were prepared with different concentration of Fe from 0 to 5000 pg ml-' (0-0.5%). Fig. 2(a) shows the results of the measurement of ion suppres- sion effect due to Fe interference. The reason is not clear but a small increase in intensities was observed at low Fe concen- trations. On the whole the intensities of six elements examined fell with increasing concentration of Fe. After the internal standardization by In and Bi was applied to the mixture of Pr Tb Ho and Tm the sensitivity changes became very small as shown in Fig.2(b). It is clearly shown that the internal standardization solves the problem of ion suppression effect. Although high concentrations of iron causes a large ion suppression effect in the determination of R-EEs reliable analyt- ical results could be obtained by using In and Bi as internal standards. REE Monoxide In addition to the examination of matrix effects another possible problem was investigated. In determining trace Nuclear reaction 139La (n y ) 14'La 14'Ce (n y ) 14'Ce '52Sm (n y ) 153Sm '"Eu (n y) lszEu 159Tb (n y ) 16'Tb 174Yb (n y ) 175Yb 58Fe (n y ) 59Fe 176Lu (n y ) 177Lu Isotopic abundance of target (YO) 99.9 88.4 26.7 47.8 31.8 100 2.60 0.28 Cross-section for thermal neutronlbarn 9.0 0.58 208 4000 100 2300 23.0 1.2 Half-life of produced nuclide 40.3 h 32.5 d 47.1 h 13.5 years 72.3 d 4.19 d 6.68 d 44.5 d y-ray used for analysis/ keV 1596 145 103 1407 29 8 396 208 1099 26 Journal of Analytical Atomic Spectrometry January 1995 VoE. 10UI 3 c 8 1.5 In 2 L .- 1.0 P E 0.5 - 100 7 6o t 50 ' I I I I I 0 1000 2000 3000 4000 5000 IFel/pg mi-' Fig.2 Effect of (a) ion suppression due to Fe inference In; A Pr; 0 Tb; 0 Ho; X Tm; and M Bi and (b) correction of suppression by internal standardization using In and Bi 0 Pr; A Tb; 0 Ho; and 0 Tm elements by ICP-MS monoxide ions (MO+) sometimes inter- fere with the determination of metallic ions (M'). In the case of REEs oxide ions of light REEs (and Ba) potentially interfere with the measurement of metallic ions of heavy REEs. The formation yield of monoxide ions of REEs (and Ba) and their contributions to metallic ions are summarized in Table 3.Table 3 clearly shows that the interference due to oxide ions was not so significant for the determination of REEs. For example in the case of Pr the formation yield of 141Pr160 relative to I4'Pr is 0.659 x lo-' and the monoxide ion disturbs a metallic ion of 157Gd. In the case of Sample 2 (Gd 438 ng g-l see Table 4) 157Gd concentration is calculated to be 69 ng g-' based on an isotopic abundance of 157Gd (0.157). The amount of 141Pr160 was calculated to be 1.67 ng 8-l by multiplying the Pr concentration in Sample 2 (253 ng g-') (see Table 4) by the formation yield of MO+:M+ in Table 3 (0.00659).This value (1.67 ng g-') is within the experimental error of 157Gd (k6 ng g-?. Results of ICP-MS and INAA The results of ICP-MS for all the samples are summarized in Table 4. These data were obtained by using response cali- bration curves determined with a mixture of REEs including In and Bi as internal standards. The results of INAA for the BIF samples are also shown in Table 4 for comparison. As can be seen the ICP-MS data and those obtained by INAA were highly consistent with each other for the determination of Table 3 Formation-yield of monoxide ions of REEs and Ba and their contributions to metallic ions of REEs; values in parentheses are natural abundances of corresponding nuclides (in YO) Monoxide 1 3 7 ~ ~ 1 6 0 141pr 1 6 0 143~d160 1 47sm 1 6 0 1 4 9 ~ ~ 1 6 0 1 5 0 ~ ~ 1 6 0 l5O~d160 1 5 3 ~ ~ 1 6 0 156~d 1 6 0 159~b160 Formation yield 0.065 0.659 0.678 0.134 0.134 0.134 0.678 0.054 0.388 0.264 [MO' :M+(%)] Disturbed nuclide 153E~ (52.2) 157Gd (15.7) 159Tb (100) 163Dy (24.9) 166Er (33.6) 166Er (33.6) 169Tm (100) I7'Yb (21.9) 1 6 5 ~ ~ (100) 175Lu (97.4) Nuclide concentration in Sample 2/ng g-' 120_+11 69+6 66+4 123 + 5 124 & 6 132f4 132f4 52f6 73+9 56+6 Contribution of MO+ to nuclide concerned/ng g-' 0.15 1.67 0.87 0.05 0.04 0.02 0.40 0.07 0.35 0.14 10 I I Tarnple3 I I 10 Sample 6 100 Sample 15 (d) i I l l 1 I I 1 I I l l I I L 1 1 1 I I I I I I I l l I 1 I l l I ) La Pr Sm Gd Dy Er Yb La Pr Sm Gd Dy Er Yb Ce Nd Eu Tb Ho Tm Lu Ce Nd f u Tb Ho Tm Lu Fig.3 Comparison of chondrite-normalized REE patterns determined by 0 ICP-MS and A INAA for (a) (b) samples with low level Fe and (c) (d) samples with high level Fe Journal of Analytical Atomic Spectrometry January 1995 VoZ.10 27Table 4 Analytical data obtained for samples 1-15 by ICP-MS and INAA (all REEs are in units of vg g-'); the deviation was obtained by the standard deviation of three measurements and by counting statistics for ICP-MS and INAA respectively 1 2 3 4 5 INAA 1.44 f 0.04 2.23 f 0.25 -* - 0.184 f 0.005 0.193 f0.012 - ICP-MS 1.87 f0.04 2.7 1 f 0.03 0.253 f 0.013 1.05 fO.01 0.230f0.018 0.229 f 0.022 0.438 50.037 0.066 f 0.004 0.492 f 0.021 0.124 f 0.006 0.394f0.012 0.052 f 0.007 0.332 f 0.039 0.058 f 0.006 INAA 1.69f0.04 2.54 k 0.22 ICP-MS 1.61 f0.02 2.16 f 0.05 0.209 f 0.015 0.882+_0.017 0.177f0.022 0.179 f 0.021 0.340 & 0.025 0.055 f 0.007 0.355 0.053 0.096 f 0.006 0.295 f0.012 0.040 & 0.003 0.255 f 0.037 0.04 1 f 0.003 INAA 1.46 k 0.04 2.02 f 0.08 - - 0.163 f0.004 0.169 f 0.009 0.049 f 0.008 - - ICP-MS 0.437 f 0.0 15 0.636 f 0.004 0.083 f 0.006 0.380 f 0.013 0.097 k 0.02 1 0.088 f 0.010 0.196 f 0.018 0.034 f 0.002 0.240 f 0.020 0.064 & 0.001 0.209 f 0.007 0.029 f 0.008 0.208 fO.018 0.037 f 0.005 INAA 0.336 f 0.023 - ICP-MS 0.789 f0.020 1.03 f 0.02 0.1 16 f 0.01 3 0.446 f 0.037 0.126 f 0.042 0.10 1 f 0.009 0.188f0.021 0.030 f 0.002 0.236 f 0.005 0.056 f 0.007 0.202 f 0.001 0.030f 0.001 0.185 f0.038 0.038f0.003 INAA ICP-MS 1.66 f 0.01 2.10 f 0.06 0.226 f 0.010 0.969 f 0.022 0.220k0.019 0.193 k 0.008 0.335 f 0.020 0.063 f 0.001 0.430 k 0.015 0.109 f0.007 0.352 f 0.004 0.049 f 0.004 0.283 f 0.013 0.048 * 0.001 Element La Ce Pr Nd Sm Eu Gd Tb DY Ho Er Tm Yb Lu 0.965 f 0.035 1.30 f 0.14 b - 0.088 f 0.003 0.095 f 0.009 - - 0.235 f 0.006 0.238 f0.012 0.082 fO.010 - 0.100 * 0.004 0.102 f 0.007 - 0.051 f 0.006 - 0.190 f 0.036 0.044 f 0.009 - 0.267 f 0.042 0.090 f 0.013 - 0.21 5 f 0.039 0.041 0.007 0.398 f 0.039 0.072 f 0.01 1 0.219 f 0.028 0.039 f 0.006 Lu v) v) ul 47.1 f 0.2 18.8 k 0.1 39.7 f 0.03 38.8f0.3 Fe (YO) 54.6 f0.2 6 7 8 9 10 Lu 0 ICP-MS 0.773 f 0.044 0.873 f 0.029 0.095 f 0.012 0.362 f 0.052 0.047 f 0.024 0.062 f 0.023 0.156f0.039 0.017 f 0.003 0.102 f 0.027 0.037 f 0.002 0.120 & 0.01 5 0.01 1 f 0.008 0.097 f 0.022 0.016 f0.009 INAA 0.969 f 0.037 0.968 f 0.049 - - 0.065 & 0.002 0.054 f 0.006 0.021 f 0.003 - - ICP-MS 2.19 f 0.06 2.85 f 0.06 0.254 f 0.004 0.888 f 0.059 0.173f0.016 0.175 f 0.017 0.39 1 f 0.029 0.046 f 0.009 0.377 f 0.056 0.109 fO.O1O 0.343 f0.021 0.045 20.003 0.306 2 0.020 0.052 +_ 0.002 INAA 1.77 k0.04 2.39 f 0.14 - - 0.168 f0.005 0.179 f 0.007 ICP-MS INAA ICP-MS 1.23 f 0.07 1.60f0.02 0.200f0.017 0.796 f0.073 0.235 _+ 0.037 0.244 f 0.009 0.396f0.011 0.08 1 2 0.01 1 0.582 f 0.033 0.135 fO.004 0.467 f0.037 0.073 f 0.008 0.43 1 f 0.036 0.065 f 0.009 INAA 1.04 f 0.04 1.44 & 0.16 ICP-MS 1.88 f0.05 2.29 f 0.07 0.234 f 0.013 0.921 f 0.052 0.198+0.008 0.204 f 0.012 0.3 5 1 f 0.040 0.060 f 0.003 0.488 f 0.038 0.1 16 f 0.006 0.372 f 0.02 1 0.056 f 0.006 0.367 & 0.048 0.057 f 0.005 INAA 3.77 0.04 4.87 k0.04 0.473 f 0.02 1.80f0.03 0.293 f 0.015 0.290 k 0.009 0.567 & 0.010 0.083 0.003 0.640 f 0.038 0.175f0.013 0.564 k 0.033 0.078 f 0.006 0.462 f 0.03 1 0.087 f 0.006 3.3 1 f 0.07 4.46 f 0.22 1.77 +_ 0.04 2.69 f 0.23 La Ce Pr Nd Sm Eu Gd Tb DY Ho Er Tm Yb Lu - 0.194 f 0.005 0.207 f 0.017 - 0.276 f 0.007 0.292 f 0.012 0.101 f 0.009 - - 0.209 k 0.006 0.212f0.010 0.084 f 0.010 - - 0.393 f 0.042 0.070 f 0.010 - 0.538 f0.049 0.11 3 f 0.013 - 0.386 f0.044 0.069 fO.010 0.1 16 & 0.015 0.016 k0.003 0.319 f0.036 0.060 f 0.008 38.2 2 0.3 50.4 f 0.4 40.8 f0.3 57.6 & 0.5 Fe (%) 1.53 fO.01REEs. Considering that a set of data for 14 REEs is obtained by ICP-MS for each sample the ICP-MS method seems to be superior to INAA for the analysis of geological samples such as the BIF studied in this work.The REE data for the Isua sedimentary rock samples were normalized to C1 chondrite values" and some typical REE patterns are shown in Fig. 3 where both REE patterns obtained by ICP-MS and INAA are compared. A strongly positive Eu anomaly of roughly equal magnitude and an enrichment of light REEs are confirmed for all the samples. t 2 +I c! I A' +I +I +I +I +I +I +I +I +I +I +I +I +I +I Consideration of REE Pattern In natural materials all the REEs are trivalent except Ce and Eu. The Ce4+ ion may occur in place of Ce3+ under highly oxidizing conditions whereas Eu2+ rather than Eu3 + is stable under reducing conditions. These two exceptions provide inter- esting and potentially informative anomalies in REE abun- dance patterns for many rocks.The Eu3+:Eu2+ equilibria in an aqueous solution are illustrated on an E,-pH diagram'' and on an fo,-pH diagram.12 Based on the latter diagram SverjenskyI2 showed that the Eu stability increases dramati- cally as temperature increases and suggested the importance of these systematics in hydrothermal systems. Because any Eu in the aqueous phase should be divalent above about 250°C most minerals in equilibrium with an aqueous phase at tem- peratures higher than about 250°C would have either positive or negative Eu anomalies. One possible explanation for a positive Eu anomaly in BIF samples analysed in this work is hinted at by these consider- ations. Since the end of the 1970s hydrothermal spring vents have been discovered at many locations around the world.The temperature of these springs is observed to be more than 300 OC.I3 Considering that the submarine hydrothermal activity on the primitive Earth must have been stronger than that observed in the present day it seems reasonable to suppose that divalent Eu was preferentially provided from submarine hot springs and was then taken up in BIF on the bottom of ocean 3800 x lo6 years ago. 'c! +I 0 2 . . 0 0 0 0 - * $3 I +I +I I 2 2 +I W 4 E The authors thank S. Maruyama (Tokyo Institute of Technology University) and T. Masuda (Shizuoka University) for furnishing the BIF sample used in this study and K. Yanai and H. Kojima at National Institute of Polar Research for slicing the BIF sample. We are indebted to the Reactor Committee of the University of Tokyo for use of the reactor facilities of Rikkyo University.This work is partly supported by a Grant-in-Aid of the Ministry of Education Science and Culture Japan (No.02640453 to M.E.). ( A N N m H m - - r - 4 C ' l h l * 9 9 9 9 9 9 9 E 0 0 0 0 0 0 0 +I +I +I +I +I +I +I d m 4 m t 3 r - r - m g q o q m r r r - w o A + y ? ? y q 0 0 0 0 0 o o 4 m m m m d 8 8 8 S 8 8 8 8a3;ggs 0 0 0 0 0 0 0 +I +I +I +I +I +I +I 0 0 0 0 0 0 0 ooNmbNmO\ 2 +I 'c! m W REFERENCES 0 0 1 Lichte F. E. Meier A. L. and Crock J. G. Anal. Chem. 1987 59 1150. 2 Hirata T. Shimizu H. Akagi T. Sawatari H. and Masuda A. Anal. Sci. 1988 4 637. 3 Doherty W. Spectrochim. Acta. Part B 1989 44 263. 4 Moorbath S. O'Nions R. K. and Pankhurst R. J. Nature 1973 245 138. 5 Allaart J. H. in The Early History of the Earth ed. Windley B. F. Wiley London 1976 pp. 177-189. 6 Appel P. W. U. Econ. Geol. 1979 74 45. 7 Appel P. W. U. Precamb. Res. 1983 20 243. 8 Appel P. W. U. in Precambrian Iron-Formations eds. Appel P. W. U. and LaBerge G. Theophrastus Athens 1987 pp. 31-68. Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 299 Shimizu H. Umemoto N. Masuda A. and Appel P. W. U. Geochim. Cosmochim. Acta 1990 54 1147. 10 Anders E. and Ebihara M. Geochim. Cosmochim. Acta 1982 12 Sverjensky D. A Earth Planet. Sci. Lett. 1984 67 70. 13 Miller S. L. and Bada J. L. Nature (London) 1988 334 609. 46 2363. 11 Brookins D. G. in Geochemistry and Mineralogy of Rare Earth Elements Reviews in Mineralogy 21 eds. Lipin B. R. and McKay G. A. Min. SOC. Am. Washington 1989 pp. 201-225. Paper 4103532A Received June 13 I994 Accepted September 12 1994 30 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10

ISSN:0267-9477    

DOI:10.1039/JA9951000025

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Determination of Arsenic in Environmental and Biological Samples by Flow Injection Inductively Coupled Plasma Mass Spectrometry MENG-FEN HUANG SHIUH-JEN JIANG* AND CHORNG-JEV HWANG Department of Chemistry National Sun Yat-Sen University Kaohsiung Taiwan 804 Republic of China A simple and very inexpensive in situ nebulizer-hydride generator was used with inductively coupled plasma mass spectrometry (ICP-MS) for the determination of arsenic in environmental and biological samples. The application of hydride generation (HG)-ICP-MS alleviated the spectral interferences and sensitivity problems of arsenic determinations encountered when conventional pneumatic nebulization is used for sample introduction. The sample was introduced by flow injection to minimize deposition of solids on the sampling orifice.The arsenic in the sample was reduced to AS(III) with L-cysteine before being injected into the HG system. A detection limit of 0.003 ng ml-' was obtained for arsenic. The method has been successfully applied to the determination of arsenic in National Research Council of Canada reference materials CASS-2 (Nearshore Seawater Reference Material for Trace Metals) NASS-3 (Open Ocean Reference Material for Trace Metals) and SLRS-2 (Riverine Water Reference Material for Trace Metals) and in National Institute of Standards and Technology Standard Reference Material 2670 Toxic Metals in Freeze-Dried Urine. Precision was less than 5% and analysis results were within 6% of the certified values for all determinations. Keywords Inductively coupled plasma mass spectrometer; arsenic; flow injection; hydride generation; biological and environmental samples Inductively coupled plasma mass spectrometry (ICP-MS) is a relatively new technique for trace multielement and isotopic analysis'.' and still has some limitations.A highly saline sample can cause both spectral interferences and matrix effects. Spectral overlaps are seen when the polyatomic ions from the matrix such as ArNa' C10' or ArCl' overlap with analyte ions such as 63Cu+ 51V' or 75A~+ respectively. Changes in analyte counting rates are observed with high levels of salts particularly heavy matrix The determination of arsenic in environmental and biological systems is gaining increasing importance mainly because of the ubiquitous nature of this element and the toxic character- istics of some arsenic species.Interference by ArCl' occurs in the determination of arsenic in high chloride content samples by ICP-MS. Generally chloride interference is either removed by correction procedures7 or chemical separation procedures such as column separation or hydride generation (HG) Sample introduction by HG has been applied in several ICP-MS methods for the determination of ar~enic.~-'~ However one of the major drawbacks of these analyses is that the acid HCl used for HG could form the molecular ion ArCl' which interferes with arsenic determinati~n.~ In the * To whom correspondence should be addressed. Journal of Analytical Atomic Spectrometry present work a simple continuous-flow HG system without conventional gas-liquid phase separation has been employed as a sample introduction device for flow injection (F1)-ICP-MS ana1y~is.l~~'~ With this system only a minimal and inexpensive modification of existing standard equipment is required.Furthermore L-cysteine was employed as the pre-reductant with this reagent only a mild nitric acid condition is required for ~G.13315-19 These combinations reduced Arc1 + molecular interference significantly. Finally the sample was introduced by FI to minimize deposition of solids on the sampling orifice. The sampler would clog in a few minutes if the difficult urine and seawater matrices were introduced continually with the sample introduction system used in the present work. Results obtained for the determination of arsenic by FI-ICP-MS with in situ HG-nebulization are presented in this paper.EXPERIMENTAL ICP-MS Device and Conditions An Elan 5000 ICP-MS instrument (Perkin-Elmer SCIEX Thornhill Ontario Canada) was used. Samples after passing through the HG system were introduced with a crossflow pneumatic nebulizer with a spray chamber of Scott type. The ICP conditions were selected to maximize ion signals while a solution containing 10 ng m1-l arsenic in 0.1 moll-' HNO was continuously introduced into the hydride generator. The sensitivity of the instrument varied slightly from day-to-day. The operating conditions used throughout this work are summarized in Table 1. Table 1 Instrumentation and conditions Plasma conditions Rf power/W Plasma gas flow/] min-' Intermediate gas flow/l min Aerosol gas flow/l min-' Mass spectrometer settings Bessel box lens/V Bessel box plate lens/V Photon stop lens/V Einzel lenses 1 & 3/V Resolution Baseline time/ms Points per spectral peak Number of replicates Reading per replicate Sweeps per reading Dwell time/ms Replicate time/ms* Transfer frequency 1 1100 14 0.9 1.03 10.95 - 65.90 - 10.05 2.97 Normal 5000 1 1 103 20 20 41200 Replicate * Replicate time = (dwell time) x (sweeps per reading) x (readings per replicate).Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 31Data acquisition parameters used for this study are listed in Table 1. The element selected FI peaks were recorded in real time and stored on the hard disk with the 'graphic' software. Under the combination of dwell time sweeps per reading and readings per replicate a data point could usually be obtained in 1 s.Either peak height or peak area of the flow injection peak can be used for data handling. Flow Injection System A simple FI system was used throughout this study. It was assembled from a six port injection valve (Rheodyne Type 50) with a 200 pl sample loop. The carrier solution (0.05 mol 1-' HNO,) was delivered with a peristaltic pump. The schematic diagram of the FI system is shown in Fig. 1. Hydride Generation System and Conditions In this study a continuous-flow in situ HG-nebulizer sample introduction system was coupled with ICP-MS for arsenic determination with FI analysis. With this sample introduction system the entire injected sample was nebulized. The nebuliz- ation process in which the liquid is shattered into fine droplets in an Ar stream is a very effective way to purge AsH3 from the liquid probably more so than bubbling Ar through a static reservoir of bulk liquid as in a conventional gas-liquid separ- ator.Almost all the arsenic is liberated from the droplets as ASH and then goes to the plasma. The schematic diagram of the in situ HG-nebulizer and the experimental facility is presented in Fig. 1. The operating conditions for HG were optimized by FI analysis using 10 ng ml-' arsenic(Ir1) as the model solution. This solution was loaded into the injection loop and injected into the HG system. Operating parameters which could affect the efficiency of hydride formation concentration of HNO volume of mixing coil and the concentration of NaBH4 were studied in order to optimize the conditions. Interferences Studies Since a conventional pneumatic nebulizer instead of a gas- liquid separator was used in this study the chloride still reached the plasma and the ArCl' interference was still present.In order to demonstrate the effectiveness of this FI-HG system for alleviating the interference of ArCl' on Asf a solution of 10 ng ml-' arsenic was spiked with increasing concentrations of chloride (0 100 1000 10000 pg ml-') as NH,Cl. These solutions were injected into the HG-ICP-MS instrument and the arsenic signals were determined and compared with the results obtained when a conventional pneumatic nebulizer was used. Transition metal interference (Cu Ni and Co) in the determi- nation of arsenic by HG-ICP-MS was also carefully investi- gated.This was done by spiking 10ngml-' arsenic with various concentrations of Cu Ni and Co. These solutions were analysed and the arsenic signals were obtained and compared with the signals obtained for the interferent-free solution. Reagents and Sample Preparation Analytical-reagent grade chemicals were used without further purification. The applicability of the method to real samples was demonstrated by the analysis of National Research Council of Canada (NRCC) seawater reference materials CASS-2 ( Nearshore Seawater Reference Material for Trace Metals) NASS-3 (Open Ocean Reference Material for Trace Metals) and SLRS-2 ( Riverine Water Reference Material for Trace Metals). As AS(III) shows better sensitivity in the arsine gener- ation process it is preferred to reduce other arsenic species to AS (111) with pre-reducing agents before arsine generation.20*21 The sample pre-treatment procedure used is as follows an 80 ml portion of the water sample was transferred into a 100ml volumetric flask followed the addition of a suitable amount of 1 mol 1-' HNO and L-cysteine and dilution to the mark with distilled de-ionized water.The final solution contained 1% L-cysteine and 0.1 mol 1-' HNO and this solution was heated in a water bath at 100 "C for 30 min. In a separate experiment it was found that As(v) monomethylar- sonic acid and dimethylarsenic acid were quantitatively reduced to AS(III) by the pre-reduction procedure described above. Another reference material of high salinity [National Institute of Standards and Technology Standard Reference Material (SRM) 2670 Toxic Metals in Freeze-Dried Urine] was also analysed.The solid provided was digested by the following procedure the contents of one sample bottle were reconstituted with 20ml of water and poured into a Teflon PFA vessel followed by the addition of 5 ml of nitric acid. The vessel was sealed and then heated inside a microwave oven (CEM MDS-2000). After cooling the digest was diluted 50 times and treated with the same pre-reductant procedure described above. RESULTS AND DISCUSSION Selection of FI Operating Conditions Acid concentration is critical in the determination of arsenic by HG. Thus various concentrations of HNO solution were tested as the carrier solution for the FI system. The result is shown in Fig.2. Since the injected samples contained 0.1 moll-' HNO and 1% L-cysteine the concentration of HNO in the carrier did not affect the arsenic signal signifi- cantly. In fact the arsenic ion signal decreased when the HN03 concentration was greater than 0.05 moll-'. Thus 0.05 mol 1-' HNO was selected as the carrier in the following experiments. Selection of HG Conditions Fig. 3 shows the peak area of the FI peak as a function of sodium tetrahydraborate. The optimum concentration is 0.3% as shown in Fig. 3. Compared with conventional pneumatic 200 pI Injector 200 pi Mixing coil (1 mi min-') .... .... 0.3 % NaBH in 0.02 mol I-' NaOH (1 rnl min-') Per i sta I t ic pump Fig. 1 Schematic diagram of FI-HG-ICP-MS 32 Journal of Analytical Atomic Spectrometry January 1995 Vol.101.5 1.6 3 1.4 C 0 .- 1.2 > .- c - 0) 1.0 fE 0 0.1 0.2 [HNO,l/mol I - ' ' ' ' Fig. 2 Effect of carrier solution composition on arsenic signal. Concentration of NaBH was 0.3% in 0.02 moll-' NaOH. All the solution flow rates were set to 1.0 ml min-l. All the data were measured relative to the first point loo 1 0 0.2 0.4 0.6 0.8 1.0 [NaBH,] (%) Fig.3 Effect of NaBH concentration on arsenic signal. Carrier solution of FI system was 0.05 moll-' HNO,. Injected arsenic concen- tration was 10 ng ml-I in 0.1 moll-' HNO and 1% L-cysteine. All the solution flow rates were set to l.Omlmin-'. All the data were measured relative to the first point nebulization a 75 times improvement in the arsenic ion signal was obtained when 0.3% NaBH was used as reductant in the HG system.This concentration is much lower than the concen- tration used in conventional methods.12.22 One possible expla- nation for this is that the use of L-cysteine could improve arsine generation at a low concentration of NaBH,. Furthermore as the concentration increases the amount of hydrogen generated increases as well. The increased hydrogen production appears to have a detrimental effect on the ICP-MS system. Thus the optimum NaBH concentration is a compro- mise between the increase in the amount of arsenic introduced and the decrease in the ionization efficiency of the plasma. No obvious sampler blocking was observed over four hours of analysis when 0.3% NaBH was used as reductant. Since a suitable amount of L-cysteine had been added during sample pretreatment no extra L-cysteine was needed in the HG system.In separate experiments it was found that the volume of the mixing coil did affect the ion signal significantly a 200 pl mixing coil was used in the following experiments. In summary the optimum operating conditions of the FI-HG system are presented in Fig. 1. Selection of ICP Operation Conditions The performance of an ICP-MS instrument is strongly depen- dent on operating conditions.'3J3 The two key parameters are the aerosol gas flow rate and the plasma forward power. The dependence of the arsenic ion signal on the aerosol gas flow rate is depicted in Fig. 4. Although not illustrated here the dependence of the arsenic ion signal on the plasma forward power is similar to that reported previously.12*22 0.8 1 I 0.95 1.00 1.05 1.10 Aerosol g a s flow rate/l min-' Fig.4 Effect of aerosol gas flow rate on arsenic ion signal.Plasma forward power was 1.1 kW. All the data were measured relative to the first point Flow Injection Peaks and Detection Limit Typical FI peaks obtained for 200 pl injections of two solutions containing 1 ng ml-' arsenic and 10000 pg ml-1 chloride respectively are shown in Fig. 5. As shown in Fig. 5 10000pgml-' C1 will produce a signal equivalent to 0.3 ng ml-' arsenic at m/z 75 with this HG sample introduction method. Repeatability was determined using seven injections of a 1 ng ml-1 arsenic test solution. The relative standard deviation of the peak heights for these seven injections was less than 2% for arsenic. Calibration curves based on peak heights were linear for arsenic in the range tested (0.1-10 ng ml-I).Sensitivity for arsenic was 5700 countsml s-' ng-' and the background was about 400 counts s-' at m/z 75. The detection limit was estimated from these calibration curves based on the usual definition as the amount (or concentration) necessary to yield a net signal equal to three times the standard deviation of background noise. The absolute detection limit was 0.6 pg corresponding to a relative value 3 pg ml-I. The detection limit obtained in this work is comparable to or better than previous results with similar technique^.^-^' The reagent blank was found to contain 20pg of arsenic which could be a result of contaminants in the L-cysteine and HN03 used in the sample pre-treatment ( pre-reductant).Interference Studies The relative arsenic signal with and without HG of 10 ng ml-1 arsenic solution is shown in Fig. 6. It can be seen that the ArCl' interference is removed at up to 10000pgml-' of 10000 r 1 c I v1 v) 3 *-' 8 -. c 2 4- C 0 0 A I 4000 ::I 2000 0 20 40 60 80 100 120 E I u t io n ti m e/s Fig. 5 Typical flow-injection peaks of A 1 ng ml-l As and B 10000 pg ml-' C1. Reagent blank was subtracted in both elution peaks. Operating conditions of FI hydride generation are given in Fig. 1 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 334 l - I - .P I 3 PI 0 ' I I I 10 100 1000 10000 [Chloridel/pg ml ' Fig. 6 Effect of increasing chloride concentration on relative As signal in ICP-MS with @ hydride generation sample introduction and 0 conventional nebulization. Actual concentration of arsenic was 10 ng ml-'.Operating conditions of FI hydride generation are given in Fig. 1 120 I 1 100 p=+4 2o t I u 0' I I l l I 1 0.1 1 10 100 1000 10000 [Transition metal ionl/pg ml-' Fig.7 Effect of increasing concentration of Ni and Cu on arsine generation 0 10 ng ml-' As in 0.1 moll-' HN03 and presence of Cu; @ 10 ng ml-' As in 1% L-cysteine and 0.1 moll-' HNO and presence of Cu; 0 10 ng ml-' As in 0.1 moll-' and presence of Ni; B 10ngml-' As in 1% L-cysteine and 0.1 moll-1 HNO and presence of Ni. Operating conditions of FI hydride generation are given in Fig. 1 chloride when the sample was introduced with HG. The data with conventional nebulization show a larger positive bias thus demonstrating the value of HG for alleviating ArCl' interference. L-cysteine has proved to be very efficient in reducing inter- ferences in the determination of arsenic by HG and atomic spe~trometry.'~-'~ The efficiency of L-cysteine at reducing interferences from transition metal ions is illustrated in Fig.7. In Fig. 7 the interference effects are compared of Ni(r1) and Cu(n) in the determination of arsenic with and without the addition of L-cysteine as a releasing agent. Recoveries were calculated by comparison with the arsenic standard in the absence of the interfering ion. In the absence of L-cysteine 10 pg ml-' of Ni(r1) and 10 pg ml-' of CU(II) reduce the arsenic signal severely. However with the addition of 1% L-cysteine there was no significant interference from 100 pg ml-' of Ni(I1) or 1000 pg ml-' of CU(II).Although not illustrated here other transition metals showed similar results. These results are in agreement with those reported previously with similar atomic- spectroscopic technique^.'^-'^ Determination of Arsenic in Riverine Water and Urine In order to prove the suitability of the system in real sample analysis several reference samples were analysed. A 200 pl portion of the low C1 content SLRS-2 was analysed for arsenic using the FI-HG system. The concentration of arsenic present in the solution was quantified by the standard additions method and the result is presented in Table2. This result compares satisfactorily with the certified value. Concentrations of arsenic in high C1 content NIST SRM 2670 were also determined by FI-HG-ICP-MS.The results are presented in Table 2. This experiment indicated that arsenic in urine could be readily determined by HG-ICP-MS using the FI procedure. No obvious molecular ion overlap interference was observed. Determination of Arsenic in Seawater Samples A sample with a large concentration of chloride forms the molecular ion 40Ar35C1+ that interferes with the determination of 75A~+. The extent of interference is such that a direct determination of arsenic in a concentrated chloride sample is impossible. When the interfering signal (ArC1') is stable and not much larger than the analyte signal (As') the ArCl' contribution to the ion signal can be subtracted from the total ion signal according to the following equation i7'As=i(75)-3.08 x i(77)+0.993 x i(78) where i7'As is the ion signal of arsenic at m/z 75 and i(75) i( 77) and i( 78) are the total ion signals at m/z 75 77 and 78 respectively.As shown in Fig. 5 10000 pg ml-' C1 only pro- duces a signal equivalent to the signal produced by 0.3 ng ml-' arsenic at m/z when HG was used. The correction equation described above should be suitable for subtracting ArCl' contribution at m/z 75. In order to demonstrate the effectiveness of this method for alleviating the ArC1' interference. Two high chloride content samples (NRCC NASS-3 and CASS-2) were analysed for arsenic. The amount of arsenic present in each sample was determined by the standard additions method. The ArC1' interference was removed by the correction equation described above.The results are given in Table2. These results agree with the certified value. Since FI sample introduction was used and only a small volume of sample was injected the sensitivity of arsenic did not change too much even when seawater was analysed. The value of HG with ICP-MS for the quantification of arsenic in matrices containing high concentration of C1- has been demonstrated convincingly. This research was supported by a grant from the National Science Council of the Republic of China. Table 2 FI-HG-ICP-MS analysis of arsenic in selected reference materials. (n = 4) Sample SLRS-2 Riverine Water NIST 2670 Urine (elevated level) NIST 2670 Urine (normal level) CASS-2 Seawater NASS-3 Seawater Approximate C1- concentration/pg ml- < 10 4400 4400 30000 30000 1 Arsenic concentration/ng ml-' This work* 0.78 -t 0.04 480+ 10 59k2 1.08 f 0.03 1.68 + 0.02 Reference value 0.77 -t 0.09 480 & 100 (60) 1.01 & 0.07 1.65f0.19 * Mean f standard deviation.34 Journal of Analytical Atomic Spectrometry January 2995 VoL 10REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 Houk R. S. Fassel V. A. Flesch G. D. Svec H. J. Gray A. L. and Taylor C. E. Anal. Chem. 1980 52 2283. Houk R. S. Anal. Chem. 1986,58 97A. Tan S. H. and Horlick G. Appl. Spectrosc. 1986 40 445. Tan S. H. and Horlick G. J. Anal. At. Spectrorn. 1987 2 745. Olivares J. A. and Houk R. S. Anal. Chem. 1986 58 20. Douglas D. J. and Kerr L. A. J. Anal. At. Spectrom. 1988,3,749. Jiang S . -J. Lu P. -L. and Huang M. -F. J. Chin. Chem. SOC. 1994 41 139. Plantz M. R. Fritz J. S.Smith F. G. and Houk R. S Anal. Chem. 1989,61 149. Story W. C. Caruso J. A. Heitkemper D. and Perkins L. J. Chromatogr. Sci. 1992 30 427. Branch S. Corns W. T. Ebdon L. Hill S. and ONeill P. J. Anal. At. Spectrom. 1991 6 155. Stroh A. and Viillkopf U. J. Anal. At. Spectrom. 1993 8 35. Haraldsson C. Pollak M. and Ohman P. J. Anal. At. Spectrom. 1992 7 1183. Hwang C. -J. and Jiang S. -J. Anal. Chim. Acta. 1994 289 205. 14 15 16 17 18 19 20 21 22 23 Hwang J. D. Huxley H. P. Diomiguardi J. P. and Vaughn W. J. Appl. Spectrosc. 1990 44 491. Brindle I. D. Le X. -C. and Li X. -F. J. Anal. At. Spectrom. 1989 4 227. Chen H. Brindle I. D. and Le X. -C. Anal. Chem. 1992,64,667. Brindle I. D. Alarahi H. Karshman S. Le X. -C. Zheng S. and Chen H. Analyst 1992 117 407. Welz B. and Sucmanova M. Analyst 1993 118 1425. Chen H. -W. Brindle I. D. and Zheng S. -G. Analyst 1992 117 1603. Anderson R. Thompson M. and Culbard E. Analyst 1986 Haring B. J. Van Delft W. and Born C. M. Fresenius' Z. Anal. Chem. 1982 310 217. Welz B. He Y. and Sperling M. Talanta 1993 40 1917. Jiang S. -J. and Houk R. S. Spectrochim. Acta Part B 1988 43 405. 111 1143-1152 1153-1158. Paper 4/04443F Received July 20 1994 Accepted September 19 1994 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 35

ISSN:0267-9477    

DOI:10.1039/JA9951000031

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Electrothermal Graphite Furnace Atomic Absorption Signal for Gold in Organic Matrices Journal of Analytical Atomic Spectrometry SHOJI IMAI KYOICHI OKUHARA TOSHIYUKI TANAKA AND YA S U H I S A H AYA S H I Department of Chemistry Joetsu University of Education Joetsu Niigata 943 Japan KENGO SAITO Nissei Sangyo SI Centre Sakamachi Shinjuku Tokyo 160 Japan The electrothermal atomic absorption signal for gold deposited after pyrolysis of organic matrices was investigated. The signal shape was altered by pyrolysis of a volatile organic matrix (methanol propan-1-01 and pentane-l,9diol) and also a non- volatile matrix (ascorbic acid glucose and sucrose) with a low-temperature shift of signal and the formation of a shoulder (peak) on the tail. Pyrolysis of the organic matrix produced two types of carbon residue (active carbon and a thermally stable carbon residue).The early shift occurred as a result of the formation of smaller microdroplets of Au by adsorption of the analyte on the active carbon. The latter shift resulted from the formation of larger sized microdroplets by admission diffusion or transport of the analyte into the inside of the thermally stable carbon residue. These mechanisms were supported by kinetic investigations. Keywords Electrothermal atomic absorption spectrometry; condensed phase distribution; organic matrix eflect; active carbon formation; gold It has been reported by McNally and Holcombe,' Lynch et aL2 and Imai and Hayashi3 using kinetic analysis in electrothermal (graphite furnace) atomic absorption spectrometry that the desorption of Au occurs from microdroplets as solution depos- ition is used.The existence of adsorbed atoms microdroplets and two-dimensional islands on graphite for several atoms including Au was supported by Ganz et al.'s work using scanning tunnelling micro~copy.~ Arthur and Cho5 reported the adsorption and desorption kinetics of Cu and Au on a single graphite crystal and illustrated that both adsorbed atoms can move on the single-crystal graphite and form droplets or caps. The Arrhenius activation energy (E,) for Au desorption was increased from 217 to 307 kJ mol-' which was responsible for the increase in the number density of Au atoms from 1.1 x lOI3 to 9.55 x lOI4 C M - ~ . ~ Recently Fonseca et aL6 also reported a tendency for the E value to increase with increasing analyte mass e.g.113 kJ mol-' for 0.02-0.05 ng and 235 kJ mol-' for 0.17 ng for Ag and 120 kJ mol-' for 0.045 ng and 330 kJ mol-' for 0.59 ng for Au. Vaporization of Ag and Au appears to occur from varying sizes of microdroplets or adsorbed atoms depending on the analytical conditions. The decreasing influence of the graphite as the droplet size becomes larger might explain the increase in E observed with increasing concentration. The highest E values obtained for both metals approach the respective AHv and indicate desorption from the surface of large microdroplets. The lowest E might represent the interaction between individual adsorbed atoms and the graphite surface. It was concluded from the increase in E when a mechanically roughened graphite furnace was used that the tendency of the microdroplets to disperse on graphite seems to be lowered by mechanical roughening of the furnace surface which probably increases the number of active sites on the graphite.Pyrolysis of organic compounds in an inactive gas forms some reductant gases (H2 CH4 CO COz etc.) and carbons having active sites (active carbon and pyrolytic graphite). When ascorbic acid is pyrolysed in a graphite furnace with an argon atmosphere at temperatures above 700 K a cracked thermally stable carbon surface forms which can be observed by scanning electron microscopy (SEM) after release of active carb0n.3.~ Gold adsorbed in the cracked thermally stable carbon residue leads to a shift of the signal pulse to a later time.3 This shifted signal begins to decrease and the standard signal to be restored at temperatures in the range 1270-1460 The Arrhenius activation energy and the pro- cess controlling the reaction rate for the desorption of Au is also altered from 250f 10 kJ mol-' with a D4 mechanism (based on three-dimensional diffusion with spherical symmetry) for conventional solution deposition to 413 & 15 kJ mol-' with a D4 mechanism for 5% ascorbic acid ~olution.~ Although in electrothermal atomic absorption spectrometry a temperature above the boiling-point of the solvent has been used as the pre-treatment temperature (drying or pyrolysis) for organic matrix solution samples there are few reports of interference from the organic s o l ~ e n t .~ . ~ Iwamoto et aL8 concluded that active carbon provided by the organic solvent altered the tin atomization mechanism.Tserovsky et al.' reported the influ- ence of chlorine-containing organic solvents on cadmium cobalt and lead. One possibility is thermal decomposition (including carbonization) of solvent molecules adsorbed on the graphite furnace wall or on its surface. In this work Au standard solution was deposited after an organic matrix (methanol propan-1-01 pentane-1,5-diol ascor- bic acid glucose sucrose etc.) had been pyrolysed in the pyrolytic graphite-coated electrothermal graphite (PG) furnace and its atomic absorption signal was measured. The pyrolysis provided a number of carbon residues such as active carbon and thermally stable carbon residue. This work was undertaken to study the influence of the pyrolysed residue of the organic matrix on the condensed phase distribution and desorption of Au.EXPERIMENTAL Apparatus A Hitachi Model 2-8000 flame and graphite furnace atomic absorption spectrometer equipped with a Zeeman-effect back- ground corrector and an optical temperature-control system (Hitachi Model 180-0341) was used. A 20 pl volume of sample solution was injected by an automatic sampler. The peak height and area (integrated absorbance) were automatically Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 37printed out and displayed by using a Hitachi data processor. The analytical wavelength and slit width were 242.8 and 1.3 nm respectively. An Oki personal computer If-800 Model 50 was used to record the absorbance sighal profiles (20ms interval).Output data from the optical temperature controller were acquired at 4 ms intervals by the personal computer and subsequently stored on a diskette. The output data were calibrated by using the inner wall temperature monitored through the sample injection hole by a Chino Model IR-AH1S radiation thermometer. The temperature data were calibrated by using an Pt-Rh thermocouple. For this thermometer the wavelength is 960nm and the uncertainty is 0.5% up to 1500 K 1.0% up to 2300 K and 2.0% up to 3300 K. Reagents An aliquot of a commercially available stock standard solution (1000 ppm HAuC1 in 1 mol dm-3 HC1; Wako) was diluted with water to a suitable concentration before use as a working standard solution. Organic substances (Wako) were of analyt- ical-reagent grade.Distilled de-ionized water was purified with a Milli-QII system (Millipore). High-purity Ar (99.995%) prepared by Takachiho Chemical Industry was used. Procedure A 20 p1 volume of organic matrix solution sample was deposited in the graphite furnace by the automatic sampler. It was pyrolysed according to a heating programme consisting of drying at 120 "C (30 s) and pyrolysing at 700 "C (20 s ramp time 5 s hold time). This process is termed 'matrix pyrolysis'. During the matrix pyrolysis the inner Ar gas flow was 200 ml min-'. After cooling 20 pl of the Au standard solution were injected by the sampler. The standard atomization con- ditions given in Table 1 were applied. A gold standard solution was measured among repetitive measurements with the organic matrix pyrolysis.Kinetic Method3 The absorbance at maximum absorption (Amax; peak height) is proportional to the atomic vapour concentration at maximum absorption [M](g),,, Amax = a C M 1 (g)max (1) where a is a proportionality constant. Both [M](g), and A, are proportional to the initial analyte concentration in the condensed phase. The absorbance measured at time t A is directly proportional to the atomic vapor concentration at time t [M](S)~ 4 = a CMl(g)t (2) Both [M](g) and A are proportional to the atomized analyte concentration at time t. Amax and A are also proportional to the initial number of analyte atoms (No) and the number of analyte atoms atomized until time t (NJ. Hence the fractional conversion (a) can be represented by a = Nz /NO = C M 1 ( g)t /C M 1 ( g)max = Az /Amax (3) Table 1 Standard atomization conditions for Au Stage Drying Pyrolysis Atomization Cleaning TemperaturerC 120 700 2500 2900 Ramp time/s 30 20 0 0 Hold time/s 0 5 3 3 ml min-l 200 200 0 200 Inner gas flow/ Coats and Redfern's method," which involves a process con- trolling the reaction rate for the solid-state reaction under linear heating conditions was used for kinetic analysis of Au desorption In [ g(a)T -2] = - E,R-' T - ' +In [ARP(dT/dt)- 'E,-'] where g(a) is a function that depends on the process controlling the reaction rate a is the fractional conversion dT/dt is the heating rate of the furnace wall A is a frequency factor P= 1 - 2X + 6X2 - 24X3 + 120X4 + a * - X = RT/E T is absolute temperature and R is the universal gas constant.The process- controlling functions are summarized in Table 2. If the best fitted function [g(a)] is properly selected in order to investigate a particular reaction a plot of the right-hand side of eqn. (4) uersus T-' should be a straight line from the slope of which E can be calculated. (4) RESULTS AND DISCUSSION Table 3 presents A and integrated absorbance (AJ) values for 0.4ng of Au at various concentrations of solutions of methanol (MeOH) propan-1-01 (PrOH) and pentane-1,Sdiol [Pe(OH)2] pyrolysed using the standard matrix pyrolysis program. Although these compounds have boiling-points below the matrix pyrolysis temperat~re,'~ there is an influence of the solvent on the absorbance responses which decreases with increasing concentration.The effects of the pure organic solvents ethanol butan-1-01 ethylene glycol propane-1,3-diol butane-lP-diol ethyl acetate hexane cyclohexane and isobutyl methyl ketone were also examined and there were significant decreases in sensitivity. For tin in organic matrices (heptane cyclohexane hexane etc.) formation of active carbon available for reduction of tin has been reported by Iwamoto et al.* in a pyrolysis study with kinetic investigations. Other matrices with low boiling-points such as 1,2-dichloroethane chloroform and carbon tetrachloride affect the absorption response of Cd Co and Pb.' Active carbon vaporizes as different species such as CO COz carbon atoms and carbon particulates. One possibil- ity for the loss mechanism of Au is that when the carbon particulates are released from the furnace in the temperature range 970-1070 K Au occluded in the carbon particulates leaves the furnace without re-adsorption on secondary collisions with the furnace wall.Typical transient signals for the atomic absorption of Au at various concentrations of MeOH PrOH or Pe(OH) are shown in Fig. 1 in which the time axis is labelled in such a way that zero time has elapsed before the atomization stage of the heating cycle. Measurements on the Au standard solution were made among repetitive measurements using the same matrix solution. No alteration in the signal shape for the Au standard was observed. It was found that when PrOH pyrolysis was carried out the peak shifted to an earlier time and a shoulder on the tail could be observed at 1% PrOH.At 100% PrOH the shoulder on the tail grew to a peak. The alteration of signal shape was less extensive for MeOH. For Pe(OH) Table 2 Function g(a) for a controlled reaction Notation* g(a) t Notation* &)t R a Fl -ln(l-a) R2 l-(I-a)1/2 A3/2 [ - In( 1 - o()]'/~ R3 1 -(1-41/3 A2 [ - l n ( l - ~ ) ] ~ / ~ D1 a2 A3 [-ln(l-a)]1/3 D2 A4 [-In( 1 - a)I1I4 ( 1 - a) In( 1 - a) + a D3 I 1 - ( 1 - 41/312 D4 ( 1 - 2 ~ / 3 ) - ( 1 - a ) ~ / ~ * The notation of Sharp et d." was used. f The function g(a) is summarized by Reich and Stiva1a.l' 38 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10Table 3 Relative values of maximum absorbance (Amm) and integrated absorbance (As) for 0.4 ng of Au at various concentrations of organic matrix used for the matrix pyrolysis stage Methanol Concentration ("/I Amax AS 0 1 .00 f 0.01 1.00 f 0.02 0.001 0.88 f 0.02 1.03 fO.01 0.01 0.87 f 0.02 0.95 f 0.01 0.1 0.84 f 0.00 0.96 f 0.01 1 0.86 & 0.00 0.95 f 0.00 Propan-1-01 Pentane-175-diol Amax AS Amax AS 1.00~0.01 1 .00 k 0.0 1 1 .OO f 0.03 1.00 f O .O 1 0.80 f 0.03 0.91 & 0.00 0.93 k 0.00 1.00 f 0.02 0.86 f 0.01 0.95 f 0.01 0.92 f 0.00 0.97 & 0.00 0.74 f 0.02 0.90 f 0.01 0.91 fO.O1 0.98 f 0.03 0.74 f 0.01 0.88 f 0.00 0.90 f 0.00 0.96 f 0.01 0.40 . 3273 0.50 Q S m +? a v) 51 ( b ) 1 n 0.50 r 1 I (c' 1 2 .n 0 0.50 1 .oo 1.50 Tim e/s Fig. 1 Atomic absorption signal for 0.4 ng of Au at various concen- tration of organic matrix used for the matrix pyrolysis stage. (a) Methanol 1 0; 2 0.1; 3 1; 4 100%. (b) Propan-1-01 1 0; 2 0.1; 3 1; 4 100%.(c) Pentane-1,5-diol 1 0; 2 1; 3 5%. Full scale of temperature 273-3273 K the leading signal shifted to an earlier time at 1% Pe(OH),. With 5% Pe(OH) a considerable bulge can be observed on the tail. The half-widths of the Au signal with 0 1 and 5% Pe(OH) pyrolysis are 0.25 0.28 and 0.30 s respectively. The increase in the half-width supports the formation of the small third peak in the tail. An earlier time shift of the signal has been reported by McNally and Holcombe' in the aerosol deposition of Au on the furnace wall compared with solution deposition. Imai and Hayashi3 also reported that the rising edge of the Au signal increased after 20 shots when a new PG furnace was fitted which is caused by considerable degradation of the PG surface.Fonseca et aL6 described that when the drying temperature was increased from 80 to 300 "C an earlier shift of the signal occurred as a result of the formation of smaller size microdroplets. Imai and Hayashi3 have also reported the effect of coating the furnace wall with carbon on the atomic absorption signal for Au after one pyrolysis of 5% m/v ascorbic acid solution over the range 670-2640 K a gold standard solution was injected and its atomic absorption signal was measured. A peak on the tail appeared. They concluded that Au may interact more strongly with the thermally stable carbon residue than the PG furnace wall. A smooth surface of the carbon residue with many cracks was observed by SEM of the inner furnace wall after 100 atomization cycles with 1% m/v ascorbic a ~ i d .~ . ~ The appearance of a peak on the tail with pyrolysis of the solvent (Fig. 1) suggests the formation of a cracked thermally stable carbon residue on the PG surface inherent on the furnace wall by pyrolysis of the organic solvent. Other organic solvents (ethanol butanol ethyl acetate hexane cyclohexane and isobutyl methyl ketone) gave similar alterations in the signal shape The graphite furnace used has a sample compartment (of length 6mm and i.d. 6mm). Sample solution is injected through an injection hole (diameter 2 mm) at the centre of the sample compartment. When 20 pl of sample were deposited an aqueous solution of the organic matrix of methanol propa- no1 or pentanediol was spread in the sample compartment not outside it. Pure methanol or propanol was spread to a length of 18mm until 6mm from the edge of the sample compartment as the solvent deposited.During drying the solvent crept back from the cooler ends of the furnace to the sample compartment because the solvent evaporated in the latter. When 20 pl of Au standard solution were deposited after pyrolysis of the organic matrix it did not spread outside the sample compartment in the same way as the Au standard only. The physical spreading cannot result in the formation of a third peak. Of course the early shift of the signal cannot be explained by physical spreading. Another possibility for the formation of the third peak is delayed atomization of Au from the thermally stable carbon residue due to a simple delayed heating. It has been reported that in order to investigate the effect of coating the tube wall with pyrolysed ascorbic acid on the atomic absorption signal for Pb after pyrolysis of 1% ascorbic acid solution by 20 and 100 atomization cycles with an NPG furnace a Pb standard solution was injected and its atomic absorption signal was meas~red.~ The Tapp value for 20 cycles was in agreement with that for 100 cycles.These Tapp values were in agreement with that for Pb in the PG furnace. Further evidence is that there is no difference between Tapp values with and without 1% m/v ascorbic acid in the PG furnace. These results indicate that there is no delayed heating of the pyrolysed ascorbic acid. The mass of carbon residue for pyrolysed organic solvents used should be signifi- cantly less than that for the pyrolysed ascorbic acid.Therefore significantly delayed heating of the carbon residue does not occur. Fig. 2 shows the absorption response at various matrix Journal of Analytical Atomic Spectrometry January 1995 Vul. 10 391.1 I o) 1.0 z z s -g 0.9 .- F - ii $ 0.8 n 7 I A 1 I I 500 1000 1500 2000 2500 u.1 - Matrix pyrolysis ternperaturdK Fig. 2 Effect of matrix pyrolysis temperature on maximum absorption response for 0.4 ng of Au 0 1% propan-1-ol; 0 10% propan-1-01; 0 1% methanol; and A 1% pentane-1,5-diol. An uncertainty of 0.02 can be considered in these absorption values pyrolysis temperatures without any change in the pyrolysis temperature for Au. It is observed with 10% PrOH that the value of A, increases with increase in the matrix pyrolysis temperature reaches a constant value at 900 K remaining constant upto 1200 K and there is a slight dip at 1500 K.For 1 Yo PrOH the dip can be clearly observed. At matrix pyrolysis temperatures above 1200 K the absorbance decreases and reaches a minimum at 1550K. It is restored in the range 1500-1950 K and above 2000 K it remains constant. Pe(OH) gave a similar result. With MeOH the first restoring step cannot be observed. The following scenario for the behaviour of the pyrolysis residue can be suggested. The number of active carbon sites decreases with increasing matrix pyrolysis temperature. Most of the active carbon is released in the temperature range 950-1070 K3 and the thermally stable carbon residue cannot be released and remains on the furnace surface. The carbon residue decomposes by oxidation at a temperature above approximately 1200-1300K.Active carbon is formed as an intermediate of decomposition of the thermally stable carbon residue. Most of the carbon residue is released at approximately 1900 K. Above 2000 K the conventional surface of the furnace is restored. Fig. 3 shows typical transient signals for Au at various matrix pyrolysis temperatures. At matrix pyrolysis tempera- tures of 720 560 and 700 K for MeOH PrOH and Pe(OH) which are in the temperature range representing a decrease in absorbance a shift of the signal to earlier times is observed. At 1090 1020 and 1060 K which are in the temperature range representing constant absorbance the signal is in agreement with that without the matrix pyrolysis.However at 1380 1580 and 1550 K which are in the temperature range representing the dip there is a shift of the signal to earlier times or a shoulder on the rising edge. The absorption response on the rising edge disappears at temperatures above 2000K. The alteration of the signal shape supports the scenario for the thermal behaviour of the organic matrix pyrolysis product involving active carbon formation below 900 K release of active carbon in the range 950-1070 K and release of the heat- stable carbon residue via active carbon as an intermediate in the range 1200-1900 K. For the desorption of Au without the matrix pyrolysis the D mechanism based on three-dimensional diffusion with spherical symmetry (Ginstling-Brounshtein equation) was chosen in order to give the best possible fit; the E value obtained was 250 f 10 kJ mol- .3 For the earlier shifted signal 0.50 0.50 0 0.30 0.50 0.70 Time/s 1 .oo Fig.3 Effect of the matrix pyrolysis temperature on atomic absorp- tion signal for 0.4 ng of Au. (a) 1% Methanol 1 without matrix pyrolysis; 2 720; 3 1090; 4 1380; 5 2230K. (b) 1% Propan-1-01 1 without matrix pyrolysis; 2 560 3 1020; 4 1580; 5 2260 K. (c) 1% Pentane-1,j-diol 1 without matrix pyrolysis; 2 700; 3 1060; 4 1550; 5 2090 K. Full scale of temperature 273-3273 K obtained in 1% PrOH the F1 mechanism based on a first- order reaction was chosen and the E value obtained was 160+ 10 kJ mol-I. Fonseca et aL6 reported that the E value for Au decreased with decrease in the microdroplet size. They also reported an increase in the E value (approximately 46 kJ rno1-l with a pyrolysis temperature of 300 "C) using the mechanically roughened furnace whose surface is very rich in mechanically created active sites and concluded that the number of active sites on the graphite led to a decrease in the tendency of Au to diffuse on the graphite leading to the formation of smaller sized microdroplets.Although active carbon is very rich in active sites a decrease in the E was actually obtained. When the sample is deposited on the furnace wall analyte [AuClJ- might be adsorbed on the active carbon because it is an excellent adsorbent. With increase in the furnace temperature smaller sized microdroplets are formed and metal particles might not easily diffuse across the surface because of the metal-graphite interactions produced by the presence of the active sites and as a result remain bound to the smaller sized microdroplets.These smaller microdroplets lead to a decreased E value and an earlier time shift. 40 Journal of Analytical Atomic Spectrometry January 1995 Wol. 100 1 .oo Time/s 2.00 Fig. 4 Atomic absorption signal for 0.4 ng of Au with various ascorbic acid concentration in PG furnace 1 0; 2 0.02; 3 0.1; 4 1% m/m. Full scale of temperature 273-3273 K Fig. 4 presents typical transient signals for Au with ascorbic acid pyrolysis with and without the matrix. A similar effect of ascorbic acid concentration on the signal shape to that for organic solvent matrices was obtained an earlier shift of the signal was obtained at 0.02% ascorbic acid and with increasing ascorbic acid concentration a new peak appeared on the tailing edge.At 1% ascorbic acid a new peak was obtained as a clear single signal. Formation of two types of carbon residue (active carbon and cracked thermally stable carbon residue) by pyrol- ysis of ascorbic acid has been reported by background absorp- tion during atomization and scanning electron microscopic (SEM) observation of the furnace wall after 100 atomization cycles with 1% ascorbic For the early peak with the pyrolysis of 0.02% ascorbic acid the D1 mechanism based on a one-dimensional diffusion parabolic law was chosen in order to give the best possible fit; the E value obtained was 200f20 kJmol-'. There is a 50 kJ mol-' decrease in E which indicates the formation of smaller microdroplets by adsorption of the analyte on the active carbon.The SEM photograph (Fig. 7 in ref. 3) of the heat-stable carbon residue produced by pyrolysis of ascorbic acid presents a smooth surface with many cracks whose width is approximately 200nm. Pores of size above 50nm play an important role in the admission diffusion or transport into the inside of adsorb- ent. A clear single peak signal shifted to later time was also observed for 1% glucose and sucrose. For the desorption of Au with pyrolysis of 1% ascorbic acid 1% glucose and 1% sucrose the D D3 (Jander equation) and D3 mechanism based on three-dimensional diffusion with spherical symmetry was chosen in order to give the best possible fit; the E values obtained were 440k20 430f 15 and 362+ 15 kJ mol-l respectively.These E values are close to or larger than the heat of formation of gaseous Au (366 kJ mol-l). The appear- ance temperature and temperature of maximum absorbance for the adsorbed Au are 1720k 30 and 1970k 30 K respect- ively. These data represent desorption from the surface of larger sized microdroplets interacting with the graphite surface. The following process can be proposed for the later shifted peak formation when the sample is deposited on the furnace wall the solution might be transferred inside the cracked thermally stable carbon residue during drying. With increase in furnace temperature large-sized microdroplets are formed and metal particles might not easily diffuse across the surface because of adsorption in the macropores. In the atomization stage vaporization of Au occurs from the large microdroplets.This mechanism can be also proposed as an atomization mechanism for the third peak observed for 100% MeOH and PrOH. CONCLUSION Organic solvents and non-volatile organic matrices during the atomization cycle provide active carbon and a PG layer on the surface of the furnace and Au partly adsorbs in both carbon products. Smaller sized microdroplets of Au are formed as [AuCl,]- adsorbs on the active carbon producing a decrease in the tendency of Au microdroplets to grow during the drying and pyrolysis stages. As the Au sample solution disperses in the thermally stable carbon residue larger sized microdroplets are formed because the macropores lead to a decrease in the tendency of Au microdroplets to diffuse on the graphite surface during the pyrolysis or atomization stage. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 McNally J. and Holcombe J. A. Anal. Chem. 1987 59 1105. Lynch S. Sturgeon R. E. Loung V. T. and Littlejohn D. J. Anal. At. Spectrom. 1990 5 311. Imai S. and Hayashi Y. Bull. Chem. SOC. Jpn. 1992 65 871. Ganz E. Sattler K. and Clarke J. Surf. Sci. 1989 33 219. Arthur J. R. and Cho A. Y. Surf. Sci. 1973 36 641. Fonseca R. W. McNally J. and Holcombe J. A. Spectrochim. Acta Part B 1993 48 79. Imai S. and Hayashi Y. Anal. Chem. 1991 63 772. Iwamoto E. Miyazaki N. Okubo S. and Kumamaru T. J. Anal. At. Spectrom. 1989 4 433. Tserovsky E. Arpadjan S. and Karajova I. J. Anal. At. Spectrom. 1993 8 85. Coats A. W. and Redfern J. P. Nature (London) 1964 201 68. Sharp J. H. Brindley G. W. and Char N. N. J. Am. Ceram. SOC. 1966 47 379. Reich L. and Stivala S. S. Thermochim. Acta 1979 34 287. Handbook of Chemistry and Physics ed. West R. C. CRC Press Boca Raton FL 67th edn. 1980. Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 41

ISSN:0267-9477    

DOI:10.1039/JA9951000037

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Physical Behaviour of Nickel and Copper Modifiers Used in the Determination of Selenium by Electrothermal Atomic Absorption Spectrometry TARIQ M. MAHMOOD HUANCHENG QIAO AND KENNETH W. JACKSON* Wadsworth Center for Laboratories and Research New York State Department of Health and School of Public Health State University of New York Journal of Analytical Atomic Spectrometry P.O. Box 509 Albany N Y 12201 -0509 USA Scanning electron microscopy and visual examination were used to study the physical changes occurring with temperature when Ni and Cu were used as modifiers for Se. During the pyrolysis stage of the electrothermal atomizer heating cycle the Ni or Cu matrix was observed to shrink as the metal salt decomposed to the oxide and then the metal. This may have resulted in physical entrapment of Se which coprecipitated with the excess of modifier salt during the drying stage and this could contribute significantly to the stabilizing effect of Ni and Cu.Pyrolysis curves for Se in the presence of Ni or Cu show a characteristic dip or decrease in thermal stability at a pre-treatment temperature of about 800 "C. However replacement of the Ar purge gas by H during the atomizer drying stage eliminated this dip and this may be due to chemical or physical effects. During the atomization heating stage the modifiers formed molten droplets and analyte atomization was governed by its kinetically controlled release from these droplets. This is considered to be the major cause of analyte stabilization during atomization. Keywords Electrothermal atomic absorption spectrometry; selenium atomization; stabilization by modifiers; nickel and copper modifiers Metal modifiers are generally used for the thermal stabilization of Se during its determination by electrothermal atomic absorp- tion spectrometry (ETAAS); otherwise Se is lost by volatiliz- ation during thermal pre-treatment at temperatures as low as 200 "C.In addition to permitting higher pre-treatment tempera- tures modifiers also delay appearance of the analyte during the atomization stage i.e. until the graphite furnace has reached a higher and more stable temperature. Nickel is the most commonly used modifier for Se typically stabilizing the analyte up to a pyrolysis temperature of about 1200 0C.1,2 However several other metals have been used successfully as modifiers including Cu27 and Pd.4+5 Many reports on the modification of Se by Ni and other metals have assumed that stabilization occurs through the formation of less volatile chemical species.Ediger' suggested that a selenide is formed with Ni and this was supported by Styris,6 who used a combination of atomic absorption and mass spectrometry to study the desorption of NiSe from a graphite surface at atmospheric pressure. This compound dissociated at a tempera- ture of about 800°C unless excess of Ni was present when the dissociation temperature increased to about 1200 "C. A sug- gested explanation for the low temperature decomposition was the formation of a ternary Se-C-Ni alloy which decomposes first to SeC and then to Se. However excess of Ni blocks the active carbon sites preventing formation of the alloy and * To whom correspondence should be addressed.hence retaining NiSe until it dissociates thermally at the higher temperature. Droessler and Holcombe7 suggested that stabiliz- ation occurs through interaction of Se with excess Ni on the graphite surface but they did not believe that this involved the formation of a selenide. Modification of Se and several other elements by a mixture of Pd and Mg was studied by Qiao and Jackson,' who showed that excess Pd must be present to stabilize the analyte and that the integrated absorbance of Se varied with the amount of Pd. Examination of the graphite surface by scanning electron microscopy (SEM) showed that the extent of stabilization depended on the size of the Pd droplets on the surface. This led to the conclusion that stabilization is physical in nature occurring through entrapment of the analyte in the Pd droplets.The characteristic delay in absorbance signal in the presence of Pd was attributed to the kinetically controlled release of analyte out of molten palladium droplets. The present study was undertaken to determine whether similar physical pro- cesses may contribute to the stabilization of Se by Ni and Cu. EXPERIMENTAL Apparatus and Reagents A Perkin-Elmer HGA 500 electrothermal atomizer was mounted in a modified Perkin-Elmer Model 2280 atomic absorption spectrometer. As described previously,' the elec- tronics of the spectrometer were by-passed to provide rapid signal processing. Standard Perkin-Elmer pyrolytic graphite- coated graphite tubes were used.The graphite tube wall temperature was monitored during the atomization stage of the heating cycle by focusing an optical pyrometer (Series 1100 Ircon Niles IL USA) on to the inside wall through the sample introduction hole. The spectrometer provided accurate correlation of the pyrometrically measured tube wall tempera- ture with absorbance and time which was essential for the atomization studies described in this paper. Electron micro- graphs of graphite surfaces w@e obtained on a scanning electron microscope (Autoscan; ETEC Hayward CA USA). The same magnification was used throughout as shown on the scale at the bottom of each micrograph. Stock standard solutions containing 10 mg 1-' of Se" Ni and Cu were prepared by dilution of 10000mg 1-l certified reference solutions (Spex Industries Edison NJ USA) in distilled de-ionized water containing 0.5% HNO .These solutions were further diluted to appropriate concentrations with distilled de-ionized water. The H2 purge gas (MGI Valley Forge PA USA) was 99.999% pure. Procedures Aliquots (20 pl) of solution were introduced into the graphite furnace by means of an Eppendorf micropipette. The normal operating conditions for the determination of Se involve the Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 43use of stabilized temperature platform conditions. However the platform temperature lags behind the temperature of the wall and cannot be measured accurately. As this work required accurate measurement of the graphite surface temperature a platform was not used and the sample was pipetted directly onto the inside wall of the tube.The electrothermal atomizer operating conditions and heating cycle are given in Table 1. RESULTS AND DISCUSSION Measurement of Graphite Tube Surface Temperature For this research it was necessary to obtain accurate tempera- ture measurements of the inside surface of the graphite tube. This was complicated by the behaviour of the sample during thermal pre-treatment. After depositing a liquid sample on the inside wall at the tube centre and then heating to the drying temperature of 130 "C the liquid droplet was observed to split into two droplets which flowed rapidly toward the tube ends. This resulted in two salt deposits about half way between the tube centre and its ends after the drying stage of the furnace heating cycle was complete.Further migration of these deposits did not occur prior to sample vaporization during the atomiz- ation stage. Routinely the tube temperature was measured pyrometrically at the centre (through the sample introduction hole). However it is knowng that a temperature gradient exists along the tube length during the atomization stage of the heating cycle so it was necessary to establish the difference in temperature between the tube centre and the region of the sample deposit. A hole was drilled through the graphite contact cones and the tube mid-way between the centre and one end of a tube. The optical pyrometer was then used to measure the temperature through this hole and the sample introduction hole when the atomization stage heating ramp in Table 1 was applied.Below 900 "C there was no measurable temperature differ- ence between the two positions i.e. the temperature gradient that presumably caused the initial migration of the sample droplets occurred only during the first few seconds of heating to the drying temperature. However the measured temperature in the region of the sample deposit was 30°C lower than the tube centre at 900"C and 100°C lower at 1900°C. During the atomization temperature studies the tube temperature meas- ured in the centre was corrected for this difference. Stabilization During Thermal Pretreatment Pyrolysis curves Pyrolysis curves for 2 ng of Se in the presence of various amounts of nickel are shown in Fig.l(a). In the absence of modifier severe analyte loss occurs even at the lowest pyrolysis temperature (200"C) and Se is mostly lost at a pyrolysis temperature of 800 "C (the boiling point of Se is 684 "C). The presence of a large excess of modifier stabilizes Se up to a pyrolysis temperature of about 1200 "C as noted by several Table 1 Instrumental operating parameters ETA stage Parameter Dry Pyrolyse Cool Atomize Clean Ramp time/s 20 10 10 1 5 Hold time/s 50 30 20 4 5 TemperaturePC 130 Various 200 2300 2650 Wavelength 196.0 nm Purge gases Ar 300 ml min-'; or H2 50 ml min-' (flow stopped during atomization stage) 0.8 r 1 r BY 0.6 0.4 - 0.2 . C D I I I I I I 0 200 400 600 800 1000 1200 1400 1600 Pyrolysis tern perature/"C Fig. 1 Dependence of the stabilization of 2 ng of Se on the amount of (a) Ni and (b) Cu during the pyrolysis stage of thermal pre- treatment.Amounts of Ni and Cu A 0; B 0.1; C 2; D 4; E 20 pg researchers in the past. However a dip in the pyrolysis curve occurred at about 800°C. A similar dip has been reported e.g. Welz et aL2 noted that the pyrolysis curve for SeIV had a dip in the presence of 20 pg of Ni. In this work the dip was more pronounced when smaller amounts of Ni (< 4 pg) were used. (Pyrolysis curves obtained under conven- tional platform atomization conditions also showed the dip when using these amounts of Ni.) A dip was also seen at a pyrolysis temperature of about 800°C when Cu was used as a modifier [Fig. l(b)] but a smaller excess of modifier (2 pg) was required to eliminate the dip compared with the addition of Ni [Fig.l(a)]. Welz et aL2 explained the dip by suggesting that Se forms a molecular species with Ni that is volatilized at pyrolysis temperatures below 1000 "C but it forms a molecule that is stable up to 1200°C if a higher pyrolysis temperature is used. Styris6 noted that NiSe dissociates at 800°C through its interaction with the graphite surface but is stable to 1200 "C in the presence of excess Ni. This would explain the improve- ment in stabilization in the 800-1200 "C temperature range with excess Ni in Fig. l(u) but does not explain the dip i.e. why small amounts of Ni then provide improved stabilization if the pyrolysis temperature is increased from 800 to 1000°C. Physical behaviour of the modijier with respect to temperature The pyrolysis curves in Fig.1 show a dependence of Se recovery on the amount of added Ni or Cu. Excess of modifier in addition to removing the dip in the curve results in a lower recovery of Se at all pyrolysis temperatures. Previ~usly,~ when increasing amounts of Pd modifier were added to Se lower 44 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10recoveries were also noted with a large excess of the modifier. This was attributed to physical entrapment of the analyte in molten modifier particles and its subsequent slow release. Frech et d." noted low recoveries of Se in the presence of Ni and Cu modifiers and suggested that sensitivity loss of Se occurs as a result of its secondary adsorption on condensed modifier particles at the cooler tube ends.However this was seen only in the presence of a large excess of Ni or Cu modifier compared with the amounts used in this work. In order to investigate whether physical effects are also significant when only 20pg of Ni or Cu are used as modifiers for Se their appearance after pre-treatment at various temperatures was examined visually and by SEM. Aliquots containing 20 pg of Ni were pipetted onto the inside walls of four pyrolytic graphite-coated tubes which were then heated to 130°C to dry the deposit. Three of the tubes were further heated to pyrolysis temperatures of 600 900 and 1200 "C respectively using the heating times shown in Table 1. The tubes were then cooled removed and broken along their length to reveal the deposit. Electron micrographs of these deposits are shown in Fig.2(a). Initially Ni was present as the nitrate which would be expected to undergo decomposition to the oxide and then the metal as the temperature increased. The crystalline deposit seen after heating to 130°C was green. This was Ni(N03)3-6H,0 which melted (melting point 57 "C) and recrystallized on cooling the tube. The deposits obtained after heating to 600 900 and 1200°C were a mixture of NiO and Ni with the relative proportion of Ni obviously increasing with temperature. All three deposits were silver in colour indicating the presence of the metal but there was almost certainly a large proportion of the oxide present in the deposit that was heated to 600°C. Droessler and Holcombe7 noted the presence of NiO at temperatures up to about 900°C.The electron micrographs show progressive shrinking of the matrix with increasing temperature reflecting the increasing density of the deposit as it changed from the nitrate to the oxide and then the metal. The experiment was repeated with aliquots containing 20pg of Cu and the electron micrographs are shown in Fig. 2(b). In this instance a blue crystalline deposit of Cu(NO3),-3H,0 was seen after heating to 130 " C. This salt 4- melted (melting-point 11 5 "C) and recrystallized on cooling. After heating to 600 "C the nitrate had decomposed to produce a mixture of Cu,O and CuO as evidenced by the mixed red and black colour of the deposit. At 900"C some metallic Cu was visible in addition to the coloured oxide deposit and after heating to 1200°C the deposit appeared to consist entirely of Cu metal.Unlike Ni Cu had melted (melting-point 1100 "C) during the 1200°C heating stage and it is seen on the micrograph to have agglomerated to form large droplets. As with Ni the matrix volume decreased with increasing tempera- ture owing to increased density of the deposit. When trace amounts of Se are present chemical interaction with Ni or Cu probably occurs most likely resulting in the formation of selenides. However the physical association of Se with the large excess of matrix metal must be considered and this will be similar for both Ni and Cu. During the drying stage (13O"C) the matrix salt (nitrate) was seen to crystallize and this would result in co-crystallization or co-precipitation of Se probably as H,SeO or its salt.As the pre-treatment tempera- ture increased and the matrix underwent shrinking as it was converted into the oxide the Se salt also decomposed to the oxide and may have become physically entrapped in the matrix. At higher temperatures as the matrix oxide decom- posed to the metal chemical interaction undoubtedly occurred between Se and the matrix but it is considered that Se also continued to be entrapped in the excess Ni or Cu. Stabilization of Se during pre-treatment can be attributed both to the formation of chemical bonds with the matrix metal and to its physical entrapment. 130°C (a) 900% 130°C 600% 1200% 600°C (b) 12004 Fig.2 Scanning electron micrographs of deposits of (a) Ni and (b) Cu on the graphite tube wall after pyrolysis of their nitrates at the temperatures indicated Pyrolysis curves in the presence of H2 The most pronounced dip in the pyrolysis curves for Se occurred when 2 pg of Ni [Fig.1 (a)] or 0.1 pg of Cu [Fig. 1 (b)] were used. Pyrolysis curves were again obtained using these amounts of each modifier but H was substituted for the Ar purge gas during the drying and/or pyrolysis stages of thermal pre-treatment. The resulting pyrolysis curves for Se in the presence of Ni [Fig. 3(a)3 and Cu [Fig. 3(b)] show that the addition of H has eliminated the dip completely even when Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 450.4 0.2 v) 0 C m \ +! s o u m u 0.8 r 1 0 200 400 600 800 1000 1200 1400 1600 Pyrolysis temperaturePC Fig.3 Effect of substituting H2 for the Ar purge gas during the thermal pre-treatment of 2 ng of Se in the presence of (a) 2 pg of Ni and (b) 0.1 pg of Cu.A Ar only; By H2 during drying and Ar during pyrolysis; C Ar during drying and H during pyrolysis; D H during drying and pyrolysis H was only introduced during the 130°C drying stage. The following are possible reasons for this behaviour using Ni as an example but analogous explanations could be presented for Cu. (1) If the dip occurs through the formation of a more stable selenide (e.g. NiSe) at pyrolysis temperatures > 1000 "C compared with the less stable selenide (e.g. NiSe,) at lower pyrolysis temperatures H may be promoting reduction of the less stable selenide at low temperatures. (2) Even when it was introduced only during the drying stage H was effective at high pyrolysis temperatures indicating that it is adsorbed strongly on graphite at 130°C.It may then be blocking active carbon sites thus preventing the formation of the ternary Ni-C-Se alloy proposed by In such a case the selenide would remain stable to 1100-1200 "C as when excess modifier was present. (3) Hydrogen promotes earlier reduction of the metal salts to their oxides and the oxides to the metals. This was seen clearly by examining the Cu deposit after stopping pre-treatment at various temperatures. After pre-treatment at 300"C the deposit appeared to be 100% Cu metal with no indication of the red or black oxides. In the absence of H2 Cu metal was not observed below 900 "C. This lower temperature reduction would result in more effective entrapment of Se in the modifier at lower temperatures.Stabilization During Atomization Fig.4(a) shows an absorbance signal for 2 ng of Se in the presence of 20pg of Ni. In the absence of Ni Se had an appearance time of 1.5 s (640 "C) but the absorbance signal in fa) 4s (1 820 "C) 3s (1 500 "C) 2s (940 "C) (b) 1s (330 "C) 2s (940 "C) 3s (1 500 "C) Fig. 4 Absorbance signals and electron micrographs of the modifier deposits after interrupting the atomization heating stage at various times. (a) 20 pg of Ni modifier; (b) 20 pg of Cu modifier this figure shows that the modifier stabilized Se to a later appearance time of 3.0 s (1500 "C). The physical appearance of the modifier deposits was studied by stopping the atomiz- ation stage of the heating programme after a pre-determined time allowing the tube to cool breaking it apart and examin- ing the deposits by SEM.This was done after 2 3 and 4 s into the atomization stage and the resulting electron micrographs are also shown in Fig. 4(u). After 2 s into the atomization stage the wall temperature was 940 "C and the modifier deposit was a mixture of Ni and NiO. In the absence of Ni Se was not stabilized at this temperature and stabilization by Ni may be attributed to the formation of Ni-Se bonds and/or the physical entrapment of Se in the Ni/NiO deposit as discussed above. The electron micrograph after 3 s (1500 "C) shows the modifier to be present as molten droplets of Ni metal. At this tempera- ture Se and Ni began to co-vaporize as this is the appearance temperature of both metals.However the electron micrograph obtained after 4 s (1820 "C) shows that all of the Ni had not yet vaporized even though the Se absorbance signal was well past its peak. Therefore vaporization of Se between about 3 and 5 s involved its migration out of molten Ni droplets. Atomization of Se most likely occurs via the breaking of Se-Ni bonds and this may contribute to the stabilization of Se during 46 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10Table 2 Experimental activation energies for the atomization of Se (2 ng) in the presence of various amounts of Ni and Cu Activation energy/kJ mol-' Amount of modifier/pg Ni modifier Cu modifier 0.1 248 f 4 143 f 2 2 334 f 24 239 f 8 4 371 f 6 324f11 8 440f 16 408 f 10 6 401 f 4 1 374 f 12 the atomization stage.Also contributing however is the energy required to release Se from its physical entrapment in the molten Ni droplets. The fact that the absorbance signal is suppressed in the presence of excess Ni [Fig. l(a)] and that the extent of this suppression depends on the amount of the excess indicates that this physical effect may be dominant compared with the breaking of Se-Ni bonds. The absorbance signal for Se in the presence of 20 pg of Cu [Fig.4(b)] is almost identical with that in the presence of Ni [Fig. 4(u)] and a similar argument can be presented for the mechanism of stabilization. However in this case the evidence for stabilization through the physical entrapment of Se in the Cu matrix may be even stronger. After 2 s into the atomization stage when the wall temperature was 940"C Cu had already formed small droplets of the metal. After 3 s (1500°C) when the Se signal began to appear the Cu had melted and the small droplets had agglomerated into larger droplets.If as discussed previously for stabilization by Pd,5 the rate-limiting step leading to atomization is migration of analyte out of the droplets then larger droplets will result in greater stabilization. The pyrolysis curves in the presence of H using Ni [Fig 3(a)] and Cu [Fig 3(b)] modifiers show that when H was present at a high pyrolysis temperature (e.g. 1200°C with Ni and 1000°C in the presence of Cu) stabiliz- ation was less effective than when no H2 was present or when it was present only during the drying stage of the furnace.Examination of the electron micrographs obtained after heat- ing to this temperature showed smaller droplets in the presence of H,. Hence the reduced stabilization may have occurred through faster migration of Se out of the smaller Ni or Cu droplets. The atomization of Se in the presence of Ni and Cu was studied kinetically. Amounts of Ni and Cu ranging from 0.1 to 8 pg were added to 2 ng of Se. In all instances the release of Se was a first-order process as determined by the method of McNally and Holcombe.12 Experimental activation energies measured by Smets' method,13 are presented in Table2. For this first-order release process the activation energy of both modifiers increased with increasing excess of modifier and this is suggestive of a physical effect. CONCLUSION Both chemical and physical effects may contribute to the stabilization of Se by Ni and Cu.At pyrolysis temperatures below 700-8OO0C small amounts (0.1 pg) of Ni or Cu are sufficient to stabilize 2 ng of Se as shown in Fig. 1. This stabilization may be due to the formation of selenides with Ni or Cu and/or the entrapment of Se species in the excess of modifier. Stabilization in the region of the characteristic dip at a pyrolysis temperature of about 800 "C was improved either by addition of excess of modifier or by the introduction of H during the drying stage of the furnace heating cycle. This supports the suggestion by Styris6 that blocking of active carbon sites can prevent the formation of the thermally unstable Se-C-Ni alloy as H is strongly adsorbed on the carbon surface.Improved stabilization may also occur through more effective entrapment of Se in the larger excess of modifier. Improved stabilization at a pyrolysis temperature of about 1000°C (i.e.. after the dip) may be due to the formation of a more stable selenide at the higher temperature or it may be explained by more effective entrapment of Se when the modifier is heated to a temperature high enough to produce the metal oxide. The strongest evidence for a physical mechanism of stabilization is obtained from the delay in analyte appearance during the atomization stage and the decreased absorbance that is obtained when the modifier is in large excess. The high analyte appearance temperature (1500 "C) results from the entrapment of Se in Ni or Cu metal until the temperature is sufficiently high for Se to migrate out of the modifier as both analyte and modifier co-volatilize. This is similar to the pre- viously reported physical mechanism of modification by pal- l a d i ~ m .~ The process of migration of the modifier from the analyte may be similar to that described by Hinds et all4 for the release of Si from molten gold droplets in a graphite furnace. They suggested that thermal gradients in the droplet induce convection currents that carry the analyte to the droplet surface. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Ediger R. D. At. Absorpt. Newsl. 1975 14 127. Welz B. Schlemmer G. and Voellkopf U. Spectrochim. Acta Part B 1984 39 501. Kirkbright G. F. Hsiao-Chuan S. and Snook R. D. At. Spectrosc. 1980 1 85. Schlemmer G. and Welz B. Spectrochim. Acta Part B 1986 41 1157. Qiao H. and Jackson K. W. Spectrochim. Acta Part B 1991 46 1841. Styris D. L. Fresenius' J. Anal. Chem. 1986 323 710. Droessler M.S. and Holcombe J.A. Spectrochim. Acta Part B 1987 42 981. Allen E. and Jackson K. W. Anal. Chim. Acta 1987 192 355. Falk H. Glissman A. Bergann L. Minkwitz G. Schubert M. and Skole J. Spectrochirn. Acta Part B 1985 40 533 Terui Y. Yasuda K. and Hirokawa K. Anal. Sci. 1991 7 397. Frech W. Li K. Berglund M. and Baxter D. C. J. Anal. At. Spectrom. 1992 7 141. McNally J. and Holcombe J. A. Anal. Chem. 1987 59 1105. Smets B. Spectrochim. Acta Part B 1980 35 33. Hinds M. W. Brown G. N. and Styris D. L. J. Anal. At. Spectrom. 1994 9 1411. Paper 4/04 759A Received August 2 1994 Accepted September 13 1994 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 47

ISSN:0267-9477    

DOI:10.1039/JA9951000043

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Application of Palladium- and Rhodium- plating of the Graphite Furnace in Electrothermal Atomic Absorption Spectrometry EWA BULSKA AND WOJCIECH JEDRAL Department of Chemistry University of Warsaw 02-093 Warsaw Poland Palladium- and Rh-plating of the graphite furnace has been evaluated as a method of introducing the metallic form of Pd and Rh for chemical modification in electrothermal atomic absorption spectrometry. It is shown that by electroplating Pd and Rh onto the inner surface of the tube the pretreated graphite surface may resemble the behaviour of the corresponding modifier. The resulting metallic layer is very effective in inhibiting the loss of volatile elements (e.g. As and Se) as well as reducing the influence of oxide and carbide formation (e.g. Si). The advantage of the proposed procedure of introduction of a solid chemical modifier is that the pretreated tubes exhibit an extended analytical lifetime for the determination of As and Se up to 80 and 160 firings in the presence of Pd and Rh respectively.In the case of Si the Rh-plated graphite tube could last for about 100 firings. Keywords Electrothermal atomic absorption spectrometry; modijiers; palladium and rhodium-plated graphite tubes; arsenic selenium and silicon Chemical modification has been incorporated as an integral part of the stabilized temperature platform furnace concept by Slavin et a2.l The aim of chemical modification is to obtain optimal analytical conditions by changing the thermochemical behaviour of both the analyte and matrix components.' Since the introduction of Pd as a chemical modifier for electrothermal atomic absorption spectrometry3 it has been established as a modifier with universal appli~ability.~.~ Palladium combined with magnesium nitrate5-' or has become the most widely used modifier under routine analytical conditions.The high efficiency and universality of Pd-based modifiers can be explained by the unique catalytic properties of this metal. It has been reported9-12 that Pd must be in a particular chemical form such as the metallic form in order to act as an effective modifier. Palladium is known to form inter-metallic compounds and solid solutions with the elements to be determined in the graphite furnace.13 Besides the thermal stabilization of volatile elements another aspect of modifier action could be related to impregnation of the tube surface enhancing the direct contact of analyte with graphite.This is of special importance when carbide forming elements are determined. Ortner and Kantuscher14 improved the detection of Si by impregnation of the electrographite tubes with tungsten solution. Also W Ta Zr Mo V and Ti were used for impregnation of the porous graphite s~rface.'~ In the presence of Pd a 5-fold increase in the sensitivity was observed.16 In this case Pd must be introduced with each sample injection. Michaelis et ~ 1 . ' ~ reported life-times of more than 400 atomization cycles for TaC-coated platforms. Long- time performance of a modifier was first introduced as a concept of 'permanent modifier' by Shuttler et a1.l' The purpose of the present study was to investigate the performance of Pd and Rh after electroplating onto the inner Journal of Analytical Atomic Spectrometry surface of the graphite tube as a permanent chemical modifier with respect to a possible increase in the maximum pyrolysis temperature for volatile elements (e.g.As and Se) and a decrease in the formation of oxide and carbide for carbide forming elements (e.g. Si). Electroplating results in a continu- ous metallic film on the graphite surface. The film may significantly enhance losses of the elements determined. The quality of the deposited metallic film is not expected to be critical because the furnace operating temperature is usually higher than the melting-point of the metal. Therefore the structure of the metallic film should change during the first heating to atomization temperature.The thickness of the film however must be very small. A thick film might decrease the overall electric resistance of the furnace. This can change the rate of furnace temperature increase and finally can cause the real tube temperature to deviate from the set temperature or may decrease the life time of the graphite tube. EXPERIMENTAL Apparatus An atomic absorption spectrometer Model Video 22 (Thermo Jarrel Ash) equipped with a Perkin-Elmer HGA-400 graphite furnace atomizer was used throughout this work. Since the system was not equipped with an autosampler solutions were injected manually using a 20 pl micro-pipette. Hollow cathode lamps for As Se and Si were used at wavelengths of 197.3 196.0 n and 251.6 nm respectively. Different types of graphite tubes were used for the investi- gation uncoated electrographite (EG) tubes pyrolytic graphite coated electrographite (PC) tubes and electroplated (EPC) tubes.All tubes (EG and PC) were commercially available Perkin-Elmer products. The EPC tubes were prepared from EG tubes by electrodeposition of the modifier (Pd or Rh) onto the surface. The time-temperature programme used is given in Table 1. Reagents Standard stock solution containing lo00 mg 1-1 of the elements being investigated were prepared from Titrisol concentrate (Titrisol Merck). Working standard solutions were prepared daily by appropriate dilution with 0.1 % HNO,. Palladium nitrate (1 mg ml-l) and rhodium chloride (1 mg ml-') were used as chemical modifiers.The composition of the electrolytic bath for Pd- and Rh-plating is shown in Table 2. All sample containers glassware and autosampler cups were soaked in 10% v/v nitric acid for 24 h and then rinsed thoroughly with doubly distilled water. All reagents and solu- tions were regularly checked for possible contamination with the elements investigated. Journal of Analyticd Atomic Spectrometry January 1995 Vol. 10 49Table 1 Graphite furnace temperature programme Programme I used for the determination of investigated elements- Step 1 2 3 4 5 Temperat ure/"C 90 120 -* -t 2700 Parameter Ramp time/s 5 10 5 0 1 Hold time/s 10 20 10 4 2 Read - ON - - - Programme 2 used for thermal pre-treatment of the modifier$ in graphite furnace- Parameter Step 1 2 3 TemperaturePC 90 120 1200 Ramp time/s 5 5 5 Hold time/s 10 20 10 *Variable.7 Atomization temperature As 2200 "C; Se 2200 "C; Si 2500 "C. $20 p1 contained 2 pg of Pd or 3 p of Rh. Procedures The modifiers were used as follows. (i) The modifier solution was injected first dried and pyrolysed (Table 1 Programme 2) to obtain Pd or Rh in its reduced form then the sample was injected. (ii) The modifier was deposited by electroplating onto the inner surface of the graphite tube. Preparation of the metal-plating tubes EPC A simple set-up consisting of a constant current source a Pt anode and a holder for the graphite furnace (acting as a cathode) was used to electrodeposit the metal (Fig. 1). An additional voltmeter was used for measuring the voltage between the electrodes to assure that no short connection occurred between the electrodes during the electroplating.The EC graphite tube was cleaned before use by heating at 2500 "C for 5 s in the atomizer while purging argon gas through it. After cooling the tube was wrapped with a Teflon band to protect the outside surface from metal deposition then fixed into the metal holder. Platinum wire was carefully introduced inside the tube and both electrodes (graphite tube and Pt-wire connected as shown in Fig. 1) were immersed into a cylindrical glass cell (id. 0.9 cm) containing 2ml of electrolytic bath solution. Experimental details for the metal-plating procedure are shown in Table 3. After several minutes of electroplating a significant amount of the metal has been moved from the bath to the tube surface.Decreasing the concentration of the metal compound in the bath influences the current efficiency of the electroplating process. To obtain good repeatability of the process for each electroplating a fresh electrolytic bath solution was used. After the electroplating cycle was finished the tube was washed in a stream of doubly distilled water and dried at room temperature. Next the tube was fixed in the HGA unit slowly dried at a temperature of about 80°C and then heated Table 2 Electrolytic bath composition 1 H- Fig. 1 Unit used for electroplating Pt platinum anode; GF graphite tube; H Holder; S glass separator; CS constant current source; and V voltmeter Table 3 Conditions used for Ph- and Rh-plating of the graphite tubes Electrolytic bath Current density/mA cm-2 Current efficiency (YO) TemperaturePC Time/min Pd 0.2 50 80 60 Rh 0.6 20 40 45 to 2000°C.After this procedure the modified EPC tube was ready to be used in further investigations. RESULTS AND DISCUSSION As many elements are subjected to losses during the pyrolysis step chemical modification techniques are recommended to decrease the volatility of the analyte.2 Arsenic and Se were studied as an example of volatile elements for which Pd has been reported to be a suitable chemical modifier.6 On the other hand Si was chosen to investigate the application of a modifier to the determination of the refractory elements. Although Si is an element of low volatility the formation of oxide and carbide is the main reason for decreased atomization efficien~y.'~~~~ Therefore the application of Pd and Rh for those elements was investigated.The application of a modifier can be realized by pre-mixing with a sample or by separate injection into the furnace. The effectiveness of thermal pre- treatment of Pd has been reported in many application^.^^^ In these studies the modifier solution was injected first then dried and pyrolysed in order to obtain Pd in its reduced forrn. Therefore the appropriate aliquot containing Pd must be introduced before each sample injection. In order to simplify the procedure efforts have been made to stabilize the reduced- Pd modifier. Shuttler et used Ir to stabilize Pd for permanent trapping of the hydride. In this study electroplating pre-treatment of the graphite tube was used in order to obtain a permanent modification effect for the determination of As Se and Si.Pd-plating Rh-plating Compound Amount/g per 100 ml Compound Amount/g per 100 ml PdCI 1.66 RhZ ( s04)3 0.25 Na2HP04 * 12 H,O 20 Sulfuric acid (d = 1.8 g cm-3) 30 (NH4)2HP04 * 12 H2O 5 Benzoic acid 0.2 50 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10Table 4 Maximum pre-treatment temperatures ("C) in the presence of Pd and Rh modifiers Pd Rh Thermal Electro- Thermal Electro- Element No modifier pre-treatment* plating pre- treatment * plating As 900 1300 1300 1450 1450 Se 300 1200 1200 1400 1400 Si 1200 1200 1200 1500 1600 *Pd or Rh solution (20 p1; 1 mg m1-l) was injected dried and pyrolysed before sample injection. Thermal stabilization studies The pyrolysis curves for As and Se under different conditions e.g.in the absence and in the presence of Pd and Rh are shown in Fig. 2,(a) and (b). The maximum pre-treatment temperature applied under the different conditions are presented in Table 4. The results indicate that Pd modifier used in both modes e.g. thermal pre-treatment or electroplating thermally stabil- izes As up to 1300°C and Se up to 1200°C. Comparison of the results obtained with Pd and Rh modifiers shows that the latter cause better thermal stabilization for both elements up to 1450°C for As and 1400°C for Se. The data are in good agreement with the observations of Tsalev and Slaveykova.21 This is to be expected when comparing the melting- and boiling-points for Pd (m.p. = 1550 "C; b.p. = 2900 "C) and Rh (m.p.=1970°C; b.p.=370OoC).These data lead to the con- clusion that the substantial improvement in the maximum pre- treatment temperature observed experimentally in the presence of Rh is related to its higher melting-point. Different behaviour was observed in the case of Si [Fig. 2(c)]. Silicon is a refractory element with a high melting-point (m.p. = 1420°C). Therefore in the presence of Pd the pyrolysis curve for Si exhibits similar behaviour as compared with the case 0.4 I 1 1 0.2 0.1 0 0 500 1000 1500 2000 Temperatu re/"C Fig.2 Thermal pre-treated curves for (a) 1 ng of Se (b) 1.5 ng of As and (c) 2 ng of Si. Graphite tubes were used 0 without modification; 0 Pd-plated; and . Rh-plated where no Pd was added. However the significant increase in the integrated absorbance value indicates that Pd acts as a modifier enhancing the efficiency of the atomization. This could be explained by the formation of inter-metallic (Si-Pd) compounds decreasing the possibility of forming silicon oxide or silicon carbide molecules. After electroplating of the graphite tube with Rh the increase of sensitivity is not as pronounced compared with Pd [see Fig.2(c)]. However the maximum pyrolysis temperature was increased up to 1600°C for the determination of Si. Analytical figure of merit The sensitivity [characteristic masses (mo) defined as the mass of analyte in pg which provides an integrated absorbance of 0.00441 for the elements investigated under various conditions are shown in Table 5. From these data it is clear that in the case of As and Se the Pd or Rh modifiers have no influence on sensitivity.Note that when no modifier was used the data obtained relate to conditions when the pyrolysis temperature did not exceed 900 "C for As and 300 "C for Se. It should be noted from Table 5 that the use of Pd or Rh results in a lower characteristic mass for Si. This is probably due to the fact that the modifier protects the analyte from direct contact with the graphite surface and/or with oxygen present in the gas phase. Therefore the formation of silicon oxide and carbide is less probable hence the sensitivity for the determination of Si is enhanced. It is interesting to note that the sensitivity is always better when electroplating pre-treatment of the modifier was used for the determination of Si.Thermal pre-treatment of the modifier improves the sensitivity by a factor of 3.6 for Pd and 2.3 for Rh compared with when no modifier was used. The better results (by a factor of 1.6) were obtained when the graphite surface was covered with a metallic layer of the modifier. It is believed that in case of Pd- or Rh-plating the whole surface of the tube is coated while the thermal pre-treatment allows only a limited area (e.g. the site of the droplet) to be covered. However it is difficult to conclude whether the improvements obtained when using electroplating are caused only by a larger Table 5 Characteristic masses (m,) of As Se and Si for different types of graphite tubes surface (in pg). Note that the maximum pre-treatment temperatures for the determination of m were as described in Table 4.EG uncoated electrographite; PC pyrolytic graphite-coated electro- graphite; TP thermal pre-treatment of modifier solution (Table 1 Program 11); EPC electroplating of the modifier onto the graphite surface EG - tubes PC-tubes No No Element modifier Pd-TP Pd-EPC modifier Rh-TP Rh-EPC As 22 18 18 21 19 16 Se 28 30 26 32 30 28 Si 340 94 58 210 90 52 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 51area being covered by the modifier and/or by the different more even and dense coverage of the graphite surface. Analytical lifetime of the modified tubes In view of the improved performance of the electroplated graphite tubes relatively long useful lifetimes were achieved. In the case of Rh-plated tubes the integrated absorbance for the determination of Si remained the same [relative standard deviation (RSD) = 3% for 10 determinations] for about 100 firings (Table 6).However after 100 atomization cycles the integrated absorbance decreased to the level obtained with uncoated graphite tubes. Microscopic studies of the graphite tubes with and without plating Fig. 3 shows three types of electrographite tubes at 200x magnification an unused EC tube; an EPC tube after Pd-plating cycle; and an EPC tube after 60 firings. Microscopic images of the surface at 200 x magnification are not as detailed as scanning electron micrographs which can be found in a number of publication^.'^.^^ However the important infor- mation relating to the history of the surface can be clearly evaluated from the images presented.Two images [Fig. 3(a) and (b)] show the difference between the surface of an unused EC tube before and after Pd-plating. The surface showed on Fig. 3(b) is much smoother compared with that of the new tube [Fig. 3(a)] and shows the deposition of a Pd metallic layer onto the tube after the plating process (as described under Experimental). Fig. 3(c) which shows an image of the Pd-plated surface after 60 firings demonstrates that the coating decreases substantially exposing the initial structure of the electrographite surface. This may explain the experimental results obtained for Si an element which is particularly sensitive to the quality of the tube surface. The Si sensitivity test indicates a gradual decrease of integrated absorbance after about 55-60 atomization cycles.CONCLUSION The practical advantages of the use of electroplated tubes were illustrated through thermal stabilization studies characteristic mass values and analytical life-time of the plating coating. An empirical investigation of the thermal stability of the metals investigated showed that both Pd and Rh permitted signifi- cantly higher pyrolysis temperatures for Se and As. In the case of Si both modifiers improved the sensitivity by a factor of 4.5 for Pd and a factor of 3 for Rh. It can be assumed that in the pre-injection mode the reducing properties of hot graphite would reduce Pd and Rh to the elemental form. Once reduced both metals become very effective modifiers. However this investigation showed that pre-injection of the modifier solution into the graphite tube and heating to 1000°C was not nearly as effective as electro- reduction in an electrolytic-bath.The graphite surface pre- treated by plating with Pd or Rh may resemble the behaviour of the corresponding modifiers and therefore act as a solid chemical modifier. Microscopic images show that in the case of Pd the metallic layer is stable up to about 60 atomization cycles. In view of the improved performance of the electroplated Table 6 Analytical lifetime (firings) of improved tubes performance Element Pd-thermal Pd-plating Rh-thermal Rh-plating As 8 80 20 160 Se 10 80 20 160 Si 1 60 10 100 (a ) Fig. 3 Surfaces of the tubes used in HGA-400 atomizer made from electrographite (a) surface of an unused EC tube; (b) EPC tube surface after Pd-plating cycle followed by heating to 2000°C; (c) EPC tube surface after 60 firings under condition for silicon determination (Table 1 Programme I) coating of the graphite tube low characteristic masses were obtained for both modifiers and a relatively long useful lifetime was achieved in the case of Rh-plating.Pyrolysis temperatures of 1400 "C-1600 "C were possible for the elements investigated in this study. Obviously before a chemical modifier can be widely used it must be carefully evaluated in a variety of sample matrices; detailed investigations are in progress. This research was carried out as part of the BST 472/2/94 project. 52 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10REFERENCES 1 Slavin W. Manning D. C. and Carnrick G.R. At. Spectrosc. 1981 2 135. 2 Tsalev D. L. Slaveykova V. I. and Mandjukov P. B. Spectrochim. Acta Rev. 1990 13 225. 3 Shan X.-Q. and Ni Z-M Acta Chim. Sin. 1979,37 261. 4 Welz B. Schlemmer G. and Mudakavi J. R. J. Anal. At. Spectrom. 1987 2 45. 5 Schlemmer G. and Welz B. Spectrochim. Acta. Part B 1986 41 1157. 6 Welz B. Schlemmer G. and Mudakavi J. R. J. Anal. At. Spectrorn. 1988 3 93. 7 Welz B. Schlemmer G. and Mudakavi J. R. J. Anal. At. Spectrom. 1988 3 695. 8 Welz B. Schlemmer G. and Mudakavi J. R. Anal. Chem. 1988 60 2567. 9 Voth-Beach L. M. and Shrader D. E. J. J. Anal. At. Spectrom. 1987 2 45. 10 Bulska E. Grobenski Z. and Schlemmer G. J. Anal. At. Spectrom. 1990 5 203. 11 Knowles M. B. and Brodie K. G. J. Anal. At. Spectrom. 1988 3 511. 12 13 14 15 16 17 18 19 20 Knowles M. B. and Brodie K. G. J. Anal. At. Spectrom. 1989 4 305. Volynsky A. Tikhomirov S. and Elagin A. Analyst 1991 116 145. Ortner H. M. and Kantuscher E. Talanta 1975 22 581. Fritzche H. Wegscheider W. Knapp G. and Ortner H. M. Talanta 1979 26 219. Fuchs-Pohl G. R. Solinska K. and Feig H. Fresenius J. Anal. Chem. 1992,343 711. Michaelis M. R. A. Wegscheider W. and Ortner H. M. J. Anal. At. Spectrom. 1988 3 503. Shuttler I. L. Feuerstein M. and Schlemmer G. J. Anal. At. Spectrom. 1992 7 1299. Frech W. and Cedergren A. Anal. Chim. Acta 1980 113 227. Rademeyer C. J. and Vermaak I. J. Anal. At. Spectrom. 1992 7 347. 21 Tsalev D. and Slaveykova I. Spectrosc. Lett. 1992 25 221. 22 Ortner H. M. Schlemmer G. Welz B. and Wegscheider W. Spectrochim. Acta Part B 1985 40 959. Paper 4/02 755 H Received May 10 1994 Accepted August 31 1994 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 53

ISSN:0267-9477    

DOI:10.1039/JA9951000049

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Automatic Preparation of Milk Dessert Slurries for the Determination of Trace Amounts of Aluminium by Electrothermal Atomic Absorption Spectrometry MARCO A. z. ARRUDA MERCEDES GALLEGO AND MIGUEL VALCARCEL* Department of Analytical Chemistry Faculty of Sciences University of Cbrdoba E- 14004 Cdrdoba Spain A method for the direct determination of aluminium in milk desserts is proposed. The method uses a flow injection system connected semi-on-line to a graphite furnace atomic absorption spectrometer through an autosampler for preparation of the slurries addition of a chemical modifier and dilutiow homogenization in a mixing chamber. Calibration is performed with aqueous standards. The flow system can be used to implement the standard additions method and investigate the effect of potential interferents in parallel by using two injection loops and the merging-zones mode.The slurries prepared contained up to 10% m/v. Aluminium was determined in various milk desserts at concentrations between 0.007 and 0.121 mg per 100 g. Keywords Aluminium determination; milk dessert analyses; electrothermal atomic absorption spectrometry; slurry sample introduction; flow injection Interest in the potential link between high aluminium contents in tissues and various neurodegenerative disorders such as Alzheimer's disease has drawn attention to the intake of aluminium from food drinking water parenteral nutrition or dialysis fluids in individuals with chronic renal disease.' There are several compilations of aluminium contents in foods and the most comprehensive of which was published by Pennington.2 Based on a total dietary study (TDS) on foods commonly consumed in the USA the main contributor to the aluminium content of the American diet is seemingly the grain and cereal product group followed by the dairy product group.The aluminium content increases from fluid cow milk to dairy products (e.g. yoghurt butter cheese); the mean aluminium content in yoghurt ranges from less than 0.1 to 0.112mg per 1OOg on a wet basis.4 Delves et ~ 1 . ~ recently studied the aluminium content in UK foods and beverages and found the relative bioavailability of the element from these foods to vary widely as does uptake by adult individuals. Because of its typically low content the most commonly used techniques for measuring aluminium in foods are electrothermal (graphite furnace) atomic absorption spectrometry (ETAAS) and induc- tively coupled plasma atomic emission spectrometry (ICP- AES).1,2 Direct analysis by ETAAS has previously been used with liquid foods such as milk fruit juices drinks and infusions; many solid foods require acid digestion (ideally with concen- trated nitric acid).However acid digestion of foods with high fat contents (e.g. dairy products) is potentially hazardous. One alternative to solid food pre-treatment is direct introduction of the sample as a slurry viz. a suspension of finely powdered sample in water or another solvent. This technique minimizes or avoids some typical problems encountered in sample pre- * To whom correspondence should be addressed. Journal of Analytical Atomic Spectrometry treatment such as contamination or analyte However running calibrations or using the standard additions method with solid or slurry samples still poses serious problem^.^ Aluminium has been widely determined in foods by ETAAS,1-3 but very rarely by using a The main interferences in the determination of aluminium in foodstuff by ETAAS arise from volatilization losses of Al,Cl from chloride-rich media and variable enhancements of the aluminium atomic signal by some ions present in foods (e.g.Po43- SO4,- Ca2+) and carbonaceous residues formed during electrothermal decomposition.' These interferences can be magnified by the slurry technique. A variety of chemical reagents [e.g. Mg(N03)2 Pd(N03) K2Cr207 NH4N03] have been used to decrease matrix interferences as far as possible prior to the atomization step in food analyse~;'~-'~ in any event the palladium salt is seemingly gaining wide accept- ance as a modifier for many elements including aluminium.'6-'8 The flow injection (FI) technique has been widely used in connection with flame atomic absorption spectrometry ( FAAS)19-22 and ICP-AES23 for the determination of metals in food slurries but comparatively rarely with ETA AS owing to the difficulties involved in their coupling (in fact only semi- on-line FI systems have so far been combined with ETAAS in~trumentationl~.~~).The aim of this work was to avoid sample weighing dilution and homogenization in preparing milk dessert slurries by using an automated preparation module that allows aqueous stan- dards to be automatically inserted in such a way that Cali- bration (whether conventional or by use of the standard additions method) can be implemented automatically with no sample weighing.The module was coupled to the instrument autosampler for determining aluminium in milk desserts. EXPERIMENTAL Apparatus A Perkin-Elmer (Uberlingen Germany) Model 1100 B atomic absorption spectrometer fitted with an HGA-700 graphite furnace and an AS-70 furnace autosampler was used. Background absorption was corrected by using a deuterium lamp in all experiments. A Perkin-Elmer aluminium hollow- cathode lamp operated at 25 mA and pyrolytic graphite-coated tubes (Perkin-Elmer part No. B-013-5653) with L'vov plat- forms (Perkin-Elmer part No. B-012-1091) were also used.Aluminium atomic absorption was measured at 309.4 nm by using a 0.7 nm spectral bandpass. Atomization signals (in the peak-area mode) were printed on a Epson (Wembley UK) FX-850 printer. The temperature programmes used are described in Table 1. The FI system was constructed from a Gilson (Villiers-Le-Bel France) Minipuls-2 peristaltic pump fitted with poly(viny1 chloride) tubing a laboratory-made three-piece injector commutator12 and a customized 1 ml Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 55Table 1 Furnace conditions used to obtain the pyrolysis-atomization curves in the analysis of yoghurt slurry samples. The injected volume was 20 pl of sample + 10 p1 of modifier for the conventional determination For optimization Final choice Step Temperature/”C Hold/s 1 100 35 2 200 15 3 800 5 4 Variable 10 5 Variable 4 6 2650 1 Temperature/”C Hold/s 100 35 200 15 800 5 1700 15 26QO 4 26.50 1 Ar flow rate/ Ramp/s ml min-’ 10 300 15 300 10 300 15 300 0 0 1 300 PTFE mixing chamber described el~ewhere.’~ A Heidolph magnetic stirrer was used to homogenize samples.Reagents All reagents used were of analytical-reagent grade (Merck Darmstadt Germany) and high-purity water obtained with a Milli-Q water-purification system (Millipore) was employed throughout. A lOOOmgl-’ A1 stock standard solution was prepared by dissolving 1.OOO g of aluminium wire in 20 ml of concentrated H2S04 plus 50ml of concentrated HN03 and diluting to 1 1 with water. Working standard solutions contain- ing 40-400 pg 1-’ of A1 were prepared from the stock standard solution by serial dilution with 0.2% v/v HNO prior to use.The standards were diluted tenfold in the FI manifold. Several modifiers including aqueous magnesium nitrate palladium nitrate and lanthanium nitrate dissolved at concen- trations between and 0.1 mol 1-’ were tested. Cleaning and Storage Material All PTFE vessels were cleaned by soaking in 10% v/v HNO for 48 h rinsing five times with water and filling with water until use.12 No glass vessels were used in order to minimize aluminium release and adsorption. Yoghurt samples were stored refrigerated (4 “C) in their plastic packages until analysis. Sample Preparation Milk dessert samples were preliminarily homogenized manu- ally with a spatula for 2 min. Samples containing fruit pieces were ground to complete homogeneity in a blender. Three different sample preparation procedures were used as follows.(1) Dry ashing a 2.5 g portion of natural yoghurt was placed in a platinum crucible and evaporated to dryness in a sand- bath followed by ashing at 600 “C for 40 min. The ash was then extracted to 25 ml with 0.2% v/v HN03. (2) Wet ashing a 2.5 g portion of natural yoghurt was placed in a platinum crucible and mixed with 5 ml of concentrated H2S04 plus 5ml of concentrated HN03 and evaporated to dryness in a sand-bath; after evaporation a fresh 5 ml portion of concentrated H2S04 plus 5 ml of concentrated HNO was added followed by evaporation to dryness twice more. Finally the resulting residue was dissolved to 25ml with 0.2% v/v HNO .(3) Direct preparation of yoghurt slurries by diluting 2.5 g of yoghurt to 25 ml with 0.2% v/v HNO and homogenizing in an ultrasonic bath for 10 min. For aluminium measurements diluted samples were placed in autosampler cups. A reagent blank was also prepared simultaneously in procedures 1 and 2. The National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) SRMl549 Non-fat Milk Powder was dried to constant mass by freeze-drying at 6 Pa for 24 h after which an accurately weighed amount of approxi- mately 1.25 g was mixed with 25 ml of 0.2% v/v HN03. The slurry thus formed was shaken before analysis in order to homogenize the solid particles in the solution. Conventional Procedure In order to obtain a calibration graph 2Opl of standard solution containing 5 10 20 30 or 40 pg I-’ of A1 (or diluted yoghurt sample) and 10 pl of 0.1 moll-’ magnesium nitrate plus 0.01 moll-’ palladium nitrate as chemical modifier were introduced sequentially into the graphite furnace. The blank solution consisted of 20 pl of 0.2% v/v HNO and 10 pl of the chemical modifier; both this and a standard solution containing 15 pg 1-1 of A1 (for re-sloping) were run after every five samples.All measurements were made in triplicate. Accuracy and Precision of Slurry Deposition The accuracy and precision of slurry sample deposition into a graphite tube were determined from recovery studies according to Lynch and Littlejohn.I8 The recovery studies give an estimate of the accuracy of the autosampler deposition if the programmed volume is taken as a true volume.The AS-70 autosampler was programmed to inject 20 pl of slurry. The mass of slurry actually introduced into the graphite furnace was determined by weighing the autosampler cups before and after sample deposition. The volume of slurry deposited was then calculated by dividing the mass into the slurry density. The mean value and precision (sr YO) were calculated in several slurry volume determinations (n = 8 ) ; the accuracy was calcu- lated by dividing the mean slurry volume deposited into the programmed volume. Flow Injection Procedure The flow injection system used is depicted in Fig. 1. Initially the manually homogenized milk dessert or the standard was aspirated through loop L at a flow rate of 1.5 ml min-’ while the chemical modifier C0.l mol 1-1 Mg(N03),+0.01 moll-’ Pd(N03)2] and the carrier (0.2% v/v HN03) were recycled outside the measurement line of the injector commutator.As the commutator was switched to its alternative position 200 pl of standard or sample were inserted into the carrier stream at a flow rate of 0.7 ml min-’ and then merged with the chemical modifier at 0.3 ml min-’ at merging point X; the mixed solution was passed through the mixing chamber for dilution and homogenization of the slurry. After mixing the solution was loaded into an autosampler cup for 120 s (2 ml). The ratio of the flow rate of the carrier to that of the chemical modifier used allowed the required dilution (1 +9) of the slurry sample for the determination of aluminium. In order to implement the standard additions method and investigate potential interferences with the proposed method two loops (one for the sample and the other containing different standard or interferent ions concentrations) were included in the FI system; also the original carrier stream (0.2% v/v 56 Journal of Analytical Atomic Spectrometry January 1995 Vol.10c T L W - 1 I g I @ IC Yoghurt d MC ETAAS v Fig. 1 FI manifold used for the determination of A1 in milky desserts M chemical modifier; C carrier stream; L sample loop (200 p.1); IC injector-commutator; MC mixing chamber; P peristaltic pump; W waste. Flow rate of carrier and chemical modifier 0.7 and 0.3 ml min- ' respectively HN03) at 0.7 ml min-l was split into two streams circulating at 0.35 ml min-l. Therefore as the commutator was switched the contents of both loops were injected into the carrier stream and the sample and standard/interferent were mixed in the merging-zones mode.The operational sequence was then continued as stated above. RESULTS AND DISCUSSION Optimization of the Conventional Procedure Errors in volumetric sampling of slurries relative to aqueous solutions can be attributed to several sources; some arise from the slurry (e.g. viscosity density) and others from the sample injector (e.g. wettability material composition). These physico- chemical properties affect the accuracy and precision of sample deposition and hence must be controlled for complete optimiz- ation of the operational procedure method. The slurry sample introduction process was studied by manually shaking directly prepared slurries prior to manual injection in order to prevent settling out of material. The accuracy and precision with which natural yoghurt slurry was deposited into a graphite furnace up to a concen- tration of 50% m/v is shown in Fig. 2.The accuracy was higher than 100% in all instances so the slurry volumes deposited by the autosampler injector were always higher than the programmed volume (20 pl); however above a 10% slurry concentration the mean volume remained constant at 20.4 pl. This increased volume may be the result of a higher density 110 90 95 [ 0 5 10 20 50 Slurry concentration (% m/v) Fig. 2 Accuracy and precision of slurry introduction into a graphite furnace. Error bars indicate 95% confidence intervals (for precision as sr) of the slurries relative to distilled water.The precision of sample deposition was acceptable (s < 8%); however it became worse with decreasing slurry concentration probably as a result of a steeper concentration gradient in the bulk slurry. Based on the results the injector can be used for introduction of slurry samples containing up to 50% m/v with acceptable accuracy and precision. The furnace programme used is shown in Table 1; it included two temperature ramps in the drying step in order to prevent splattering of the sample on the L'vov platform owing to the high boiling-point of the matrix. The pyrolysis step also included two temperature ramps in order to overcome the potential effect of the carbonaceous residue by exploiting the low volatility of aluminium.Maximum sensitivity was achieved by stopping the internal argon flow through the furnace during the atomization step. Under these conditions the signal-to- noise ratio was optimum and the background absorbance was very small and corrected by the deuterium lamp. Because direct measurements of aluminium in the yoghurt samples provided high analyte concentrations and background signals (approximately 0.3 absorbance per second) both of which are limiting factors in considering the extent of dilution factor first the yoghurt dilution was studied. Different dilution factors were tested (1 + 1 1 +4 1 + 9 and 1 + 19 m/v) for a commercially available natural yoghurt. A dilution factor of 1 +9 m/v was chosen as optimum because it resulted in a lower background signal than 1 + 1 and 1 +4 dilutions and provided an aluminium concentration in the central region of the calibration graph.Aluminium oxides carbides cyanamides and cyanides have been detected in the furnace near the atomization temperature of aluminium; these compounds may result in surface losses of aluminium and account for the relatively low atomization efficiency for aluminium.25 If these aluminium-containing species are dissociated at temperatures other than the atomiz- ation temperature they may give rise to broadened or distorted analyte signals. Chemical modifiers are an excellent choice for circumventing these problems. We used a natural yoghurt sample diluted 1 + 9 and a standard solution of 20 pg I-' of A1 plus various chemical modifiers (Fig. 3) at a fixed atomiz- ation temperature of 2600 "C and various pyrolysis tempera- tures.In the absence of a chemical modifier the aluminium present in the natural yoghurt started to volatilize at about 1100°C and the standard solution at 1500°C. In the presence of a chemical modifier however the pyrolysis temperature for the yoghurt was similar to that for the aqueous aluminium standard solution. Although differences in the background signals obtained in the presence of the different chemical modifiers were very small 0.1 moll- Mg( NO& plus 0.01 moll-' Pd(N03)2 was chosen as the optimum modifier as it resulted in a slightly higher sensitivity for the sample. A 0.01 mol 1-1 La(NO,) solution also tested as a chemical modifier was discarded because the aluminium sensitivity started to decrease above about 1500 "C.Flow Injection System After manual homogenization the yoghurt sample was aspir- ated into a 200 pl sample loop. The sample aspiration flow rate was critical; the optimum pump tubing diameter-rotation speed combination was 2.3 mm id. and 200 rev min-l which allowed the loop to be filled with the yoghurt sample at 1.5 ml min-'. In order also to use the optimum dilution factor ( 1 + 9 m/v) for the conventional procedure the sample volume injected into the FI system (200~1) was diluted to a final volume of 2 ml in the autosampler cup. The modifier flow rate (0.3mlmin-') should be roughly half that of the carrier solution (0.7 ml min-I) in order that the ratio of diluted sample volume introduced into the furnace (20pl) to the chemical Journal of Analytical Atomic Spectrometry January 1995 VoE.10 570.15 la’ I I b 900 1300 1700 2100 Pyrolysis temperature/”(= Fig. 3 Influence of pyrolysis temperature of (a) natural yoghurt manually diluted tenfold and (b) 20 pg 1-1 of A1 standard A in the absence of chemical modifier and B in the presence of 0.1 mol I-’ Mg(N03)2; C 0.01 moll-’ Pd(N03)2; and D 0.1 mol 1-1 Mg(N03)2 plus 0.01 mol 1-1 Pd(N03)2. Injected volumes 20 pl (sample) and 10 p1 (chemical modifier). Furnace conditions as in Table 1 modifier volume (10 pl) for the conventional procedure be identical with that used in the FI procedure. These flow rate values ensure negligible carry-over of sample into the FI system. Finally the potential advantages of the automatic slurry preparation method over its manual counterpart were checked by determining the precision achieved with both.Thus ten slurries of the same yoghurt were prepared by manual dilution (1 + 9 m/v) and homogenized in the ultrasonic bath for 10min or in the proposed FI system where ten sequential injections of 200 pl of the same yoghurt were performed. The results obtained showed the manual procedure to be poorly reproducible (the repeatability as s was 15.8%) and the automatic dilution procedure to be acceptably precise (the repeatability as s was 6.5%) because of its reduced human participation (no weighing dilution or homogenization of the sample is needed). For comparison it should be noted that 200 pl of yoghurt weighed about 205 mg as the yoghurt density was about 1.025 g m1-I.Determination of Aluminium By using the proposed method aluminium could be determined over the linear range from 4 ,to 40 pg 1-1 (r>0.998; n=6); however the FI system depicted in Fig. 1 increased the linear range from 40 to 400 pg I-’ owing to the dilution factor (1 + 9) used. The detection limit calculated according to IUPAC recommendations,26 was found to be 6 pg 1-1 (0.58 pg per 100 g) for the FI system. The results obtained for commercially available natural yoghurt were precise [s = 6.2% as repeat- ability (n = 15) and s = 10.6% as reproducibility (n= lo)]. A calibration graph for slurries was constructed by using the standard additions method; for this purpose a second 200 pl loop for injection of aqueous standards containing 25-250 pg I-’ of A1 was incorporated into the FI system as described under Flow Injection Procedure.Both the natural yoghurt and the standards were diluted tenfold inside the manifold. The high consistency between the aluminium concen- trations in the diluted natural yoghurt obtained by using the standard additions (0.01 10 + 0.0003 mg per 100 g) and FI (0.0109 +0.0002 mg per 100 g) methods indicates that the proposed method can be calibrated with liquid standards. A t-test was made to compare the concentrations of aluminium provided by the FI and standard addition procedures (95% confidence interval) and no significant difference was observed. Selectivity Potential interferences with the determination of aluminium were investigated by studying most major ions usually present in the mineral fraction of natural y o g h ~ r t ; ~ ~ for this we used an FI system similar to that for implementation of the standard additions method and injected interferent ions at concen- trations ten times higher than in natural yoghurt uia the second 200 pl loop both the sample and interferent ions finally being diluted to a volume of 2ml.The ion concentrations assayed were 10 mg ml-I Na+ (nitrate) 15 mg ml-1 Ca2+ (nitrate) 20 mg ml-1 K+ (nitrate) 15 mg ml-I C1- (ammonium salt) 5 mg ml-1 S042- (CuSO,) and 50 mg ml-1 (KH2P04). No interferences were observed; the differences in the analytical response relative to diluted natural yoghurt in the absence of interferent ions were small (- 3.0 to + 10.90/,). Therefore none of these ions interfere with the determination of aluminium at concentrations ten times higher than those typically present in natural yoghurt. Analysis of Milk Desserts In order to check the applicability of the proposed method to the direct determination of aluminium in milk desserts the same natural yoghurt was analysed after different pre- treatments (dry and wet digestion see Sample Preparation).The results obtained in ten consecutive determinations were 0.01 1 +0.0003 0.01 1 +0.0004 and 0.035 & 0.001 mg per 100 g (on a wet basis) for the direct FI method and the dry and the wet process respectively. The blank signals obtained by dry ashing were negligible and similar to those provided by the direct process; on the other hand the blank signal obtained by wet digestion was about twice that corresponding to the real content in the natural yoghurt sample which can be ascribed to aluminium contamination during acid sample pre- treatment and also to the glassware (pipettes) employed. Therefore wet digestion was discarded for sample preparation as the aluminium concentrations obtained exceed the actual contents in natural yoghurt.In order to validate the accuracy of the proposed method the analytical procedure was applied to a milk reference standard supplied by NIST SRM 1549 Non-fat Milk Powder (uncertified aluminium concentration 0.2mg per 100 g). For this purpose an accurately weighed amount of approximately 1.25g was mixed with 25ml of 0.2 v/v HN03. The average content found by ten consecutive determinations on independent test portions of the reference material was 0.197+0.012 mg per 100 g.The results obtained demonstrate the accuracy of the proposed method. Hence the proposed slurry method is a good alternative to the determi- nation of aluminium in this type of sample by using ashing digestion a widely accepted procedure. The proposed method was applied to the determination of aluminium in commercially available milk desserts. The results obtained in five individual determinations of aluminium by using a dilution factor of 1 +9 and their standard deviations are given in Table 2. A dilution factor of 1 + 19 or 1 + 39 was used in the FI system for samples with high aluminium 58 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10Table 2 Aluminium contents in various milky desserts (dilution factor 1 + 9) as determined by using the proposed FI method (n = 5) Yoghurt Natural Pineapple (flavoured) Banana (flavoured) Macedbnia (flavoured) Raspberry (flavoured) Wood fruits* Pear (flavoured) Bifidus plum Peach (with fruit)* Lemon (flavoured) Coconut (flavoured) Strawberry (flavoured) Skim strawberry (flavoured) Skim apple (with fruit) Chocolatet Vanilla custard? Egg custard? A1 concentration/mg per 100g 0.01 1 k 0.0006 0.016It.:0.0015 0.010 _+ 0.0007 0.013 k0.0012 0.007 f O.OOO1 0.042 f 0.0035 0.026 f0.0018 0.029 f 0.0030 0.054 f0.0054 0.007 & 0.0007 0.010 k 0.0003 0.030 & 0.003 0.021 & 0.0004 0.019 f 0.0017 0.068 f 0.0043 0.121 k0.006 0.073 t- 0.0072 * 1 + 19 dilution factor.t 1 + 39 dilution factor. contents in conjunction with a sample loop volume of 100 or 50 pl respectively; the final volume was 2 ml.Taking into account that the density of this type of dessert is approximately 1.03&0.01 g ml-’ the amount of A1 con- tained in the 200 pl of injected sample is about 205 mg which allows the aluminium content per 100 g of milky dessert to be readily calculated. As can be seen from the results (Table 2 ) (a) the presence of fruit pieces increases the A1 content of the yoghurt because fruit contains more aluminium than does cow milk2 (b) the higher A1 contents of custard and chocolate yoghurt may be contributed in part by eggs or chocolate and/or additives and (c) one yoghurt (approximately 125 g) contributes to aluminium intake but at a non-toxic level (the allowed average dietary intake of A1 is about 6 mg d-I).’ Finally it is interesting to note that the proposed method can be used for the direct determination of aluminium (and probably also other metals at low levels) in milk desserts by using aqueous standards for calibration with no need for sample (slurry) weighing dilution or homogenization; the results thus obtained are comparable to those achieved by dry digestion of the sample.The Spanish CICyT is acknowledged for financial support (Project PB93-0717). M.A.Z. Arruda is also grateful to the Conselho Nacional de Desenvolvimento Cientifico e Tecnol6gico - CNPq (Brasilia Brazil) and to the Programa de Cooperacih Cientifica con Iberoamkrica (Madrid Spain) for additional financial support. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Aluminium in Food and the Environment ed.Massey R. C. and Taylor D. Royal Society of Chemistry London 1991. Pennington J. A. T. Food Addit. Contam. 1987 5 161. Vaessen H. A. M G. van de Kamp C. G. and Szteke B. Z . Lebenm.-Unters.-Forsch. 1992 194 456. Pennington J. A. T. and Jones J. W. in Aluminum in Health a Critical Review ed. Gitelman H. J. Marcel Dekker New York 1988. Delves H. T. Sieniawaska C. E. and Suchak B. Anal. Proc. 1993 30 358 Bendicho C. and de Loss-Vollebregt M. T. C. J. Anal. At. Spectrom. 1991 6 353. Caroli S. Microchem. J. 1992 45 257. de Benzo Z. A. Velosa M. Ceccarelli C. de la Guardia M. and Salvador A. Fresenius’ J. Anal. Chem. 1991 339 235. Minami H. Zhang Q. Itoh H. and Atsuya I. Microchem. J. 1994 49 126. Frech W. and Baxter D. C. Fresenius’ J. Anal. Chem. 1987 328,400. Gervais L. S. and Salin E. D. J. Anal. At. Spectrom. 1991,6,41. Arruda M. A. Z. Gallego M. and Valcarcel M. Anal. Chem. 1993 65 3331. Arruda M. A. Z. Gallego M. and Valcarcel M. Analyst 1994 119 779. Tsalev D. Z. At. Spectrosc. 1991 12 169. de Benzo Z. A. Velosa M. Ceccarelli C. and de la Guardia M. Fresenius’ J. Anal. Chem. 1991 339 235. Littlejohn D. Egila J. N. Gosland R. M. Kunwas U. K. Smith C. and Shan X. Q. Anal. Chim. Actu. 1991 250 71. Welz B. Schlemmer G. and Mudakavi J. R. J. And. At. Spectrom. 1992 7 1257. Lynch S. and Littlejohn D. J. Anal. At. Spectrom. 1989 4 157. Andrade J. C. Strong F. C. 111 and Martin N. J. Talanta 1990 37 711. Morales-Rubio A. Salvador A. and de la Guardia M. Fresenius’ J. Anal. Chem. 1992 342 452. Haswell S. J. and Barclay D. Analyst 1992 117 117. Gluodenis T. J. Jr. and Tyson J. F. J. Anal. At. Spectrom. 1993 8 697. Fagioli F. Landi S. Locatelli C. Righini F. Settimo R. and Magarini R. J. Anal. At. Spectrom. 1990 5 519. Arruda M. A. Z. Gallego M. and Valcarcel M. J. Anal. At. Spectrom. 1994 9 657. Redfield D. A. and Frech W. J. Anal. At. Spectrom. 1989,4,685. Analytical Methods Committee Analyst 1987 112 199. Tamime A. Y. and Robinson R. K. Yogur Cienciu y Tecnologia Acribia Zaragoza 1991. Paper 4104524F Received July 25 1994 Accepted September 19 1994 Journal of Analytical Atomic Spectrometry January 1995 VoE. 10 59

ISSN:0267-9477    

DOI:10.1039/JA9951000055

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Flashlamp Continuum AAS Time Resolved Spectra* HELMUT BECKER-ROSS STEFAN FLOREK REINHARD TISCHENDORF AND GISELA R. SCHMECHER Institut fiir Spektrochemie und angewandte Spektroskopie Laboratorium fiir spektroskopische Methoden der Umweltanalytik Rudower Chaussee 5 D-12489 Berlin Germany For flashlamp continuum atomic absorption spectrometry (FLACAAS) a continuum spectrum of high intensity throughout the entire UV-VIS spectral range is provided typically by xenon flashlamps. These lamps offer high intensity in the UV which is however strongly fluctuating. This drawback may be compensated for by using the simultaneously recorded spectral vicinity of the absorption line for correction. In order to accomplish this type of measurement a high resolution spectrometer and a multipixel photodetector are required.This paper describes such a combination of an Cchelle spectrometer and a linear-array charge coupled device (CCD) detector with a graphite furnace atomizer and a xenon flashlamp for AAS-measurements at a repetition rate of 10 Hz. The determination of thallium (absorption line 276.787 nm) in natural seawater in the presence of palladium (interfering line 276.309 nm) used as modifier demonstrates the effective background correction and the possibility for sensitive analysis of complex samples by time-resolved continuum AAS. The characteristic mass of thallium was determined to be 28 pg the limit of detection in seawater amounts to 20 pg I-'. Keywords Continuum-source atomic absorption spectrometry; xenon-Jlashlamp; kchelle spectrometer; charge coupled device detector; thallium Continuum-source atomic absorption spectrometry (AAS) has several advantages compared with conventional AAS,1-3 especially the coincident measurement of the background absorption the expanded dynamic range and the possibility of simultaneous measurements of several elements making it an attractive method for the analysis of complex samples.On the other hand the instrumentation used for continuum-source AAS must fulfil some special requirements a source emitting a continuum spectra of high intensity throughout the entire range from 190nm to 850nm; a spectrometer providing a resolution as high as R>50000 within this spectral range; a multipixel photodetector for simultaneous registration of one or several small spectral intervals each partial spectrum com- prising an absorption line with its spectral vicinity; and data collection and processing equipment for evaluating the recorded partial spectra and for determinating the background corrected absorbance. The above mentioned advantages can be exploited with the flash lamp continuum AAS (FLACAAS) developed in our laborat~ry.~?~ Xenon flashlamps provide the continuum spectra of high intensity that are needed.In the short-wavelength UV range between 190 and 250nm flashlamps offer higher emis- sion intensities in comparison to other continuum sources.6 However the repeatability of the spectral intensities from flash- to-flash is not good and intensity fluctuations of up to 30% can be encountered. This drawback may be compensated for * Presented at the XXVIII Colloquium Spectroscopium Internationale (CSI) York UK June 29-July 4 1993.Journal of Analytical Atomic Spectrometry by using the simultaneously recorded spectral neighbourhood of the absorption line for correction. In order to observe the temporal formation of absorption signals we measured sequences of 20 to 50 flashes at a repetition rate of about 10 Hz. EXPERIMENTAL Our FLACAAS device (Fig. 1) consists of the following compo- nents which were developed and built in our laboratory unless otherwise stated power supply and ignition triggering unit for the Xe-flas hlamp; Xe-flas hlamp modified for end-on o bser- vation (type QXA 18 Q-ARC Cambridge UK); AAS graphite furnace atomizer and autosampler (AAS-3 with EA-3 Carl Zeiss Jena); echelle spectrometer in tetrahedral mounting; linear-array charge-coupled device (CCD) detector 5 12 pixel pixel size 23 pnx480 pm (CCD L 172 Werk fur Fernschelektronic Berlin Germany); and computer-aided CCD controller.An Cchelle grating (75 grooves mm-' blaze angle 64") and a quartz prism (suprasil prism angle 25") are mounted within the Cchelle spectrometer in such a way that the directions of dispersion are standing perpendicular to each other. The resulting two-dimensional spectrum is focused by a spherical mirror (focal length 500 mm focal ratio f/5) into a focal area with a size of about 60 mm x 60 mm. The spectrum consists of 97 spectral orders (850 nm corresponds to order number 28 190nm corresponds to order number 125) where the length of the orders is varying with the wavelength (from 14mm to 64mm) and the width of the orders is determined by the slit height of the entrance slit (slit height 0.2 mm slit width 0.02mm).To record a selected partial spectrum the linear- array CCD detector is moved to the corresponding spectral position in the focal area by a suitable mechanical device. This way we are able to achieve sequential measurements of different elements. These measurements could also be performed simul- taneously if such a large area CCD image detector for the recording of the whole spectrum was available. As an example of the necessity for effective background correction we measured thallium in the presence of a high concentration of palladium. When measuring thallium and palladium at 276.787 and 276.309 nm respectively the CCD array covers a 1.74nm wide partial spectrum in the 87th Cchelle order resulting in a spectral bandwidth per pixel of about 3.3pm.The atomization step of the graphite furnace atomizer triggers the flash lamp to operate at lOHz with a partial spectrum recorded for each flash. RESULTS The partial spectra of the individual flashes keep their spectral shape within a spectral range as small as 1.74nm in spite of the fact that their intensities change from flash to flash. Therefore the spectra can be made practically congruent by multiplication with a numerical factor which depends on the actual flash intensity. Thus it is possible to correct for the flash-to-flash intensity variations as well as the differences of Journal of Analytical Atomic Spectrometry January 1995 Vol.10 61/ / Capacitor charging supply . and trigger - J I Xenon flashlamp polychromator CCD linear array 1 furnace monochromator Hollow cathode lamp I Temperature controller Fig. 1 Scheme of the FLACAAS device used in connection with the AAS-3 spectrometer sensitivity of the individual pixels of the array. These correc- /T--. tions are carried out by use of the average of the first 12 spectra measured before the absorption appears thus obtaining the so called intensity corrected absorption spectra shown in Fig. 2. Finally the absorbance spectra are baseline corrected by using the mean value of the spectral absorbance within intervals at both sides of the analytical line. These intervals have a width of 33 pm (10 pixels) and are located at a distance of 17 pm ( 5 pixels) from the line centre.The residual fluctu- ations of the absorbance spectra are predominantly due to shot noise as can be clearly seen from the averaged spectra in Fig. 3. Fig. 2 Intensity corrected absorption spectra for the determination of T1 in natural seawater diluted in de-ionized water by a factor of 20 and with 20 pg Pd as modifier time sequence of 34 partial spectra recorded with a repetition rate of 10Hz; and wavelength section of the recorded partial spectra (pixel range No. 101-412 wavelength range 276.085-277.155 nm respectively; spectral bandwidth 3.3 pm per pixel; pixel No. 166 Pd 276.309 nm; pixel No. 310 T1 276.787 nm) 8 N a N Fig. 3 Baseline corrected absorbance spectra in the spectral vicinity of T1 276.787 nm time sequence of 19 partial spectra recorded with a repetition rate of 10 Hz; wavelength section of the recorded partial spectra (pixel range No.290-330; spectral bandwidth 3.3 pm per pixel; and sample 20 pl of 1 + 19 diluted seawater (salinity 0.18%) prepared by adding T1 standard for a 4pg 1-' concentration with 20pg Pd as modifier. (a) Single sample and (b) average from a series of 9 equivalent samples 62 Journal of Analytical Atomic Spectrometry January 1995 Vol. 100.10 3.3 / .3 3.3 Fig. 4 Baseline corrected absorbance spectra for different T1 concen- trations in the vicinity of T1 276.787 nm time sequence of 34 partial spectra recorded with a repetition rate of 10 Hz; wavelength section of the recorded partial spectra (pixel range No. 290-330; spectral bandwidth 3.3 pm per pixel); and sample 20 pl of 1 + 19 diluted sea- water (salinity 0.18%) prepared by adding T1 standards with 20 pg Pd as modifier.TI concentrations (a) 5 (b) 15 and (c) 25 pg 1-' In order to prove the effectiveness of the background correction we determined thallium in natural seawater the salinity of which was 3.5%. The seawater was diluted by a factor of 20 in deionized water and from this solution samples with different thallium concentrations were prepared by adding suitable thallium standards. A 20 pl portion of Pd (NO,) (Merck Ultrapure) Solution (1 g 1-l in 3% HNO,) equivalent 0- 5 10 15 20 25 30 Con cent ra t ion/pg I - ' Fig. 5 Calibration curve for T1 in diluted seawater using standard additions sample 20 pl of 1 + 19 diluted seawater (salinity 0.18%) prepared by adding T1 standard with 20 pg Pd as modifier.Absorbance data are temporal peak heights recorded by the pixel at the centre of T1 276.787 nm absorption line to 20 pg of Palladium was used as modifier and added to 20 pl of sample seawater in the furnace for thermal stabilization of thallium. The whole sample was dried ( 100°C 40 s) ashed (9OO0C 15 s) and atomized (full power 2700 "C 2 s) in the conventional way. In Figs. 2 and 4 the intensity corrected and baseline corrected absorption spectra of thallium are shown in the presence of the strong absorption of the neighbouring palladium line. From the calibration curve in Fig. 5 the characteristic mass of 28 pg/0.0044 A was determined. For comparison the characteristic mass for the determination of thallium for a commercial line source ETAAS spectrometer with wall atomization (Perkin Elmer HGA 6000) is given as 15 pg/0.0044 A. The calculation of the detection limit is based on the spectral noise of the absorbance spectra in the vicinity of the absorption line which is comparable to the time dependent baseline noise of the line source AAS if the used spectral vicinity is free from structured background absorption.The used vicinity around the thallium line includes 133 pm (40 pixel) with the exception of the central range of 56pm (17 pixel). Taking 3 times the standard deviation of the spectral absorbance in the vicinity of the absorption line the detection limit of thallium was determined to be 20pg absolute and 20 pg 1-1 for the determination of thallium in seawater.CONCLUSIONS The baseline corrected absorbance spectra shown in Fig. 3 and Fig. 4 as well as the calibration curve in Fig. 5 demonstrate that time-resolved continuum AAS can successfully be employed for sensitive analysis of complex samples. In spite of their intensity fluctuations flashlamps can be used provided the spectral vicinity of an absorption line is included in the evaluation. Further studies are being carried out comparing FLACAAS background correction with other methods. The authors wish to thank Dr T. Florek for his help in the evaluation and presentation of the spectra. The financial support by the Senatsverwaltung fur Wissenschaft und Forschung des Landes Berlin and the Bundesministerium fur Forschung und Technologie is gratefully acknowledged. REFERENCES 1 2 O'Haver T. C and Messmann J. D. Prog. anal. Spectrosc. 1986 9 483. Moulton G. P O'Haver T. C and Hardy J. M. J. Anal. At. Spectrom. 1990 5 145. Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 633 Jones B. T. Mignardi M. A. Smith B. W. and Winfordner J. D. 4 Schmidt K. P. Becker-Ross H. and Florek S. Spectrochim. Acta Part B 1990 45 1203. 5 Becker-Ross H. Florek S. and Schmidt K. P. in 6. CAS 1991 ed. Welz B. Bodenseewerk Perkin-Elmer fiberlingen 1991 6 Gavrilov V. E and Gavrilova T. V. Opt. Spektrosk. 1991,70,511. Paper 4/05 389C Received September 5 1994 Accepted October 17 1994 J. Anal. At Spectrom. 1989 4 647. pp. 497-504. 64 Journal of Analytical Atomic Spectrometry January 1995 Kd. 10

ISSN:0267-9477    

DOI:10.1039/JA9951000061

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

Arruda Marco A. Z. 55 Becker-Ross Helmut 61 Bulska Ewa 49 Caruso Joseph A. 7 Ebihara Mitsuru 25 Florek Stefan 61 Furuta Naoki 25 Gallego Mercedes 55 JANUARY 1995 Gomez John 15 Hayashi Yasuhisa 37 Huang Meng-Fen 31 Hwang Chorng-Jev 3 1 Imai Shoji 37 Jackson Kenneth W. 43 Jedral Wojciech 49 Jiang Shiuh-Jen 31 Mahmood Tariq M. 43 Marawi Isam 7 Miyazaki Akira 1 Okuhara Kyoichi 37 Olson Lisa K. 7 Qiao Huancheng 43 Roehl Raimund 15 Saito Kengo 37 Schmecher Gisela R. 61 Tanaka Toshiyuki 37 Tao Hiroaki 1 Tischendorf Reinhard 61 Uchino Tomonori 25 Valcarcel Miguel 55 Wang Jiansheng 7 Woodhouse Leslie R. 15 Journal of Analytical Atomic Spectrometry January 1995 Vol. 10 65

ISSN:0267-9477    

DOI:10.1039/JA9951000065

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY INSTRUCTIONS TO AUTHORS The Journal of Analytical Atomic Spectrometry (JAAS) is an international journal for the publication of original research papers communications and letters concerned with the development and analytical application of atomic spectro- metric techniques. The journal is published monthly and also includes compre- hensive reviews on specific topics of interest to practising atomic spectroscopists and incorporates the literature reviews which were previously published in Annual Reports on Analytical Atomic Spectroscopy (ARAAS). Additional Special Conference Issues are also published. Manuscripts intended for publication as papers or communications must describe original work related to atomic spectrometric analysis. Papers on all aspects of the subject will be accepted including fundamental studies novel instrument developments and practical analytical applications. As well as atomic absorption atomic emission and atomic fluorescence spectrometry papers will be welcomed on atomic mass spectrometry X-ray fluorescence/emission spec- trometry and secondary emission spectrometry.Papers describing the rneasure- ment of molecular species where these relate to the characterization of sources normally used for the production of atoms or concerning for example indirect methods of analyses will also be acceptable for publication. Papers describing the development and applications of hybrid techniques involving atomic spec- trometry (e.g. GC coupled AAS and HPLC-ICP) will be particularly welcome.Manuscripts on other subjects of direct interest to atomic spectroscopists including sample preparation and dissolution and analyte preconcentration procedures as well as the statistical interpretation and use of atomic spectro- metric data will also be acceptable for publication. Although short articles are acceptable the Society strongly discourages fragmentation of a substantial body of work into a number of short publications. Unnecessary fragmentation will be a valid reason for rejection of manuscripts. There is no page charge for papers published in JAAS. The following types of papers will be considered. Original research papers. Communications which must be on an urgent matter and be of obvious scientific importance. Rapidity of publication is enhanced if diagrams are omitted but tables and formulae may be included.Communications receive priority and are usually published within 2-3 months of receipt. They are intended for brief descriptions of work that has progressed to a stage at which it is likely to be valuable to workers faced with similar problems. A fuller paper may be offered subsequently if justified by later work. Although publication is at the discretion of the Editor communications will be examined by at least one referee. Reviews which must be a critical evaluation of the existing state of knowledge on a particular facet of analytical chemistry. However original work may be included. Simple literature surveys will not be accepted for publication. It is desirable that potential review writers should contact the Editor before embarking on their work.Copyright. The whole of the literary matter (including tables figures diagrams and photographs) in JAAS is Royal Society of Chemistry copyright and may not be reproduced without permission from the Society or such other owner of the copyright as may be indicated. Papers that are accepted must not be published elsewbere except by permission. Submission of a manuscript will be regarded as an undertaking that the same material is not being considered for publication by another journal in any language. All authors submitting work for publication are required to sign an exclusive copyright licence. All submissions should be accompanied by a completed form (a blank for photocopying is reproduced at the end of these instructions) without which publication cannot proceed.US Associate Editor. Papers from North America can be submitted to Dr. J. M. Hardy US Department of Agriculture Beltsville Human Nutrition Research Center BLDG 161 BARC-EAST Beltsville MD 20705 USA. Manuscripts. Papers should be typewritten in double spacing on one side only of the paper. Copies of any related relevant unpublished material and raw data should be made available on request. Each table and illustration should be on a separate sheet at the end of the text; three copies of text and illustrations should be sent to the Editor JAAS "be Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB44WF or directly to the US Associate Editor and a further copy retained by the author.Administration and Publication Procedure. Receipt of a contribution for consideration will be acknowledged immediately by the Editorial Office. The acknowledgement will indicate the paper reference number assigned to the contribution. Authors are particularly asked to quote this number on all subsequent correspondence. All papers (including conference presentations submitted for special issues) are sent simultaneously to at least two referees whose names are not disclosed to the authors. On the basis of the referees' reports the Editor decides whether the paper is suitable for publication either unchanged or after appropriate revision. This decision and relevant comments of the referees are communicated to the author. Differences of opinion are mediated by the Editor possibly after consultation with further referees or in the last resort by the Editorial Board. When rejection of a paper is recommended the Editor informs the author and returns the top copy of the manuscript.Authors have the right to appeal to the Editorial Board if they regard a decision to reject as unfair. Authors will receive formal notification when papers are accepted for publication. Proofs. The address to which proofs are to be sent should accompany the paper. Proofs should be carefully checked and returned immediately (by first class mail air mail express mail or fax). Particular attention should be paid to numerical data both in the tables and text. Offprints. Fifty offprints of each paper are supplied free. Notes on the Writing of Papers for JAAS Manuscripts should be in accordance with the style and usage shown in recent copies of JAAS.Conciseness of expression is expected clarity is increased by adopting a logical order of presentation with suitable paragraph or section headings. Spellings should be in accordance with the Oxford English Dictionary. To facilitate abstracting and indexing by Chemical Abstracts Service and other abstracting organizations it would be helpful if at least one forename could be included with each author's family name. The corresponding author should be clearly indicated. accuracy precision and selectivity. Descriptions of methods should be supported by experimental results showing The recommended order of presentation is as indicated below (a) Title. This should be as brief as is consistent with an adequate indication of the original features of the work.The title should usually include the analyte being determined or identified the matrix and the analytical method used. (b) Summary. A summary of about 250 words giving the salient features and drawing attention to the novel aspects should be provided for all papers. It should be essentially independent of the main text and include relevant quantitative information such as detection limits precision and accuracy data. (c) Keywords. Up to five keywords or key phrases indicating the topics of importance in the work described should be included after the summary. ( d ) Aim of investigation. A concise introductory statement of the novel features of the work and the object of the investigation with any essential historical background followed if necessary by a brief account of preliminary experimental work with relevant references.Description of the experimental procedures. Working details must be given concisely. Analytical procedures should be given in the form of instructions; we1 known operations should not be described in detail. Suppliers of equipment and materials and their locations should be mentioned. 67(A Results and Discussion Results are best presented in tabular or diagram- matic form (but not both for the same results) followed by an appropriate statistical evaluation which should be in accordance with accepted practice. For example a new procedure for multi-element determinations which produced results for which the concentration of 8 out of 10 of the elements determined in a standard reference material were statistically indistinguish- able from the certificate values should be described in those terms and not referred to as ‘excellent agreement’.This is particularly important in the summary. Any discussion should comment on the scope of the method and its validity followed by a statement of any conclusions drawn from the work. A separate conclusions section is not encouraged but if included it should not simply duplicate statements in the discussion. ( g ) Acknowledgements. Contributions other than co-authors companies or sponsors may be acknowledged in a separate paragraph at the end of the paper. Titles may be given but not degrees. (h) References. References should be numbered serially in the text by means of superscript figures e.g.Foote and Delves,’ Burns et al? or .... in a recent - - - paper ...3 and collected in numerical order under ‘References’ at the end of the paper. They should be listed with all the authors’ names and initials in the following form (double-spaced typing) Yerian T. D. Christian G. D. and REiEka J. Analyst 1986 111 865. Sharp B. L. Barnett N. W. Burridge J. C. Littlejohn D. and Tyson J. F. J. Anal. At. Spectrom. 1988 3 133R. Committee for Analytical Methods for Residues of Pesticides and Veterinary Products in Foodstuffs and the Working Party on Pesticide Residues of the Ministry of Agriculture Fisheries and Food Analyst 1985 110 765. Hara H. Horva G. and Pungor E. Analyst 1988,113 1817; Anal.Abstr. 1989,51 6H57. Norwitz G. and Keliher P. N. Analyst 1987 112 903 (and references cited therein). L‘vov B. V. Polzik L. K. Romanova N. P. and Yuzeforsku A. I. J. Anal. At. Spectrom. in the press. OConnor A. Sigma St. Louis MO personal communications 1989. Appelqvist R. Ph.D. Thesis University of Lund Sweden 1987. Journal titles should be abbreviated according to the Chemical Abstracts Service Source Index (CASSI). The abbreviation for this journal is J. Anal. At. Spectrom. For books the edition (if not the first) the publisher and the place and date of publication should be given followed by the page number. 1 Harrison W. W. and Donohue D. L. in Treatise on Analytical Chemistry eds. Kolkhoff I. M. and Winefordner J. D. Wiley New York 2nd edn. British Pharmacopoeia 1988 HM Stationery Office London 1988 vol.1 RMiEka J. and Hansen E. H. Flow Injection Analysis 2nd edn. Wiley New York 1988 pp. 299-304. Moody G. J. and Thomas J. D. R. in Ion Selective Electrodes in Analytical Chemistry ed. Freiser H. Plenum New York 1978 ch. 4. Beauchemin D. and Craig J. M. in Plasma Source Mass Spectrometry. The Proceedings of the Third Surrey Conference on Plasma Source Mass Spectrometry University of Surrey July 16th-l9th 1989 eds. Jarvis K. E. Gray A. L. Jarvis I and Williams J. G. The Royal Society of Chemistry Cambridge 1990 pp. 25-42. OfJicial Methods of Analysis of the Association of OfJicial Analytical Chemists ed. Horwitz W. Association of Official Analytical Chemists Arlington VA 13th edn. 180 sect. 20.104. 1989 pt.1 VO~. 11 ch. 3. pp. 189-235. 2 3 4 5 p. 140. 6 Authors must in their own interest check the lists of references against the original papers; second-hand references are a frequent source of error. References to conference abstracts which have not been published in the open literature are not acceptable. The number of references must be kept to a minimum. Nomenclature. Current internationally recognized (IUPAC) chemical nomenclature should be used. Common trivial names may be used but should first be defined in terms of IUPAC nomenclature. A listing of all relevant IUPAC nomenclature publications appears in the February issue. Symbols and units. The SI system of units as recommended by IUPAC should be followed. Their basis is the ‘Systkme Internationale d‘Unitts’ (SI).A detailed treatment is given in the ‘Green Book’ Quantities Units and Symbols in Physical Chemistry (Blackwell Oxford 1988 edn.). The following will be the guidelines used (a) A metric system will always be used in preference to a non-metric one. (b) SI will be the standard usage. (c) The units used to record the definitive values of ‘critical data’ or quantities measured to a high degree of accuracy will be SI. These units are summarized in the Appendix. The effect on current style of papers for JAAS includes the following (a) dimensions should preferably be given in metres (m) or in millimetres (b) temperatures should be expressed in K or ‘c (not OF); (c) wavelengths should be expressed in nanometres (nm) not mp; (d) frequency should be expressed in Hz (or kHz etc.) not in c/s or c.P.s.; rotational frequency can be denoted by use of s-’; in mass spectrometry signal intensity should be expressed in counts s-’ and not in Hz; (mm); (e) radionuclide activity should be expressed in becquerels (Bq); (f) the micron (p) will not be used; will be 1 pm.When non-SI units are used they must be adequately explained unless their definition is obvious (e.g. “C and A). The derivation of derived non-SI units should be indicated. Abbreviations. Abbreviational full stops are omitted after the common contrac- tions of metric units (e.g. ml g pg mm) and other units represented by symbols. Abbreviations other than those of recognized units should be avoided in the text except after definition. Upper case letters without points should be used for abbreviations for techniques and associated terms subsequent to definition e.g.HPLC AAS XRF UV NMR SCE. The abbreviations Me Et Pr“ Bun Bu’ Bu‘ Bus Ph Ac Alk Ar and Hal can be used; others should be defined. Substituents should be indicated by R (one) or by R’ R2 R3 .. . (more than one). Percentage concentrations of solutions should be stated in internationally recognized terms. Thus the symbols ‘m’ instead of ‘w’ for mass and ‘v’ for volume are to be used. The following show the manner of expressing these percentages together with an acceptable alternative given in parentheses YO m/m (g per 100 g); YO m/v (g per 100ml); YO v/v. Further implications of the use of the term ‘mass’ are that ‘relative atomic mass’ of an element (A,) replaces atomic weight and ‘relative molecular mass’ of a substance (M,) replaces molecular weight.Concentrations of solutions of the common acids are often conveniently given as dilutions of the concentrated acids such as ‘dilute hydrochloric (1 + 4)’ which signifies 1 volume of the concentrated acid mixed with 4 volumes of water. This avoids the ambiguity of 1 4 which might represent either 1 + 4 or 1 + 3. Dilutions of other solutions should be expressed in a similar manner. Molarity is generally expressed as a decimal fraction (e.g. 0.375 mol dm-3). Tables and diagrams. Table column headings should be brief. Tables consisting of only two columns can often be arranged horizontally. Tables must be supplied with titles and be so set out as to be understandable without reference to the text.Either tables or graphs may be used but not both for the same set of results unless important additional information is given by so doing. The information given by a straight-line calibration graph can usually be conveyed adequately as an equation or statement in the text Column headings and graph axis labels should be in accord with SI conven- tions. Thus the expression of numerical values of a physical quantity should be dimensionless i.e. the quotient of the symbol for the physical quantity and the symbol for the unit used e.g. p/Pa or some mathematical function of a number e.g. In (p/Pa). Further examples are v/cm-’ I/cm mass of substance/g and flow rate/ml min-’. For units which are already dimensionless i.e. ratios such as % or ppm the type of ratio is indicated in parentheses e.g.e (YO) or e (ppm). The diagonal line (solidus) will not be used to represent ‘per’. In accordance with the SI system units such as grams per millilitre are already expressed in the form g ml-’. It should be noted that the ‘combined’ unit g ml-’ must not have any ‘intrusive’ numbers. To express concentration in grams per 100 millilitres the word ‘per’ will still be required Concentration/g per 100 ml. It may be preferable for an author to express concentrations in grams per litre (g I-’) rather than grams per 100 ml. Diagrams will be retraced and lettered if necessary in order to achieve uniform line thickness and lettering size and style. However all diagrams should be carefully and clearly drawn on good quality paper and should be carefully and clearly lettered.If possible chromatograms and spectra complicated flow charts circuit diagrams etc. should be supplied as artwork for direct reproduction in order to avoid time-consuming and expensive redrawing. The clearest copy should be without lettering.Three complete sets of illustrations should be provided two sets of which may be made by any convenient copying process for transmission to the referees. Photographs. Photographs can be submitted if they convey essential infor- mation that cannot be shown in any other way. They should be submitted as glossy or matt prints made to give the maximum detail. Colour photographs All diagrams should be accompanied by a separately typed set of captions. be accepted Only when a photograph to show Some Wherever possible extensive identifying lettering should be placed in the caption rather than on lines on graphs etc.feature and can be either as prints Or transparencies. Appendix I The SI System of Units In the SI system there are seven base units- Physical quantity length mass time electric current thermodynamic temperature amount of substance luminous intensity Symbol for Name Symbol quantity of unit for unit 1 metre m kilogram t second I ampere T kelvin n mole I candela m kg A K mol cd S There are two supplementary dimensionless units for plane angle (radian rad) and solid angle (steradian sr). Some derived SI units that have special names are as follows- Name Physical of unit frequency force pressure stress energy work heat power electric charge electric potential electric capacitance electric resistance electric conductance magnetic flux magnetic flux density inductance Celcius temperature plane anle solid angle hertz newton pascal joule watt coulomb volt farad ohm siemens weber tesla henry degree Celcius radian steradian Examples of other derived SI units with no special names or symbols are- Physical quantity area volume density velocity angular velocity acceleration pressure kinematic viscosity diffusion coefficient dynamic viscosity electric field strength magnetic field strength luminance Symbol for unit Hz N Pa J W C V F !a2 S Wb T H "C rad sr SI unit square metre cubic metre kilogram per cubic metre metre per second radian per second metre per second squared newton per square metre square metre per second newton second per square metre Certain units will be allowed in conjunction with the SI system e.g.- volt per metre ampere per metre candela per square metre Physical quantity Name of unit time plane angle volume magnetic flux density (magnetic induction) temperature t energy pressure mass minute degree litre gauss degree Celsius electronvolt bar unified atomic mass unit Symbol for unit min 1 G "C eV bar 0 U Symbol for SI unit m2 m3 k m-3 m s-l rad s-' m s - ~ N m-2 m2 s-' N s m-2 V rn-l A rn-l cd rn-' Dejinition of unit 60s (n/180) rad lo-' m3=dm3 10-4 T t / T = T/K - 273.16 1.6021 x lo-'' J lo5 Pa 1.660 54 x kgThe other common units of time (e.g.hour and day) will continue to be used in appropriate contexts. Decimal multiples and submultiples have the following names and symbcds (for use as prefixes)- 10-3 milli m 103 kilo k 10-9 nano n 109 gisa G micro P lo6 mega M 10l2 pic0 P 10l2 tera T 1015 femto f 1015 peta P lo2' zepto z I d ' zetta Z 1024 yocto Y 1024 yotta Y 1 0I8 atto a 1 oI8 exa E Compound prefixes (e.g.mpm) should not be used; lo-' m= 1 nm. Appendix II Abbreviations Whenever suitable elements may be referred to by their chemical symbols and compounds by their formulae. the first place of mention. The following abbreviations will be used extensively in the Atomic Spectrometry Updates and may be used in original papers provided that they are defined at a.c. AA AAS AE AES AF AFS AOAC APDC ASV CCP CMP CRM cw dc DCP DDDC DMF DNA EDL EDTA EDXRF EIE EPMA ETA ETAAS ETV EXAFS FAAS FAB FAES FAFS FI FPD FT FTMS GC GD GDL GDMS Ge( Li) HCL hf HG HPGe HPLC IAEA IBMK ICP ICP-MS IR IUPAC alternating current atomic absorption atomic absorption spectrometry atomic emission atomic emission spectrometry atomic fluoresence atomic fluoresence spectrometry Association of Official Analytical Chemists ammonium pyrrolidinedithiocarbamate (ammonium pyrrolidin- 1 -yl anodic-stripping voltammetry capacitively coupled plasma capacitively coupled microwave plasma certified reference material continuous wave direct current d.c.plasma diammonium diethyldithiocarbamate N N-dimethylformamide deoxyribonucleic acid electrodeless discharge lamp ethylenediaminetetraacetic acid energy dispersive X-ray fluorescence easily ionizable element electron probe microanalysis electrothermal atomization electrothermal atomic absorption spectrometry electrothermal vaporization extended X-ray absorption fine structure spectroscopy flame AAS fast atom bombardment flame AES flame AFS flow injection Flame photometric detector Fourier transform Fourier transform mass spectrometry gas chromatography glow discharge glow discharge lamp glow discharge mass spectrometry lithium-drifted germanium hollow cathode lamp high frequency hydride generation high-purity germanium high-performance liquid chromatography International Atomic Energy Agency isobutyl methyl ketone (4-methylpentan-2-one) inductively coupled plasma inductively coupled plasma mass spectrometry infrared International Union of Pure and Applied Chemistry dithioformate) LA LC LEAFS LEI LMMS LOD LTE MECA MIP MS NAA NaDDC NIES NIST NTA OES PIGE PIXE PMT PPm PTFE QC rf REE(s) RIMS RM RSD SEC SEM SFC Si ( Li) SIMAAC SIMS SR SRM SSMS STPF TCA TIMS TLC TOP0 TXRF uhf uv VDU vuv WDXRF XRF PPb SIB S/N laser ablation liquid chromatography laser-excited fluorescence spectrometry laser-enhanced ionization laser microprobe mass spectrometry limit of detection local thermal equilibrium molecular emission cavity analysis microwave-induced plasma mass spectrometry neutron activation analysis sodium diethylidithiocarbamate National Institute for Environmental Studies National Institute of Standards and Technology nitrilotriacetic acid optical emission spectrometry particle-induced gamma-ray emission particle-induced X-ray emission photomultiplier tube parts per billion parts per million polytetrafluoroethylene quality control radiofrequency rare earth element(s) resonance ionization mass spectrometry reference material relative standard deviation signal to background ratio size-exclusion chromatography scanning electron microscopy supercritical fluid chromatography lithium-drifted silicon simultaneous multi-element analysis with a continuum source secondary ion mass spectrometry signal to noise ratio synchrotron radiation Standard Reference Material spark source mass spectrometry stabilized temperature platform furnace trichloroacetic acid thermal ionization mass spectrometry thin-layer chromatography trioctylphosphine oxide total reflection X-ray fluorescence ultra-high-frequency ultraviolet visual display unit vacuum ultraviolet wavelength dispersive X-ray fluorescence X-ray fluorescence The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge UK CB44WF.Telephone +44 (0) 1223 420066; Fax +44 (0) 1223 420247; Internet RSC I @ RSC.ORG

ISSN:0267-9477    

DOI:10.1039/JA9951000067

出版商:RSC    

年代:1995

数据来源: RSC

摘要:

INSTRUCTIONS FOR AUTHORS (1 995) APPENDIX 111 IUPAC Publications on Nomenclature and Symbolism 1 .O Compilations 1.1 Nomenclature of Organic Chemistry a 550-page hardcover volume published in 1979 available from Pergamon Oxford. Section A Hydrocarbons Section B Fundamental heterocyclic systems Section C Characteristic groups containing carbon hy- drogen oxygen nitrogen halogen sulfur selenium and tellurium Section D Organic compounds containing elements not exclusively those referred to in the title of Section C Section E Stereochemistry Section F General principles for the naming of natural products and related compounds Section H Isotopically modified compounds 1.2 A Guide to IUPAC Nomenclature of Organic Compounds a 182-page hardcover volume published in 1993 available from Blackwell Scientific Publications Oxford to be used in conjunction with item 1.1.1.3 Nomenclature of Inorganic Chemistry a 278-page hardcover volume published in 1990 available from Blackwell Scientific Publications Oxford. Chapter 1 General aims functions and methods Chapter 2 Grammar Chapter 3 Elements atoms and groups Chapter 4 Formulae Chapter 5 Names based on stoichiometry Chapter 6 Neutral molecular compounds Chapter 7 Names for ions substituent groups and radicals and salts Chapter 8 Oxoacids and derived anions Chapter 9 Co-ordination compounds Chapter 10 Boron hydrides and related compounds 1.4 Biochemical Nomenclature and Related Documents a 348-page softcover manual published in 1992 by Portland Press Ltd. for IUBMB and available from the publisher (59 Portland Place London W1N 3AJ UK).The contents are as follows Nomenclature of organic chemistry. Section E Stereo- chemistry (1974) Nomenclature of organic chemistry. Section F Natural products and related compounds (1 976) Isotopically modified compounds Recommendations for the presentation of thermodynamic and related data in biology (1985) Citation of bibliographic references in biochemical journals (1 97 1) Nomenclature and symbolism for amino acids and peptides ( 1983) Abbreviated nomenclature of synthetic polypeptides or polymerized amino acids (1 97 1) Abbreviations and symbols for the description of the conformation of polypeptide chains (1 969) Nomenclature of peptide hormones (1 974) Nomenclature of glycoproteins glycopeptides and peptidoglycans (1985) Nomenclature of initiation elongation and termination factors for translation in eukaryotes (1 988) Nomenclature of multiple forms of enzymes (1976) Symbolism and terminology in enzyme kinetics (198 1) Nomenclature for multienzymes (1989) Abbreviations and symbols for nucleic acids poly- nucleotides and their constituents (1970) Abbreviations and symbols for the description of the conformations of polynucleotide chains (1 982) Nomenclature for incompletely specified bases in nucleic acid sequences (1 984) Carbohydrate nomenclature.Part I (1969) Nomenclature of cyclitols (1973) Numbering of atoms in myo-inositol(1988) Conformational nomenclature for five- and six-membered ring forms of monosaccharides and their derivatives (1980) Nomenclature of unsaturated monosaccharides (1 980) Nomenclature of branched-chain monosaccharides ( 1980) Abbreviated terminology of oligosaccharide chains (1 980) Polysaccharide nomenclature (1 980) Symbols for specifying the conformation of polysaccharide chains (1 98 1) Nomenclature of lipids (1 976) Nomenclature of steroids (1 989) Nomenclature of quinones with isoprenoid side chains (1 973) Nomenclature of carotenoids (1970) and amendments (1 974) Nomenclature of tocopherols and related compounds (1981) Nomenclature of vitamin D (1 98 1) Nomenclature of retinoids (1981) Prenol nomenclature (1986) Nomenclature of phosphorus-containing compounds of biochemical importance ( 1976) Nomenclature and symbols for folic acids and related compounds (1 986) Nomenclature for vitamins B-6 and related compounds (1 973) Nomenclature of corrinoids (1 973) Nomenclature of tetrapyrroles (1 986) 1.5 Compendium of Analytical Nomenclature a 280-page hardcover volume published in 1987 available from Blackwell Scientific Publications Oxford The contents are as follows Presentation of the Results of Chemical Analysis Solution Thermodynamics (activity coefficients equilibria Recommendations for Terminology to be used with Precision Balances Recommendations for Nomenclature of Thermal Analysis Recommendations for Nomenclature of Titrimetric Analysis Electrochemical Analysis Analytical Separation Processes (precipitation liquid- liquid distribution zone melting and fractional crystallis- ation chromatography ion exchange) Spectrochemical Analysis (radiation sources general atomic emission spectroscopy flame spectroscopy X-ray emission spectroscopy molecular methods) Recommendations for Nomenclature of Mass Spec- trometry Recommendations for Nomenclature of Radiochemical Methods Surface Analysis (including photoelectron spectroscopy) PH)INSTRUCTIONS FOR AUTHORS (1 995) 1.6 Compendium of Macromolecular Nomenclature a 172-page hardcover volume published in 199 1 available from Blackwell Scientific Publications Oxford.The contents are as follows Basic Definitions of Terms Relating to Polymers Stereochemical Definitions and Notations Relating to Polymers Definitions of Terms Relating to Individual Macromolecules their Assemblies and Dilute Polymer Solutions Definitions of Terms Relating to Crystalline Polymers Nomenclature of Regular Single-strand Organic Polymers Nomenclature for Regular Single-strand and Quasi-single- strand Inorganic and Coordination Polymers Source-based Nomenclature for Copolymers A Classification of Linear Single-strand Polymers Use of Abbreviations for Names of Polymeric Substances 1.7 Compendium of Chemical Terminology IUPAC Recommendations a 456-page volume published in 1987 available in hardcover and softcover from Blackwell Scientific Publications Oxford.1.8 Quantities Units and Symbols in Physical Chemistry a 166-page softcover volume published in 1993 by Blackwell Scientific Publications Oxford. 2.0 Documents not included in the compil- ations 2.1 Boron Compounds Nomenclature of inorganic boron compounds (Pure Appl. Chem. 1972,30,681). Delta Convention Nomenclature for cyclic organic compounds with contiguous formal double bonds (Pure Appl.Chem. 1988,60,1395). Recommendations for the names of elements of atomic number greater than 100 (Pure Appl. Chem. 1979,51 381). Enzyme Nomenclature (1992) published by Academic Press in hardcover and softcover editions. Revision of the extended Hantzsch-Widman system of nomenclature for heteromonocycles (Pure Appl. Chem. 1983 55,409). Names for hydrogen atoms ions and groups and for reactions involving them (Pure Appl. Chem. 1988,60 11 15). Nomenclature of inorganic chemistry. Part 11. 1. Isotopically modified compounds (Pure Appl. Chem. 1981,53 1887). Treatment of variable valence in organic nomenclature (Pure Appl. Chem. 1984,56,769). Nomenclature of hydrides of nitrogen and derived cations anions and ligands (Pure Appl. Chem.1982,54,2545). Extension of Rules A-1.1 and A-2.5 concerning numerical terms used in organic chemical nomenclature (Pure Appl. Chem. 1986,58 1693). Nomenclature of polyanions (Pure A&. Chem. 1987,59,1529). Nomenclature of regular double-strand (ladder and spiro) organic polymers (Pure Appl. Chem. 1993,65 1561). Structure-based nomenclature for irregular single-strand organic polymers (Pure Appl. Chem. 1994,6fi 873). Nomenclature of Elements and Compounds Elements Enzymes Heterocyclic Compounds Hydrogen Isotopically Modijied Compounds Lambda Convention Nitrogen Hydrides Numerical Terms Po lyan ions Polymers Radicals and Ions Revised nomenclature for radicals ions radical ions and related species (Pure Appl.Chem. 1993,65 1357). Chemical nomenclature and formulation of compositions of syntheticandnaturalzeolites(Pure Appl. Chem. 1979,51,1091). Zeolites 2.2 Terminology Symbols and Units and Presentation of Results Glossary of terms used in physical organic chemistry (Pure Appl. Chem. 1994,66 1077). Glossary of atmospheric chemistry terms (Pure Appl. Chem. 1990,62 2167). English-derived abbreviations for experimental techniques in surface science and chemical spectroscopy (Pure Appl. Chem. 1991,63,887). Andy tical Recommendations for publication of papers on a new analytical method based on ion exchange or ion-exchange chromatography (Pure Appl. Chem. 1980,52,2555). Recommendations for presentation of data on compleximetric indicators 1. General (Pure Appl.Chem. l979,51 1357). Recommendations for publishing manuscripts on ion-selective electrodes (Pure Appl. Chem. 1981,53 1907). Recommendations on use of the term amplification reactions (Pure Appl. Chem. 1982,54,2553). Recommendations for the usage of selective selectivity and related terms in analytical chemistry (Pure Appl. Chem. 1983 Nomenclature for automated and mechanised analysis (Pure Appl. Chem. 1989,61 1657). Nomenclature for sampling in analytical chemistry (Pure Appl. Chem. 1990,62 1193). Nomenclature for chromatography (Pure Appl. Chem. 1993 65 819). Nomenclature of kinetic methods of analysis (Pure Appl. Chem. 1993,65 2291). Nomenclature for liquid-liquid distribution (solvent extraction) (Pure Appl. Chem. 1993,65,2373). Nomenclature for supercritical fluid chromatography and {extraction (Pure Appl.Chem. 1993,65,2397). Nomenclature and terminology for analytical pyrolysis (Pure Appl. Chem. 1993,65,2405). Nomenclature for the presentation of results of chemical analysis (Pure Appl. Chem. 1994,66 595). Recommendations for nomenclature in laboratory robotics and automation (Pure Appl. Chem. 1994,66,609). Glossary for chemists of terms used in biotechnology (Pure .4ppl. Chem. 1992,64 143). Selection of terms symbols and units related to microbial processes (Pure Appl. Chem. 1992,64 1047). Physicochemical quantities and units in clinical chemistry with special emphasis on activities and activity coefficients (Pure 44ppl. Chem. 1984,56 567). Quantities and units in clinical chemistry (Pure Appl. Chem. 1979,51,2451).Quantities and units in clinical chemistry nebulizer and flame properties in flame emission and absorption spectrometry (Pure Appl. Chem. 1986,58 1737). List of quantities in clinical chemistry (Pure Appl. Chern. 1979 51,2481). Proposals for the description and measurement of carry-over effects in clinical chemistry (Pure Appl. Chem. 1991,63 301). Quantities and units for metabolic processes as a function of time (Pure Appl. Chem. 1992,64 1569). General 55 553). Biotechnology ClinicalINSTRUCTIONS FOR AUTHORS (1995) Quantities and units for electrophoresis in the clinical laboratory (Pure Appl. Chem. 1994,66,891). Quantities and units for centrifugation in the clinical laboratory (Pure Appl. Chem. 1994,66,897). Definitions terminology and symbols in colloid and surface chemistry.I (Pure Appl. Chem. 1972 31 577). IT Hetero- geneous catalysis (Pure Appl. Chem. 1976 46 71). Part 1.14 Light scattering (provisional) (Pure Appl. Chem. 1983,55,931). Reporting experimental pressure-area data with film balances (Pure Appl. Chem. 1985,57,621). Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Pure Appl. Chem. 1985,57,603). Reporting data on adsorption from solution at the solid/ solution interface (Pure Appl. Chem. 1986 58,967). Manual on catalyst characterization (Pure Appl. Chem. 1991 63 1227). Thin films including layers terminology in relation to their preparation and characterization (Pure Appl. Chem. 1994 66 1667). Nomenclature for transfer phenomena in electrolytic systems (Pure Appl.Chem. 1981,53 1827). Electrode reaction orders transfer coefficients and rate constants-amplification of definitions and recommendations for publication of parameters (Pure Appl. Chem. 1980,52,233). Classification and nomenclature of electroanalytical techniques (Pure Appl. Chem. 1976,45,81). Recommendations for sign conventions and plotting of electrochemical data (Pure Appl. Chem. 1976,45 131). Electrochemical nomenclature (Pure Appl. Chem. 1974,37,499). Recommendations on reporting electrode potentials in non- aqueous solvents (Pure Appl. Chem. 1984,56,461). Definition of pH scales standard reference values measurement of pH and related terminology (Pure Appl. Chem. 1985,57,53 1). Interphases in systems of conducting phases (Pure Appl.Chem. 1986,58 437). The absolute electrode potential an explanatory note (Pure Appl. Chem. 1986,58,955). Electrochemical corrosion nomenclature (Pure Appl. Chem. 1989,61 19). Terminology in semiconductor electrochemistry and photo- electrochemical energy conversion (Pure Appl. Chem. 1991,63 569). Nomenclature symbols definitions and measurements for electrified interfaces in aqueous dispersions of solids (Pure Appl. Chem. 1991,63 895). Nomenclature symbols and definitions in electrochemical engineering (Pure Appl. Chem. 1993,65 1009). Terminology and conventions for microelectronic ion-selective field effect transistor devices in electrochemistry (Pure Appl. Chem. 1994,66 565). Symbolism and terminology in chemical kinetics (provisional) (Pure Appl.Chem. 1981,53,753). Kinetics of composite reactions in closed and open flow systems (Pure Appl. Chem. 1993,65,2641). Recommended standards for reporting photochemical data (Pure Appl. Chem. 1984,56,939). Glossary of terms used in photochemistry (Pure Appl. Chem. 1988,60 1055). Expression of results in quantum chemistry (Pure Appl. Chem. 1978,50,75). Reactions Nomenclature for organic chemical transformations (Pure Appl. Chem. 1989,61,725). Colloids and Surface Chemistry Electrochemistry Kinetics Photochemistry Quantum Chemistry System for symbolic representation of reaction mechanisms (Pure Appl. Chem. 1989,61,23). Detailed linear representation of reaction mechanisms (Pure Appl. Chem. 1989,61 57). Rheological Properties Selected definitions terminology and symbols for rheological properties (Pure Appl.Chem. 1979,51 1215). Recommendations for publication of papers on methods of molecular absorption spectrophotometry in solution (Pure Appl. Chem. 1978,50,237). Recommendations for the presentation of infrared absorption spectra in data collections. A Condensed phases (Pure Appl. Chem. 1978,50,231). Definition and symbolism of molecular force constants (Pure Appl. Chem. 1978,50 1709). Nomenclature and conventions for reporting Mossbauer spectroscopic data (Pure Appl. Chem. 1976,45,211). Recommendations for the presentation of NMR data for publication in chemical journals. A Proton spectra (Pure Appl. Chem. 1972,29,625). B Spectra from nuclei other than protons (Pure Appl. Chem. 1976,45,217). Presentation of Raman spectra in data collections (Pure Appl.Chem. 1981,53 1879). Names symbols definitions and units of quantities in optical spectroscopy (Pure Appl. Chem. 1985,57,105). A descriptive classification of the electron spectroscopies (Pure Appl. Chem. 1987,59 1343). Presentation of molecular parameter values for IR and Raman intensity (Pure Appl. Chem. 1988,60 1385). Recommendations for EPR/ESR nomenclature and conven- tions for presenting experimental data in publications (Pure Appl. Chem. 1989,61,2195). Nomenclature symbols units and their usage in spectro- chemical analysis. VII. Molecular absorption spectroscopy UV and visible (Pure Appl. Chem. 1988 60 1449); VIII. Nomenclature system for X-ray spectroscopy (Pure Appl. Chem. 1991,63,735); X. Preparation of materials for analytical atomic spectroscopy (Pure Appl.Chem. 1988 60 1461); XII. Terms related to electrothermal atomization (Pure Appl. Chem. 1992 64 253); XITI. Terms related to chemical vapour generation (Pure Appl. Chem. 1992,64,261). Recommendations for nomenclature and symbolism for mass spectroscopy (Pure Appl. Chem. 1991,63,1541). Symbols for fine and hyperfine structure parameters (Pure Appl. Chem. 1994,66 571). Definitions of terms relating to phase transitions of the solid state (Pure Appl. Chem. 1994,66 577). A guide to procedures for the publication of thermodynamic data (Pure Appl. Chem. 1972,39 395). Assignment and presentation of uncertainties of the numerical results of thermodynamic measurements (Pure Appl. Chem. 198 1,53 1805). Notation for states and processes; significance of the word ‘standard’ in chemical thermodynamics and remarks on commonly tabulated forms of thermodynamic functions (Pure Appl. Chem. 1982,54 1239). Standard quantities in thermodynamics fugacities activities and equilibrium constants for pure and mixed phases (Pure Appl. Chem. 1994,66 533). Recommendations for nomenclature and tables in biochemical thermodynamics (Pure Appl. Chem. 1994,66,1641). Glossary for chemists of terms used in toxicology (Pure Appl. Chem. 1993,65 2003). Spectroscopy Solid State Thermodynamics Toxicology

ISSN:0267-9477    

DOI:10.1039/JA9951000071

出版商:RSC    

年代:1995

数据来源: RSC