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The AnalystThe Analytical Journal of The Royal Society of ChemistryAdvisory Board*Chairman: J. D. R. Thomas (Cardiff, UK)D. Betteridge (Sunbury-on-Thames, UK)E. Bishop (Exeter, UK)W. L. Budde (USA)*C. Burgess (Ware, UK)D. T. Burns (Belfast, UK)"M. S. Cresser (Aberdeen, UK)L. de Galan (The Netherlands)D. Dyrssen (Sweden)"A. G. Fogg (Loughborough, UK)"C. W. Fuller (Nottingham, UK)V. D. Goldberg (London, UK)J. Hoste (Belgium)A. Hulanicki (Poland)W. S. Lyon (USA)H. V. Malmstadt (USA)"C. J. Jackson (London, UK)"P. M. Maitlis (Sheffield, UK)E. J. Newman (Poole, UK)T. 8. Pierce (Harwell, UK)E. Pungor (Hungary)J. R8iitka (Denmark)P. H. Scholes (Middlesbrough, UK)D. Simpson ( Thorpe-le-Soken, UK)R. M. Smith (Loughborough, UK)W. I.Stephen (Birmingham, UK)M. Stoeppler (Federal Republic of Germany)K. C. Thompson (Sheffield, UK)"A. M. Ure (Aberdeen, UK)A. Walsh, K.B. (Australia)G. Werner (German Democratic Republic)T. S. West (Aberdeen, UK)"P. C. Weston (London, UK)J. D. Winefordner (USA)P. Zuman (USA)"Members of the Board serving on the Analytical Editorial BoardRegional Advisory EditorsFor advice and help to authors outside the UKDr. J. Aggett, Department of Chemistry, University of Auckland, Private Bag, Auckland, NEWDoz. Dr. sc. K. Dittrich, Analytisches Zentrum, Sektion Chemie, Karl-Marx-Universitat, Talstr.Professor L. Gierst, Universite Libre de Bruxelles, Faculte des Sciences, Avenue F.-D.Professor H. M. N. H. Irving, Department of Analytical Science, University of Cape Town,Dr.0. Osibanjo, Department of Chemistry, University of Ibadan, Ibadan, NIGERIA.Dr. G. Rossi, Chemistry Division, Spectroscopy Sector, CEC Joint Research Centre,Dr. 1. RubeSka. Geological Survey of Czechoslovakia, Malostranske 19, 118 21 Prague 1,Professor K. Saito, Coordination Chemistry Laboratories, Institute for Molecular Science,Professor M. Thompson, Department of Chemistry, University of Toronto, 80 St. GeorgeProfessor P. C. 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ISSN:0003-2654    

DOI:10.1039/AN98611FX041

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALAO 111(11) 1225-1352 (1986)The AnalystNovember 198612251231123512391245124912551261126512731281128512891293129713011307131 11317132113251331133513391341The Analytical Journal of The Royal Society of ChemistryCONTENTSTechniques for Evaluating Control of Automated Multi-determinant Analytical Instruments by Computer-Mu rray T.Fisher, Julian Lee, M. Kelly MaraElectrodes in Series. Simultaneous Flow Injection Determination of Chloride and pH with Ion-selective Electrode-Modified Platinum Wire Glucose Oxidase Amperometric ElectrodeG. J. Moody, G. S. Sanghera, J. D. R. ThomasDifferential Pulse Cathodic Stripping Voltammetric Investigation of Cr042-, Mo042-, W042- and VO,--M. Rasul Jan, W.Franklin SmythSensitive Adsorptive Stripping Voltammetric Measurements of Antihypertensive Drugs-Joseph Wang, TimothyTapia, Mojtaba BonakdarSimultaneous Determination of Major and Trace Elements in Urinary Calculi by Microwave-assisted Digestion andlnductively Coupled Plasma Atomic Emission Spectrometric Analysis-Michael Alexander Erich Wandt, MichelAndre Bruno PougnetInductively Coupled Plasma Emission Spectrometric Determination of Boron and Other 0x0-anion Forming Elementsin Geological Materials-Gwendy E.M. Hall, Jean-Claude PelchatExtraction of Iron(lll), Gold(lll), Galliumjlll), Thallium(lll), Antimony(V) and Antimony(ll1) from Hydrochloric AcidSolution with Crown Ethers-Hideko Koshima, Hiroshi OnishiLiquid Chromatographic Procedure for the Separation and Characterisation of Simple Urea - Formaldehyde ReactionProducts-Peter R.Ludlam, James G. King, Robert M. AndersonSelectivity and Efficiency Measurements in High-performance Liquid Chromatography Using Micellar Hexadecyl-trimethylammonium Bromide in the Mobile PhaseFrank G. P. Mullins, (the late) Gordon F. KirkbrightHigh-performance Liquid Chromatography with Anodic Amperometric Detection for the Determination of Cefotaximeand its Metabolites-Huguette Fabre, Marie Dominique Blanchin, Ubbo TjadenTetracyanoethylene in Pharmaceutical Analysis. Part 1. A Spectrophotometric Method for the Determination of SomePharmaceutically Important Hydrazine and Pyrazolone Derivatives-F. A. I brahim, M. S. Rizk F. BelalAllylthiourea as a Reagent for the Spectrophotometric Determination of Osmium-Basilio MorelliLeucoquinizarin as an Analytical Spectrophotometric and Fluorimetric Reagent.Part 2. Determination of Beryllium-Spsctrophotometric Determination of Trace Amounts of Silver with 5-[4-(2-Methyl-3-hydroxy-5-hydroxymethyl)py-Anisaldehyde-4-phenyI-3-thiosemicarbazone as an Analytical Reagent for the Extractive Spectrophotometric Determi-Pre-concentration and Determination of Aquatic Sulphide by Visible Spectrophotometry-Dennis P. DeSalvo, KennethAutomated Flow Injection Spectrophotometric Determination of Zinc Using Zincon: Applications t o Analysis ofDetermination of the Stoicheiometry of Complexes by Flow Procedures. Molar-ratio and Asmus Methods-J. MartinezBioluminescence Assays with lmmobilised Bacterial Luciferase Using Flow Injection Analysis-Abdul Nabi, Paul J.Kinetic - Fluorimetric Study of the Catalytic Effect of Manganese(ll1 on the Air Oxidation of Morin-F.J. Lopez Benet, F.Optical Fibre Titrations. Part 3. Construction and Performance of a Fluorimetric Acid - Base Titrator with a Blue LED as aJacobus F. van StadenMiguel Angel Bello Lopez, Manuel Callejon Mochon, Jose L. Gomez Ariza, Alfonso Guiraum Perezridylenejrhodanin-R. Escobar Godoy, Alfonso Guiraum Pereznation of Gold-Kinthada M. M. S. Prakash, L. D. Prabhakar, D. Venkata ReddyW. Street, Jr.Waters, Alloys and Insulin Formulations-Michael A. Koupparis, Paraskevi I. AnagnostopoulouCalatayud, P. Campins Falco, M. C. Pascual MartiWorsfoldHernandez Hernandez, J. Medina Escriche, R.Marin SaezLight SourceOtto S. Wolfbeis, Bernhard P. H. Schaffar, Erhard KaschnitzSHORT PAPERSDetermination of Nitrite Ion Using the Reaction with 4-Aminobenzotrifluoride and 1-Naphthol-Darwish AminSelective Spectrophotometric Determination of Palladium(ll) with Phenanthraquinone MonothiosemicarbazoneQuantitative Determination of Sulphamethazine and Carbadox in Animal Feeds by Paired Ion High-performance LiquidKamini Shravah, Prem Prakash Sinha, Sharwan Kumar SindhwaniChromatography-Eddie D. McGarycontinued inside back coverTypeset and printed by Heffers Printers Ltd, Cambridge, Englan1343 Direct Determination of Chlorhexidine in Urine by High-performance Liquid Chromatography-Paul Wainwright,1345 Titrations in Non-aqueous Media. Part IV.Solvent Effects on Basicity of Aliphatic Amines-Turgut Gunduz, Ned2Michael CookeGunduz, Esma Kill$, Adnan Kenar1349 BOOK REVIEWSERRATUM1352 Phthalic Anhydride as an Impurity in Industrial Atmospheres: Assay in Air Samples by Gas Chromatography withElectron-capture Detection-Pirkko Pfaffli1987 PITTSBURGHCONFERENCEOnce again, the RSC is organising a tour groupfor Members of the Society attending thePittsburgh Conference. Travel will be with TWAfrom London Heathrow to Kennedy, New York,and will include coach transfer to Atlantic Cityand accommodation on a room-only basis inselected hotels close to the Convention Centre.Additional requirements such as transfer toHeathrow and personal onward itineraries afterthe meeting can be catered for, as well as carhire, assistance with visa3 etc.The pressure on hotel space in Atlantic City isenormous, as any visitor to previous PittsburghConferences will testify. Our rooms are alreadyreserved, so booking with the RSC Group isyour guarantee of good accommodation and atrou ble-free meeting.For further details, please quote ReaderService Number 001 or telephone KarenMizel on 01-437 8656 extension 250.BUREAU OF ANALYSED SAMPLES LTD.announce the availability of two newEURONORM CERTIFIEDREFERENCE MATERIALSECRM 287-1 High Boron Stainless Steel(chip or disc material)ECRM 587-1 18.7% B Ferro-Boron(finely divided material)for further details and/or a copy of thelatest BAS Catalogue or OverseasReference Materials List, write, telex ortelephone to:BAS Ltd., Newham Hall, Newby,Middlesbrough, Cleveland, TS8 9EATelex: 587765 BASRIDTelephone: (0642) 317216001 for further information. See page iv. 002 for further information. See page iv

ISSN:0003-2654    

DOI:10.1039/AN98611BX043

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST NOVEMBER 1986 VOL. 111 1225 Techniques for Evaluating Control of Automated Multi-determinant Analytical Instruments by Computer Murray T. Fisher and Julian Lee Applied Biochemistry Division Department of Scientific and Industrial Research Private Bag Palmerston North New Zealand M. Kelly Mara Applied Mathematics Division Department of Scientific and Industrial Research Private Bag Wellington, New Zealand Analytical data collected from calibration standards and other quality control standards using an amino acid analyser (18 ninhydrin products) and a plasma emission spectrometer (20 elements) are logged regularly during analysis periods. Principal components are derived from the data using principal component analysis and those that contain the most variation (usually first three) are plotted on cumulative sum charts (Cusums).Changes in the physico-chemical control of instruments can be clearly demonstrated and out of control events identified. The computer program can be run on any computer with sufficient memory to handle large matrix transformations. The technique is applicable to any instrument measuring several or many variables. Keywords Amino acids; ICP-AES; quality assurance; principal component analysis; Cusums There has recently been a rapid growth in the use of automated instrumentation for multi-determinant analysis. Attention has focused on the importance of quality assurance (QA) associated with these analytical instruments and analysts are complementing subjective assessment based on experience and skill with more objective criteria.The aim of the investigation reported in this paper was to devise and test an objective QA technique for monitoring the control of automated multi-channel analytical instruments. The technique presented involves the collection com-puterised manipulation and interpretation of sets of data derived from the repetitive assay of reference materials or control solutions. In this laboratory both an amino acid analyser and an inductively coupled plasma emission spec-trometer (ICP-AES) are routinely used to assay biological materials. For the amino acid analyser a data set consists of up to twenty ninhydrin positive products from a protein hydrolysate. ICP-AES data sets contain data for more than 20 elements in a sample digest. Ideally a multi-determinant QA technique would need to consider simultaneously all the data in a set and be able to relate that set to previous sets.It should be sufficiently flexible to be applied to sets of control data from both types of multi-channel instruments and be quick to use. Since the introduction of Shewhart charts,l>* their use for process control has become widespread. A more recent control chart is the cumulative sum (Cusum) ~ h a r t . 3 > ~ Con-struction and operating procedures for the charts are de-scribed elsewhere.5 The advantages of the Cusum chart are its strong visual impact and its ability to detect more clearly the subtle changes in the process that may not have emerged in Shewhart charts of the same data. However the properties of these charts have been examined mainly when only one process characteristic is being measured.When several, possibly related characteristics are being observed accurate statistical control becomes more difficult. The simple approach to monitoring multi-channel instrumental variation is to assume that all measured charac-teristics are independent. A Cusum chart may then be constructed for each variable. The process is then considered to be “out of control” if one or more of the charts demonstrates such a condition. There are however several major weaknesses in this approach. Firstly the independence is rarely justified. Secondly even if independence is a suitable assumption the false alarm risks increase dramatically with the number of elements. For example using a multi-channel instrument with ten determinants the use of ten individual charts each with a false alarm risk of 0.05 makes the over-all false alarm risk 1-(0.9510) = 0.4.That is an “out of control” condition will be indicated for 40% of the time when in fact the process is running on target. When the measurements are correlated the calculation of this error rate becomes unduly complex. In addition the simultaneous handling of ten control charts is far too cumbersome. What is therefore required is a more sophisticated multi-variate technique which also possesses the important property of being quick and simple to use. In order to decide which determinant or combination of determinants is contributing most to the variation the use of principal component analysis (PCA) combined with Cusum plotting seems an appropriate technique.The use of principal components (PCs) to monitor production processes has been advocated earlier.68 Traditionally PCA has been used to describe multi-variate data sets and to examine the relation-ships between the original variables. PCA looks for a few linear combinations that can sum-marise the data losing in the process as little information as possible. These linear combinations of the original variables are designed to account for as high a percentage of the variation among the variables with as few PCs as possible. Our procedure consists of generating the PCs from a suitable, stable (equality of variance) set of data and then producing Cusum plots of the scores of the weighting in the first few PCs.The method of PCA transforms the original set of correlated measurements into a mutually orthogonal (independent) set of new uncorrelated variables that are linear combinations of the originals. PCA involves finding the eigenvalues and eigenvectors of the sample correlation or covariance matrix. A detailed description of the method has been given by Jackson.9 Of the several methods9 of assessing how many PCs to retain to describe the data adequately we chose the most commonly used method that of considering the percentage variation accounted for by each PC. gxperimental Instrumentation The amino acid analyser used was an LKB (Cambridge UK) 4150 Alpha using a sodium citrate buffer pH gradient with an 11 X 10-6 m particle size cation-exchange resin.Post-column derivatisation was by reduced ninhydrin reagent. The 570- and 440-nm detector responses were plotted together with pea 1226 ANALYST NOVEMBER 1986 VOL. 111 processing and area integration using a Shimadzu (Kyoto, Japan) CR-2AX Chromatopac connected to a Shimadzu INP R2A instrument. Detailed operating conditions have been given previously.10 The conditions were optimised to give >95% separation between serine and threonine and arginine, the last peak off the column eluted within 95 min. The plasma emission spectrometer used was an Applied Research Laboratories (Sunland CA) 34800 inductively coupled plasma source (ICP) and a vacuum polychromator (Paschen-Rounge system) equipped with a movable primary slit. A standard quartz torch was used with a GMK nebuliser system (Lab-Test) and a Gilson Minipuls I1 peristaltic pump.The analytes were measured at the following lines (nm) A1 I, 308.22; As I 189.04; B I 249.68; Cd 11,226.50; Co 11,228.62; Cr 11 267.72; Cu I 324.75; Fe 11 259.94; Mg 11 279.08; Mn 11 257.61; Mo 11 202.03 Na I 589.60; Ni 11 231.60; Pb 11, 220.35; Se I 203.99; Sn 11 189.98; Sr I 407.77; and Zn I, 213.86. Plasma operating conditions are described else-where.11712 Analyses were carried out under conditions optimised for simultaneous multi-elemental analysis. Materials The calibration standard for the amino acid analyser used was a commercial amino acid hydrolysate mixture containing 17 acids plus ammonium sulphate (No. 20079 Pierce Chemical Co. Rockford IL USA).The in-house reference sample used in this study was prepared as follows. Lipid and carbohydrate were extracted from freeze-dried fish material by the Folch procedure.13 The remaining protein residue was then hydrolysed with 6 M HC1 by an in-house modification of a standard procedure. 14 The in-house reference hydrolysate was assayed with each batch of hydrolysates of biological material. Twenty-two data sets containing assays of up to 15 amino acids (plus ammonia) were recorded and stored in the computer. For the ICP the instrumental control monitoring procedures used were similar to those documented by Botto.15 A 2 M HC1 blank solution was prepared from re-distilled constant-boiling HCl. This solution was used to make a check standard which contained all the elements analysed by the instrument at levels of one hundred times their respective 30 detection limits (approximately equal to ten times the background equivalent concentration).This standard was used routinely to monitor any calibration drift within batch runs. Data Collection and Analysis Amino acid data sets containing results of the analysis of 15 amino acids plus ammonia from the calibration standard and the fish hydrolysate were recorded and stored in separate data files on a VAX 11/780 computer. For unoxidised protein hydrolysates the amino acids cystine and methionine were not reported because of the breakdown of sulphur-containing amino acids during sample hydrolysis. The ICP intensity data of the emission lines measured by assaying the check standard were acquired using the ICP computer.The data were then chronologically logged on the VAX. The measured intensities of the emission lines ratioed to the Ca I1 317.93 nm line were also logged. Data manipulation and the computations of PCs were performed using a computer program which made use of Minitab. A computed value or score for each multivariate data set at each event is derived from the PCs. The Cusums of the scores for each of the main (usually the first three) PCs were plotted by computer against the control sample number (event). These events are in a chronological sequence that may be days hours etc. or batch order. Results and Discussion Amino Acids The PCs derived from the AA data are presented in Table 1. For the calibration standard the first PC derived from the data shows that all amino acids contribute more or less equally to the 52% of the total variation.The opposite sign of the coefficient for arginine means that it varies in a different direction; otherwise the sign is arbitary. This finding of equal contribution to the variation might be expected because the assay of a commercially prepared standard mixture represents the ideal separation in terms of being free of sample matrix effects. For the second PC however mainly histidine lysine, ammonia and arginine contribute to a further 28% of total variation. These four determinants are eluted by buffer three, which has a six-fold greater molarity compared with buffers one and two. This greater molarity results in an eluate stream with a higher absorbance.The associated base line change just prior to the elution of these four and the slight decrease in base-line stability point to possible reasons for these amino acids contributing more to the over-all variation. Further, arginine is the last peak to elute and has the greatest peak area to height ratio or band broadening. For the in-house reference fish material PC analysis of the data reveals that for the first component glutamic and aspartic acids and arginine contribute to 49% of the total variation. Here glutamic acid might be expected to exhibit some variation owing to its peak having a slight trailing base over the proline eluting close behind. Arginine again might be expec-ted to vary for the same reasons but aspartic acid’s contri-bution to the variation is not readily explained in terms of separation.For the second PC (26%) glutamic acid histidine and lysine stand out probably for the above reasons. The third PC (llYo) shows that arginine and glutamic acid are again the main variants. It is worth noting that for both materials most of the variation is accounted for by the first three principal com-ponents. Although the components contributing to the variation were usually the same in both the standard and the reference material aspartic and glutamic acids and arginine give higher weightings in the first PC of the latter. This may indicate matrix effects from the biological material. These differences emphasise the need for using quality assurance reference materials that are similar in nature to the “un-knowns.” The amino acid analyser operator’s log book was also consulted to find possible reasons for the changes in slope of the Cusum of the first PC (Fig.1) coincident with changes in instrumental chemistry. It was found that the bottle of buffer one was almost empty on day 3 and was changed for 4 1 of fresh buffer on day 4 (event 4). The log book also showed that a fresh ninhydrin colour reagent of slightly different absorbance was introduced into the analyser on day 17 (event 17). The second and third PC Cusums showed no significant change in slope. ICP-AES Table 2 gives the total PC variation calculated from the covariance matrix for 17 elements determined by ICP-AES in a standard check sample. This standard is run every 40th sample (hourly).The data shown cover a 6-h period for each of three consecutive days during the analysis of about 750 samples. A fresh normalisation of the stored calibration graphs was made at the beginning of each day using a high and low standard otherwise no further adjustment to the calibra-tion graphs was made. Most of the over-all variance is accounted for by the first PC (71.5%). Three PCs account for 97% of the total variance in the data. The elements apart from Pb and Se contributed more or less equally to the over-all variance in the first PC. The same sign for the vectors of all the elements indicates a positively correlated variation. The examination of the concentration data indicated a downward drift within each day’s run.Selenium contributed markedly to the over-all variance because of higher values obtained on the second day’s run and also due to poorer over-all precision. Indeed Table 1. Amino acids. Weightings for the first three PCs from the correlation coefficients between amino acids determined in both the calibration over 22 consecutive daily runs Principal MPC . . 0.22 0.17 0.29 0.27 0.21 0.25 0.21 0.28 0.25 0.26 0.27 0.25 0.28 component Asp Thr Ser Glu Gly Ala Val Met Ile Leu N-Leu Tyr Phe Calibration standard: 2ndPC . . 0.05 0.04 0.09 0.00 0.07 0.06 0.00 0.00 0.07 0.09 0.05 0.06 0.04 3rdPC . . 0.15 0.03 0.33 0.65 0.06 0.13 -0.1 -0.27 -0.16 -0.09 -0.18 -0.20 -0.46 In-house reference material: 1StPC . . 0.41 0.12 0.12 0.57 0.13 0.22 0.19 -0.04 -0.08 0.25 - 0.05 0.08 2ndPC .. 0.05 0.01 0.02 0.30 0.04 0.03 -0.08 -0.05 -0.02 -0.03 - -0.01 -0.02 3rd PC . . 0.07 0.20 -0.06 -0.6 0.03 -0.04 0.09 -0.09 0.04 -0.03 - -0.01 0.03 Table 2. ICP elements. Weightings for the first two PCs from the correlation coefficients between elements determined in a “check” standard run Principal component A1 As B Cd c o Cr c u Fe Mg Mn Mo Ni Pb 1stPC . . 0.19 0.27 0.22 0.25 0.26 0.17 0.12 0.1 0.26 0.08 0.22 0.26 0.34 2ndPC . . -0.08 0.2 -0.26 0.04 0.03 -0.06 -0.04 -0.27 -0.55 4 - 5 3 -0.01 -0.07 0.04 Table 3. ICP element ratios. Weightings for the first two PCs from the correlation coefficients of emission line intensities ratioed to the intensity containing each of the elements at a concentration designed to give 10 times the background equivalent concentration (10 BEC) Principal component A1 As B Cd Co Cr Cu 1StPC .. 0.33 0.06 0.31 0.02 0.05 0.05 0.32 0.13 0.08 0.11 0.12 0.73 0.08 0.00 2ndPC . . 0.10 0.11 0.38 0.14 0.19 0.07 0.03 0.17 0.15 0.15 0.25 0.46 0.21 0.33 Fe Mg Mn Mo Na Ni P 1228 ANALYST NOVEMBER 1986 VOL. 111 $ 3 0 541 I 1 4 \ 36 30 24 18 12 ---6 -0 --6 -Fig. 1. Amino acids. Cusum plots for the first three principal components of data from daily analyses of a calibration standard containing 16 amino acids plus ammonia. Buffer and reagent changes made at points A and B respectively 1 0.5 0 E 2 -0.5 0 -1.0 -1.5 -2.0 v 2nd PC 1 I 1 I I I I I I 2 4 6 8 10 12 14 16 18 Eventlh Fig. 2. ICP-AES. Cusum plots for the first two principal components of concentration data from the calibration standard (18 elements) run hourly over a 6-h period on three consecutive days.Slope changes indicate daily normalisation of calibration graphs 1 I 0 2 4 6 8 10 12 14 16 18 20 Eventiday Fig. 3. ICP-AES. Cusum plots for the first two principal components of emission intensity data (ratioed to the Ca I1 317.93 nm emission line) of a calibration standard analysed daily at the start of each batch of analyses (1 month period). Arrow indicates new calibration Se and Pb are the least sensitive of the emission lines measured. The second PC indicates a different pattern of variation among the elements. Magnesium and Mn and again Se, contribute the most to the variation. The reasons for this are not readily apparent.The Cusum plots for the first and second PC are shown in Fig. 2. Within each PC the daily drift is well illustrated with an abrupt change in slope indicating the start of each daily run. The use of the Cusum’s associated V-masks indicates that the analysis process is “in control,” however, within each daily run. The marked change in slope of the Cusum at the start of each day’s run reflects the renewed normalisation of the calibration graphs. A different check standard is routinely run before the start of each batch of analyses. The decision to proceed with further analyses depends on the performance of the instrument as reflected in the data from this standard. Several years of emission intensity data have been logged from measurements made on a “check” solution containing all the elements.A pattern has emerged showing changes in emission response in relation to changes in instrumental settings. Consequently a standardised procedure now operates to ensure an optimum response for the analysis of all determinants. Element emission line intensities (mV) are ratioed to the Ca I1 317.92 nm emission line. These ratios are systematically examined for departure from a pre-set value. Criteria similar to that outlined by BottolS are used. The first two PCs and their Cusums are shown for a typical run sequence (approximately 1 month) in Table 3 and Fig. 3, respectively. This particular sequence has been chosen to illustrate the effect of an instrument re-tuning and ensuing re-calibration on the Cusum plot which occurred on day 12 (event 12 Fig.3) and is reflected in the change of slope in the Cusum for the first PC. In the first PC (Table 3) the elements Na Al Cu B and to a lesser extent Sr contribute the most to the over-all variation. This observed pattern may be explained in part by the known response behaviour of the measured elements to various plasma processes.1~19 The emission lines Na I 589.59 nm A1 I 308.22 nm Cu I 324.75 nm B I 249.68 nm and Sr I 407.77 nm show maximum emission intensities outside the “compromise” plasma observation zone. 11 Consequently these elements exhibit responses that are sensitive to slight changes in those instrument parameters which contribute to effective shifts in the plasma stability of this zone viz. changes in the aerosol carrier gas flow-rate.This drift contributes to a greater daily variability in the observed intensities for these elements. For the technique to be routinely usable as a control method it is hoped that the first few (say a maximum of three or four) principal components account for most of the variability. In the data given in this work the variation among the elements is highly correlated and this is reflected in the observation that only two or three PCs are necessary to describe near to or over 90% of the total observed variation. Additionally it is necessary to keep in mind the important question “Does the process seem in control?” In order to answer this it is important that changes that are evident in the Cusum plots on the individual assayed components are also demonstrated in the Cusum charts of the chosen PCs.Conclusion The combined approach of PC analysis and selected automatic Cusum charting has been shown to be effective in monitoring the control of our analytical instruments during multi-determinant assays. This QA technique can be used on any reference data to monitor the control of any multi-determinant instrument and could be a feature of the instrument’s QA software. We thank the following for their help G. F. Filby for data entry Mr. P. Thakurdas for programming and Dr. J. R. Sedcole for helpful discussions ANALYST NOVEMBER 1986 VOL. 111 1229 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Shewhart W. A. “Economic Control of the Quality of Manufactured Product,” Van Nostrand New York 1931.Westgard J. O. Barry P. L. and Hunt M. L. Clin. Chem., 1981 27 493. Page E. S. Biometrika 1954 41 100. Ewan W. D. and Kemp K. W. Biometrika 1960 47 363. “Guide to Data Analysis and Quality Control Using Cusum Techniques,” BS 5703 Parts 1-4 British Standards Institution, London 1980. Jackson J . E. and Morris R. H. J. Am. Stat. Assoc. 1957, 52 186. Jackson J. E. Commun. Stat. Theory Methods 1985,14,2657. Woodall W. H. and Ncube M. M. Technometrics 1985 27, 285. Jackson J. E. J. Qual. Technol. 1980 12 201. Fisher M. T. in Richards E. L. Editor “Developments in Food Analysis.” Symposium on Food Chemistry Food Tech-nology Department Massey University New Zealand 1983, Lee J. ICP Inf. Newsl. 1983 8 553. p. 21. 12. 13. 14. 15. 16. 17. 18. 19. Lee J. Sedcole J. R. and Pritchard M. W. Spectrochim. Acta Part B 1985 41 12. Folch J. Lees M. and Sloane S. G. H. J. Biol. Chem. 1957, 226 497. Horwitz W. W. Editor “Official Methods of Analysis of the Association of Official Analytical Chemists,” Thirteenth Edi-tion Third Supplement “Changes in Methods,” AOAC, Philadelphia 1982 p. 496. Botto R. R. Spectrochim. Acta Part B 1984,39 95. Boumans P. W. J. M. and de Boer F. J. Specrrochim. Acta, Part B 1975 30 309. Anderson T. A. Burns D. W. and Parsons M. L., Spectrochim. Acta Part B 1984 39 559. Houk R. S . and Olivares J. A. Spectrochim. Acta Part B , 1984,39 575. Caughlin B. L. and Blades M. W. Spectrochim. Acta Part B 1984 39 1583. Paper A61109 Received April 8th 1986 Accepted June 11 th 198

ISSN:0003-2654    

DOI:10.1039/AN9861101225

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST NOVEMBER 1986 VOL. 111 1231 Electrodes in Series. Simultaneous Flow Injection Determination of Chloride and pH with Ion-selective Electrodes Jacobus F. van Staden Department of Chemistry University of Pretoria Pretoria 0002 South Africa Chloride and pH can be determined simultaneously by flow injection potentiometry with a series electrode arrangement at a rate of 60 samples per hour with a standard deviation of 1.5% for chloride and 1% for pH. Samples (30 pl) are injected into a carrier buffer solution (pH 7.6) containing 0.5 mol dm-3 of potassium nitrate and mol dm-3 of sodium dihydrogen phosphate as an ionic strength adjustment buffer. The sample -buffer zone formed is transported through a laboratory-made coated tubular solid-state chloride-selective electrode via a glass membrane micro pH combination electrode on to the reference electrode (for chloride).The method is suitable for the determination of chloride in the range 20-5000 mg dm-3 and a pH range from 3 to 10. Keywords Chloride determination; pH determination; simultaneous determination; flow injection analysis; ion-selective electrodes The use of electrochemical detection in flowing streams has grown rapidly in recent years.1-5 There are many examples of potentiometric detection with glass pH electrodes69 and also with other membrane electrodes.1,4>5JG16 However in most of the methods reported the emphasis was placed on the determination of a single species in a sample. A survey of the recent literature indicated a lack of procedures describing the simultaneous determination of more than one species in the same sample,17 which could make the flow injection analysis (FIA) concept more attractive for routine laboratories.By using the cascade electrode arrangement RfiiiCka et al. 1 were able to determine sodium and potassium simultaneously in blood serum. In this configuration the stream of electrolyte cascaded from the potassium to the sodium electrode and then to a constant-level reservoir in which the reference electrode was located. Mascini and Palleschils used the same principle for the simultaneous determination of glucose and urea in serum samples but in their arrangement the cascade elec-trodes were placed opposite each other with the stream of electrolyte cascading between the two electrodes. Virtanenlg developed a method for the simultaneous determination of potassium sodium calcium and chloride in serum by placing four cascade ion-selective electrodes sequentially in an FIA system with the reference electrode downstream.The errors in the analysis of samples due to mutual interferences from some species in the determination were corrected with the aid of regression coefficients which were determined by measure-ments of known mixtures. The same idea of electrodes in series was implemented by Hansen et aZ.20 for the simul-taneous determination of pH and calcium in serum. In their system the carrier buffer was pumped via a flow-through capillary glass electrode (G299 Radiometer) to a cascade calcium-selective electrode. The reference electrode located at the bottom of the calcium electrode received both the sample flow after impact with the calcium sensor and an additional reagent stream of buffer.The additional buffer stream was added to dilute the sample in such a way that the composition of the solution surrounding the reference elec-trode almost remained constant. Flow-through tubular arrangements for ion-selective elec-trodes have been reported recently. 1 2 - 1 4 ~ 6 ~ 2 2 In this geo-metric mode the sample solution is channelled through the tubular configuration across the sensing membrane surface in a kind of open path. The incorporation of a tubular ion-selective electrode into the conduits of a flow injection system seems an ideal design as the hydrodynamic flow conditions can be kept constant throughout the flow system.This approach opens new dimensions in the development of the simultaneous determination of more than one species in a single sample by placing tubular electrodes in series into the conduits of a flow injection system. This paper describes the exploitation of this concept in a study of the simultaneous determination of chloride and pH in a single sample. Experimental Reagents and Solutions All reagents were prepared from analytical-reagent grade chemicals unless otherwise specified. Doubly distilled de-ionised water was used throughout. The water was tested beforehand for traces of chloride. All solutions were de-gassed before measurements by the use of a water vacuum pump. Ionic strength adjustment buffer reagent (ISA B ) Dissolve 2.76 g of sodium dihydrogen phosphate monohy-drate in 1500 cm3 of distilled water in a 2-dm3 calibrated flask, add 101.11 g of potassium nitrate and swirl the flask gently until the solid has completely dissolved.Dilute the solution quantitatively to 1900 cm3 with distilled water. Adjust the pH carefully to 7.6 by adding sodium hydroxide or nitric acid. Dilute this solution to 2 dm3 with distilled water. For 0.1 and 1.0 mol dm-3 potassium nitrate solution 20.222 and 202.22 g of potassium nitrate are used respectively. Buffer and chloride standard solutions Dissolve 32.9680 g of dried sodium chloride in 2 dm3 of distilled water to give a stock solution with a chloride concentration of 10000 mg dm-3. Combined working solu-tions containing chloride in the range 20-5000 mg dm-3 and a pH range of 3-10 are prepared by suitable dilution of the chloride stock solution and as described in Tables 10.25, 10.37 10.43 10.45 and 10.5 in the book by Perrin and Dempsey ,23 respectively.Apparatus Electrodes Tubular flow-through chloride-selective cell. The construc-tion preparation and conditioning of the coated tubular flow-through solid-state chloride-selective membrane was similar to the procedure previously described. l 1232 ANALYST NOVEMBER 1986 VOL. 111 Micro combination p H electrode. A Schott micro pH combination electrode with a Type N60 cylindrical glass membrane Ag - AgCl internal reference elements zero potential pH value = 7 platinum junction glass resistance ( R ) at 25 "C = 600 MB shaft diameter 3 mm and an operating range of pH 0-14 in the temperature range 20-80 "C was used.The final arrangement of the electrodes in the flow system is shown in Fig. 1. The carrier solution containing the sample is first channelled through the tubular chloride-selective elec-trode then via the glass membrane on to the reference electrode. Flow system The electrodes were incorporated into the conduits of a flow injection system as shown schematically in Fig. 2. The injection valve system was a Carle microvolume two-position sampling valve (Carle Catalogue No. 2014) with two identical sample loops each having a volume of 30 1.11. The sampling unit (Cenco) was used together with a Cenco peristaltic pump that supplied a constant stream of samples to the sampling valve system.The valve system was actuated on a time basis that was correlated with the sampler unit. A 60-s cycle Micro - pH combination electrode Electrode holder- - '' ~ ' li I I l l I Shielded cable to ionalyzer I l l ' Glass membrane-i-) ' ; i Coated insoluble Ag metal inorganic salt Fig. 1. silver chloride electrode surface is ca. 2 mm i.d. and 5 mm long Electrodes arrangement into the flow system. The active Sampler sampling time was used giving the system a capacity of about 60 samples h-1; the sampling valve was actuated every 58 s. The carrier and reagent streams were pumped with a Cenco peristaltic pump operating at 10 rev. min-1. Tygon tubing (0.51 mm i.d.) was used to construct the manifold. Mixing coils were made by winding appropriate lengths of the Tygon tubing on Perspex rods (15 mm 0.d.).The carrier stream, containing a solution of the ionic strength adjustment buffer reagent was pumped at a constant flow-rate of 3.9 cm3 min-1. To avoid the slight pulsation originating at the peristaltic pump and also sample plug pulsation pulse suppressors were used. For plug pulsation 105 cm x 0.51 mm i.d. transmission tubing was incorporated just after the sampling valve. Pump pulsation was avoided by the incorporation of 200 cm X 0.51 mm i.d. transmission tubing as a pulse suppressor between the pump and the sampling valve. The potentials were measured at room temperature with an Orion Research (Model 901) microprocessor Ionalyzer. The detector output was recorded with a two-channel Cenco recorder (Catalogue No.34195-041). The constructed flow-through tubular indicator electrodes were used in conjunction with an Orion 90-02 double-junction reference electrode with 10% potassium nitrate as the outer chamber filling solution. Results and Discussion Two typical recorder output series taken at a rate of 60 determinations per hour are given in Figs. 3 and 4. The results were obtained by injecting 30 1-11 of mixed sodium chloride pH standard solutions into pH 7.6 sodium dihydrogen phosphate (10-2 mol dm-3) ionic strength adjustment buffer carrier solutions. The experimental conditions for both series were the same except for a change from 0.1 mol dm-3 potassium nitrate solution in Fig. 3 to 1.0 mol dm-3 potassium nitrate solution in Fig. 4 in the ionic strength adjustment carrier solution.No difficulty was experienced in the determination of pH in both series provided that the precautions as previously described by RfiiiEka and Hansen4.24 were taken [Figs. 3(b) and 4(b)]. Although R8iiCka and Hansen4.24 used sodium chloride as the ionic strength adjustment solution, which is not possible in this instance the results indicated that potassium nitrate was also suitable for this purpose. The incorporation of the tubular chloride-selective electrode before the glass membrane (pH) electrode shows no signifi-cant influence on the peak shape. This means that the effect of the incorporated tubular system on the sample - buffer zone is negligible which proves the assumption that the hydrody-namic flow conditions can be kept constant through the microprocessor - - .- . x { T w o - p e n C recorder J Reference electrode -=? iona I yzer \ r combination electrode cm3min Pert sta I t ic Fig. 2. rate 60 h-1 Manifold and flow diagram of the FIA system. Valve loop size 30 p1; sampler 60 s; wash 0 s; valve actuation at 58 s; samplin ANALYST NOVEMBER 1986 VOL. 111 1233 ( b ) pH 9.9 3.2 L I I ( C) pH = 8.6 B D F H AI cl EIG~I nnnnnnrinn BDF H pH = 6.1 Fig. 3. Typical strip-chart recording for the simultaneous flow injection analysis of chloride and pH with the FIA s stem of Fig. 2 using 0.1 rnol dm- KNO, 10-2mol dm-3 NaH2P04 &H adjusted to 7.6) ionic strength adjustment buffer carrier and reagent solutions. (a) Recorder trace for a series of standard chloride solutions each solution in triplicate.Recorder paper speed 1 mm rnin-'; recorder range 20 mV. Chloride concentrations A 5000; B 4000; C 3000; D, 2000; E 1000; F 500; G 250; H 100; I 80; J 60; K 40; and L 20 m dm-3 (p.p.m.). (b) Recorder trace for a series of standard pH sofutions each solution in triplicate. Recorder paper speed 1 mm min-'; recorder range 50 mV. Numerals on calibration peaks refer to pH values. (c) Recorder trace demonstrating the influence of chloride concentration on the sensitivity of the pH readout of a pH 6.1 and 8.6 solution each chloride interference injected in triplicate. Recorder paper speed 1 mm min-1; recorder range 50 mV. Chloride concentrations in pure buffer solutions A 0; B 100; C 250; D 500; E 1000; F 2000; G 3000; H 4000; and I 5000 mg dm-3 (p.p.m.) 9.9 7.6 111.I 3.2 II" AI cl EIGI I B DF H DH = 6.1 Fig. 4. Typical strip-chart recording for the simultaneous flow injection analysis of chloride and pH with the FIA system of Fig. 2 and 1.0 rnol dm-3 KN03 10-2 mol dm-3 NaH2P04 (pH adjusted to 7.6), ionic strength adjustment buffer carrier and reagent solutions. (a) Recorder trace for a series of standard chloride solutions each solution injected in triplicate. Recorder paper speed 1 mm min-l; recorder ran e 20 mV. Chloride concentrations A 5000; B 4000; C, 3000; D 2008; E 1000; F 500; G 250; H 100; I 80; J,.60; K 40; and L 20 mg dm-3 (p.p.m. j. (bj Recorder trace for a series of standard pH solutions each solution injected in triplicate. Recorder paper speed 1 mm min-1; recorder range 50 mV.Numerals on calibration peaks refer to pH values. ( c ) Recorder trace demonstrating the influence of chloride concentration on the sensitivity of the pH readout of a pH 6.1 and 8.6 solution each chloride interference injected in triplicate. Recorder paper speed 1 mm min-'; recorder range 50 mV. Chloride concentrations in pure buffer solutions A 0, B 100; C 250; D 500; E 1000; F 2000; G 3000; H 4000; and I 5000 mg dm-3 (p.p.m.) A I Fig. 5. Recorder trace for a series of standard chloride solutions with the FIA system of Fig. 2 using 0.5 mol dm-3 KN03 and 10-2 rnol dm-3 NaH2P04 (pH adjusted to 7.6) ionic strength adjustment buffer carrier and reagent solutions. Each solution injected in triplicate. Recorder paper speed 1 mm min-l; recorder range 20 mV.Chloride concentrations A 5000; B 4000; C 3000; D 2000; E 1000; F 500; G 250; H 100; I 80; J 60; K 40; and L 20 mg dm-3 (p.p.m.) tubular chloride-selective electrode. The calibration graph is still linear between pH 3 and 10 and the precision is good (the coefficients of variation were less than 1% for ten injections). Figs. 3(c) and 4(c) demonstrate the influence of 0-5000 mg dm-3 of chloride on the sensitivity of the pH readout. It is clear from the results obtained that a variation of chloride content between the two limits has no effect on the pH results. It was obvious from preliminary experiments that the flow injection conditions for the determination of chloride pre-viously described16 were not suitable for use in the simul-taneous determination of chloride and pH.The results indicated that the combination of dihydrogen phosphate with potassium nitrate carrier solution has an effect on the tubular chloride-selective electrode system. A mixture containing 1 .O mol dm-3 of potassium nitrate and 10-2 rnol dm-3 of sodium dihydrogen phosphate at pH 7.6 as a carrier solution tends to give a positive base-line drift [Fig. 4(a)]. This effect became large when 30-p1 standard solutions containing less than 250 mg dm-3 of chloride were injected. A decrease of the potassium nitrate strength to 0.1 rnol dm-3 in the pH 7.6 ionic strength adjustment buffer carrier solution resulted in a less stable measuring system for chloride [Fig. 3(a)] with a lower precision at the same time.Optimum working conditions in terms of stability and precision (the coefficients of variation were less than 1.5% for ten injections) are obtained by using 0.5 rnol dm-3 of potassium nitrate together with 10-2 mol dm-3 of sodium dihydrogen phosphate at a pH of 7.6 as carrier solution (Fig. 5 ) for the chloride determination which also suited the simultaneous determination of both com-ponents very well. Conclusion The simultaneous determination of chloride and pH with a flow injection system at a sampling rate of about 60 samples per hour and a standard deviation of less than 1.5% for chloride and 1% for pH is made possible by using electrodes in series in the procedure described in this paper 1234 ANALYST NOVEMBER 1986 VOL. 111 The author thanks the Council for Scientific and Industrial Research Pretoria and the University of Pretoria for financial support.He also thanks Miss M. L. Aveling for assistance in performing some of the experiments. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. References RfiiiEka J. Hansen E. H. and Zagatto E. A. Anal. Chim. Acta 1977 88 1. Pungor E. Fehkr Zs. Nagy G. Toth K. Horvai G. and Gratzl M. Anal. Chim. Acta 1979 109 1. Toth K. Nagy G. Fehkr Zs. Horvai G. and Pungor E., Anal. Chim. Acta 1980 114 45. Rfiiitka J. and Hansen E. H. “Flow Injection Analysis,” Wiley Chichester 1981. “Flow Injection Analysis Bibliography,” Tecator AB Hoga-nas Sweden 1985. Rfiiitka J. Hansen E. H. and Ghose A. K. Anal. Chem., 1979 51 199. Zagatto A. E. Reis B.F. Bergamin F” H. and Krug F. J., Anal. Chim. Acta 1979 109 45. Astrom O. Anal. Chim. Acta 1979 105 67. Basson W. D. and Van Staden J. F. Lab. Pract. 1980 29, 632. Hansen E. H. Krug F. J . Ghose A. K. and RfiiiEka J . , Analyst 1977 102 714. Hansen E. H. Ghose A. K. and RfiiiEka J . Analyst 1977, 102 705. Van der Linden W. E. and Oostervink R. Anal. Chim. Acta, 1978 101 419. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. Meyerhoff M. E. and Kovach P. M. J . Chem. Educ. 1983, 60 766. Frend A. J. Moody G. J. Thomas J . D. R. and Birch B. J., Analyst 1983 108 1357. A1 Hitti I. K. and Thomas J. D. R. Anal. Lett. 1985 18, 975. Van Staden J. F. Anal. Chim. Acta 1986 179 407. Luque de Castro M. D. and ValcBrcel M. Analyst 1984, 109 413. Mascini M. and Palleschi G. Anal. Chim. Acta 1983 145, 213. Virtanen R. in Pungor E. Editor “Ion-selective Electrodes 3. Proceedings of the Third Symposium Matrafiired Hungary, October 1980; Analytical Symposium Series,” Volume 8, Elsevier Amsterdam 1981 p. 375. Hansen E. H. RfiiiEka J. and Ghose A. K . Anal. Chim. Acta 1978 100 151. Mascini M. and Palleschi G. Anal. Chim. Acta 1978 100, 215. Alegret S. Alonso J. Bartroli J. Paulis J. M. Lima, J. L. F. C. and Machado A. A. S. C. Anal. Chim. Acta 1984, 164 147. Perrin D. D. and Dempsey B. “Buffers for pH and Metal Ion Control,” Chapman and Hall London 1974. Rfiiitka J . and Hansen E. H. Anal. Chim. Acta 1984,161, 1. Paper A61162 Received May 23rd 1986 Accepted June 25th 198

ISSN:0003-2654    

DOI:10.1039/AN9861101231

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST NOVEMBER 1986 VOL. 111 1235 Modified Platinum Wire Glucose Oxidase Amperometric Electrode G. J. Moody G. S. Sanghera and J. D. R. Thomas Department of Applied Chemistry Redwood Building UWIST PO Box 13 Cardiff CFI 3XF UK Aflow injection system incorporating a modified platinum wire amperometric enzyme electrode is described. Glucose oxidase was covalently attached to an activated platinum surface to form an enzyme electrode which was then incorporated in a laboratory-built three-electrode flow-through cell. The system exhibited good linearity (for glucose concentrations of 0.1-20 mM) where log (current/A) = 0.992 log ([glucose]/~) -3.94 with a correlation coefficient of 0.999. Response times (<25 s) and wash times (<30 s) were short and a lifetime of 9 h was obtained for continuous exposure to 2.5 and 10 mM glucose.Normal use during the flow injection analysis of glucose gave lifetimes of 10 d. Keywords Amperometric glucose sensor; enzyme electrode; flow injection analysis; modified platinum electrode An enzyme electrode essentially consists of a layer of immobilised enzyme held over a suitable electrochemical sensor such as the Clark electrode.’ This assembly combines the specificity of an enzyme with the sensitivity of potentio-metric2.3 and amperometric3 electrodes for a wide range of substrates. Over the past decade the chemical modification of elec-trodes in order to provide an electrode surface more selective than bare metal has become well established. The attachment of suitable redox centres to the bare metal can be achieved by direct covalent bonding,4 coating with a polymer film5 and the covalent attachment of an enzyme directly on to a chemically modified electrode surface.6 The last of these is a logical development as the thinner membrane accelerates the diffu-sion of substrate to and the diffusion of product(s) from the active sensor zones.The direct covalent attachment of an enzyme on to a chemically modified electrode surface has good prospects, especially for the microfabrication of simple implantable sensors. The use of glucose oxidase in the presence of oxygen for the direct electrochemical detection of glucose is usually based on the amperometric measurement of hydrogen per-oxide at a platinum - enzyme electrode. However the use of mediators7 and conducting organic salts8 can lead to a sensor that is potentially independent of oxygen concentration in the vicinity of the probe.Thus ideally an enzyme sensor for implantation would be small in size and by the agency of redox mediators would be independent of oxygen concen-tration. Although this goal remains elusive present develop-ments with oxygen independent sensors and miniature devices are a step in this direction. This paper describes a miniature enzyme electrode consist-ing of glucose oxidase covalently attached to a silanised and anodised platinum wire surface via the bifunctional glutar-aldehyde enzyme immobilising reagent. Its response charac-teristics were determined in a three-electrode amperometric mode by monitoring the anodic decomposition of hydrogen peroxide.Experimental Reagents Glucose oxidase (E.C. 1.1.3.4 100 IU mg-1 purified from Aspergillus niger) glutaraldehyde (25% aqueous solution), p a ( +)-glucose and 3-aminopropyltriethoxysilane were obtained from Sigma Chemical (Poole Dorset UK) and platinum wire from Goodfellow Metals (Cambridge UK). All other materials were of the best analytical grade available. Glucose standards were prepared from a fresh stock solution of P-D(+)-glucose (1 M) in 0.1 M orthophosphate buffer (pH 6.0). The carrier stream phosphate buffer was sodium di-hydrogen orthophosphate (0.1 M) adjusted with sodium hydroxide solution. Immobilisation of Enzyme Essentially the method incorporated a simplification of the chemical modification of platinum outlined by Yao ,9 followed by the attachment of glucose oxidase via the bifunctional reagent glutaraldehyde using a procedure similar to that described for controlled porosity glass by Masoom and Townshend.10 This approach avoided the more complicated thin film approach of Ya0,9 which involved the use of bovine albumin.The platinum wire electrodes were cleaned by successive bathing for 10 min in hot concentrated nitric chromic and hydrochloric acids respectively followed by electrochemical treatment in sulphuric acid (0.5 M) with voltammetric cycling between 0 and +1.3 V (relative to Ag - AgC1) for 2 h or alternatively overnight. Cyclic voltammetry was then used to indicate “clean” platinum wires in each instance. Prior to silanisation the clean platinum wire was anodised at +2.50 V (relative to Ag - AgCI) in sulphuric acid (0.5 M) for 5 min.After thorough washing with de-ionised water and drying the anodised platinum wire was refluxed for 45 min in anhydrous 3-aminopropyltriethoxysilane in toluene (10% V/V). Glutaraldehyde (2.5% VIV) was prepared by a 1+9 dilution of the stock solution with phosphate buffer (0.1 M pH 7.0). The platinum wire was then placed in nitrogen-saturated glutaraldehyde in a stoppered flask for 1 h while nitrogen was bubbled through at 10-min intervals to maintain anaerobic conditions. After thorough washing in fresh phosphate buffer the wire was placed in glucose oxidase (10 mg cm-3) in the phosphate buffer and nitrogen deoxygenation continued as for the first hour. Before use the platinum wire was immersed in the enzyme solution overnight at 4 “C.The scheme for the platinum wire anodisation and subsequent glucose oxidase immobilisation is shown in Scheme 1. Apparatus The cyclic voltammetric approach to activating the platinum wire was carried out with a potentiostat (Bruker E130M). The detector cell (Metrohm EA1102) was based on a three-electrode assembly incorporating a silver - silver chloride reference electrode a glassy carbon auxiliary electrode and a platinum wire working electrode (length 2.5 cm diameter 0.1 cm). All voltammograms were recorded on an X - Y recorder (Omnigraphic Model 2000) 1236 Y lu a 20 ANALYST NOVEMBER 1986 VOL. 111 -OEt Activation 3-Aminopropyl I Pt - Pt-0 Pt-0- Si -0Et I Anodisation -triethoxysilane Pt - 0-Si-OEt I I II I I (CH2)3 N CH (CH2)3 CH-"Enzyme Scheme 1 Glucose -(CH-213 I i" Glutaraldehyde OEt 1 I I 11 I I Pt- 0 -Si-OEt (CH2)J N CH (CH2)3 CHO The anodic decomposition of hydrogen peroxide a product of the enzyme catalysis was monitored by setting the platinum wire enzyme electrode at +600 mV (relative to Ag - AgC1) and measuring the change in current.The electrode was used in a three-electrode system in a laboratory-built flow-through cell. The cell design was such that the reference (silver wire coated with silver chloride) and auxiliary (platinum wire) electrodes were placed in a stationary solution of saturated potassium chloride and contacted with a flowing buffer stream by means of a T-junction (Fig.1). A slight back-pressure from a potassium chloride reservoir maintained a stationary phase for the reference and auxiliary electrodes whereas the working electrode was positioned in the flowing stream. When not in use the electrode was stored at 4°C in the pH 6.0 phosphate buffer. Electrode potentials were controlled and the currents monitored with a potentiostat (Metrohm VA-detector E611). A Linear y - t chart recorder (Model 500) was used to record the flow injection signals. Sample propulsion was achieved with a four-channel peristaltic pump (Ismatec Model IP-4) and sample injections were made with a manual (PTFE) valve (Tecator). All connecting tubing was of PTFE (nominal i.d. 1.27 mm). Pump pulsation was reduced with a suppressor A-I H /D ? J Fig.1. Amperometric flow-through cell. A Perspex block; B, reference electrode chamber; C auxiliary electrode chamber; D, enzyme electrode chamber; E sample inlet; F sample outlet; G from saturated potassium chloride reservoir; H platinum wire enzyme electrode; I electrode connector; and J silicone-rubber seal situated immediately after the pump. Static noise was con-trolled by earthing the flowing stream immediately after the injection valve. Results Response to Glucose Prior to the calibration of the platinum wire enzyme electrode its optimum pH range and the effect of flow-rate were investigated. For assessing the optimum pH a glucose standard (1 mM) was injected (500 mm3 samples) over the electrode at a buffer flow-rate of 2.5 cm3 min-1.The pH effect was investigated over the range 4.5-8.0 with sample injections at 0.5 pH unit intervals. The resulting peak height versus pH profile (Fig. 2) exhibits a plateau region between ca. pH 5.8 and 6.5. Hence all further work was carried out at pH 6.0. The effect of the flow-rate of the carrier stream at pH 6.0 over the range 0.5-4 cm3 min-1 was investigated relative to the peak height of a glucose standard (1 mM). The resulting peak height versus flow-rate profile (Fig. 3) increased almost linearly until a limiting value was reached for flow-rates above 3.2 cm3 min-1. A more detailed investigation over the flow-rate range 2-4 cm3 min-1 showed a clear optimum response at around 3.2 cm3 min-1 and there was little change for higher flow-rates.Hence a flow-rate of 3.5 cm3 min-1 was adopted in this study. The electrode was calibrated at the optimised pH and flow-rate with glucose standards over the range 0.1-30 mM. Fig. 4 illustrates a typical chart recorder output and Fig. 5 shows the corresponding calibration. The calibration was linear over the range 0.1-10 mM glucose with excellent response times (<25 s) and wash times (<30 s). The linear portion of the calibration graph corresponds to log(current/A) = 0.992 log ([glucose]/~) - 3.94 with a correlation coefficient of 0.999. 2 100 & a E 7f) 120 u) 1 Y lu a 80 I I I 5 6 7 8 Phosphate buffer (100 mM) pH Fig. 2. samples Effect of pH on glucose (1 mM) response for 500-mm3 140 2 $ 100 Y $.- 01 I I I I 1.0 2.0 3.0 4.0 Flow-rateicm3 min-l Fig.3. Effect of flow-rate on glucose (1 mM) response for 500-mm3 samples. 0 Electrode 1 d old; A electrode 4 d old; . electrode 8 d ol ANALYST NOVEMBER 1986 VOL. 111 1237 5 rnin Scan Fig. 4. electrode Chart recorder output for glucose calibration for 3 d old 0-J 4- -1 L 0, a L Y m a -.--2 Log([glucoselimM) Fig. 5. Calibration graph for glucose Discussion Activation of Platinum Wire Platinum electrodes may be rendered more active by pulsing the electrode between anodic and cathodic potentials. 11.12 It has been suggested11 that the pulsing technique roughens the platinum surface. Roughening has been attributed to a re-distribution of surface metal ions as a direct result of the formation and breakdown of platinum - oxygen bonds.Essentially anodic - cathodic treatment results in metal from the electrode surface dissolving on the anodic sweep and a fraction of it being re-deposited on the cathodic sweep. This process is equivalent to surface evaporation and selective condensation to produce a clean fresh metal surface. Cyclic voltammetry was used to monitor the activation of the platinum wire electrode. The changing shape of the voltammogram during activation and a typical voltammetric profile for such a modified platinum electrode are shown in Fig. 6(a). As the fractional coverage of impurities is reduced ~~ 0 0.65 1.3 VoltageN Fig. 6. Cyclic voltammograms illustrating the effect of activation and silanisation of the platinum electrode.(a) Change in shape of the curve during activation; (b) activated platinum wire and (c) silanised platinum wire during activation there is a corresponding increase in oxygen adsorption (beyond +1.1 V vs. Ag - AgCl for the anodic branch) and desorption (ca. +0.6 V vs. Ag - AgCl for the cathodic branch) as depicted in Fig. 6(a) and (b). Attempts to immobilise enzyme on an inactivated platinum wire proved unsuccessful further emphasising the importance of electrode surface modification by activation. The anodisation time recommended by Ya09 (1 h at +2.5 V vs. SCE) was reduced in this work to 5 min without any decrease in the over-all performance of the enzyme electrode. Biegler and Woods13 demonstrated that the maximum oxygen coverage was attained within ca.1 s for an electrode set at >2.2 V (vs. SHE) in sulphuric acid (1 M). Consequently the reduction of anodisation time reported here still provides for the maximum oxygen coverage of the platinum wire. Following anodisation the platinum wire was silanised as described and immediately after silanisation it was examined by cyclic voltammetry [Fig. 6(c)]. The disappearance of the oxygen desorption previously noted at ca. +0.6 V [see Fig. 6(b) and 6(c)] clearly indicates the extensive coverage of the platinum surface by the action of the silanising agent. Response Characteristics The optimum pH for the platinum enzyme electrode lies between 5.8 and 6.5. Other workers have reported a broad pH range of 4.0-7.0 with a maximum response around pH 5.5 for solubilised glucose oxidase.14.15 The extent of such pH shifts is a direct result of the change in the microenvironment of the enzyme and is related to the immobilisation technique and the nature of the support material.The increasing current response to glucose with increasing flow-rate is unexpected (Fig. 3) because as the flow-rate is increased the residence time of the substrate over the electrode decreases and consequently a decrease in current response would be expected. However the observed phe-nomenon may be associated with the proximity of the enzym 1238 ANALYST NOVEMBER 1986 VOL. 111 to the platinum. As the flow-rate is increased there is turbulence and the degree of substrate diffusion to the electrode and of products away from the electrode is increased.An optimum response is reached at a flow-rate of 3.2 cm3 min-1 but a further increase produces no change in the glucose response. The flow-rate might need to be adjusted for real samples such as blood serum as in flow injection systems there can be differences arising from viscosity considerations. Important parameters when considering immobilised en-zymes are the lifetime durability and storage suitability and stability. The modified platinum wire enzyme electrode exhibited a good and reproducible response to variable glucose levels for daily use with flow injection analysis samples over a period of 10 d after which there was a sudden inactivation of the electrode. For a continuous exposure to glucose achieved by pumping glucose (10 and 2.5 mM) over the electrode at 3.5 cm3 min-1 the electrode functioned well for 9 h before inactivation.The relatively short over-all lifetimes compared with those observed for an electrode with glucose oxidase immobilised on nylon mesh16 (loading 22 nmol cm-2 min-1) may relate to the enzyme loading on the wire (5-10 nmol cm-2 min-I) small surface area and/or weakness in the nature of the Pt - 0 bonding. Masoom and Townshendl0 reported glucose oxidase activity of up to 1 year for 3-aminopropyltriethoxysilane - glutaraldehyde - glucose oxidase on controlled-porosity glass (CPG) which has a much larger usable surface area. The large surface area of CPG used in a reactor provides a highly active immobilised system so that some loss of activity has a negligible effect on glucose response.The modified platinum wire carries a thin layer of immobilised enzyme but there is the advantage that the sensor is in dwelling. However an additional factor in reducing electrode lifetime is the setting of the electrode at an anodic potential that may facilitate desorption of the oxygen, resulting in the premature loss of enzyme activity by the breaking of the Pt - 0 bonds which are however weaker than the Si - 0 bonds of controlled porosity glass. The authors thank the Department of Trade and Industry (Laboratory of the Government Chemist) for financial sup-port. Thanks are also extended to Mrs. Geraldine Alliston of the Laboratory of the Government Chemist for very helpful discussions. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. References Clark L. C. and Lyons C. Ann. N . Y. Acad. Sci. 1962 102, 29. Guilbault G. G. Ion-Sel. Electrode Rev. 1982 4 187. Karube I. and Suzuki S . Ion-Sel. Electrode Rev. 1984,6,15. Lehhart J. R. and Murray R. W. J. Electroanal. Chem., 1977 78 195. Murthy A. S. N. and Reddy S . Electrochim. Acta 1983,28, 473. Ianniello R. M. Lindsay T. J. and Yacynych M. Anal. Chem. 1982 54 1980. Cass A. E. G. Davis G. Francis G. D. Hill H. A. O., Aston W. J. Higgins I. J. Plotkin E. V. Scott L. D. L. and Turner A. P. F. Anal. Chem. 1984 56 667. Albery W. J. and Bartlett P. N. J. Chem. SOC. Chem. Commun. 1984 234. Yao T. Anal. Chim. Acta 1983 148 27. Masoom M. and Townshend A. Anal. Chim. Acta 1984, 166 111. Woods R. Electroanal. Chem. 1976 9 9. Gilman S . Electroanal. Chem. 1967 2 111. Biegler T. and Woods R. J. Electroanal. Chem. 1969 20, 73. Bright H. J. and Appleby M. J. Biol. Chem. 1969 224, 3625. Weibel M. K. and Bright H. J. J. Biol. Chem. 1971 246, 2734. Moody G. J. Sanghera G. S . and Thomas J. D. R. Analyst, 1986 111 605. Paper A61141 Received May 12th 1986 Accepted June 16th 198

ISSN:0003-2654    

DOI:10.1039/AN9861101235

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1986, VOL. 111 1239 Differential Pulse Cathodic Stripping Voltammetric Investigation of Cr04*-, Mo042-, W042- and V03- M. Rasul Jan* and W. Franklin Smytht Department of Chemistry, University College Cork, Cork, Ireland The differential pulse cathodic stripping voltammetric behaviour of Cr042-, Moo4*-, W042- and V03- has been investigated and applied to the determination of trace concentrations of these oxyanions. Detection limits of 5.6 X lO-7,6.1 x 10-8, 1 . 1 x 10-7 and 8 x 10-8 M and quantitation limits of 1.87 x 1.1 X 10-6 and 2.7 x M have been calculated for the cathodic stripping voltammetric determination of Cr042-, W042-, Mo042- and V03-, respectively. The effects of equimolar and lower concentrations of selected cationic and anionic interferents on their differential pulse cathodic stripping voltammetric behaviour have also been examined.These reveal that certain heavy metal cations such as Pb", Cull, Znll, Cdil and Agl can compete with Hgl for the appropriate oxyanions and that anions such as S*- and I-, which form partially insoluble mercury salts, can compete for sites around the mercury drop. Keywords: Differential pulse cathodic stripping voltammetry; oxyanions 2.03 X The polarographic behaviour of Cr042- and Mo042- has been described in detail elsewhere,, with the reduction of MoVI receiving the most attention.1-18 These studies were usually conducted in hydrochloric and sulphuric acid solutions and showed multi-step reductions. The catalytic effect of MoVI in the concentration range 4 X 10-7-4 x M on the reduction of nitrate can be used quantitatively for the determination of the former.5 The stripping voltammetric behaviour of Cr042-, MOO^^-, W042- and V03- has received some attention in recent years.Vydra et aZ.19 summarised the literature in this field. The d.c. cathodic stripping of these ions in 0.05 M potassium nitrate at a hanging mercury drop electrode, after the formation of the corresponding Hg22+ compounds at a positive potential, has yielded quantitative methods for the determination of Mo042-, W042- and V03- in the range 3 X 10-6-10-5 M . ~ O The reaction Mo042- --+ Mo02.2H20, carried out on a mercury electrode, has been proposed for the determination of M0042- in 3 M sodium chloride down to a concentration of 5 X 10-6 M by chronopotentiometric stripping.21 The selective adsorption of W042- on the hanging mercury drop electrode in the zero current state has been recommended for the stripping determination of this anion in the concentration range 1 x 10-7-2 x 10-6 M, using a plating potential of +0.2 V and a solution buffered at pH 3.6.22 Owing to the importance of these anions in environmental chemistry, this study was carried out to develop more sensitive voltammetric methods by which the oxyanions could be determined.The differential pulse mode was chosen for the stripping investigations. The selectivity of these methods was also evaluated with respect to the determination of the oxyanions in the presence of other cations and anions. Experimental Apparatus All experiments were performed using a Princeton Applied Research (PAR) Model 174 A polarograph with a PAR Model 303 hanging mercury drop electrode (HMDE).Voltammo- grams were recorded on a PAR Model RE 0074 X - Y recorder. The electrode system was constructed with a platinum wire auxiliary electrode and a saturated calomel electrode as a reference electrode, together with the hanging mercury drop electrode. Oxygen-free nitrogen was used for de-gassing the system and a Kent Model EIL 7055 pH meter was used for the pH measurements. Reagents All solutions were diluted with de-ionised water unless stated otherwise. All glassware was washed with Decon 90 and thoroughly rinsed with de-ionised water. Solution preparation Standard stock solutions and interfering cation and anion solutions were prepared using the method reported earlier.23 Procedure Solutions (10-5 M) of oxyanions were prepared in a 0.05 M potassium nitrate supporting electrolyte, and 10 ml of this solution were taken for the sample cell.The solution was de-gassed by bubbling oxygen-free nitrogen through the solution for 4 min, after which a flow of nitrogen was maintained over the solution throughout the analysis. After bubbling the nitrogen through the solution and a 30 s quiescent time, the solution was electrolysed at an appropriate positive potential (+0.15-0.20 V) for 1-5 min and was then scanned in a negative potential direction at 10 mV s-1 to obtain the DP stripping peak using a medium-sized hanging mercury drop. The interfering ions were injected through the side orifice in the cell using a 100 1.11 micropipette.Limits of detection (LOD) and quantitation (LOO) were determined and calculated by the method of M0rrison.2~ Results Optimisation of DPCSV Parameters for the Determination of CrOd2-, Mo042-, W042- and V03- The effect of initial potential, Eel, plating time and pH on the DPCSV behaviour of Cr042-, M0042-, W042- and V03- were studied. The conditions that gave rise to the most sensitive determination of the oxyanions in 0.05 M potassium nitrate supporting electrolyte were then selected and are presented in Table 1. * Present address: Department of Chemistry, University of Peshawar, N. W.F.P. , Peshawar, Pakistan. t Present address: Department of Pharmacy, Medical Biology Centre, Queens University of Belfast, Belfast BT9 7BL, UK. Effect of Concentration on the DPCSV Behaviour of Cr042-, Mo042-, WO& and VOj- The effect of concentration on the DPCSV behaviour of the oxyanions was studied under optimised conditions.For1240 ANALYST, NOVEMBER 1986, VOL. 111 Cr042- at 10-5 M and lower concentrations, only one peak, at a peak potential of E, = 0 V, is observed. At concentrations greater than 10-5 M more than one peak is observed, showing multi-layer formation phenomena. The optimum concentra- tion range for the determination of Cr042- by this method is 10-5-1.8 X 10-6 M in 0.05 M potassium nitrate (pH 6) supporting electrolyte. For MOO^^- at 10-5 M concentration and higher, two peaks are observed, showing multi-layer formation. One peak is observed at -0.04 V and the other at -0.28 V. At concentra- tions of 1 0 - 6 ~ and lower only one peak is observed for Mo042-, at -0.08 V.This peak is of analytical importance at concentrations lower than 10-5 M. At a concentration of 10-5 M, V03- also shows the multi-layer formation phenomena. At pH 4, 5 and 6, V03- gives a two-peak pattern, one peak with a peak potential of -0.03 V and the other at -0.1 V. The peaks are independent of pH at pH 4-6. The effect of plating time on the V03- signal was studied. Only the first peak shows a proportional increase with plating time. This increase suggests that there is an outer multi-layer formed by HgV03 and Hg(V03)2 around the mercury drop. The monolayer is strongly bound to the mercury drop and is stripped at more negative potentials. At lower concentrations only one peak is observed for the DPCSV of VO3-.Also, the peak potential ( E p ) varies with concentration. As the concentration increases, the peak potential moves towards more negative potentials. Multi-layer formation at higher concentrations is also observed for the DPCSV behaviour of W042-. At pH 6, W042- shows two peaks, one at Ep -0.07 V and the other at Ep = -0.235 V. The latter peak shows no increase with plating time. The first peak is of analytical importance and was chosen for the study. At lower concentrations only the first peak is observed. Effect of Interfering Ions on the DPCSV Behaviour of Cr042- and Mo042- Cr042-, Mo042-, W042- and V03- all stripped at the same potential and so inevitably interfered with each other. The effects of cationic and anionic interferences of equimolar and sub-equimolar concentrations were studied for each oxyanion in turn.These studies are illustrated for Cr042- in Table 2. Among the cations studied, equimolar concentrations of PbII, Zn" and AgI interfere with the DPCSV signal of 10-5 M Cr042-, with recoveries of 86.8,89.7 and 90.3%, respectively. This decrease is due to the competitive complexation of Cr042- with these heavy metals, thus reducing a certain percentage of the Cr04*- available for determination by DPCSV. At a concentration of 10-6 M these cations do not interfere. Equimolar concentrations of NaI, Ca" and F- also interfere, with recoveries of 116, 117 and 119%, respectively. At a concentration one order of magnitude lower, this effect starts to decrease. Equimolar concentrations of Br- and 9- do not affect the Cr042- peak recovery, but the DPCSV of Cr042- in the presence of S2- shows an interfering peak at approximately 0 V and a residual HgS stripping peak at -0.7 V (Fig.1). This shows a competition between Hg2Cr04 Table 1. Optimum DPCSV conditions for the determination of C T O ~ ~ - , Mo042-, W042- and V03- Optimum pH using 0.05 M KN03 as Initial potential, Plating time/ supporting Oxyanion E,,N vs. SCE min electrolyte c1-0~~- . . +0.2 5 6 wo42- . . +0.2 2 6 V03- . . +0.2 5 6 Mo042- . . +O. 15 5 6 (or HgCr04) and HgS for sites around the mercury drop and seriously impairs the usefulness of the DPCSV determination of Cr042- in the presence of equimolar concentration of S2-. I- is also a serious interferent in that it strips at a slightly more negative potential, i.e., -0.15 V, when it is present on its own.When it is added as an interferent to Cr042- no separate peak is observed for I- and it adds to the Cr042- peak with a resulting recovery of 172.2%. The effect of equimolar and lower concentrations of selected cations and anions on the DPCSV behaviour of M Mo042- is given in summarised form in Table 3. Among the cations studied, only Pb" significantly interferes at equimolar concentrations, reducing the Mo042- peak by +0.2 0.0 -0.2 -0.4 -0.6 -0.8 Vo I tag eiV Fig. 1. Effect of equimolar concentrations of S2- on the DPCSV behaviour of Cr042-. Scan rate, 20 mV s-l; modulation, 25 mV Table 2. Effect of equimolar and lower concentrations of selected cations and anions on the DPCSV behaviour of 10-5 M Cr04*- in 0.05 M KN03 supporting electrolyte (pH 6) Interferent added CU" .. . . . . Cd" . . . . . . Ni" . . . . . . Pb" . . . . . . Pb" . . . . . . Ca" . . . . . . Ca" . . . . . . Ca'I . . . . . . Na' . . . . . . Na' . . . . . . Na' . . . . . . Na' . . . . . . Na' . . . . . . Zn" . . . . . . Zn" . . . . . . Agr . . . . . . Ag' c1- F- . . F- . . . . . . . . . . . . . . . . . . . . . . I- . . . . . . . . I- . . . . . . . . Concentration of interferenth 10-5 10-5 10-5 10-5 10-5 10-7 10-5 10-7 10-5 10-5 10-5 10-5 10-5 10-7 10-5 10-5 10-6 10-6 10-6 10-8 10-9 10-6 10-6 10-6 10-6 Recovery, % 100 100 100 100 117 114.3 100 116 116 115.1 114.8 101.7 89.7 100 90.3 100 100 119 100 172.2 136.4 100 100 100 86.8ANALYST, NOVEMBER 1986, VOL. 111 1241 15.5%.This could be due to competitive complexation of Mo042- with Pb". I- is the main anionic interference at an equimolar concentration, as it cathodically strips at the same potential. An equimolar concentration of S2- reduces the Mo042- peak by 13%. This is presumably due to the competition of S2- and Mo042- for sites around the mercury drop. S2- strips at a more negative potential (-0.7 V). The same effect was observed for the DPCSV behaviour of mixtures of S 2 - and Cr042-. Equimolar concentrations of F- and C1- reduce the MOO^^- peak by 4 and 19%, respectively. Effect of Interferences on the DPCSV Behaviour of V03- The effect of equimolar concentrations of various cations and anions on the DPCSV behaviour of 10-5 M V03- was studied under optimum analytical conditions and the results are summarised in Table 4.Equimolar concentrations of Ca", Agl, C1-, F- and Br- have no effect on the recovery of the V03- peak. An equimolar concentration of PbII gives a serious interference. In the presence of an equimolar concentration of Pb", the first peak of VO3- is observed with a 40% recovery, whereas the Table 3. Effect of equimolar and lower concentrations of selected cations and anions on the DPCSV behaviour of 10-5 M Mo0,2- in 0.05 M KN03 supporting electrolyte (pH 6) Concentration of Interferent added interferenth Cd" . . . . . . 10-5 Pb" . . . . . . 10-5 Pbl' . . . . . . 10-6 CUT' . . . . . . 10-5 Zn" . . . . . . 10-5 Na' . . . . . . 10-5 Ag' . . . . . . 10-5 Ca" . . . . . . 10-5 I- . . . . . . . . 10-5 I- . . . . . . . .10-6 F- . . . . . . . . 10-5 F - . . . . . . . . 10-6 €3- . . . . . . 10-5 a- . . . . . . 10-5 a- . . . . . . 10-6 s2- . . . . . . 10-5 s2- . . . . . . 10-6 Recovery, % 84.5 100 100 100 100 100 100 350 100 100 100 100 100 99.0 95.9 81.0 87.0 Table 4. Effect of equimolar and lower concentrations of selected cations and anions on the DPCSV behaviour of M V03- in 0.05 M KN03 supporting electrolyte (pH 6) Recovery, YO E, = - 0.03 V E, = -0.1 V Concentration of interferenth CU" . . . . . . 10-5 72.7 85.1 Zn" . . . . . . 10-5 82.8 86.0 Ni" . . . . . . 10-5 91.1 91.8 Cd" . . . . . . 10-5 73.7 78.0 Interferent added CU" . . . . . . 10-6 100 100 Zn" . . . . . . 10-6 100 100 Ni" . . . . . . 10-6 100 100 Cdl' . . . . . . 10-6 98.7 100 Na' . . . . . . 10-5 102.8 100 Cal' .. . . . . 10-5 100 100 Ag' . . . . . . 10-5 100 100 Pb' . . . . . . 10-5 40.0 0.0 Pb" . . . . . . 10-6 100 100 s2- . . . . . . 10-6 100 100 1- . . . . . . 10-5 100 0.0 I- . . . . . . 10-6 100 100 c1- . . . . . . 10-5 100 100 Br- . . . . . . 10-5 100 100 F- . . . . . . 10-5 100 100 S2- . . . . . . 10-5 80.0 87.2 second totally disappears. The disappearance of the second and the decrease of the first peak are presumably due to the formation of lead vanadate [Pb(V03)2] after the successful competition with Hg22+ or Hg2+ for complexation with the VO3- anion. The total disappearance of the second peak and partial disappearance of the first suggest that the PbII competes successfully for V03- in the monolayer state and is partly successful on the multi-layer. The effect of PbII on the DPCSV behaviour of V03- is shown in Fig.2. The interfer- ence effect of PbII is no longer observed when it is present one order of magnitude lower than V03-. Equimolar concentra- tions of &I1, ZnII, Ni" and CdII decrease the VO3- peaks with peak recoveries of 72.7, 85.7% (peak 1 and peak 2); 82.8, 86.01; 91.1, 91.8; 73.7, 78.0%, respectively, owing to the complexation of V03- with these heavy metal cations, affecting both the multi-layer and monolayer states of HgV03 - Hg(V03)2. In the presence of these cations the first peak is generally more affected than the second and this can be explained by the cations preferring the multi-layer of HgV03 - Hg(V03)2 around the mercury drop to the monolayer. The anions S2- and I- interfere with the HgV03 - Hg(V03)2 stripping peak at equimolar concentrations. V03- and S2- compete for sites around the mercury drop to form their respective salts, resulting in a decrease in the HgV03 - Hg(V03)2 stripping peak.In the presence of an equimolar concentration of I- (Fig. 3), the second peak of V03- totally disappears, with the appearance of a reduced I- peak at the expected potential of approximately -0.1 to -0.2 V. I- in this instance effectively disrupts the monolayer of HgV03 - Hg(V03)2 around the mercury drop as compared with S2-. To determine V03- by this method the concentration of PbII and I- should be at least one order of magnitude lower than the concentration of V03-. Effect of Interferences on the DPCSV Behaviour of WO42- The effect of equimolar and lower concentrations of selected cations and anions on the DPCSV behaviour of 10-5 M W042- was studied and is given in sumarised form in Table 5.Equimolar concentrations of CuII, Pb", Na', Ni", Zn", AgI, C1- and F- have no effect on the peak recovery of W042-. 16.0 1 I I I +0.2 0 +0.2 0 - Vo I t a g elV .2 Fig. 2. Effect of equimolar concentrations of Pb'* on the DPCSV behaviour of V03- in 0.05 M potassium nitrate supporting electrolyte (pH 6). Scan rate, 10 mV s-1; modulation amplitude, 25 mV; plating time, 5 min; starting potential, +0.2 V1242 I I 8 - ANALYST, NOVEMBER 1986, VOL. 111 -.+ 1o-5Mvo3- Table 5. Effect of equimolar and lower concentrations of selected cations and anions on the DPCSV behaviour of 10-5 M W042- in 0.05 M KN03 supporting electrolyte (pH 6) Concentration of In terferen t added in terferen t/M Recovery, YO Cu" .. . . . . Pbrl . . . . . . Nar . . . . . . Cd" . . . . . . Cd" . . . . . . Carr . . . . . . Ca" . . . . . . Nirl . . . . . . ZnT1 . . . . . . Agr S2- S2- Br- Br- I- . I- . C1- F- , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-6 10-6 10-6 10-6 10-6 99 100 100 93 100 97 100 101 99 100 46 100 71 100 55 100 100 100 +0.2 0 -0.2 -0.4 Vo ltag elV Fig. 3. Effect of equimolar concentrations of I- on the DPCSV behaviour of 10-5 M V03- in potassium nitrate supporting electrolyte (PH 6 ) . Scan rate, 10 mV s-1; modulation amplitude, 25 mV; plating time, 2 min Equimolar concentrations of Cd" and Ca" slightly interfere, reducing the HgW04 - Hg2W04 stripping peak by 7 and 3%, respectively.Certain anions are the only serious interferences at equimolar concentrations on the DPCSV behaviour of W042-. Equimolar concentrations of Br-, S2- and I- reduce the stripping peak with recoveries of 71, 46 and %YO, respectively. The corresponding mercury salts of Br-, S2- and I- presumably also adsorb on the mercury drop and compete for sites on the surface with HgW04 - Hg2W04, hence giving the reduced recoveries. Analytical Applications This voltammetric method of determination is very sensitive for the determination of the oxyanions investigated. The limits of detection of these oxyanions were determined and the limit of quantitation and relative standard deviation near the detection limit were calculated and are shown in Table 6.The DPCSV behaviour of V03- at a concentration near the detection limit is shown in Fig. 4. This method could be used for the determination of any of the oxyanions studied in mixtures if the concentration of the interferent anion is one order of magnitude lower in concentration. Some of the cations studied do interfere with the DPCSV behaviour of Table 6. Limits of detection and quantitation of the oxyanions by DPCSV using the conditions described in Table 1 Limit of Limit of Relative standard Oxyanion detection/M quantitationh deviation,% Cr04*- . . 5.6 x 10-7 1.87 X 10-6 0.93 Mo042- . . 1.1 x 10-7 1.1 x 10-6 0.85 vo3- . . 8 X 10-8 2.7 x 10-7 0.29 wo42- . . 6.1 x 10-8 2.03 x 10-7 1.15 0 -0.2 -0.4 VoltagelV Fig.4. Repetitive scans at a concentration near the detection limit for V03- by DPCSV in a 0.05 M potassium nitrate supporting electrolyte (pH 6) these oxyanions, such as PbII, CuII, Zn", CdlI and Agl, whereas S2- and I- are anionic interferents. This method could be utilised for the determination of any of the oxyanions at trace levels in order to monitor them in biological or environmental samples, Conclusion The interference effects of the different cations and anions can be classified under the following headings. Complexation Certain heavy metal cations such as Pb", Cu", Zn", Cd" and AgI can reduce the DPCSV peaks of the oxyanions studied by their competition with Hg*+ - Hg22+ for complexation with the oxyanions. V03- is mainly affected by this process.Competition for Sites This is generally observed for those anions which also form partially insoluble mercury salts such as S2- and I-. They compete for sites around the mercury drop and result in decreased peak(s) for the DPCSV signal of the appropriate oxyanions. Anomalous Effects The effect of some cations, e . g . , Na', on the DPCSV behaviour of oxyanions is anomalous. The presence of these cations has enhancement effects on the DPCSV peaks of some of the oxyanions, possibly due to catalysis of the mercury - oxyanion reaction. References 1. Parry, E. P., and Yakubik, M. G., Anal. Chem., 1954, 26, 1294.ANALYST, NOVEMBER 1986, VOL. 111 1243 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. Wolter, M., Wolf, D. O., and Vonstackelbery, M., J . Electroanal.Chem., 1969, 22, 221. Uhl, F. A., Z. Anal. Chem., 1937, 110, 102. Kolthoff, I. M., and Hodra, I., J. Electroanal. Chem., 1961,4, 369. Johnsen, M. G., and Robinson, R. J., Anal. Chem., 1961, 33, 336. Haight, G. P., Anal. Chem., 1951, 23, 1505. Haight, G. P., Anal. Chem., 1953, 25, 642. Haight, G. P., J . Am. Chem. SOC., 1954, 76, 4718. Haight, G. P., and Sager, W. F., J. Am. Chem. SOC., 1952,74, 6056. Rechnitz, G. A., and Laitinen, H. A , , Anal. Chem., 1961,33, 1473. Lanza, P., Ferri, D., and Buldini, P. L., Analyst, 1980, 105, 379. Lingane, J. J., and Kolthoff, I. M., J . Am. Chem. SOC., 1940, 62, 952. Williams, W. J., “Handbook of Anion Determination,” Butterworths, London, 1979, p. 249. Kolthoff, I. M., and Parry, E. P., J . Am. Chem. SOC., 1951,73, 5315. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. Yatsimirskii, K. B., and Budarin, L. I., Zh. Neorg. Khim., 1962, 7, 1824. O’Shea, T. A., and Parker, G. A . , Anal. Chem., 1972,44, 184. Zelinka, J., Bartusek, M., and Okac, A., Collect. Czech. Chem. Commun., 1974, 39, 83; Anal. Abstr., 1976, 27, 676. Morales, A., Gonzales, B. F., and Diaz, C., Chemist Analyst, 1967,56, 89. Vydra, F., Stulik, K., and Julakova, E., “Electrochemical Stripping Analysis,” Ellis Horwood, New York, 1976, pp. 25& 254. Geyer, R., Henze, G., and Jenze, J., 2. Tech. Hochschule Chem. Carl Schorlemmer, 1966, 8, 98. Lagrange, P., and Schwing, J. P., Anal. Chem., 1970,42,1844. Berge, H., and Ringstorff, H., Anal. Chim. Acta, 1971, 55, 201. Jan, M. R., and Smyth, W. F., Analyst, 1984, 109, 1187. Morrison, G. H., Anal. Chem., l980,52,2241A. Paper A41368 Received October 23rd, I984 Accepted June 26th, I986

ISSN:0003-2654    

DOI:10.1039/AN9861101239

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1986, VOL. 111 1245 Sensitive Adsorptive Stripping Voltammetric Measurements of Antihypertensive Drugs Joseph Wang,* Timothy Tapia and Mojtaba Bonakdar Department of Chemistry, New Mexico State University Las Cruces, NM 88003, USA Controlled adsorptive accumulation of reserpine, rescinnamine and hydralazine on carbon electrodes provides the basis for sensitive stripping measurement schemes for these compounds. Cyclic voltammetry is used to explore the interfacial and redox behaviours. The detection limits are reserpine, 2 x 10-9 M, rescinnamine, 3 x 10-9 M, and hydralazine, 1 x 10-8 M. The adsorptive stripping response is evaluated with respect to various experimental conditions. Exchange to a blank solution corrects for major interferences. The relative standard deviation at the sub-micromolar level ranges from 5 to 9%.Applicability to measurements in urine is illustrated. Keywords Reserpine; h ydralazine; stripping voltammetry; adsorptive accumulation; antihypertensive drugs Adsorptive stripping voltammetry has been demonstrated to be a highly sensitive electroanalytical method for the determi- nation of a wide range of electroactive compounds.'-3 The method utilises controlled interfacial accumulation of the analyte on to the electrode surface as an effective pre- concentration step, prior to the voltammetric determination of the surface species. This extends the scope of stripping voltammetry towards additional analytes that cannot be pre-concentrated electrolytically. Among these are numerous compounds of pharmaceutical significance; reducible drugs such as diazepam and nitrazepam, 1 digoxin4 and tetracyclines5 have been determined at a hanging mercury drop electrode, whereas oxidisable drugs, e.g., chlorpromazine ,6 adriamycin7 and tricyclic antidepressants8 have been determined at various carbon electrodes.This paper describes sensitive adsorptive stripping pro- cedures for the determination of trace amounts of several antihypertensive agents. The determination of the widely used Rauwolfia alkaloid reserpine, its related drug rescinnamine and the vasodilator hydralazine at various carbon electrodes is described. These compounds are electrochemically active. There have been several earlier studies on the polarographic determination of reserpine, particularly using a.c. polaro- graphy and an aprotic organic solvent system.9-11 Such studies yielded detection limits in the 10-5 M range, thus allowing convenient tablet assays. Reserpine and rescinnamine also exhibit an anodic response. This was exploited recently for amperometric detection following liquid chromatography.12 Similarly, the oxidation of hydralazine was used for amper- ometric detection following liquid chromatography. 1 3 ~ 4 Sen- sitive voltammetric measurements of these drugs, based on their anodic behaviour at carbon electrodes, have not been attempted. As illustrated in this study, such behaviour can be coupled with the interfacial properties of reserpine, rescinn- amine and hydralazine to yield a highly sensitive adsorptive stripping procedure. Hence, detection limits at the nanomolar concentration level are obtained.The characteristics of such procedures are described in this paper. Experimental Apparatus A 10-ml voltammetric cell (Model VC-2, Bioanalytical Systems) was used. The cell was joined to the working electrode, reference electrode (Ag - AgC1, Model RE-1, Bioanalytical Systems) and platinum wire auxiliary electrode through holes in its Teflon cover. A magnetic stirrer and a stirring bar (1.2 cm in length) provided the convective * To whom correspondence should be addressed. transport during the pre-concentration. In experiments involving the medium exchange, a second (measurement) cell was used. The carbon working electrodes included a glassy carbon disc (3 mm in diameter, Bioanalytical Systems) and a laboratory-made carbon paste disc (3 mm in diameter), prepared by mixing graphite powder (Acheson 38) and Nujol oil (40% oil by mass).A fresh carbon paste surface was used daily, with the surface being smoothed on a computer card. The glassy carbon surface was polished daily with a 0.05-pm alumina slurry, rinsed with de-ionised water and allowed to air-dry . Stripping and cyclic voltammograms were recorded with EG & G Princeton Applied Research Models 364 and 264 polarographic analysers, respectively. Reagents Stock solutions (5 x M) of the antihypertensive agents (Sigma) were prepared daily. The hydralazine solution was prepared by dissolving the compound in de-ionised water. Reserpine and rescinnamine were dissolved in acetic acid and ethanol, respectively, and then diluted with de-ionised water.The supporting electrolyte was 0.05 M phosphate buffer, prepared from a 1 + 4 mixture of KH2P04 and K2HP04 and adjusted to pH 4.0 with H3P04. All solutions were prepared from de-ionised water and analytical-reagent grade chemicals. The urine samples were obtained from a healthy volunteer and diluted (1 + 4) with the supporting electrolyte prior to use. Procedure The pre-concentration step was performed by immersing the working carbon electrode into a stirred (ca. 400 rev. min-1) 10-ml sample solution for a given time period. During this period the electrode was held at 0.0 V (reserpine, rescinn- amine) or -0.3 V (hydralazine). The stirring was then stopped and the surface species were determined by applying an anodic potential scan (a differential pulse waveform for reserpine and rescinnamine and a d.c.ramp for hydralazine). In experiments involving medium exchange, the pre-concentration proceeded at an open circuit; the electrode was then transferred into an electrolytic blank solution where an anodic potential scan was applied. To clean the surface of the remaining accumulated species, the electrode was held at +1.4 V (reserpine, rescinnamine) and +1.3 V (hydralazine) for 60 s; a subsequent scan was used to indicate the absence of memory effects. Results and Discussion Determination of Reserpine and Rescinnamine The accumulation of organic compounds at carbon paste electrodes usually proceeds via a mixed (adsorptive - extrac-1246 ANALYST, NOVEMBER 1986, VOL. 111 I 400 nA I B I I I 1 I I 1.0 0.8 0.6 0.4 0.2 0 E N Fig. 1.Repetitive cyclic voltammograms for 5 x 10-6 M reserpine (A) and rescinnamine (B), following 3- and 2-min stirring periods, respectively, at 0.0 V. Scan rate, 100 mV s-l; electrolyte, phosphate buffer (pH 4); electrode, carbon paste (a, T I I I 0.4 0.6 0.8 EIV Fig. 2. Differential pulse voltammograms for 6 x 10-8 M reserpine (a) and rescinnarnine (b) following (A) 0 and (B) 3 min pre- concentration. Differential pulse ramp with 50 mV amplitude and 5 mV s-l scan rate. Other conditions as in Fig. 1 tive) process. Fig. 1 shows repetitive cyclic voltammograms at a carbon paste electrode for 5 x 10-6 M reserpine (A) and rescinnamine (B). Stirring the solution prior to the first scan (designated as 1) results in large anodic peaks [at 0.71 V (A) and 0.75 V (B)] because of the oxidation of the accumulated drugs.Substantially smaller peaks are observed on continued scanning, indicating desorption (from the surface) and “back- extraction” (from the electrode interior) of the reaction product. Eventually, a stable response, corresponding to the contribution of the solution species alone, is observed. No peaks are observed in the cathodic branch, indicating an irreversible redox process. According to Adams,lS the anodic oxidation of methoxy-substituted indole alkaloids, including reserpine-like compounds, involves the introduction of a hydroxy group at the indole 5-position. By the use of 5 x 10-6 M solutions, surface saturation was observed after 120 s (reserpine) and 180 s (rescinnamine).The response for the surface-attached drugs under these condi- tions was used to determine the surface coverage and scan rate dependence. For example, the amounts of charge consumed during the cyclic voltammetry experiment by the redox 12 0 8 .-a . .-! 4 0 8oo . . P 400 I 0 I I I ( a ) 2 4 6 rimin Fig. 3. Dependence of the reserpine (A) and rescinnamine (B) peak current (a) and peak current enhancement (b) on the pre-concentra- tion time. Other conditions as in Fig. 2 process at saturation, i.e., 0.79 pC (reserpine) and 0.59 yC (rescinnamine), correspond to surface coverages of 3.2 X 10-11 and 2.5 x 10-11 mol cm-2, respectively. Such values reflect the similar molecular structures of the drugs. Graphs of log (peak current) vs. log (scan rate) for the surface-attached compounds over the 5-500 mV s-1 range were linear. These graphs had slopes of 0.76 (correlation coefficient 0.997) and 0.72 (correlation coefficient 0.998) for reserpine and rescinn- amine, respectively.Thus, a deviation from an ideal behavi- our of surface species (slope 1.00) is observed. The change of scan rate from 50 to 500 mV s-1 resulted in positive shifts in peak potential from 0.71 to 0.80 V (reserpine), and from 0.76 to 0.82 V (rescinnamine). Graphs of peak current vs. scan rate were linear over this range. No change in peak potentials was observed over the 5-50 mV s-1 scan rate range. The spontaneous adsorption of reserpine and rescinnamine can be used as an effective pre-concentration step prior to the voltammetric determination of these drugs.The resulting adsorptive stripping procedure offers a convenient determina- tion at the sub-micromolar and nanomolar concentration levels. For example, Fig. 2B shows differential pulse voltam- mograms at a carbon paste electrode that was dipped in stirred 6 x 10-8 M solutions of reserpine (a) and rescinnamine ( b ) for a 3-min pre-concentration period. Also shown (A) is the corresponding response without accumulation. For the short pre-concentration period used, a significant improvement in the sensitivity is observed. Detection limits of about 2 X 10-9 M for reserpine and 3 X 10-9 M for rescinnamine are estimated based on the signal to noise characteristics (SIN = 3) of the data shown in Fig. 2B. ‘Thus, 12 and 19 ng of reserpine and rescinnamine, respec- tively, can be detected in the 10 ml of solution used, i.e., 1.2-1.9 ng ml-1. Compared with the previous a.c.polaro- graphic procedures for reserpine the adsorptive stripping approach lowers the detection limit by four orders of magnitude. Attempts to perform adsorptive stripping measurements, based on the reduction process at the hanging mercury drop electrode, yielded a substantially inferior adsorptive stripping response. The extent of accumulation, and accordingly the resultingANALYST, NOVEMBER 1986, VOL. 111 ( a ) 1247 ( b) response, is affected by the solution conditions. The response was examined in the presence of various supporting electro- lytes, e.g. , sodium hydroxide, phosphate buffers (pH 4.0, 7.4 and 9.0), ammonium chloride and hydrochloric acid. The best results (with respect to peak enhancement and reproducibil- ity) were obtained with a phosphate buffer (pH 4.0); this electrolyte was used in subsequent work.Fig. 3(a) shows the dependence of the peak current on the pre-concentration time for reserpine (A) and rescinnamine (B). Both compounds exhibit similar current - time profiles; the peaks increase rapidly with time at first and then level off. Full surface coverage is approached for pre-concentration times longer than 4 min. At this point, the peak current enhancements, relative to direct measurements, are 12 (reserpine) and 8 (rescinnamine) [Fig. 3(b)]. Obviously, a trade-off would be required when optimising the pre-concen- tration. For convenient determination at the 5 x 10-8 M level, a pre-concentration time of 3 min is usually sufficient (e.g., Fig.2). Fig. 4 shows the dependence of the peak current on the reserpine (A) and rescinnamine (B) concentration using a 1 min pre-concentration. A curvature in the calibration graphs is observed over the 1.25 x 10-8 - 7.5 x 10-8 M range tested. Such behaviour is consistent with a process that is limited by the interfacial accumulation of the analyte. Accordingly, determination should be based on the use of calibration graphs and not the method of standard additions. The reciprocal plots, lli vs. llc, yielded straight lines over the concentration range examined in Fig. 4 (not shown). Such linearity is expected on the basis of the Langmuir adsorption model and may also be useful for the determination.Replicate peaks observed for the same sample solution illustrate the precision of the method. A series of six measurements of 6 x 10-8 M reserpine yielded a mean peak current of 0.67 PA, a range of 0.59-0.70 pA and a relative standard deviation of 9% (2 min pre-concentration; other conditions as in Fig. 2). High selectivity is yet another important advantage of the voltammetric determination of reserpine and rescinnamine based on interfacial accumulation. The selectivity advantage is obtained by incorporating the “medium-exchange” proce- dure716J7 i.e., the transfer of the electrode (with the accumu- lated drug) to a blank solution prior to the voltammetric scan. In this way, effective discrimination against interferences due to dissolved electroactive species is achieved.For example, Fig. 5(a) demonstrates the direct measurement of 2.5 x 10-7 M reserpine in a diluted (1 + 4) urine sample. Determination is not feasible by performing the voltammetric measurement in 0 2.5 5 7.5 Concentration ( x 10-8 M) Fig. 4. Dependence of the peak current on reserpine (A) and rescinnamine (B) concentration using 1 min pre-concentration. Other conditions as in Fig. 2 0 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.8 E N 5. Measurements of reserpine in (a) diluted (1 + 4) urine and M (a); in the presence of 1 x 10-4 M ascorbic acid with (B) and without 1.25 X 1 0 - 7 ~ ( b ) . Pre-concentration time: 2 min. Other conditions as in Fig. 2 medium exchange. Reserpine concentration: 2.5 x 0.8 0.6 0.4 0.2 0.0 -0.2 EIV Fig. 6. Repetitive cyclic voltammograms for 1 x 10-5 M hydralazine at a glassy carbon electrode following 1 min stirring at -0.3 V.Scan rate. 20 mV s-l: electrolvte. ohosohate buffer (DH 4)1248 ANALYST, NOVEMBER 1986, VOL. 111 -0.2 0.0 0.2 0.4 0.6 E N Fig. 7. M hydralazine at a glassy carbon electrode after different pre-concentration times: A, 0; B, 30; .C, 120; and D, 300 s. Pre-concentration at -0.3 V with 400 rev. min-1 stirring. Scan rate, 50 mV s-l; electrolyte, phosphate buffer (pH 4.0) Determination of Hydralazine The interfacial accumulation of the antihypertensive agent hydralazine is indicated from repetitive cyclic voltammograms recorded after a 1 min stirring period at -0.3 V (Fig. 6). The drug exhibits an irreversible oxidation peak at +0.25 V. The first scan (designated as 1) yields a large current response owing to the oxidation of the adsorbed species.Subsequent voltammograms, recorded on continued scanning, yielded much smaller peaks, indicating the rapid desorption of the product. The current enhancement, associated with the interfacial accumulation, allows the determination of trace amounts of hydralazine based on the adsorptive stripping approach. Fig. 7 shows linear scan voltammograms for 8 x 10-7 M hydralazine after different pre-concentration periods. Determination at this level is not feasible without pre-concentration (A). The peak height increases rapidly with increasing pre-concentra- tion time, indicating enhancement of the hydralazine concen- tration on the glassy carbon surface. For example, 30 and 300 s pre-concentration periods yield 10- and 40-fold enhancements of the peak current, respectively, relative to that attained without pre-concentration. As a result, hydralazine can be easily determined at the sub-micromolar concentration level; a detection limit of about 1 x 10-8 M is estimated based on the signal to noise characteristics (SIN = 3) of the 300 s pre-concentration voltammogram (D) .The adsorptive stripping hydralazine response is affected by the pre-concentration potential and the solution conditions. For example, a gradual increase of the peak (up to 70%) was observed on changing the pre-concentration potential from 0.0 to -0.3 V; no further change in current was observed at -0.4 and -0.5 V (1 x 10-6 M hydralazine, 2 min pre- concentration). Strong accumulation and well defined peaks were observed in phosphate buffer solutions of pH 4.0 and 7.4.A pH 9.0 phosphate buffer solution yielded an inferior performance. A -0.3 V pre-concentration potential and pH 4.0 phosphate buffer were used for the determination of hydralazine. Fig. 8 shows the dependence of the hydralazine peak current on the pre-concentration time (A) and the bulk concentration of the drug (B). The peak increases rapidly with time at first and then levels off (with some decrease for times Linear scan voltammograms for 8 X Timeimin 0 2 4 6 8 10 I 1 I I 0 5 10 15 20 Concentrationil 0-7 M Fig. 8. Dependence of the hydralazine peak current on pre-concen- tration time (A) and concentration (B). Pre-concentration time: B, 120 s. Concentration: A, 8 x 10-7 M. Other conditions as in Fig.7 longer than 5 min). A well defined concentration dependence is indicated from the calibration graph, with a curvature that represents the corresponding adsorption isotherm. The adsorptive stripping response of hydralazine is highly reproducible. Ten successive measurements yielded a mean peak current of 0.76 PA, a range of 0.71-0.85 yA and a relative standard deviation of 5% (5 x 10-7 M hydralazine, 2 min pre-concentration). In conclusion, highly sensitive voltammetric measurements of several antihypertensive agents are feasible after their interfacial accumulation and oxidation at various carbon electrodes. Improved selectivity is obtained using the medium-exchange procedure. The entire pre-concentration - medium-exchange - voltammetric scheme can be easily accomplished using a flow injection system,17 as is desirable in the clinical laboratory, Besides the analytical utility, the new knowledge of the interfacial behaviour may offer better understanding of the pharmaceutical activity of these drugs, particularly of their interaction with biosurfaces.This work was supported by the American Heart Association and the National Institutes of Health (Grants No. RR08136-12 and GM 30913-03). 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. References Kalvoda, R., Anal. Chim. Acta, 1982, 138, 11. Wang, J., Am. Lab., 1985, 17, 41. Wang, J., “Stripping Analysis: Principles, Instrumentation and Applications,” VCH, Deerfield Beach, FL, 1985. Wang, J., Mahmoud, J. S . , and Farias, P. A. M., Analyst, 1985, 110, 855. Wang, J., Peng, T., and Lin, M. S . , J . Bioelectrochem. Bioenerg., 1986, 15, 147. Jarbawi, T. R., and Heineman, W. R., Anal. Chim. Acta, 1982, 154, 359. Chaney, C. E., and Baldwin, R. P., Anal. Chem., 1982, 54, 2556. Wang, J., Bonakdar, M., and Morgan, C., Anal. Chem., 1986, 58, 1024. Schaar, J. C., and Smith, D. E., J . Electroanal. Chem., 1979, 100, 145. Woodson, A. L., and Smith, D. E., Anal. Chem., 1970, 42, 242. Taira, A., and Smith, D. E., J . Assoc. Off. Anal. Chem., 1978, 61, 941. Wang, J., and Bonakdar, M., J . Chromatogr., in the press. Shah, M. H., and Stewarts, J. T., J. Pharm. Sci., 1984,72,989. Ravichandran, K., and Baldurin, R. P., J . Chromatogr., 1985, 343, 99. Adams, R. N., “Electrochemistry at Solid Electrodes,” Marcel Dekker, New York, 1979, p. 323. Wang, J., and Freiha, B., Anal. Chim. Acta, 1983, 148, 79. Wang, J., and Freiha, B., Anal. Chem., 1983, 55, 1285. Paper A61169 Received May 30th, 1986 Accepted June 27th, 1986

ISSN:0003-2654    

DOI:10.1039/AN9861101245

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1986, VOL. 11 1 1249 Simultaneous Determination of Major and Trace Elements in Urinary Calculi by Microwave-assisted Digestion and Inductively Coupled Plasma Atomic Emission Spectrometric Analysis Michael Alexander Erich Wandt* and Michel Andre Bruno Pougnett Department of Physical Chemistry, University of Cape Town, Private Bag, Rondebosch, 7700, Republic of South Africa A procedure that permits the simultaneous determination of major, minor and trace elements in urinary calculi by inductively coupled plasma atomic emission spectrometry is described. The dissolution of samples is achieved with a commercial microwave oven using a mixture of nitric and perchloric acids. Ca, Mg, P, Al, Cu, Fe, K, Li, Mn, Mo, Na, Pb, S, Sr and Zn were determined in more than 100 South African stones.Keywords: Urinary calculi; major and trace element determination; inductively coupled plasma atomic emission spectrometry; microwave-assisted digestion Since its introduction more than two decades ago, inductively coupled plasma atomic emission spectrometry (ICP-AES) has found widespread applications in the analysis of biological samples.l-3 The advantages of the ICP-AES analysis of human pathological concretions reported previously4>5 and the posi- tive results obtained in the simultaneous determination of the major elements of human calculi (Ca, Mg, P),4,5 have prompted additional investigations involving trace element determinations. In recent years, the functions of trace elements in the human body and the environment and their importance for medical practice have been increasingly recognised in the biomedical field.6.7 Although most mechanisms concerning the behaviour of trace elements in biological systems are far from being understood , many researchers are convinced that trace elements play a major role in causing diseases such as urolithiasis.8-11 In addition to the metabolic role, attention has been focused on the trace element content of human concretions.The aim of this study was to develop a method whereby both major and trace elements of urinary calculi could be quantified simultaneously. Preliminary studies showed that trace element concentra- tions in the sample solutions prepared4 were too low to allow the accurate determination of concentrations and that more concentrated samples were required.When the stone mass was increased , the time-consuming dissolution step was further lengthened, thereby limiting the speed of the analysis. A microwave-assisted digestion procedure was therefore developed. This shortened sample preparation times con- siderably owing to more rapid and efficient digestion. Subse- quently more than 100 urinary calculi obtained from Cape Town hospitals were analysed for three major (Ca, Mg and P) and 12 trace elements (Al, Cu, Fe, K, Li, Mn, Mo, Na, Pb, S, Sr and Zn). In this paper the sample preparation procedure and ICP experimental conditions developed for this purpose are described. * Present address: Council for Scientific and Industrial Research, National Accelerator Centre, Van de Graaff Group, Ion-solid Interaction Division, PO Box 72, Faure, 7131, Republic of South Africa.t Present address: Council for Scientific and Industrial Research, National Accelerator Centre, Van de Graaff Group, Nuclear Analytical Chemistry Division, PO Box 72, Faure, 7131, Republic of South Africa. Experiment a1 Instrumentation and Apparatus All experimental work was performed on a two-channel Plasma-200 ICP spectrometer (Allied Analytical Systems). This instrument is an updated model of the IL Plasma-100 used in the previous study4 and has been described by Smith et a l l 2 The model employed in this study is fitted with two scanning monochromators, the standard air path and a vacuum monochromator, which allows the observation of emission lines in vacuum below 300 nm. A commercially available microwave oven (Sharp Model R6950 E) with a stainless-steel cavity, operating at 2.45 GHz with a maximum output power of 650 W, was used.Digestions were carried out in 50-ml Erlenmeyer flasks covered with small beakers to prevent spattering and possible sample losses. In this way cross-contamination was also minimised. An acid fume scrubber was constructed from a flask containing an approximately 2 M KOH solution and a beaker filled with water.13 These were connected to a desiccator, which could accommodate up to five digestion vessels. The whole assembly was stationary on a thick glass plate, which could be easily placed in the oven cavity. Samples and Standards Over 100 urinary calculi were selected from a collection of about 550 human stones from two Cape Town hospitals.The criteria for including a stone in the selection were based on the available mass (more than 250 mg was required) and on its composition as determined by X-ray powder diffraction (XRD). The aim was to obtain significant numbers of calculi in each of the three major stone groupings, viz., calcium oxalate, phosphate and uric acid stones. Chips from the larger specimens or whole stones were ground to fine powders. Approximately 250-mg aliquots of these powders were transferred into the Erlenmeyer flasks and 2 ml of concentrated nitric acid (65%) and 1 ml of concentrated perchloric (90%) acid (both Riedel-de-Haen, analytical-reagent grade) were added. The flasks were then covered with small beakers and placed in the desiccator, which was sealed with high-vacuum silicone grease. After coupling with the acid fume scrubber , the entire assembly was placed in the microwave oven.Three minutes of uninterrupted irradia- tion were usually sufficient to obtain clear solutions. Although some samples required only ca. 1 min for the reaction to be completed, all samples were exposed to the microwaves for1250 ANALYST, NOVEMBER 1986, VOL. 111 the same length of time. In a few flasks, clear solutions were not obtained and they were returned to the oven (after adding a few drops of nitric acid) for a further few minutes treatment. After cooling, the solutions were transferred quantitatively into 50-ml calibrated flasks containing 1 ml of concentrated nitric acid and 1 ml of 1% mlVTriton X-100 surfactant (BDH Chemicals).These were diluted to volume with de-ionised, distilled water, which was used throughout for all prepara- tions. All solutions were stored in polyethylene bottles, which had previously been leached with nitric acid. No precipitation was observed after storage for more than 3 months. Acid fumes produced by the digested samples could escape through small lips in the rims of the Erlenmeyer flasks. The resulting over-pressure in the desiccator then forced the evolving acid fumes through the KOH solution where they were neutralised. No acid fumes could be detected (by smell) in the oven cavity after removing the sample container, and no signs of corrosion were found after completing this study. The alkaline solution and the water were routinely changed after three successive digestions in the oven.This was found to be necessary to prevent boiling of the liquids by the fast microwave heating. Stock standard solutions (10 mg ml-1) of calcium and magnesium were prepared by dissolving calcium carbonate and magnesium metal flakes (both Johnson Matthey, Spec- pure), respectively, with a few drops of nitric acid. (NH4)H2P04 (Merck, analytical-reagent grade) was used as a phosphorus standard of the same concentration. The primary trace element standards (1 mg ml-l) used were Spectrosol solutions (BDH Chemicals), except for sulphur and lithium, for which standards were prepared from (NH4)2S04 (BDH Chemicals, analytical-reagent grade) and LiCl (Merck, Titri- sol), respectively. Standards of lower concentrations were obtained by serial dilution of these stock solutions with a blank, prepared by subjecting acids alone to the whole preparative procedure.Mixed element standards for ICP calibration purposes were prepared in the same way. ICP Experimental Conditions Optimisation of the instrumental parameters followed the procedures already d e ~ c r i b e d . ~ Firstly, the most sensitive prominent spectral lines were investigated for each (trace) element of interest for potential interferences, e.g., spectral overlap and background shifts. The effect of the major elements Ca, Mg and P and some minor elements, such as Al, K and Na, on the analyte emission were evaluated by observing the recorded intensity profiles on a video display. These were obtained by pre-nebulisation mixing14 of various concentrations of analyte and concomitants, e.g., 1 mg ml-1 of Ca and 10 pg ml-1 of Fe.The advantage of this method is that it does not require the very tedious procedure of preparing two-element mixtures of the analyte together with all potential interferents. It thus allows fast and easy evaluation of spectral lines and background correction positions. All the analytical wavelengths used are summarised in Table 1, together with other important line parameters. The intensity measurements were divided between the two monochromator systems (channels A and B) for time-saving reasons. The viewing height of channel B (vacuum monochro- mator) cannot be individually adjusted for different elements for any one analytical programme. This parameter is usually optimised and set manually for the least sensitive element in the programme. On the other hand, observation heights used in connection with channel A could be optimised for each element separately and the heights utilised are also listed in Table 1.Where necessary, automatic background correction facilities were used (Table 1). Detection limits in solution (30) achieved for the analytical lines using the given settings and instrumental conditions (Table 2) are also included in Table 1. An estimate of the detection limits for each element in the calculi (expressed as ng mg-1 of stone mass) was calculated by taking into account the dilution factor (50 ml) and an average mass of 265 mg (mean of all weighings). Multi-element standard solutions were used to optimise the instrumental conditions.The effects of varying r.f. power, nebuliser driving pressure (carrier gas flow-rate) and sample feed rate were studied. All these analytical variables are, however, interdependent and changing one might affect the optimum conditions for the others. Further, some system variables, such as the nebuliser driving pressure, cannot be optimised for each element separately. Therefore, compro- mise settings, which would give the “best” performance for all analytes, had to be chosen. These conditions are listed in Table 2. After setting the spectrometer to the optimised parameters, it was first calibrated for each element using the blank and the standards listed in Table 3. This calibration was carried out mainly to confirm the linearity of the calibration graph over the entire expected concentration range.Re-calibration of the instrument during analysis was performed after every 10-15 samples with the highest concentration standard and the blank only, except for Ca, Mg and P. Blank readings were taken after every fifth sample in order to monitor the drift of the instrumental parameters. Results and Discussion In order to check for the possible loss of elements during the microwave digestion procedure, a series of recovery tests using aqueous 10 pg ml-1 standards were undertaken. As part Table 1. Wavelength data Detection limits Ca . . Mg . . P . . A1 . . c u . * Fe . . K . . Li . . Mn . . Mo . . Na . . Pb . . s . . Sr . , Zn . . Element Wavelengthhm . . . . . . . . 315.89 . . . . . . . . 279.81 .. . . . . . . 213.62 . . . . . . . . 237.32 . . . . . . . . 324.75 . . . . . . . . 259.94 . . . . . . . . 769.90 . . . . . . . . 670.78 . . . . . . . . 257.61 . . . . . . . . 203.84 . . . . . . . . 589.59 . . . . . . . . 220.35 . . . . . . . . 182.04 . . . . . . . . 346.45 . . . . . . . . 213.86 Background correction Monochromator - Air path Rhs Air path - Air path - Vacuum Rhs Air path - Vacuum - Air path - Air path - Air path Rhs Vacuum - Air path Lhs Vacuum Lhs Vacuum - Air path - Vacuum Viewing height/mm 25 14 14 14 5 14 14 2 - - - - - 14 - Solution/ 30 40 90 54 5 4 940 7 5 8 30 70 110 30 5 vgl-’ Calculus/ ng mg- * 6 8 17 10 1 1 180 1.5 1 1.5 6 14 21 6 1ANALYST, NOVEMBER 1986, VOL. 111 125 1 of a general investigation of microwave-assisted dissolution, many elements in addition to those determined in calculi were included in this part of the study (Al, Cd, Co, Cr, Cu, Fe, K, Mn, Mo, Na, Ni, Pb, S, Se, Sr, Ti, V and Zn).Multi-element solutions were subjected to the same preparative steps as the samples, in duplicate. No loss of any of the elements was observed. These favourable results do not, however, exclude the possibility of elemental loss if the particular element is incorporated in a more complex matrix or in samples where volatile species can be formed. A major shortcoming in the verification of the method was the lack of a suitable reference material. As no certified (urinary) stone standards are available, the accuracy of the entire analytical procedure was evaluated using US National Bureau of Standards Standard Reference Materials (NBS SRMs).l3 In general, good agreement with certified or reported values was obtained.Three comparatively large calculi were chosen to test the precision of the method described. Five separate aliquots were prepared from each of these and mean concentrations found are listed in Table 4 together with the standard deviations (SD) and relative standard deviations (RSD). For the three major elements (Ca, Mg and P) the reproducibility was found to be comparable to that in the previous study4 and ranged from 1.5 to 2.9% RSD. The precision for the trace elements varied from 1.0 to 74.4% RSD. However, when concentration values below five times the detection limit are excluded, a mean RSD of 5.1% is obtained. Table 2. ICP operating conditions Power .. . . . . . . . . . . . . Plasma coolant gas flow . . . . . . . . Sample feed rate . . . . . . . . . . Nebuliserdrivingpressure . . . . . . Aerosolcarrierflow-rate . . . . , . Pump delay . . . . . . . . . . . . Peak window . . . . . . . . . . Integration time . . . . . . . . . . Observation height . . . . . . . . Number of readings . . . . , . . . 1.2kW 13 1 min-1 1 ml min-’ 206.8 kPa (30 lb in - 0.4 1 min-l 30 s 0.067 nm 3s 2-25 mm, varied 3 Table 3. Calibration standards Element Standarddmg 1-1 Ca . . . . . . . . , . . . . . 2000,1000,500,100 Mg, P . . . . . . . . . . . . . . 1000,500,200,100 Na, K . . . . . . . . . . . . . . 100,50,10 S . . . . . . . . . . , . . . . . 20,10,5,2,1,0.5 Al,Cu,Fe,Li,Mn,Mo,Pb,Sr,Zn . . 10,5,2,1,0.5 Aliquots of 16 large stones, which had been analysed for Ca, Mg and P in the previous study,4 were prepared and re-analysed.Mean deviations of 6.9, 5.6 and 4.2% for Ca, Mg and P, respectively, were obtained when comparing the two analyses. These figures show excellent agreement between the conventional “h~t-plate”~ and microwave-assis- ted digestion procedures. Potassium could not be determined at the same time as the other elements because of the low sensitivity of the 769.90 nm line. In order to measure low concentrations of this element, the standard photomultiplier tube in channel A (Hamamatsu R 106 UH) was replaced by a more red-sensitive photomulti- plier (Hamamatsu T 955). This model is sensitive up to 930 nm compared with 650 nm for the standard tube, thus giving better results at longer wavelengths.Lithium and Mn could not be determined in any of the calculi because of their very low concentrations. It can therefore be concluded that if these elements occur in stones they do so at concentrations below ca. 1 ng mg-1. Copper, Mo and Pb concentrations were found to be below the detection limits (1, 1.5 and 14 ng mg-1) in 68, 51 and 64% of all cases, respectively. The determination of Si was at first attempted. However, as a result of the poor precision achieved during trial analyses the attempt was abandoned. One reason for the difficulties generally experienced when determining this element lies in the necessity of stabilising the silicon ion in solution. In acidic media this is usually achieved by including HF (fluoride ion) in the digest, which is precluded in this instance as a result of incompatibility with the torchs’ quartz tubes.Further, erosion of the silica ICP torch and subsequent introduction of spurious Si into the plasma are additional unwanted possibilities.15 In digests of cystine calculi, sulphur concentrations exceeded the dynamic range of the calibration. These samples were therefore diluted five-fold and then analysed again. On the assumption that these stones were 100% cystine, good agreement with the expected stoicheiometric sulphur value (26.7% mlm) was obtained. Of the 102 calculi analysed in this study, 14 belong to the calcium oxalate (CaOx) group, 18 to the CaOx - apatite (APA) group, 45 to the struvite (STR) - APA group and 19 to the uric acid (UA - UAD) - CaOx group.Two calculi containing urates, one STR - calcium oxalate monohydrate (COM) and three cystine stones were also found.16 In the CaOx group, COM was the major component (ie., >50%) in 12 cases and calcium oxalate dihydrate (COD) in 2, whereas in the CaOx - APA group COM was predominant in 3 calculi, COD in 11 and APA in 3. In the STR - APA group, struvite occurred in 25 calculi at concentrations greater than 50% and apatite in 14. In the UA - CaOx group, UAD (uric acid Table 4. Replicate analysis of three stone samples (mean of five preparations) Concentration? % mlm ng mg-1 Stone* Ca Mg P A1 Cu Fe K Mo Na Pb S Sr Zn S1, APA - STR Mean 4.21 7.80 12.11 36.8 N.d. N.d. 3280 4.2 3431 N.d. 134 68.0 206 RSD, % 2.9 1.8 1.9 7.5 - - 5.3 24.5 2.4 - 3.6 13.2 2.8 SD 0.12 0.14 0.23 2.7 - - 172 1.0 83 - 4.8 9.0 5.9 S2, APA - COM Mean 29.19 0.25 9.46 71.9 3.9 23.0 1003 2.2 5913 114 1851 141 1381 SD 0.45 0.004 0.17 3.6 0.7 1.6 104 0.5 120 12.7 39.0 4.9 13.5 RSD, Yo 1.5 1.8 1.8 5.0 19.1 7.0 10.4 22.4 2.0 11.2 2.1 3.5 1.0 S3, UA - UAD Mean 0.40 N.d.0.04 N.d. 2.4 3.7 649 N.d. 459 N.d. 463 N.d. 4.5 SD 0.01 - 0.001 - 1.8 1.9 80 - 21.7 - 7.7 - 0.9 RSD, % 2.9 - 2.5 - 74.4 51.4 12.3 - 4.7 - 1.7 - 20.1 * APA, apatite; COM, calcium oxalate monohydrate (whewellite); STR, magnesium ammonium phosphate hexahydrate (struvite); UA, uric t N.d., not detectable. acid; UAD, uric acid dihydrate.1252 ANALYST, NOVEMBER 1986, VOL. 111 Table 5. Elemental concentrations in four major stone groups. Ca, Mg and P expressed as 70 rnirn, other elements as ng mg-1.Value(s) below the detection limit are set to half of the detection limit concentration and are identified by (d). Ca Mg P A1 c u Fe K Mo Na Pb S Sr Zn Element . . * . . . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median . . Range Mean Median All instances (n = 102) 15.82 17.43 2.38 0.25 6.67 6.67 32 31 <0.50-10 1.4 0.50(d) <0.50-156 27 20 <90-6756 1737 1325 <0.75-8.3 2.2 0.75(d) 129-50042 <0.0 1-31.43 <0.01-9.50 <0.01-16.79 4.0-89 4670 2695 <7.0-139 22 7.0(d) 134-271 000 8564 542 <3.0-622 121 90 <0.50-1381 270 166 CaOx (n =14) 23.18 24.94 0.09 0.03 0.07-1.44 0.99 0.33 <5.0-89 25 17 0.59 0.50( d) 6.0-51 30 25 1031 53 1 1.3 0.75( d) 92% 10636 2763 1651 <7.0-131 27 7.0(d) 10.22-28.1 1 <0.0 1-0.87 <0.5&1.7 367-4059 <O. 75-4.1 372-1633 1022 1127 12-622 113 60 21-1316 210 65 CaOx - APA (n = 18) 23.34-29.56 26.63 26.53 0.30 0.18 1.22-1 1.11 4.51 3.48 30 29 <0.50-10 2.1 0.50( d) 9.0-129 48 33 350-3270 1063 810 <0.75-3.1 1.2 0.75( d) 1428-15212 3884 2616 <7 A-119 47 43 345-2081 906 792 44-462 126 94 483 418 0.03-1.85 12-72 113-1381 APA - STR ( n = 45) 1.30-31.43 15.25 15.35 0.56-9.50 5.02 5.41 5.80-16.79 12.65 13.04 27-73 47 46 <0.50-71 1.1 0.50(d) <0.50-156 24 18 2914 2702 <0.75-8.3 3.3 3.4 1002-12392 6671 6437 <7.0-139 19 7.0(d) 134-1428 478 424 12-459 180 148 26-994 345 303 1042-6756 UA - CaOx (n = 19) <0.01-23.68 5.81 1.22 <0.01-0.15 0.03 0.01 <0.01-1.58 0.18 0.04 4.0-21 8.7 5.0(d) <O.50-5.9 1.6 0.50( d) <0.50-79 18 11 <90- 1265 393 289 <0.75-3.0 1.3 0.75( d) 129-1738 662 459 <7.0-14.1 7.4 7.0(d) 341-1097 605 572 C3.0-126 18 3.0(d) 2.1-131 16 8.2 dihydrate) was detected in 4 stones, whereas COM was the prevailing phase in 3 of them, compared with UA in 14. Range, mean and median elemental concentrations measured are summarised in Table 5 for the four major stone groups. Comparison of these results with those obtained by other researcherslOJ7-19 was found to be difficult, because of the different approaches in publishing concentration values.Often these are reported as “as received,” “dry mass” or “YO ash.” In instances where no mean ash portions or component information are given to supplement the data, calculation of meaningful concentration values becomes an impossible task. One possible reason for the inconsistent concentration values observed could be the degree to which different stone groups (e.g., calcium oxalates, APA - STR, UA, etc.) are present in the total number of calculi sampled in each instance. This parameter influences reported concentration values to a great extent. For example, from Table 5 , it can be clearly seen that trace elements are far less concentrated in uric acid stones than in apatite stones. Strontium and zinc levels especially are exceptionally low in the former group.An additional reason for the disagreement in results might be the way in which mean concentrations are evaluated. Levinson et al., 10 for example, set all concentration values that were too low for determination at zero. In this study, these values were arbitrarily set at half the detection limit. In other studies, these figures are not considered at all when calculating the mean. To further illustrate this, Table 5 shows the mean (median) Pb concentration in CaOx calculi as 27 (7.0) ng mg-l; when discarding all values below the lower limit of detection, the mean (median) lead concentration becomes 62 (44) ng mg-l! In most studies, however, detection limits or figures for accuracy and precision are not stated.Differences observed between similar investigations might, nevertheless, be real, i.e., stem from regional differences of the collection sites, giving rise to factors such as dissimilar drinking waters or diets. Investigating a causative connection between trace element content and stone formation was, however, beyond the scope of this study. Further, the limited number of such studies does not yet permit any conclusions to be drawn in this direction from the available data. A more systematic approach is therefore warranted for trace element studies in human concretion analysis. Conclusion Inductively coupled plasma atomic emission spectrometry has been successfully applied to the simultaneous determination of major, minor and trace elements in urinary stones.This technique was found to be an extremely useful tool in the analysis of calculi and could be easily adapted to accommodate additional elements. Rapidity, cost effectiveness and ease of operation have been achieved (i) by using a microwave-assisted wet digestion procedure, (ii) by employing a single set of operating conditions and calibration graphs and (iii) by determining all elements directly without pre-concentration. The microwave decomposition procedure employed in this study undoubtedly had a positive influence on the analytical accuracy andANALYST, NOVEMBER 1986, VOL. 111 1253 precision of the results. It is acknowledged, however, that the large sample mass required for precise concentration measurements precludes some of the smaller calculi for analysis by this method.Also, accuracy is limited by inhomo- geneities that are invariably found in the sampled aliquots. The lack of stone standards constitutes another limitation in the attempt to improve analytical reliability. Most recently an “animal bone” standard (IAEA H-5) was introduced ,20,21 which currently provides the closest match between a standard and stone matrix. Unfortunately, this standard was not available for this investigation. An independent check of the accuracy of ICP-AES (and XRD) analyses was obtained by participations in three interlaboratory tests (urinary calculus analyses) organised by the German Society for Clinical Chemistry. These tests confirmed that good accuracy and precision were obtained with (quantitative) ICP-AES and (qualitative) XRD tech- niques.16 Some of the trace elements explored were found to be at concentrations too low to be measured with ICP-AES. However , the detection limits achieved under the compromise settings selected for analytical parameters in this study could possibly be improved by optimising the conditions specifically for the low concentration elements occurring in calculi. Further improvement may be achieved by employing pre- concentration or more sensitive techniques. Future technical developments of the sample introduction system of ICPs and new sample preparation techniques will without doubt over- come these present shortcomings. The quantitative determination of trace elements in calculi is essential for understanding their aetiology. It is now accepted that the crystallisation processes occurring during the formation of stones are influenced by these elements, even if these are present in minute concentrations only.8.9 Although their functional role in urinary calculi is still unknown, many of the elements studied in this investigation were shown to promote or inhibit the precipitation of calculi.s.9 It is hoped that a comprehensive (multivariate) statistical analysis of the data obtained22 will contribute to a better understanding of the stone-forming process. The financial support of the Council for Scientific and Industrial Research (CSIR, South Africa) and the Medical Research Council (MRC, South Africa) in the person of Dr.Rodgers is gratefully acknowledged. The authors thank Miss B. Collocot for the loan of the microwave oven.References 1. 2. 3. 4. 5. Mermet, J. M., and Hubert, J., Prog. Anal. At. Spectrosc., 1982, 5 , 1. Schramel, P., Spectrochim. Acta, Part B, 1983, 38, 199. Olsen, S. D., Rama, D. B. K., and Bohmer, R. G., ChemSA, 1985, 11, 144. Wandt, M. A. E., Pougnet, M. A. B., and Rodgers, A. L., Analyst, 1984, 109, 1071. Wandt, M. A. E., Pougnet, M. A. B., and Rodgers, A. L., in Schwille, P. O., Smith, L. H., Robertson, W. G., and Vahlensieck, W. , Editors, “Proceedings of the 5th Interna- tional Symposium on Urolithiasis and Related Clinical Research,” Plenum, New York, 1985, p. 699. Feinendegen, L. E., and Kasperek, K., Trace Elem. Anal. Chem. Med. Biol., Proc. Int. Workshop, lst, 1980, p. 1. Schramel, P., and Xu-Li-Giang, ICP Inf Newsl., 1982,7,429. Meyer, J. L., and Angino, E. F., Invest. Urol., 1977, 14, 347. Hesse, A., Schneider, H.-J., and Berg, W., Zentralbl. Pharm., 1978, 117, 753. Levinson, A. A., Nosal, M., Davidman, M., Prien, E. L., Sr., Prien, E. L., Jr., and Stevenson, R. G., Invest. Urol., 1978,15, 270. 11. Thomas, W. C., Jr., Proc. SOC. Exp. Biol. Med., 1982, 170, 321. 12. Smith, S. B., Jr., Schliecher, R. G., Dennison, A. G., and McLean, G. A . , Spectrochim. Acta, Part B, 1983, 38, 157. 13. Pougnet, M. A. B., and Wandt, M. A. E., ChemSA, 1986,12, 16. 14. Pougnet, M. A. B., Orren, M. J., and Haraldsen, L., Int. J. Environ. Anal. Chem., 1985, 21, 213. 15. Lichte, F. E., Hopper, S . , and Osborn, T. W., Anal. Chem., 1980, 52, 120. 16. Wandt, M. A. E. , Dissertation, Department of Physical Chemistry, University of Cape Town, 1986. 17. Donev, I . , Mashkarov, S . , Maritchkova, L., and Gotsev, G., J. Radioanal. Chem., 1977, 37, 441. 18. Nagy, Z . , Szabo, E., and Kelenhegyi, M., Z. Urol., 1963,56, 185. 19. Hesse, A., Dietze, H.-J., Berg, W., and Hienzsch, E., Eur. Urol., 1977, 3, 359. 20. Lee, J., ICP Inf. Newsl., 1983, 8, 553. 21. Mahanti, H. S., and Barnes, R. M., Anal. Chim. Acta, 1983, 151, 409. 22. Wandt, M. A. E . , and Underhill, L. G., J. Urol., submitted for publication. 6. 7. 8. 9. 10. Paper A61163 Received May 23rd 1986 Accepted June 6th, 1986

ISSN:0003-2654    

DOI:10.1039/AN9861101249

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1986, VOL. 111 1255 Inductively Coupled Plasma Emission Spectrometric Determination of Boron and Other 0x0-anion Forming Elements in Geological - Materials* Gwendy E. M. Hall and Jean-Claude Pelchat Geological Survey of Canada, 60 1 Booth Street, Ottawa, KIA OE8, Canada A simple, rapid method is described for the determination of boron in different types of geological samples. Measurement is made by inductively coupled plasma emission spectrometry on an aqueous leach of a sodium carbonate - nitrate melt, which effectively separates the analyte from potentially interfering major elements such as iron, calcium and magnesium. A determination limit of 1 pg g-1 of B is achieved with a precision of about 3% (relative standard deviation) at levels greater than 5 pg 9-1 of B.Application of this method to include the determination of vanadium down to 4 pg g-l, molybdenum down to 2 pg g-1 and tungsten down to 5 pg g-1 is demonstrated by the use of 18 international reference standards. Extension of this method to include the determination of chromium and phosphorus is cautioned, as success is dependent on the sample type. Keywords: Boron determination; 0x0-anion forming elements; geological materials; inductive1 y coupled plasma emission spectrometry Boron is an important trace constituent of the hydrothermal fluids from which several types of mineral deposit are precipitated and it is frequently found in anomalous amounts in the host rocks of these deposits. However, the use of this element as an indicator of mineralisation has been handicapped by the absence of effective analytical methods for geological materials.The boron content of geological materials has been deter- mined almost exclusively in the past by one of two techniques: emission spectrography using a d.c. arc1 and spectropho- tometry based on the formation of the boron - curcumin complex.2 Recently, Baucells et al.3 have improved on the emission spectrographic method to achieve a minimum detectable concentration of 11 pg g-1 of B and Troll and Sauerer4 have combined extraction of boron by ethylhexane- 1,3-diol (after carbonate fusion) with spectrophotometry of the carminic acid complex to determine boron in the range 1-1000 pg g-1. The determination of boron in rhyolites and tektites in the range 10-200 pg g-1 has been described by Kluger and KoeberF using the tetrafluoroborate-selective electrode at 1-2 "C (to prevent hydrolysis) after dissolution with hydrofluoric acid and buffering with hexamethylene- tetramine.However, this method, together with those based on spectrophotometry, has not been applied routinely to the analysis of many types of geological samples, largely owing to their lack of simplicity and universality. Higgins6 determined boron in 18 international reference standards by prompt- gamma neutron-activation analysis and obtained good agree- ment with literature values at high levels, but the correlation was poor at low abundances, probably owing to uncertainty in the sodium correction factor. In 1982, Owens et al.7 published the first paper to describe a method to determine boron specifically in geological refer- ence materials by inductively coupled plasma emission spec- trometry (ICP-ES).A carbonate fusion was carried out and the solution was neutralised and measured against similarly prepared synthetic standards using a Perkin-Elmer ICP/5000 spectrometer. A detection limit of 5 pg g-1 was obtained. Borsier and Garcia8 later described an automated ICP method to determine major and trace elements, including boron, in geological samples after a sodium peroxide fusion. The detection limit and precision were poor. In 1984, Din9 * Geological Survey of Canada Contribution No. 20786. described an elaborate procedure to separate boron from potentially interfering iron by successive fusions with potas- sium dihydrogen phosphate and potassium hydroxide prior to ICP emission measurement at 249.68 nm.Thompson and WalshlO commented on the lack of exploitation of ICP emission gectrometry for boron by analysts in geochemistry. Subsequently, Walshll described a method to determine boron in rocks by ICP-ES on a solution obtained by aqueous leaching of a potassium carbonate fused melt from which the bulk of the potassium had been precipitated using perchloric acid. I t is this approach that has been investigated here, modified and extended to determine other elements in addition to boron. A strong attack is required for boron-bearing minerals, such as tourmaline, so fusions with alkali metal carbonates, alone and with oxidants, were examined. Potassium rather than sodium carbonate was thought to be desirable because the potassium could be precipitated later as its perchlorate salt, whereas sodium carbonate has the advantage of a lower melting point (853 vs.903 "C) and is not hygroscopic. The temperature and time of fusion were both optimised once the preferred decomposition was chosen. As the major portion of analytical time is often spent on the decomposition stage, other elements of interest that would also be brought into solution were determined, viz., molybdenum, vanadium, chromium, tungsten and phosphorus, which form oxy-anions after fusion. A thorough study was made of all emission lines of suitable sensitivity for each element, checking for spectral interferences by scanning a 0.08 nm window centred on each line while aspirating high concentrations of likely interferents. The spectral line atlas compiled by Brenner and Eldad12 was found to be useful in planning this interference study.Experimental Reagents De-ionised, distilled water was used throughout. Carbonates and nitrates were of Baker analysed reagent grade. Individual standard stock solutions were obtained from Spex Industries, Metuchen, NJ, USA. All linear polyethylene laboratory ware was washed in 30% nitric acid and repeatedly rinsed with de-ionised, distilled water.1256 ANALYST, NOVEMBER 1986, VOL. 111 Instrumentation A Jobin-Yvon (ISA, Metuchen, NJ, USA) Model 38 high- resolution sequential ICP emission spectrometer was used. Details of the instrumentation and operating conditions used are given in Tables 1 and 2, respectively.The path from the viewing zone of the argon plasma to the entrance of the spectrometer was flushed with nitrogen, as was the spec- trometer itself, allowing emission measurement in the low ultraviolet region of the spectrum. Both Meinhard and GMK nebulisers were tested. The sample gas flow was regulated with a mass flow controller for better precision, and a humidifier was used with the nebuliser to improve high salt tolerance. Procedure Preliminary investigation of sample decomposition methods Prior to deciding the final flux mixture, various fusions and sinters were investigated. International reference materials were used to test the accuracy and precision of these decompositions. First, potassium carbonate alone and a 5 : 1 mixture of K2C03 and KN03 were tested in a muffle furnace at 950-1050 "C.Potassium, rather than sodium, as the cation initially appeared beneficial because perchloric acid could be added after the dissolution, resulting in precipitation of insoluble potassium perchlorate. It was thought that this would drastically decrease the dissolved salt content of the analyte solution at the ICP and hence reduce the problem of nebuliser clogging and drift. However, a salt build-up was seen to occur at the top of the torch and clogging was still evident with both the Meinhard and GMK nebulisers. It was found that platinum crucibles were seriously attacked by the flux, especially in the presence of a sample containing a high concentration of Fe". Nickel crucibles were used instead, but occasional creeping up and over the walls occurred.Decom- position by sintering over a flame (heating below the melting-point of the flux) was attempted, followed by addition of HC104. Low results were obtained for Mo, V, Cr and W; these were attributed to incomplete attack. Table 1. Instrumentation R.f. generator . . . . 2.5 kW, frequency 27.12 MHz Monochromator . , . . 1-m Czerny-Turner, nitrogen-purged for Grating . . . . . . Holographic3600groovesmm-~, Torch . . . . . . . . Jobin-Yvon demountable quartz with Nebuliser . . . , . , Meinhard concentric, Type C high salt low UV wavelengths resolution 0.01 nm first order argon sheathing gas (TR-30-C2) with Scott-type spray chamber Pump . . . . . . . . Gilson, peristaltic, Model Minipuls I1 Computer . . . . . . Columbia Commander Micro, 96 kbyte memory; dual floppy disc; software by Jobin-Yvon Table 2.Operating conditions R.f. forward power . . Plasma gas flow-rate . . Auxiliary gas flow-rate . . Sample gas flow-rate . . Nebuliser pressure . . Sample uptake rate . . Slit widths: Entrance . . . , . . Exit . . . . . . Height . , . . . . Photomultiplier tube . . Observationzone . . 1.05 kW (<lo W reflected) 13 1 min-' 0.15lmin-I 0.6 1 min-1 38 Ib in-2 1.35 ml min-I 40 pm 40 pm 7 mm 1200 v 12 mm above initial radiation zone An alternative flux consisting of Na2C03 and NaN03 (oxidant) was tested, and, as reduction of the Na content of the analyte solution was not possible via precipitation, the salt tolerance level of the ICP for alkaline sodium solutions was established. It was found that a 4% Na2C03 solution could be nebulised for hours without clogging.Fig. 1 depicts the variation in the signal intensity of each analyte standard with time; each point represents the mean of three 0.5s integration readings. The relative standard deviation (RSD) ranges from 1.6% for B to 2.9% for Mo, indicating no deleterious effect of the high salt concentration. Recommended sample decomposition A 200-mg sample, ground to at least - 100 mesh, was placed in a 25-ml nickel crucible and thoroughly mixed with 1 g of the flux, a 5 : 1 mixture of Na2C03 and NaN03. The crucible was placed in a muffle furnace and the temperature raised to 900 "C and maintained there for 15 min following the melting stage. After cooling, the contents of the crucible were leached with water and warmed on a hot-plate, stirring to ease dissolution.The contents (ca. 20 ml) were transferred into a 50-ml polyethylene test-tube and warmed for several hours. After cooling, the solution was centrifuged and the clear supernatant liquid transferred into a 25-ml polyethylene calibrated flask and diluted to volume with water. The pH of this solution was 12. Calibration Blanks and calibration standards were taken through a procedure similar to the decomposition using Eppendorf micropipettes to deliver accurate amounts of standard stock solutions directly on to the flux itself. The results were compared with those for calibration standards made from the background matrix of "fused blank" solution. Analyte spectral wavelengths were chosen to be the most sensitive available, with the least amount of interferences likely to be encountered with typical sample material.The positions for background correction measurement were deter- mined by studying spectral line atlases and by scanning the 202.03 nrn 2.93% 2.14% ;I---- 1 pg ml-1 E 207.91 nrn > c .- w I I .- .- 249.77 nrn 1.59% 1 pg ml-l .- Y 2.00% 1 pg ml-l 2 Cr II 267.71 nrn 31 1.83 nrn I .awO 15 30 45 60 75 Time/mi n Fig. 1. Variation of emission signal with timeANALYST, NOVEMBER 1986, VOL. 111 1257 analyte lines while nebulising samples with high contents of potentially interfering elements. These wavelengths are shown in Table 3 together with the standard concentrations used for calibration. There is an aluminium recombination interference on the Mo 202.03-nm line, necessitating correc- tion on both sides of the line.Correction coefficients were found to be unnecessary with the chosen wavelengths. An integration time of 500 ms was selected as the optimum for each measurement. Recalibration was carried out after ten samples. Analysis of international standard samples Eighteen reference materials from the US Geological Survey (USGS) , the Canadian Certified Reference Materials Project (CCRMP), Group International de Travail (GIT-IWG) and the Institute of Geophysical and Geochemical Prospecting, China (IGGE) were analysed by the proposed method. The analysis was carried out in two steps: it was found to be more efficient to determine P, Mo and W for the entire suite of samples and then to determine B, Cr and V in a second step because the scanning rate of the JY-38 is slow.With the knowledge that the mineral chromite was unlikely to be attacked efficiently by a single fusion with the carbonate - nitrate mixture, the standard IGS 30 (Institute of Geological Sciences, UK) containing 23.95% of Cr was included to test the recovery at high levels. Analysis of “in-house-” control samples The method described was also applied to a suite of “in-house” control rock standards collected from sediment- hosted Pb - Zn deposits in the Yukon Territory, which had been well characterised by various analytical techniques. 13 These samples contain up to 5% of sulphur, contained in the minerals sphalerite, galena, pyrite (sulphide) and barite (sulphate). As the sulphide was thought to have a deleterious effect on the oxidative, alkaline fusion, the samples were initially ignited at 900 “C for 30 min and the results compared.The international reference standard GSD-6 was included in this test for comparison purposes. Results and Discussion The alkaline carbonate fusion allows separation of oxyanions, such as borate, from major element cations in geological samples, such as calcium and magnesium, and hence aids in minimising possible interferences in ICP-ES measurements. Iron did not pose a problem as a potential spectral interferent as most of the element remains in the carbonate - oxide residue; this is in agreement with Bock,l4 who found less than 0.1% of solubilised iron after a carbonate fusion. GXR-1, which contains about 25% of Fe, yielded a solution for analysis containing only 5 pg ml-1 of Fe.Thus, the lengthy sample preparation procedure described by Din9 proved unnecessary. The recovery of synthetic solutions carried through the fusion procedure was >%YO for all elements and thus it was concluded that there was no significant loss in the sample preparation steps. The solution detection limit for each analyte, defined as that concentration generating a signal equal to three times the standard deviation of the blank signal (ten readings), is shown in Table 4. The corresponding real detection limits in the samples themselves (factor of 125) are degraded by the presence of the analytes, especially boron, in the flux reagents. Here, the determination limit is defined as the instrumental detection limit (30) times the dilution factor multiplied by a constant that differs between elements and accounts for the variability introduced during sample prepara- tion prior to measurement.This constant was not calculated statistically, but was conservatively chosen based on the data. The sensitivity for molybdenum and tungsten is not adequate for many geological samples, as indicated by a comparison of the determination limits and concentration ranges found in rocks15 (Table 4); however, it was thought useful to include these two elements in this “package” for geochemical explora- tion purposes. The determination limit established for molyb- denum is double that obtained by atomic absorption spec- trometry (AAS) on a routine basis in our laboratories and that for tungsten is double that obtained by the spectrophotometric dithiol method.16 The results obtained for four separate determinations (over a period of 3 months) of boron and the other refractory elements in 18 geological reference materials are given in Table 5 together with the consensus literature values.1lJ7-20 The “consensus” values,l7J8 with their statistically based uncertainty estimate, are shown in order to give the reader an appreciation of the quality of data used by compilers.The absence of a question mark in the other citations implies a “recommended” or “usable” value as opposed to a “pro- posed” value. The comparison of results obtained on pre-ignited vs. unignited samples, which were analysed in duplicate, is given in Table 6. The values shown in parentheses are the authors’ “accepted” values13 arrived at by different analytical tech- niques performed at various laboratories.With reference to Tables 5 and 6, the data obtained for each element will be discussed individually. Boron The accuracy obtained by the proposed method (Table 5) appears reasonable, considering the paucity of previous data for establishing recommended values. The results obtained by this method lie within 6% of the recommended values given for GXR-1, GXR-4, SY-3 and GSD-6, the only samples of the entire group for which reliable values are assigned by the compilers. There are too few data for MRG-1 to comment on the accuracy of the mean boron value (1.9 pg g-1) obtained. The literature values cited by Gladney et al. 17 for BCR-1 range from 0.7 to 12 pg g-1 of B, another indication of the difficulties encountered in the determination of boron at these levels.Neither Abbey20 nor Govindarajulg reported boron values for SDC-1. Our method gives values for BCR-1, SDC-1 and SGR-1 that are considerably lower than those given by Walshll by a similar method. The precision ranges from 1.7% RSD for MA-N to 47% RSD near the determination limit for MRG-1 and averages 3.4% above 5 pg 8-1 of B. The method appears to be effective with samples that contain significant Table 3. Spectral lines and calibration standards Background positionlnm Analytical Element wavelengthlnm Low High P . . . . . . 178.225 I - 0.020 Mo . . . . 202.03011 0.016 0.019 W . . . . . . 207.911 I1 - 0.024 B . . . . . . 249.773 I - 0.020 Cr .. . . . . 267.716 I1 - 0.019 V . . . . . . 311.838 I1 - 0.016 Calibration standardslyg ml-I Low Medium High Reagent blank 10 50 Reagent blank 1.0 3.0 Reagent blank 1.0 3.0 Reagent blank 1 .O 3.0 Reagent blank 1.0 3.0 Reagent blank 1.0 3.01258 ANALYST, NOVEMBER 1986, VOL. 111 Table 4. Detection and determination limits and precision data obtained by the proposed method of analysis Detection limit in Element solution*lpg ml-1 B . . . . . . . . 0.002 Mo . . . . . . 0.006 v . . . . . . . . 0.005 Cr . . . . . . 0.004 w . . . . . . 0.015 P . . . . . . . . 0.05 Determination limit in sample?/ 1 .o 2.0 4.0 2.0 5 50 g-l Typical RSD, YO ( n = 4) 2.5 at 32 pg g-1 (QLO-1) 14 at 8 pg g -1 (GSD-6) 2.4 at 90 pg g-l (GXR-4) 6 at 13 pg g-l (GXR-1) 7 at 28 pg g-l (GSD-6) 2.5 at 780 pg g-l (MAG-1) Concentration range in igneous and sedimentary rocks$/ g-l 3-100 0.2-2.6 20-250 4-2980 170-1100 0.1-1.8 * Defined as the concentration of an element in 4% Na2C03 - NaN03 solution that gives an emission signal equal to three times the 1- Based on a 0.2-g sample with 1.0 g of flux, diluted to a final volume of 25 ml.$ Reference 15. standard deviation of the blank. Table 5. Analysis of international reference standards by the proposed method. All values in yg g-l unless noted otherwise Mean f SD (n = 4) Sample B AGV-1 (andesite) . . 6.1 f 0.4 BCR-1 (basalt) . . . . 2.2 f 0.4 BHVO-1 (basalt) . . ~ 1 . 0 MAG-1 (marine mud) . . QLO-1 (quartz latite) . . 32.2 f 0.8 (6.9 f 3.8)* (6 f 4),* (4.8)$ (3)$ 132 f 3 * 130?),§ (130)$ ~- (37?)7§ (32)$ RGM-1 (rhyolite) .. 23.8 f 0.9 SCo-1 (shale) . . . . SDC-1 (mica schist) . . SGR-1 (shale) . . . . STM- 1 (nepheline syenite) . . GXR-1 (jasperoid) . . GXR-4 (copper mill-head) . . GXR-5(soil) . . . . SY-3(syenite) . . . . MRG-l(gabbro) . . FeR-2 (iron formation) MA-N(granite) . . . . GSD-6 (stream sediment) . . * Reference 17. t Reference 19. $ Reference 11. § Reference 20. 7 Reference 18. (31?),§ (23)$ 71.5 f 1.9 (66?),§ (73)$ 10.1 ? 0.7 (14)$ 50.3 f 1.4 (50?),§ (68)$ 4.0 f 0.4 (5)$ 15.1 f 0.6 (15.3)§ 4.0 f 1.1 (4.3)§ 19.8 f 0.4 (20 f 8)7J 104 f 2.8 1.9 f 0.9 (13?)§ 56.8 k 1.1 (61?)1- 17.2 f 0.3 (17?)§ 48.2 f 2.1 (1 lo)§ (5W Mo 2.3 f 0.3 (2.8 f l.O)* <2.0 (2.8 f 1.7)* <2.0 2.3 f 0.3 2.3 f 0.4 (2.6?) § 2.5 f 0.3 (2.3?)§ 2.4 f 0.4 (1.4?)§ <2.0 34.5 k 1.2 (36?)§ 5.0 f 0.3 (5.2)§ 17.8 f 2.2 (15 f 6)fi 311 f 4 (310 f 40)7 30.2 f 1.4 (28 f 6)7 <2.0 (2.5?)§ <2.0 3.5 f 0.5 <2.0 (l?)§ (1?)§ (3711- 8.1 f 1.1 (7.8)§ V 118 k 3 (123 a 12)* 413 t- 6 (404 f 40) * 299 f 5 (320?) § 138 4 3 (140)§ 50.3 f 2.1 11.6 k 0.8 (14?)§ 129 f 3 (135?)§ 94.8 k 3.2 (105?)§ 124 f 2 (125)§ <4.0 81.2 k 2.3 (61) 8 (79 f 9)7 90.1 +_ 2.2 (90 _t 5)fi 57 f 3.9 (66 f 11)7 47.1 ? 1.9 (51)s 511 f 10 (520)§ 30.4 k 2.3 (37?) t <4.0 (4.6?) § 140 f 3 (140)§ Cr 12.4 f 1.1 11.9 5 0.8 (16 f 4)* 328 f 4 (300) § 107 f 3 (105)§ <2.0 (4.2?)§ <2.0 (4?)§ 73.2 5 2.2 (71?)§ 70.5 f 2.3 (66?)0 32.7 f 2.9 (12 f 3)* (33?)§ (4?)§ <2.0 13.2 f 0.8 (13 f 3)7 68.8 f 3.1 (64 f 6)7 108 f 3 (106 f 9)fi 6.2 f 1.2 489 f 6 (450)§ 44.9 f 3.0 <2.0 (lo)§ (47P (3?)§ 192 f 4 (190)§ P 2125 f 14 1547 f 29 (1580 f 150)* (2100 f 200)* 0.118% k 0.004% (0.122%)§ 0.078% 2 0.002% (O.O78% ?) § 0.115% 4 O.OOI% (O.113%)§ 0.015% f O.OOI% 0.100% f 0.003% (0 .O96% ?)O O.O7O% f 0.002% (0.078%) § 0.121% f 0.002% (0.126 Yo ?) § (0.002% ?) § 0.072% f 0.002% (O.O69%)§ 615 f 7 (630 & 80)7 1280 +_ 27 311 f 6 (320 f 40)7 ( 130O)l-l 0.226% f 0.004% (0.23 Yo ) § 0.021% f 0.001% (0.026%) 0 0.116% f 0.002% (O.I16%)’f 0.601% f 0.004% (O.606%)§ O.1O3% 0.002% (0.100%)§ W <5 <5 (0.4?)§ <5 (0.06?)1- <5 <5 <5 (1.6?)§ <5 <5 (0.8?)§ <5 (0.53)t <5 (3.8?)§ 203 _t 6 (210 f 40)7 3 1 f 4 (32 ? 3)fi <5 (1.1 f 0S)Y <5 <5 <5 66 -C 2 (70?)§ 26 f 2 (2515 amounts of sulphur (Table.6) and prior ashing has no effect; the comparison data were obtained from various commercial laboratories using hydroxide fusion and ICP-ES and spectro- photometry.Molybdenum The accuracy, indicated by the results and comparative data in Table 5 , is good. Although the mean value obtained some- times appears significantly different from that cited by Gladney et a1.173 (BCR-1, GXR-1, GXR-5), it always falls within the range. The values obtained by this method for BCR-1, GXR-1 and GXR-5 are close to those given by Abbey.20 The average precision at concentrations greater than 5 pg 8-1 of Mo is 7% RSD. The data presented in Table 6 for the “in-house” control samples agree well with the “accepted” values obtained by AAS after an HF - HC104 - HN03 attack under pressure. The determination limit, with a\o 00 a\ c 0 B Mo V Cr P W r Table 6. Analysis of “in-house” control samples, with and without ashing at 900 “C.Values in yg g-l unless noted otherwise + A* Bt F A* B t Sample A* Bt XY29 (sulphide mineralisation in carbonaceous, cherty mudstone, 3.5% S) . . 31,31 32,31 (3W (167) (102) (64) (64) (293) (74) (50) XY03 (carbonaceous, cherty mudstone, 0.9% S) . . . . . . . . . . . . . . 166,168 170,169 NSH-1 (carbonaceous, siliceous shale, 0.7% S) . . . . . . . . . . . . . . 102,99 101,103 CHRT (carbonaceous chert, 0.7% S) . . , . 65,65 66,64 SLBA (weakly baritic, massive sulphide + cherty mudstone, 2.3% S) . . 63,65 61,63 . BASL (baritic massive sulphide + cherty mudstone, 4.9% S) . . . . . . . . . . 291,288 289,293 XYPC (phosphatic chert, 3.1% S) . . . . 72,71 75,72 GSD-6 .. . . . . . . . . . . . . 51,49 50,48 * A, Ignited at 900 “C. t B, Unignited. $ Values in parentheses are accepted values. A* B1- A* B t A* B t 449 , 460 445,458 (461) 393,395 400,408 (395) 173,162 49,56 (172) O.35%, 0.32% 0.30% , 0.29% (0.43 ‘/o ) 6.7,6.1 7.0,6.4 (6) 229,235 237,234 (235) 73,75 68,72 (76) 394,404 413,401 (430) 521,512 528,525 270,260 265,262 (517) (260) 82,86 83,88 68,68 61,67 (85) (71) O.I5%, 0.15% O.I5%, 0.15% (0.15 Yo) 0.11%,0.12% 0.12%,0.12% (0.12%) (560) 343,351 318,317 <5 <5 171,180 169,183 (4) ( 182) (147) 150,144 136,145 782,787 782,792 (770) 197,189 190,197 (196) 86,90 78,54 (89) 60,43 70,68 (300) 0.10%,0.10% 0.10%,0.10% (0.1OYo) O.84%, 0.76% OM%, 0.94% (2.96% ) 5.9,6.9 7.4,6.8 11,lO (7) 12,11 (10) (25) 27,25 24,28 24,21 22,20 27,29 32,29 7.9,7.8 7.5,g.l (23) (31) (7.8) 82,85 86,82 465,468 458,469 138,142 141,139 (86) (460) (140) 34,36 21,24 149,156 100,56 191,193 189,190 (35) (149) (190)1260 ANALYST, NOVEMBER 1986, VOL.111 dilution factor of 125, is adequate only for samples enriched above crustal abundance. Vanadium The results for vanadium compare well with literature values, with the possible exceptions of those for QLO-1, SY-3 and MRG-1, which appear slightly low. The value of 57 pg 8-1 for GXR-5 also seems low; however, Abbey20 recommends a value of 60 pg g-1 of V. This small bias to the low side is not borne out in the analysis of “in-house” controls where the data agree well with those obtained by AAS. The determination limit of 4 pg 8-1 is sufficient and the RSD averages 3.5%.Chromium There are three samples in Table 5 for which the results indicate significant deviations (positive and negative) from the recommended values, viz., BHVO-1, SY-3 and MRG-1. No apparent reason is evident and the repeatability of these values is excellent (e.g., 1.2% RSD for BHVO-1). Chromite is a difficult mineral to solubilise and a fusion of this type must be repeated several times for complete dissolution to take place unless a stream of oxygen is introduced above the melt. This fact was verified when the proposed method was applied to the international reference samples DTS-1 (dunite) and PCC-1 (peridotite), for which valuesofonly0.10% ofCr (cf.., 0.42%20)and0.11% ofCr(cf., O.28yo2O), respectively, were obtained. Analysis of the IGS reference sample IGS 30 recovered only 9.9% of the total chromium.It was also observed that the recovery was poor for samples containing significant amounts of sulphur, and this led to the analysis of in-house controls with and without prior ashing. It can be seen from Table 6 that the Cr values are low and erratic in samples containing >2% of sulphur, unless they are ignited prior to fusion, whereupon they agree well with established values obtained by AAS or ICP-ES measurement following fusion with Na202 or LiB02. Phosphorus Most of the results for phosphorus obtained by this method compare very favourably with the recommended values in Table 5 , with the possible exceptions of SDC-1 and MRG-1, which are slightly low. The precision averages 2.3% RSD. However, perusal of Table 6 will quickly indicate that this method fails drastically when applied to the in-house controls containing >2% of sulphur.The values in parentheses were obtained by ICP-ES following fusion with LiB02 and showed good agreement between laboratories using this now common method. The recovery is particularly poor for the samples BASL and SLBA, containing barite, and for XYPC, the phosphatic chert with 17% of CaO. It is likely that the phosphate anion has remained in the insoluble residue with barium and calcium carbonates and the solubility would be improved with a greater flux to sample ratio. Tungsten Most of the international reference samples analysed contain tungsten at levels below this determination limit of 5 pg 8-1; agreement for the remaining four samples is good.The results are also very comparable for the in-house controls where the established data are derived from application of the alkaline fusion - dithiol spectrophotometric method.16 A study is currently in progress to lower the determination limit to a more practical level of 0.1 pg g-l by ICP mass spectrometry. Conclusion It has been demonstrated that the ICP-ES determination of boron in a wide range of geological materials decomposed by sodium carbonate - sodium nitrate fusion is accurate with good precision of about 3% RSD. The method also provides excellent data for vanadium and is reliable for the determina- tion of molybdenum and tungsten at levels above crustal abundances, that is, greater than 2 pg g-1 of Mo and 5 pg g-1 of W. When applying this method to the analysis of geological materials for chromium, care must be taken to ignite the samples prior to fusion if more than 2% of sulphur is present.The low results obtained on applying this method to the determination of phosphorus in baritic or sulphidic samples limit its usefulness and caution is advised, although good agreement was shown in the data on 18 international reference standards. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20 * References Dale, L. S., Appl. Spectrosc., 1979, 33, 404. Dible, W. T., Truog, E., and Berger, K. C., Anal. Chem., 1954, 26, 418. Baucells, M., Lacort, G., Roura, M., and Rauret, G., Appl. Spectrosc., 1984, 38, 572. Troll, G., and Sauerer, A., Analyst, 1985, 110, 283. Kluger, F., and Koeberl, C., Anal. Chim. Acta, 1985,107,127. Higgins, M. D., Geostand. Newsl., 1984, 7, 31. Owens, J . W., Gladney, E. S . , and Knab, D., Anal. Chim. Acta, 1982, 135, 169. Borsier, M., and Garcia, M., Spectrochim. Acta, Part B, 1983, 38, 123. Din, V. K., Anal. Chim. Acta, 1984, 159, 387. Thompson, M., and Walsh, J. N., “A Handbook of Inductively Coupled Plasma Spectrometry,” Blackie, Glasgow, 1983, p. 99. Walsh, J. N., Analyst, 1985, 110, 959. Brenner, I. B., and Eldad, H., ZCPZnf. Newsl., 1984, 10,451. Hall, G. E. M., and Vaive, J. E., in “Current Research, Part A,” Geological Survey of Canada, Ottawa, 1986, Paper 86-IA, p. 71. Bock, R., “A Handbook of Decomposition Methods in Analytical Chemistry,” Blackie, Glasgow, 1979, p. 111. Rose, A. W., Hawkes, H. E., and Webb, J. S., “Geochemistry in Mineral Exploration,” Academic Press, London, 1979, p. 553. Stanton, R. E., “Rapid Methods of Trace Analysis for Geochemical Application,” Arnold, London, 1966, p. 86. Gladney, E. S., Burns, C. E., and Roelandts, I., Geostand. Newsl., 1983, 7, 3. Gladney, E. S., Burns, C. E., and Roelandts, I., Geostand, Newsl., 1984, 8, 119. Govindaraju, K., Geostand. Newsl., 1984, 8, 3. Abbey, S . , “Studies in Standard Samples of Silicate Rocks and Minerals 1969-1982,” Geological Survey of Canada, Ottawa, 1983, Paper 83-15, 114pp. Paper A6189 Received March 17th, 1986 Accepted June 16th, 1986

ISSN:0003-2654    

DOI:10.1039/AN9861101255

出版商:RSC    

年代:1986

数据来源: RSC

摘要:

ANALYST, NOVEMBER 1986, VOL. 111 1261 Extraction of Iron( Ill), Gold( Ill), Gallium( Ill), Thallium( Ill), Antimony(V) and Antimony(ll1) from Hydrochloric Acid Solution with Crown Ethers* Hideko Koshima and Hiroshi Onishit University o f Tsu ku ba, Sa ku ra -m ura, Iba ra ki- ken 305, Japan C h I oroform solutions of d icyclo hexyl-I 8-crown-6 (DC 18C6), d i benzo- 18-crown-6 (DB 18C6) and 18-crown-6 (18C6) efficiently extracted iron(lll), gold(lll), gallium(lll), thallium(lll) and antimony(\/) from solution in hydrochloric acid. Extraction with 15-crown-5 (15C5) and 12-crown-4 (12C4) was poor. Antimony(l1l) in the presence of titanium(ll1) chloride was efficiently extracted only with DC18C6. When tervalent iron, gold, gallium and thallium were extracted from acidic lithium chloride solution, even 15C5 and 12C4 gave good extractabilities.The molar ratio of crown ether to the metal ions, except antimony(lll), in the extracted species is probably 1 : 1, and the metals are probably extracted as chloro complexes, e.g., HFeC14 and LiFeCI4. Iron and gallium in aluminium-base alloys were determined after their separation by DC18C6 extraction. Keywords: Crown ethers; extraction; chloro complexes; hydrochloric acid solution; acidic lithium chloride solution Crown ethers have been used extensively for the extraction of alkali and alkaline earth metals.l>2 In a previous paper,3 the extraction of iron(II1) from hydrochloric acid and acidic lithium chloride solutions with crown ethers was briefly described. Iron(II1) was thought to be extracted as chloro complex(es) , This assumption suggested the possibility of extracting other metals that form chloro complexes, e.g., gallium(II1) and thallium(II1). Extraction of gold(II1) with dibenzo-18-crown-6 (DB 18C6) from potassium chloride and lithium chloride solutions was reported by Gloe et ~ 1 .~ Vasilikiotis et aZ.5 have added crown ethers to isobutyl methyl ketone to improve the extraction of gold(II1) from hydro- chloric acid solution. More recently, Caletka et a1.6 have described the extraction of tantalum with dicyclohexyl-18- crown-6 (DC18C6) from fluoride solution. The purpose of this work was to demonstrate the validity of the above assumption. The nature of the extracted species was also investigated. Experimental Reagents and Apparatus Chloroform solutions of five crown ethers [DC18C6, DB18C6, 18-crown-6 (18C6), 15-crown-5 (15C5) and 12-crown-4 (12C4)] ,3 standard solutions of gold(1II) ,7 gallium(III), thallium(1,III) and antimony(II1) and 125Sb* were prepared as described previously. A standard iron(II1) solution for investi- gating the extracted species was prepared by dissolving FeC13.6H20 in water and standardising the solution iodime- trically.9 A standard lithium(1) solution was prepared by dissolving lithium choride in water.An NaI(T1) scintillation counter (well type), a flame atomic absorption (and emission) spectrometer (Nippon Jarrell-Ash, AA-782) and a spectro- photometer (Shimadzu UV-120-02, 1-cm cell) were used. Procedure Ten-millilitre aliquots (or 2-ml aliquots for gold and antimony) of 0.2 mM gold(III), 1 mM gallium(III), 0.1 mM thallium(II1, I) or 0.1 mM antimony(V, 111) containing an adequate activity of l25Sb in hydrochloric acid or 0.1 M hydrochloric acid - lithium chloride solution were shaken with an equal volume of 50 mM crown ether in chloroform for 5 min.* Presented at the 34th Annual Meeting of the Japan Society for Analytical Chemistry, Kobe, Japan, October 1985. t To whom correspondence should be addressed. Gold was determined by atomic absorption spectrometry (AAS) after diluting an aliquot of the organic phase with methanol. Gallium was determined by AAS after shaking the organic phase with 10 ml of 0.1 M hydrochloric acid for 5 min (back-extraction). Thallium was determined by AAS after shaking the organic phase with 10 ml of 0.05 M sulphuric acid - 0.1 M sodium sulphite for 5 min.Antimony was determined by measuring the count rate of 125Sb after transferring a 1-ml portion of the organic phase into a polyethylene test-tube. In order to investigate the extracted species, hydrogen ion, lithium and iron concentrations were determined by sodium hydroxide titration using phenolphthalein as an indicator, by flame emission spectrometry and by AAS, respectively. Results and Discussion Extraction of Gold(II1) Graphs of the extraction of gold(II1) from solution in hydrochloric acid with five crown ethers are shown in Fig. 1. A 100% amount of the gold(II1) with 18C6 and 59% with 15C5 were extracted from a 6 M hydrochloric acid solution after shaking for 0.5-5 min. The effect of the gold(II1) concentration on the extraction with DC18C6 and 18C6 from a 6 M hydrochloric acid solution was investigated; 10&97% of gold(II1) was extracted with both DC18C6 and 18C6 from 0.2-25 mM gold(II1) solutions.1 0 2 4 6 8 1 0 1 2 Initial HCI concentrationiM Fig. 1. Extraction of gold(II1) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: AuIII, 0.2 mM in 2 ml of HCI; crown ether, 50 mM, 2 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E , 12C41262 ANALYST, NOVEMBER 1986, VOL. 111 The extraction behaviour of gold(II1) from 0.1 M hydro- chloric acid - lithium chloride solutions with DC18C6, DB18C6 and 18C6 (Fig. 2) was similar to that from the hydrochloric acid solutions (Fig. 1). 15C5 and 12C4 gave good extractabilities from lithium chloride solutions.Extraction of Gallium(II1) Graphs of the extraction of gallium(II1) from solution in hydrochloric acid with five crown ethers are shown in Fig. 3. The gallium(II1) that had been extracted with 18C6 and 15C5 from an 8 M hydrochloric acid solution could be back-extracted with an equal volume of 0.1 M hydrochloric acid. The shaking time of 1-10 min for both extraction and back-extraction gave over-all recoveries of 100% with 18C6 and of 73% with 15C5. A 100% amount of the gallium(II1) was extracted with DC18C6, DB18C6 and 18C6 from 1-25 mM gallium(II1) solutions in 8 M hydrochloric acid. When 225 mM gallium(II1) was extracted with DB18C6, the extracted species deposited during the extraction also occurred in the extraction of iron.3 The deposit was soluble in acetone.From 0.1 M hydrochloric acid - lithium chloride solutions, gallium(II1) was efficiently extracted not only with DC18C6, DB18C6 and 18C6 but also with 15C5 and 12C4 (Fig. 4). Extraction of Thallium(II1) Graphs of the extraction of thallium(II1) from solution in hydrochloric acid with five crown ethers are shown in Fig. 5. The thallium(II1) that had been extracted with 18C6 and DB18C6 from a 6 M hydrochloric acid solution could be back-extracted with an equal volume of 0.05 M sulphuric acid - 0.1 M sodium sulphite. The shaking time of 1-10 min for both extraction and back-extraction gave over-all recoveries of 96% with 18C6 and of 51% with DB18C6. A 9%92% amount of thallium(II1) with DC18C6 and 96-95% with 18C6 were extracted from 0.1-20 mM thallium(II1) solutions in 6 M hydrochloric acid.Thallium(1) in the presence of titanium(II1) chloride as a reducing agent was poorly extracted with DC18C6, DB18C6 and 18C6 from hydrochloric acid solutions (Fig. 6). Thallium [initially thallium(I)] in the absence of titanium(II1) chloride, however, was extracted to some extent with DC18C6 and 18C6 from 28 M hydrochloric acid solutions (Fig. 6). Thallium(1) is probably oxidised by air to thallium(II1) in the presence of DC18C6 and 18C6 and then extracted, as in the examples of the adsorption on activated carbon,s Amberlite XAD resins and Chelex 100.7 The extraction behaviour of thallium(II1) from 0.1 M hydrochloric acid - lithium chloride solutions with DC18C6, DB18C6 and 18C6 (Fig. 7) was similar to that from hydro- chloric acid solutions (Fig.5). In contrast, 15C5 and 12C4 gave good extractabilities. Extraction of Antimony(V) and Antimony(II1) Graphs of the extraction of antimony(V) with five crown ethers from hydrochloric acid solutions containing ammonium cerium(1V) sulphate as an oxidising agent are shown in Fig. 8. A 100% amount of antimony(V) was extracted with DC18C6 from a 10 M hydrochloric acid - 2 mM cerium(1V) solution after shaking for 1-5 min. The effect of antimony(V) concentration on the extraction was investigated: DC18C6 extracted 100% of antimony(V) from 0.1-5 mM antimony(V) solutions that were 10 M in hydrochloric acid and 2-15 mM in cerium(1V). When antimony(V) was extracted with 18C6 from 20.1 mM antimony(V) solutions in 2 6 M hydrochloric acid - 2 mM cerium(IV), the extracted species deposited.The extraction of 21 mM antimony with DB18C6 from 2 6 M hydrochloric acid - 5 mM cerium(1V) also produced deposits. Graphs of the extraction of antimony(II1) in the presence of titanium(II1) chloride are shown in Fig. 9. A 9694% amount of antimony(II1) was extracted with DC18C6 from 0.1-25 mM antimony(II1) solutions in 7 M hydrochloric acid - 20 g 1-1 titanium(II1) chloride. Nature of the Extracted Species The stoicheiometry of the extracted species was investigated by the molar ratio method. Plots of the percentage extraction of gold(III), gallium(III), thallium(II1) and antimony(V) with 18C6 or DC18C6 from hydrochloric acid solutions against the 2olkz--J 0 2 4 6 8 1 0 1 2 Initial LiCl concentrationh Fig.2. Extraction of gold(II1) from acidic lithium chloride solution with a chloroform solution of crown ether. Conditions: AuIII, 0.2 mM in 2 ml of 0.1 M HCI - LiCI; crown ether, 50 mM, 2 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E , 12C4 l o o r 80 r 0 2 4 6 8 1 0 1 2 Initial HCI concentrationh Fig. 3. Extraction of gallium(II1) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: GaIII, 1 mM in 10 ml of HCI; crown ether, 50 mM, 10 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E , 12C4 Initial LiCl concentrationh Fig. 4. Extraction of gallium(II1) from acidic lithium chloride solution with a chloroform solution of crown ether. Conditions: GaIlf, 1 mM in 10 ml of 0.1 M HCI - LiCI; crown ether, 50 mM, 10 ml. A , DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E, 12C4ANALYST, NOVEMBER 1986, VOL.111 1263 0 2 4 6 8 1 0 1 2 Initial HCI concentrationh Fig. 5. Extraction of thallium(II1) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: T P , 0.1 mM in 10 ml of HCI; crown ether, 50 mM, 10 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E, 12C4 8 40 0 .- +- 2 20 u 0 2 4 6 8 1 0 1 2 Initial HCI concentrationh Fig. 6. Extraction of thallium(1) and thallium (initially I) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: TI, 0.1 mM, 10 ml; crown ether, 50 mM, 10 ml. A, DC18C6, TI' in HCI - 20 g 1-1 TiC1,; B, DB18C6, TI1 in HCl - 20 g 1-l TiCl,; C, 18C6, Tll in HCI - 20 g 1-l TiC1,; D, DC18C6, T1 !njtially I in HCI; E, DB18C6, T1 (initially I) in HC1; and F, 18C6, TI !initially I] in HCl loot-@-+ 0 2 4 6 8 1 0 1 2 Initial LiCl concentrationh Fig.7. Extraction of thallium(II1) from acidic lithium chloride solution with a chloroform solution of crown ether. Conditions: T P , 0.1 mM in 0.1 M HC1 - LiC1, 10 rnl; crown ether, 50 mM, 10 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E, 12C4 100 - 80 - 8 $ 60 2 fi 40 - .- c - u 20 - 0 2 4 6 8 1 0 1 2 Initial HCI concentrationh Fig. 8. Extraction of antimony(V) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: SbV in HCl - 2 mM CeIV, 2 ml; crown ether, 50 mM, 2 ml. A, DC18C6,O.l mM Sbv; B, DB18C6, 0.1 mM Sbv; C, 18C6, 0.01 mM Sbv; D, 15C5,O.l mM Sbv; and E, 12C4, 0.1 mM SbV & 60 0 .- U 40 X w 20 0 2 4 6 8 1 0 Initial HCI concentrationh Fig.9. Extraction of antimony(II1) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: SbIII, 0.1 mM in HCI - 2 g 1-1 TiCl,, 2 ml; crown ether, 50 mM, 2 ml. A, DC18C6; B, DB18C6; C, 18C6; and D, 15C5 I R A I 100 $? 80 C 0 .- 60 h 4- 4 0 , 0 1 2 3 Molar ratio, [crown ether1 [metal] Fig. 10. Plots of percentage extraction of metals with crown ether from hydrochloric acid solution against molar ratio of crown ether to metal. A, 2 ml of 10 mM Au"' in 6 M HC1,2 ml of 2-25 mM 18C6; B, 10 ml of 10 mM Gal" in 8 M HCI, 10 ml of 2-30 mM 18C6; C, 10 ml of 10 mM T P in 6 M HCI, 10 ml of 2-25 mM 18C6; D, 2 ml of 5 mM SbVin 10 M HCI - 11 mM CeIV, 2 ml of 1-15 mM DC18C6; and E, 2 ml of 10 mM SbIrl in 7 M HCI - 20 g 1-1 TiCI3, 2 ml of 2-30 mM DC18C6 ratio [crown ether]/[metal] gave sudden breaks at ratios of 1.0-1.2 (Fig.10). These results indicate a molar ratio of 1 : 1 in the extracted species. The same result was obtained with ir0n(II1).~ Plots of percentage extraction of gold(III), gal- lium( 111) and thallium( 111) from acidic lithium chloride solutions with 18C6 (figures omitted) were similar to those from hydrochloric acid solutions, also indicating a molar ratio of 1 : 1. Gloe et aZ.4 have shown that the gold(II1) species extracted from potassium chloride solution with DB18C6 has a molar ratio of 1 : 1. The ratio of DC18C6 to antimony(III), however, could not be determined (Fig. 10). On the assumption that HFeC14 is extracted with crown ether from hydrochloric acid solution and that LiFeC14 is extracted from lithium chloride solution, the molar ratios of hydrogen ion to iron and of lithium to iron in the organic phases were determined as follows.A hydrochloric acid or lithium chloride (not acidified) solution of 0.1 M iron(II1) was shaken with an equal volume of 0.1 M DC18C6 in chloroform. An aliquot of the separated organic phase was shaken with water (back-extraction) and hydrogen, lithium and iron ions were determined in the aqueous phase. The hydrogen ion concentration was calculated by the procedure of Nachtrieb and Conway.1° As shown in Table 1, a molar ratio of 1 : 1 was obtained for both [H+]/[Fe] and [Li]/[Fe]; this indicates the validity of the above assumption. The results shown in Table 1 also indicate that hydrogen and lithium ions are extracted with DC18C6 from hydrochloric acid and lithium chloride solutions not containing iron(III), but presumably HFeC14 and LiFeC14 are extracted preferentially.1264 ANALYST, NOVEMBER 1986, VOL.111 Table 1. Molar ratios of hydrogen ion or lithium to iron in the organic phase after extraction with DC18C6 Organic phase after extraction Aqueous solution Solution of Ferrr/M ~ M H C I . . . . . . 0 0 0.1 ~ M H C I . . . . . . 0 0 0.1 6 ~ L i C 1 . . . . . . 0 0 0.1 8 ~ L i C l . . . . . . 0 0 0.1 CHCl, solution of DC 18C6/~ 0 0.1 0.1 0 0.1 0.1 0 0.1 0.1 0 0.1 0.1 H+ or Li/M <0.001 0.036 0.093 <0.001 0.114 0.099 0 0.006 0.087 0 0.031 0.098 Molar ratio Fe/M or [Li] : [Fe] 0 0.95 : 1.0 0 0.098 0 1.0: 1.0 0 0.099 0 0.98 : 1.0 0 0.089 0 0.99 : 1.0 0 0.099 [H+I Table 2.Determination of iron and gallium in NBS aluminium-base alloys Present method* Relative Element Certified standard Sample determined value, Yo Average, ‘/O deviation, % SRM85b . . . . . . Fe 0.24 0.231 2.6 SRM858 . . . . . . Fe 0.078 0.0780 3.6 SRM85b . . . . . . Ga 0.019 0.0197 2.2 * Six aliquots of the sample solution were taken for each separation and determination. When iron(II1) and gallium(II1) solutions in hydrochloric acid were extracted with DB18C6 in chloroform, the extracted species deposited. The deposits were filtered off using a suction pump and were dried in a silica gel desiccator. The elemental analyses of the deposits were C 42.38, H 4.83, Fe 9.47 and C1 24.11; and C 41.34, H 4.74, Ga 11.65 and C1 23.11%, respectively.On the basis of the contents of C, Fe (or Ga) and C1, a DB18C6: Fe (or Ga) : C1 ratio of 1 : 1 : 4 is obtained. The absorption spectra of iron(III), gold(II1) and thal- lium(II1) extracted from solution in hydrochloric acid with the crown ethers were similar to those of the chloro complexes of the metals in hydrochloric acid solutions. The absorbances of iron(II1) in the organic phase at about 250, 320 and 360 nm were much higher than those in hydrochloric acid solution. These results suggest that the metals are extracted as the chloro complexes. Determination of Iron and Gallium in Aluminium-base Alloys The extraction method was applied to the separation and determination of iron and gallium in National Bureau of Standards (NBS) aluminium-base alloys.A 0.5-g sample was dissolved in hydrochloric acid (1 + 1) by heating and the solution was diluted to 50 ml with hydrochloric acid (1 + 1). A 5-ml aliquot of this solution was transferred into a separating funnel and 5 ml of concentrated hydrochloric acid were added. The solution was shaken with 5 ml of 50 mM DCl8C6 in chloroform for 5 min. The separated organic phase was shaken with 10 ml of 0.1 M hydrochloric acid for 5 min and the aqueous phase (back-extract) was adjusted to 20 ml with 0.1 M hydrochloric acid. Iron and gallium were then determined by AAS and spectrophotometry with Rhodamine B ,I1 respec- tively. The calibration graphs were established without the extractive separation. The results are shown in Table 2. The authors thank the Radioisotope Centre of the University of Tsukuba for permitting the tracer work. The elemental analysis was carried out by the Chemical Analysis Centre of the University. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Kolthoff, I. M., Anal. Chem., 1979, 51, 1R. Cheng, K. L., Ueno, K., and Imamura, T., “CRC Handbook of Organic Analytical Reagents,” CRC Press, Boca Raton, FL, 1982, p. 127. Koshima, H., and Onishi, H., Anal. Sci., 1985, 1, 389. Gloe, K., Miihl, P., Kholkin, A. I., Meerbote, M., and Beger, J., Isotopenpraxis, 1982, 18: 170. Vasilikiotis, G. S . , Papadoyannis, I. N., and Kouimtzis, Th. A., Microchem. J., 1984, 29, 356. Caletka, R., Hausbeck, R., and Krivan, V., Fresenius 2. Anal. Chem., 1985, 320, 665. Koshima, H., Anal. Sci., 1986, 2, 255. Koshima, H., and Onishi, H., Anal. Sci., 1985, 1, 237. Japanese Industrial Standard, JIS K 8142, 1976. Nachtrieb, N. H., and Conway, J. G., J. Am. Chem. SOC., 1948,70, 3547. Hasegawa, Y., Inagake, T., Karasawa, Y., and Fujita, A., Talanta, 1983, 30, 721. Paper A41147 Received May 27th, 1986 Accepted June 16th, I984

ISSN:0003-2654    

DOI:10.1039/AN9861101261

出版商:RSC    

年代:1986

数据来源: RSC