Zeeman-effect Background Correction Research Articles

Arsenic determination in naphtha by electrothermal atomic absorption spectrometry after preconcentration using multiple injections

Naphtha is a petroleum fraction containing C4–C15 hydrocarbon compounds and is used as feedstock for petrochemical processes which are affected profoundly by trace amounts of arsenic. A simple method for arsenic determination in naphtha using electrothermal atomic absorption spectrometry with polarized Zeeman-effect background correction was developed. Multiple injections were used for direct preconcentration in the graphite tube, eliminating sample pretreatment. Doehlert experimental designs were used to find the best settings for the furnace program parameters. Modifier concentration, number of multiple injections and sample volume were also optimized with the same multivariate approach. With three 45 µL sample injections, ashing temperature 1200 °C, atomization temperature 2700 °C and ashing time 60 s, a detection limit of 0.5 µg L−1 and a characteristic mass of 61 pg were achieved, using 3000 mg L−1 Pd(NO3)2 as the chemical modifier. The relative signal standard deviation was found to be 9.0% at the 2.3 µg.L−1 level. Results from several naphtha test samples showed arsenic levels typically below 3.0 µg L−1. The high degree of automation of the proposed method minimized technician sample handling allowing its application for routine analysis. This procedure has been used for arsenic determination in naphtha feeds processed in the Braskem Petrochemical (Salvador, Bahia, Brazil).

Influence of experimental parameters on the determination of antimony in seawater by atomic absorption spectrometry using a transversely heated graphite furnace with Zeeman-effect background correction.

Spectroscopic and electrothermal conditions for the determination of antimony in seawater using a transversely heated graphite furnace with Zeeman-effect background correction have been optimized with the use of an a priori calculation of the detection limit. The lowest limit of detection was obtained with a 2 nm spectral curvatures bandwidth and the use of an electrodeless discharge lamp; however, these experimental conditions resulted in strong premature curvature of calibration curves. Pd(NO(3))(2) can be recommended as a chemical modifier because seawater interference effects are minimized and pretreatment curves up to 1500 degrees C can be used permitting the removal of the major part of the saline matrix before atomization. Under optimized spectroscopic and electrothermal conditions the obtained limit of detection of Sb in seawater was about 0.4 microg L(-1).

Determination of arsenic in petroleum refinery streams by electrothermal atomic absorption spectrometry after multivariate optimization based on Doehlert design

This paper reports the development of a methodology for the determination of arsenic in petroleum refinery aqueous streams containing large amounts of unknown volatile organic compounds, employing electrothermal atomic absorption spectrometry with polarized Zeeman-effect background correction. In order to make the procedure applicable, the influence of chemical modification and the drying step was examined. Also, pyrolysis and atomization temperatures and the amount of nitric acid added to the sample were optimized using a multivariate approach based on Doehlert matrix. Obtained results indicate that, in this kind of sample, arsenic must be determined by standard addition procedure with a careful control of the drying step temperature and ramp pattern. In order to evaluate the accuracy of the procedure, a test was performed in six spiked samples of petroleum refinery aqueous streams and the relative errors verified in the analysis of such samples (added As between 12.5 and 190 μg l −1) ranged from −7.2 to +16.7%. The detection limit and the relative standard deviation were also calculated and the values are 68 pg and 7.5% (at 12.5 μg l −1 level), respectively.

Simultaneous determination of As, Cd, Cr and Pb in aqua regia digests of soils and sediments using electrothermal atomic absorption spectrometry and fast furnace programs

A method was developed for the simultaneous multi-element determination of As, Cd, Cr and Pb in aqua regia digests of soils and sediments using an electrothermal atomic absorption spectrometer with a transversely heated graphite atomizer and longitudinal Zeeman-effect background correction. A fast furnace program with no pyrolysis stage or chemical modifier was used, and the total duration of the time-temperature program of the graphite furnace was 45 s. The method detection limits calculated from blank samples were 9.5 μg l −1, 0.18 μg l −1, 6.2 μg l −1 and 2.5 μg l −1 for As, Cd, Cr and Pb, respectively. Sample preparation procedures are briefly described. The accuracy of the method was confirmed with a certified reference soil (recoveries 90–110%, within-batch RSD most often less than 5% with six replicates) and with 12 sediment samples from an international proficiency test. z-scores were calculated for the results of the sediment samples with 46 satisfactory and only 2 questionable results. Some analytical problems that were encountered during analysis are described. Fast furnace programs were found to be suitable for the simultaneous determination of the four elements in aqua regia digests of soils and sediments.

Reference values of selenium in plasma in population from Barcelona. Comparison with several pathologies

Plasma selenium reference values from healthy donors in the metropolitan area of Barcelona are determined. A random sample from 156 healthy adults (control group) is analysed by using electrothermal atomic absorption spectrometry with Zeeman effect background correction. The relationship between several pathologies and Se content is also evaluated. Se content from 64 samples from subjects with chronic renal failure and 54 from subjects suffering from several malignancies are determined and the results are compared to the reference values. Moreover, Se contents are determined and compared in two groups of children, healthy (19 samples) and children of mothers infected with HIV-1 (16 samples). In the control group, Se plasma concentration ranges between 50 and 145 μg · L −1 (82.2 ± 17.5 μg · L −1). Significantly lower values are found in the two pathologies studied (malignancy and chronic renal failure), compared to the control group. However, no significant differences in Se content are found between the two groups studied regarding malignancy and chronic renal failure. In children of mothers infected with HIV-1, Se status is significantly lower than that of healthy children.

Determination of lead, copper, zinc, magnesium, calcium and iron in fresh eggs by atomic absorption spectrometry

Abstract In this study, lead, copper and zinc, calcium, magnesium and iron in fresh egg samples have been determined by electrothermal and flame atomic absorption spectrometry (ETAAS–FAAS) with Zeeman-effect background correction. Y+Pd+citric acid (CA) has been found a powerful modifier mixture for the determination of Pb, Cu and Zn. Maximum pyrolysis and optimum atomization temperatures of analyte elements were determined in the presence or absence of modifiers. Atomization and background profiles of the analyte elements studied in the presence of Y+Pd+CA have been compared with other modifiers such as Mg+Pd and Mg+PO43−. The detection limits obtained were 1.88, 0.71, 0.03 ng/ml for Pb, Cu and Zn in ETAAS, 14.0, 32.3, 68.6 and 18.9 ng/ml for Mg, Ca, Fe and Zn in FAAS, respectively. The reliability of the measurements was confirmed by analysing a certified reference material, NIST, whole egg powder 8415. The percent recovery ranges of analytes were from 96.7 to 101%.

Control of spectral and non-spectral interferences in the determination of thallium in river and marine sediments using solid sampling electrothermal atomic absorption spectrometry

The direct analysis of solid samples using electrothermal (graphite furnace) atomic absorption spectrometry (ETAAS) has been investigated for the determination of thallium in river and marine sediment reference materials, because complete digestion of sediment samples requires the use of hydrofluoric acid and/or an alkaline fusion, and the extraction with aqua regia might be incomplete and cause interferences in the determination of thallium. The determination of thallium in river sediments using direct solid sampling ETAAS was straight forward, and could be carried out with good accuracy even without the use of a chemical modifier or calibration against aqueous standards. The analysis of marine sediments, in contrast, proved to be extremely difficult due to severe spectral and non-spectral interferences. The latter ones were caused by the relatively high chloride content of marine sediments, compared to river sediments, and could eventually be controlled by the addition of ammonium nitrate as a chemical modifier together with ruthenium as a permanent modifier. The spectral interference could only be overcome with Zeeman-effect background correction, and was most likely caused by sulfate. After optimization of the procedure, thallium in marine sediment reference materials could be determined by calibration against a certified river sediment reference material. According to the experience gained with river sediments, it might be assumed that aqueous standards could equally be used for calibration; this approach, however, was not further investigated. The results were in good agreement with non-certified ‘information’ values for thallium and with results obtained by ICP-MS using electrothermal vaporization and isotope dilution calibration. A characteristic mass of 13 pg was obtained, and the limit of detection of the proposed method, based on the zero-mass response (three times the standard deviation of 10 atomization cycles with empty platforms), was around 0.02 µg g−1 Tl.

Electrothermal atomic absorption spectrometric determination of selenium in biological fluids with rhodium modifier compared with hydride generation atomic spectrometric techniques

Analytical procedures for direct electrothermal atomic absorption spectrometric (ET-AAS) determination of selenium in urine, blood serum and solubilized hair, employing rhodium modifier (10–20 μg) in a transverse-heated graphite atomizer (THGA) with integrated pyrolytic graphite-coated platform and longitudinal Zeeman-effect background correction were developed. Results for urine were compared with flow-injection hydride generation with in-atomizer trapping of hydrogen selenide in Ir–Zr treated THGA (FI-HG–ET-AAS) and with continuous flow hydride generation coupled with a non-dispersive atomic fluorescence spectrometry (CF-HG–ND-AFS). Two different bomb decompositions proved useful: (i) urine sample (1 ml) soaked overnight with HNO 3, followed by pressurized digestion with HNO 3 in a microwave oven, then H 2O 2 added, and bomb decomposition completed with HNO 3–H 2O 2, then selenium pre-reduced to Se(IV) in 4.8 M HCl; and (ii) sample (1 ml) soaked overnight with HBr–BrO 3 −, then pressurized digestion in a microwave oven, followed by quantitation by FI-HG–ET-AAS or CF-HG–ND-AFS with standard addition calibration. Several certified reference materials (urine, blood serum and hair) as well as the NIES candidate CRM No. 18 ‘Human Urine’ from the National Institute of Environmental Studies (NIES) (Tsukuba, Japan) were analyzed and the results are in agreement between techniques and with certified values. Preference is given to the direct ET-AAS determination of Se in biological liquids after two- to threefold dilution in the presence of 10 μg of Rh. Pyrolysis and atomization temperatures are within 1100–1200°C and 2100–2200°C, respectively, and the ‘end-capped’ graphite tubes are preferred for better sensitivity and lower background absorbance. The limits of detection of the direct ETAAS are approximately 6 ng ml −1 Se in biological fluids. For 24 paired samples of blood serum and urine from non-exposed individuals (Sofia, Bulgaria), selenium levels are: serum 66.5±15.5 (45.5–116.4) ng ml −1 and urine 16.8±8.1 (6.0–41.9) ng ml −1.

A new strategy for preparation of hair slurries using cryogenic grinding and water-soluble tertiary-amines medium

The investigation of trace metal contents in hair can be used as an index of exposure to potentially toxic elements. Direct determination of Cd, Cu and Pb in slurries of hair samples was investigated using an atomic absorption spectrometer with Zeeman-effect background correction. The samples were pulverized in a freezer/mill for 13 min, and hair slurries with 1.0 g l −1 for the determination of Cu and Pb, and 5.0 g l −1 for the determination of Cd, respectively, were prepared in three different media: 0.1% v/v Triton X-100, 0.14 mol l −1 HNO 3, and 0.1% v/v of CFA-C, a mixture of tertiary amines. The easiest way to manipulate the hair samples was in CFA-C medium. The optimum pyrolysis and atomization temperatures were established with hair sample slurries spiked with 10 μg l −1 Cd 2+, 30 μg l −1 Pb 2+, and 10 μg l −1 Cu 2+. For Cd and Pb, Pd was used as a chemical modifier, and for Cu no modifier was needed. The analyte addition technique was used for quantification of Cd, Cu, and Pb in hair sample slurries. A reference material (GBW076901) was analyzed, and a paired t-test showed that the results for all elements obtained with the proposed slurry sampling procedure were in agreement at a 95% confidence level with the certified values. The cryogenic grinding was an effective strategy to efficiently pulverize hair samples.

Simultaneous determination of cadmium and lead in wine by electrothermal atomic absorption spectrometry

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l −1 HNO 3 and in 1+1 v/v diluted wine using mixtures of Pd(NO 3) 2+Mg(NO 3) 2 and NH 4H 2PO 4+Mg(NO 3) 2 as chemical modifiers. With 5 μg Pd+3 μg Mg as the modifiers and a two-step pyrolysis (10 s at 400°C and 10 s at 600°C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 μl of sample (wine+0.056 mol l −1 HNO 3, 1+1, v/v) dispensed into the graphite tube, analytical curves in the 0.10–1.0 μg l −1 Cd and 5.0–50 μg l −1 Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 μg l −1 for Cd, 0.8 μg l −1 for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 μg l −1 and for Pb at 500 μg l −1. The relative standard deviations ( n=12) were typically <8% for Cd and <6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Pb was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreement at the 95% confidence level.

The determination of low lead levels in the bone of lead-depleted mice by graphite furnace atomic absorption spectrometry.

Low lead levels in the femurs of mice fed with a lead-depleted diet have been determined by use of electrothermal atomic absorption spectrometry with Zeeman-effect background correction. The method is based on the use of Mg(NO3)2/Pd as matrix modifier which enables significant reduction of the spectral interferences prevalent if chemical modifiers based on NH4H2PO4 with either Ca or Mg are used for samples rich in Ca3(PO4)2 matrix. The method was developed and validated by use of the NIST standard reference material 1486 bone. Bones were decomposed in a pressurized microwave-heated system using 70% nitric acid. Forty-three mice femurs, with a mass of 74.62 +/- 12.54 mg, were dissolved in concentrated nitric acid. The lead results found in SRM 1486 (1.25 +/- 0.15 microg g(-1), n = 9) were in good agreement with the certificate (1.335 +/- 0.014 microg g(-1)). Recoveries of 200 ng lead added to the SRM before or after digestion were 99.0 +/- 1.4% and 98.5 +/- 1.6%, respectively. The lead detection limit in bone samples is 0.06 microg g(-1) dry mass. This method is, therefore, suitable for the determination of very low lead levels (0.06-0.20 microg Pb kg(-1) bone) in the femurs of mice fed a diet with lead level of < 20 microg kg(-1).

Determination of silicon in nickel-based alloys using electrothermal atomic absorption spectrometry with longitudinal Zeeman-effect background correction and zinc oxide pretreatment

The determination of Si in the nickel-based alloy matrices by electrothermal atomic absorption spectrometry (ET-AAS) has been studied. A longitudinal Zeeman-effect correction with end-capped transversely heated graphite atomizer (THGA) is used. When measured at 251.6 nm, spectral interference mainly from Fe is found. Pretreatment for the removal of Ni and Fe from the sample solution of the nickel-based alloys is required. The effects of various modifiers including ethylenediaminetetraacetic acid (EDTA), Mg(NO 3) 2, NH 4H 2PO 4, Pd(NO 3) 2, and tartaric acid are evaluated in terms of the optimization of accuracy, sensitivity and the minimization of background absorption. Sample pretreatments including ammonium and zinc oxide precipitation are evaluated in terms of reducing the non-specific absorption. ZnO precipitation gives more accurate and precise results. The proposed method has been validated with certified reference materials of nickel-based alloys. Values for the silicon content ranged between 0.521 and 0.016%. The characteristic mass is 33.1 pg and the detection limit is 24.8 pg when 20 μl was injected for each ET-AAS measurement. The recovery for the proposed method ranges from 95 to 105%.

Determination of heavy metal contents in human colostrum samples by electrothermal atomic absorption spectrophotometry.

Determination of lead, cadmium, nickel, chromium, manganese and copper levels in colostrum samples (n = 30), collected from middle-class mothers, was carried out by electrothermal atomic absorption spectrophotometer (ETAAS) with Zeeman effect background correction using a tungsten-palladium-citric acid chemical modifier mixture. A wet-ashing procedure was applied to dissolve the samples and to remove the fat. The graphite furnace temperature programme for analytes determined by ETAAS was studied, and the optimum pyrolysis temperatures of Pb, Cd, Ni, Cr, Mn and Cu were determined in the presence of the modifier mixture. Detection limits of Pb, Cd, Cu, Mn and Cr were determined using a modifier mixture solution. Zinc and iron levels were determined by Zeeman flame atomic absorption spectrometer (F-AAS). Heavy metal levels (mean values) found in colostrum samples were 14.6 microg/l of Pb, 2.8 microg/l of Cd, 27.8 microg/l of Ni, 8.6 microg/l of Cr, 43.2 microg/l of Mn, 278 microg/l of Cu, 12.9 mg/l of Zn, and 3.5 mg/l of Fe. These metal levels were compared with results from other studies in different countries.

Determination of bismuth, indium and lead in spiked sea water by electrothermal atomic absorption spectrometry using tungsten containing chemical modifiers

The determination of bismuth, indium and lead in spiked synthetic and natural sea water by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction was investigated using tungsten containing chemical modifiers and tartaric acid (TA) as a reducing agent. Maximum pyrolysis and optimum atomization temperatures for the analyte elements were determined in the presence and absence of various modifiers. The lowest detection limits of 8.5, 4, and 1.3 μg l −1 and characteristic mass values of 0.07, 0.04 and 0.02 ng for Bi, In and Pb, respectively, were obtained using the W+Pd+TA mixed modifier, which was found to be most powerful for the determination of Bi, In and Pb spiked into synthetic and natural sea water. The relative error was decreased from 51 to 0.2% for Bi, from 42 to 2% for In and from 51 to 1.2% for Pb by using the proposed W+Pd+TA modifier mixture.

Determinação direta de crômio em açúcar e leite por espectrometria de absorção atômica com atomização eletrotérmica em forno de grafite

A fast and direct method for the determination of Cr in milk and cane sugar suspensions using graphite furnace atomic absorption spectrometry with Zeeman-effect background correction is described. No sample pre-treatment was necessary, minimizing the risk of contamination. The concentration of chromium in cane sugar was evaluated using Cr reference solutions prepared in 1% v/v HNO3 solution. The milk samples were introduced into the furnace with a mixture of amines for avoiding the autosampler blockage and foaming of milk. Chromium determination in milk was based on the standard additions method (SAM). The limit of detection and characteristic mass for cane sugar sample (30 mL) were 0,13 ng/ml and 4,3 pg, and for milk sample (10 mL) were 0,23 ng/ml and 7,8 pg, respectively. The graphite tube lifetime was 300 firings for sugar-cane sample and 100 firings for milk sample. The heating program was implemented in 68 s.

On-line emulsification of lubricating oils in a flow-injection system for chromium determination by electrothermal atomic absorption spectrometry

A simple and quick procedure has been developed for the on-line preparation of a one phase emulsion in a flow injection (FI) system for chromium determination by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction. The entire FI system was controlled by a computer, independent of the spectrometer. A 1-ml plug of sample solution was injected into the carrier stream of hexane and was subsequently mixed with streams of 3.8% (m/v) sodium chloride, 5.0% (v/v) sodium dodecylsulfate (SDS) and 5.0% (v/v) of sec-butanol. The flow rates of the carrier, sodium chloride, SDS and sec-butanol streams were 1.0, 0.5, 0.5 and 0.2 ml min−1, respectively. The sonication of the flowing solutions improved the stability of the emulsion and provided quantitative recoveries. An emulsified sub-sample of 200-µl was collected in a capillary of a sampling arm assembly. Thereafter, 20 µl of this sample solution were introduced by means of positive displacement with air through a time-based solenoid injector (TBSI) in the graphite tube atomizer. The furnace program included two drying steps (at 110 and 130 °C) to minimize the sputtering of the sample in the atomizer. In all instances, the pyrolysis, atomization and cleaning temperatures of 1600, 2400 and 2500 °C were used to obtain good peak profiles with low background signals without the addition of any chemical modifier. The method provides a linear range for chromium from 7.0 to 50 µg l−1 and a limit of detection of 4.0 µg l−1, which corresponds to 6.0 ng g−1. The results were precise (0.6–0.8% RSD) and the recovery values found in the analysis of spiked samples ranged from 99.2 to 102.2%. The agreement between the observed and certified values obtained from two NIST Standard Certified Materials was good. The method described is satisfactory for determining chromium in new and used lubricating oil samples.

Appraisal of different electrothermal atomic absorption spectrometric methods for the determination of strontium in biological samples

A comparative study of various potential chemical modifiers (La, Mg, Pd, Ni, Ta, Lu, Sm, Eu, Ho, Er, Tm and Tb) as well as of different background correction procedures (deuterium and Zeeman effect) and atomization techniques (wall and platform) for the direct determination of strontium in biological samples was carried out. Two instruments, one with deuterium and the other with Zeeman effect background corrections have been used to perform the experiments. Although La, Mg, Pd, Ta and Lu had a positive effect, lanthanum alone provided the best performance for the determination of strontium in whole blood, urine and bone digests using wall atomization without deuterium background correction. However, neither chemical modifier produced any significant improvement in sensitivity when Zeeman effect background correction with integrated platform atomization was used. Under the optimized conditions, the characteristic masses were 0.82 and 2.20 pg and the detection limits (3 σ) were 0.13 and 0.30 μg l −1 with wall atomization and with Zeeman effect background correction respectively. Recovery studies and analysis of standard reference materials certified for strontium were performed to assess the accuracy. The results for the determination of strontium in real samples with wall atomization and lanthanum as chemical modifier, agreed well with those obtained with Zeeman effect background corrector with a precision typically between 0.5 and 3%. Both procedures can be recommended, and the choice will depend on instrument availability.

Direct determination of chromium in gelatine by graphite furnace atomic absorption spectrophotometry

A fast and direct method for the determination of Cr in gelatine using graphite furnace atomic absorption spectrophotometry with Zeeman-effect background correction is described. No sample pre-treatment was necessary, minimizing the risk of contamination. The concentration of chromium in gelatine was directly evaluated applying the standard additions method from a metal spiked gelatine (0.5% m/v) dispersed in 1% v/v nitric acid solution. The heating program was implemented in 68 s. The estimated mean characteristic mass is 3.4 pg Cr for a 15 μl sample. The Cr values determined in gelatine with the proposed procedure are in close agreement with those obtained by employing an acid digestion procedure ( r = 0.9987).

Determination of chromium in urine by electrothermal atomic absorption spectrometry using different chemical modifiers

The effects of the chemical modifiers Eu, Mg(NO 3 ) 2 , Pd, Eu-Pd and Ni and the use of longitudinally (with deuterium lamp background correction) and transversally (with Zeeman effect background correction) heated atomizers on the determination of chromium in urine samples were studied. When longitudinally heated atomizers were used, the background absorption was too high for the addition of most species, such as Mg(NO 3 ) 2 , Pd, Eu-Pd and Ni, rendering its use unsuitable for the determination of chromium in urine. The addition of Eu led to lower background signals. However, when longitudinally heated atomizers were used larger background absorption signals were observed on addition of a modifier. In contrast, with transversally heated atomizers the background absorption signals were low and were not influenced by the addition of a modifier, except when Mg(NO 3 ) 2 was added. In this case, the atomization signal shapes and the sensitivity were improved. The characteristic masses (m 0 ) and limits of detection (3σ) were 2.2 and 3.3 pg and 0.02 and 0.04 µg Cr l –1 for the longitudinally (using Eu as modifier) and transversally [using Mg(NO 3 ) 2 ] heated atomizers, respectively. Recovery studies and analysis of standard reference materials certified for chromium were performed to asses the accuracy. The results for the determination of chromium in real samples with both background correction procedures agreed well with a precision between 0.8 and 2.5%. Both procedures can be recommended and the choice will depend on instrument availability.

Determination of selenium in biological tissue samples rich in phosphorus using electrothermal atomization with Zeeman-effect background correction and (NH 4) 3RhCl 6+citric acid as a mixed chemical modifier

Spectral interferences from phosphorus on the determination of selenium in biological tissue materials were not observed when a Zeeman-effect background correction was used with rhodium as a chemical modifier. A suppression effect on the selenium signal resulted when the concentration of phosphorus present was greater than 1.0 mg ml −1. Rhodium was found to be more effective than palladium in overcoming the phosphate interference. Analytical procedures for the direct determination of trace selenium in standard reference materials by graphite furnace atomic absorption spectrometry following sample dissolution in nitric acid and hydrogen peroxide using a microwave oven has been described. The results obtained agreed favourably with the certified values.