Evaluation of electrochemical hydride generation for the determination of arsenic and selenium in sea water by graphite furnace atomic absorption with in situ concentration

A continuous flow electrochemical hydride generation technique coupled with in situ concentration in a graphite furnace has been developed for determination of As and Se in seawater. Lead is used as cathode material for the production of arsine and hydrogen selenide. The efficiency of generation of arsine from As(III) is 86 ± 6%, that from As(V) ranges from 73% to 86%. The efficiency of generation of hydrogen selenide from Se(IV) is 60 ± 5% and from Se(VI) is 30 ± 5%. The hydrides are trapped in an iridium-palladium coated graphite furnace prior to atomization. Absolute detection limits and concentration detection limits of 84 pg (3s_blank) and 84 pg ml⁻¹ for determination of As using 1 ml sample volume and 75 pg (3s_blank) and 7.5 pg ml⁻¹ for determination of Se using 10 ml sample volumes are obtained, respectively. The precision of replicate measurement for the analysis of reference materials at the 1.3 μg l⁻¹ level for As(III) (0.8 ng absolute mass level) and at the 0.042 μg l⁻¹ level for Se(IV) (0.42 ng absolute mass level) is better than 4% and 23% (relative standard deviation, RSD), respectively. The RSD values quoted above for Se include errors introduced by the sample preparation procedure.     

流动注射-氢化物-石墨炉原子吸收光谱法应用研究 Ⅲ.痕量锗的测定

本文采用自制的氢化物-石墨炉自动进样器及流动注射仪,直接测定了一些环境试样中的痕量锗,并研究了测定条件。该方法灵敏度高,线性范围宽,操作简单,速度快,耗样量少。特征质量:5.7 pg/0.0044A;检出限:1.3 pg;测定速度:30个样/h;回收率:99.5％～104％。     

Preconcentration and separation of copper(II), cadmium(II) and chromium(III) in a syringe filled with 3-aminopropyltriethoxysilane supported on silica gel

In this study, a syringe was filled with silica gel loaded with 3-aminopropyltriethoxysilane, for the separation and preconcentration of copper, cadmium and chromium prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS) in seawater. For this purpose, a syringe was filled with 0.5 g of modified silica gel and the sample solution was drawn into the syringe and ejected back again. The analyte elements were quantitatively retained at pH 5. Then, the elements sorbed by the silica gel were eluted with 2.0 M of HCl and determined by GFAAS. At optimum conditions, the recovery of Cu, Cd and Cr were 96-98%. Detection limits (3delta) were 6.6, 7.5 and 6.0 micro g L(-1) for Cu, Cd and Cr, respectively. The elements could be concentrated by drawing and discharging several portions of sample successively but eluting only once. Cu, Cd and Cr added to a seawater sample were quantitatively recovered (>95%) in the range of the 95% confidence level. The method proposed in this paper was compared with a column technique. Optimum experimental conditions, reproducibility, precision and recoveries of both techniques are the same, but the syringe technique is much faster, easier and more practical than the column technique. It is a portable system and allows one to make the sorption process in the source of sample. In addition, the risk of contamination is less than in the column technique.     

Determination of trace indium in urine after preconcentration with a chelating-resin-packed minicolumn

A simple and rapid chelating-resin-packed column has been developed for preconcentration of trace indium in biological samples. A large-sized urine sample was pumped through a minicolumn at a flow rate of 1.0 mL/min by using a peristaltic pump, and the eluents were analyzed using graphite furnace atomic absorption spectrometry (GFAAS). Four commercially available chelating resins including Chelex-100, Amberlite IRC-50, Duolite GT-73, and Celite 545-AW were studied for evaluating the indium sorption performance. Several parameters, such as pH, resin amount, eluent volume, eluent flow rate, and the volume of sample, were investigated and optimized. A 100-200 mL of the sample was loaded into a column containing 1.2 g of wet Chelex-100 and subjected to the ion-exchange procedure. The retained analytes were eluted with 5.0 mL of 0.1 M HNO(3) and quantified by GFAAS. The correlation coefficient in the range 10-250 ng/mL was of 0.9994. The limit of detection of the proposed method was 2.75 ng/mL. The method developed was successfully applied to analysis of spiked urine samples with good recoveries of 93-103% (n = 6) and reproducibility (relative standard deviation < 4.9%). The accuracy of procedure was confirmed by indium determination in spiked certified reference materials.     

流动注射预富集─石墨炉原子吸收联用测定海水中痕量钼

用二乙基二硫代氨基甲酸钠作络合剂、乙醇作洗脱液的流动注射固相吸附萃取预富集─石墨炉原子吸收联用测定海水中痕量钼。设计了以固定体积取样法为基础的预富集装置。考察了实验参数对分析性能的影响。本法能在线分离干扰、富集被测物,当样品上柱体积为1.35mL时,富集倍数为13.3倍,检测下限为0.027μg/L,用于测定海水等标样中钼含量,精密度较好。     

Capillary injection device for in situ pre-concentration of trace elements in graphite furnace-atomic absorption spectrometry

A device for in situ pre-concentration of trace elements in graphite furnace-atomic absorption spectrometry (GF-AAS), which is based on the direct introduction of the sample solution into the furnace by a fused silica capillary, is described. Experimental conditions have been optimized for the determination of several elements at the sub pg/g level with a CV always better than 15%. A deposition yield of approximately 95% was estimated by depositing a solution containing NaCl 0.002 M. A very simple and effective device for handling a sample under contamination-free conditions is also described which allowed a CV less than 10% to be obtained for replicate determinations of Cd in blank samples at 0.4 pg/g. The overall analytical system was validated by recovery studies carried out on standard solutions and spiked snow samples. Measurements were performed at 1, 5 and 50 pg/g, and the error was always lower than 20, 10 and 5%, respectively. The evaluation of the experimental detection limits which ranged in the interval 0.1–4 pg/g is finally discussed.     

Determination of trace elements in seawater by electrothermal atomic absorption spectrometry with and without a preconcentration step

The determination of the trace metals Cd, Pb and Cu in seawater by electrothermal atomic absorption spectrometry (ETA-AAS) has been investigated. A combination of the platform with mixed palladium nitrate-magnesium nitrate as matrix modifier and Zeeman background correction allows Cd an Pb to be determined by aqueous standard calibration in appropriately diluted seawater samples. Copper can be determined in undiluted seawater samples without chemical modification using a standard additions method. Detection limits (3) of 2.97,5.27 and 1.1 gl^–1 are obtained for Cd, Pb and Cu respectively. A Kelex-100 impregnated silica C18 material (Kelex 100-C18) has been tried and has proved to be effective as a column packing for extraction/preconcentration of these metals from seawater. Using the column extraction method, the sensitivity of the graphite furnace technique is enhanced 50-fold using a 10 l injection volume. Thus, the determination of the studied three metals in seawater at the ng.l^–1 level could be achieved.     

A Simple and Sensitive HPLC Method for Antipyrine in Plasma

Abstract

A rapid, simple and sensitive high-performance liquid chromatographic (HPLC) method was developed for the determination of antipyrine in small volume (50 μl) of plasma samples. Aminopyrine was employed as the internal standard. The sample preparation is a direct plasma protein precipitation procedure so is less tedious and rapid. The assay employs a column packed with a C₁₈ reversed-phase material (5 μm Nucleosil) with an isocratic mixture of acetonitrile and water (25:75, v/v) as the mobile phase. The eluant was detected at 254 nm. The assay achieves the level of sensitivity (0.5 μg/ml) and accuracy required to obtain meaningful data about the single-dose pharmacokinetics of antipyrine in guinea pig and rat. The method gave high reproducibility with coefficients of variation less than 5%.     

Solid-phase extraction of vinblastine and vincristine from plasma and urine: variable drug recoveries due to non-reproducible column packings

A sensitive and selective high-performance liquid chromatographic (HPLC) method for the determination of vinblastine and vincristine in plasma and urine is described. The drugs are isolated from 1.0 ml of the biological fluid with a solid-phase extraction column (Bond-Elut Diol). The HPLC method was combined with electrochemical detection at +850 mV versus an Ag/AgCl reference electrode. The detection limit is 100 pg for vinblastine and 250 pg for vincristine with a signal-to-noise ratio of 3, which permits the determination of these compounds in biological fluids at the nanogram level. Evaluation of the isolation method revealed that the drug recoveries and the reproducibility of the extraction procedure depend on the batch number of the solid-phase extraction column used.     

A back-extraction procedure for the dithiocarbamate solvent extraction method. Rapid determination of metals in seawater matrices

Summary A ligand exchange liquid/liquid extraction method using dithiocarbamate complexes is elaborated for the graphite furnace atomic absorption spectrometry (GF-AAS) of seawater and marine interstitial water. Palladium is used for the exchange. This metal ensures a rapid and quantitative back-extraction. It simultaneously works as matrix modifier in the GF-AAS analysis. The proposed method is evaluated in the analysis of lead, copper, nickel, and cadmium in CASS-II marine reference seawater and samples from the North Sea. A microanalytical variant of the method is applied in marine interstitial water analysis down to sample volumes of 500 l.     

Coprecipitation with metal hydroxides for the determination of beryllium in seawater by graphite furnace atomic absorption spectrometry

Coprecipitation first with magnesium hydroxide, next with tin(IV) hydroxide is developed for the determination of traces of beryllium in sea-water. To a 200-ml sample is added a sodium hydroxide solution to form magnesium hydroxide at pH 11.5, on which beryllium is quantitatively coprecipitated. The precipitate is separated by centrifugation and dissolved in 2 ml of 12 mol/l hydrochloric acid. The resulting solution (ca. 10 ml) is mixed with 2 mg of tin (IV) carrier and the pH is adjusted to 5.0 to collect the beryllium on tin (IV) hydroxide, leaving magnesium ions in the solution. The tin (IV) hydroxide is centrifuged, dissolved in 0.1 ml of 5 mol/l hydrobromic acid, and then diluted to 1 ml with water. Magnesium is so added as to be 500 g/ml for increasing the sensitivity about four times, and the beryllium in the solution is determined by graphite furnace atomic absorption spectrometry. The experiments with synthetic seawater samples showed that pg — g amounts of beryllium can be coprecipitated on the metal hydroxides and beryllium at the low ng/1 level can be determined with reasonable precision (RSD < 10%). The detection limit of the proposed method is 0.5 ng/l of beryllium in seawater.     

Hydride generation-electrostatic deposition-graphite furnace atomic absorption spectrometric determination of arsenic,selenium and antimony

A system is described and evaluated for the in situ collection of generated hydrides of As, Se and Sb in a graphite furnace using a high voltage electrostatic field. Analytical figures of merit are derived using graphite furnace atomic absorption detection and a characterization of the electrostatic deposition (ED) process is presented based on optimization studies. Absolute detection limits (LOD) of 30, 16 and 33 pg were obtained for As, Se and Sb, respectively, reflecting overall generation/collection efficiencies of 80±5, 71±3 and 62±6%, respectively. Precision of replicate determination was typically 4% R.S.D. at a concentration 40-fold above the LOD for a 1 ml sample volume. The accuracy of the approach was demonstrated through the analysis of coastal seawater and marine sediment certified reference materials.     

Determination of trialkyllead species in water samples

An analytical compound procedure is described for the determination of trimethyl- and triethyllead in water samples like rain, melted snow, and surface waters. The method consists of an enrichment step (adsorption onto and elution from silica gel), a chromatographic separation with column switching (HPLC including pre-column enrichment), and a spectrophotometric detection (chemical reaction detector). The detection limits for the whole procedure, starting with 500 ml sample volume, are 15 pg/ml and 20 pg/ml for trimethyl- and triethyllead resp. The standard deviation for repeated analysis of a sample containing 90 pg Et3Pb+/ml is calculated to +/- 4%. The method also covers the analysis of the chemically mixed trialkyllead species Me2EtPb+ and MeEt2Pb+. The investigation of several water samples taken from different locations shows the presence of trimethyl- and triethyllead in the concentration range of 20-100 pg/ml.     

Determination of mercury in environmental samples by cold vapour generation and atomic-absorption spectrometry with a gold-coated graphite furnace

Mercury is determined at below the pg/ml level by a combination of cold vapour generation, trapping in a gold-coated graphite furnace and atomic-absorption detection. The mercury is reduced to the element by stannous chloride, stripped from solution by a stream of nitrogen and collected on a gold-coated porous graphite disk in a graphite furnace. It is then atomized by increasing the graphite furnace temperature and detected by an atomic-absorption spectrophotometer. The absolute detection limit and the characteristic mass were found to be 5 and 20 pg for 0.0044 absorbance, respectively. The concentration limit of detection was 0.1 pg/ml for a 50-ml sample, and the linear dynamic range covered three orders of magnitude. The precisions of the measurements were 2.7% for 0.1 ng and 2.6% for 2 ng of mercury. Analyses of NBS and NIES reference materials showed quantitative recovery. Analytical results obtained by the technique are presented for natural waters, marine biota and sediments.     

石墨炉原子吸收分光光度法测定空气中的铍

对300余个样品进行监测,选择灵敏度高的石墨管和最佳基体,提高灰化、原子化的温度,确立了石墨炉原子吸收法测定空气中铍含量的实验条件。样品采用干灰化消解法,最佳溶剂为质量分数l％的硝酸溶液,利用仪器内置的样品浓度计算程序,绘制工作曲线直接获得样品中铍的含量。方法检出限为0．021μg／L,测定结果的相对标准偏差小于2％（n=6）,线性范围为0～6．5μg／L,加标回收率为91．6％～107％。     

Electrothermal vaporisation ICP-mass spectrometry (ETV-ICP-MS) for the determination and speciation of trace elements in solid samples - A review of real-life applications from the author's lab

The use of electrothermal vaporisation (ETV) from a graphite furnace as a means of sample introduction in inductively coupled plasma mass spectrometry (ICP-MS) permits the direct analysis of solid samples. A multi-step furnace temperature programme is used to separate the vaporisation of the target element(s) and of the matrix components from one another. Sometimes, a chemical modifier is used to enable a higher thermal pre-treatment temperature, by avoiding premature analyte losses (stabilisation) or promoting the selective volatilisation of matrix components. In almost all instances, accurate results can be obtained via external calibration or single standard addition using an aqueous standard solution. Absolute limits of detection are typically ~1 pg, which corresponds to 1 ng/g for a typical sample mass of 1 mg. Real-life applications carried out in the author's lab are used to illustrate the utility of this approach. These applications aim at trace element determination in industrial and environmental materials. The industrial materials analysed include different types of plastics - Carilon, polyethylene, poly(ethyleneterephtalate) and polyamide - and photo- and thermographic materials. As samples from environmental origin, plant material, animal tissue and sediments were investigated. Some applications aimed at a multi-element determination, while in other, the content of a single, but often challenging, element (e.g., Si or S) had to be measured. ETV-ICP-MS was also used in elemental speciation studies. Separation of Se-containing proteins was accomplished using polyacrylamide gel electrophoresis (PAGE). Subsequent quantification of the Se content in the protein spots was carried out using ETV-ICP-MS. As the volatilisation of methylmercury and inorganic mercury could be separated from one another with respect to time, no chromatographic or electrophoretic separation procedure was required, but ETV-ICP-MS as such sufficed for Hg speciation in fish tissue.     

Speciation of n-butyltin compounds by atomic absorption spectrometry with an electrothermal quartz furnace after hydride generation

A method is described for the speciation of n-butyltin compounds. The compounds are volatilized from aqueous solution, trapped on a chromatographic packing material contained in a teflon column, and separated on the basis of differing boiling points. The column is attached directly to an electrothermal quartz furnace of an atomic absorption spectrometer for detection at 224.61 nm. Absolute detection limits (3σ) are 11–45 pg as tin, calibration curves are linear to 13 ng, and reproducibility at the 2-ng level ranges from 5% for mono-n-butyltin to 18% for tri(n-butyl)tin.     

Proconcentration of trace elements from high-purity thorium and uranium on Chelex-100 and determination by graphite furnace atomic absorption spectrometry with Zeeman-effect background correction

Preconcentration of trace impurities form large-sized samples of uranium metal and thorium oxide using a small column of Chelex-100 followed by their determination using graphite furnace atomic absorption spectrometry (GFAAS) is reported. A 0.5–10-g amount of the sample (uranium metal or thorium oxide) was dissolved, complexed with ammonium carbonate and subjected to the ion-exchange procedure. The retained analytes were eluted with 2–4 M nitric acid and brought to a small volume for a final dilution to 10-25 ml for their determination using GFAAS. The validity of the separation procedure and recoveries at μg kg⁻¹ levels was checked by standard addition; the recoveries were> 95%.     

Determination of total tin in silicate rocks by graphite furnace atomic absorption spectrometry

A method is described for the determination of total tin in silicate rocks utilizing a graphite furnace atomic absorption spectrometer with a stabilized-temperature platform furnace and Zeeman-effect background correction. The sample is decomposed by lithium metaborate fusion (3 + 1) in graphite crucibles with the melt being dissolved in 7.5% hydrochloric acid. Tin extractions (4 + 1 or 8 + 1) are executed on portions of the acid solutions using a 4% solution of trioctylphosphine oxide in methyl isobutyl ketone (MIBK). Ascorbic acid is added as a reducing agent prior to extraction. A solution of diammonium hydrogenphosphate and magnesium nitrate is used as a matrix modifier in the graphite furnace determination. The limit of detection is > 10 pg, equivalent to > 1 μg l^?1 of tin in the MIBK solution or 0.2–0.3 μg g^?1 in the rock. The concentration range is linear between 2.5 and 500 μg l^?1 tin in solution. The precision, measured as relative standard deviation, is < 20% at the 2.5 μg l^?1 level and < 7% at the 10–30 μg l^?1 level of tin. Excellent agreement with recommended literature values was found when the method was applied to the international silicate rock standards BCR-1, PCC-1, GSP-1, AGV-1, STM-1, JGb-1 and Mica-Fe. Application was made to the determination of tin in geological core samples with total tin concentrations of the order of 1 μg g^?1 or less.     

Hydride Generation Graphite Furnace Atomic Absorption Determination of Bismuth in Clinical Samples with in Situ Preconcentration

A sensitive method for the determination of bismuth in clinical samples using hydride generation/trapping and atomization in a graphite furnace is described. Addition of Pd-Ir to the furnace tube surface before hydride trapping leads to great improvement in the sensitivity of the method. Calibration is achieved with simple aqueous standards carried through this same procedure. An absolute detection limit (3σ) of 100 pg and a concentration detection limit of 20 ng/liter are obtained using 5-ml sample volumes. Corresponding precisions of 8-12% are typical for analyses of these samples. Microwave-assisted sample digestion procedures using HNO₃ and H₂O₂ were used to decompose clinical materials. The method was used to determine Bi in human blood, serum, urine, and tissue before and after intake of therapeutic doses of colloidal bismuth citrate.