Derivative hydride generation atomic absorption spectrometry and determination of lead traces in waters

Fundamentals of derivative hydride-generation atomic absorption spectrometry (DHGAAS) are described. A linear relationship was obtained between the derivative absorbance and the concentration of analysis in a sample. The new DHGAAS method was applied to the determination of traces of lead in water. The conditions affecting the derivative absorbance of lead were evaluated and optimized. The detection limit and sensitivity of the proposed method were 26 times and 8.8 times better, respectively, than those of conventional hydride-genera-tion atomic absorption spectrometry. The characteristic concentration (for a derivative absorbance of 0.0044) and detection limit (3sigma) for lead were 0.017 and 0.096 ng mL(-1), respectively, for a 2 mV min(-1) sensitivity range setting. The recovery range was 92.5-103%.     

Electrochemical hydride generation atomic absorption spectrometry for determination of cadmium

An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead-tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett-Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20 ng ml⁻¹of cadmium. The concentration detection limit (3σ, n = 8) of 0.2 ng ml⁻¹ and repeatability (relative standard deviation, n = 7) of 3.1% were achieved at 10.0 ng ml⁻¹. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.     

Determination of lead in dialysis concentrates using flow injection hydride generation atomic absorption spectrometry

Flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) was used for determination of lead in dialysis concentrates. The parameters such as acidity, concentration of oxidising and reducing agents and argon gas flow rate were investigated to reach the best peak height sensitivity. No significant background signal was observed at high salt concentrations. The detection limit, concentration giving a signal equal to three times standard deviation of the blank signal, was 0.7 ng ml⁻¹ for a 500 μl injection volume. Precision of the measurements at the 20 ng ml⁻¹ level was 3.7% R.S.D. The dialysis concentrates analysed by FI-HGAAS were found to have 10-70 ng ml⁻¹ of lead. The same samples were analysed by ETAAS after removing the matrix using solid phase extraction with Chelex 100. The results were in agreement with those obtained by FI-HGAAS.     

Flow injection hydride generation electrothermal atomic absorption spectrometry with in-atomizer trapping for the determination of lead in calcium supplements

Lead hydride was generated from acid solution, containing potassium ferricyanide as an oxidizing agent, by the reaction with alkaline borohydride solution. The effects of reaction conditions (hydrochloric acid, ferricyanide and borohydride concentrations), and the lengths of reaction and stripping coils were studied. The effects of trapping temperature and argon flow rate were also investigated. Under the conditions giving the best peak area sensitivity, the detection limit (concentration giving a signal equal to three S.D. of the blank signal) was 0.12 mug l(-1) for a 1000 mul injection volume. The detection limit was improved to 0.03 mug l(-1) when the ferricyanide was purified by passage through a cation-exchange resin. Two calcium supplement materials were analyzed by the flow injection (FI)-hydride generation (HG)-electrothermal atomization atomic absorption spectrometry (ETAAS) method, giving values of 0.55 and 0.66 mug g(-1), in agreement with results obtained by previously validated methods. For a 500-mg sample the limits of detection and quantification were 0.006 and 0.02 mug g(-1), respectively.     

Determination of lead in wines by hydride generation atomic absorption spectrometry.

The optimization of lead hydride generation in aqueous ethanolic media and the influence on its generation of the wine components, both white and red, have been studied. These interferences were overcome by careful control of the parameters affecting hydride generation and the procedure was applied to the determination of Pb in wines. The method is fast, accurate and sensitive and can be used to quantify 24 ppb of Pb in wines.     

Evaluation of oxidant media for the determination of lead in food slurries by hydride generation atomic absorption spectrometry

Several oxidant media were evaluated for the generation of lead hydride from slurry samples and their application to the determination of lead in vegetables and fish by hydride generation atomic absorption spectrometry. Three oxidant - acid media were compared: hydrogen peroxide - nitric acid, ammonium persulphate - nitric acid and potassium dichromate - lactic acid. The powdered samples were suspended in Triton X-100 and shaken with 10.0 g of blown zirconia spheres until a slurry was formed. The potassium dichromate - lactic acid medium was the most satisfactory for the determination of lead in fish and vegetables, providing the lowest detection limits as a result of its high sensitivity and low blank values. The ammonium persulphate - nitric acid medium gave good accuracy, precision and selectivity for vegetables (1-2 p.p.m. of lead); however, with fish (0.1-1 p.p.m. of lead) it was only a semi-quantitative medium for the determination of lead owing to its lack of sensitivity and selectivity. The hydrogen peroxide - nitric acid medium was unsatisfactory for the generation of lead hydride from slurry samples because of decomposition of hydrogen peroxide by the organic matter in the sample.     

Ultratrace determination of tin by hydride generation in-atomizer trapping atomic absorption spectrometry

A quartz multiatomizer with its inlet arm modified to serve as a trap (trap-and-atomizer device) was employed to trap tin hydride and subsequently to volatilize collected analyte species with atomic absorption spectrometric detection. Generation, atomization and preconcentration conditions were optimized and analytical figures of merit of both on-line atomization as well as preconcentration modes were quantified. Preconcentration efficiency of 95 ± 5% was found. The detection limits reached were 0.029 and 0.14 ng mL⁻¹ Sn, respectively, for 120 s preconcentration period and on-line atomization mode without any preconcentration. The interference extent of other hydride forming elements (As, Se, Sb and Bi) on tin determination was found negligible in both modes of operation. The applicability of the developed preconcentration method was verified by Sn determination in a certified reference material as well as by analysis of real samples.     

Use of a surfactant in the determination of arsenic by flow injection hydride generation atomic absorption spectrometry

The possible benefits of the addition of an anionic surfactant, didodecyldimethylammonium bromide, in the determination of arsenic, by flow injection hydride generation atomic absorption spectrometry using a flame-heated quartz tube atomizer, were studied in the light of previous reports concerning the effects of surfactants on chemical vapor generation procedures. Concentrations of arsenic between 5 and 30 μg l⁻¹ were used. Calibrations in the presence and absence of the surfactant in the sample solution were not significantly different, either for the case where vesicles were formed in the presence of the analyte or where they were preformed in the surfactant solution and then added to the analyte. The surfactant had no effect on recoveries in the presence of copper, nickel or bismuth. The addition of the surfactant to the acid carrier and/or borohydride streams had no effect. It is proposed that there may be a greater role for surfactants in the improvement of the processes by which the hydride is transferred to the bulk gas phase than has been attributed in previous reports on this subject.     

Optimized procedure for the determination of antimony in lipid-rich environmental matrices by flow injection hydride generation atomic absorption spectrometry

An analytical procedure for the reliable determination of Sb in digests of lipid-rich environmental matrices in the low ng l-1-range based on flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) has been developed. Prior to HG-AAS, aliquots (250 to 320 mg) of dry samples were mineralized with 3 ml nitric acid and 0.5 ml of each sulfuric and perchloric acids in open digestion vessels made of glassy carbon in a heating block. Procedure detection and quantification limits of a previously developed procedure for the determination of Sb in plant materials by FI-HG-AAS were decreased with respect to the lower Sb concentrations in animal tissues, the sensitivity of the instrumental response was increased, and the composition of the acid digestion mixture was re-optimized for lipid-rich samples. The accuracy and precision of the developed procedure was evaluated by the analysis of the two reference materials Bovine Liver 1577a and Pig Kidney CRM 186. These reference materials have been additionally spiked with appropriate amounts of Sb to obtain recovery data. The solution detection limit (3 sigma) in digested samples was 0.021 microgram l-1, the detection limit for the whole procedure based on the dry powders was 7 pg g-1, the method quantification limit for a reliable determination of Sb was 23 pg g-1. The reproducibility of repetitive measurements was 6.0% at 0.1 microgram Sb l-1 and 2.2% at 0.5 microgram Sb l-1. Calibration curves were linear from 0.05 to 3 micrograms Sb l-1. To demonstrate the suitability of the developed method, concentrations of Sb have been determined in pigeon eggs (approximately 2 ng Sb g-1), as well as in bream livers (approximately 4 ng g-1) and in deer livers (approximately 5 to 8 ng g-1) from animals living in remote and urban-industrialized areas of Germany, respectively.     

Flow injection micelle-mediated methodology for determination of lead by electrothermal atomic absorption spectrometry

A simple and sensitive flow injection micelle-mediated method was developed for the determination of trace Pb by electrothermal atomic absorption spectrometric (ET-AAS). The formation of the analyte-entrapped surfactant micelles by online merging of the analyte solution with O,O-diethyldithiophosphate solution and Triton X-114 solution sequentially, the adsorption of the resultant analyte-entrapped surfactant micelles onto a microcolumn packed with silica gel. The adsorbed analyte was then eluted with methanol and determined by ET-AAS. With consumption of 6.0 mL sample solution, a detection limit of 0.016 μg L⁻¹, and a concentration factor of 21.6 were obtained at a sample throughput of 20 h⁻¹. The relative standard deviation was 5.1% (c = 2.0 ng mL⁻¹, n = 7). The method has been successfully applied to the analysis of trace Pb in water sample with recoveries ranging from 94.0 to 99.0%. The certified reference material was also analyzed for validation, and the determined value obtained was in good agreement with the certified value.     

Determination of lead by hydride generation atomic absorption spectrometry : Part 1. A new medium for generating hydride

A new medium, used to generate lead hydride, was optimized as 0.3% (w/v) oxalic acid-2% (w/v) ammonium cerium (III) nitrate-8% (w/v) potassium tetrahydroborate-1% (w/v) sodium hydroxide solution; 950°C is used for atomization. The characteristic concentration (0.0044 absorbance) obtained under these conditions was 0.04 ng ml^?1. The application of this medium to soil and ferromagano-brass samples is illustrated.     

A flow injection/hydride generation system for the determination of arsenic by inductively-coupled plasma atomic emission spectrometry

A flow-injection system is described for the semi-automatic determination of arsenic (10–1000 μg l^?1) by hydride generation and inductively-coupled plasma atomic emission spectrometry. The elements which were found to interfere were Co, Ni, Ag, Au, Bi, Te and Sn. Standard reference materials were analyzed with good accuracy. Approximately 200 injection h^?1 are possible. The detection limit is 1.4 ng arsenic.     

Preconcentration and determination of tellurium in garlic samples by hydride generation atomic absorption spectrometry

A procedure for the determination of traces of total tellurium (Te) in garlic (Allium sativa) is described that combines hydride generation atomic absorption spectrometry with preconcentration of the analyte by coprecipitation. The samples, each spiked with lanthanum nitrate (20 mg/L), are introduced into an Amberlite XAD-4 resin and mixed with ammonium buffer (pH 9.1). Te is preconcentrated by coprecipitation with the generated lanthanum hydroxide precipitate. The precipitate is quantitatively collected in the resin, eluted with hydrochloric acid, and then transferred into the atomizer device. Considering a sample consumption of 25 mL, an enrichment factor of 10 was obtained. The detection limit (3sigma) was 0.03 microg/L, and the precision (relative standard deviation) was 3.5% (n = 10) at the 10 microg/L level. The calibration graph using the preconcentration system for Te was linear with a correlation coefficient of 0.9993. Satisfactory results were obtained for the analysis of Te in garlic samples.     

Speciation of major arsenic species in seawater by flow injection hydride generation atomic absorption spectrometry

Arsenic present at 1 microg L(-1) concentrations in seawater can exist as the following species: As(III), As(V), monomethylarsenic, dimethylarsenic and unknown organic compounds. The potential of the continuous flow injection hydride generation technique coupled to atomic absorption spectrometry (AAS) was investigated for the speciation of these major arsenic species in seawater. Two different techniques were used. After hydride generation and collection in a graphite tube coated with iridium, arsenic was determined by AAS. By selecting different experimental hydride generation conditions, it was possible to determine As(III), total arsenic, hydride reactive arsenic and by difference non-hydride reactive arsenic. On the other hand, by cryogenically trapping hydride reactive species on a chromatographic phase, followed by their sequential release and AAS in a heated quartz cell, inorganic As, MMA and DMA could be determined. By combining these two techniques, an experimental protocol for the speciation of As(III), As(V), MMA, DMA and nonhydride reactive arsenic species in seawater was proposed. The method was applied to seawater sampled at a Mediterranean site and at an Atlantic coastal site. Evidence for the biotransformation of arsenic in seawater was clearly shown.     

Speciation of major arsenic species in seawater by flow injection hydride generation atomic absorption spectrometry

Arsenic present at 1 μg L^–1 concentrations in seawater can exist as the following species: As(III), As(V), monomethylarsenic, dimethylarsenic and unknown organic compounds. The potential of the continuous flow injection hydride generation technique coupled to atomic absorption spectrometry (AAS) was investigated for the speciation of these major arsenic species in seawater. Two different techniques were used. After hydride generation and collection in a graphite tube coated with iridium, arsenic was determined by AAS. By selecting different experimental hydride generation conditions, it was possible to determine As(III), total arsenic, hydride reactive arsenic and by difference non-hydride reactive arsenic. On the other hand, by cryogenically trapping hydride reactive species on a chromatographic phase, followed by their sequential release and AAS in a heated quartz cell, inorganic As, MMA and DMA could be determined. By combining these two techniques, an experimental protocol for the speciation of As(III), As(V), MMA, DMA and non-hydride reactive arsenic species in seawater was proposed. The method was applied to seawater sampled at a Mediterranean site and at an Atlantic coastal site. Evidence for the biotransformation of arsenic in seawater was clearly shown.     

Influence of oxidising agents in lead determination by hydride generation direct flame atomic absorption spectroscopy

Summary The influence of Cr₂O₇ ^2–, MnO₄ ^–, Ce⁴⁺, H₂O₂ and S₂O₈ ^2– as oxidising agents in lead determination as volatile covalent hydride using NaBH₄ is reported in this paper.The reaction conditions for every oxidising agents (pH, quantity and concentration of the oxidising agent, quantity and concentration of the NaBH₄ and reaction time) are optimized, determining sensitivity and detection limit by measuring the peak height.The recovery of lead from solution has been measured by flameless atomic absorption spectroscopy.A linear relationship the logarithm of absorbance values and the redox potential of the system is obtained with a correlation coefficient of 0.999. The results and their interpretation are given in this paper.

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Der Einflu oxidierender Reagentien auf die Bleibestimmung mittels Flammenatomabsorptionsspektrometrie nach Hydridbildung

Zusammenfassung Es wird über den Einfluß der Oxidantien Cr₂O₇, MnO₄ ^–, Ce⁴⁺, H₂O₂ und S₂O₈ ^{2 –} auf die Bleibestimmung als kovalentes Hydrid berichtet. Für jede oxidierende Substanz werden die Reaktionsbedingungen optimiert (pH, Menge und Konzentration des Oxidans, Menge und Konzentration von NaBH₄ und Reaktionszeit), um Empfindlichkeit und Nachweisgrenze durch Peakhöhenauswertung zu bestimmen.Die Wiederfindungsrate wurde durch elektrothermale Atomabsorptionsspektrometrie von Blei in der Lösung bestimmt.Der Zusammenhang zwischen dem Logarithmus der Extinktion und dem Redoxpotential des Oxidans ergibt eine lineare Beziehung mit einem Korrelationskoeffizienten von 0.999. Die Ergebnisse und deren Interpretation werden in dieser Arbeit beschrieben.

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Paper presented to Euroanalysis V. Cracow, August 1984.     

On-line preconcentration system for bismuth determination in urine by flow injection hydride generation inductively coupled plasma atomic emission spectrometry

An on-line bismuth preconcentration and determination system implemented with hydride generation inductively coupled plasma atomic emission spectrometry (HG-ICP-AES) associated to flow injection (FI) was studied. Quinolin-8-ol and Amberlite XAD-7 were used for the retention of bismuth, at pH 4.5. The bismuth complex was removed from the micro-column with nitric acid. The detection limit value for the preconcentration of 100 ml of aqueous solution was 0.02 ng ml(-1) with a relative standard deviation (R.S.D.) of 3.5%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for bismuth was linear with a correlation coefficient of 0.999 at levels near the detection limits up to at least 100 ng ml(-1). The method was successfully applied to the determination of bismuth in human urine samples.     

Electrochemical hydride generation for the determination of hydride forming elements by atomic fluorescence spectrometry

The determinations of As, Bi, Ge, Sb and Se were performed by atomic fluorescence spectrometry following their electrochemical hydride generation. An electrochemical hydride generator based on a screw-thread seal arrangement, working in a continuous flow mode was used. The effects of cathode material, shape and area of material, catholyte, sample flow rate, applied current, catholyte solution concentration and interference of transition metals on signal intensity were studied. Five kinds of materials including lead, graphite, copper, tungsten and platinum with different shapes were tested as cathode materials. The signal obtained from a 3-dimensional electrode was higher than that from a 2-dimensional electrode under the same conditions. The signal intensity of Ge in HNO₃ medium within a narrow concentration range of 0.05–0.10 mol L^{− 1} was stronger than that in other acidic medium, such as HCl and H₂SO₄. However, the signal intensity of Ge was rapidly decreased with HNO₃, HCl and H₂SO₄ concentration increasing, and then reached approximately zero. In general, limits of detection and a precision were improved using a graphite cathode in H₃PO₄ medium. The analysis of the reference materials showed good agreement with the certified values for As, Bi, Ge, Sb and Se. The method was successfully applied in the determination of As, Bi, Ge, Sb and Se in traditional Chinese medicine samples.     

Electrochemical hydride generation for the determination of hydride forming elements by atomic fluorescence spectrometry

The determinations of As, Bi, Ge, Sb and Se were performed by atomic fluorescence spectrometry following their electrochemical hydride generation. An electrochemical hydride generator based on a screw-thread seal arrangement, working in a continuous flow mode was used. The effects of cathode material, shape and area of material, catholyte, sample flow rate, applied current, catholyte solution concentration and interference of transition metals on signal intensity were studied. Five kinds of materials including lead, graphite, copper, tungsten and platinum with different shapes were tested as cathode materials. The signal obtained from a 3-dimensional electrode was higher than that from a 2-dimensional electrode under the same conditions. The signal intensity of Ge in HNO₃ medium within a narrow concentration range of 0.05–0.10 mol L^− 1 was stronger than that in other acidic medium, such as HCl and H₂SO₄. However, the signal intensity of Ge was rapidly decreased with HNO₃, HCl and H₂SO₄ concentration increasing, and then reached approximately zero. In general, limits of detection and a precision were improved using a graphite cathode in H₃PO₄ medium. The analysis of the reference materials showed good agreement with the certified values for As, Bi, Ge, Sb and Se. The method was successfully applied in the determination of As, Bi, Ge, Sb and Se in traditional Chinese medicine samples.     

A simple and sensitive continuous hydride generation system for the determination of arsenic and selenium by atomic absorption and atomic fluorescence spectrometry

The development and optimization of a continuous hydride generation system for atomic absorption spectrometry (a.a.s.) and atomic fluorescence spectrometry (a.f.s.) is described. Sodium tetrahydroborate(III) solution and sample solution are delivered by two small peristaltic pumps to a gas/liquid separator. The evolved hydrides are swept to a miniature argon/hydrogen diffusion flame burning on a borosilicate glass tube. Detection limits (2σ) obtained for arsenic are 0.8 ng ml^-1 by a.a.s. and 0.34 ng ml^-1 by a.f.s., and for selenium 0.5 ng ml^-1 by a.a.s. and 0.13 ng ml^-1 by a.f.s. Linear working ranges are typically 1–100 ng ml^-1 with a typical measurement time of 1 min per sample or standard.