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.     

Determination of major antimony species in seawater by continuous flow injection hydride generation atomic absorption spectrometry

The capabilities and limitations of the continuous flow injection hydride generation technique, coupled to atomic absorption spectrometry, for the speciation of major antimony species in seawater, were investigated. Two pre-concentration techniques were examined. After continuous flow injection hydride generation and collection onto a graphite tube coated with iridium, antimony was determined by graphite furnace atomic absorption spectrometry. The low detection limits obtained (∼5 ng l⁻¹ for Sb(III) and ∼10 ng l⁻¹ for Sb(V) for 2.5 ml seawater samples) permitted the determination of Sb(III) and total antimony in seawater with the use of selective hydride generation and on-line UV photooxidation. The number of samples that can be analyzed is about 15 per hour for Sb(III) determinations and 10 per hour for total antimony determinations. The analysis of seawater samples showed that Sb(V) was the predominant species, even in the presence of important biological activity.     

Speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry

A simple procedure was developed for the speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry (EcHG–AAS), without pre-reduction of As(V). Glassy carbon was selected as cathode material in the flow cell. An optimum catholyte concentration for simultaneous generation of arsine from As(III) and As(V) was 0.06 mol l⁻¹ H₂SO₄. Under the optimized conditions, adequate sensitivity and difference in ratio of slopes of the calibration curves for As(III) and As(V) can be achieved at the electrolytic currents of 0.6 and 1 A. The speciation of inorganic arsenic can be performed by controlling the electrolytic currents, and the concentration of As(III) and As(V) in the sample can be calculated according to the equations of absorbance additivity obtained at two selected electrolytic currents. The calibration curves were linear up to 50 ng ml⁻¹ for both As(III) and As(V) at 0.6 and 1 A. The detection limits of the method were 0.2 and 0.5 ng ml⁻¹ for As(III) and As(V) at 0.6 A, respectively. The relative standard deviations were of 2.1% for 20 ng ml⁻¹ As(III) and 2.5% for 20 ng ml⁻¹ As(V). The method was validated by the analysis of human hair certified reference material and successfully applied to speciation of soluble inorganic arsenic in Chinese medicine.     

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.     

Determination of total arsenic in seawater by hydride generation atomic fluorescence spectrometry

In this work, the determination of total As in seawater by hydride generation atomic fluorescence spectrometry was studied. The influence of the chemical, flow and instrumental parameters were investigated and optimized. The pre-reduction of As(V) to As(III) was performed using KI plus ascorbic acid in 3.5 mol L^− 1 HCl medium. No multiplicative interference was present and external aqueous calibration could be used. The limit of detection was 36 ng L^− 1, while the repeatability was 2% (n = 10), at a 500 ng L^− 1 concentration level. The sample throughput was 15 h^− 1 if triplicate measurements were made. The accuracy was assessed by the analysis of a seawater certified reference material and excellent agreement between the obtained and certified values was verified. The procedure was used for the analysis of seawater offshore samples collected at the Brazilian coast and results ranging from 860 to 1200 ng L^− 1 were found.     

On-line preconcentration and speciation of arsenic by flow injection hydride generation atomic absorption spectrophotometry

A flow injection-column preconcentration-hydride generation atomic absorption spectrophotometric (FI-column-HGAAS) method was developed for determining μg/l levels of As(III) and As(V) in water samples, with simultaneous preconcentration and speciation. The speciation scheme involved determining As(V) at neutral pH and As(III + V) at pH 12, with As(III) obtained by difference. The enrichment factor (EF) increased with increase in sample loading volume from 2.5 to 10 ml, and for preconcentration using the chloride-form anion exchange column, EFs ranged from 5 to 48 for As(V) and 4 to 24 for As(III + V), with corresponding detection limits of 0.03-0.3 and 0.07-0.3 μg/l. Linear concentration range (LCR) also varied with sample loading volume, and for a 5-ml sample was 0.3-5 and 0.2-8 μg/l for As(V) and As(III + V), respectively. Sample throughput, which decreased with increase in sample volume, was 8-17 samples/h. For the hydroxide-form column, the EFS for 2.5-10 ml samples were 3-23 for As(V) and 2-15 for As(III + V), with corresponding detection limits of 0.07-0.4 and 0.1-0.5 μg/l. The LCR for a 5-ml sample was 0.3-10 μg/l for As(V) and 0.2-20 μg/l for As(III + V). Sample throughput was 10-20 samples/h. The developed method has been effectively applied to tap water and mineral water samples, with recoveries ranging from 90 to 102% for 5-ml samples passed through the two columns.     

Determination of As(III) and total inorganic arsenic by flow injection hydride generation atomic absorption spectrometry

A simple procedure was developed for the direct determination of As(III) and As(V) in water samples by flow injection hydride generation atomic absorption spectrometry (FI–HG–AAS), without pre-reduction of As(V). The flow injection system was operated in the merging zones configuration, where sample and NaBH₄ are simultaneously injected into two carrier streams, HCl and H₂O, respectively. Sample and reagent injected volumes were of 250 μl and flow rate of 3.6 ml min⁻¹ for hydrochloric acid and de-ionised water. The NaBH₄ concentration was maintained at 0.1% (w/v), it would be possible to perform arsine selective generation from As(III) and on-line arsine generation with 3.0% (w/v) NaBH₄ to obtain total arsenic concentration. As(V) was calculated as the difference between total As and As(III). Both procedures were tolerant to potential interference. So, interference such as Fe(III), Cu(II), Ni(II), Sb(III), Sn(II) and Se(IV) could, at an As(III) level of 0.1 mg l⁻¹, be tolerated at a weight excess of 5000, 5000, 500, 100, 10 and 5 times, respectively. With the proposed procedure, detection limits of 0.3 ng ml⁻¹ for As(III) and 0.5 ng ml⁻¹ for As(V) were achieved. The relative standard deviations were of 2.3% for 0.1 mg l⁻¹ As(III) and 2.0% for 0.1 mg l⁻¹ As(V). A sampling rate of about 120 determinations per hour was achieved, requiring 30 ml of NaBH₄ and waste generation in order of 450 ml. The method was shown to be satisfactory for determination of traces arsenic in water samples. The assay of a certified drinking water sample was 81.7±1.7 μg l⁻¹ (certified value 80.0±0.5 μg l⁻¹).     

Speciation of arsenic compounds by HPLC with hydride generation atomic absorption spectrometry and inductively coupled plasma mass spectrometry detection

An arsenic specific detection system utilizing on-line microwave digestion and hydride generation atomic absorption spectrometry (MD/HGAAS) is described for arsenic speciation by using high performance liquid chromatography (HPLC). Both ion exchange chromatography and ion pair chromatography have been studied for the separation of arsenite, arsenate, monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA), and arsenobetaine (AB). When the commonly used mobile phases, phosphate and carbonate buffers at pH 7.5, are used on an anion exchange column, arsenite and AB co-elute. However, selective determination of these two arsenic compounds can be achieved by using the new detection system. Partial separation between arsenite and AB can be achieved by increasing the mobile phase pH to 10.3 and by using a polymer based anion exchange column. The detection limit obtained by using anion exchange chromatography with MD/HGAAS detection is approximately 10 ng/ml (or 200 pg for a 20-mul sample injection) for arsenite, DMAA and AB, 15 ng/ml (or 300 pg) for MMAA, and 20 ng/ml (or 400 pg) for arsenate. Complete separation of the five arsenic compounds is achieved on a reversed phase C18 column by using sodium heptanesulfonate as ion pair reagent. Comparable resolution between chromatographic peaks is obtained by using MD/HGAAS detection and inductively coupled plasma mass spectrometry (ICPMS) detection.     

氢化物-原子吸收光谱法测定冶金企业废水中的砷

采用HNO3/HClO4(体积比10∶1)消解冶金废水样品,经6mol.L-1 HCl溶液酸化后,加入碘化钾(3%)、抗坏血酸(1%)及硫脲(1%)混合溶液进行还原,用氢化物-原子吸收光谱法(HG-AAS)测定了样品中的As含量.结果表明,该方法的检出限为0.297μg/L,相对标准偏差RSD为5.463%,样品加标回收率为93%～108%;其操作方便、选择性好、灵敏度高、干扰少,适合于复杂废水中微量和痕量As的测定.     

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.     

Determination of selenium in blood plasma and serum by flow injection hydride generation atomic absorption spectrometry

A flow injection hydride generation atomic absorption spectrometric (AAS) method has been used to determine the selenium concentrations of human serum and plasma samples following digestion with nitric, sulphuric and perchloric acids. In the hydride generation process, reduction was carried out by sodium tetrahydroborate to produce a hydride that was atomized in a flame-heated atomisation cell. The method had a detection limit of 1.2 ng ml-1 and a sensitivity of 2.1 ng ml-1. Within-run precisions of 5.8% at 20 ng ml-1 and 4.5% at 80 ng ml-1, and between-run precisions of 4.8% at 69 ng ml-1 and 3.4% at 80 ng ml-1 were obtained. An inter-laboratory comparison study with a graphite furnace AAS method was carried out and the results showed excellent agreement. The flow injection method of sample introduction allowed the use of a sample volume of 330 microliters with an injection rate of 90 injections per hour.     

Determination of total arsenic and toxicologically relevant arsenic species in fish by using electrothermal and hydride generation atomic absorption spectrometry

A scheme for the determination of total As by electrothermal atomic absorption spectrometry (ETAAS) and the sum of toxicologically relevant arsenic species (As(III), As(V), monomethylarsonate (MMA) and dimethylarsinate (DMA) using hydride generation AAS (HGAAS) in fish samples was developed. Simple and fast microwave assisted extraction in tetramethylammonium hydroxide (TMAH, 0.075% m / v) or in water-methanol mixture (80 + 20 v / v) for 20 min is proposed for quantitative leaching of arsenic species from fish tissue. Total As was measured by ETAAS directly in the TMAH extract under optimal instrumental parameters (pyrolysis temperature 1400 °C and atomization temperature 2000 °C) with Pd as modifier ensuring thermal stabilization and isoformation of all extracted arsenic species. The analytical features of the method are as follows: limit of detection (LOD) 0.45 μg g^− 1 (dry wt.), within-run and between-run precision in the range 4-8% and 5-12%, respectively, for arsenic contents 0.5-30 μg g^− 1 and recoveries 98-102%. The sum of toxicologically relevant arsenic species (As(III) + As(V) + MMA + DMA) was determined by flow injection HGAAS directly from the TMAH extract or water-methanol mixture and trapping of arsines onto Zr-Ir coated graphite tube followed by ETAAS measurement. l-cysteine is used as reagent for leveling off responses of different arsenic species in the presence of TMAH or water-methanol mixture. The LODs achieved are 0.0038 and 0.0031 μg g^− 1 (dry wt.), respectively, for fish extracts in TMAH and in water-methanol mixture. Within-batch and between-batch RSDs are in the range 3-5% and 4-7% for arsenic contents of 0.009-0.25 μg g^− 1 (dry wt.) for TMAH extracts and 2-4% and 3-6% for methanol water extracts, respectively. Selective reaction media for generation of respective hydrides from arsenic species were recommended for further speciation purposes in methanol-water extracts, viz. citrate buffer (pH 5.2) for the determination of As(III), 0.2 mol L^− 1 acetic acid for the determination of As(III) + DMA and 7 mol L^− 1 hydrochloric acid for the determination of inorganic As(III) + As(V). LODs are 0.0035, 0.0051 and 0.0046 μg g^− 1 (dry wt.) for As(III), DMA and As(V). The relative standard deviation is 4-8% for three arsenic species at As levels of 0.009-0.5 μg g^− 1 (dry wt.). The accuracy of the proposed speciation scheme is confirmed by the analysis of certified reference materials.     

Determination of arsenic by hydride generation with a long absorption cell for atomic absorption spectrometry

A method is described for the determination of arsenic involving hydride generation and atomic absorption spectrometry with an improved long graphite-tube furnace capable of considerably higher temperatures than the conventional quartz-tube heaters. Arsine is generated with sodium tetrahydroborate, held in a nitrogen-cooled trap and then swept with helium into an alumina tube (19 cm long) placed within the graphite furnace. The optimum conditions for determination of arsenic are given. The detection limit is 0.2 ng ml^?1 with RSD of 2–3%. Results for various NBS Standard Reference Materials agreed well with expected values and were as follows: orchard leaves, 10 ± 1 μg g^?1; tomato leaves, 0.28 ± 0.03 μg g^?1; bovine liver, 0.046 ± 0.005 μg g^?1.     

Speciation of inorganic arsenic in a sequential injection dual mini-column system coupled with hydride generation atomic fluorescence spectrometry

The separation and speciation of inorganic arsenic(III) and arsenic(V) are facilitated by employing a novel sequential injection system incorporating two mini-columns followed by detection with hydride generation atomic fluorescence spectrometry. An octadecyl immobilized silica mini-column is used for selective retention of the complex between As(III) and APDC, while the sorption of As(V) is readily accomplished by a 717 anion exchange resin mini-column. The retained As(III)-PDC complex and As(V) are effectively eluted with a 3.0 mol L⁻¹ hydrochloric acid solution as stripping reagent, which well facilitates the ensuing hydride generation process via reaction with tetrahydroborate. With a sampling volume of 1.0 mL and an eluent volume of 100 μL for both species, linear ranges of 0.05-1.5 μg L⁻¹ for As(III) and 0.1-1.5 μg L⁻¹ for As(V) are obtained, along with enrichment factors of 7.0 and 8.2, respectively. Precisions of 2.8% for As(III) and 2.9% for As(V) are derived at the concentration level of 1.0 μg L⁻¹. The practical applicability of the procedure has been demonstrated by analyzing a certified reference material of riverine water (SLRS-4), in addition to spiking recovery in a lake water sample matrix.     

Determination of trace arsenic in hydrofluoric acid by hydride generation and atomic absorption spectrometry

Practical procedures are given for determination of arsenic(III) and (V) in hydrofluoric acid by means of hydride generation and atomic absorption spectrometry. Arsenic(III) can be determined by direct generation of arsine with sodium borohydride in hydrochloric/hydrofluoric acid medium, arsenic(V) being only slightly reduced under the conditions used. For its determination, arsenic(V) has to be prereduced with potassium iodide, and even then its reduction to arsenic(III) and then arsine is far from complete. It is possible to determine it in presence of arsenic(III) by a difference method, but this is recommended only if the As(V)/As(III) ratio is greater than 1. Total arsenic can be determined after oxidation of As(III) and evaporation of most of the hydrofluoric acid. The limit of determination is 5 g/l for arsenic(III) and 0.25 g/l for total arsenic; the relative standard deviation is about 10%.     

Determination of arsenic in glycerine by flow injection,hydride generation and inductively-coupled plasma/atomic emission spectrometry

The determination of low concentrations of arsenic in glycerine is investigated with flow injection for the introduction of analyte and tetrahydroborate reagent for arsine generation, separation in a vapor-liquid flow cell, and inductively-coupled plasma/atomic emission spectrometry (i.c.p./a.e.s.). Peak areas are used to quantify arsenic in the concentration range 0.12–3.0 μg ml^?1. Peak areas for prepared standards exhibited average deviations of about 1.4% for this concentration range. The slope and intercept for a least- squares fit of area (nanocoulombs) vs. concentration (μg ml^?1) were 10.9 ± 0.17 and 0.46 ± 0.3, respectively.     

Speciation analysis of inorganic arsenic by microchip capillary electrophoresis coupled with hydride generation atomic fluorescence spectrometry

A novel method for speciation analysis of inorganic arsenic was developed by on-line hyphenating microchip capillary electrophoresis (chip-CE) with hydride generation atomic fluorescence spectrometry (HG-AFS). Baseline separation of As(III) and As(V) was achieved within 54 s by the chip-CE in a 90 mm long channel at 2500 V using a mixture of 25 mmol l(-1) H3BO3 and 0.4 mmol l(-1) CTAB (pH 8.9) as electrolyte buffer. The precisions (RSD, n=5) ranged from 1.9 to 1.4% for migration time, 2.1 to 2.7% for peak area, and 1.8 to 2.3% for peak height for the two arsenic species at 3.0 mg l(-1) (as As) level. The detection limits (3sigma) for As(III) and As(V) based on peak height measurement were 76 and 112 microg l(-1) (as As), respectively. The recoveries of the spikes (1 mg l(-1) (as As) of As(III) and As(V)) in four locally collected water samples ranged from 93.7 to 106%.     

微型氢化物发生-原子吸收光谱法测定纺织品中的痕量砷和锑

采用三毛细管微型在线氢化发生技术和装置, 建立了氢化物发生-电热石英管原子吸收法测定纺织品中痕量As、 Sb的分析方法. 研究了共存离子对As、 Sb检测的干扰及消除方法. 结果表明: 该方法除Co、 Sn对As和Ni对Sb有干扰外, 其它干扰元素允许量都较大. 采用酒石酸和KI混合掩蔽剂可抑制Co、 Sn对As和Ni对 Sb的干扰. As和Sb的检出限分别为0.7和0.4 ng/L, 已用于测定纺织品中痕量As和Sb的分析.     

Optimization and validation of arsenic determination in foods by hydride generation flame atomic absorption spectrometry

A hydride generation flame atomic absorption spectrometric method was developed and optimized to quantitate arsenic (As) in foods. A wet digestion of the samples with HNO3 + H2O2 was performed and excess oxidants were eliminated by addition of hydrochloric acid and urea. As5+ in As3+ was then reduced by potassium iodide. The As3+ solution was analyzed by generation of arsine with sodium tetrahydroborate. As determination ranged from 2.5 to 20 microg/L, with a determination coefficient of 0.997. The limits of detection (LOD) and quantitation (LOQ) were 0.6 and 2.1 microg/L, respectively. The method was validated and good results were obtained for recovery, precision, accuracy, LOD, and LOQ. This method is now used to analyze foods from Rwanda.     

Determination of arsenic in sea water by sorbent extraction with hydride generation atomic absorption spectrometry

A rapid and sensitive sorbent extraction hydride generation-flow injection analysis atomic absorption spectrometric (HG-FIAS-AAS) method is described for the determination of As(III) and As(V) based upon online preconcentration on a microcolumn packed with activated alumina. In the present procedure these arsenicals are complexed with quinolin-8-ol-5-sulphonic acid from neutral solutions in the flow injection system and adsorbed on the column. The preconcentrated species are eluted with 10% HCl, mixed with 0.5% sodium borohydride and carried to the HG-FIAS cell with a carrier gas flow rate of 75 ml min(-1). The retention efficiency is found to be better than 98% with sensitivity enhancement of 12 and 10 for As(III) and As(V), respectively, for a 20 s preconcentration period. The respective detection limits are 0.05 and 2 ng ml(-1) for As(III) and As(V). The throughput of the samples is found to be 60 h(-1), with a loading time of 20 s. The method has been applied to sea water samples.