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.     

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).     

Multielemental speciation of As, Se, Sb and Te by HPLC-ICP-MS

An anion exchange HPLC-ICP-MS procedure allowing the simultaneous multielemental speciation analysis of arsenic, selenium, antimony and tellurium has been developed. Four arsenic species (As^III, As^V, monomethylarsonic acid and dimethylarsinic acid), two selenium species (Se^IV and Se^VI) may be determined in a single run as well as one antimony (Sb^V) and one tellurium species (Te^VI). Alternatively Sb and/or Te may be used as internal standards for As and Se speciation studies. Optimisation of ICP-MS conditions led to satisfactory relative (0.01 (Sb^V) to 1.8 (Se^VI) ng ml⁻¹) and absolute detection limits (1–180 pg). Reproducibility ranged from 3.1 to 5.6% and the linearity was verified in the 0–200 ng ml⁻¹ range.     

Direct determination of arsenic in acid digests of plant and peat samples using HG-AAS and ICP-SF-MS

A new analytical procedure for the reliable and direct determination of arsenic (As) in nitric acid digests of ombrotrophic peat samples in the low ng l⁻¹ range has been developed based on hydride generation-atomic absorption spectrometry (HG-AAS). The pre-reduction capabilities of KI/ascorbic acid and of l-cysteine in nitric acid digests of peat and plant samples for the conversion of As(V) to As(III) were tested systematically. Samples were digested with high purity nitric acid in a high-pressure microwave autoclave at 240 °C and subsequently measured using HG-AAS or ICP-SF-MS (inductively coupled plasma-sector field-mass spectrometry). Using KI/ascorbic acid as pre-reductant, the accuracy and precision were poor when digests of complex matrices, such as peat were analyzed for As by HG-AAS. However, 10 g l⁻¹ l-cysteine was successfully employed as pre-reductant in diluted nitric acid digests (3%, v/v) of peat samples prior to hydride generation of As with 0.5% (m/v) of NaBH₄ and 7 mol l⁻¹ HCl. The analytical procedure was critically evaluated by analyzing several certified plant reference materials, two in-house peat reference materials and by the determination of As in diluted digests of peat samples with ICP-SF-MS. The results for the determination of As in various peat and plant materials showed excellent agreement with the reference values. The method detection limits for the determination of As by the optimized HG-AAS procedure and by ICP-SF-MS were 23 ng g⁻¹ and 1.4 ng g⁻¹ in solid peat, respectively. The newly developed analytical procedure was applied to the determination of As in selected peat samples. Results for As in these peat samples obtained by the developed HG-AAS procedure and the optimized procedure for the determination of As with ICP-SF-MS were highly correlated (R² = 0.993, n = 12).     

As, Bi, Sb and Sn determination in atmospheric particulate matter by direct solid sampling-hydride generation-electrothermal atomic absorption spectrometry

A novel, rapid and simple method by hydride generation-electrothermal atomic absorption spectrometry (HG-ETAAS) after direct As, Bi, Sb and Sn hydrides generation from untreated filters of atmospheric particulate matter (PM₁₀ and PM_2.5) was optimised. PM₁₀ and PM_2.5 were not subjected to any pre-treatment: circular portions between 0.28 and 6.28 cm² were directly placed into the reaction vessel of a batch mode generation system. A 2⁸ × 3/64 Plackett–Burman design was used as a multivariate strategy for the evaluation of the effects of several variables affecting the hydride generation, trapping and atomisation efficiencies. Trapping temperature was the most statistically significant variable for As, Bi and Sn. Atomisation temperature was also statistically significant for Sb determination. Optimum values of significant variables were selected by using univariate optimisation approaches. An aqueous calibration method was used throughout. The developed method has been found to be precise with relative standard deviations of 6.2, 5.3, 9.1 and 7.5% for 11 determinations in a filter sample containing 0.7, 1.0, 1.4 and 1.7 μg l⁻¹ for As, Bi, Sb and Sn, respectively. Results obtained by direct solid sampling-HG-ETAAS have been found statistically comparable with those obtained after conventional method based on an acid digestion followed to ICP-MS. Absolute detection limits were 37, 15, 30, and 41 ng l⁻¹ for As, Bi, Sb and Sn, respectively. Detection limits referred to the air volume sampled (in the range of 0.020–0.050 ng m⁻³) were low enough for the determination of several hydride-forming elements from PM₁₀ and PM_2.5 samples collected in a non-polluted suburban area of A Coruña (NW Spain).     

Efficiency and mechanism of new poly(acryl-phenylamidrazone phenylhydrazide) chelating fiber for adsorbing trace Ga, In, Bi, V and Ti from solution

A new po1y(acrylphenylamidrazone phenylhydrazide) chelating fiber is synthesized from polyacrylonitrile fiber and used for preconcentration and separation of trace Ga(III), In(III), Bi(III), V(V) and Ti(IV) from solution (5–50 ng ml⁻¹ Ti(IV) or V(V) and 50–500 ng ml⁻¹ Ga(III), In (III) or Bi(III) in 1000–100 ml of solution can be enriched quantitatively by 0.15 g of fiber at a 4 ml min⁻¹ flow rate in the pH range 5–7 with recoveries >95%). These ions can be desorbed quantitatively with 20 ml of 4 M hydrochloric acid at 2 ml min⁻¹ from the fiber column. When the fiber which had been treated with concentrated hydrochloric acid and washed with distilled water until neutral was reused eight times, the recoveries of the above ions by enrichment were still >95%. Two-hundred-fold to 10 000-fold excesses of Cu(II), Zn(II), Ca(II), Mn(II), Cr(III), Fe(III), Ba(II) and Al(III) caused little interference in the determination of these ions by inductively coupled plasma-atomic emission spectrometers (ICP-AES). The relative standard deviations for enrichment and determination of 50 ng ml⁻¹ Ga, In or Bi and 10 ng ml⁻¹ V or Ti are in the range 1.2–2.7%. The contents of these ions in real solution samples determined by this method were in agreement with the certified values of the samples with average errors <3.7%.     

Simultaneous determination of total arsenic and total selenium in Chinese medicinal herbs by hydride generation atomic fluorescence spectrometry in tartaric acid medium

By HG-AFS, a new method was proposed for simultaneous determination of total arsenic and total selenium existed in the Chinese medicinal herbs in tartaric acid medium. The effects of analytical conditions and coexisting ions on the fluorescence signal intensity of analytes were investigated. The proposed method was provided with linear response ranges above 22 μg l⁻¹ for As and 44 μg l⁻¹ for Se, and the detection limits of 0.13 and 0.12 μg l⁻¹ were obtained for As and Se respectively. The recoveries of 93.8–96.1% for As and 95.3–99.1% for Se, and the precision of 1.2–3.8% and 2.4–5.3% (R.S.D., n = 8) respectively, were obtained via simultaneous determined four samples of Chinese medicinal herbs and three certified botanic reference materials successfully. The proposed method has the advantages of simple operation, high sensitivity and high efficiency.     

Determination of arsenic and antimony by microwave plasma atomic emission spectrometry coupled with hydride generation and a PTFE membrane separator

The performance of a microwave plasma torch (MPT) discharge atomic emission spectrometry (AES) system directly coupled with hydride generation (HG) for the determination of As and Sb has been studied. The argon MPT system can sustain a stable plasma over a wide range of carrier and support gas flow rates with optimum performance at 250 and 1450 ml min⁻¹, respectively. The presence of trace amount of water in the MPT discharge is found to affect the detection limits and the signal to noise ratio. A PTFE membrane separator is applied for hydride introduction and water rejection. In addition, the membrane cell separator also improves the signal to noise ratio by serving as a pressure buffer to minimize noise due to pressure fluctuation. Detection limits (3σ) of 8.1 and 3.2 ng ml⁻¹ are obtained with the analytical lines As I 228.812 nm and Sb I 259.809 nm, respectively at an MPT power of 135 W. The detection limits are improved when a concentrated sulfuric acid cell is placed after the membrane cell to further remove water. This double cell system yields detection limits of 5.3 and 2.1 ng ml⁻¹ for As and Sb, respectively under the same operating conditions. Linear dynamic ranges of three orders of magnitude could be obtained.     

Speciation analysis of arsenic and selenium compounds in environmental and biological samples by ion chromatography-inductively coupled plasma dynamic reaction cell mass spectrometer

An inductively coupled plasma mass spectrometer (ICP-MS) was used as an ion chromatographic (IC) detector for the speciation analysis of arsenic and selenium. The arsenic and selenium species studied included arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), selenite [Se(IV)] and selenate [Se(VI)]. Gradient elution using (NH₄)₂CO₃ and methanol at pH 9 allowed the chromatographic separation of all species in less than 12 min. Effluents from the IC column were delivered to the nebulization system of ICP-DRC-MS for the determination of arsenic and selenium. The potentially interfering ³⁸Ar⁴⁰Ar⁺ and ⁴⁰Ar⁴⁰Ar⁺ at the selenium masses m/z 78 and 80 were reduced in intensity by approximately 3 orders of magnitude by using 0.6 mL min⁻¹ CH₄ as reactive cell gas in the DRC while an Rpq value of 0.3 was used. Meanwhile, arsenic was determined as the adduct ion ⁷⁵As¹²CHH⁺ at m/z 89, which is more sensitive than ⁷⁵As. The limits of detection for arsenic and selenium were in the range of 0.002–0.01 ng mL⁻¹ and 0.01–0.02 ng mL⁻¹, respectively, based on peak height. The relative standard deviation of the peak areas for five injections of 5 ng mL⁻¹ As and Se mixture was in the range of 2–4%. The concentrations of arsenic and selenium species have been determined in urine samples collected locally. The major As and Se species in urines were AsB, DMA and probably selenosugar at concentration of 20–40, 15–19 and 17–31 ng mL⁻¹, respectively. The recoveries were in the range of 94–105% for all the determinations. This method has also been applied to determine various arsenic compounds in two fish samples. In this study, a simple and rapid microwave-assisted extraction method was used for the extraction of arsenic compounds from fish. The arsenic species were quantitatively leached with an 80% v/v methanol solution in a focused microwave field during a period of 5 min.     

A simple and sensitive assay of nucleic acids based on the enhanced resonance light scattering of zwitterionics

A new assay of nucleic acids at nanogram level was established based on the enhanced resonance light scattering (RLS) signals of two zwitterionics cocamidopropyl hydroxysultaine (HSB) and lauryl betaine (BS-12). Under optimum conditions, the weak RLS signal of HSB is enhanced by nucleic acids, and the enhanced RLS intensity is proportional to the concentration of nucleic acids in the range of 0.02–7.3 mg l⁻¹ for calf thymus DNA and 0.01–8.6 mg l⁻¹ for fish sperm DNA. The detection limits were 1.5 ng ml⁻¹ for calf thymus DNA and 1.9 ng ml⁻¹ for fish sperm DNA. Plasmid DNA extracted from K-12-HB101 colt was determined with satisfactory results.