Analysis of arsenic compounds by capillary electrophoresis using indirect UV and mass spectrometric detections

CE with indirect UV and mass-spectrometric detection was used for the simultaneous determination of arsenic acid (As(V)), arsenous acid (As(III)), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), trimethylarsine oxide (TMAO), tetramethylarsonium ion (TMA(+)), arsenobetaine (AB), and arsenocholine (AC). In the CE-indirect UV analysis, a baseline separation of arsenic species was successfully achieved by using a basic background solution (BGS) for anions and an acidic BGS for cations, respectively. The LOD values in CE-indirect UV for the individual analytes were 7.8, 12.5, 7.8, 12.5, 62.5, 125, 250, and 62.5 ppm, respectively. To achieve sensitive and selective analysis, CE coupled with ESI-MS was applied to the determination of arsenic compounds. The organic arsenic species were successfully separated with a higher sensitivity by CE-MS using the acidic BGS. The LODs in CE-MS for MMA, DMA, TMAO, TMA(+), AB, and AC were 1.0, 0.1, 0.01, 0.1, 0.01, and 0.01 ppm, respectively. In contrast, the analysis of inorganic arsenic species (As(V) and As(III)) resulted in a lower detectability in CE-MS compared to that obtained with the CE-indirect UV analysis. However, the speciation of eight arsenics by CE-MS was successfully achieved in a single run by switching the ESI polarity during MS detection.     

Induction of mitotic arrest and aneuploidy by organic arsenic compounds in human lymphocytes

Inorganic arsenic is methylated in the mammalian body to methylarsonic acid (MMA), dimethylarsinic acid (DMA) and trimethylarsine oxide (TMA). To achieve a more precise understanding of arsenic carcinogenicity, we examined the genotoxic effects of organic arsenic compounds on human lymphocytes by assessing induction of mitotic arrest, sister chromatid exchange (SCE) and aneuploidy. MMA, DMA and TMA arrested mitosis, DMA induced hyperdiploid cells, and DMA and TMA induced tetraploid cells. Of the three arsenic metabolites tested, DMA had the strongest effects on cell mitosis and aneuploidy induction. DMA arrested mitosis and induced c-mitosis significantly. These results suggest that DMA arrests mitosis and induces aneuploidy through spindle disruptions similar to those observed with known spindle poisons, such as colchicine or vinblastine. Since aneuploidy has been thought to be associated with tumor induction or neoplastic transformation, induction of aneuploidy by organic metabolites of arsenic may play a major role in arsenic carcinogenesis in humans. © 1997 John Wiley & Sons, Ltd.     

Total arsenic determination and speciation in infant food products by ion chromatography-inductively coupled plasma-mass spectrometry

Health risk associated with dietary arsenic intake may be different for infants and adults. Seafood is the main contributor to arsenic intake for adults while terrestrial-based food is the primary source for infants. Processed infant food products such as rice-based cereals, mixed rice/formula cereals, milk-based infant formula, applesauce and puree of peaches, pears, carrots, sweet potatoes, green beans, and squash were evaluated for total and speciated arsenic content. Arsenic concentrations found in rice-based cereals (63-320 ng/g dry weight) were similar to those reported for raw rice. Results for the analysis of powdered infant formula by inductively coupled plasma-mass spectrometry (ICP-MS) indicated a narrow and low arsenic concentration range (12 to 17 ng/g). Arsenic content in puree infant food products, including rice cereals, fruits, and vegetables, varies from <1 to 24 ng/g wet weight. Sample treatment with trifluoroacetic acid at 100 degrees C were an efficient and mild method for extraction of arsenic species present in different food matrixes as compared to alternative methods that included sonication and accelerated solvent extraction. Extraction recoveries from 94 to 128% were obtained when the summation of species was compared to total arsenic. The ion chromatography (IC)-ICP-MS method selected for arsenic speciation allowed for the quantitative determination of inorganic arsenic [As(III) + As(V)], dimethylarsinic acid (DMA), and methylarsonic acid (MMA). Inorganic arsenic and DMA are the main species found in rice-based and mixed rice/formula cereals, although traces of MMA were also detected. Inorganic arsenic was present in freeze-dried sweet potatoes, carrots, green beans, and peaches. MMA and DMA were not detected in these samples. Arsenic species in squash, pears, and applesauce were not detected above the method detection limit [5 ng/g dry weight for As(III), MMA, and DMA and 10 ng/g dry weight for As(V)].     

Simultaneous determination of dimethylarsinic acid and monomethylarsonic acid after derivatization with thioglycol methylate by gas chromatography/mass spectrometry

A gas chromatography/mass spectrometry (GC/MS) method has been developed to determine two methylated arsenic species in human urine samples. The yield of derivatization for dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) using thioglycol methylate (TGM) was measured. The detection limit for the derivatized DMA and MMA using the GC/MS method are 0.95 and 0.8 ng cm-3, respectively. This simple and rapid method has good precision and accuracy. Fragmentation routes of derivatized MMA and DMA are suggested on accurate mass measurements.     

Speciation of dimethylarsinic acid and monomethylarsonic acid by solid-phase microextraction-gas chromatography-ion trap mass spectrometry

A solid-phase microextraction (SPME) method has been developed to determine two methylated arsenic species in human urine samples by GC-MS. The direct extraction of the methyl arsenic compounds by SPME after thioglycol methylate derivatization was studied. Direct extraction with SPME was suitable for the determination of trace levels of dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) in urine samples. Four different commercial SPME fibers were tested for the extraction of methyl arsenic compounds, and the best results were obtained using the polydimethylsiloxane coating. The extraction and desorption time profiles of DMA and MMA were determined. The detection limits for DMA and MMA using the SPME-GC-MS method were 0.12 and 0.29 ng/ml, respectively. The method is linear in the 1 to 200 ng/ml range.     

Optimisation of sample treatment for arsenic speciation in alga samples by focussed sonication and ultrafiltration

A procedure for arsenic species fractionation in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) by extraction is described. Several parameters were tested in order to evaluate the extraction efficiency of the process: extraction medium, nature and concentration (tris(hydroxymethyl)aminomethane, phosphoric acid, deionised water and water/methanol mixtures), extraction time and physical treatment (magnetic stirring, ultrasonic bath and ultrasonic focussed probe). The extraction yield of arsenic under the different conditions was evaluated by determining the total arsenic content in the extracts by ICP-AES. Arsenic compounds were extracted in 5 mL of water by focussed sonication for 30 s and subsequent centrifugation at 14,000 × g for 10 min. The process was repeated three times. Extraction studies show that soluble arsenic compounds account for about 65% of total arsenic.

An ultrafiltration process was used as a clean-up method for chromatographic analysis, and also allowed us to determine the extracted arsenic fraction with a molecular weight lower than 10 kDa, which accounts for about 100% for all samples analysed.

Speciation studies were carried out by HPLC–ICP-AES. Arsenic species were separated on a Hamilton PRP-X100 column with 17 mM phosphate buffer at pH 5.5 and 1.0 mL min⁻¹ flow rate. The chromatographic method allowed us to separate the species As(III), As(V), MMA and DMA in less than 13 min, with detection limits of about 20 ng of arsenic per species, for a sample injection volume of 100 μL. The chromatographic analysis allowed us to identify As(V) in Hizikia (46 ± 2 μg g⁻¹), Sargassum (38 ± 2 μg g⁻¹) and Chlorella (9 ± 1 μg g⁻¹) samples. The species DMA was also found in Chlorella alga (13 ± 1 μg g⁻¹). However, in Laminaria alga only an unknown arsenic species was detected, which eluted in the dead volume.     

Urinary arsenic speciation by high-performance liquid chromatography/atomic absorption spectrometry for monitoring occupational exposure to inorganic arsenic

Total urinary arsenic determinations are often used to assess occupational exposure to inorganic arsenic. Ingestion of sea food can increase the normal background levels of total arsenic in urine by up to an order of magnitude, but this arsenic has relatively little toxicity; it is tightly bound as arsenobetaine. The excretion of inorganic arsenic and its metabolites dimethylarsenic acid (DMA) and monomethylarsonic acid (MMA) is not influenced by the consumption of arsenic from sea food. Specific measurements of DMA, MMA and inorganic arsenic provide a more reliable indicator or exposure than total urinary arsenic levels. An automated atomic absorption method involving high-performance liquid chromatographic separation of the arsenic species and continuous hydride generation is described for the determination of arsenite, arsenate, DMA and MMA at μg As l^?1 levels. The method is used to study normal urinary arsenic levels in laboratory staff and arsenic excretion by exposed workers.     

Speciation of arsenic by hydride generation-atomic absorption spectrometry (HG-AAS) in hydrochloric acid reaction medium

The effects on the absorbance signals obtained using HG-AAS of variations in concentrations of the reaction medium (hydrochloric acid), the reducing agent [sodium tetrahydroborate(III); NaBH(4)], the pre-reducing agent (l-cysteine), and the contact time (between l-cysteine and arsenic-containing solutions) for the arsines generated from solutions of arsenite, arsenate, monomethylarsonic acid (MMA), and dimethylarsenic acid (DMA), have been investigated to find a method for analysis of the four arsenic species in environmental samples. Signals were found to be greatly enhanced in low acid concentration in both the absence (0.03-0.60 M HCl) and the presence of l-cysteine (0.001-0.03 M HCl), however with l-cysteine present, higher signals were obtained. Total arsenic content and speciation of DMA, As(III), MMA, and As(V) in mixtures containing the four arsenic species, as well as some environmental samples have been obtained using the following conditions: (i) total arsenic: 0.01 M acid, 2% NaBH(4), 5% l-cysteine, and contact time<10 min; (ii) DMA: 1.0 M acid, 0.3-0.6% NaBH(4), 4.0% l-cysteine, and contact time <5 min; (iii) As(III): 4-6 M acid and 0.05% NaBH(4) in the absence of l-cysteine; (iv) MMA: 4.0 M acid, 0.03% NaBH(4), 0.4% l-cysteine, and contact time of 30 min; (v) As(V): by difference. Detection limits (ppb) for analysis of total arsenic, DMA, As(III), and MMA were found to be 1.1 (n=7), 0.5 (n=5), 0.6 (n=7), and 1.8 (n=4), respectively. Good percentage recoveries (102-114%) of added spikes were obtained for all analyses.     

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.     

Extraction of arsenic species from spiked soils and standard reference materials

The abilities of various extractants to recover four arsenic species [As(iii), As(v), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA)] from soils spiked with 20 micro g g(-1) As were investigated. The extractants were water, buffer solutions (citrate and ammonium dihydrogen phosphate), acidic solutions (phosphoric acid and acetic acid), a basic solution (sodium hydroxide) and household chemicals (vinegar and Coca Cola). Gentle shaking at room temperature with each extractant for 24 h gave different recoveries for the different arsenic species. With 0.1 M NaOH solution 46% As(iii), 53% DMA, 100% MMA and 84% As(v) were recovered. A rapid extraction procedure using a sonicator probe has been developed to obtain higher extraction efficiencies. Extracts of arsenic-spiked soil, SRM 2711 Montana soil and SRM 2709 San Joaquin soil were analyzed by HPLC-ICP-MS. In the SRM water extracts, DMA and MMA were identified in addition to inorganic arsenic. The solution detection limits (3s) were 0.1, 0.12, 0.13 and 0.15 ng mL(-1) for As(iii), DMA, MMA and As(v), respectively for HPLC-ICP-MS.     

Determination of arsenite,arsenate, monomethylarsonic acid and dimethylarsinic acid in cereals by hydride generation atomic fluorescence spectrometry

A fast, sensitive and simple non-chromatographic analytical method was developed for the speciation analysis of toxic arsenic species in cereal samples, namely rice and wheat semolina. An ultrasound-assisted extraction of the toxic arsenic species was performed with 1 mol L^− 1 H₃PO₄ and 0.1% (m/v) Triton XT-114. After extraction, As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) concentrations were determined by hydride generation atomic fluorescence spectrometry using a series of proportional equations corresponding to four different experimental reduction conditions. The detection limits of the method were 1.3, 0.9, 1.5 and 0.6 ng g^− 1 for As(III), As(V), DMA and MMA, respectively, expressed in terms of sample dry weight. Recoveries were always greater than 90%, and no species interconversion occurred. The speciation analysis of a rice flour reference material certified for total arsenic led to coherent results, which were also in agreement with other speciation studies made on the same certified reference material.     

Arsenic speciation in Chinese brake fern by ion-pair high-performance liquid chromatography-inductively coupled plasma mass spectroscopy

Ion-pair reverse-phase HPLC-inductively coupled plasma (ICP) MS was employed to determine arsenite [As(III)], dimethyl arsenic acid (DMA), monomethyl arsenic (MMA) and arsenate [As(V)] in Chinese brake fern (Pteris vittata L.). The separation was performed on a reverse-phase C18 column (Haisil 100) by using a mobile phase containing 10 mM hexadecyltrimethyl ammonium bromide (CTAB) as ion-pairing reagent, 20 mM ammonium phosphate buffer and 2% methanol at pH 6.0. The detection limits of arsenic species with HPLC-ICP-MS were 0.5, 0.4, 0.3 and 1.8 ppb of arsenic for As(III), DMA, MMA, and As(V), respectively. MMA has been shown for the first time to experimentally convert to DMA in the Chinese brake fern, indicating that Chinese brake fern can convert MMA to DMA by methylation.     

Supercritical fluid extraction and gas chromatography analysis of arsenic species from solid matrices

A method in combination with derivatization-supercritical fluid extraction(SFE) and gas chromatography(GC) for the speciation and quantitative determination of dimethylarsinate(DMA), monomethylarsonate(MMA) and inorganic arsenic in solid matrices was investigated. Thioglycolic acid methyl ester(TGM) and thioglycolic acid ethyl ester(TGE) were evaluated as derivatization reagents. The effects of pressure, temperature, flow rate of supercritical CO_2, extraction time, modifier and microemulsion on the efficiency of extraction were systematically investigated. The procedure was applied to the analysis of real soil and sediment samples. Results showed that TGE was more effective for arsenic speciation as a derivatization reagent. Modifying supercritical CO_2 with methanol can greatly improve the extraction efficiency. Further, the addition of microemulsion containing surfactant Triton X-100 can further enhance recoveries of arsenic species. The optimum extraction conditions were 100 ℃, 30 MPa, 10 min static and 25 min dynamic extraction with 5%(v/v) methanol, and surfactant modified supercritical CO_2. Detection limits in solid matrices were 0.15, 0.3 and 1.2 mg/kg for DMA, MMA and inorganic arsenic,respectively. The method was validated by the recovery data. The resulting method was fast, easy to perform and selective in the extraction and detection of various arsenic species in solid matrices.     

Excretion patterns of arsenic and its metabolites in human saliva and urine after ingestion of Chinese seaweed

There are no reports in scientific literature on arsenic species in human saliva after seaweed exposure. The present article reports for the first time the regular excretion patterns of arsenic in the saliva of volunteers with one-time ingestion of Chinese seaweed. Total arsenic and speciation analyses were carried out by high-performance liquid chromatography–inductively coupled plasma–mass spectrometry (HPLC-ICP-MS). Results show that the excretion time of total arsenic in saliva is a trifle earlier than that in urine, total arsenic in human saliva also shows a regular excretion pattern like that in urine within 72 h after exposure to seaweed. For speciation analysis, four species, including the major dimethylarsinic acid (DMA) species, were detected in urine prior to seaweed intake. Six species were detected in urine after seaweed ingestion, including DMA, methylarsonic acid (MMA), oxo-dimethylarsinoylethanol (oxo-DMAE), thio-dimethlyarsenoacetate (thio-DMAA), arsenite (As^III) and arsenate (As^V). In saliva samples, three species were found before seaweed ingestion, with the major peak identified as As^III. After consumption, the kinds of arsenic metabolites in saliva were less than those in urine. The major species was inorganic arsenic (iAs As^III+As^V), followed by DMA, MMA and a trace amount of oxo-DMAE. Taken together, the present study suggests that saliva assay can be used as a potential tool for understanding the regular excretion pattern of total arsenic after seaweed ingestion. Whether or not it’s an efficient tool for assessing arsenic metabolites in humans exposed to seaweed requires further investigation.     

液相色谱-电感耦合等离子体质谱法测定稻米中的5种砷形态

建立了稻米中砷酸根[As（Ⅴ）]、亚砷酸根[As（Ⅲ）]、砷甜菜碱（AsB）、一甲基砷（MMA）和二甲基砷（DMA）的液相色谱-电感耦合等离子体质谱（LC-ICP-MS）检测方法。以0.3 mol/L硝酸水溶液为提取试剂,样品在石墨消解仪中于95 ℃消解1.5 h,上清液供LC-ICP-MS分析。5种砷形态采用Dionex IonPac AS19阴离子交换柱（250 mm×4 mm）分离,经ICP-MS检测。比较了4种提取液对稻米中5种砷形态的提取效率,并对提取溶剂的浓度、提取温度和提取时间等条件进行了优化。通过加标回收试验结合测定标准物质考察了方法准确度及精密度,在2个加标水平上各形态的回收率为89.6%~99.5%,RSD（n=5）不大于3.6%,大米标准物质中各形态之和的测定结果与其标准值吻合,5种砷形态的线性范围AsB和DMA为0.05~200 μg/L,As（Ⅲ）和MMA为0.10~400 μg/L,As（V）为0.15~600 μg/L,方法检出限为0.15~0.45 μg/kg。结果表明,本方法简单、灵敏、耐用,可用于稻米中5种砷形态的准确定量和风险评估。     

Speciation of arsenic using capillary gas chromatography with atomic emission detection

A gas chromatography method with atomic emission detection (GC-AED) for the determination of dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and inorganic arsenic was optimized. The analytes were derivatized in the sample solutions with methyl thioglycolate (TGM) and the products were extracted into cyclohexane before an aliquot of this organic phase was directly injected into the chromatograph. The procedure was applied to the analysis of seawaters, wines, beers and infant foods, the last requiring an additional enzymatic reaction prior to analyte derivatization. Detection limits in seawaters and beverages were 0.05, 0.15 and 0.8 ng mL⁻¹ for DMA, MMA and inorganic arsenic, respectively. In infant foods the detection limits were 1, 10 and 25 ng g⁻¹ for DMA, MMA and inorganic arsenic, respectively. Inorganic arsenic was detected in some of the seawater samples and three of the wines analyzed at concentration levels in the range 1-40 ng mL⁻¹, and DMA in several of the infant foods in the range 20-80 ng g⁻¹. The method was validated by analyzing a certified reference material and by recovery studies. All the samples were also analyzed by hydride generation and atomic fluorescence spectrometry (HG-AFS), which provided data for the total arsenic content.     

Arsenic speciation by ion-exchange separation and graphite-furnace atomic-absorption spectrophotometry

As(III), As(V), monomethylarsenic acid (MMA) and dimethylarsenic acid (DMA) were determined by graphite-furnace atomic-absorption spectrophotometry after separation of the species by ion-exchange chromatography. The detection limits (ng/ml) were DMA 0.02, MMA 2.0, As(V) 0.4 and total arsenic 4.0. As(III) was determined by difference. This system gave better detection limits and/or shorter analysis times than previously reported systems.     

Optimization of the solubilization, extraction and determination of inorganic arsenic [As(III) + (As(V)] in seafood products by acid digestion, solvent extraction and hydride generation atomic absorption spectrometry

A method for the selective quantitative determination of inorganic arsenic [As(III) + As(V)] in seafood was developed. In order to do so, various procedures for the solubilization and extraction of inorganic arsenic quoted in the literature were tested. None provided satisfactory recoveries for As(III) and As(V) in real samples. Consequently, a methodology was developed which included solubilization with HCl and subsequent extraction with chloroform. The arsenic was solubilized in 9 mol l-1 hydrochloric acid. After reduction by hydrobromic acid and hydrazine sulfate, the inorganic arsenic was extracted into chloroform, back-extracted into 1 mol l-1 HCl, dry-ashed, and quantified by hydride generation-atomic absorption spectrometry (HG-AAS). The analytical features of the method are as follows: detection limit, 3.07 ng g-1 As (fresh mass); precision (RSD), 4.0%; recovery, As(III) 99%, As(V) 96%. In the optimized conditions, other arsenic species--dimethylarsinic acid (DMA), arsenobetaine (AB), arsenocholine (AC) and tetramethylarsonium-ion (TMA+)--were not co-extracted. However, different percentages of minor species were extracted with chloroform: monomethylarsonic acid (MMA) 100%, and trimethylarsine oxide (TMAO) 3-10%. Real samples and reference materials of seafood (DORM-1, DORM-2, TORT-2, CRM-278 and SRM-1566a) were analyzed. The analysis of DORM-1 provided an inorganic arsenic value of 124 +/- 4 ng g-1 As, dry mass (dm), which is very close to the value obtained by other authors using high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) and ionic chromatography-hydride generation-atomic absorption spectrometry (IC-HG-AAS).     

Coupled high performance liquid chromatography-microwave digestion-hydride generation-atomic absorption spectrometry for inorganic and organic arsenic speciation in fish tissue

A high performance liquid chromatography-microwave digestion-hydride generation-atomic absorption spectrometry (HPLC-MW-HG-AAS) coupled method is described for As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB) and arsenocholine (AsC) determination. A Hamilton PRP-X100 anion-exchange column is used for carrying out the arsenic species separation. As mobile phase 17 mM phosphate buffer (pH 6.0) is used for As(III), As(V), MMA and DMA separation, and ultrapure water (pH 6.0) for AsB and AsC separation. Prior to injection into the HPLC system AsB and AsC are isolated from the other arsenic species using a Waters Accell Plus QMA cartridge. A microwave digestion with K(2)S(2)O(8) as oxidizing agent is used for enhancing the efficiency of conversion of AsB and AsC into arsenate. Detection limits achieved were between 0.3 and 1.1 ng for all species. The method was applied to arsenic speciation in fish samples.     

Evaluation of atomic fluorescence spectrometry as a sensitive detection technique for arsenic speciation

The potential of coupling anion-exchange high-performance liquid chromatography, hydride generation and atomic fluorescence spectrometry (HPLC–HG–AFS) for arsenic speciation is considered. The effects of hydrochloric acid and sodium tetrahydroborate concentrations on signal-to-background ratio, as well as argon and hydrogen flow rates, were investigated. Detection limits for arsenite, dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and arsenate were 0.17, 0.45, 0.30 and 0.38 μg l⁻¹, respectively, using a 20-μl loop. Linearity ranges were 0.1–500 ng for As(III) and MMA (as arsenic), and 0.1–800 ng for DMA and As(V) (as arsenic). Arsenobetaine (AsB) was also determined by introducing an on-line photo-oxidation step after the chromatographic separation. In this case the limits of detection and linear ranges for the different species studied were similar to the values obtained previously for As(V). The technique was tested with a human urine reference material and a volunteer's sample. © 1998 John Wiley & Sons, Ltd.