Chromatography-hydride Generation-atomic Fluorescence Spectrometry Research Articles

Trimethylselenonium ion determination in human urine by high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry optimization of the hydride generation step.

This work describes the intricacies of the determination of the trimethylselenonium ion (TMSe) in human urine via high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS). By definition, this technique requires that the separated TMSe can be online converted into a volatile compound. Literature data for the determination of TMSe via the hydride generation technique are contradictory; i.e., some authors claim that direct formation of volatile compounds is possible under reduction with NaBH4, whereas others reported that a digestion step is mandatory prior to conversion. We studied and optimized the conditions for online conversion by varying the mobile phase composition (pyridine, phosphate, and acetate), testing different reaction coils, and optimizing the hydride generation conditions, although technically no hydride (H2Se) is formed but a dimethylselenide (DMSe). The optimized conditions were used for the analysis of 64 urine samples of 16 (unexposed) volunteers and the determination of low amounts of TMSe (LOD = 0.2ngmL-1). Total (specific gravity-corrected) selenium concentrations in the urine samples ranged from 7.9 ± 0.7 to 29.7 ± 5.0ngmL-1 for individual volunteers. Four volunteers were characterized as TMSe producers (hINMT genotype GA) and 12 were non-producers (hINMT genotype GG). Urine of TMSe producers contained 2.5 ± 1.7ngmL-1 of TMSe, compared to 0.2 ± 0.2ngmL-1 for non-producers.

Enhanced adsorption of inorganic arsenic by Mg-calcite under circumneutral conditions

Calcite is an important reservoir for arsenic (As) and strongly affects its mobility in various geological environments. However, the method by which bulk As is taken up by calcite needs to be better understood. To broaden our understanding, Mg-containing calcite (Mg-calcite), which is a ubiquitous form of calcite in nature, was investigated to determine its As adsorption capacity. Laboratory experiments were conducted under aerobic and anaerobic conditions using synthetic pure calcite (Ca10Mg0) and Mg-calcite (Ca9Mg1, Ca8Mg2). As speciation (determined using chromatography techniques, such as ion chromatography-hydride generation-atomic fluorescence spectrometry (IC-HG-AFS)) and microscopic characterization (field-emission scanning electron microscopy coupled with energy-dispersive spectroscopy (FE-SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS)) were coupled to investigate the adsorption capacity and potential mechanisms of As adsorption by Mg-calcite. The results showed that Mg-calcite exhibited an As adsorption capacity that was several times higher than pure calcite, especially for As(III). Based on microscopic characterizations, the substitution of CO3/OH groups with As-O groups and the formation of complexes on the Mg-calcite surface are the dominant mechanisms of arsenate (As(V)) adsorption. The doping of Mg into calcite results in a lattice contraction effect that provides additional space for the substitution of larger As oxyanions for carbonate ions. In parallel, as evidenced by the potentiometric automatic titration results, the presence of Mg in calcite led to an increased density of surface positive charges, which promotes greater adsorption of negatively charged As. In addition to the substitution of CO3 groups with As-O groups, the enhanced adsorption of As(III) by Mg-calcite was also attributed to the larger amount of H-bonding yielded by the addition of Mg. To the best of our knowledge, this is the first experimental investigation to quantify the adsorption of As by Mg-calcite, and it provides new insights into the fate and transport of inorganic As by carbonates in aqueous environments.

Arsenite oxidation and (thio)arsenates formation in arsenite- and sulfide-containing solution under air atmosphere

Thioarsenic species are widely existed in transitional environments with varying redox potential such as hot springs and paddy fields, where arsenite, sulfide and thioarsenites may be exposed to ambient air. However, arsenic speciation, especially the kinetics of arsenic transformation in such scenarios are not well studied. Here we present results from both kinetic experiments and computational information on the formation mechanisms of thioarsenic species from the sulfide-driven oxidation of arsenite (13.3 μM) under air atmosphere at circumneutral pH (6.5–10.5, covering the usual groundwater pH range). Ion chromatography-hydride generation atomic fluorescence spectrometry (IC-HG-AFS) was used for the determination of non-thiolated arsenic and thioarsenate species as well as indirect identification of thioarsenites at environmentally relevant As concentration. Results showed that the ambient air facilitated the thiolation and oxidation of arsenite, during which thioarsenites were served as intermediates. It was supported by our ab initio DFT calculation showing that the activity towards oxidation was in the order of: monothioarsenite > dithioarsenite > trithioarsenite > arsenite. The thiolation of arsenite was decreased with pH with a rate constant of 0.2–1.7 h−1; while the oxidation of thioarsenites by air was increased with pH with a rate constant of 0.1–0.45 h−1. The results of this study shall improve our mechanistic understanding on the formation of thioarsenic, and shed light on the potential intermediate roles played by thioarsenites in environments with varying redox potential or intermittent anoxia, such as paddy fields, peatlands, hot springs etc.

Arsenic Trioxide Therapy During Pregnancy: ATO and Its Metabolites in Maternal Blood and Amniotic Fluid of Acute Promyelocytic Leukemia Patients.

Acute promyelocytic leukemia (APL) is extremely fatal if treatment is delayed. Management of APL in pregnancy is a challenging situation. Arsenic trioxide (ATO) is successfully applied to treat APL. ATO can be transformed into different arsenic species [arsenite (AsIII), monomethylated arsenic (MMA, consists of MMAIII and MMAV), dimethylated arsenic (DMA, consists of DMAIII and DMAV), and arsenate (AsV)], which produce different toxic effects. Investigating the maternal and fetal exposure to arsenic species is critical in terms of assessing maternal and fetal outcomes, choice of optimal treatment, and making decisions for attempting to preserve the obstetrical and fetal wellbeing. In this study, maternal blood and amniotic fluid (AF) from APL patients treated with ATO in pregnancy and blood samples of non-pregnant patients were collected. Concentrations of inorganic arsenic (iAs, iAs = AsIII+AsV), MMA, and DMA were analyzed by high-performance liquid chromatography–hydride generation–atomic fluorescence spectrometry (HPLC–HG–AFS). The difference in arsenic species of plasma between pregnant patients and non-pregnant patients, distribution of arsenic compounds in AF and maternal plasma, and arsenic penetration into AF were explored. The outcomes of pregnant women treated with ATO and their fetus were analyzed. No significant differences in arsenic concentration, percentage, and methylation index [PMI: primary methylation index (MMA/iAs); SMI: secondary methylation index (DMA/MMA)] between pregnant women and non-pregnant women (p > 0.05) were observed. The mean ratios of AF to maternal plasma were as follows: iAs, 2.09; DMA, 1.04; MMA, 0.49; and tAs, 0.98. Abortion rate is higher with the diagnosis at an earlier gestational age, with 0%, 67%, and 100% of pregnancies ending in abortion during the third, second, and first trimester, respectively. The age of the pregnant women, the dose of ATO, and the duration of fetal exposure in utero had no influence on fetal outcomes. All APL women achieved complete remission (CR). Collectively, ATO and its metabolites can easily cross the placenta. Levels and distribution of arsenic species in maternal plasma and AF gave evidence that arsenic species had a different ability to penetrate the placenta into AF (iAs > DMA > MMA) and indicated a relatively high fetal exposure to ATO and its metabolites in utero. Gestational age at diagnosis was more likely to be closely related to fetal outcomes, but had no effects on mother outcomes.

Arsenic-Related Health Risk Assessment of Realgar-Containing NiuHuangJieDu Tablets in Healthy Volunteers Po Administration

Realgar, an arsenic-containing traditional Chinese medicine of As2S2, has significant therapeutic effects for hundreds of years. NiuHuangJieDu tablets (NHJDT) is one of the most commonly prescribed realgar-containing preparations for the treatment of sore throat, swelling, and aching of gums. However, realgar-containing TCMs raise great safety concerns due to the adverse effects reported by arsenic poisoning. In this study, the arsenic-related health risk assessment of NHJDT was conducted in healthy volunteers after single and multiple doses oral administration. Blood, plasma, and urine samples were collected after dosing at predetermined time points or periods. Simple, rapid, and sensitive methods were established for the quantification of total arsenic and arsenic speciation in biological samples. The total arsenic and arsenic speciation were determined by hydride generation-atomic fluorescence spectrometry (HG-AFS) and high-performance liquid chromatography–hydride generation–atomic fluorescence spectrometry (HPLC-HG-AFS), respectively. No significant fluctuation of total arsenic was observed in human blood, and no traces of arsenic speciation were found in human plasma. Dimethylarsenic acid was detected as the predominated arsenic species in human urine after dosing. Therapeutic dose administration of NHJDT was relatively safe in single dose for the limited blood arsenic exposure, but long-term medication may still pose health risks due to the accumulation of arsenics in blood and its extremely slow excretion rate. Therefore, arsenic exposure should be carefully monitored during realgar-containing TCM medication, especially for long-term regimen. The results obtained in this study will provide scientific references for the clinical application of realgar and its-containing TCMs.

Pharmacokinetic Characteristics, Tissue Bioaccumulation and Toxicity Profiles of Oral Arsenic Trioxide in Rats: Implications for the Treatment and Risk Assessment of Acute Promyelocytic Leukemia.

Oral arsenic trioxide (ATO) has demonstrated a favorable clinical efficiency in the treatment of acute promyelocytic leukemia (APL). However, the pharmacokinetic characteristics, tissue bioaccumulation, and toxicity profiles of arsenic metabolites in vivo following oral administration of ATO have not yet been characterized. The present study uses high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) to assess the pharmacokinetics of arsenic metabolites in rat plasma after oral and intravenous administration of 1 mg kg−1 ATO. In addition, the bioaccumulation of arsenic metabolites in blood and selected tissues were evaluated after 28 days oral administration of ATO in rats at a dose of 0, 2, 8, and 20 mg kg−1 d−1. The HPLC-HG-AFS analysis was complemented by a biochemical, hematological, and histopathological evaluation conducted upon completion of ATO treatment. Pharmacokinetic results showed that arsenite (AsIII) reached a maximum plasma concentration rapidly after initial dosing, and the absolute bioavailability of AsIII was 81.03%. Toxicological results showed that the levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and white blood cells (WBC) in the 20 mg kg−1 d−1 ATO group were significantly increased compared to the control group (p < 0.05). The distribution trend of total arsenic in the rat was as follows: whole blood > kidney > liver > heart. Dimethylated arsenic (DMA) was the predominant bioaccumulative metabolite in the whole blood, liver, and heart, while monomethylated arsenic (MMA) was the predominant one in the kidney. Collectively, these results revealed that oral ATO was rapidly absorbed, well-tolerated, and showed organ-specific and dose-specific bioaccumulation of arsenic metabolites. The present study provides preliminary evidence for clinical applications and the long-term safety evaluation of oral ATO in the treatment of APL.

Characteristics of arsenic species in cerebrospinal fluid (CSF) of acute promyelocytic leukaemia (APL) patients treated with arsenic trioxide plus mannitol.

Arsenic speciation in cerebrospinal fluid (CSF) is critical for treatment/prevention of central nervous system (CNS) relapse in acute promyelocytic leukaemia (APL) patients treated with arsenic trioxide (ATO). Previous study showed low total arsenic level in CSF of APL patients. Mannitol infusion was applied to improve blood-brain barrier (BBB) permeability for arsenic. Arsenite (AsIII ), monomethylarsonic acid (MMAV ), dimethylarsinic acid (DMAV ), and arsenate (AsV ) in CSF and plasma were analysed by high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS). The profile and concentration of arsenic species in CSF from APL patients administered ATO alone and in combination with mannitol were compared. The overall distribution trend of arsenic species in CSF was AsIII , DMAV > MMAV > AsV . Arsenicals accumulated in CSF with administration frequency. The permeability of BBB for AsIII was higher than that for MMAV and DMAV . Arsenic concentration in CSF was much lower than that in plasma. There were significantly higher arsenic species concentrations in CSF of APL patients treated with mannitol than that without mannitol. Mannitol infusion significantly increased AsIII penetration into CSF, which was beneficial to optimize efficacy in APL patients with CNS relapse.

Polymorphisms in arsenic (+ 3 oxidation state) methyltransferase (AS3MT) predict the occurrence of hyperleukocytosis and arsenic metabolism in APL patients treated with As2O3.

Polymorphisms in arsenic (+ 3 oxidation state) methyltransferase (AS3MT) have been shown to be related to interindividual variations in arsenic metabolism and to influence adverse health effects in acute promyelocytic leukemia (APL) patients treated with arsenic trioxide (As2O3). The occurrence of hyperleukocytosis with As2O3 treatment seriously affects the early survival rate of APL patients, but no definite explanation for such a complication has been clearly established. To clarify the causes of this situation, AS3MTpolymorphisms 14215 (rs3740390), 14458 (rs11191439), 27215 (rs11191446), and 35991 (rs10748835) and profiles of plasma arsenic metabolites were evaluated in a group of 54 newly diagnosed APL patients treated with single-agent As2O3. High-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) was used to determine the concentrations of plasma arsenic metabolites. Plasma arsenic methylation metabolism capacity was evaluated by the percentage of inorganic arsenic (iAs), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), primary methylation index (PMI, MMA/iAs), and secondary methylation index (SMI, DMA/MMA). The results showed that APL patients who developed hyperleukocytosis had ahigher plasmaiAs%, but alower MMA% and PMI than those who did not develop hyperleukocytosis during As2O3 treatment. In addition, patients with the AS3MT 14215 (rs3740390) CC genotype had significantly higher plasma iAs% and incidence of hyperleukocytosis, but lower PMI than patients with the CT + TT genotype. Conversely, we did not observe statistically significant associations between the occurrence of hyperleukocytosis and AS3MT 14458 (rs11191439), 27215 (rs11191446), and 35991 (rs10748835) polymorphisms in our study subjects. These results indicated that AS3MT 14215 (rs3740390) might be used as an indicator for predicting the occurrence of hyperleukocytosis in APL patients treated with As2O3.

Effect of continuous venovenous haemodialysis on outcome and pharmacokinetics of arsenic species in a patient with acute promyelocytic leukaemia and acute kidney injury.

This study presents outcome and pharmacokinetics of arsenic trioxide (ATO) metabolites in patients on continuous venovenous haemodialysis (CVVHD). Of 3 acute promyelocytic leukaemia patients receiving CVVHD in management of acute kidney injury, only 1 patient was included. The patient presented disseminated intravascular coagulation and acute kidney injury before induction therapy was conducted. CVVHD was performed and ATO was initiated. Species of ATO metabolites in plasma and effluent were analysed using high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry. Plasma concentrations of AsIII , monomethylarsonic acid and dimethylarsinic acid with CVVHD were lower than those without CVVHD. Area under the concentration-time curve from 0 to the last sample with quantifiable concentration of AsIII without CVVHD was significantly higher than that with CVVHD (292.10ngh/mL vs 195.86ngh/mL, P=.037), which were not observed for monomethylarsonic acid and dimethylarsinic acid. Dialysate saturation of arsenic species was remarkable, especially for AsIII . Complete remission was achieved and renal function recovered. In this study, ATO can be used safely and effectively to treat acute promyelocytic leukaemia patients undergoing CVVHD without dose adjustment.

Application of enzymatic probe sonication for selenium speciation in animal feeds

Enzymatic probe sonication (EPS) was investigated as a novel and alternative technology for the extraction of five Se species SeCys2, MeSeCys, Se (IV), SeMet and Se (VI) from animal feeds. The critical parameters of EPS such as enzyme types, ultrasonic power, sample/enzyme ratio, extraction time and temperature were carefully optimized. Under current conditions, one sample can be extracted in 60s, in contrast to several hours required by the conventional enzymatic methods Moreover, the extraction is performed in pure water, no further temperature control or pH adjustment is needed, and therefore the risk of species interconvertion is drastically reduced or inhibited. The Se species were separated and quantitatively determined by high-performance liquid chromatography-hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS), which allows the separation of organic and inorganic Se species in a single chromatographic run. The newly developed method was successfully applied to the determination of Se species in 18 feed samples collected from markets and local farms. Concerning the feed samples studied, the results of this work suggest that stricter measures should be taken to control the Se-enriched feed supplements in terms of Se species.

HPLC-HG-AFS determination of arsenic species in acute promyelocytic leukemia (APL) plasma and blood cells

Arsenic trioxide (ATO) has been successfully used in the treatment of acute promyelocytic leukemia (APL). To clarify the arsenic species in APL patients, high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) and HG-AFS methods were developed and validated to quantify the plasma concentrations of inorganic arsenic (As(III) and As(V)) and methylated metabolites (MMA and DMA), and the total amounts of arsenic in blood cells and plasma. Blood cells and plasma were digested with mixtures of HNO3H2O2 and analyzed by HG-AFS. For arsenic speciation, plasma samples were prepared with perchloric acid to precipitate protein. The supernatant was separated on an anion-exchange column within 6min with isocratic elution using 13mM CH3COONa, 3mM NaH2PO4, 4mM KNO3 and 0.2mM EDTA-2Na. The methods provided linearity range of 0.2–20ng/mL for total arsenic and 2.0–50ng/mL for four arsenic species. The developed methods for total arsenic and arsenic species determination were precise and accurate. The spiked recoveries ranged from 81.2%-108.6% and the coefficients of variation for intra- and inter-batch precision were less than 9.3% and 12.5%, respectively. The developed methods were applied successfully for the assay of total arsenic and arsenic species in 5 APL patients. The HPLC-HG-AFS may be a good alternative for arsenic species determination in APL patients with its simplicity and low-cost in comparison with HPLC-ICP-MS.

Speciation of Antimony in Soils and Sediments by Liquid Chromatography–Hydride Generation–Atomic Fluorescence Spectrometry

The methodology for antimony speciation was optimized for liquid chromatography coupled to hydride generation – atomic fluorescence spectrometry. An anion exchange column was employed with isocratic elution. Ammonium tartrate was shown to be the optimum mobile phase and extracting solution for this analysis. The highest efficiency and resolution for the antimony species was achieved using 5 percent methanol in 300 millimoles per liter ammonium tartrate acidified with hydrochloric acid to pH 4.5. The retention times of antimony(V), trimethylantimony, and antimony(III) were 2.6, 3.9, and 5.2 minutes, respectively. The calibration curves were linear with limits of detection of 0.1, 0.2, and 0.43 microgram per liter for antimony(III), antimony(V), and trimethylantimony, respectively. The precision, evaluated by the relative standard deviation, ranged from 1.2 to 5.3 percent. The average recovery from these environmental samples by a single-step procedure was approximately 26 percent. The results also revealed that the correlation between the sum of each species by the single-step procedure and total digestion was significant for the investigated soils and sediments.

Speciation Determination of Selenium in Seafood by High-Performance Ion-Exchange Chromatography-Hydride Generation-Atomic Fluorescence Spectrometry

A high-performance ion-exchange chromatography coupled with hydride generation-atomic fluorescence spectrometry (HPIEC-HG-AFS) method was developed for simultaneous speciation of selenium in seafood. Three selenium species including of selenocystine (Se-Cys), selenome-thionine (Se-Met), and selenite Se(IV) were separated on an anion-exchange column (PRP-X100) with eluent of 30 mM NH4H2PO4 and methanol (39:1, v/v) in 10 min at the flow rate of 1.0 mL min−1. Variables affecting the HG-AFS detection of selenium species were optimized. The optimum conditions found were the following: reducing agent, 2.0 % of KBH4, and 5.0 % of HCl; lamp current, 90 mA; photomultiplier tube voltage, 280 V; flow rate of carrier gas, 300 mL min−1; and shielding gas, 800 mL min−1. Under the optimized conditions, the good linearity of calibration curves (R 2 > 0.999) between signal of fluorescence and concentration of selenium species was obtained in the range of detection limits (DLs), 80 μg L−1, and the DLs of Se-Cys, Se-Met, Se(IV) were 1.66, 0.990, 1.10 μg L−1, respectively. The repeatability of the method, expressed as relative standard deviation, was less than 5.0 % (n = 10), and the average recoveries for spiked test were from 87.3 to 103 % for three analytes in real seafood samples. The developed HPIEC-HG-AFS method was successfully applied for the speciation of selenium in seafood samples.

Arsenic speciation in natural sulfidic geothermal waters

The speciation of arsenic in natural sulfidic geothermal waters was studied using chemical analyses and thermodynamic aqueous speciation calculations. Samples were collected in three geothermal systems in Iceland, having contrasting H2S concentrations in the reservoir (high vs. low). The sampled waters contained 7–116ppb As and <0.01–77.6ppm H2S with pH of 8.56–9.60. The analytical setup used for the determination of arsenic species (Ion Chromatography-Hydride Generation Atomic Fluorescence Spectrometry, IC-HG-AFS) was field-deployed and the samples analyzed within ∼5min of sampling in order to prevent changes upon storage, which were shown to be considerable regardless of the sample storage method used. Nine aqueous arsenic species were detected, among others arsenite (HnAsIIIO3n-3), thioarsenite (HnAsIIIS3n-3), arsenate (HnAsVO4n-3), monothioarsenate (HnAsVSO3n-3), dithioarsenate (HnAsVS2O2n-3), trithioarsenate (HnAsVS3On-3) and tetrathioarsenate (HnAsVS4n-3). The results of the measured aqueous arsenic speciation in the natural geothermal waters and comparison with thermodynamic calculations reveal that the predominant factors determining the species distribution are sulfide concentration and pH. In alkaline waters with low sulfide concentrations the predominant species are AsIII oxyanions. This can be seen in samples from a liquid-only well, tapping water that is H2S-poor and free of oxygen. At intermediate sulfide concentration AsIII and AsV thio species become important and predominate at high sulfide concentration, as seen in two-phase well waters, which have high H2S concentrations in the reservoir. Upon oxidation, for instance due to mixing of the reservoir fluid with oxygenated water upon ascent to the surface, AsV oxyanions form, as well as AsV thio complexes if the sulfide concentration is intermediate to high. This oxidation process can be seen in samples from hot springs in the Geysir geothermal area. While the thermodynamic modeling allows for a first-order estimation of the dominant species, discrepancies between the model results and the field data highlight the fact that for such dynamic chemical systems the exact speciation cannot be calculated, thus on-site and preferentially in-situ analysis is of crucial importance.

Speciation of Arsenic in Rice by High-Performance Liquid Chromatography–Hydride Generation-Atomic Fluorescence Spectrometry with Microwave-Assisted Extraction

Arsenic speciation in paddy rice is of considerable interest due to its impact on the food safety and human health. In this study, a simple methodology was developed to simultaneously extract and analyze As species in rice from China. Arsenic species, including arsenite (As(III)), arsenate (As(V)), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA), were extracted by methanol-water (50:50, v/v) containing 0.02 mol L−1 nitric acid with a microwave-assisted procedure, and then determined by high performance liquid chromatography–hydride generation-atomic fluorescence spectrometry (HPLC–HG-AFS). The results showed that the method has good efficiency (>90%) for rice, indicating that there were no significant losses or transformations of arsenic during sample treatment and analysis. The limits of quantification (LOQ) of the method were 8.0, 20, 12, and 12 ng g−1 for As(III), As(V), DMA, and MMA, respectively. When this method was applied to the analysis of rice, As(III) had the highest concentration, followed by DMA, As(V), and MMA. The estimated weekly intake of inorganic As from rice by Chinese people accounted for 11.83% of the provisional tolerable weekly intake. The As speciation results in this study suggest that the risk associated with As in rice to human health may be negligible.

Determination of arsenic speciation in sulfidic waters by Ion Chromatography Hydride-Generation Atomic Fluorescence Spectrometry (IC-HG-AFS)

A method for the analysis of arsenic species in aqueous sulfide samples is presented. The method uses an ion chromatography system connected with a Hydride-Generation Atomic Fluorescence Spectrometer (IC-HG-AFS). With this method inorganic AsIII and AsV species in water samples can be analyzed, including arsenite (HnAsIIIO3n−3), thioarsenite (HnAsIIIS3n−3), arsenate (HnAsVO4n−3), monothioarsenate (HnAsVSO3n−3), dithioarsenate (HnAsVS2O2n−3), trithioarsenate (HnAsVS3On−3) and tetrathioarsenate (HnAsVS4n−3). The peak identification and retention times were determined based on standard analysis of the various arsenic compounds. The analytical detection limit was ~1–3µgL−1 (LOD), depending on the quality of the baseline. This low detection limit makes this method also applicable to discriminate between waters meeting the drinking water standard of max. 10µgL−1 As, and waters that do not meet this standard. The new method was successfully applied for on-site determination of arsenic species in natural sulfidic waters, in which seven species were unambiguously identified.

Pharmacokinetic properties of arsenic species after oral administration of Sargassum pallidum extract in rats using an HPLC-HG-AFS method

Sargassum pallidum is one of the Traditional Chinese Medicine widely used for phlegm elimination and detumescence. Arsenic is present in high concentration in seaweed belonging to the genus Sargassum. Therefore, the consumption of S. pallidum is a route of exposure to arsenic. Since the toxicity of arsenic is highly dependent on its chemical speciation, the determination of total arsenic is not adequate to assess the risks. Here, a high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) was developed for determination of the common arsenic species including arsenite [As(III)], dimethylarsinate (DMA), methylarsonate (MMA) and arsenate [As(V)] simultaneously. This method was applied to study the pharmacokinetic profile of these arsenic species in rats after oral administration of S. pallidum extract at different doses. The described assay was validated for limit of quantification, linearity, intra-day and inter-day precisions, accuracy, extraction recovery and stability according to the FDA validation guidelines. As(III) or MMA was not detected in any samples collected at all time points using the present HPLC-HG-AFS method. As(V) and DMA in the S. pallidum could be readily absorbed and eliminated in rats. A trend of dose-dependence was shown for DMA and As(V) in the drug concentration–time profiles. This study would be helpful for the apprehension of the action mechanism and clinical application of medicinal seaweeds.

Adsorption and photocatalytic decomposition of roxarsone by TiO2 and its mechanism

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid) has been widely used as organic arsenic additive in animal industry. In this study, the adsorption of roxarsone on TiO₂ under dark conditions, the photocatalytic decomposition of roxarsone under UV/TiO₂, and the possible photocatalytic pathway were investigated. At the initial concentration of 5-35 mg/L, the adsorption of roxarsone fitted well with the pseudo-second-order kinetics. The isotherms analysis showed that the Langmuir model was better than the Freundlich and Dubinin–Radushkevich models for describing the adsorption process. After 7 h of photocatalytic decomposition, a complete disappearance of roxarsone was achieved. The pH value has a significant effect on both adsorption and photocatalytic decomposition of roxarsone. The results of high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) and gas chromatography-mass spectrometry (GC/MS) analyses proved the cleavage of the As-C bond during the photocatalytic decomposition process by TiO2 and the intermediates of the decomposition. Based on the results, a possible photocatalytic decomposition pathway was proposed.

Liquid chromatography–hydride generation–atomic fluorescence spectrometry determination of arsenic species in dog plasma and its application to a pharmacokinetic study after oral administration of Realgar and Niu Huang Jie Du Pian

A high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) method was developed for the simultaneous determination of four arsenic species (As(III), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and arsenate As(V)) in dog plasma. Good separation of the four arsenic species was achieved within 15min on an anion-exchange column with isocratic elution using 15mmol/L KH(2)PO(4) (pH 5.9) as eluent at a flow rate of 1.0mL/min. The assay was linear over the range of 1.25-200, 1.56-200, 1.34-172, and 2.50-200ng/mL with the detection limits of 0.80, 1.00, 0.86 and 2.00ng/mL for As(III), DMA, MMA and As(V), respectively. The method was validated for selectivity, precision, accuracy and recovery and then applied to a comparative pharmacokinetic study of the arsenic species in beagle dogs after a single oral administration of Realgar (24.32mg/kg, equivalent to 11.31mgAs/kg) alone or Niu Huang Jie Du Pian (a patent traditional Chinese medicine (TCM), 380mg/kg, equivalent to 28.45mgAs/kg), respectively. DMA was found to be the predominant species in the dog plasma after dosing, with As(V) appeared as the quickly eliminating one. No traces of MMA and As(III) were detected at any sampling time points. The main pharmacokinetic parameters found for DMA p.o. administration of Realgar and Niu Huang Jie Du Pian were as follows: C(max) (14.7±4.2) and (57.0±32.0)ng/mL, T(max) (2.4±0.5) and (2.5±0.5)h, AUC(0-36) (151.1±12.9) and (635.9±418.2)ngh/mL, AUC(0-∞) (206.0±44.5) and (687.2±425.1)ngh/mL, t(1/2) (16.2±7.9) and (9.4±2.2)h, respectively. The influence of compounding in Niu Huang Jie Du Pian on the pharmacokinetics of arsenics was shown with increased transformation of DMA and its faster elimination rate.

Detection of inorganic arsenic in seaweed food using HPLC-HG-AFS

The inorganic arsenic(iAs) in seaweed food is an important safety index in seafood quality detection. High performance liquid chromatography-hydride generation-atomic fluorescence spectrometry(HPLC-HG-AFS) was used to determine the iAs in seaweed food. The concentration of extraction reagents,the extraction time and instrument conditions were optimized. A new method to determine the content of inorganic arsenic in seaweed food using HPLC-HG-AFS was obtained:firstly the seaweeds were extracted with 1.2 mol/L HCl at 70 ℃ for 1 h ,then the extracts were oxidized with hydrogen peroxide,and finally were analyzed by HPLC-HG-AFS under the condition of 15 mmol/L(NH4) 2HPO4 flow phase(pH=6.0). The average recovery rates of 0.10 mg/kg and 1.00 mg/kg AsⅢ in samples were all above 92% and the relative standard deviations were all below 4% with a high accuracy. The present study proved that HPLC-HG-AFS was a reliable method to determine the iAs in seaweed food and provide enough evidences for the establishment of the standard for iAs in seaweed food.