PRP-X100 Anion-exchange Column Research Articles

Speciation analysis of arsenic in edible mushrooms by high-performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry

Some varieties of edible mushrooms can accumulate high contents of arsenic, which is a public health concern. In this study, we developed a high-performance liquid chromatography method linked to inductively coupled plasma triple quadrupole mass spectrometry (HPLC-ICP-MS/MS) for sensitive and accurate determination of arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenocholine and arsenobetaine in edible mushrooms. The six arsenic species were extracted ultrasonically from mushrooms using ultrapure water at 60 °C as the solvent, separated on a PRP-X100 anion exchange column (4.1 × 250 mm, 10 µm), with 20 mmol/L NH4HCO3 and 50 mmol/L (NH4)2CO3 as the mobile phase, and quantified using ICP-MS/MS in the oxygen reaction mode. The linear range of the method was 0.5 µg/L–100 µg/L with detection and quantification limits of 2.5 µg/kg–10 µg/kg (S/N = 3), and 8 µg/kg–33 µg/kg (S/N = 10), respectively. This method was applied successfully to the detection and speciation of arsenic in eight varieties (266 samples) of mushrooms. Our results indicated that most wild edible mushrooms contained organic arsenic, mainly arsenobetaine and arsenocholine. However, the inorganic arsenic content of Armillariella tabescens (3.63 mg/kg) and parts of the cultivated Agaricus blazei murrill (up to 4.50 mg/kg) were relatively high, which is potential risk to the health of consumers.

Optimized extraction of inorganic arsenic species from a foliose lichen biomonitor.

To assess the two most toxicologically relevant species of As, namely arsenite (As(III)) and arsenate (As(V)), chromatographic separations often require two separate chromatographic columns to address the co-elution of arsenobetaine (AsB) with As(III). This issue is typically observed using conventional isocratic methods on anion exchange columns, increasing cost and analysis time. Here, we optimize the extraction of inorganic As from a lichen air biomonitor and develop an isocratic method for the chromatographic separation of five common As species on a PRP X-100 anion exchange column, resulting in the complete baseline separation of all species under study. This method was then applied to lichen biomonitors from an urban and rural site to demonstrate its use. In order of abundance, the various arsenic species in lichens from the urban site in South Africa were As(V) > As(III) > AsB > dimethylarsinic acid (DMA) > monomethylarsonic acid (MMA), and As(V) > AsB > As(III) > DMA > MMA for the rural site, where MMA was present in extremely low, non-quantifiable concentrations in lichens from both sites. Total concentrations of As were higher in samples from the urban site (6.43 ± 0.25 μg/g) than in those from the rural site (1.87 ± 0.05 μg/g), with an overall extraction efficiency of 19% and 40%, respectively. The optimized method utilized relatively inexpensive solvents and is therefore low-cost and eco-friendly in comparison with conventional chromatographic techniques. This is the first study which addresses the optimized extraction and characterization of As species in a South African lichen biomonitor of air pollution. Graphical abstract .

Speciation analysis of arsenic compounds in seafood by ion chromatography-atomic fluorescence spectrometry

Ion chromatography-ultra violet-hydride generation-Atomic Florescence Spectrometry was applied to detect 5 arsenic species in seafoods. The arsenic species studied include arsenobetaine (AsB), arsenite (As(III)), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), and arsenate (As(V)), which were extracted from samples using 2% formic acid. Gradient elution using 33 mmol L−1 CH3COONH4 and 15 mmol L−1 Na2CO3 with 10 mL CH3CH2OH at pH 8.4 allowed the chromatographic separation of all the species on a Hamilton PRP-X100 anion-exchange column in less than 8 min. In this study, an ultrasound extraction method was used to extract arsenic species from seafood. The extraction efficiency was good and the recoveries from spiked samples were in the range of 72.6%–109%; the precision between sample replicates was higher than 3.6% for all determinations. The detection limits were 3.543 μg L−1 for AsB, 0.426 μg L−1 for As(III), 0.216 μg L−1 for DMA, 0.211 μg L−1 for MMA, and 0.709 μg L−1 for As(V), and the linear coefficients were greater than 0.999. We also developed an application of this method for the determination of arsenic species in bonito, Euphausia superba, and Enteromorpha with satisfactory results. Therefore, it was confirmed that this method was appropriate for the detection of arsenic species in seafood.

Experimental evaluation of sampling, storage and analytical protocols for measuring arsenic speciation in sulphidic hot spring waters

Recently developed analytical techniques allowed for the detection of a range of dissolved arsenic-sulphur species in sulphur-rich environments. These so called thioarsenates are unstable, however, and can degrade upon handling and storage. An experiment evaluating the effect of exposure to air on arsenic and sulphur-enriched geothermal waters demonstrated a near to complete loss of thioarsenate species to arsenite or arsenate during short oxidation times. In contrast, thioarsenic standards were stable for the duration of analysis in spite of exposure to air. For samples containing thio-methylated arsenic species, the extent of oxidation varied for different methylated arsenic species. This study recommends flash freezing of samples in liquid nitrogen immediately after recovery and further storage under anaerobic conditions at −80°C. A second experiment to test the efficiencies of different HPLC columns for separating arsenic species resulted in the preference for an IonPac column with NaOH as the mobile phase when analysing arsenic thioanions, over the commonly used PEEK PRP-X100 anion exchange and Atlantis C18 reverse phase column with ammonium phosphate mobile phases. Distinct separation of thio-methylated arsenic species with the IonPac column, however, was not successful potentially due to matrix components. Acceptable detection, separation and quantification of thio-methylated arsenic species were only achieved with the Atlantis C18 column. This study shows that preservation and analysis of samples is matrix dependent, which holds important implications for efforts to interpret arsenic speciation in geothermal waters, especially those of low pH (2–3), low oxygen (≤49% saturation), low iron (≤5mgL−1) and high sulphur concentrations (≥91mgL−1).

Simultaneous Analysis of SbIII, SbV and TMSb by High Performance Liquid Chromatography–Inductively Coupled Plasma–Mass Spectrometry Detection: Application to Antimony Speciation in Soil Samples

This study was conducted to develop a method for the simultaneous separation and detection of antimonite (Sb(III)), antimonate (Sb(V)) and trimethyl antinmony (TMSb) species in soils, using ultrasonic-aided citric acid extraction and high-performance liquid chromatography-inductively coupled plasma-mass spectrometry separation and detection. The extractions were performed using various chemical solutions. The separation was conducted on a PRP-X100 anion exchange column (25 cm × 4.1 mm i.d., 10 µm) using an isocratic elution program. The various factors of the elution procedure, e.g., pH, elution concentration and retention time, were optimized for the best separation of the three Sb species. It was found that two consecutive extractions using 100 mmol/L citric acid at pH 2.03 resulted in the highest extraction efficiency, 53%. The optimal elution procedure was obtained by using 200 mmol/L ammonium tartrate with 4% methanol as the mobile phase at pH 5.0. Under these conditions, the retention times for Sb(III), Sb(V) and TMSb species were 3.8, 2.1 and 6.8 min with detection limits of 0.03, 0.02 and 0.05 µg/L, respectively. Spiked recoveries for Sb(III), Sb(V) and TMSb ranged from 88 to 118%. The proposed method is reliable for antimony speciation in soil samples.

HPLC‐ICP‐MS method development to monitor arsenic speciation changes by human gut microbiota

Inorganic arsenic (iAs) has been classified as a type 1 carcinogen and has also been linked to several noncancerous health effects. Prior to 1995, the As(V) methylation pathway was generally considered to be a detoxification pathway, but cellular and animal studies involving MMA(III) (mono metyl arsonous acid) and DMA(III) (dimethyl arsinous acid) have indicated that their toxicities meet or exceed that of iAs, suggesting an activation process. In addition, thiolated arsenic metabolites were observed in urine after oral exposure of inorganic arsenic in some studies, for which the toxicological profile was not yet fully characterized in human cells. Studies have revealed that microorganisms from the gut environment are important contributors to arsenic speciation changes. This presystemic metabolism necessitates the development of protocols that enable the detection of not only inorganic arsenic species, but also pentavalent and trivalent methylated, thiolated arsenicals in a gastrointestinal environment. We aim to study the biotransformation of arsenic (As) using a Simulator of the Human Intestinal Microbial Ecosystem (SHIME). To be able to analyze the arsenicals resulting from biotransformation reactions occurring in this system, a method using liquid chromatography hyphenated to an inductively coupled plasma mass spectrometer (HPLC-ICP-MS) was developed. A Hamilton PRP-X100 anion exchange column was used. The method allowed separation, identification and quantification of As(III) (arsenite), As(V) (arsenate), DMA(V) (dimethylarsinicacid), MMA(V) (monomethylarsonicacid) and MMMTA (monomethylmonothioarsenate). Attempts to optimize the same method for also separating MMA(III) and DMA(III) did not succeed. These compounds could be successfully separated using a method based on the use of a Zorbax C₁₈ column. The properties of the column, buffer strength, pH and polar nature of mobile phase were monitored and changed to optimize the developed methods. Linearity, sensitivity, precision, accuracy and resolution of both methods were checked. The combination of the two methods allowed successful quantification of arsenic species in suspensions sampled in vitro from the SHIME reactor or in vivo from the human colon and feces.

Concentration distributions of dissolved Sb(III) and Sb(V) species in size-classified inhalable airborne particulate matter

In order to obtain more accurate assessments of global contamination by potentially toxic antimony (Sb) and the toxicological effects of Sb on ecosystems, speciation analysis of inorganic Sb species in size-classified airborne particulate matter (APM) was performed. Thirteen fractions of size-classified APM (with aerodynamic diameters: Dp 11 μm) were collected on a filter by using a multistage cascade impactor sampler. Speciation analysis of inorganic Sb(III) and Sb(V) was performed by using HPLC-ICP-MS. Portions of sample-loaded filters were sonicated with 30 mmol l−1 citric acid under purified N2 in order to avoid the oxidation of Sb(III) to Sb(V) during the extraction process. Sb(III) and Sb(V) were separated on a PRP-X100 anion exchange column using a mixture of 10 mmol l−1 EDTA and 1 mmol l−1 phthalic acid (pH 4.5) as a mobile phase, and they were subsequently detected by ICP-MS. The size distributions of the total Sb concentration exhibit a bimodal profile in which peaks corresponded to fine (0.50–0.70 μm) and coarse (3.6–5.2 μm) fractions. The speciation analysis demonstrated for the first time that Sb(III), which is the more toxic form, is dominated by coarse fractions whereas Sb(V) is distributed in both the fine and coarse fractions. The presented high-resolution size distributions of inorganic Sb species will provide helpful information in discussing both health risks by inhalation exposure to Sb and the extent of the effects of emission sources by atmospheric circulation.

Determination of tranexamic acid in cosmetic products by high-performance liquid chromatography coupled with barrel plating nickel electrode

Tranexamic acid (TA) is an important reagent in cosmetic skin-whitening formulation and a drug for the inhibition of plasminogen to plasmin in blood. Since there is no chromophore in tranexamic acid molecule to enable direct analysis by UV–visible absorption spectrophotometry, derivatization is thus required by excluding use of UV or fluorescence detection. We report here a relatively simple electrochemical TA detection method by using a barrel plating nickel electrode. Chromatographic separation was performed on a Hamilton PRP-X100 anion-exchange column (150 mm × 4.1 mm i.d., 10 μm particle size) with a (85:15, v/v) mixture of 0.1 mol l −1 NaOH and acetonitrile as mobile phase and pumped at a flow rate of 0.9 ml min −1. By detecting at +0.55 V vs. Ag/AgCl, the calibration plot was linear in the concentration window of 3–1000 ppm with regression coefficient and detection limit (S/N = 3) of 0.9993 and 0.13 ppm (0.84 μmol l −1), respectively. Successive injections ( n = 10) of 50 ppm tranexamic acid showed a R.S.D. value of only 0.3% indicating good reproducibility of the proposed system. The method was successfully applied to the analysis of the content of tranexamic acid in cosmetic products and proved to be suitable for rapid and reliable quality control.

Sample pre-treatment to eliminate cationic methylated arsenic for determining arsenite on an anion-exchange column by high performance liquid chromatography–inductively coupled plasma mass spectrometry

Co-elution of cationic methylated arsenic, e.g. arsenobetaine may interfere with the determination of arsenite on the Hamilton PRP-X100 anion-exchange column using a phosphate buffer isocratically. Therefore, a sample pre-treatment method with self-packed AG MP-50 cation-exchange cartridges was proposed, which enables the arsenite determination in samples containing arsenobetaine on a PRP-X100 column using a phosphate buffer (pH 5.6) isocratically. Methylated arsenic, including dimethylarsinic acid, trimethylarsine oxide, tetramethylarsonium ion, arsenobetaine and arsenocholine, with concentrations below 1000 μg As L −1, may be completely retained in the AG MP-50 cartridge without any changes of arsenite, arsenate and monomethylarsonic acid speciation. Such retention was independent of the pH and matrix. It is proposed to be based on hydrophobic interaction. With the help of AG MP-50 cartridges, 11 arsenic species were detected in fish (DORM-2), mussels (BCR-477) and red algae ( Porphyra tenera) in 10 min on the PRP-X100 column using a phosphate buffer isocratically. Arsenite was the only minor species (up to 0.9%) among all water extractable arsenic species in fish, mussel and red algae.

Measurement of total antimony and antimony species in mine contaminated soils by ICPMS and HPLC-ICPMS

This paper describes the measurement of total antimony and antimony species in "real world" mine contaminated sediments using ICPMS and HPLC-ICPMS. Low and high temperature microwave extraction procedures (90 degrees C and 150 degrees C, respectively) using a range of nitric-hydrochloric acid combinations were examined as to their efficacy to extract antimony from six mine contaminated soils and a certified reference material. The use of the higher temperature with nitric-hydrochloric acid (1:2 (v/v)) was suitable to release antimony from sediments and the certified reference material, NIST 2710 Montana soil. Antimony concentrations obtained using this acid mixture were similar to those obtained using a more aggressive extraction with nitric, hydrochloric, perchloric and hydrofluoric acid mixture. A 25 mM citric acid solution at 90 degrees C for 15 min extracted 47-78% of antimony from soils. A Hamilton PRP X-100 anion exchange column with 20 mM EDTA mobile phase, pH 4.5, flow rate 1.5 mL min(-1) and column temperature of 50 degrees C was used to separate antimony species. Column recoveries ranged from 78-104%. The predominant form of antimony was Sb(5+). Little conversion of Sb(5+) occurred (<5%) during extraction, however, significant conversion of Sb(3+) occurred (approximately 36%). The extraction of antimony species with citric acid should be useful in the determination of inorganic antimony available to plants, as plants commonly excrete carboxylic acids, including citric acid, into their rhizospheres to mobilise trace elements for nutritional purposes.

Arsenic Species Determination in Biological Tissues by HPLC - ICP - MS and HPLC - HG - ICP - MS

The use of high-pressure liquid chromatography coupled directly or by a hydride generation system to an inductively coupled plasma mass spectrometer for the unambiguous measurement of 13 arsenic species in marine biological extracts is described. The use of two chromatography systems; a Supelcosil LC-SCX cation-exchange column eluted with a 20 mM pyridine mobile phase adjusted to pH 2.2 and 2.6 with formic acid, with a flow rate of 1.5 mL min−1 at 40°C, and a Hamilton PRP-X100 anion-exchange column eluted with 20 mM NH4H2PO4 buffer at pH 5.6, with a flow rate of 1.5 mL min−1 at 40°C, was required to separate and quantify cation and anion arsenic species. Under these conditions, arsenous acid could not be separated from other arsenic species and required the use of an additional hydride generation step. Arsenic species concentrations in a locally available Tasmanian kelp (Durvillea potatorum), a certified reference material (DORM-2), and a range of commercially available macroalgae supplements and sushi seaweeds have been measured and are provided for use as in-house quality control samples to assess the effectiveness of sample preparation, extraction, and measurement techniques.

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 2S 2O 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.

Measurement of arsenic species in marine macroalgae by microwave-assisted extraction and high performance liquid chromatography–inductively coupled plasma mass spectrometry

The measurement of arsenic species (arsenoribosides, arsenate, dimethyl arsenic and monomethyl arsenic) in marine macroalgae by microwave-assisted extraction and HPLC–ICP-MS is described. The extraction of arsenic from three different macroalgae classes was optimised using a chemometric approach, with solvent composition and sample mass being the two significant factors influencing the extraction of arsenic. Extraction temperature and extraction time did not significantly influence the extraction of arsenic from macroalgae. The optimised conditions for arsenic extraction (methanol (%)) were: 56% for phaeophyta, 66% for rhodophyta and 78% for chlorophyta, (sample mass in 10 ml of solvent) 0.05 g for phaeophyta, 0.07 g for rhodophyta and 0.08 g for chlorophyta. When two extractions were used, the percentage of arsenic extracted from macroalgae was greater than 88%. Unambiguous separation and identification of three arsenoribosides (phosphate-, sulfonate- and sulfate-arsenoriboside) was achieved by chromatographing extracts on a Hamilton PRP X-100 anion exchange column with ammonium phosphate buffer as the mobile phase at a pH of 9.2. The unambiguous separation and identification of the glycerol-arsenoriboside was achieved by chromatographing extracts on a Supelcosil SCX cation exchange column with a pyridine–formic acid buffer as the mobile phase at a pH of 2.6.

Determination of selenoethionine by flow injection-hydride generation-atomic absorption spectrometry/high-performance liquid chromatography-hydride generation-high power nitrogen microwave-induced plasma mass spectrometry

A simple direct flow injection hydride generation atomic absorption spectrometric method was developed using sodium tetrahydroborate and hydrochloric acid for the determination of selenoethonine (Seet) that excluded any chemical pretreatment prior to hydride generation. The detection limit (3 σ of blank) of the method was 0.25 ng ml −1 selenium (standard solutions in Milli-Q water). The reproducibility (R.S.D. of three analyses performed on three different days) and the repeatability (R.S.D. of seven successive analyses) of the method were 9.2% for 5.05 ng ml −1 and 2.8–9.5% for 20.0–1.00 ng ml −1 of standard selenium (Milli-Q water), respectively. The calibration graph was linear up to 20.0 ng ml −1. This HG method is very promising and was successfully applied for the on-line estimation of Seet (spiked) in human urine with using high-performance liquid chromatography-hydride generation-high power nitrogen microwave-induced plasma mass spectrometry (HPLC-HG-N 2-MIP-MS). The separation was performed on a GS-220 gel-permeating column with a 25 mM tetramethylammonium hydroxide+25 mM malonic acid buffer (pH 7.5), which showed 26–30% signal suppression due to less volatile hydride formation from Seet among the mobile phases examined. The recovery of Seet that was prepared in the above mobile phase is about 74% as that of the Seet prepared in Milli-Q water. In the PRP-X100 anion-exchange column with the 15 mM phosphate (pH 7.0) mobile phase, Seet eluted out after 600 s keeping a broad peak with enlarging the baseline signal. The concentration of selenite found in the human urine was 3.6±0.2 μg l −1 and that agreed well with the high-performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) value (3.8±0.2 μg l −1).

Complexation effect of antimony compounds with citric acid and its application to the speciation of antimony(iii) and antimony(v) using HPLC-ICP-MS

In this work, a complexation effect of Sb compounds with citric acid was observed using electrospray mass spectrometry (ES-MS). It was found that both Sb(III) and Sb(V) could form complexes readily with citric acid in an aqueous solution at room temperature. These complexes were found to be very stable in various matrices (moat water and aqueous extracts of airborne particulate matter), therefore, a novel HPLC-ICP-MS analytical method for the speciation of Sb(III) and Sb(V) in environmental samples was developed by using the observed complexation effect. Sb(III)- and Sb(V)-citrate complexes were separated on a PRP-X100 anion-exchange column with 10 mmol l−1 EDTA–1 mmol l−1 phthalic acid (pH 4.5) as a mobile phase. All complexes were retained on the separation column, and none of them eluted in the solvent front. Low detection limits of 0.05 µg l−1 and 0.07 µg l−1 were achieved for Sb(III) and Sb(V), respectively. The calibration curves were linear over the range of 1.0–250 µg l−1 for the investigated Sb species. The precisions, evaluated by using the relative standard deviation (%RSD) with a 2 µg l−1 standard solution, were 1.8% and 3.3% for Sb(III) and Sb(V), respectively. Several advantages of the developed method, such as improving chromatographic separation, stabilizing Sb compounds in a water sample, and preventing Sb(III) from oxidizing to Sb(V) during the ultrasonic-assisted and microwave-assisted extraction of an airborne particulate matter (APM) sample using 26 mmol l−1 citric acid as an extraction solvent, and alleviating the adsorption of Sb compounds on the sample surface, were observed. The developed method enabled us to detect the most toxic Sb specie, Sb(III), in an APM sample for the first time.

Urinary antimony speciation by HPLC-ICP-MS

This is the first study to report on the determination of Sb species in urine. To this end, HPLC was coupled online to an ICP-MS instrument using ultrasonic nebulization (USN) or hydride generation (HG) for sample introduction into the ICP-MS. The high chloride concentration in urine seriously hampered the chromatographic separation of Sb(V) and Sb(III) on the Dionex AS14 anion exchange column. Distinct signal suppression, shifting of retention times and severe peak broadening did not allow the application to urine samples. Progress to avoid these problems in HPLC-USN-ICP-MS could be made by employing a Hamilton PRP-X100 anion-exchange column. However, Na eluting in the void volume of the column gave rise to a Na-induced peak overlapping with the Sb(V) signal when USN was used to aspirate the HPLC eluents into the plasma. Therefore, a HG system was placed between the HPLC and ICP-MS instrumentation to overcome this dilemma. Thus, Sb(V) and Sb(III) were separated in urine with the PRP-X100 column using 20 mM EDTA at pH 4.7 as the mobile phase. Similarly, an ION-120 anion-exchange column was employed to separate trimethylantimony dichloride (TMSbCl2) and Sb(V) with a mobile phase containing 2 mM NH4HCO3 and 1 mM tartaric acid at pH 8.5. Detection limits of 20 ng l−1, 12 ng l−1 and 8 ng l−1 for Sb(V), TMSbCl2 and Sb(III), respectively, could be established in a 1 + 2 diluted urine matrix. The developed HPLC-HG-ICP-MS method was applied to the speciation of Sb in the urine of occupationally exposed and non-exposed subjects. Additionally, two lyophilised urine reference materials were investigated. Sb(V) was by far the predominant Sb species, followed by TMSbCl2. Only ultratraces of Sb(III), if any detectable, could be found. The sum of the concentrations of Sb(V), Sb(III) and TMSbCl2 in urine samples ranged between 51 and 78% of their total Sb concentrations.

Determination of 'arsenosugars' in algae with anion-exchange chromatography and an inductively coupled plasma mass spectrometer as element-specific detector.

The retention behavior of four naturally occurring dimethylarsinoylribosides with -CH2-CHOH-CH2X (X = OH, HO3POCH2CHOHCH2OH, SO3H, OSO3H) as aglycones, of arsenous acid, arsenic acid, methylarsonic acid, and dimethylarsinic acid was investigated on a Hamilton PRP-X100 anion-exchange column with aqueous solutions of ammonium dihydrogen phosphate (20 mmol/L) in the pH range of 3.8-9.0 as mobile phase. A HP 4500 inductively coupled plasma mass spectrometer (ICP-MS) served as arsenic-specific detector. The influence of pH, temperature, and the concentration of methanol in the mobile phase on the retention times of these arsenic compounds was explored. An aqueous 20 mM ammonium dihydrogen phosphate solution at pH 5.6 at a column temperature of 40 degrees C was considered optimal as it allowed the separation of seven of the arsenic compounds within 16 min. Only arsenous acid and the ribose with the glycerol aglycone have overlapping signals with both migrating almost with the solvent front. At a concentration of 0.50 ng As mL(-1) the relative standard deviations (n = 3) of the signal areas of the eight arsenic compounds was in the range from 3.5 to 8.1%. The linear calibration curves (peak areas) from 0.5 to 10 ng/mL had correlation coefficients > 0.997. Extracts obtained from the brown algae Fucus spiralis and Halidrys siliquosa were chromatographed under the optimized conditions. Both species contained the sulfate riboside as the major arsenic compound (approximately 55% of total extractable arsenic) together with the sulfonate- and phosphate riboside. Arsenic acid was a significant constituent of Halidrys siliquosa (approximately 6.5%), but was not detected in Fucus spiralis.

Determination of selenite and selenomethionine by HPLC-HG-high power N2-MIP-MS: a suitable coupling for selenium speciation

The coupled technique, high performance liquid chromatography (HPLC) continuous hydride generation [flow-cell, with sodium tetrahydroborate (0.3% in 0.2% NaOH) and hydrochloric acid (3 M)] high power nitrogen microwave induced plasma [1.3 kW; 2.45 GHz, with an Okamoto cavity in a surface-wave mode (rectangular waveguide; WRJ-2)] mass spectrometry (N2-MIP-MS) has been investigated for selenite and selenomethionine (Semet) determination. The high power N2-MIP-MS was successfully coupled with a HG system that is attached with a PRP-X100 anion exchange column. It was studied as an element specific detector for the optimization and determination of selenite and Semet using the major isotope of selenium (m/z 80). The adjusted HG system was very promising for the direct determination of the selenite and Semet without derivatization prior to HG. The N2-MIP was stable in coupling with the HG system. The separation was performed with a phosphate buffer (15 mM at pH 7.0), which showed minimum suppression of volatile hydride formation from Semet among the mobile phases examined. The recovery of Semet (98–104%), prepared in the phosphate mobile phase, was almost same as that of Semet prepared in Milli-Q water. The detection limits of selenous acid and Semet obtained with the optimized HPLC-HG-N2-MIP-MS system were 0.73 and 8.7 µg l−1, respectively. The repeatability (RSD for three successive analyses) achieved for selenous acid and Semet were within 2.3–5.2%. The combined HPLC-HG-N2-MIP-MS was applied to the determination of selenium compounds in human urine. The separation of selenite and Semet (spiked) in human urine was reasonable. The concentration of selenite found in the human urine was 3.7 ± 0.2 µg l−1 which agreed well with the HPLC-ICP-MS value (3.8 ± 0.2 µg l−1). Furthermore, in urine the retention times of selenite and Semet were shifted towards the solvent front. The spectroscopic interference due to calcium was removed.

Arsenic Speciation in Human Urine Reference Materials Using High-Performance Liquid Chromatography with Inductively Coupled Plasma Mass Spectrometric Detection

Six arsenic compounds including arsenocholine, arsenobetaine, dimethylarsinic acid, methylarsonic acid, arsenous acid and arsenic acid were separated by high-performance liquid chromatography (HPLC) on a Hamilton PRP-X100 anion-exchange column using isocratic elution and detected by inductively coupled plasma mass spectrometry (ICP-MS). This analytical procedure was applied to the speciation of arsenic compounds in human urine. The influence of urine matrix on the separation of arsenic compounds was evaluated and the determination of arsenic compounds was not hampered by the ArCl interference which has often been encountered in ICP-MS. Three human urine reference materials, SRM 2670 normal level, SRM 2670 elevated level and Lyphocheck urine metal control 1, were analyzed with respect to arsenic compounds by HPLC-ICP-MS. The results were found to be in good agreement with the certified total arsenic concentration in the reference materials. Six arsenic compounds were detected. Arsenobetaine was found to be present in all of the investigated human urine reference materials.

The separation of dimethylarsinic acid, methylarsonous acid, methylarsonic acid, arsenate and dimethylarsinous acid on the Hamilton PRP-X100 anion-exchange column

In order to separate the potential arsenite metabolites methylarsonous acid and dimethylarsinous acid from arsenite, arsenate, methylarsonic acid and dimethylarsinic acid, the pH-dependent retention behaviour of all six arsenic compounds was studied on a Hamilton PRP-X100 anion-exchange column with 30 mM phosphate buffers (pH 5, 6, 7, 8 and 9) containing 20% (v/v) methanol as mobile phase and employing an inductively coupled plasma atomic emission spectrometer (ICP–AES) as the arsenic-specific detector. Baseline separation of dimethylarsinic acid, methylarsonous acid, methylarsonic acid, arsenate and dimethylarsinous acid was achieved with a 30 mmol dm−3 phosphate buffer (pH 5)–methanol mixture (80:20, v/v) in 25 min. Arsenite is not baseline-separated from dimethylarsinic acid under these conditions. Copyright © 1999 John Wiley & Sons, Ltd.