University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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X. Chris Le

Abbrev:
Le, X.C.
Other Names:
Address:
Department of Public Health Sciences, University of Alberta, Edmonton, Alberta, T6G 2G3, Canada
Phone:
+1-780-492-6416
Fax:
+1-780-492-7800

Citations 9

"Arsenic Speciation Analysis"
Talanta 2002 Volume 58, Issue 1 Pages 77-96
Zhilong Gong, Xiufen Lu, Mingsheng Ma, Corinna Watt and X. Chris Le

Abstract: Nearly two dozen arsenic species are present in the environmental and biological systems. Differences in their toxicity, biochemical and environmental behaviors require the determination of these individual arsenic species. Considerable analytical progresses have been made toward arsenic speciation analysis over the last decade. Hyphenated techniques involving a highly efficient separation and a highly sensitive detection have become the techniques of choice. Methods based on high-performance, liquid chromatography separation with inductively coupled plasma mass spectrometry, hydride generation atomic spectrometry, and electrospray mass spectrometry detection have been shown most useful for arsenic speciation in environmental and biological matrices. These hyphenated techniques have resulted in the determination of new arsenic species, contributing to a better understanding of arsenic metabolism and biogeochemical cycling. Methods for extracting arsenic species from solid samples and for stabilizing arsenic species in solutions are required for obtaining reliable arsenic speciation information. (C) 2002 Elsevier Science B.V. All rights reserved.

"Low Pressure Chromatographic Separation Of Inorganic Arsenic Species Using Solid Phase Extraction Cartridges"
Talanta 1998 Volume 47, Issue 3 Pages 787-796
Serife Yalçin and X. Chris Le*

Abstract: Routine water analysis of arsenic species requires simple, inexpensive, rapid and sensitive methods. To this end, we have developed two methods, which are based on the use of inexpensive solid phase extraction (SPE) cartridges as low pressure chromatographic columns for separation and hydride generation atomic absorption spectrometry (HGAAS) and hydride generation atomic fluorescence spectrometry (HGAFS) for detection of arsenic. Both anion exchange and reverse phase cartridges were successfully used to separate arsenite [As(III)] and arsenate [As(V)]. The composition, concentration, and pH of eluting buffers and the effect of flow rate were systematically investigated. Speciation of inorganic As(III) and As(V) were achieved within 1.5 min, with detection limits of 0.2 and 0.4 ng/ml, respectively. Both isocratic and step gradient elution techniques were suitable for the baseline resolution of As(III) and As(V) using anion exchange cartridges. Application of the methods to the speciation of As(III) and As(V) in untreated water, tap water, and bottled water samples were demonstrated. Results from the speciation of arsenic in a standard reference material water sample using these methods were in good agreement with the certified value and with inter-laboratory comparison results obtained using HPLC separation and inductively coupled plasma mass spectrometric detection (HPLC-ICPMS).
Arsenate ion Arsenic(3+) Arsenic(5+) Arsenite Environmental Waste Water Mineral Sample preparation Fluorescence Solid phase extraction Speciation Volatile generation Reference material C18 Resin Column

"Speciation Of Arsenic Using Solid Phase Extraction Cartridges"
J. Environ. Monit. 2001 Volume 3, Issue 1 Pages 81-85
Serife Yalçin and X. Chris Le

Abstract: Various solid phase extraction (SPE) cartridges were investigated for speciation of arsenite [As(III)], arsenate [As(v)], monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). Cartridges containing different types of sorbent materials were tested for arsenic retention and elution characteristics. Alumina cartridges were found to completely retain all thr four target arsenic species, and are suitable for removal and pre-concentration purposes. For speciation analysis, different arsenic species were separated on the basis of their selective retention on and elution from specific cartridges. DMA was retained on a resin-based strong cation exchange cartridge and eluted with 1.0 M HCl. MMA and As(v) were both retained on a silica-based strong anion exchange cartridge and sequentially eluted with 60 mM acetic acid (for MMA) and 1.0 M HCl [for As(v)]. As(III) was not retained on either cartridge and remained in solution. Arsenic species in solution and those eluted from the cartridges were subsequently quantified by using flow injection with hydride generation atomic fluorescence spectrometry (FI-HGAFS) and hydride generation atomic absorption spectrometry (FI-HGAAS). A detection limit of 0.05 µg L-1 arsenic in water sample was achieved using HGAFS. An application of the method was demonstrated at a drinking water treatment facility. As(III) and As(v) species were determined in water at various stages of treatment. The method is suitable for routine determination of trace levels of arsenic in drinking water to comply with more stringent environmental regulations.

"Unstable Trivalent Arsenic Metabolites, Monomethylarsonous Acid And Dimethylarsinous Acid"
J. Anal. At. Spectrom. 2001 Volume 16, Issue 12 Pages 1409-1413
Zhilong Gong, Xiufen Lu, William R. Cullen and X. Chris Le

Abstract: Two key arsenic metabolites, monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)), have recently been detected in human urine. There is an increasing interest in the speciation of these metabolites in humans because of their demonstrated effects on cellular toxicity and DNA damage. However, there is no information on the oxidative stability of these arsenic species. It is not known whether and to what extent these trivalent metabolites are changed during sample handling and storage. The objective of this study was to demonstrate the oxidative conversion of these arsenic species during sample storage. We compared the effects of the storage temperature (25, 4, and -20°C) and storage duration (up to 5 months) on the stability of MMA(III) and DMA(III) in de-ionized water and in human urine. We used HPLC with hydride generation atomic fluorescence detection for the speciation of arsenic. This method provided sub-mug L-1 to low-mug L-1 detection limits for each arsenic species. We found that the oxidation of MMA(III) and DMA(III) was matrix and temperature dependent. Low temperature conditions (4 and -20°C) improved the stability of these arsenic species over the room temperature storage condition. MMA(III) in de-ionized water was relatively stable for almost 4 months, when stored at 4 or -20°C with less than 10% of MMA(III) oxidized to MMA(V). In contrast, most of MMA(III) ( 90%) in urine was oxidized to MMA(V) over the 5 month period under the 4 or -20°C storage condition. At 25°C, MMA(III) in urine was completely oxidized to MMA(V) within a week. DMA(III) in deionized water was stable for only 2-3 days, being rapidly oxidized to DMA(V). DMA(III) in urine was completely oxidized to DMA(V) within a day at 4 or -20°C. The conversion of DMA(III) to DMA(V) in urine at 25°C was complete in 17 h. These results show that MMA(III) and DMA(III) are much less stable than other arsenic species, and their stability depends on sample matrix and temperature.

"Speciation Of Submicrogram Per Liter Levels Of Arsenic In Water: On-site Species Separation Integrated With Sample Collection"
Environ. Sci. Technol. 2000 Volume 34, Issue 11 Pages 2342-2347
X. Chris Le, Serife Yalcin, and Mingsheng Ma

Abstract: Speciation of arsenic is crucial for assessing health implications from arsenic ingestion and for effective removal of arsenic from water. We report a method for the speciation of submicrogram per liter levels of arsenic in water. The method incorporates water sample collection with on-site arsenic species separation. The method is based on selective retention of arsenic species on specific solid- phase cartridges followed by selective elution and hydride generation atomic fluorescence analysis of the arsenic species. The use of a membrane filter, a resin-based strong cation-exchange cartridge, and a silica-based strong anion-exchange cartridge allows for the speciation of particulate arsenic and soluble arsenite, arsenate, monomethylarsonate, and dim ethylarsinate species. Detection limit is on the order of 0.05 µg/L. The method is suitable for direct water sample collection and on-site separation of arsenic species by flowing a measured volume of water sample through the filter and cartridges connected in serial. A particular advantage of this approach is to maintain the integrity of original arsenic species in the sample. It overcomes the common problem of instability of arsenic species after water sampling and during sample storage and handling. Applications of the method are demonstrated to the speciation of arsenic in well water, raw (untreated) river water, bottled water, and a standard reference material (SRM 1643d). Results agree well with the certified values of the SRM.

"Determination Of Monomethylarsonous Acid, A Key Arsenic Methylation Intermediate, In Human Urine"
Environ. Health Perspect. 2000 Volume 108, Issue 11 Pages 1015-1018
X. Chris Le, Mingsheng Ma, Xiufen Lu, William R. Cullen, H. Vasken Aposhian, and Baoshan Zheng

Abstract: In this study we report on the finding of monomethylarsonous acid [MMA(III)I in human urine. This newly identified arsenic species is a key intermediate in the metabolic pathway of arsenic biomethylation, which involves stepwise reduction of pentavalent to trivalent arsenic species followed by oxidative addition of a methyl group. Arsenic speciation was carried out using ion-pair chromatographic separation of arsenic compounds with hydride generation atomic fluorescence spectrometry detection. Speciation of the inorganic arsenite [As(III)], inorganic arsenate [As(V)], monomethylarsonic acid [MMA(V)], dimethylarsinic acid [DMA(V)], and MMA(III) in a urine sample was complete in 5 min. Urine samples collected from humans before and after a single oral administration of 300 mg sodium 2,3-dimercapto-1-propane sulfonate (DMPS) were analyzed for arsenic species. MMA(III) was found in 51 out of 123 urine samples collected from 41 people in inner Mongolia 0-6 hr after the administration of DMPS. MMA(III)in urine samples did not arise from the reduction of MMA(V) by DMPS. DMPS probably assisted the release of MMA(III) that was formed in the body. Along with the presence of MMA(III), there was an increase in the relative concentration of MMA(V) and a decrease in DMA(V) in the urine samples collected after the DMPS ingestion.
Speciation

"Determination Of Arsenic Metabolic Complex Excreted In Human Urine After Administration Of Sodium 2,3-dimercapto-1-propane Sulfonate"
Chem. Res. Toxicol. 2002 Volume 15, Issue 10 Pages 1318-1323
Zhilong Gong, Guifeng Jiang, William R. Cullen, H. Vasken Aposhian, and X. Chris Le

Abstract: Sodium 2,3-dimercapto-1-propane sulfonate (DMPS) has been used to treat acute arsenic poisoning. Presumably DMPS functions by chelating some arsenic species to increase the excretion of arsenic from the body. However, the excreted complex of DMPS with arsenic has not been detected. Here we describe a DMPS complex with monomethylarsonous acid (MMA(III)), a key trivalent arsenic in the arsenic methylation process, and show the presence of the DMPS-MMA(III) complex in human urine after the administration of DMPS. The DMPS-MMA(III) complex was characterized using electrospray tandem mass spectrometry and determined by using HPLC separation with hydride generation atomic fluorescence detection (HGAFD). The DMPS-MMA(III) complex did not form a volatile hydride with borohydride treatment. On-line digestion with 0.1 M sodium hydroxide following HPLC separation decomposed the DMPS-MMA(III) complex and allowed for the subsequent quantification by hydride generation atomic fluorescence. Arsenite (As-III), arsenate (As-V), monomethylarsonic, acid (MMA(V)), dimethylarsinic acid (DMA(V)), MMA(III), and DMPS-MMA(III) complex were analyzed in urine samples from human subjects collected after the ingestion of 300 mg of DMPS. The administration of DMPS resulted in a decrease of the DMA(V) concentration and an increase of the MMA(V) concentration excreted in the urine, confirming the previous results. The finding of the DMPS-MMA(III) complex in human urine after DMPS treatment provides an explanation for the inhibition of arsenic methylation by DMPS. Because MMA(III) is the substrate for the biomethylation of arsenic from MMA(V) to DMA(V), the formation of DMPS-MMA(III) complex would reduce the availability of MMA(III) for the subsequent biomethylation.

"Speciation Of Dimethylarsinous Acid And Trimethylarsine Oxide In Urine From Rats Fed With Dimethylarsinic Acid And Dimercaptopropane Sulfonate"
Anal. Chem. 2003 Volume 75, Issue 23 Pages 6463-6468
Xiufen Lu, Lora L. Arnold, Samuel M. Cohen, William R. Cullen and X. Chris Le

Abstract: Speciation of arsenic in urine from rats treated with dimethylarsinic acid (DMAV) alone or in combination with dimercaptopropane sulfonate (DMPS) were studied. Methods were developed for the determination of the methylarsenic metabolites, especially trace levels of dimethylarsinous acid (DMAIII) and trimethylarsine oxide (TMAO), in the presence of a large excess of DMAV. Success was achieved by using improved ion-exchange chromatographic separation combined with hydride generation atomic fluorescence detection. Micromolar concentrations of DMAIII were detected in urine of rats fed with a diet supplemented with either 100 µg/g of DMAV or a mixture of 100 µg/g of DMAV and 5600 µg/g of DMPS. No significant difference in the DMAIII concentration was observed between the two groups; however, there was a significant difference in TMAO concentrations. Urine from rats fed with the diet supplemented with DMAV alone contained 73 ± 30 µM TMAO, whereas urine from rats fed with the diet supplemented with both DMAV and DMPS contained only 2.8 ± 1.4 µM TMAO. Solutions containing mixtures of 100 µg/L DMAV or TMAO and 5600 µg/L DMPS did not show reduction of DMAV and TMAO. The significant decrease (p < 0.001) of the TMAO concentration in rats administered with both DMAV and DMPS suggests that DMPS inhibits the biomethylation of arsenic.

"Speciation Of Key Arsenic Metabolic Intermediates In Human Urine"
Anal. Chem. 2000 Volume 72, Issue 21 Pages 5172-5177
X. Chris Le, Xiufen Lu, Mingsheng Ma, William R. Cullen, H. Vasken Aposhian, and Baoshan Zheng

Abstract: Biomethylation is the major human metabolic pathway for inorganic arsenic, and the speciation of arsenic metabolites is essential to a better understanding of arsenic metabolism and health effects. Here we describe a technique for the speciation of arsenic in human urine and demonstrate its application to the discovery of key arsenic metabolic intermediates, monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)), in human urine. The study provides a direct evidence in support of the proposed arsenic methylation pathway in the human. The finding of MMA(III) and DMA(III) in human urine, along with recent studies showing the high toxicity of these arsenicals, suggests that the usual belief of arsenic detoxification by methylation needs to be reconsidered, The arsenic speciation technique is based on ion pair chromatographic separation of arsenic species on a 3-mum particle size column at 50°C followed by hydride generation atomic fluorescence detection. Speciation of MMA(III), DMA(III), arsenite (As-III), arsenate (As-V), monomethylarsonic acid(MMA(V)), and dimethylarsinic acid (DMA(V)) in urine samples is complete in 6 min with detection limits of 0.5-2 µg/L. There is no need for any sample pretreatment. The capability of rapid analysis of trace levels of arsenic species, which resulted in the findings of the key metabolic intermediates, makes the technique useful for routine arsenic speciation analysis required for toxicological and epidemiological studies.
Temperature