Arsenic speciation in biological samples by on-line high performance liquid chromatography-microwave digestionhydride generation-atomic absorption spectrometry

Determination and speciation of arsenic in drinking water samples by X-ray spectrometry technique

Arsenic is ranked as the first compound in the Substance Priority List 2023 by the Agency for Toxic Substances and Disease Registry (ATSDR). The most prominent entrance to the human body is through drinking water wherein the predominant species are arsenite and arsenate. The more toxic As(III) has rigorously threatened human health worldwide; hence, speciation and separation are the need of the hour. In this article, we have reported a simple method of arsenic speciation by wavelength dispersive X-ray fluorescence (WD-XRF) spectrometer. Valence to core (VtC) electronic transitions, i.e., AsKβ2,5 fluorescence lines were used for arsenic speciation. This speciation study by WD-XRF entails direct measurement of activated alumina pellets containing arsenate and arsenite species adsorbed from water sample without separation of the trivalent and pentavalent species. This is the first report wherein the X-ray technique has been explored for speciation analysis of arsenic and the biggest advantage of the method lies in its applicability to direct analysis of synthesized nanotubes or other solid-phase extraction sorbents entrapping both the arsenic species. For determination of total arsenic using activated alumina as adsorbent, the most intense AsKα1,2 analytical lines were used and the instrumental limit of detection and the lower limit of quantification were 0.23 μg/L and 0.89 μg/L, respectively. For speciation, these limits were calculated to be 50 μg/L and 200 μg/L, respectively.

Bioaccumulation, biotransformation and trophic transfer of arsenic in the aquatic food chain

The occurrence, distribution, speciation, and biotransformation of arsenic in aquatic environment (marine and freshwater) have been studied extensively by several research groups during last couple of decades. However, most of those studies have been conducted in marine waters, and the results are available in a number of reviews. Speciation, bioaccumulation, and biotransformation of arsenic in freshwaters have been studied in recent years. Although inorganic arsenic (iAs) species dominates in both marine and freshwaters, it is biotransformed to methyl and organoarsenic species by aquatic organisms. Phytoplankton is considered as a major food source for the organisms of higher trophic levels in the aquatic food chain, and this autotrophic organism plays important role in biotransformation and distribution of arsenic species in the aquatic environment. Bioaccumulation and biotransformation of arsenic by phytoplankton, and trophic transfer of arsenic in marine and freshwater food chains have been important concerns because of possible human health effects of the toxic metalloid from dietary intake. To-date, most of the studies on arsenic biotransformation, speciation, and trophic transfer have focused on marine environments; little is known about these processes in freshwater systems. This article has been reviewed the bioaccumulation, biotransformation, and trophic transfer of arsenic in marine and freshwater food chain.

On-line coupling of an ultraviolet titanium dioxide film reactor with a liquid chromatography/hydride generation/inductively coupled plasma mass spectrometry system for continuous determination of dynamic variation of hydride- and nonhydride-forming arsenic species in very small microdialysate samples

We describe a method for continuously monitoring both hydride- and nonhydride-forming arsenic species in 10-microL microdialysate samples by coupling together on-line high-performance liquid chromatography (HPLC), a post-column UV/TiO2 film reactor, and hydride generation (HG) inductively coupled plasma mass spectrometry (ICP-MS). To maximize the signal intensities of the desired arsenic species, we optimized the photocatalytic oxidation efficiency of the analyte species and used a rapid on-line pre-reduction process to convert the oxidized species into As(III) prior to HG-ICP-MS determination. The UV/nano-TiO2 film reactor was manufactured by coating nano-TiO2 onto the interior of a glass tube. Impregnation and sol-gel methods were employed to deposit the TiO2 films, and their effectiveness for the oxidation of organic arsenicals was compared. To enhance the decomposition efficiency of organic arsenicals, we investigated the effects of the acidity and the composition of the column effluent. Because of the improved HG efficiency toward the tested arsenicals and the adoption of a segmented flow technique to retain the peak resolution in our on-line LC-UV/nano-TiO2 film reactor-HG-ICP-MS instrument, the detection limits for arseneous acid [As(III)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenic acid [As(V)], and arsenobetaine (AsB) were all in the submicrogram-per-liter range (based on 3 sigma) for 10-microL injections. A series of validation experiments--analyses of certified reference urine and rabbit serum samples--indicated that these methods can be applied satisfactorily to the continuous determination of As(III), MMA, DMA, As(V), and AsB in blood and in the extracellular space of target organs.

Current perspectives in analyte extraction strategies for tin and arsenic speciation

Nowadays, reliable and robust detectors can be considered standard laboratory instrumentation, which, for most of the elements provide quantitation limits in the lower ng/g range. Despite these advances in detector technology, sample preparation is by far the most important error source in modern analytical method development and can be judged as the "Achilles' heel" of any analytical process regarding reliability of the obtained results and time consumption. The aim of the present review is to highlight modern trends for tin and arsenic speciation, as these analytes can be considered as models for challenges in modern method development in this field. First background information, legislative aspects and current needs are elucidated. Then the role of sample treatment within the process of method development in speciation is discussed, followed by a presentation of modern extraction techniques, matching the requirements for arsenic and tin speciation analysis: to provide mild conditions in order to ensure species preservation, to improve species recovery, to enhance sample throughput and to be suitable for hyphenation with chromatographic separation systems. The review includes applications on tin and arsenic speciation, covering the period of 2001-2006.

Occurrence of arsenic contamination in Canada: sources, behavior and distribution

Recently there has been increasing anxieties concerning arsenic related problems. Occurrence of arsenic contamination has been reported worldwide. In Canada, the main natural arsenic sources are weathering and erosion of arsenic-containing rocks and soil, while tailings from historic and recent gold mine operations and wood preservative facilities are the principal anthropogenic sources. Across Canada, the 24-h average concentration of arsenic in the atmosphere is generally less than 0.3 microg/m3. Arsenic concentrations in natural uncontaminated soil and sediments range from 4 to 150 mg/kg. In uncontaminated surface and ground waters, the arsenic concentration ranges from 0.001 to 0.005 mg/L. As a result of anthropogenic inputs, elevated arsenic levels, above ten to thousand times the Interim Maximum Acceptable Concentration (IMAC), have been reported in air, soil and sediment, surface water and groundwater, and biota in several regions. Most arsenic is of toxic inorganic forms. It is critical to recognize that such contamination imposes serious harmful effects on various aquatic and terrestrial organisms and human health ultimately. Serious incidences of acute and chronic arsenic poisonings have been revealed. Through examination of the available literature, screening and selecting existing data, this paper provides an analysis of the currently available information on recognized problem areas, and an overview of current knowledge of the principal hydrogeochemical processes of arsenic transportation and transformation. However, a more detailed understanding of local sources of arsenic and mechanisms of arsenic release is required. More extensive studies will be required for building practical guidance on avoiding and reducing arsenic contamination. Bioremediation and hyperaccumulation are emerging innovative technologies for the remediation of arsenic contaminated sites. Natural attenuation may be utilized as a potential in situ remedial option. Further investigations are needed to evaluate its applicability.

Effect of natural organic matter on arsenic release from soils and sediments into groundwater

Arsenic (As) contamination in groundwater has received significant attention recently. Natural and anthropogenic sources contribute to the worldwide occurrence of As contamination. As speciation is an important factor related to its toxic and mobile behavior. The release of As from soils and sediments into groundwater is governed by several geophysicochemical processes, of which, As sorption behavior is of principle significance. This review paper summarizes existing information regarding the effects of natural organic matter (NOM) on the fate and mobility of As species in the environment. NOM may enhance the release of As from soils and sediments into the soil solution, thereby facilitating As leaching into the groundwater. The main influencing mechanisms include competition for available adsorption sites, formation of aqueous complexes, and/or changes in the redox potential of site surfaces and As redox speciation. NOM may also serve as binding agents, thereby reducing As mobility. However, comparably little research has been performed on this aspect. Since most investigations have been done on purified minerals under laboratory conditions, further research involving various geological materials under natural environmental conditions is required. Development of proper geochemical conceptual models may provide means of predicting the role of NOM in arsenic leaching and/or immobilization.

Phytoextraction and phytofiltration of arsenic

Arsenic, a ubiquitous contaminant in groundwater and soils, is currently drawing much public attention. Arsenic-contaminated soils can be cleaned up via phytoextraction-the use of plants to extract the arsenic from soil and transport it into aboveground tissues. Arsenic removal from polluted soils can be carried out using hyperaccumulator ferns like the Chinese brake fern Pteris vittata, which accumulates very high concentrations of the element in aboveground tissues. The capacity of the plant to take up large concentrations of arsenic, even at low levels in soil, illustrates efficient bioaccumulation. The possibility of using Pteris ferns to remove arsenic from water by phytofiltration has been proposed.

Arsenic speciation analysis in water samples: a review of the hyphenated techniques

Interests in the determination of different arsenic species in natural waters is caused by the fact that toxic effects of arsenic are connected with its chemical forms and oxidation states. In determinations of water samples inorganic arsenate (As(III), As(V)), methylated metabolities (MMAA, DMAA) and other organic forms such as AsB, AsC, arsenosugars or arsenic containing lipids have the most importance. This article provides information about occurrence of the dominant arsenic forms in various water environments. The main factors controlling arsenic speciation in water are described. The quantification of species is difficult because the concentrations of different forms in water samples are relatively low compared to the detection limits of the available analytical techniques. Several hyphenated methods used in arsenic speciation analysis are described. Specific advantages and disadvantages of methods can define their application for a particular sample analysis. Insufficient selectivity and sensitivity of arsenic speciation methods cause searching for a new or modifications already existing techniques. Some aspects of improvement and modifications of the methods are highlighted.

Distribution of elements binding to molecules with different molecular weights in aqueous extract of Antarctic krill by size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry

The distribution of silver, arsenic, cadmium, cobalt, chromium, copper, iron, manganese, nickel, lead, selenium and zinc binding to species with different molecular weight in aqueous extract of krill was studied by on-line size-exclusion chromatography (SEC)/inductively coupled plasma mass spectrometry (ICP-MS). The extract was fractionated in three fractions with different molecular weight (MW) ranges (>20,000 relative molecular mass (rel. mol. mass), 2000-20,000 rel. mol. mass and <2000 rel. mol. mass), which were further analyzed by SEC with columns having different optimum fractionation ranges in order to obtain more detailed information about the MW distribution of the elements. Various distribution profiles for the target elements among different MW ranges were observed. The results obtained indicated that manganese, zinc, silver, cadmium and lead species were mostly distributed in the higher MW range (>20,000 rel. mol. mass). In the case of chromium, iron, cobalt, arsenic and selenium, most of them bind to species with lower MW (<2000 rel. mol. mass). Only copper and nickel species was predominantly present in middle MW range (2000-20,000 rel. mol. mass). Further speciation of arsenic compounds in the small MW fraction was carried out with anion exchange chromatography (AEC) coupled with ICP-MS. The results showed that the dominant arsenic species in this fraction is As(III) (63% of extractable arsenic), while As(V) (13%) and two unknown arsenic species (19% and 5%, respectively) are present in lower amounts.

Determination of arsenic species in fish, crustacean and sediment samples from Thailand using high performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS)

Suitable techniques have been developed for the extraction of arsenic species in a variety of biological and environmental samples from the Pak Pa-Nang Estuary and catchment, located in Southern Thailand, and for their determination using HPLC directly coupled with ICP-MS. The estuary catchment comprises a tin mining area and inhabitants of the region can suffer from various stages of arsenic poisoning. The important arsenic species, AsB, DMA, MMA, and inorganic arsenic (As III and V) have been determined in fish and crustacean samples to provide toxicological information on those fauna which contribute to the local diet. A Hamilton PRP-X100 anion-exchange HPLC system employing a step elution has been used successfully to achieve separation of the arsenic species. A nitric acid microwave digestion procedure, followed by carrier gas nitrogen addition- (N2)-ICP-MS analysis was used to measure total arsenic in sample digests and extracts. The arsenic speciation of the biological samples was preserved using a Trypsin enzymatic extraction procedure. Extraction efficiencies were high, with values of 82-102%(As) for fish and crustacean samples. Validation for these procedures was carried out using certified reference materials. Fish and crustacean samples from the Pak Pa-Nang Estuary showed a range for total arsenic concentration, up to 17 microg g(-1) dry mass. The major species of arsenic in all fauna samples taken was AsB, together with smaller quantities of DMA and, more importantly, inorganic As. For sediment samples, arsenic species were determined following phosphoric acid (1 M H3PO4) extraction in an open focused microwave system. A phosphate-based eluant, pH 6-7.5, with anion exchange HPLC coupled with ICP-MS was used for separation and detection of AsIII, AsV, MMA and DMA. The optimum conditions, identified using an estuarine sediment reference material (LGC), were achieved using 45 W power and a 20 minute heating period for extraction of 0.5 g sediment. The stability and recovery of arsenic species under the extraction conditions were also determined by a spiking procedure which included the estuarine sediment reference material. The results show good stability for all species after extraction with a variability of less than 10%. Total concentrations of arsenic in the sediments from the Pak Pa-Nang river catchment and the estuary covered the ranges 7-269 microg g(-1)and 4-20 [micro sign]g g(-1)(dry weight), respectively. AsV was the major species found in all the sediment samples with smaller quantities of AsIII. The presence of the more toxic inorganic forms of arsenic in both sediments and biota samples has implications for human health, particularly as they are readily 'available'.

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.

Stability of arsenobetaine levels in manufactured baby foods

The stability of arsenobetaine in baby foods under different experimental conditions is evaluated. Total arsenic was analyzed by electrothermal atomic absorption spectrometry, and the speciation of arsenicals was carried out by coupling liquid chromatography to hydride generation-atomic absorption spectrometry. The highest arsenic levels in the analyzed baby foods corresponded to those containing plaice (2 to 3 microg/g). The speciation data indicated that arsenobetaine, a nontoxic species, was the only arsenical present in the baby foods analyzed at levels between 0.2 and 3 microg/g. Two different procedures for extracting arsenicals from baby foods, involving a water-methanol-chloroform mixture and enzymatic hydrolysis, were tested, and similar results were obtained. Furthermore, the arsenobetaine levels remained unchanged when the baby foods were stored for different times or when the samples were freeze-dried, thus confirming the stability of arsenobetaine and the nonappearance of other arsenic species by interconversion. The reliability of the procedure was checked by analyzing a certified reference material.

Sample preparation, extraction efficiency, and determination of six arsenic species present in food composites

Several sample preparation techniques were investigated to maximize the efficiency of arsenic species extraction from food composites. The optimized method includes lyophilization of food followed by prewashing with acetone and extraction by sonication with 50/50 methanol/water. Six arsenic species were separated and quantitated using an ammonium carbonate buffer system by ion exchange chromatography coupled to inductively coupled plasma mass spectrometry. The performance of the method for speciated arsenic components was evaluated using a matrix containing high fat food composite fortified with arsenic species. A certified reference material, dogfish muscle, was used to evaluate extraction methods for total arsenic content in food composites. More than 200 food composite samples were analyzed during an 18 month period, demonstrating the reliability of the analytical method over a long time period.

Understanding of peak deterioration in hyphenated speciation systems due to gas-liquid separation in the hydride generation interface

In hyphenated speciation systems with a hydride generation interface one of the processes influencing peak deterioration is gas-liquid separation. A mathematical model was developed to calculate attenuation, signal tailing and resolution loss of HPLC peaks due to gas-liquid separation. It was shown experimentally--using an HPLC-hydride generation-atomic fluorescence spectrometry system for arsenic speciation--that the mathematical model predicts peak deterioration well. This allowed us to study the parameters influencing the deterioration, viz. gas-liquid separation parameters (gas-liquid separator head space volume and purge gas volume flow-rate) and HPLC peak parameters [width (ratio) and resolution] theoretically, simulating HPLC peaks with gaussian functions.