Arsenic speciation sampling

The samples were collected in polyethylene bottles and stored at 4°C. Water samples were stabilized for arsenic speciation using phosphoric acid to yield a final concentration of 10 mM [2]. Wet material was used for the extraction and the dry weight was calculated by weighing a different part of the sample after drying (105°C). 

Importantly, neither arsenobetaine nor arsenocholine forms an arsine on treatment with borohydride solutions. Consequently, arsenobetaine and arsenocholine may remain undetected in samples, seawater for example, when arsines are generated and determined in an arsenic speciation analysis. The technique HPLC/ICP-MS is most suitable for the analysis of these (non-arsine-forming) compounds (49). Use of the highly sensitive ICP-MS detector allows application of small quantities of material to the chromatography column, thereby obviating possible sample matrix effects previously observed for arsenobetaine (50). 

J. A. Day, M. Montes-Baydn, A. P. Vonderheide, and J. A. Caruso, A Study of Method Robustness for Arsenic Speciation in Drinking Water Samples by Anion Exchange HPLC-ICP-MS, Anal. Bioanal. Chem. 2002,373, 664. 

A detailed interlaboratory study of arsenic speciation in six different kinds of marine organisms was published (El Moll et al., 1996). Detection of arsenic species in the sample extracts was performed by means of LC-ICP-OES for AB and AC, and by HG-AAS for As111, Asv, MMA and DMA. Many precautions were taken to avoid contamination and losses of analytes, and to improve the accuracy of the results. Data for total As, extractable As, residual As and AB were reported. 

Kim, Y.T., H. Yoon, C. Yoon, and N.C. Woo. 2007. An assessment of sampling, preservation, and analytical procedures for arsenic speciation in potentially contaminated waters. Environ. Geochem. Health 29 337-346. 

Garbarnio, J.R., A.J. Bednar, and M.R. Burchardt. 2002. Methods of analysis by the US geological survey national water quality laboratory—arsenic speciation in natural water samples using laboratory and field methods. U.S. Geological Survey, Water-Resources Investigations Reports 02-4144. 

With a DGT device, Cr(III) can be bound to the chelex resin because of its cationic nature, whereas Cr(VI) is not bound to the resin (it has an anionic nature) but is present in the diffusive gel layer (as in a DET probe), reaching equilibrium with Cr(VI) in the aquatic system. Hence, Cr(VI) can be measured in the diffusive layer and Cr(III) in the resin layer.44 For Mn the same procedure can be adopted. The oxidized Mn(IV) species form colloids or even larger particles and will not be sampled by the DGT probe, whereas Mn(II) species are free or labile complexes. For Fe speciation, DGTs with open pores and with restricted pores are often used. Since in aquatic systems, Fe(III) is present mostly as a ligand complex or in colloidal form, the restrictive pore size excludes these forms and makes only Fe(II) species available to the restrictive DGT,45 whereas the open-pore DGT allows the passage of Fe(II) and small and labile Fe(III) complexes. In the case of arsenic speciation, As(III) and As(V) diffuse through the diffusive gel layer of the DGT, but only As(III) is immobilized on the chelating resin layer As(V) remains in the diffusive layer as an anionic compound. 

Sanz, E., R. Munos-Olivas, and C. Camara. 2005. Evaluation of a focused sonication probe for arsenic speciation in environmental and biological samples. J. Chromatogr. A 1097 1-8. 

The lead contents of 206 soil samples determined by AAS indicated that such determination provides a useful parameter for soil comparison and discrimination in forensic science (Chaperlin 1981). Soil investigations near a former smelter in Colorado revealed that historic use of arsenical pesticides has contributed significantly to anthropogenic background concentrations of arsenic on certain residential properties. A variety of forensic techniques including spatial analysis, arsenic speciation and calculation of metal ratios were successful in the separation of smelter impacts from pesticide impacts (Folkes, Kuehster, and Litle 2001). 

Further work by the Caruso group [52] used MLC for arsenic speciation studies with detection by ICP-MS. As (III), As (V), dimethylarsenic (DMA), and monomethylarsenic (MMA) were separated (Fig. 10.8). Cetyltrimethylammonium bromide (0.05 M) was used to form the micelles along with a mobile phase of 10% propanol and 0.02 M borate as buffer. Dirty samples such as urine were analyzed easily by this method of LC. 

There have been few elemental speciation studies in the literature involving cation-exchange chromatography (CEC) coupled to ICP-MS. A cation-exchange column was used by Larsen et al. [57,69] for arsenic speciation in several seafood sample extracts. The chromatography was optimized for the separation of arsenocholine, trimethylarsinic, trimethylarsine oxide, inorganic As, and two unknown cationic arsenic compounds. A mobile phase of 20 mM pyridinium ion, at pH 2.65, was used to perform the separation (Fig. 10.10). 

E. H. Larsen, G. Pritzl, S. H. Hansen, Arsenic speciation in seafood samples with emphasis on minor constituents an investigation using high-performance liquid chromatography with detection by inductively coupled plasma mass spectrometry, J. Anal. Atom. Spectrom., 8 (1993), 1075-1084. 

K. J. Lamble, S. J. Hill, Arsenic speciation in biological samples by on-line high performance liquid chromatograph microwave digestion hydride generation atomic absorption spectrometry, Anal. Chim. Acta, 334 (1996), 261-270. 

Arsenic speciation strongly depends on the ratio of methanol to water used in the extraction phase. Since the introduction of one of the first methanolic extraction protocols for As speciation [107], almost all organic samples for As speciation were prepared using this extraction medium with the aid of sonication or shaking. This method is easy to use because methanol can be quickly removed after extraction, for example, by evaporation or speed-vacuum instruments. On the other hand, As metabolism is dependent on proteins at each step of the As detoxification process. Arsenic is transported, methylated, and excreted via combination with proteins [108], Any kind of sample preparation irreversibly changing the protein structure may result in the release of As at each detoxification stage. 

Sanz, E., Munoz-Olivas, R., Camara, C., Sengupta, M., Kumar, A.S. Arsenic speciation in rice, straw, soil, hair and nails samples from the arsenic-affected areas of Middle and Lower Ganga plain. J. Environ. Sci. Health A 42, 1695-1705 (2007)... 

Gomez-Ariza, J.L., Sanchez-Rodas, D., frunaculada, G.I., Morales, E. A comparison between ICP-MS and APS detection for arsenic speciation in environmental samples. Talanta 51, 257-268 (2000)... 

Day, J.A., Montes-Bayon, M., Vonderheide, A.P., Caruso, J.A. A study of method robustness for arsenic speciation in drinking water samples by anion exchange HPLC-ICP-MS. Anal. Bioanal. Chem. 373, 664-668 (2002)... 

It is the purpose of this paper to describe some of the major mechanisms that control arsenic in aquatic systems. Particularly, this paper addresses the problem of arsenic speciation and compartmentalization in sediments. To this end, results obtained from speciation, compartmentalization, kinetic, and adsorption studies using both field and laboratory samples will be interfaced in a descriptive model for arsenic in heterogeneous systems. The model has particular significance... 

Results and Discussion. Arsenic speciation in the sediments spiked with MMAA is shown plotted as a function of time in Figure 9. The results of the DMAA experiment are shown in Figure 10. Error limits were estimated from scatter in FAA measurements. The lines connecting the experimental data points were drawn to make trends in concentrations easier to see and were not meant to imply linear changes in concentration with time between samples. 

Laboratory methods. Huorimetry has been used widely for selenium analysis in environmental samples but is being superseded by more sensitive instrumental methods. Some of the instmmental methods used for arsenic speciation and analysis can also be used for selenium. In particular, HPLC and HG can separate selenium into forms suitable for detection by A AS, AFS (Ipolyi and Fodor, 2000), or ICP-AES (Adkins et al, 1995). Only Se(IV) forms the hydride, and so Se(VI) must be prereduced to Se(IV) if total selenium is to be determined. This is normally achieved using warm HCl/KBr followed by co-precipitation with La(OH)3 if necessary (Adkins et al., 1995). KI is not used, since it tends to produce some Se(0), which is not reduced by HG. La(OH)3 collects only Se(IV), so the prereduction step to include the contribution from Se(VI) is required before co-precipitation. Other methods of preconcentration include co-precipitation of Se(IV) with hydrous iron oxide or adsorption onto Amberlite IRA-743 resin (Bueno and Potin-Gautier, 2002). 

Demesmay C. and Olle M. (1997) Application of microwave digestion to the preparation of sediment samples for arsenic speciation. Fresen. J. Analyt. Chem. 357, 1116-1121. 

Ebden and coworkers used coupled chromatography-atomic spectroscopy for arsenic speciation. Beauchemin and collaborators identified and determined arsenic species in dogfish muscle. The arsenic species were identified using liquid chromatogra-phy-inductively coupled plasma-MS, TLC and electron impact-MS. Results indicate that arsenobetaine constitutes about 84% of the arsenic present in the sample analysed. 

Spectroscopic techniques (particularly infrared, x-ray photoelectron, and x-ray absorption spectroscopy) have been applied to fill the information gap about chemical speciation and interfacial reactions of As in model and natural materials. They have been used to determine the stmcture of x-ray amorphous particles involved in interfacial reactions, to identify the types of sorption reactions occurring in simplified model systems containing As and one or more phases, and to identify the valence and speciation of predominant As species present in natural, heterogeneous materials. This chapter summarizes much of the recent spectroscopic information on arsenic speciation in minerals and other solid phases that are analogous to phases present in aquifer sediments. These data are primarily derived from analysis of synthetic samples or natural model compounds. 

The presence of elevated metals and arsenic in the sediments corresponds with the high concentration of dissolved constituents in the wells installed in the reservoir sediment (HLA, 1987 Titan, 1996 Woessner et al., 1984). In these wells, TDS is commonly over 1,400 mg/1, dissolved arsenic ranges from ca. 100 to 10,000 Xg/I, Mn from ca. 0.1 to 25 mg/1 and iron from ca. 1 to 60 mg/1. Arsenic speciation results show that samples from within reservoir sediment and the adjacent contaminated aquifer are dominated by As(III) (Moore et al, 1988). 

P. Richter, R. Seguel, I. Ahumada et al.. Arsenic Speciation in Environmental Samples of a Mining Impacted Sector of Central Chile, J. Chilean Chem. Soc. 49(4), 333-339, Dec. (2004). 

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