Water speciation analysis

The aim of this work was to investigate the arsenic mobilization from the tailings material (200 - 500 pg/g As) into the seepage water (up to 3.5 mg/L As) and the process of seepage water effluent forming an immobilized precipitate (up to 8 % As) in the creek. Different analytical methods for the determination of total concentrations and different sequential extraction methods as well as hyphenated techniques for speciation analysis were applied to follow the way of the arsenic in this environment. 

Fig. 2.4. Speciation analysis of drinking water spiked with 10 ppb Pb2+ as a function of sample pH performed with Pb2+-selective electrode described in Ceresa et al. [17]. The dotted line represents the behaviour calculated on the basis of lead-carbonate complexation [12]. Reprinted from Ref. [12] (p. 205), with permission from Elsevier.

Liang, P. and Liu, R. (2007) Speciation analysis of inorganic arsenic in water samples by immobilized nanometer titanium dioxide separation and graphite furnace atomic absorption spectrometric determination. Analytica Chimica Acta, 602(1), 32-36. 

Chau, Y.K. and Wong, P.T.S., 1983. Direct speciation analysis of molecular and ionic organometals. In G.G. Leppard (ed.), Trace Element Speciation in Surface Waters. Plenum, New York, pp. 87-102. 

Total metal concentrations are often very low in natural systems and in performing speciation analysis it is necessary to measure even lower concentrations on attempting to resolve component species. Therefore, very sensitive methods are needed and there is a high risk of contamination, alteration and/or adsorption losses. The ideal speciation method would be sufficiently sensitive and selective to be used directly on natural water samples, would involve minimal perturbation of the sample, and would furnish an analytical signal directly dependent on the (chemical) reactivity of the element of interest (Buffle, 1981a) (Fig. 8.1). 

Anodic stripping voltammetry (ASV) is a very sensitive instrumental technique for the measurement of metals in solution. Of particular importance are determinations of reactive or ASV-labile metal concentrations. ASV-labile metal is defined as the fraction of the total metal concentration that is measured under a defined set of ASV and solution conditions. Labilities of metal species in natural water have been related to toxicities. Thus, one objective of speciation analysis carried out by ASV is to find conditions where the ASV-labile fraction is a close approximation to the toxic fraction of a metal. In experimental terms, the ASV-labile metal should be equal to the electroactive fraction of the metal. The latter... 

Lobinski, R. and Adams, F.C. (1992a) Sensitive speciation analysis of lead in environmental waters by capillary gas chromatography microwave-induced plasma atomic emission spectrometry. Anal. Chim. Acta, 262, 285-297. 

Lobinski, R. and Adams, F.C. (1992b) Ultratrace speciation analysis oforganolead in water by gas chromatography-atomic emission spectrometry after in-line preconcentration. J. Anal. At. Spectrom., 7, 987-991. 

Preservation of Water Samples for the Speciation Analysis of Metals. 22... 

PRESERVATION OF WATER SAMPLES FOR TH E SPECIATION ANALYSIS OF METALS... 

Some Characteristics of Storage Methods for the Speciation Analysis in Water Samples... 

Zhang, N., J.S. Suleiman, M. He, and B. Hu. 2008. Chromium (Ill)-imprinted silica gel for speciation analysis of chromium in environmental water samples with ICP-MS detection. Talanta 75 536-543. 

Pantsar-Kallio, M. and P.K.G. Manninen. 1999. Optimizing ion chromatography-inductively coupled plasma mass spectrometry for speciation analysis of arsenic, chromium and bromine in water samples. Int. J. Environ. Anal. Chem. 75 43-55. 

The advantage of the selective adsorption of a particular element oxidation state has been exploited for on-line element preconcentration and speciation analysis of Cr by FAAS. Cespon Romero et al. [21] described an FIA system employing a minicolumn made of a chelating resin containing poly(aminopho-sphonic) acid groups, able to selectively retain Cr(III) ions. An FIA manifold was employed for efficient preconcentration and subsequent elution of Cr(III) with a small volume of 0.5 M HC1. The original sample was also treated with ascorbic acid to reduce Cr(VI) to Cr(III) and total Cr is determined as Cr(III) after appropriate retention and elution. Eluates are introduced into an N20-acetylene flame connected to the column outlet. The concentration of Cr (VI) is obtained by difference. Employing a sample volume of 6.6 mL, LoD for total Cr is 0.2 pg l-1. A study of FI operational variables, interferences, and precision is reported for the analysis of tap, mineral, and river waters. 

Finally, a combination of bidirectional electrostacking (a technique related to isotacophoresis and CE) with ET-AAS has been investigated by He et al. [38]. Although it cannot be considered a routine analytical technique as yet, the method offers interesting potentialities for speciation analysis of Cr(III) and Cr(VI) in waters, with respective LoDs of 6 and 5 ng ml-1, arising from preconcentration factors of around 10. 

Concentrations and speciation of As in poultry are of particular interest since this is the most widely eaten meat in many countries. Chickens are extensively fed E>sh meal and water that may contain a relatively high amount of As. A method was developed for the speciation analysis of As in chicken meat. Different procedures were optimized for the recovery of As compounds without destroying the original compounds. Two AE-HPLC columns were compared for the separation of As species prior to on-line detection by ICP-MS. The two species found were dimethylarsinic acid and arsenobetaine [26]. 

On the basis of the experience accrued so far, the extraction efficiency can be affected by both the nature of the sample under test and the As species actually present in the sample. The lipid content of the sample and the presence of As species with hydrophobic residues play a key role in this context. As a consequence, it may be useful to remove or partition lipids with an organic solvent prior to the methanol-water extraction in order to increase the extraction efficiency. This approach is also viable to prevent emulsification of methanol and lipids, which could otherwise significantly reduce the extraction efficiency [26]. Thus, sample preparation prior to As speciation usually starts with the chloroform-methanol extraction, followed by centrifugation of the sample solution to remove solid particles. Subsequently, after the addition of methanol and water, the supernatant is separated in a funnel. The amount of As remaining in the organic phase is usually quantified as total As by wet digestion after solvent evaporation. Obviously, this entails the loss of all speciation information related to the lipid-soluble As species [2]. Speciation analysis is finally carried out on the methanol-water phase, usually after solvent evaporation (see Table 19.2). 

Enhancing the Se levels in crops can be achieved by adding organic amendments (manure of Se-supplemented farmed animals) or inorganic Se to mineral fertilizers [116, 117]. The use of sodium selenate-enriched fertilizers in Finland resulted in increased Se levels in different foods and, consequently, the average serum Se in the population improved over the period 1984 D1988. ICP-MS was used to study the feasibility of wheat enrichment by selenate addition to soil fertilizers [118]. AE-HPLC-ICP-MS was optimized for the separation of selenite, selenate, selenocysteine, and selenomethionine. Total Se determination and speciation analysis were performed in water extracts and in enzymatic digests of wheat samples. It was shown that a major part of the selenate taken up by cereals was converted to selenomethionine. 

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