Chromium speciation sampling

Veecoutere K, and Cornelis R (1995) Chromium speciation in environmental and biological samples. In Quality Assurance for Environmental Analysis, Qubvauviller Ph, Maiee EA and Geiepink B, eds. pp 195-213. Elsevier, Amsterdam. 

On-line anion exchange LC/ICP-MS methods for selenium and chromium speciation have been published [30], In studies of selenium speciation in environmental samples LC/ICP-MS and LC/ ESI-MS methods have been used for the determination of both inorganic and organic selenium species [43]. For the determination of methyl selenide, strong anion exchange and RP chromatography have been employed [43], while for the determination of seleno-aminoacids, IP RP chromatography with on-line detection based on ICP-MS has been successfully employed [44],... 

Difficulties have been observed in the preservation of samples for speciation of chromium. Chromium speciation in seawater was determined on board ship shortly after samples had been collected (Abollino et at., 1991). Some samples were frozen, and analysed later in a laboratory. However, significantly lower concentrations of Crvl were observed in these latter samples. Thus, sea-going analytical methods for the determination of Crm and total chromium are of particular importance (Mugo and Orians, 1993). The volatile trifluoroacetyl-acetone derivative of Crm was formed and then concentrated by extraction into toluene. Chromium was determined by means of a gas chromatograph equipped with an electron capture detector. Total chromium was determined as Cr111 after reduction. The detection limits were 0.062 and 0.255 nmol dm 3 total chromium. A useful method was described for sampling natural water in the field, and for the preservation of Crm and Crvl species for subsequent analyses in a laboratory (Cox and McLeod, 1992). Water samples were drawn through small columns packed with activated alumina, which had been prepared previously. Chromium species were retained on the columns. 

Because hexavalent chromium is the toxic form of the metal, a number of researchers have focused on methods for distinguishing between chromium(III) and chromium(VI). Analytical techniques for chromium speciation in liquid matrices were reviewed recently (Marques etal. 2000). There are concerns about chromium as a drinking water contaminant in some areas, and samples most frequently analyzed were standard waters, potable waters and wastewaters. 

The methodologies used for chromium speciation in liquid samples are very diverse preconcentration on different types of columns, chemical reactions such as complexation or oxidation-reduction, and other separation procedures have been used and will be reviewed briefly below. These pretreatments with subsequent atomic spectrometric determination allow good limits of detection and recoveries for samples with low concentrations of chromium (Comelis 1996). Polarography is also suitable for the determination of chro-... 

Chromium speciation is very often performed in workplace air and a careful selection of the filter medium used for collecting dusts is of paramount importance. Cellulosic filters and glass fibre filters containing binders are ordinarily unsuitable, as these filter types can lead to significant reduction of Cr(Vt). Filter materials acceptable for sampling of airborne Cr(VI) include PVC, PVF, PTFE or quartz fibre filters. ... 

For chromium speciation with ICP-DRC-MS analysis, ammonia was selected as the reaction gas. Airborne Cr(VI) was separated from Cr(III) using a silica gel determination of ultratrace quantities of Cr(VI) was possible using preconcentration via complexation and ICP-DRC-MS. For aqueous samples, ion pair reversed phase HPLC was applied. ... 

Iodine speciation has been successfully carried out using capillary electrophoresis coupled to inductively coupled plasma mass spectrometry. The status of iodine species (such as thyroxine, triiodothyronine or iodide) in serum or urine can give information about the malfunction of the thyroid gland and can explain other metabolic abnormalities. Chromium speciation is not normally required in biological samples because the body converts all of the Cr + to Cr + and so the measurement of total chromium in blood and urine is referred to when in fact Cr + has been determined. Chromium speciation has been carried out in bacteria culture medium, which has used to convert Cr + to Cr ". ... 

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

Ahern et al. [ 195] have discussed the speciation of chromium in seawater. The method used coprecipitation of trivalent and hexavalent chromium, separately, from samples of surface seawater, and determination of the chromium in the... 

Cox, A.G. and McLeod, C.W. (1992) Field sampling technique for speciation of inorganic chromium in rivers. Mikrochim. Acta, 109, 161-164. 

Girard, L. and Hubert, J. (1996) Speciation of chromium (VI) and total chromium determination in welding dust samples by flow injection analysis coupled to atomic absorption spectrometry. Talanta, 43,1965-1974. 

Arsenic, chromium, mercury, selenium, and tin have been the object of numerous investigations. Because some of them are classified as probable human carcinogens23-25 (strictly speaking, some of their species), the accurate assessment of concentration and speciation in environmental matrices is enormously important. Unfortunately, such factors as chemical reactions between species, low concentration, microbial activity, redox conditions, as well as the presence of other dissolved metal ions, may cause the amounts and distributions of chemical species in a sample to vary. In response to these problems, analytical research efforts have focused on developing techniques enabling the original valence state of the metals to be preserved. Table 2.3 lists some of these stabilization methods. 

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 term speciation is used to describe any analytical procedure in which the amounts of an element in discrete chemical forms are determined, as opposed to the total amount of an element in the sample. For example, it may be of interest to determine the amounts of Cr3 + and Cr042 in environmental samples, if the two ionic species have different toxicities, rather than the total amount of chromium. In this instance ion exchange may be used to separate the cationic and anionic species.23 Sometimes all the species to be determined may be either cationic or anionic, as in the case of the determination of Fe2+ and Fe3+ or S2, S032-, and S042-. Sometimes inorganic and organically bound forms may be determined, as in the case of arsenic species in natural waters.24 Where flame spectrometric determination has been employed in speciation studies of this type, selected key references may be found in the element-by-element section of Chapter 6. 

A combination of IPC and inductively coupled plasma (ICP) MS was extensively explored for the speciation of phosphorus, arsenic, selenium, cadmium, mercury, and chromium compounds [108-118] because it provides specific and sensitive element detection. Selenium IPC speciation was joined to atomic fluorescent spectrometry via an interface in which all selenium species were reduced by thiourea before conventional hydride generation [119], Coupling IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes with cold vapor generation and atomic fluorescence detection was successfully validated [120]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of Cr(III) and Cr(VI) [121] and arsenic compounds employing hydride generation [122]. 

IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes, coupled to cold vapor generation and atomic fluorescence detection, was successfully validated [18]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of arsenic compounds employing hydride generation [17]. In the analytical speciation of chromium using in... 

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