Indicators, speciation analysis

Selenium Speciation in Edible Animal Tissues Reports on Se specia-tion analysis in edible animal tissues have been scarce. Speciation analysis of Se in cod muscle tissue was performed by separating the species using both RP- and SE-HPLC prior to ICP-MS detection. The main Se compound found in enzymatic hydrolysates was selenomethionine [42], This selenocompound was absent in MeOHDHCl extracts, indicating that Se was mainly incorporated into proteins. A number of unidentiFed Se species were also detected in cod muscle tissue, the separated Se compounds being quantised on-line by post-column isotope dilution [42], Soluble Se compounds extracted from muscles of chicken, turkey, duck, ostrich, lamb, cattle, and pig were separated by SEC with ICP-MS detection. Four peaks were observed, but distribution of Se among these peaks varied considerably in tissues from different animal species [86]. 

A rather rare example indicating the possibility of speciation analysis is the determination of ionic copper, in the range from 20 to 90 pg H using a copper-selective electrode in a sample of wine when the total copper content is in the range from 0.10 to 1 mgH The sample is modified very little by the addition of a 10% volume of ImolH KNO3, as should be done with standard solutions. 

Electrospray MS that allows a precise ( lDa) determination of molecular mass is an invaluable tool for the identification and a prerequisite for further characterization of compounds in speciation analysis. ESTMS has been applied mostly to commercial standards or synthetic preparations. Pneumatically assisted ESTMS is used to identify Se-adenosylhomocysteine in an extract of selenized yeast. Selenium in garlic has been speciated by parallel ICP-MS and electrospray tandem MS. A novel selenium metabolite in rat mine, the selenosugar di-asteriomer Se-methyl-N-acetylhexosamine, has been identified by this method. It should be emphasized that when authentic standards are not available the use of tandem MS is vital to confirm selenium speciation indicated by means of hyphenated seleni-mn-specific detection. 

The advantages of SIA methodology indicated above and the commercial availability of such instrumentation generated wide interest in it and led to the development of numerous different applications in various fields of chemical analysis. They are most commonly used with spectrophotometric detection but numerous electrochemical detections were also employed (Barnett et al., 1999 Perez-Olmos et al., 2005). Sequential injection analysis methods with various detections were developed for environmental analysis (Cerda et ah, 2001 Miro and Hansen, 2006 Mesquite and Rangel, 2009), and also for speciation analysis (Van Staden and Stefan, 2004). These are considered a useful tool for clinical and biochemical analysis (Economou et ah, 2007), and even as an alternative approach to process analytical chemistry (Barnett et ah, 1999). 

An MPFS-MCFIA set-up for the spectrophotometric determination, solid-phase extraction (SPE), and speciation analysis of iron is shown in Figure 4.15 [53]. In this system, the use of a solenoid valve allows the flow deviation toward the chelating disk to carry out SPE procedures when necessary. Thus, the determination of iron is feasible in a wide range of concentrations. However, micropumps cannot overcome the back-pressure from the SPE disk. For example, deviations as high as 2 pL were found in the indicated stroke volume of 8 pL/stroke micropumps requiring periodic recalibration. 

Only slightly less accurate ( 0.3—0.5%) and more versatile in scale are other titration techniques. Plutonium maybe oxidized in aqueous solution to PuO " 2 using AgO, and then reduced to Pu" " by a known excess of Fe", which is back-titrated with Ce" ". Pu" " may be titrated complexometricaHy with EDTA and a colorimetric indicator such as Arsenazo(I), even in the presence of a large excess of UO " 2- Solution spectrophotometry (Figs. 4 and 5) can be utilized if the plutonium oxidation state is known or controlled. The spectrophotometric method is very sensitive if a colored complex such as Arsenazo(III) is used. Analytically usehil absorption maxima and molar absorption coefficients ( s) are given in Table 10. Laser photoacoustic spectroscopy has been developed for both elemental analysis and speciation (oxidation state) at concentrations of lO " — 10 M (118). Chemical extraction can also be used to enhance this technique. 

Addition of EGA to the analysis of atmospheric aerosol particles has permitted an independent speciation and determination of the nitrogenous component for samples which have not had chemical or physical pretreatment. The discovery from ESCA analyses that a substantial fraction of the particulate nitrogen exists chemically bound to the carbonaceous fraction has been confirmed by EGA. The indication from ESCA and EGA that inorganic sulfate... 

There are few methods which can measure well-defined metal fractions with sufficient sensitivity for direct use with environmental samples (approach B in Fig. 8.2). Nevertheless, this approach is necessary in the experimental determination of the distribution of compounds that are labile with respect to the time scales of the analytical method. Recent literature indicates that high-performance liquid (HPLC) and gas chromatographic (GC) based techniques may have such capabilities (Batley and Low, 1989 Chau and Wong, 1989 van Loon and Barefoot, 1992 Kitazume et al, 1993 Rottmann and Heumann, 1994 Baxter and Freeh, 1995 Szpunar-Lobinska et al, 1995 Ellis and Roberts, 1997 Vogl and Heumann, 1998). The ability to vary both the stationary and mobile phases, in conjunction with suitable detector selection (e.g. ICP-MS), provides considerable discriminatory power. HPLC is the superior method GC has the disadvantage that species normally need to be derivatised to volatile forms prior to analysis. Capillary electrophoresis also shows promise as a metal speciation tool its main advantage is the absence of potential equilibria perturbation, interactions... 

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). 

Many stability constant measurements have been made and an indication of how misleading the analysis using them can be is provided by Findlow et al. (46) These authors aimed to calculate the speciation of aluminum in human and bovine milk using two sets of stability constants for AP -citrate. Calculations with one set of constants indicated —80% of the AP+ was bound into neutral complexes, but the second set of constants, considered to be more accurate than the first, showed that less than 10% of the AP was in the form of neutral complexes. 

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