Environmental contaminants, isotope ratio mass

Compound specific stable isotope analysis using gas chromatography combined with an isotope ratio mass spectrometer - GC-IRMS (see also Chapter 7) - is now a mature analytical technique in environmental science and technology, especially in the area of contaminant source attribution and in assessing the biodegradation of contaminants.108 Several studies have focused on 13C/12C, 180/160 and 170/160 isotope ratio measurements for volatile organic and metalor-ganic compounds to study isotope fractionation effects and to identify contamination in the environment.109... 

Selenium (masses 74, 76, 77, 78, 80, and 82 Table 1) and chromium (masses 50, 52, 53 54 Table 1) are treated together in this chapter because of their geochemical similarities and similar isotope systematics. Both of these elements are important contaminants in surface and ground water. They are redox-active and their mobility and environmental impact depend strongly on valence state and redox transformations. Isotope ratio shifts occur primarily during oxyanion reduction reactions, and the isotope ratios should serve as indicators of those reactions. In addition to environmental applications, we expect that there will be geological applications for Se and Cr isotope measurements. The redox properties of Se and Cr make them promising candidates as recorders of marine chemistry and paleoredox conditions. 

Environmental monitoring of nuclear contamination, including the determination of the concentration and isotope ratios of long-lived radionuchdes, such as uranium, plutonium isotopes, thorium, Np, Se, Sr, I and others, at trace and ultratrace levels, is a fast growing and fascinating application field for inorganic mass spectrometry." " Among the environmentally important radionuclides, I, Sr, uranium and transuranium elements are of special importance. For example, the natural I inventory in the atmosphere, hydrosphere and biosphere has been estimated to be about 263 kg. ... 

In the best of instruments, isotope ratio errors may occur as a result of inefficient counting, from mass bias, and other causes. Correction standards at approximately the same concentrations as quality control (QC) samples and unknown samples are used to correct for these sources of error. A natural uranium spike is used because low-concentration endogenous uranium in the base urine and any small amounts of contamination from environmental sources are presumed to be natural, thus will not affect the true ratio in the event of environmental contamination. Correction with an unadulterated isotope ratio is assured. Considering the nature of the urine sample and the problems that must be overcome for uranium accurate isotope ratio analysis with acceptable sample throughput, two sample preparation... 

Momoshima, N., Kakiuchi, H., Maeda,Y., Hirai, E., and Ono,T. (1997). Identification of the contamination source of plutonium in environmental samples with isotopic ratios determined by inductively coupled plasma mass spectrometry and alpha- spectrometry. J. Radioanal. Nucl. Chem. 222(1-2), 213. 

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