Environmental science isotope ratio measurements

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... 

Accurate mass measurement of atoms and molecules Structure analysis of organic compounds Quantitative analysis of inorganic and organic compounds Fundamentals of gas-phase ion chemistry Measurement of physical properties of ions Elemental analysis Precise isotope ratio measurements Environmental science ... 

Isotope dilution mass spectrometry (ID-MS) is widely accepted as a quantification procedure of proven accuracy in elemental analysis and isotope ratio measurements [4]. Several areas of research in nuclear science, geochronology, medicinal chemistry, environmental science, and agricultural science have benefited from this technique. ID-MS is applicable to all elements that have at least two stable isotopes. Monoisotopic elements can be analyzed only if they have a long-lived natural or artificial radioisotope. For example, iodine and thorium have been determined with spikes of the long-lived isotopes 29i and 25 Th, respectively [44]. TI-MS and ICP-MS are the methods of choice for accurate ID-MS analysis. ICP-MS has the advantage that several elements can be analyzed simnltaneously under the same experimental conditions. Other ionization techniqnes discussed in this chapter have also been coupled with ID-MS. 

Elements in nature come in forms called isotopes that differ only in the number of their neutrons. Most isotopes are stable and can be distinguished from their counterparts simply by their masses. Remarkably, isotopes are associated with a few simple and mass-dependent traits that result in a wide range of useful isotopic signals in natural processes. Coupled with the invention of the isotope ratio mass spectrometer in 1940s (McKinney et al., 1950 Nier, 1947) stable isotope signals provide the basis for application of stable isotopes to environmental sciences. Stable isotopes are denoted by their atomic mass such as and for the two stable isotopes of carbon, and 0, and for the stable isotopes of oxygen. Because the heavy isotope is normally rare (e.g., -1.1% for i c, 0.2% for 0, and 0.04% for O), routine measurements of the absolute isotopic concentrations is difficult and not reliable. Alternatively, the ratio, R, of the rare to the abundant isotopes is measured, such as... 

Lead isotope ratios can provide analytical information about sources of lead contamination whereas lead concentration measurements cannot. Due to this fact, studies of the isotopic composition of lead are commonly used in environmental science as well as in geological and anthropological studies. Among all of the naturally occurring lead isotopes only °" Pb is nonradiogenic, whereas ° Pb, ° Pb, and ° Pb are daughter products from the radioactive decay of and Th, respectively. This fact... 

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