Element ratios tracer applications

The first ever application of a radiotracer in a biological experiment dates back to 1923 when George de Hevesy used Pb to study plant uptake of lead from solution [5]. His seminal work was honored by the Nobel Prize in Chemistry in 1943 and made him the father of isotope tracing, a tool that is still indispensable in virtually any area of scientific research. The first use of a stable isotope to study mineral metabolism was reported in 1963, when Lowman and Krivit injected stable Fe together with radioactive Fe into a human subject to compare the plasma clearance of the two isotopes [6]. However, it was not until the 1980s that stable isotope techniques were explored systematically to study mineral and trace element metabolism in humans. This was not only due to the increasing recognition of health hazards associated with the use of radioisotopes. Mass spectro-metric techniques had to be refined to measure isotope ratios of the heavier elements at a precision suitable for the exploitation of isotopically enriched elements as tracers. Stable isotopic labels are made up from the same isotopes as the natural element, from which they differ only in terms of composition, that is, in the relative abundances of their isotopes. 

It was detected by Urey, Brickwedde and Murphy in 1932. It occurs in all natural compounds of hydrogen including water, as well as in free hydrogen molecules at the ratio of about one part per 6,000 parts hydrogen. The principal application of deuterium is in tracer studies for measuring rates and kinetics of chemical reactions. It also is used in thermonuclear reactions and as a projectile in cyclotrons for bombardment of atomic nuclei to synthesize isotopes of several transuranium elements. Deuterium oxide, D2O, or heavy water is used as a neutron moderator in nuclear reactors. 

Murozumi et al. (9) determined the concentration of Pb in Greenland and Antarctic snow and ice by Isotope Dilution Mass Spectrometry (IDMS) (27). They added pure Pb tracer to their samples before chemically processing them. Both the mass of tracer and the water sample were measured. After thoroughly mixing the tracer with the sample Pb was isolated in a chemically pure form and the isotopic ratios were measured in a mass spectrometer. Simple comparison of the ° Pb abundance with the abundance of other isotopes in the mass spectrum allowed the amount of Pb in the sample to be determined. The technique is not limited to Pb, but is applicable to any element with two or more stable or... 

Dilution with stable isotopes offers the possibility of performing tracer experiments but also of circumventing systematic errors. The principle [518] can be applied for every element which has at least two stable or longlife isotopes. For its application the analyte with a known isotopic composition but which differs from that of the sample is added to a known amount of sample, and mixed thoroughly. The isotopic abundance ratio R then is given by ... 

A major attraction is the ability to perform isotope ratio measurements, e.g., in many geological applications to determine the age of rocks, biological and geological fractionation of elements, anthropogenic origin, stable isotope tracer studies, and isotope dilution analysis. In this respect, magnetic sector... 

Conventional applications of IDMS in quantitative elemental analysis usually involve the use of a single isotopically enriched tracer/spike. This is different in metabolic studies. The use of two or more tracers of the same element in parallel permits the use of more refined study designs and methodologies, as discussed later. When two isotopic labels X and Y are used in parallel [9], the tracer to tracee ratio for label Y in the sample can be calculated using... 

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