iSOTOPE ANALYSIS OF CLINICAL SAMPLES
Isotopes are atoms of a specific element that have different masses. In nature, most elements occur as a mixture of several so-called stable isotopes in more or less constant proportions. For example, magnesium with masses 24, 25 and 26 amu (units of mass) in the proportions 79:10:11. Certain elements also occur as unstable (radioactive) isotopes.
In analyses using ICP-MS, different isotopes of an element are always measured separately. The concentration can in principle be calculated from any one of the element's isotopes, which enhances the reliability of the analysis.
The quantitative relationship of isotopes (calculated by the number of atoms) is measured between pairs of isotopes for a given element. ALS Scandinavia has access to a multicollector ICP-MS for high precision isotope ratio measurements (down to 0.001% relative standard deviation), which enables, e.g., geological dating. The precision of isotope ratio analyses by ICP-SFMS is under optimal conditions better than 0.05% relative standard deviation. This is not as good as for MC-ICP-MS, but still sufficient to separate lead from different sources, e.g. in toxicological investigations, by the natural variation in isotope composition.
Tracers are used primarily in biological and medical research. An element can be "marked" by means of a stable, enriched isotope of that element for the purpose of studying the uptake and distribution of the element in an organism. Here stable isotopes are an attractive alternative to radioactive isotopes since they carry no risk of radiation.
Isotope dilution is a sophisticated method for quantitative analysis of elements. After "spiking" the sample with a stable enriched isotope of an element, the original concentration of that element can be calculated from the measured change in one or more isotope ratios. Isotope dilution has several advantages over conventional quantitative analyses and generally provides greater accuracy.