lsotopes are atoms of a specific element with different masses. In nature, most elements occur as mixtures of several stable isotopes in more or less constant proportions. Magnesium, e.g., consists of isotopes with masses 24, 25 and 26 amu (atomic mass units) in the ratio 79:10:11. Certain elements also occur as unstable (radioactive) isotopes.
Using ICP-MS, different isotopes of an element are always measured separately. The concentration can theoretically be calculated from any one of the element's isotopes, which enhances the reliability of the analysis.
The quantitative relationship of isotopes is measured between pairs of isotopes for a given element. ALS has access to multicollector technology (MC-ICP-MS) that gives very high precision (down to approximately 0.001% relative standard deviation) in isotope ratio measurements. This allows for, i.a., geological dating. ICP-SFMS gives a uncertainty down to approximately 0.05%. This uncertainty is enough to separate Pb from different sources by its natural variation in isotope composition for, e.g., toxicological investigations.
Trace Element Studies
Tracers are used for monitoring of chemical processes, mainly within biological and medical research. An element can be "marked" with an enriched stable isotope of that element for the purpose of studying its transformation and distribution in, e.g., organisms. The use of stable isotopes is preferred to the use of radioactive isotopes in these applications considering that they do not pose any radiation risks. For more on Trace Elements, click here.
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.