Enriched stable isotopes of elements used as tracers: methods of presenting high-performance liquid...

High-performance liquid chromatography (HPLC) of biological fluids and tissue cytosolic preparations was employed in conjunction with argon-induced inductively coupled plasma mass spectrometry (ICP-MS) to investigate the distribution of stable isotopes as tracers. The common way of presenting the data from the ICP-MS is by plotting the count rates versus the retention time of HPLC fractions. Additional information can be derived, e.g., the composite peaks can be further resolved, and the level of enrichment in various biological components can be expressed by alternative ways of presenting these data. The two additional approaches described here involve presenting the ratios of enriched tracer with a suitable naturally abundant mass number of the same element, and by expressing the extent of enrichment by the tracer isotope in a given fraction to that of the same mass number in the fraction derived from an untreated source. Each method of presentation has different merits and drawbacks. The data therefore may be best presented in more than one way to emphasize the conclusions from a given experiment. Observations are presented after simultaneously injecting stable isotopes of three essential elements, copper, selenium and zinc, into mice. Plasma and liver cytosolic fractions were analysed and data represented in different ways as indicated above.