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A number of minerals contained in foods are essential nutrients for humans, animals, and/or plants. While most vitamins are very well absorbed, most essential minerals are not. Usual absorption of minerals ranges from less than 1% to over 90%. The bioavailability of dietary minerals must be considered when determining whether the diet contains enough, too little, or too much. By using stable isotope tracers as labels, the metabolic fate of minerals in a specific day's diet, a specific meal, or a food can be distinguished from minerals from other sources and followed. A number of mass spectrometric methods have been used to measure stable isotopes. Magnetic sector, thermal ionization mass spectrometry (TIMS) is used routinely in our laboratory to study bioavailability of Zn, Cu, and Fe. Other mass spectrometric methods that are less precise, but useful for many applications requiring isotopic determinations include quadrupole TIMS, inductively coupled plasma mass spectrometry (ICP/MS), and fast atom bombardment mass spectrometry (FAB/MS). One of the major advantages of stable isotope studies is that multiple isotopes of the same mineral can be used simultaneously and multiple minerals can be studied simultaneously. The use of stable isotopes for studies of bioavailability of minerals in foods has gained widespread interest in recent years. The approach is expected to be applied to an increasing number of food science and nutrition problems in the future.
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PMID:Bioavailability of dietary minerals to humans: the stable isotope approach. 191 May 21

Enriched fecal and urine samples were prepared using ion-exchange column chromatography for analysis by Inductively Coupled and Fast Atom Bombardment Mass spectrometry (ICP-MS, FAB-MS) to compare precision between methods. Unenriched samples of human milk, feces, and whole blood were prepared similarly to monitor instrumental precision and analytical error. A least squares fit of the ICP-MS results vs the FAB-MS for 70Zn/64Zn gave a slope of 0.98, with a relative standard deviation (RSD) of only 0.7%. The results for 68Zn/64Zn gave a slope of 0.82, with a RSD of 14%. For unenriched tissues, all potential interferences were removed by the preparation procedure with no significant differences between preparation for isotope ratios of 70Zn/64Zn, 68Zn/64Zn, 67Zn/64Zn, and 66Zn/64Zn. Poisson counting statistics are a major contribution to the total analytical error indicating the usefulness of this procedure for enrichment studies.
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PMID:Determination of isotope ratios in human tissues enriched with zinc stable isotope tracers using inductively coupled plasma-mass spectrometry (ICP-MS). 768 26

Thermal ionization mass spectrometry (TIMS) is the best of four currently used techniques for obtaining results of high accuracy and precision in studies of metal metabolism. TIMS is also the most general technique because it allows measurements of all the metallic elements of interest. The highest absolute sensitivity as well as the ability to determine multiple elements are simultaneously obtained with inductively coupled plasma mass spectrometry (ICP-MS). Current results with this technique show that, although element quantification may be done with acceptable accuracy and precision, use of ICP-MS in metabolic studies at low levels of isotopic labels may be limited. The most favorable elements for study using ICP-MS in metabolic studies appear to be Mg, Zn and possibly Fe. Use of this technique is limited further by isobaric interferences from plasma jet ion molecule reactions, and metabolic studies of Ca are particularly limited. Acceptable levels of accuracy and precision have been obtained from fast atom bombardment-secondary ion mass spectrometry (FAB-SIMS), which has allowed these approaches to be used in metabolic studies of ZN, Fe and Ca, but the approaches are ultimately limited by hydride isobaric interferences. Both FAB-SIMS and gas chromatography-mass spectrometry of metal chelates have the advantage of using widely available instrumentation. GC-MS of metal chelates has been shown to be useful in studies of Cr and Se metabolism and for the determination of a number of other metals. Values of accuracy and precision from use of this approach have been satisfactory.
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PMID:Analytical instruments for stable isotopic tracers in mineral metabolism. 855 22