Trace determination and isotopic analysis of the elements in life sciences by mass spectrometry

The main ionization methods in a mass spectrometer for isotope ratio determinations of the elements are discussed in this review. These methods are thermal ionization, spark source, electron impact, inductively coupled plasma and field desorption. As concerns thermal ionization, electron impact and field desorption, a survey of the possibilities of isotope analyses in the periodic table of the elements is given. Besides kinetic studies, trace element determination by isotope dilution technique is the main application for isotope ratio measurements of the elements. The definitive method, isotope dilution mass spectrometry, is discussed as a potential tool for achieving accurate and precise trace analyses. Using field desorption mass spectrometry, one example of calcium kinetics in man and one example of thallium trace determination in an animal tissue are given. Other metal trace analyses with the isotope dilution technique are presented for biological and medical samples using positive thermal ionization mass spectrometry. Negative thermal ions are formed for the mass spectrometric analysis of non-metals and non-metal compounds in food samples, e.g. for iodine and nitrate in milk powder. Preliminary results with the isotope dilution technique are presented for a new quadrupole thermal ionization mass spectrometer which is a low-cost instrument and can be easily handled.