Technical and clinical aspects of spectrometric analysis of trace elements in clinical samples.
The capabilities of ICP-MS far exceed the slow, single-element analysis of GFAAS for determination of multiple trace elements. Additionally, its sensitivity is superior to that of DCP, ICP, and FAAS. The analytic procedure for ICP-MS is relatively straightforward and bypasses the need for digestion in many cases. It enables the physician to identify the target trace element(s) in intoxication cases, nutritional deficiency, or disease, thus eliminating the treatment delays experienced with sequential testing methods. This technology has its limitations as well. The ICP-MS cannot be used in the positive ion mode to analyze with sufficient sensitivity highly electronegative elements such as fluorine, because F+ is unstable and forms only by very high ionization energy. The ICP mass spectrometers used in most commercial laboratories utilize the quadrupole mass selector, which is limited by low resolution and, thus, by the various interferences previously discussed. For example, when an argon plasma is used, selenium (m/e 80) and chromium (m/e 52) in serum, plasma, and blood specimens are subject to polyatomic and molecular ion interferences. Low-resolution ICP mass spectrometers can therefore be used to analyze many trace elements, but they are not universal analyzers. High-resolution ICP-MS can resolve these interferences, but with greater expense. With the advent of more research and development of new techniques, some of these difficulties may be overcome, making this technique even more versatile. Contamination during sample collection and analysis causes falsely elevated results. Attention and care must be given to avoid contamination. Proper collection devices containing negligible amounts of trace elements should be used. Labware, preferably plastic and not glass, must be decontaminated prior to use by acid-washing and rinsed with [table: see text] de-ionized water. A complete description of sample collection and contamination has been written by Aitio and Jarvisalo as well as by Chan and Gerson. Lutz et al observed the ranges in blood shown in Table 4. We have adopted the ranges listed in Table 5 in urines of healthy, ambulatory, and community-dwelling individuals through a limited in-house study and review of literature. In conclusion, differentiation of trace element abnormalities (primary intoxication or disease versus secondary underlying disease) can be made only by utilizing results from trace element analyses in clinical specimens, medical history, and careful observation of symptoms. Repeat analysis on a second specimen collection is recommended when contamination is suspected.