Direct determination of selenium and other trace elements in serum samplesby ICP-MS

Selenium belongs to a group of trace elements of special interest in biolog ical samples for clinical diagnosis. Selenium has antioxidizing functions a nd is essential for providing the organism with triiodothyronine produced f rom thyroxine. Among several analytical techniques used to determine the Se concentration in serum, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has been us ed in the past because of its high sensitivity. Interference problems origi nating from different ions on the major Se isotopes have been described to be a limiting factor for the direct determination of Se in these matrices. Standard addition calibration or isotope dilution is often required to over come carbon-enhanced ionisation effects in biological sample matrices. In m ost cases, the typical serum sample volume which is available for the analy sis is limited to 0.5 mi or less, making multiple sample preparation for st andard addition calibration impractical. Isotope dilution requires enriched isotopes and substantial sample preparation. Furthermore, the approximate Se concentration in every sample has to be known to adjust the appropriate amount of spike to each sample. Matrix matching with methanol has been desc ribed to overcome ionisation effects but we found limiting factors of this application when other trace elements are also determined within one sample run. This paper describes an effective sample preparation method which allows th e direct determination of Se in serum without limiting the analytical capab ilities for the additional determination of Al, Cu, Ni, Co, Cd; Mn and Zn i n a single sample run by ICP-MS. Optimization procedures are presented and results of the analysis of reference samples are discussed, with a comparis on of more than 150 serum data with those obtained by the GFAAS method.