Determination of Trace and Ultratrace Elements in Human Serum With a Double Focusing Magnetic Sector Inductively Coupled Plasma Mass Spectrometer

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Abstract
The purpose of this study was to evaluate the potential of ICP-MS with a double focusing instrument for the determination of both spectrally and not spectrally interfered ultratrace elements in human serum after minimised sample pre-treatment and without using any separation or preconcentration techniques. Because of the heavy matrix (6–8% proteins and 1% inorganic compounds) of the material investigated, a higher resolving power than is available with quadrupole instruments was necessary for the determination of some elements in order to eliminate spectral interferences. This was achieved by using ICP-MS apparatus equipped with a double focusing magnetic sector MS. This type of instrument also permits lower detection limits when compared with traditional quadrupole ICP-MS instruments, mainly owing to the low instrumental background values. Determinations were carried out using external calibration and, for most of the elements, also single standard additions as calibration techniques. Both the non-spectrally interfered (Cd, Sn, Ag and U) and the spectrally interfered (Al, Si, P, S, Ti, Cr, Mn, Fe, Cu and Zn) elements were determined in a Second Generation Human Serum Reference Material. Sample preparation consisted in reconstitution of the freeze-dried material or in microwave digestion, both followed by dilution. In addition to continuous nebulization, flow injection was also applied as an introduction technique for the determination of some elements in reconstituted serum. The results for the certified elements were all within the certified range except for Cr for which a significantly higher value was obtained. The results of the remaining elements were compared with literature values where they existed. Very low concentrations could be determined: for instance a concentration as low as 98 ng l -1 was determined for Ag with a standard deviation of less than 10%. The major difficulty encountered in this study was to keep the blank values sufficiently low, which could only be achieved by using ultra-pure reagents and by working in a clean environment.

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