Role of inductively-coupled plasma-mass spectrometry (ICP-MS) in the assessment of reference values for ultra-trace elements in human serum

Inductively coupled plasma mass spectrometry (ICP-MS) was used for the determination of ultra-trace elements in normal human serum. To avoid contamination, sample preparation was kept to a minimum: serum samples were diluted 5-fold with 0.14 mol/l HNO3 and suitable internal standards (Be, In and Tl) were added to correct for matrix effects (serum) and for ion signal instability. Taking into account a 5-fold dilution of the serum sample the detection limits vary from 0.007 ng/ml (for Bi) to 0.5 ng/ml (for B). To check the accuracy of the method a ''second-generation'' biological reference material freeze-dried human serum (University of Ghent) was analyzed. Accurate results could be achieved for 10 ultra-trace elements: Li, B, Mo, Sn, Sb, Cs, Ba, Hg, Pb and Bi. As an application, serum samples from 21 apparently healthy adults were analyzed. Special attention was given to the sampling protocol of the blood in order to avoid significant contamination at the sampling stage. The following results were obtained: Li: 0.60 ng/ml (0.25 - 0.87 ng/ml), B: 13.9 ng/ml (4.1 - 25.8 ng/ml), Mo: 0.61 ng/ml (0.30 - 0.86 ng/ml), Sn: 1.02 ng/ml (0.66 - 1.46 ng/ml), Sb: 0.137 ng/ml (0.095 - 0.165 ng/ml), Cs: 0.70 ng/ml (0.50 - 0.96 ng/ml), Ba: 1.04 ng/ml (0.23 - 2.35 ng/ml), Hg: < 0.20 - 1.35 ng/ml, Pb: < 0.10 - 0.71 ng/ml, Bi: < 0.007 - 0.067 ng/ml. These results were compared with data published in the literature. It turns out that for elements like Li, Sn, Ba and Bi some (for Li and Sn) or all (for Ba and Bi) of previously reported data are markedly higher than the results obtained in this study