USE OF INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY FOR THE DETERMINATION OF ULTRA-TRACE ELEMENTS IN HUMAN SERUM

A method for the determination of 11 ultra-trace elements (Li, B, Mo, Cd, Sn, Sb, Cs, Ba, Hg, Pb and Bi) in human serum by inductively coupled plasma mass spectrometry is described. Sample preparation was kept to a minimum: serum samples were diluted 5-fold with 0.14 mol l-1 HNO3 and suitable internal standards (Be, In and TI) were added to correct for matrix effects and for ion signal instability. Special attention was given to optimization of the electrostatic lens settings and the nebulizer gas flow rate. Detection limits between 0.007 ng ml-1 (for Bi) and 0.5 ng ml-1 (for B) could be obtained, taking into account a 5-fold dilution of the serum sample, Memory effects, which can be experienced with the conventional methodology for sample introduction, leading to positive errors, were reduced to a negligible level by the use of a short (2 min) clean-out procedure. With the exception of B (1-2 ng ml-1) and Pb (0.08-0.15 ng ml-1) blank levels were shown to be below 0.1 ng ml-1. Results are given for a 'second-generation' biological reference material Freeze-Dried Human Serum (University of Ghent) and for Human Serum SRM 909 from the National Institute of Standards and Technology (for Li, Cd and Pb). Finally, serum samples from healthy individuals were analysed in order to determine typical element concentrations for normal human serum.