We studied plasma and serum samples from twelve healthy subjects. Blood samples were
collected via venous drainage phlebotomy with and without vacuum into trace metal free tubes
containing no anticoagulants (serum), or lithium heparin, or EDTA (to obtain plasma). Variable sample
standing times (0, 5, and 30 min) prior to centrifugation were allowed. Plasma and serum Pb and iron
concentrations were determined by inductively coupled plasma mass spectrometry. Plasma and serum
cell-free hemoglobin concentrations were measured.