Application of liquid chromatography inductively coupled plasma mass spectrometry to the study of protein-bound lead in human erythrocytes

The coupling of gel chromatography to ICP-MS was evaluated as a tool for the study of lead bound in vivo to proteins in erythrocytes. The chromatogram obtained showed three peaks for lead at apparent molecular masses of 240, 45 and < 10 kDa. The height of the third peak, at < 10 kDa, varied considerably on repeated analysis, probably due to interactions with the column material. However, the third peak did not affect the size of the other two peaks, and was therefore excluded from the calculations. The protein with an apparent molecular mass of 240 kDa contained approximately 80% of the protein-bound lead recovered, and may be identical with the enzyme delta-aminolevulinic acid dehydratase (ALAD). The 45 kDa peak contained 20% of the protein-bound lead recovered. It had an elution volume that was similar to, but not identical with, that of iron from hemoglobin, indicating binding to another protein of similar mass, e.g., the ALAD monomer or pyrimidine-5-nucleotidase. The recovery from the column, with the third peak excluded, was 74% for samples from occupationally exposed lead workers and 118% for samples from unexposed workers. The detection limit (twice the baseline noise) was 0.04 ng, corresponding to a blood-lead concentration of 0.01 mu mol l(-1); however, variations in recovery at low blood-lead levels suggest that the method is, so far, best suited to samples from individuals with elevated blood-lead concentrations, e.g., lead-exposed workers.