Aluminium and silicon speciation in human serum by ion-exchange high-performance liquid chromatography–electrothermal atomic absorption spectrometry and gel electrophoresis

Abstract

Speciation of aluminium and silicon in serum was studied by a reliable and sensitive high-performance liquid chromatographic–electrothermal atomic absorption spectrometric (HPLC–ETAAS) hybrid method, based on the use of a polymeric anion-exchange column (Protein-Pak DEAE-5PW). This polymer-based column minimizes the risk of aluminium losses and of silicon contamination from the column during separation. The results obtained were compared with the results of previous studies carried out using different, complementary techniques including ultramicrofiltration, gel filtration and a silica-based column for HPLC. In order to ascertain which protein(s) of serum actually bind(s) aluminium, gel electrophoresis was employed for the further separation of the column fractions obtained by HPLC and aluminium was determined in separate aliquots of the same fractions. From all the experiments, it appears that transferrin (Tf) is the only serum protein that binds aluminium and it contains about 90% of total serum aluminium. It was also confirmed that in the presence of desferrioxamine (DFO), aluminium is partly displaced from its complex with transferrin to a low molecular mass Al–DFO complex. Aluminium citrate seems to be the main low molecular mass aluminium species in serum, amounting to about 12 ± 5% of the total aluminium in an aluminium-loaded serum sample. The proposed speciation procedure permits the simultaneous identification and determination of three aluminium species in metal-spiked serum (Al–Tf, Al–DFO and Al–citrate). The results for silicon suggest that it seems to be unspecifically adsorbed to several serum proteins and its speciation is not affected by the presence of DFO. Moreover, no evidence was found to confirm possible interrelations between aluminium and silicon species in serum to justify significant aluminosilicate formation in human serum.