Binding patterns of co-existing aluminium and iron to human serum transferrin studied by HPLC-high resolution ICP-MS

Serum transferrin (Tf) is an iron-binding glycoprotein. Aluminium in the blood is bound to the transferrin. In the present study, the chemical forms of co-existing Al and Fe bound to human serum Tf were studied by combined on-line HPLC and high-resolution ICP-MS (HPLC-HR-ICP-MS). Samples were subjected to HPLC equipped with an anion-exchange column. The levels of Al-27, Fe-56 and S-32, which are interfered with by polyatomic ions such as (CN+)-C-13-N-14, (CN+)-C-12-N-15 and (CNH+)-C-12-N-14-H-1, (ArO+)-Ar-40-O-16 and (CaO+)-Ca-40-O-16, and O-16(2)+, respectively, when using quadrupole ICP-MS, were monitored simultaneously by HR-ICP-MS at a resolution of m/Deltam = 3000. Al added to apo-Tf as Al-citrate was preferentially bound to the N-lobe site almost selectively. Al in serum from a healthy person without any in vitro Al spike was present both as Al-N-Tf and Al-N,Fe-C-Tf. The chemical states were reproduced in the apo-Tf solution supplemented with Fe (Fe/Tf ratio = 0.6) and Al (Al/Tf ratio = 1) successively. The S-32 level was useful for monitoring the protein levels in the HPLC eluate. The clean-up column procedures employed reduced the detection limit for Al-27 to 0.1 mug l(-1) (3s(B)) at the middle resolution.