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 27Al, 56Fe and 32S, which are interfered with by polyatomic ions such as 13C14N+, 12C15N+ and 12C14N1H+, 40Ar16O+ and 40Ca16O+, and 16O2+, respectively, when using quadrupole ICP-MS, were monitored simultaneously by HR-ICP-MS at a resolution of m/Δm = 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 AlN-Tf and AlN,FeC-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 32S level was useful for monitoring the protein levels in the HPLC eluate. The clean-up column procedures employed reduced the detection limit for 27Al to 0.1 μg l–1 (3sB) at the middle resolution.