Quantitative determination of trace amounts of Al-citrate by anion-exchange FPLC-ETAAS

An anion-exchange fast protein liquid chromatographic-electrothermal atomic absorption spectrometric procedure (FPLC-ETAAS) was developed for determination of trace amounts of negatively charged Al-citrate in the pH range 3.5-8.0. Aqueous-4 mol dm(-3) NH4NO3 linear gradient elution at a flow rate of 1 cm(3) min(-1) was applied for 10 min to separate Al-citrate on a FPLC Mono Q HR 5/5 column. The separated aluminium species were determined 'off line' by ETAAS in 0.5 cm(3) fractions. After separation the column was regenerated for 5 min with 4 mol dm(-3) NH4NO3 and equilibrated with water. All reagents used in the separation procedure were cleaned with a silica based LiChrosorb RP-18 HPLC column to remove traces of aluminium. The main advantage of NH4NO3 as eluent lies in its ability to decompose quantitatively in the graphite tube during the ashing sti-p, which enables reproducible analysis of aluminium in the separated fractions. Using the procedure developed reproducible (RSD +/- 2.0%) and quantitative determination of negatively charged Al-citrate at a retention time of 4.5 min was obtained. The LOD was found to be 2.0 ng cm(-3) of Al-citrate. The technique was successfully applied for the determination of Al-citrate in human serum. Spiked samples (50-150 ng Al3+ cm(-3)) were microultrafiltered through a membrane filter (cut-off 30000 Da) to separate aluminium bound to transferrin from low molecular weight aluminium complexes. It was found that 15-19% of aluminium in spiked samples from healthy volunteers passed through the membrane. By applying FPLC separation it was proved that all the aluminium in the filtrate corresponded to Al-citrate. The analytical technique developed enabled quantitative and reproducible determination (RSD +/- 3.0%) of Al-citrate in spiked human serum at levels which could be found in patients undergoing long term haemodialysis. (C) 1998 Elsevier Science B.V. All rights reserved.