QUANTITATIVE-DETERMINATION OF TRACE AMOUNTS OF AL-CITRATE BY ANION-EXCHANGE FPLC-ETAAS

An anion-exchange fast protein liquid chromatographic-electrothermal a tomic absorption spectrometric procedure (FPLC-ETAAS) was developed fo r determination of trace amounts of negatively charged Al-citrate in t he pH range 3.5-8.0. Aqueous-4 mol dm(-3) NH4NO3 linear gradient eluti on at a flow rate of 1 cm(3) min(-1) was applied for 10 min to separat e Al-citrate on a FPLC Mono Q HR 5/5 column. The separated aluminium s pecies were determined 'off line' by ETAAS in 0.5 cm(3) fractions. Aft er separation the column was regenerated for 5 min with 4 mol dm(-3) N H4NO3 and equilibrated with water. All reagents used in the separation procedure were cleaned with a silica based LiChrosorb RP-18 HPLC colu mn to remove traces of aluminium. The main advantage of NH4NO3 as elue nt lies in its ability to decompose quantitatively in the graphite tub e during the ashing sti-p, which enables reproducible analysis of alum inium in the separated fractions. Using the procedure developed reprod ucible (RSD +/- 2.0%) and quantitative determination of negatively cha rged Al-citrate at a retention time of 4.5 min was obtained. The LOD w as found to be 2.0 ng cm(-3) of Al-citrate. The technique was successf ully applied for the determination of Al-citrate in human serum. Spike d samples (50-150 ng Al3+ cm(-3)) were microultrafiltered through a me mbrane filter (cut-off 30000 Da) to separate aluminium bound to transf errin 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 a ll the aluminium in the filtrate corresponded to Al-citrate. The analy tical technique developed enabled quantitative and reproducible determ ination (RSD +/- 3.0%) of Al-citrate in spiked human serum at levels w hich could be found in patients undergoing long term haemodialysis. (C ) 1998 Elsevier Science B.V. All rights reserved.