A modified FIA system for the determination of high levels of quickly reacting aluminium in aqueous solutions

We have modified Clarke et al.'s (1992) flow injection system for determining 'quickly reacting Al' (Al-qr) in natural waters, to make it applicable also to solutions having high (> 1 mM) aluminium concentrations. By decreasing the flow rate of the carrier stream, thus diluting the sample on-line, and using a very small injection volume (12 mu l), the upper end of the linear range has been increased from 2 mg Al/l to at least 30 mg/l. Good repeatability (RSD approximate to 1-3%, n = 4) was obtained, both for standard solutions and for natural waters. The quantification limit was about 100 mu g/l and the sample throughput ca. 120 injections/h. Validation with synthetic model systems (Al plus F and Al plus citrate) showed that the modified set-up gave a fractionation similar to the one of Clarke et al.'s original system. The modified set-up was also tested on soil solutions, having Al-qr concentrations in the range of 0.1 to 1.5 mM. The sensitivity to iron interference was largely reduced by the modification. However, determining Al-qr in samples from real rat stomachs, having both high Fe(III) and protein concentrations, caused an interference from Fe(III) at concentrations lower than for standard solutions.