Spectrophotometric determination of trace aluminium content in parenteral solutions by combined cloud point preconcentration–flow injection analysis

Abstract

A cloud point preconcentration and flow injection (FI) analysis methodology for aluminium(III) determination has been developed. The analyte in the initial aqueous solution was complexed with Chrome Azurol S (CAS) in the presence of the cationic surfactant benzyldimethyltetradecylammonium chloride (BDTAC). The absorption spectroscopic characteristics of the ternary complex [Al(III)–CAS–BDTAC] were examined in detail. The preconcentration step was carried out by means of the non-ionic surfactant polyethylene glycol p-nonylphenyl ether (PONPE 7.5). The enriched analyte solution was injected into an FI system using an HPLC pump. The chemical variables affecting the analytical performance of the combined methodology were studied and optimised. The developed approach was successfully applied to the determination of trace amounts of aluminium in parenteral solutions without previous treatment. Under the optimum experimental conditions, 99.9% extraction was achieved for a preconcentration factor of 50. The limit of detection was 1.12 × 10⁻⁷ mol l⁻¹. The calibration plot was linear over at least two orders of magnitude of aluminium concentration. The developed coupled methodology, which thoroughly satisfies the typical requirements for pharmaceutical control processes, is appropriate for monitoring the aluminium concentration in parenteral nutrition.