On-line separation and spectrophotometric determination of low levels of aluminum in high-salt content samples: application to analysis of hemodialysis fluids

An on-line preconcentration and matrix separation procedure for the spectrophotometric determination of low levels of aluminum in aqueous and high-salt content matrices was developed. Aluminum was preconcentrated on polyethylene powder as a complex with Chrome azurol S and, after elution, the complex was spectrophotometrically determined, without interference of the matrix. The assayed salts were sodium, potassium, magnesium and calcium chlorides and sodium acetate, usually employed in hemodialysis fluids. A polyethylene powder column was incorporated to the flow system by using a microcolumn as the loop of a six-port valve connected to an injector and to the spectrophotometric detector. Effects of eluent composition and concentration, reactor length and influence of the presence of salts on the preconcentration and elution steps were investigated. The proposed method was characterized by a precision of about 90% and a detection limit of 17 ng Al (6×10−10 mol). Recoveries from spiked samples of the salts were between 87–110%, and results were in agreement with determinations by graphite furnace atomic absorption spectrometry. The method was applied to the analysis of saline concentrates and water for hemodialysis.