Abstract: An online pre-concentration and matrix separation procedure for the spectrophotometric determination of low levels of aluminum in aqueous and high-salt content matrices was developed. Aluminum was pre-concentrated 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 pre-concentration 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 x 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.

Abstract: A simultaneous separation and pre-concentration of lead, cadmium, zinc and copper from high-salt content matrices for subsequent electrothermal atomic absorption spectrometric determination was developed. The metals were pre-concentrated on a micro-column filled with polyethylene powder impregnated with the complexing agent 1-(2-pyridylazo)-2-naphthol. The determinations, without the interference of the saline matrix, were carried out after metals elution with a small volume of an ethanolic solution of nitric acid. The saline matrices were sodium, potassium, magnesium and calcium chlorides, sodium acetate and bicarbonate, which constitute concentrates for hemodialysis. The immobilization capacity of the complexing agent is about 2.5 µmol per gram of polyethylene and the column capacity with respect to each metal is about 0.75 µmol per gram resin for copper, cadmium and zinc and 0.25 µmol per gram for lead. For the optimization of the procedure, effects of sample flow rate and pH, eluent composition and concentration, and the influence of salts on the complexation of the metals were investigated. The proposed method was characterized by a precision of about 95% (n = 3) and recoveries from spiked samples of the salts were 81-112%. All results were in agreement with those obtained by anodic stripping voltammetry, the technique used for comparison. The method was applied to the analysis of saline concentrates for hemodialysis, where the investigated metals were found in concentrations between 3.1 µg L-1 for cadmium and 90.5 µg L-1 for zinc.