Indirect determination of aluminum (III) in water samples by in-electrode coulometric titration

Abstract

A new procedure has been developed for indirect determination of aluminium(III) in water through in-electrode coulometric titration in a porous reticulated vitreous carbon electrode. It was determined through different aluminium fluoride and ferric fluoride complex stabilities. The ferric fluoride complex thereby formed was decomposed with Al(III) from the sample and an aliquot of the released Fe(III) was determined electrochemically. It was measured with an EcaFlow GLP 150 electrochemical flow analyser, while 0.2 mol L−1 sodium chloride solution was used as the electrolyte to flush the system. Calibration solutions and samples were modified in a mixed solution medium of 0.2 mol L−1 NaCl + 10 mg L−1F(I-) + 10 mg L−1Fe(III). All working parameters for electrochemical determination were optimised. The detection limit and precision were found to be 0.02 mg L−1 and 1.9% respectively. The linear concentration range was 0.05 – 8.5 mg L−1 of aluminium. After having been complexed with sodium cyanide, the iron’s interference effect was suppressed by removing it with an ion-exchange resin. Among the other influences studied, only the interference from thorium, zirconium and cerium was significant. The method was applied for the analysis of various water samples. The results were in good agreement with data from high resolution atomic absorption spectrometry.