High-sensitivity methods for sequential injection determination of the main constituents of alloys Original Research Article

A sequential injection system with spectrophotometric detection was proposed for the determination of copper, zinc and lead in brass. In view of the high analyte concentrations and the sensitivity of the involved catalytic methods, optimization of the flow system was carried out aiming mild reaction conditions. Copper and lead determinations were based on the catalytic effects of Cu2+ and Pb2+ on the oxidation rates of resorcinol and pyrogallol red by H2O2, respectively, and zinc determination involved precipitate formation after oxidation of 1-nafthylethylenediamine by K3Fe(CN)6. The analytical procedures were designed with some common parameters such as pH=9.0 (borate system), λ=530 nm, and H2O2 as oxidizing agent; system geometry was maintained. The proposed system is rugged, and base line drift is not observed during 4 h operation periods. Twenty samples are run per hour (60 determinations) and reagent consumption is minimal, thus avoiding drawbacks related to waste management. Precise results (R.S.D.<1.0%; n=7) are obtained and a detection limit of 1% (w/w) was estimated for the three analytes. Results were in agreement with flame atomic absorption spectrometry.