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

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 Cu 2+ and Pb 2+ on the oxidation rates of resorcinol and pyrogallol red by H 2O 2, respectively, and zinc determination involved precipitate formation after oxidation of 1-nafthylethylenediamine by K 3Fe(CN) 6. The analytical procedures were designed with some common parameters such as pH=9.0 (borate system), λ=530 nm, and H 2O 2 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.