Graphite-furnace atomic absorption spectrometric determination of lead, cadmium, cobalt and nickel in infant formulas and evaporated milks after nitric-perchloric acid digestion and coprecipitation with ammonium pyrrolidine dithiocarbamate.

A graphite-furnace atomic absorption method, developed for lead and cadmium, was modified to enable simultaneous determination of lead, cadmium, cobalt and nickel in infant formulas and evaporated milks. The method was assessed on the basis of analytical quality assurance results during routine analysis of samples. Detection limits (ng g-1 based on 10 g sample size for ready-to-use formulas) were 0.04-0.21 for lead, 0.004-0.015 for cadmium, 0.04-0.2 for cobalt and 0.06-0.26 for nickel. Within-series repeatability and day-to-day reproducibility (among series) coefficients of variation (CVs) were, respectively, 11.7 and 16% for lead, 2.5 and 7.5% for cadmium, 7.2 and 18.8%for cobalt, and 8.1 and 8.6% for nickel at respective concentrations of 1.89, 0.40, 1.25 and 11.8 ng g-1.