Use of Multivariate Optimization to Develop Methods for Direct Copper and Lead Determination in Breast Milk by Graphite Furnace Atomic Absorption Spectrometry

A direct method for lead and copper determination in breast milk by graphite furnace atomic absorption spectrometry, using aqueous calibration, was proposed in this study. Samples were diluted with hydroximethylaminomethane 80 % v/v, pH 8. The dilution determination for Pb and Cu was 1:1 and 1:9, respectively. Fractional factorial (24−1) and central composite designs were used to optimize experimental conditions (pyrolysis and atomization temperatures, pyrolysis time, and modifier) using 10 μL samples introduced into a graphite furnace. The methods allowed for copper and lead determination under optimized conditions with an aqueous calibration curve between 0 and 180 μg L−1 for Cu and 0 and 48 μg L−1 for Pb. The detection limits were 0.92 μg L−1 and 6.4 μg L−1 for Pb and Cu, respectively. Intra and inter-assay studies revealed coefficients of variation of 5.0 and 6.3 %, and 6.4 and 5.5 % for Pb and Cu, respectively. Recovery studies at three concentration levels (three consecutive days, n = 7/day) presented results between 107 and 109 % for Pb and 102 and 103 % for Cu. Good accuracy was obtained for both metals through recoveries studies using certified reference material (infant formula NIST® 1846). The method determined lead and copper in six samples and the concentrations ranged from 2.90 to 27.9 μg L−1 for Pb and 384 to 1,212 μg L−1 for Cu. While copper is an essential element, lead has no nutritional function and is cumulative at low concentrations. Therefore, safe, efficient, and validated methods should be available to determine its concentration in breast milk.