DIRECT DETERMINATION OF COPPER AND ZINC IN COW MILK, HUMAN-MILK AND INFANT FORMULA SAMPLES USING ELECTROTHERMAL ATOMIZATION ATOMIC-ABSORPTION SPECTROMETRY

Infant formula and powdered milk samples were suspended in a medium co ntaining 20% ethanol, 0.65% nitric acid, 6% hydrogen peroxide and 0.1% ammonium dihydrogenphosphate and directly introduced in the electroth ermal atomizer. Liquid milk samples were diluted with this suspension solution. The build-up of carbonaceous residues inside the atomizer wa s avoided by using a combination of hydrogen peroxide and nitric acid. Fast programs were used to simplify the heating cycles. Calibration w as carried out using aqueous standards and the detection limits for co pper and zinc were found to be 70 and 15 pg, respectively. The metal c ontents of several milk samples obtained by direct introduction of the samples agree with those obtained by means of a conventional procedur e based on the total dissolution of the samples. The reliability of th e methods was also confirmed by analyzing three certified reference ma terials. The free and protein binding fractions were measured by ultra filtration membrane permeability of the milk samples. (C) 1998 Elsevie r Science B.V. All rights reserved.