Determination of lead, cadmium, zinc, copper, and iron in foods by atomic absorption spectrometry after microwave digestion: NMKL1 collaborative study

A method for determination of lead, cadmium, zinc, copper, and iron by atom ic absorption spectrometry (AAS) after microwave digestion was subjected to a collaborative study in which 16 laboratories participated [including use rs of inductively coupled plasma (ICP) and ICP-mass spectrometry (MS)]. The types of samples included in the study were minced fish, wheat bran, milk powder, bovine and pig liver, mushroom, 2 simulated diets, and bovine muscl e; the last 4 were certified reference materials. These were analyzed as si ngle (4 samples), double blind (1 sample), or split level (2 samples) sampl es. Before the collaborative study, a pretrial was conducted in which 4 rea dy-made solutions and one fish tissue sample were analyzed for Pb and Cu. T he reproducibility relative standard deviation (RSDR) values, for results a bove the detection limit, ranged from 59% at 0.155 mg/kg to 16% at 1.62 mg/ kg for Pb, from 28% at 0.0124 mg/kg to 11% at 0.482 mg/kg for Cd, from 9.3% at 35.3 mg/kg to 1.7% at 147 mg/kg for Zn, from 39% at 0.241 mg/kg to 3.0% at 63.4 mg/kg for Cu, and from 17% at 7.4 mg/kg to 5.9% at 303 mg/kg for F e. The RSDR values agreed well with the norms described by the Internationa l Union of Pure and Applied Chemistry. As a complement to the AAS determina tions, a number of laboratories analyzed the samples either by ICP or by IC P-MS. The results of these analyses agreed well with the AAS results. On th e basis of the results of the collaborative study, the method was adopted O fficial First Action by AOAC INTERNATIONAL.