Determination of copper, nickel, and chromium in foods

A collaboratively studied method for Pb, Cd, As, Se, and Zn that uses a closed system digestion technique has now been extended to include 3 additional elements, Cu, Ni, and Cr. Cu is determined by either atomic absorption spectrophotometry or anodic stripping voltammetry, depending on the concentration. Ni and Cr are determined by differential pulse polarography. Analysis of National Bureau of Standards reference materials by this procedure gives values in close agreement with the accepted values. Recoveries from applesauce and chicken spiked at 0.6-4 micrograms/g are in the 92-101% range. The sensitivity of the multielement procedure is 0.34, 0.14, and 0.24 microgram/g for Cu, Ni, Cr, respectively, at the 90% confidence level.