Determination of Fe, Cu, Ni, and Mn in fats and oils by flameless atomic absorption spectroscopy

Abstract

The determination of Fe, Cu, Ni, and Mn is performed by flameless atomic absorption spectroscopy. The procedure is applicable to oils, including crudes, and also fats such as hydrogenated oils. A solution of the sample is analyzed directly, and absorbance values are compared to standards. Matrix-matching is not required, and virtually any concentration of metal can be analyzed since both sample concentration and aliquot volume are variable. Solvent selection is based on the results of a stability study and includes methyl isobutyl ketone (MIBK) for Cu and Mn determinations and MIBK with a small amount of HNO₃ added for Fe and Ni. Sensitivity approximated 80 picograms for Fe, 100 pg for Cu, 525 pg for Ni, and 30 pg for Mn. Absorbance values of appropriate aliquots, each having the equivalent of 0.10 ppm Fe, are compared to determine the effect of variation of pipette size on response. Pipette size ranged from 5 µl to 50 µl. Responses using multiple 50 µl volumes are also recorded. Sources of error in procedure, error analyses, and proper pipetting technique are given.