MANGANESE AND ZINC ANALYSIS IN MILK BY MICROWAVE-OVEN DIGESTION AND PLATFORM GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

A conventional microwave oven acid digestion system employing PTFE reactors was tested for sample digestion prior to the analysis of Mn and Zn in milk. The digestion procedure was based on sample dissolution with nitric acid using microwave heating in closed vessels. Sample treatment time in the microwave oven was reduced to 15 min. The resulting solutions, analyzed for Zn by name atomic absorption spectrometry (FAAS) and by platform graphite furnace atomic absorption spectrometry with Zeeman background correction for Zn and Mn, showed good agreement with the certified milk values (SRM-1549 nonfat milk powder, National Institute of Standards and Technology), and results were comparable to those obtained by dry mineralization in real samples. The precision of the method was about 6% for Mn and 5% for Zn by graphite furnace atomic absorption spectrometry (GFAAS) with limits of detection of 0.07 and 0.28 mu g L(-1), respectively. The digestion procedure can be used to determine Zn by FAAS and Mn by GFAAS in milk analysis. Using GFAAS, Zn can also be measured in milk fractions where it is found in smaller concentrations.