DETERMINATION OF MAJOR MINERALS IN DAIRY-PRODUCTS DIGESTED IN CLOSED VESSELS USING MICROWAVE-HEATING

A method is described for digestion of a variety of solid dairy produc ts (cheeses, caseinates, and milk powders) for subsequent determinatio n of Ca, Mg, Na, and K by flame atomic spectrophotometry. Sample prepa ration included a microwave digestion system in closed vessels. The pr ocedure has been validated for skim milk powder employing various reac tion mixtures that contain HNO3, HClO4, and H2O2. Accurate results wer e achieved for Na and K with mixtures of HNO3 and H2O2, but values for Ca and Mg were low. Although the results of these elements were impro ved when HClO4 was used instead of HNO3, greatest accuracy was obtaine d by measurement, using standard addition, of samples digested with mi xtures of HNO3 and H2O2. The assays exhibited varying degrees of preci sion when used for caseinates and cheese. The coefficients of variatio n for replicate analyses of caseinates and cheeses were lowest for Mg( 1.34 to 2.46%) and Ca (1.15 to 2.69%) and poorest for Na (3.35 to 9.02 %). However, accuracy was greater for Na and K analyses; recoveries of these elements were very close to 100% (Na, 96.3 to 99.2%; K, 97.8 to 99.8%) but recoveries of Ca and Mg were lower (Ca, 91.6 to 98.8%; Mg, 94.0 to 98.4%).