Determination of lithium content of infant formulas by flame photometry

Abstract

The lithium content of infant formulas available in Japan was determined by flame photometry using an atomic-absorption spectrophotometer with an air-acetylene flame. Formula samples were decomposed by heating with a nitric-perchloric acid mixture, concentrated until almost dryness, and then diluted with a 0.1 mol/1 hydrochloric acid solution. It was confirmed by a standard addition method that lithium was little interfered under high concentrations of the sodium and potassium contained in formulas. This method was applied to 16 Japanese infant formula samples, and the lithium content was determined: 106 ± 13 (p < 0.05) ng/g in 3 formulas for newborns; 178 ± 42 (p < 0.05) ng/g in 4 formulas for weaning infants; 118 ± 10 (p < 0.05) ng/g in 7 formulas for special use such as allergy, diarrhea and premature infants; 147 ± 40 (p < 0.05) ng/g in 7 milk-based formulas; and 123 ng/g in 2 soy-based formulas. The origin of lithium in the formulas may have been impurities of inorganic chemicals added as nutrition in manufacturing, based on correlation results between lithium and other chemical compositions of infant formulas (r = 0.94 for Li/Ca, r = 0.89 for Li/Mg, r = 0.85 for Li/Na, r = 0.90 for Li/K, r = 0.86 for Li/P and r = 0.94 for Li/Cl). As a conclusion, the daily dietary lithium intake has been estimated to be 12 μg for young infants fed on formulas and 20 μg for infants fed on weaning formulas.