LIQUID-CHROMATOGRAPHIC DETERMINATION OF FOLIC-ACID IN INFANT FORMULA AND ADULT MEDICAL NUTRITIONALS

A liquid chromatographic method for the determination of pteroylglutamic acid (folic acid) in infant formula and liquid medical nutritional diets is described. Extraction of folic acid from the sample matrix is facilitated by a partial enzymatic digestion of the sample proteins. An aliquot of the sample preparation is injected onto a strong anion exchange column (SAX) for preliminary separation, using a pH 5.3 mobile phase of 0.02M sodium acetate and 0.02M sodium sulfate. Before the elution of the folic acid from the SAX column, the eluant is directed onto an octyl bonded-phase column (C-8) by using automated switching valves. After the folic acid has been transferred to the C-8 column, the SAX column is removed from the flow path. The folic acid is eluted from the C-8 column by using an acetonitrile gradient. Detection is by absorption at 345 nm. The mean coefficient of variation is 3.6%, and the range of the recoveries of added folic acid is 95.5-100.2%. The method detection limit and method quantitation limit for infant formula are 10 and 28 mug/kg, respectively. This method is used routinely for the determination of folic acid in infant formula and liquid medical nutritional diets.