ISOCRATIC HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF TRYPTOPHAN IN INFANT FORMULAS

The application to infant formulas of a method for tryptophan determin ation by isocratic HPLC with UV detection at 254 nm, after derivatizat ion with phenyl isothiocyanate, was studied. Protein was hydrolysed by barium hydroxide at 120 degrees C for 8 h, followed by derivatization with phenyl isothiocyanate, HPLC and UV detection at 254 nm. The opti mum chromatographic conditions (pH, ionic strength of elution solvent and eluent ratio) were established. The analytical parameters (lineari ty, precision, accuracy of derivatization and limits of detection and quantification) were determined. The values obtained demonstrated that the method is useful for determining the tryptophan content of infant formulas. The tryptophan contents in six different types of infant fo rmulas were 0.535-0.848 g per 100 g of protein.