Determination of histidine by atomic absorption spectroscopy

Two atomic absorption spectrophotometric methods are described for determination of histidine. The first is based on reaction of histidine with mercury(II) ions in phosphate buffer (pH 9). The second is based on reaction of histidine with iron(III) ions in neutral medium. The precipitate formed in both methods is separated by centrifugation, and the equivalent Hg(II) or Fe(III) ions as well as surplus ions in the filtrate are determined by atomic absorption at 253.6 and 248.3 nm for Hg and Fe, respectively. Amounts of histidine are calculated from calibration graphs prepared by standard addition methods or by regression equations. The procedures were successfully applied to assay of histidine in dosage forms after thin-layer chromatographic separation. Results compared favorably with those of the official method.