Determination of methionine in protein hydrolysates by reaction with raney nickel and infrared spectroscopy

An infrared spectrophotometric determination of methionine in protein hydrolysates is suggested. The method is based on the desulphurizing action of specially purified Raney nickel on methionine, during which methane is quantitatively liberated, methane is then measured at 3020.3 cm-1 Cystine and cysteine do not interfere and can usually be determined from the difference between total sulphur and methionine sulphur. The method can be applied to protein hydrolysates, and to homogenates of internal organs. The time required for a single determination is about 40 min; the relative error is 1.2% down to a level of 200 μg.