Determination of Tryptophan with HPLC after Alkaline Hydrolysis in Autoclave using α-methyl-tryptophan as Internal Standard

A method for determination of tryptophan in feeding stuffs is described. The hydrolysis is carried out on a sample containing 10 mg nitrogen using 25 ml NaOH 4.2 mol/l at 110°C for 16 hours in an autoclave. α-methyl-tryptophan is used as internal standard. The tryptophan and the internal standard are determined by using HPLC with fluorescence detection. When analysing three known proteins the number of Trp-residues found was in good agreement with their known numbers. A good mixture linearity response for three sets of mixtures of feeding stuffs is shown.