PHENYLGLYOXAL AS A FLUOROGENIC REAGENT SELECTIVE FOR TRYPTOPHAN

A method is described for the determination of tryptophan in which phenylglyoxal is used as a fluorogenic reagent. Phenylglyoxal reacts with tryptophan when heated in an acidic aqueous solution (dilute hydrochloric acid or phosphoric acid) containing dimethyl sulphoxide at 100-degrees-C for 30 min to produce a fluorescent compound, 1-(1-hydroxybenzyl)-beta-carboline. The fluorescence excitation and emission maxima are at 385 and 460 nm, respectively. The method is simple, highly selective and sensitive for tryptophan. The detection limits are 20 and 34 pmol ml-1 in the reaction mixtures obtained by using dilute hydrochloric acid and phosphoric acid, respectively.