Sensitive determination of dissolved tryptophan in freshwater by alkaline hydrolysis and HPLC

A sensitive method involving alkaline hydrolysis and HPLC analysis has been developed to detect nanomolar levels of tryptophan dissolved in freshwater. The procedure includes 1) alkaline hydrolysis with nitrogen atmosphere in Teflon-lined Pyrex tubes with 4.2 M sodium hydroxide at 110 degreesC for 16 h, in which ascorbic acid was used as an antioxidant; 2) a determination step, in which tryptophan was separated efficiently from other amino acids by HPLC and measured by fluorescence. The mean recovery for tryptophan standard was 91.4% with an RSD of 3.3%. Using this method, dissolved tryptophan concentrations ranged from 10.91 to 41.83 nM in water samples from Lake Biwa, Japan.