Rapid and Direct Determination of Tryptophan in Water Using Synchronous Fluorescence Spectroscopy

Water samples from lakes situated in and around the area of Tsukuba Science City, Ibaraki Prefecture, Japan, were analysed using synchronous fluorescence spectroscopy and HPLC. The spectra revealed a major emission peak (lambda emm) at 340 nm corresponding to an excitation wavelength (lambda exc) position of 280 nm and a Stoke's shift, delta lambda = 60 nm. The fluorescence intensities at these wavelengths were normalised with respect to the water Raman peak, where the lambda exc was 397 nm and the lambda emm was 453 nm, and corrections were introduced to take into account absorption/re-absorption effects of the fluorescing signals caused by the sample matrix. Normalised fluorescence values correlate well with levels of tryptophan present in the samples determined by HPLC analysis (R2 = 0.99). The relationship of the observed tryptophan-like fluorescence in the water samples to the presence of free tryptophan is discussed.