Determination of serum tryptophan by isocratic high-performance liquid chromatography and ultraviolet detection

A simple method for the determination of serum tryptophan is described. Serum proteins were precipitated using ethanol, and after a centrifugation, tryptophan concentrations were measured in the supernatant using isocratic high performance liquid chromatography with ultraviolet detection at 219 nm. All serum compounds absorbing at this wavelength were eluted within 6 min; the retention time for tryptophan was 3.95 min. This method is simpler and more rapid than previously published methods, and the results are reliable. The coefficient of variation of the analysis was found to be less than 6.5%.