Simultaneous determination of urinary creatinine and aromatic amino acids by cation-exchange chromatography with ultraviolet detection.

A cation-exchange chromatographic procedure for the simultaneous determination of urinary creatinine and aromatic amino acids is described. Creatinine and amino acids were separated from organic acids and/or neutral species in urine by using a preparative cation-exchange resin column. A column packed with a cation-exchange resin of low capacity was used for the analytical separations. The elution of creatinine and aromatic amino acids was monitored at 210 nm by means of an ultraviolet detector. The relationships between concentration and peak heights were reproducible with a coefficient of variation of less than 2%, and were linear from 5 to 200 microM for each compound. Overall recoveries of the analytes were more than 95%. The method was applied to the analysis of urine of patients with disorders of amino acid metabolism, such as phenylketonuria. The concentration ratios of phenylalanine to creatinine in the patients' urine were accurately and easily determined, and were quite different from those in the urine of healthy newborns.