Determination of Tyrosine and Its Metabolites in Human Serum with Application to Cancer Diagnosis

A simple, rapid, and economical method is reported for the determination of 3,4-dihydroxyphenylalanine, tyrosine, 4-hydroxyphenyllactic acid, 4-hydroxyphenylacetic acid, 4-hydroxyphenethylamine, and 3-(4-hydroxyphenyl)propionic acid in human serum by ultra-performance liquid chromatography coupled with fluorescence detection. Separation was achieved on a C18 column with isocratic elution using 95:5 (v/v) 50 mM ammonium formate buffer at pH 5.8 and acetonitrile. Fluorescence detection was performed with excitation and emission wavelengths of 277 and 316 nm, respectively. Under the optimized conditions, all compounds were eluted within 10 min. The effectiveness of various protein precipitants was investigated for the pretreatment of serum samples and 5% perchloric acid was selected as optimal. The calibration curves were linear (correlation coefficients > 0.9996), and the limits of detection and quantification for tyrosine and its metabolites ranged from 0.016 to 0.032 mg/L and 0.040 to 0.080 mg/L, respectively. Recoveries of tyrosine and its metabolites in normal subjects and cancer patients were in the range of 86.5–102.5% and 88.3–107.3%, respectively, with RSDS of 0.3–5.7% and 0.5–4.3%. Significant differences in serum concentrations of tyrosine and 4-hydroxyphenyllactic acid were found between normal individuals and cancer patients.