[Simultaneous determination of tryptophan and tyrosine by second order derivative fluorimetry]

A new method of second order derivative fluorimetry for the simultaneous determination of tryptophan and tyrosine is described. The measurement of emission spectra is carried out with excitation at 221 nm in a KH2PO4-NaOH buffer solution (pH = 7.4). The second-derivative peak is at 318 nm and 283 nm for tryptophan and tyrosine respectively. The two amino acids can be determined directly from corresponding second order derivative signals. Linear regression equation of the calibration graph is c = 0.000 7H-0.004, with a correlation coefficient of linear regression of 0.9964 for tryptophan and c = 0.001 2H-0.0040, with a correlation coefficient of linear regressin of 0.9971 for tyrosine. The linear ranges of determination of tryptophan and tyrosine are from 0.004 to 0.200 microgram.mL-1 and from 0.002 to 0.025 microgram.mL-1, respectively. Effects of pH, temperature and foreign ions on the determination of tryptophan and tyrosine have been examined. Recovery is from 92.0% to 104% for tryptophan and 98.7% to 102.0% for tyrosine, and relative standard deviation of 3.5% and 2.8%, respectively.