Amino acids exist as enantiomers that can be separated and detected using HPLC-FLD. An optimal PMT gain and wavelength of excitation must be determined to lower the limit of detection (LOD) and quantitation (LOQ) as increasing the PMT gain amplifies the signal on the HPLC-Spectra. The HPLC-FLD spectra of OPA-IBLC derivatized histidine was measured at PMT gain 5 and 7 for the excitation wavelengths of 340-, 260-, and 240- nm. Hence, the optimal excitation wavelength and PMT gain can be determined by comparing the fluorescence spectra
