Laser-Induced Fluorescence Monitoring of Multicomponent Aromatic Amino Acids.

There have been many studies on the use of laser induced fluorescence measurements to monitor the concentrations of aromatic compounds. The emission spectra of binary and ternary mixtures of simple aromatic amino acids (tyrosine, tryptophan, and phenylalanine) are analyzed based on a rigorous model that has been previously developed by us to relate the detected signal level to the fluorophore concentration. The fluorescence signals are generally noisy, and the contributions from each fluorophore in a mixture are not at all additive due to the secondary optical effects such as the reabsorption of the fluorescence signal and the reemission of photons at lower frequencies. Fourier transform methods are employed for noise reduction, and a range of algorithms are proposed to extract information in an optimal manner from the strongly nonlinear system. Much improved concentration estimates are obtainable over those calculated directly from the linear additivity assumption when confounding effects are considered explicitly. Our results to date show that it is most difficult to detect a small amount of one component either in the presence of larger concentrations of other fluorophores or in the presence of an unknown fluorophore. The application of on-line fluorescence measurements in bioprocessing will be discussed