Abstract
The amino acids L-phenylalanine (Phe), L-tyrosine (Tyr) and L-Tryptophan (Trp) play an important role in the human body. L-Phenylalanine and L-tyrosine are precursors of several neurotransmitters, while Trp has been indicated as an aid for schizophrenic patients. These amino acids can be separated by ion exchange chromatography, and, usually, its description adopts differential mass balance equations for the stationary and mobile phases. The stochastic model can be an alternative to the traditional approach. Normally based on a microscopic view of chromatography, the random migration of a molecule is considered from a probabilistic aspect to describe the distribution function of the solute in the elution process. In the present work, the stochastic model in a fixed-bed adsorption has been studied by another point of view. The response of the adsorption column to the injection is measured as concentration vs. time at the exit of the column. Based on this, chromatographic pulses of aromatic amino acids are analyzed by Kolmogorov entropy theory. The rate of generation of information about concentration at the column exit can be identified with certain probability density function (PDF), and with a degree of the rate of generation of information of the system, characterized by the Kolmogorov entropy. The system tested is a fixed-bed, packed with poly-4-vinylpyridine cross-linked with divinyl benzene, and dilute aqueous solutions of NaCl and the aromatic amino acids Phe, Tyr, and Trp in two liquid flow rates. This work shows that is possible to reconstruct the solute effluent history using an appropriate PDF. In order to find the PDF that provides the best description of the experimental data, fourteen functions where fitted by the Least Squares Method. According to Kolmogorov-Smirnov test, Normal, Log- Normal, Logistic, Gamma, Pearson III and Beta models provided a satisfactory fit, and the dimensionless Kolmogorov entropy parameter depends on the affinity between solute and adsorbent, and the flow rate of carrier stream, implying its relation with dispersion phenomena and the nature of solute and adsorbent.
