Characterization of an unusual adsorption behavior of racemic methyl-mandelate on a tris-(3,5-dimethylphenyl) carbamoyl cellulose chiral stationary phase

• Published in: Journal of Chromatography A Vol. 1218; no. 38; pp. 6688 - 6696
• Main Authors: Enmark, Martin, Samuelsson, Jörgen, Undin, Torgny, Fornstedt, Torgny
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 23.09.2011; Elsevier
• Subjects: Adsorption; Adsorption energy distribution; Analytical chemistry; cellulose; Cellulose - analogs & derivatives; Cellulose - chemistry; Chemistry; Chiral separation; Chromatographic methods and physical methods associated with chromatography; chromatography; Chromatography, Liquid - instrumentation; desorption; enantiomers; energy; Exact sciences and technology; heat production; Moreau adsorption model; Other chromatographic methods; Perturbation peak method; Phenylcarbamates - chemistry; sorption isotherms; Stereoisomerism; Stochastic modeling; temperature; Thermodynamics; Tóth adsorption model; Tóth adsorption model; Adsorption energy distribution; Perturbation peak method; Moreau adsorption model; Stochastic modeling; Chiral separation; Tóth adsorption model; Stochastic model; Separation; Hydroxyester; Adsorption isotherm; HPLC chromatography; Organic carbamate; Perturbation method; Enantiomer; Adsorption energy; Energy distribution; Theoretical study; Retention factor; Chiral stationary phase; Ultraviolet detector; Adsorption; Optical resolution; Cellulose derivatives; Toth isotherm; Thermodynamic properties
• ISSN: 0021-9673; 1873-3778; 1873-3778
• DOI: 10.1016/j.chroma.2011.07.064

An interesting adsorption behavior of racemic methyl mandelate on a tris-(3,5-dimethylphenyl)carbamoyl cellulose chiral stationary phase was theoretically and experimentally investigated. The overloaded band of the more retained enantiomer had a peculiar shape indicating a type V adsorption isotherm whereas the overloaded band of the less retained enantiomer had a normal shape indicating a type I adsorption behavior. For a closer characterization of this separation, adsorption isotherms were determined and analyzed using an approach were Scatchard plots and adsorption energy distribution (AED) calculations are combined for a deeper analysis. It was found that the less retained enantiomer was best described by a Tóth adsorption isotherm while the second one was best described with a bi-Moreau adsorption isotherm. The latter model comprises non-ideal adsorbate–adsorbate interactions, providing an explanation to the non-ideal adsorption of the more retained enantiomer. Furthermore, the possibility of using the Moreau model as a local model for adsorption in AED calculations was evaluated using synthetically generated raw adsorption slope data. It was found that the AED accurately could predict the number of adsorption sites for the generated data. The adsorption behavior of both enantiomers was also studied at several different temperatures and found to be exothermic; i.e. the adsorbate–adsorbate interaction strength decreases with increasing temperature. Stochastic analysis of the adsorption process revealed that the average amount of adsorption/desorption events increases and the sojourn time decreases with increasing temperature.