Biomedical subjects

K Mihlbachler

Publications and source records attributed to K Mihlbachler.

4 recordsLinked to original sources

PubMed2002

Measurement and modeling of the equilibrium behavior of the Tröger's base enantiomers on an amylose-based chiral stationary phase.

The binary isotherms of the two enantiomers of Tröger's base were measured on a system made of pure 2-propanol as the mobile phase and of Chiralpak AD, a chiral stationary phase (CSP) based on amylose tri-(3,5-dimethylphenyl carbamate). The experimental data were acquired using both frontal analysis and the perturbation method. The results obtained are most unusual. The adsorption of the more-retained (-)-enantiomer is not competitive: the amount adsorbed onto the CSP at equilibrium with a constant concentration of the (-)-enantiomer is independent of the concentration of the (+) enantiomer. On the other hand, the adsorption of the less-retained enantiomer is cooperative: the amount of this (+)-enantiomer adsorbed by the CSP at equilibrium with a constant concentration of this enantiomer increases with increasing concentration of the (-)-enantiomer. Such a phenomenon has hardly ever been reported. A model equation is proposed that accounts well for all these isotherm data.

Adsorption↗

PubMed2001

Fitting adsorption isotherms to the distribution data determined using packed micro-columns for high-performance liquid chromatography.

Knowing the adsorption isotherms of the components of a mixture on the chromatographic system used to separate them is necessary for a better understanding of the separation process and for the optimization of the production rate and costs in preparative high-performance liquid chromatography (HPLC). Currently, adsorption isotherms are usually measured by frontal analysis, using conventional analytical columns. Unfortunately, this approach requires relatively large quantities of pure compounds, and hence is expensive, especially in the case of pure enantiomers. In this work, we investigated the possible use of packed micro-bore and capillary HPLC columns for the determination of adsorption isotherms of benzophenone, o-cresol and phenol in reversed-phase systems and of the enantiomers of mandelic acid on a Teicoplanin chiral stationary phase. We found a reasonable agreement between the isotherm coefficients of the model compounds determined on micro-columns and on conventional analytical columns packed with the same material. Both frontal analysis and perturbation techniques could be used for this determination. The consumption of pure compounds needed to determine the isotherms decreases proportionally to the second power of the decrease in the column inner diameter, i.e. 10 times for a micro-bore column (1 mm I.D.) and 100 times for capillary columns (0.32 mm I.D.) with respect to 3.3 mm I.D. conventional columns.

Adsorption↗

PubMed2001

Effect of the homogeneity of the column set on the performance of a simulated moving bed unit. I. Theory.

Although it is impossible to manufacture identical columns for use in a simulated moving bed (SMB) process, theoretical studies assume that all the columns in an SMB unit have identical characteristics. In practice, calculations in modeling and optimization studies are made with the average values of each column parameter set. In this report, the effects on SMB process performance caused by column-to-column fluctuations of the parameters are discussed. As a first step, we show how the differences in porosity of the columns may be taken into account with a revised set of separation conditions. Reductions in the purity of the extract and the raffinate streams are quantitatively related to the column-to-column fluctuations of the retention times of the two components arising from these porosity differences. For the sake of simplicity, the discussion first addresses the case of a four-column SMB operating under linear conditions. Then, the scope is extended to the cases of SMB units incorporating several columns in each section and to SMB units operating under nonlinear conditions.

Chromatography↗

PubMed2000

Enantioseparation of 1-phenyl-1-propanol by simulated moving bed under linear and nonlinear conditions.

Approximately optimum operating conditions needed to separate 1-phenyl-1-propanol (PP) enantiomers by simulated moving bed (SMB) were determined using the "safety margin" approach in the linear case and the "triangle theory" in the nonlinear case. Previous results showed the adsorption isotherm data to fit well to the competitive Langmuir model. This allowed the use of the triangle theory approach that applies straightforwardly to Langmuir systems. Experimentally, the operating conditions under nonlinear isotherm behavior were determined for a feed solution with a total concentration of 5 g/l. The purity of the products exceeded 98% for the raffinate and 95% for the extract. Failing to reach complete purity while the experimental conditions were chosen inside the separation zone is explained by the nonideality of the system used, which violates one of the triangle theory assumptions. The computed overall daily production rate was 11.6 g of racemic PP processed per day per kg of stationary phase, a result that compares favorably with previous ones.

Adsorption↗