Pingdong Wu

Relationship between the flow-rate of the mobile phase and retention of the stationary phase in counter-current chromatography

Abstract The retention percentages of the stationary phase ( S F ) at various flow-rates ( F c ) of 15 two-phase solvent systems were determined in three types of counter-current chromatographic apparatus equipped with small-, middle- and large-bore coiled columns. The regression analysis of S F showed a linear relationship between the square root of the flow-rate and the retention percentage of the stationary phase, i.e. S F = A − B F C where A indicates the difference in the solvent composition of the solvent system and B indicates the difference in the volume ratio of the solvents for the same composition of the solvent system.

Separation of phosphatidylcholine from soybean phospholipids by simulated moving bed

A simulated moving bed (SMB), equipped with eight silica-gel columns, was used to separate phosphatidylcholine (PC) from soybean phospholipids. The effects of flow rate in Sections 2 (Q2) and 3 (Q3), switching time, feed flow rate and feed concentration on the operating performance parameters: purity, recovery, productivity and desorbent consumption were studied. Operating conditions leading to more than 90% purity in both outlet streams have been identified, together with those achieving optimal performance. Regions leading to complete separation are observed and explained theoretically. As the mass-transfer effect was not considered, the triangle theory only gives initial guesses for the optimal operating conditions.

Chromatographic Separation of Fluoxetine Hydrochloride Enantiomers by Cellulose Chiral Stationary Phase

Abstract Fluoxetine hydrochloride enantiomers were separated by chromatography on Tris‐(3,5‐dimethylphenyl carbamate) cellulose as a chiral stationary phase (CSP). The effects of mobile phase composition, flow rate, and column temperature on capacity factor, separation factor, and resolution were studied systematically. Best separation was obtained with a mobile phase composition of hexane/isopropyl alcohol/diethylamine of 98/2/0.2 (v/v/v) at 15°C. The optimal flow rate was 0.24 mL/min from the Van Deemter equation. However, baseline resolution (RS>1.5) was achieved under a flow rate of 0.8 mL/min. Thermodynamic parameters ΔH 0, Δ S,R ΔH 0, and Δ S,R ΔS 0 were calculated. In the temperature range examined, the enthalpic contribution to the enantiomer transfer energy was found to be more significant than the entropic one.

Comparison of the performance of chiral stationary phase for separation of fluoxetine enantiomers

Separation of fluoxetine enantiomers on five chiral stationary phases (chiralcel OD-H, chiralcel OJ-H, chiralpak AD-H, cyclobond I 2000 DM and kromasil CHI-TBB) was investigated. The optimal mobile phase compositions of fluoxetine separation on each column were hexane/isopropanol/diethyl amine (98/2/0.2, v/v/v), hexane/isopropanol/diethyl amine (99/1/0.1, v/v/v), hexane/isopropanol/diethyl amine (98/2/0.2, v/v/v), methanol/0.2% triethylamine acetic acid (TEAA) (25/75, v/v; pH 3.8) and hexane/isopropanol/diethyl amine (98/2/0.2, v/v/v), respectively. Experimental results demonstrated that baseline separation (RS>1.5) of fluoxetine enantiomers was obtained on chiralcel OD-H, chiralpak AD-H, and cyclobond I 2000 DM while the best separation was obtained on the last one. The eluate orders of fluoxetine enantiomers on the columns were determined. The first eluate by chiralcel OJ-H and kromasil CHI-TBB is the S-enantiomer, while by chiralpak AD-H and cyclobond I 2000 DM is the R-enantiomer.

VAN DEEMTER PLOT IN HIGH-SPEED COUNTERCURRENT CHROMATOGRAPHY WITH A FIXED VOLUME OF STATIONARY PHASE

An adaptability of countercurrent chromatographic data to Van Deemter equation (H = A + B/u + Cu) is examined under a fixed volume of the stationary phase. Three test samples, epigallochatechin gallate (EGCG), gallocatechin-gallate (GCG), and epicatechin gallate (ECG) were separated using a two-phase solvent system of n-hexane/ethyl acetate/water (3.5:1:10, v/v/v) at various linear flow rates (u). Our mathematical treatment produced a set of formulae, HEGCG = 6.5 + 1/u + 6u; HGCG = 6.5 + 1.3/u + 7u; and HECG = 6.5 + 2.5/u + 9u, which showed excellent fit to the experimental data for each component. Constants B and C show high correlation with the partition coefficient values of three components. Based on the high correlation between log u and log H when u > 1, the plate height (H) for three components may be expressed by H = Duk, where D is the plate height at u = 1 cm/s and k, the constant for each component.

Mathematical model of the dynamics of countercurrent chromatography

A mathematical model of the dynamic behavior of countercurrent chromatography was proposed, and the model parameters, including the partition coefficient, the axial dispersion coefficient, the intraparticle diffusion coefficient and the external mass ransfer coefficient were calculated by the method of chromatogram moment analysis. Comparison of the experimental chromatograms of caffeine and theophylline determined in this work with the simulated curves computed by the proposed model showed fairly good agreement. Further, the difference between the average identified the partition coefficients by chromatogram moment analysis and the experimental values was small also, and the relationship between the external mass transfer rate and the linear velocity was similar to that obtained with solid-liquid chromatography.