LC method for the determination of oxcarbazepine in pharmaceutical preparations

A simple and accurate HPLC method for determination of oxcarbazepine (OXC) in a new tablet formulation is described. Chromatographic separation was achieved on a Diamonsil C18 column using a mobile phase consisting of acetonitrile, potassium phosphate monobasic buffer (pH 6.8) and water (36:8:56, v/v) at a flow rate of 1.0 ml/min. Absorbance was monitored at 255 nm where OXC has maximum absorption. The linear range of detection for OXC was from 9.96 to 99.6 microg/ml. The proposed method was validated for selectivity, precision, accuracy and limits of detection and quantitation, etc.

Versatile two-phase solvent system for alkaloid separation by high-speed counter-current chromatography

In order to find a versatile high speed counter-current chromatography solvent system that can be used as a general prefractionation system for most alkaloids, the crude extracts of five Chinese traditional medicinal herbs, Cortex phellodendri, Semen strychni, green tea, Sophora flavescens ait, and Datura mete L. were resolved. All separations were performed only with a two-phase system composed of CHCl3-CH3OH-water (4:3:2). The water had different acidities controlled by adding NaH2PO4 or HCl to each sample. The fractionated components were identified by thin-layer chromatography, which confirmed this solvent system was versatile and very useful for the separation of alkaloids.

[The separation of three basic drugs with carboxymethyl-poly-beta-cyclodextrin as chiral additive by capillary electrophoresis]

Five cyclodextrin derivatives, namely phosphate ester beta-CD, carboxymethyl-beta-CD(CM-beta-CD), bis-[6-oxygen-(beta-carboxymethyl-succinic acid-4-ester)] beta-CD(F-CM-beta-CD), beta-CD polymer(P-beta-CD), carboxymethyl-poly-beta-CD (CD-P-beta-CD), were used as chiral selector for separation of three basic drugs, lobeline, thiopendonesodium, flunarizine by capillary zone electrophoresis (CZE). All the five cyclodextrins have chiral separation ability to lobeline. P-beta-CD and CM-P-beta-CD have chiral recognition to thiopentonesodium and flunarizine. The results indicate that via optimizing separation conditions by varying pH and the concentration of chiral selectors the three racemic drugs could be baseline separated with 2% P-beta-CD or 0.5% CM-P-beta-CD in the buffer of 30 mmol/L Tris-H3PO4. And the best resolution ranging from 4 to 35 with CM-P-beta-CD as chiral additive was obtained within 10 min. The results were much better than those reported in other references.

[A novel chiral selector in capillary electrophoresis--beta-cyclodextrin polymer]

Three chiral selectors CM-beta-CD, EP-beta-CD, beta-CD were studied for the enatio-separation of three drugs under optimum conditions respectively. The results demonstrate that the resolving power for the drugs is as follows CM-beta-CD > EP-beta-CD > beta-CD, with the exception of lobeline. This is due to the--CH2COOCH3 group of CM-beta-CD, which will change the combination and improve the recognition on guest molecules. Although EP-beta-CD is inferior to CM-beta-CD for the separation of chlorpheniramine and verapamil, it has excellent recognition on lobeline and it has not been reported previously. In most cases EP-beta-CD is superior to beta-CD. The explanations are: (1) EP-beta-CD has good solubility in water, which enables high concentrations to be used and consequently achieves excellant separation of racemic compounds, (2) the polymerization of beta-CD changes the properties of CD units and the process produces a more rigid and different conformation from CD, (3) we must attribute much merits to the cooperation or synergism of two, three or even more CD moieties of two polymers for inclusion. Complexation with analytes possesses more than one guest part in their structure.

[Study on the separation of optical chromatography]

The relationship between the particle radius with the intensity of the applied laser radiation force is theoretically studied using a ray-optics model by analyzing the forced-status of the separated particles in the mobile phase. The laser radiation force is proportional to the square of the particle radius when the particle radius is much smaller than the laser beam radius under the condition of using a single-transverse-mode laser beam with a Gaussian intensity distribution and the particle refractive index being larger than that of the mobile phase. The retention distance is calculated and the dynamic range is discussed. Theoretically, the dynamic range of the optical chromatography can be extended by increasing laser power, decreasing the flow rate of mobile phase and focusing the laser beam.