Christel Hendrix

CYCLOHEXENE NUCLEIC ACIDS (CeNA) FORM STABLE DUPLEXES WITH RNA AND INDUCE RNASE H ACTIVITY

Cyclohexene nucleic acids (CeNA) were synthesized using classical phosporamidite chemistry. Incorporation of a cyclohexene nucleo-side in a DNA chain leads to an increase in stability of the DNA/RNA duplex. CeNA is stable against degradation in serum. A CeNA/RNA hybrid is able to activate E. Coli RNase H, resulting in cleavage of the RNA strand.

Comparative study of liquid chromatographic methods for the determination of cefadroxil

Abstract A comparative study of two isocratic liquid chromatographic methods for the determination of cefadroxil is described. The first method, prescribed in the monograph of the European Pharmacopoeia for the assay of cefadroxil, uses a classical alkyl-bonded phase (C18) as the stationary phase. This method is very similar to that prescribed by the United States Pharmacopeia. The other method uses poly(styrene- divinylbenzene). Poor reproducibility of the selectivity towards cefadroxil and related substances was observed when the first method was examined on different C18 columns. Copolymer columns, on the other hand, gave the same elution order on stationary phases from different manufacturers and of different age. Four bulk samples of cefadroxil were analysed following both methods and the results were compared.

Quantitative analysis of cefalexin by liquid chromatography on poly(styrene-divinylbenzene)

Abstract An isocratic liquid chromatographic method has been developed for assay and purity control of minocycline. All the potential impurities are well separated from the main component and from each other. The stationary phase is poly(styrene-divinylbenzene) (PSDVB), PLRP-S, 250 mm × 4.6 mm, which is heated at 60 °C. The mobile phase is 2-methyl-2-propanol (x g/100 ml) - 0.2 M potassium phosphate buffer pH 10.5 (10.0 ml) - 0.02 M tetrabutylam-monium sulphate pH 10.5 (10.0 ml) - 0.01 M sodium edetate pH 10.5 (10.0 ml) - water (up to 100 ml). The flow rate is 1.0 ml/min and UV detection is performed at 254 nm. The total analysis time does not exceed 30 min. Official standards were compared and a number of commercial bulk samples and specialties were analysed. 4-Epiminocycline, 6-deoxy-6-demethyltetracycline and 7-monodemethyl-minocycline are the main impurities. 7-Didemethylminocy-cline, 9-minocycline and some impurities of unknown identity also can be present.

Collaborative study of the analysis of tetracycline by liquid chromatography on poly(styrene-divinylbenzene)

Abstract A previously developed method for the analysis of tetracycline by liquid chromatography on poly(styrene-divinylbenzene) packing materials was examined in a collaborative study involving five laboratories and a total of seven columns. The main compound and the impurities of three tetracycline samples were determined. An analysis of variance, considering each column as a different laboratory, proved absence of consistent laboratory bias. The laboratory-sample interaction was significant. Estimates for the repeatability and the reproducibility of the method, expressed as relative standard deviations of the result of the determination of tetracycline, were calculated to be 0.9 and 1.5 % respectively

Column liquid chromatography of cefadroxil on poly(styrene-divinylbenzene)

Abstract Isocratic column liquid chromatography on a poly(styrene-divinylbenzene) stationary phase (PLRP-S, 25 cm × 0.46 cm I.D.) at 50°C allowed the separation of cefadroxil from related substances. The mobile phase was acetonitrile-0.02 M sodium 1-octanesulphonate-0.2 M phosphoric acid-water (10.5:20:5:up to 100, v/v). The flow-rate was 1.0 ml/min and UV detection was performed at 254 nm. Official standards were compared and a number of commercial bulk samples and specialities were analysed.

A comparative study of LC methods for analysis of cefradine

A comparative study of two isocratic liquid chromatographic methods for the analysis of cefradine is described. The first method is prescribed by the European Pharmacopoeia for the assay of cefradine, using classical alkyl bonded phase (C18) as the stationary phase. Poor reproducibility of the selectivity towards cefradine and its related substances was observed when this method was used and none of the C18 columns examined was able to separate cefradine completely from its potential related substances under the prescribed LC conditions. On the other hand, the second method, which uses poly(styrene-divinylbenzene) as the stationary phase, shows good selectivity even when using columns from different manufacturers and of different age. Four bulk samples of cefradine were analysed following both methods and the results were compared.

Quantitative analysis of cefradine by liquid chromatography on poly(styrene-divinylbenzene).

A method is described for isocratic analysis of cefradine by liquid chromatography on a poly(styrene-divinylbenzene) column (PLRP-S, 250 x 4.6 mm i.d.) at 50 degrees C. Cefradine is separated from its related substances using a mobile phase of acetonitrile-0.02 M sodium 1-octanesulphonate-0.2 M phosphoric acid-water (14.5:10:5:up to 100, v/v/v/v). The flow rate was 1.0 ml min-1 and UV-detection was performed at 254 nm. The method was employed for the quantitative analysis of reference substances, bulk samples and pharmaceutical dosage forms.