Liquid chromatographic resolution of the isomers of tipredane and phenylthioproline using urea-solubilized beta-cyclodextrin in the mobile phase.

Two LC assays were developed using urea-solubilized beta-cyclodextrin (beta-CD) as a mobile phase additive in combination with reversed-phase columns. A methylsilane column gave optimal resolution of the steroid tipredane from its epimer. An investigation of the effects of beta-CD concentration, column temperature, column type, and addition of ethanol on the chromatographic separation is detailed. The enantiomer and diastereoisomers of L-cis-phenylthioproline were best resolved by urea-solubilized beta-cyclodextrin and a trimethylsilane column. The elution order of L-cis-phenylthioproline relative to its stereoisomers was reversed after adding ethanol to the beta-CD containing mobile phase or by changing from a beta-CD to an acetylated beta-CD column. The resolution factors for these separations obtained using the beta-CD mobile phase were larger than those obtained using beta-CD columns. Mobile phases containing up to 0.15 M beta-CD and 8 M urea were investigated. The separation of these isomers are dramatically affected by column polarity.

Inter-laboratory transfer of HPLC methods: problems and solutions.

As high-performance liquid chromatography (HPLC), the premier analytical technique in the pharmaceutical industry, becomes more ubiquitous, methods are more frequently being transferred from one laboratory to another. This review will discuss sources of failures to reproduce HPLC procedures, ranging from sample handling and preparation, through mobile phase, injector, column, detector and data manipulation problems. Also to be considered will be the precautions that should be taken, when initially developing a method, to obviate future problems. These precautions include using stable, well-defined analytical columns, buffered mobile phases, low wavelengths (or a mass-sensitive detector) and internal tests for accuracy; based on the author's experiences. Since the laboratory that originally developed the procedure has the moral obligation and, perhaps, the regulatory responsibility to "guarantee" that the method will perform successfully elsewhere, a series of increasingly comprehensive steps will be given, based on practice, to be followed by the laboratory that could not reproduce the procedure. Also to be discussed are approaches for treating methods that were initially successful but have slowly deteriorated and now fail, and several examples of procedures that were not reproducible in some other laboratories.

High-performance liquid chromatographic analysis of nadolol and bendroflumethiazide combination tablet formulations.

A reverse-phase high-performance liquid chromatographic (HPLC) method was developed for the simultaneous assay of nadolol and bendroflumethiazide in tablet formulations. The tablets were extracted with methanol and, after centrifugation, were chromatographed. A phenyl column was used with a mobile phase of aqueous acetate buffer with sodium chloride-methanol (60:40); detection was at 270 nm. Linearity of both drugs was satisfactory. The procedure can be automated and also applied to bendroflumethiazide formulations and bulk material.

High-pressure liquid chromatography of nadolol and other beta-adrenergic blocking drugs.

A high-pressure liquid chromatographic assay was developed for the analysis of the beta-adrenergic blocking agent nadolol as a bulk material or formulated in a tablet. Other beta-adrenergic blocking drugs such as acebutolol, alprenolol, atenolol, metoprolol, oxprenolol, pindolol, practolol, propranolol, sotalol, and timolol can be chromatographed in this system. An ethylsilane column and a mobile phase consisting of 35% methanol-65% aqueous 0.0005 M hydrochloric acid-0.05 M sodium chloride are used. Detection is either at 254 nm with a variable-wavelength detector. As exemplified by nadolol, the drug content can be quantitated with or without atenolol as an internal standard.