Dual-opposite-injection CZE: theoretical aspects and application to organic and pharmaceutical compounds.

Several important figures of merit (migration time, efficiency, resolution, resolution per unit time, and electrophoretic selectivity) are quantitatively compared for the first time for conventional CZE and dual-opposite-injection CZE (DOI-CZE). Aspects of DOI-CZE relevant to the separation of organic and pharmaceutical ions (MW>120 Da) are also discussed. Two new approaches to resolve the codetection of anions and cations, hydrodynamic flow-modified DOI-CZE and polarity reversal in combination with asymmetric detector window positioning, are compared with the method of preliminary transport, a variable procedure within sequential sample introduction, using a six-component sample of organic and pharmaceutical compounds. The advantages of DOI-CZE for the simultaneous analysis of organic/pharmaceutical anions and cations are illustrated in a direct comparison of conventional CZE and DOI-CZE for the separation of a ten-component mixture of pharmaceutical ions (five ionized acids and five ionized bases).

Plate number requirements for establishing method suitability.

Establishing the suitability of an analytical system has become a routine requirement in the testing of modern pharmaceuticals. Acceptable parameters that illustrate the system is performing as intended and in an equivalent manner to the original validation are often set at the time of method validation and transferred with the method to the production laboratory. For chromatographic methods, these parameters include--but are not limited to--resolution, tailing, and plate number specifications. Transferring methods is often a seamless transition from research to quality control. However, far too often the quality group receives arguably "overzealous" and strict requirements for the method. More specifically, chromatographic methods get issued with plate number specifications that far exceed the minimum number required to achieve sufficient resolution of the analytes. Presented here is a discussion of the setting of realistic plate number specifications that still maintain the minimum resolution of the chromatographic critical pair.