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).     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Transient elastohydrodynamic drag on a particle moving near a deformable wall

We examine the prescribed time-dependent motion of a rigid particle(a sphere or a cylinder) moving in a viscous fluid close toa deformable wall. The fluid motion is described by a nonlinearevolution equation, derived using lubrication theory, whichis solved using numerical and asymptotic methods; a local linearpressure–displacement model describes the wall. When theparticle moves from rest towards the wall, fluid trapping beneaththe particle leads to an overshoot in the normal force on theparticle; a similarity solution is used to describe trappingat early times and a multiregion asymptotic structure describesfluid draining at late times. When the particle is pulled fromrest away from the wall, a peeling process (described by a quasisteadytravelling wave) determines the rate at which fluid can enterthe growing gap between the particle and the wall, leading toa transient adhesive normal force. When a cylinder moves fromrest transversely over the wall, transient peeling motion isagain observed (especially when the wall is initially indented),giving rise to an overshoot in the transverse drag. Simulationsfor a translating sphere show highly nonlinear wall deformationscharacterized by a localized crescent-shaped ridge. Despitegenerating sharp transient deformations, we found no numericalevidence of finite-time choking events.     

Determination of loads applied perpendicularly to the outer boundary of a ring using coefficients of influence

A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used, following an approach similar to the one presented in a previous paper. Examples of application are given and the possible increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined.     

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.