Precise quantitative capillary electrophoresis: Methodological and instrumental aspects

Abstract

The separation efficiency of capillary electrophoresis (CE) is said to be unrivalled by liquid chromatography for a number of applications. However, the quantitative precision, which is essential for its use in routine analysis, has been commented upon more critically. The reproducibility of CE is dependent on a number of parameters. The relative standard deviation is predominantly dependent on the absolute sample concentration. Its optimization is very important, and the use of higher concentrations is found to be more favourable. The problem of the non-linear relationship between concentration and peak data, caused by column overload, is less critical. The buffer concentrations are adjusted to the optimum sample concentrations. Validated buffer recipes and rinsing steps will lead to more stable conditions, and the trends that occur can be diminished by the stepwise use of an external standard. Much of the precision is dependent on instrumental aspects. Seven set-ups from different manufacturers were tested. Thermostating proved to be the most important parameter in achieving a reproducible dosage. Ion mobility and buffer viscosity are controlled by the temperature. These parameters influence the amount of sample that is injected by electrokinetic or hydrodynamic injection. The recording of temperature, current, voltage and power is necessary for proper documentation. Short capillaries should be usable for achieving a short analysis time and thus a large number of repetitions per unit time, which is important for statistical certainty.