Method for measuring very weak, residual electroosmotic flow in coated capillaries

Many different methods exist for measuring the velocity of electroosmotic flow in capillary electrophoresis (CE). The easiest and the most common one is photometric detection of a neutral marker. This method can be used on any CE unit, while other methods may require some modifications or special equipment. However, this method is not very suitable for measuring weak electroosmosis, since very long runs are necessary for the neutral marker to arrive at the detector. For this case, an alternative method is proposed here. It assumes that the neutral marker is injected by means of electroosmosis, then rinsed by applying a low pressure and recorded. The resulting peak is quantified and, according to the amount of sample injected, the velocity of electroosmosis can be estimated. The proposed method is much faster than the traditional one; its duration is determined mainly by the time of electroosmotic injection. It can be used for estimation of the quality of capillary coatings, for which the residual electroosmotic flow is one of the characteristics.