Design of background electrolytes for indirect photometric detections based on a model of sample zone absorption in capillary electrophoresis

A unified model has been developed to describe the relationship between the sensitivity and the electrophoretic properties of the background electrolytes (BGEs). Five photometric detection methods for capillary electrophoresis (CE) have been discussed on the basis of the model. The results obtained show that the absorption of the sample zones in BGEs is a linear function of the transfer ratios of the sample ions, the molar absorptivities of the components of the BGEs and the sample ions, and the charge numbers of the ionic species involved in the sample zones. Simulation results indicate that the transfer ratios of the sample ions decrease with the increase of the mobilities of the sample ions in different BGEs. This suggests that the mobility of the co-ion in the BGE should be larger than or equal to that of the sample ions in order to increase the transfer ratios of the sample ions. Some rules extracted from the model show that the enhancement of the detection sensitivity lies in the maximization of the transfer ratios of the sample ions in the concerned BGEs and proper selection of the detection wavelength, but the constraints on the selection of the detection conditions are different for different detection methods. Experimental observations obtained are in good agreement with the simulation results. The model can be used as a guideline in formulation of BGEs for indirect photometric detections in CE. (C) 1999 Elsevier Science B.V. All rights reserved.