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 electroly tes (BGEs). Five photometric detection methods for capillary electrophoresi s (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 o f the transfer ratios of the sample ions, the molar absorptivities of the c omponents of the BGEs and the sample ions, and the charge numbers of the io nic species involved in the sample zones. Simulation results indicate that the transfer ratios of the sample ions decrease with the increase of the mo bilities of the sample ions in different BGEs. This suggests that the mobil ity 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. So me rules extracted from the model show that the enhancement of the detectio n sensitivity lies in the maximization of the transfer ratios of the sample ions in the concerned BGEs and proper selection of the detection wavelengt h, but the constraints on the selection of the detection conditions are dif ferent 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.