Gradient Elution Moving Boundary Electrophoresis with Field-Amplified Continuous Sample Injection

The integration of simple and robust device components required for the successful adaptation of many analytical methods to multiplexed and field-portable devices often has negative effects on detection sensitivity, such as in the optical detection components in a capillary electrophoresis (CE) system. One of the simplest methods to improve sensitivity in the CE field is known as sample stacking. This method involves preparing the sample in a buffer with a different concentration (and conductivity) than that of the run buffer so that when an electric field is applied the analyte concentration is increased at the boundary between the two different buffer concentrations. Here, we describe a method in which the sample is prepared in a buffer at a lower concentration than the run buffer coupled with a recently described counterflow electrophoresis method, gradient elution moving boundary electrophoresis (GEMBE), with channel current detection. Because of the continuous sample introduction with GEMBE, we refer to the method as field-amplified continuous sample injection (FACSI). This method achieves a significantly greater signal enhancement than expected for sample stacking. For example, we achieve signal enhancement of 110x with a conductivity ratio of 8.21, and using the detection of arsenate in drinking water as a model system, we have achieved a limit of detection (LOD) improvement of approximately 60x (LODs with and without FACSI are 200 nmol/L and 12 mu mol/L, respectively) with a conductivity ratio of approximately 5.93.