In microchip electrophoresis (μ-CE), sample injection is generally achieved through cross, double-T, or T-form injector structures. In these reported approaches, the separation efficiency and detection sensitivity of μ-CE is significantly influenced by the shape and size of the sample plug introduced into the separation channel or sample leakage in separation phase. Here, we present a sandwich-injection method for controlling discrete sample injection in μ-CE. This method involves four accessory arm channels in which symmetrical potentials are loaded to form a unique parallel electric field distribution at the intersection of sample and separation channels. The parallel electric field effectuate a virtual wall to confine the shape of a sample plug and depress the spreading of the sample plug at the junction of sample and separation channels, and also prevent sample leakage during separation step. The key features of this method are the ability to inject well-defined sample plugs at the original sample concentration and the ability to control the sample plug size. The virtues of the novel injection technique were demonstrated with numerical models and validated with fluorescence visualizations of electrophoretic experiments.
Determination of Adriamycin and Its Metabolites in Biological Samples Using High Performance Liquid Chromatography. I. Analysis of Serum and Plasma by Direct Injection Method
