Application of a partial filling technique to electrophoretic analysis on microchip with T-cross channel configuration

Abstract

To achieve a high performance sample injection, we designed microchips with both T- and cross-type channel geometry (T-cross chip), which enables two sample solutions to be introduced into a separation channel simultaneously with desired volumes by a combination of gated and pinched injection techniques. The developed microchips were applied to microchip micellar electrokinetic chromatography (MCMEKC) using a partial filling (PF) technique. In the PF technique, to suppress the increase in the background noise due to the presence of a pseudostationary phase (PSP), e.g., ionic surfactant micelles in MCMEKC with mass spectrometric (MS) detection, in a background solution (BGS), the separation channel is partially filled with a PSP while the rest of the channel including the detection point is filled with the BGS without a PSP. As a result, both sodium dodecyl sulfate (SDS) micellar and sample solutions were simultaneously injected into the separation channel on the T-cross chip with a good repeatability of the injection lengths by applying programmed voltages, and a baseline separation of rhodamine derivatives was achieved within 40 s by MCMEKC, in which the micellar zone was partially injected with the PF technique. It was confirmed that the detection could be performed without any influence of SDS by the fluorescence imaging measurements. These results demonstrated that the developed T-cross chips will allow a combination of the MCMEKC separation with the MS detection by employing the PF technique for high performance analysis of biogenic compounds. In the PF–MCMEKC analysis, furthermore, the resolution of two rhodamines clearly increased from 1.30 to 1.73 with the increase of the injection length of PSP from 0.16 to 0.89 mm, whereas at the injection length of 1.47 mm the resolution decreased. Therefore, the selection of an optimal injection length on the T-cross chip is very important and the effects of the injection length on the separation processes in PF–MCMEKC were discussed on the basis of theoretical calculations.