Multistacking from two sample streams in nonaqueous microchip electrophoresis

Abstract

The translation of stacking techniques used in capillary electrophoresis (CE) to microchip CE (MCE) in order to improve concentration sensitivity is an important area of study. The success in stacking relies on the generation and control of the stacking boundaries which is a challenge in MCE because the manipulation of solutions is not as straightforward as in CE with a single channel. Here, a simple and rapid online sample concentration (stacking strategy) in a battery operated nonaqueous MCE device with a commercially available double T-junction glass chip is presented. A multistacking approach was developed in order to circumvent the issues for stacking in nonaqueous MCE. The cationic analytes from the two loading channels were injected under fi eld-enhanced conditions and were focused by micelle-to-solvent stacking. This was achieved by the application of high electric fi elds along the two loading channels and a low electric fi eld in the separation channel, with one ground electrode in the reservoir closest to the junction. At the junction, the stacked zones were restacked under fi eld- enhanced conditions and then injected into the separation channels. The multistacking was veri fi ed under a fl uorescence microscope using Rhodamine 6G as the analyte, revealing a sensitivity enhancement factor (SEF) of 110. The stacking approach was also implemented in the nonaqueous MCE with contactless conductivity detection of the anticancer drug tamoxifen as well as its metabolites. The multistacking and analysis time was 40 and 110 s, respectively, the limit of detections was from 10 to 35 ng/mL and the SEFs were 20 to 50. The method was able to quantify the target analytes from breast cancer patients.