Development of transient trapping micellar electrokinetic chromatography coupled with mass spectrometry for steroids analysis.

An on-line sample preconcentration technique based on transient trapping (tr-trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr-trapping-UV) and electrospray ionization mass spectrometry detection (tr-trapping-ESI-MS). ESI-MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI-MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI-MS system, so its interference in ESI-MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr-trapping-ESI-MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr-trapping-ESI-MS protocol showed up to 540-fold enhancements of the peak intensity and 50-fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample.

Development of a microfluidic dispensing device for multivariate data acquisition and application in molecularly imprinting hydrogel preparation.

Molecularly imprinted polymers (MIPs) are superior materials with a molecular recognition ability that apply to various applications. In order to get high specificity recognition for target molecules, selecting polymerization conditions, which provide high interaction with the target template, is crucial. However, it requires time and labor to find the optimal polymerization composition, especially for large biomolecules. The advance in the microfluidic field enables researchers to control the flow rate and divide solutions based on the design of microfluidic devices for acquiring multivariate data by simultaneously preparing samples with different conditions. In this work, we fabricated microfluidic dispensing devices with different flow path widths that can give the solution of different flow rates. The accuracy of the flow rate was compared with the simulation value. As a result, the flow rate data showed almost the same data as the simulation value, and the dispensing volume ratio showed high reproducibility. Besides, the multivariate data from mixing the fluorescent molecule and protein solutions prepared by the dispensing device and a micropipette showed no significant difference with existing laboratory equipment. Finally, the dispensing device was used for preparing MIP hydrogels for lysozyme as a template protein. We successfully acquired multivariate data on the adsorption capacity of proteins, as a result, the hydrogels provided a high imprinting factor and adsorption specificity toward lysozymes.