Optically gated vacancy electrophoresis in microfluidic devices

Microfluidics in amino acid analysis

Microfluidic devices have been widely used to derivatize, separate, and detect amino acids employing many different strategies. Virtually zero-dead volume interconnections and fast mass transfer in small volume microchannels enable dramatic increases in on-chip derivatization reaction speed, while only minute amounts of sample and reagent are needed. Due to short channel path, fast subsecond separations can be carried out. With sophisticated miniaturized detectors, the whole analytical process can be integrated on one platform. This article reviews developments of lab-on-chip technology in amino acid analysis, it shows important design features such as sample preconcentration, precolumn and postcolumn amino acid derivatization, and unlabeled and labeled amino acid detection with focus on advanced designs. The review also describes important biomedical and space exploration applications of amino acid analysis on microfluidic devices.

Monitoring the Electroosmotic Flow in Capillary Electrophoresis Using Contactless Conductivity Detection and Thermal Marks

The fundamental aspects and the capillary electrophoresis usage of thermal marks are presented. The so-called thermal mark is a perturbation of the electrolyte concentration generated by a punctual heating of the capillary while the separation electric field is maintained. The heating pulse is obtained by powering tungsten filaments or surface mount device resistors with 5 V during a few tens to hundreds of milliseconds. In the proposed model, the variation of the transport numbers with the rising temperature leads to the formation of low- and high-concentration regions during the heating. After cooling down, the initial mobilities of the species are restored and these regions (the thermal mark) migrate chiefly due to the electroosmotic flow (EOF). The mark may be recorded with a conductivity detector as part of a usual electropherogram and be used to index the analyte peaks and thus compensate for variations of the EOF. In a favorable case, 10 mmol/L KCl solution, the theory suggests that the error in the measurement of EOF mobility by this mean is only -6.5 x 10(-7) cm2 V-1 s-1. The method was applied to the analysis of alkaline ions in egg white, and the relative standard deviations of the corrected mobilities of these ions were smaller than 1%. This is a challenging matrix, because albumin reduces the EOF to 20% of its initial value after 11 runs. The combination of thermal mark, electrolysis separated, and contactless conductivity detection allowed the measurement of the EOF of a silica capillary with unbuffered KCl solution with constant ionic strength. The overall approach is advantageous, because one can easily control the chemical composition of the solution in contact with the inner surface of the capillary.