Online preconcentration of high-salt samples using pressure-assisted field-amplified sample injection in flow-gated capillary electrophoresis
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Maddukuri, Naveen, Gong, Maojun. 2019. Online preconcentration of high-salt samples using pressure-assisted field-amplified sample injection in flow-gated capillary electrophoresis -- In Proceedings: 15th Annual Symposium on Graduate Research and Scholarly Projects. Wichita, KS: Wichita State University
Capillary electrophoresis (CE) is a valuable separation method; however, its detection sensitivity is often limited by the small sample volumes injected. Different strategies have been developed to enhance the sensitivity, e.g. on-line sample preconcentration, and/or using sensitive detection such as fluorescence and mass spectrometry. Sample stacking, an effective sample preconcentration strategy, is based on the uneven distribution of electric field across a capillary filled with buffer plugs with different ionic strengths. However, the basic sample stacking method fails for high-salt containing samples. We developed a new technique for flow-gated CE to perform on-line sample preconcentration of high-salt samples such as cerebrospinal fluid (CSF). Initially, the high-salt sample was fluorogenically derivatized with 2,3-Naphthalenedicarboxaldehyde (NDA) in the presence of cyanide. Then, a sample plug was hydrodynamically injected by vacuum on the outlet side of the capillary. Third, a reversed-voltage was applied to conduct field-amplified sample injection while maintaining a counter vacuum to elongate the injection time during the pushback. Finally, a normal-polarity voltage was applied for separations. During the injection procedure, the sample solution was continuously supplied to the cross section of the flow gate via a syringe pump, which ensured the inlet of the capillary was immersed in the sample; and the sample preconcentration might rely on the electrokinetic supercharging principle. Enhancement factors of 50-100 folds at optical conditions were obtained for a series of amino neurotransmitters including ?-aminobutyric acid (GABA), valine, methionine, isoleucine, and phenylalanine, and limits of detection were lowered down to the pico-molar range. Furthermore, this strategy was applied to the determinations of primary amine neurotransmitters in CSF by using the one-point standard addition method enabled by alternative injections of the two samples. The method is expected to be useful for analyzing other high-salt containing samples with such urine and blood plasma.
Presented to the 15th Annual Symposium on Graduate Research and Scholarly Projects (GRASP) held at the Rhatigan Student Center, Wichita State University, April 26, 2019.
Research completed in the Department of Chemistry, College of Liberal Arts and Sciences