The development of capillary electrophoresis mass spectrometry interface and application of magnetic nanoparticles in capillary electrophoresis mass spectrometry
Date Issued
2011
Date
2011
Author(s)
Huang, Ju-Li
Abstract
Capillary electrophoresis mass spectrometry provides the advantages of high efficiency separation with high compound identification capability. However, several problems limit the utility of the capillary electrophoresis mass spectrometry. These problems include the operation and performance of a capillary electrophoresis mass spectrometry interface, incompatible with the nonvolatile buffer, and less sensitivity due to the use of a capillary-format column. To overcome these problems, several approaches were proposed in this work.
Using ammonium dodecyl sulfate (ADS) as the surfactant, the response of three common interfaces, sheath liquid interface, sheathless interface and low sheath flow interface in the direct coupling of microchip micellar electrokinetic chromatography with electrospray ionization mass spectrometry was studied. In the range of 10 to 40 mM surfactant, a conventional sheath liquid interface provided poorer sensitivity than both sheathless interface and low sheath flow interface. At a surfactant concentration less than 20 mM, a low sheath flow interface exhibited less sensitivity than a sheathless interface, however it outperformed the sheathless interface above 20 mM concentration. At a surfactant concentration above 20 mM, signal reduction due to dilution of the analyte compensated by signal enhancement gained from a reduction in ion suppression effect. The difference in responses of the interfaces was mainly due to the dilution effect, whereas, the effect of flow rate became an important factor when the difference in responses between the interfaces was not significant. The utility of the polymethyl methacrylate (PMMA) microchip MEKC/MS using a low sheath flow interface was demonstrated by analysis of sulfonamides at 40 mM concentration.
To simplify the CE/MS operation, a dual mode CE/MS interface based on a PDMS casting microdevice was proposed. Because of the transparency of the PDMS material, the separation column and the ESI emitter could be connected well by using a microscope. A hole fabricated on the edge of the conducting reservoir was designed for insertion of an ESI sprayer. Prior to the insertion of an ESI sprayer, the hole was filled with conducting electrolyte and thus the electric conduction could be established through the space formed between the ESI sprayer and hole. The interface could perform sheathless CE/MS operation because the formation of thin liquid film between the hole and ESI sprayer. The interface could perform the low flow CE/MS operation by removing the polyimide coating of the ESI sprayer because the formation of larger space (~15 μm). Because of the larger space, the make-up liquid could be delivered to the ESI sprayer. The CE separation integrity was preserved under both the sheathless and the low flow operation.
To increase the utility of nonvolatile buffer in CE/MS, an integrated double junction interface based on a PDMS casting microdevice for the use of phosphate buffer without the ion suppression effect was developed. This interface consists of a junction reservoir, a conducting reservoir and a microchannel. Between junction reservoir and conducting reservoir is a microchannel for analyte transfer. The junction reservoir was designed to preserve the CE separation integrity because the phosphate anion flowed from the junction reservoir to the separation capillary. Whereas the conducting reservoir could be used to establish electric contact for sheathless CE/MS operation or deliver the make-up liquid for low flow CE/MS operation. The feasibility of this interface was demonstrated with the analysis of histamine antagonists under low flow CE/MS operation and perfluorocarboxylic acids under sheathless operation at low-pH buffer and high-pH buffer, respectively.
The CE/MS sensitivity is rather limited due to the use of a capillary-format column. To improve the sensitivity, the functionalized magnetic nanoparticle (MNP) was used as concentrating probes. A simple strategy for the synthesis of boronic-acid functionalized MNP was proposed. The boronic-acid functionalized MNP shows a high selective enrichment of glycopeptides. For enrichment of the tryptic peptides derived from the asialofetuin (ASF), all the N-linked glycopeptides could be captured with this material. The use of this nanomaterial in the CE/MS not only reduces the sample complexity but also acts as concentrating probe.
Subjects
capillary electrophoresis-mass spectrometry
low sheath flow interface
sheathless interface
sheath liquid interface
integrated double junction interface
microchip micellar electrokinetic chromatography
phosphate buffer
magnetic nanoparticles
boronic acid
glycopeptide
Type
thesis
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