Development of Interfaces for Microchip Capillary Electrophoresis-Electrospray Mass Spectrometry
Date Issued
2006
Date
2006
Author(s)
Li, Fu-An
DOI
zh-TW
Abstract
Coupling a CE microchip with electrospray mass spectrometry provides more specific and universal analysis than with optical detection methods. Except a few integrated interfaces, the method of attaching a capillary sprayer remains the preferred choice. For the attachment of an external capillary sprayer, several critical aspects with the connection are the dead volume, alignment, and blockage of the channel. A simple method for making a sheathless chip-CE/ESI/MS device has been proposed. The interface was constructed based on a tapered capillary sprayer using a wire-assisted epoxy-gluing method. The wire-assisted method provided facile alignment of channels between the PMMA CE chip and an external capillary sprayer without the need for micromachining. Because the wire was in the channel during fixing, the risk of channel blockage by the epoxy was avoided. This chip CE device has minimal dead volume because the interstitial spaces were filled by a fast-fixing epoxy resin. The performance of the chip-CE/ESI/MS device was demonstrated with the analysis of peptide mixtures. The results showed that the relative standard deviation (RSD) of peak height and peak area were 3.0% and 1.3%, respectively. The reproducibility of migration time was less than 2.5%. Without any surface modification, the separation efficiency of a 6 cm channel was 650-2300 theoretical plates.
For the sheath flow interface, one major disadvantage is the dilution effect. With conventional sheath flow interface, the flow rate is in the range of several mocroliters per minute. This high flow rate of the sheath liquid induces a considerable dilution of the sample bands. A sheath liquid interface for chip CE-ESI-MS has been developed. The microdevice consisted of a PMMA CE microchip and a low-sheath-flow interface. Between the PMMA chip and the low-sheath-flow interface was a 1.5 cm fused-silica capillary transfer line. The wire-assisted epoxy-fixing method proposed in sheathless chip CE-ESI-MS interface was used to connect the transfer line. The performance of the device was demonstrated with the analysis of synthetic drugs. The results showed that the RSD of peak height and peak area were 2.1% and 2.7%, respectively. Without any surface modification, the separation efficiency of a 6 cm channel was 1600-2300 theoretical plates.
Nonvolatile buffer, such as phosphate buffer, is a popular buffer in CE/UV application. However, phosphate buffer is known to seriously suppress the analyte signal in ESI-MS. An interface capable of using phosphate buffer was developed. This interface consisted of a liquid junction and a low flow ESI interface. Phosphate buffer was added in the inlet reservoir and liquid junction reservoir. Under an acidic condition, the velocity of phosphate anion is large than EOF, so that phosphate anion will flow forward the inlet reservoir. Therefore, the phosphate anion was continuously supplied from the liquid junction into the CE column to maintain the separation efficiency. Sheath liquid was added to the low flow interface and provided the optimal composition for ESI. By using this liquid junction-low flow interface, it is possible to employ phosphate buffer in CE-ESI-MS or chip CE-ESI-MS without the suppression effect of phosphate buffer.
Subjects
電泳晶片
電灑法
質譜
chip CE
electrospray
mass spectrometry
Type
thesis
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