Porous polymer monolith assisted electrospray from a glass microdevice

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Abstract
The coupling of a lab‐on‐a‐chip microfluidic device to a nanoelectrospray ionization mass spectrometer has the potential to automate many routine analytical procedures and produce a powerful analytical tool. However, past coupling strategies have relied on complex manufacturing steps including drilling and etching the device to attach a capillary or building a nanospray emitter directly into the device. This study shows that a nanospray emitter can be easily fabricated using a porous polymer monolith (PPM) at the end of a glass microdevice. These devices are able to obtain a stable electrospray at a variety of flow rates (50–500 nL/min) but optimal results are obtained at lower flow rates (50–100 nL/min) compatible with electroosmotic flow processes. The PPM is photo‐patterned so that it can be placed in any position within the channel of the device with no dead volume. The porous character and the hydrophobic nature of the PPM both aid in development of a stable electrospray process. Total ion current traces for the constant infusion of leucine‐enkephalin and PPG show relative standard errors as low as 4%, and produce mass spectra with good signal‐to‐noise (S/N 43) from only 2 fmol of material. In addition, multiple experiments in a given day show good repeatability with variability as low as 13%, and the multiple flow paths inherent in the PPM limit sprayer clogging. Copyright © 2005 John Wiley & Sons, Ltd.