Microsphere Entrapped Emitters for Sample Preconcentration and Electrospray Ionization Mass Spectrometry

Abstract

In this study a nano-electrospray emitter is constructed by precisely positioning entrapped octadecylsilane (ODS) particles within a photoinitiated polymer at the exit aperture of a capillary. Following poly-merization, the microsphere/polymer hybrid material is able to withstand pressures greater than 4000 psi for 1 cm length of material. Smaller microspheres (3 microm) patterned at the exit aperture of a capillary generated the most sensitive/stable electrospray from 100 to 1000 nL/min and moderately stable signal under 100 nL/min. Constant infusion of a standard PPG solution from a batch of eleven emitters resulted in a relatively small variance in total ion current (TIC) counts (8%). The entrapped microsphere emitter design yields an emitter that minimizes clogging and eliminates dead volume between the chromatographic bed and the electrospray emitter. The entrapped ODS microspheres can also be used for sample preparation prior to mass spectrometry (MS) analysis. We show the solid-phase extraction and preconcentration of 20-700 fmol of a peptide (leucine enkephalin) prior to MS analysis on an emitter with 1 cm of entrapped microspheres.

Entrapment of functionalized silica microspheres with photo-initiated acrylate-based polymers

“…1 and 2 show no significant amounts of polymer, except to connect the spheres. The utility of these materials has already been demonstrated by our group, for use as a nanoelectrospray source for mass spectrometry [28] and as a column for capillary electrochromatography [27], for which separation efficiency was not hindered by the entrapping polymer. The extent to which the polymer affects the chromatographic properties of the microspheres is currently under detailed investigation in our group and will be the subject of future publication.…”

“…The columns have exceptional stability yet no interfering interstitial polymer formation, allowing lower back pressures while maintaining access to the microspheres. Our group has already demonstrated the utility of this type of material [26][27][28]. The novel entrapment procedures presented in this work can be utilized to encapsulate a bed of hydrophobic microspheres, though the general approach can be easily adapted to a variety of other types of particles.…”

Spherical and lamellar octadecylsilane hybrid silicas

“…[9] Among the employed organosilanes, octadecyltrimethoxysilane (ODS) and octadecyltrichlorosilane (OTS) have been largely used for surface chemical modification. Examples of applications of these hybrid materials in the development of self-assembled monolayers (SAMS), [10] mesoporous materiais, [11] nanocomposites, [12] pharmaceutical carriers [13] and columns for electrochromatography [14][15] are found in the literature.…”

Surface-mediated effects on porous polymer monolith formation within capillaries

“…The formulation for the porous polymer monolith is similar to that described in our previous papers [11,[26][27][28]. The polymerization mixture is composed of 67% porogenic solvent (60% acetonitrile, 20% ethanol (95%) and 20% potassium phosphate buffer (5 mM, pH -6.7)), 23% butyl acrylate, 10% 1,3-butanediol diacrylate, and 6.8-6.9 mg AIBN.…”