Sample pretreatment on a microchip with an integrated electrospray emitter

Abstract

This study presents a microbead-packed PDMS microchip with an integrated electrospray emitter for sample pretreatment prior to sheathless ESI-MS. We prove the concept of analytical functions integrated onto a cm-sized area of a single bulk material. The microchip consists of two PDMS substrates replicated from SU-8 fabricated silicon wafer masters, bonded together after oxidation by corona discharge treatment. The channel within the microchip contains a grid structure that was used to trap 5 microm hypercross-linked polystyrene beads. The beads acted as a medium for sample desalting and enrichment. Electrical contact for the sheathless ESI process was achieved by coating the integrated emitter with conductive graphite powder after applying a thin layer of PDMS as glue. The coating as well as the bond of the PDMS structures showed excellent durability. A continuous spray was obtained from the microchip for over 800 h in a long-term electrospray stability experiment. Desalting and enrichment of neuropeptides from a physiological salt solution was successful by loading the sample onto the packed beads, followed by a washing and an eluting step. The results were obtained and evaluated using a TOF MS. An LOD of approximately 20 fmol (loaded onto the beads) for angiotensin II was obtained from a sample of neuropeptides dissolved in physiological salt solution.

Methods for samples preparation in proteomic research

“…is less frequently used [384], since they require non-volatile inorganic buffers. Nevertheless, these types of chromatography are often used in biochemical purifications (using volatile buffers that overcome such problems) as they preserve the function of proteins, therefore, in order to facilitate ESI-MS analysis of eluents, on-line desalting methods were developed based on microdialysis [385], or other principles [186,386].…”

Recent progress in microchip electrophoresis–mass spectrometry

“…However, the separation efficiencies on the fabricated device are apparently low due to irreversible adsorption of the analytes onto the bare PDMS surface and the applicable BGS is limited to higher pH. To improve the separation performance, a dynamic coating with a cationic polymer, PolyE-323, has been introduced in the PDMS channel on the same device [48]. As a result, three peptides can be separated with acceptable resolutions.…”

Recent applications of capillary electrophoresis–mass spectrometry (CE–MS): CE performing functions beyond separation

“…Examples involving sample matrix cleanup include: the affinity monolithic column to immobilize low abundance proteins and remove abundant immunoglobulin G (IgG [79]); a C18-derivatized sol-gel bed to adsorb hydrophobic peptides from human urine, while washing away the hydrophilic peptides and salt ions [81], and the microextraction of ephedrine and pseudoephedrine from human plasma and urine using monolithic column [113]. In addition, microchip-based [114] sample enrichment and cleanup was demonstrated by Lindberg et al Polystyrene beads were trapped inside the separation channel to enrich angiotensin II from physiological salt solution. A washing step was performed to remove salt and other contaminants, and the purified analytes were identified with ESI-MS.…”