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Improving the sensitivity of mass spectrometry by using a new sheath flow electrospray emitter array at subambient pressures.

ABSTRACT: Arrays of chemically etched emitters with individualized sheath gas capillaries were developed to enhance electrospray ionization (ESI) efficiency at subambient pressures. By incorporating the new emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, both ionization efficiency and ion transmission efficiency were significantly increased, providing enhanced sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses of conventional ESI-mass spectrometry (MS) interfaces by placing the emitter in the first reduced pressure region of the instrument. The new ESI emitter array design developed in this study allows individualized sheath gas around each emitter in the array making it possible to generate an array of uniform and stable electrosprays in the subambient pressure (10 to 30 Torr) environment for the first time. The utility of the new emitter arrays was demonstrated by coupling the emitter array/SPIN source with a time of flight (TOF) mass spectrometer. The instrument sensitivity was compared under different ESI source and interface configurations including a standard atmospheric pressure single ESI emitter/heated capillary, single emitter/SPIN and multi-emitter/SPIN configurations using an equimolar solution of nine peptides. The highest instrument sensitivity was observed using the multi-emitter/SPIN configuration in which the sensitivity increased with the number of emitters in the array. Over an order of magnitude MS sensitivity improvement was achieved using multi-emitter/SPIN compared with using the standard atmospheric pressure single ESI emitter/heated capillary interface.

SUBMITTER: Cox JT

PROVIDER: S-EPMC4177967 | biostudies-literature | 2014 Dec

REPOSITORIES: biostudies-literature

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Improving the sensitivity of mass spectrometry by using a new sheath flow electrospray emitter array at subambient pressures.

Cox Jonathan T JT Marginean Ioan I Kelly Ryan T RT Smith Richard D RD Tang Keqi K

Journal of the American Society for Mass Spectrometry 20140328 12

Arrays of chemically etched emitters with individualized sheath gas capillaries were developed to enhance electrospray ionization (ESI) efficiency at subambient pressures. By incorporating the new emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, both ionization efficiency and ion transmission efficiency were significantly increased, providing enhanced sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses of conventional ...[more]

PMID: 24676894

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Project description:We have reported a set of electrokinetically pumped sheath flow nanoelectrospray interfaces to couple capillary zone electrophoresis with mass spectrometry. A separation capillary is threaded through a cross into a glass emitter. A side arm provides fluidic contact with a sheath buffer reservoir that is connected to a power supply. The potential applied to the sheath buffer drives electro-osmosis in the emitter to pump the sheath fluid at nanoliter per minute rates. Our first-generation interface placed a flat-tipped capillary in the emitter. Sensitivity was inversely related to orifice size and to the distance from the capillary tip to the emitter orifice. A second-generation interface used a capillary with an etched tip that allowed the capillary exit to approach within a few hundred micrometers of the emitter orifice, resulting in a significant increase in sensitivity. In both the first- and second-generation interfaces, the emitter diameter was typically 8 ?m; these narrow orifices were susceptible to plugging and tended to have limited lifetime. We now report a third-generation interface that employs a larger diameter emitter orifice with very short distance between the capillary tip and the emitter orifice. This modified interface is much more robust and produces much longer lifetime than our previous designs with no loss in sensitivity. We evaluated the third-generation interface for a 5000 min (127 runs, 3.5 days) repetitive analysis of bovine serum albumin digest using an uncoated capillary. We observed a 10% relative standard deviation in peak area, an average of 160,000 theoretical plates, and very low carry-over (much less than 1%). We employed a linear-polyacrylamide (LPA)-coated capillary for single-shot, bottom-up proteomic analysis of 300 ng of Xenopus laevis fertilized egg proteome digest and identified 1249 protein groups and 4038 peptides in a 110 min separation using an LTQ-Orbitrap Velos mass spectrometer; peak capacity was ?330. The proteome data set using this third-generation interface-based CZE-MS/MS is similar in size to that generated using a commercial ultraperformance liquid chromatographic analysis of the same sample with the same mass spectrometer and similar analysis time.

Dataset Information

Improving the sensitivity of mass spectrometry by using a new sheath flow electrospray emitter array at subambient pressures.

Publications

Improving the sensitivity of mass spectrometry by using a new sheath flow electrospray emitter array at subambient pressures.

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