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Analysis of samples stored as individual plugs in a capillary by electrospray ionization mass spectrometry.

ABSTRACT: Droplets or plugs within multiphase microfluidic systems have rapidly gained interest as a way to manipulate samples and chemical reactions on the femtoliter to microliter scale. Chemical analysis of the plugs remains a challenge. We have discovered that nanoliter plugs of sample separated by air or oil can be analyzed by electrospray ionization mass spectrometry when pumped directly into a fused silica nanospray emitter tip. Using leucine-enkephalin in methanol and 1% acetic acid in water (50:50 v:v) as a model sample, we found carry-over between plugs was <0.1% and relative standard deviation of signal for a series of plugs was 3%. Detection limits were 1 nM. Sample analysis rates of 0.8 Hz were achieved by pumping 13 nL samples separated by 3 mm long air gaps in a 75 microm inner diameter tube. Analysis rates were limited by the scan time of the ion trap mass spectrometer. The system provides a robust, rapid, and information-rich method for chemical analysis of sample in segmented flow systems.

SUBMITTER: Pei J

PROVIDER: S-EPMC2846185 | biostudies-literature | 2009 Aug

REPOSITORIES: biostudies-literature

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Analysis of samples stored as individual plugs in a capillary by electrospray ionization mass spectrometry.

Pei Jian J Li Qiang Q Lee Mike S MS Valaskovic Gary A GA Kennedy Robert T RT

Analytical chemistry 20090801 15

Droplets or plugs within multiphase microfluidic systems have rapidly gained interest as a way to manipulate samples and chemical reactions on the femtoliter to microliter scale. Chemical analysis of the plugs remains a challenge. We have discovered that nanoliter plugs of sample separated by air or oil can be analyzed by electrospray ionization mass spectrometry when pumped directly into a fused silica nanospray emitter tip. Using leucine-enkephalin in methanol and 1% acetic acid in water (50:5 ...[more]

PMID: 19555052

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Project description:Most hyphenated analytical approaches that rely on liquid chromatography-MS require relatively long separation times, produce incomplete resolution of oligosaccharide mixtures, use eluents that are incompatible with electrospray ionization, or require oligosaccharide derivatization. Here we demonstrate the analysis of heparin oligosaccharides, including disaccharides, ultralow molecular weight heparin, and a low molecular weight heparin, using a novel electrokinetic pump-based CE-MS coupling eletrospray ion source. Reverse polarity CE separation and negative-mode electrospray ionization were optimized using a volatile methanolic ammonium acetate electrolyte and sheath fluid. The online CE hyphenated negative-ion electrospray ionization MS on an LTQ Orbitrap mass spectrometer was useful in disaccharide compositional analysis and bottom-up and top-down analysis of low molecular weight heparin. The application of this CE-MS method to ultralow molecular heparin suggests that a charge state distribution and the low level of sulfate group loss that is achieved make this method useful for online tandem MS analysis of heparins. Graphical abstract Most hyphenated analytical approaches that rely on liquid chromatography-MS require relatively long separation times, produce incomplete resolution of oligosaccharide mixtures, use eluents that are incompatible with electrospray ionization, or require oligosaccharide derivatization. Here we demonstrate the analysis of heparin oligosaccharides, including disaccharides, ultralow molecular weight heparin, and a low molecular weight heparin, using a novel electrokinetic pump-based CE-MS coupling eletrospray ion source. Reverse polarity CE separation and negative-mode electrospray ionization were optimized using a volatile methanolic ammonium acetate electrolyte and sheath fluid. The online CE hyphenated negative-ion electrospray ionization MS on an LTQ Orbitrap mass spectrometer was useful in disaccharide compositional analysis and bottom-up and top-down analysis of low molecular weight heparin. The application of this CE-MS method to ultralow molecular heparin suggests that a charge state distribution and the low level of sulfate group loss that is achieved make this method useful for online tandem MS analysis of heparins.

Project description:We present the first comprehensive capillary electrophoresis electrospray ionization mass spectrometry (CESI-MS) analysis of post-translational modifications derived from H1 and core histones. Using a capillary electrophoresis system equipped with a sheathless high-sensitivity porous sprayer and nano-liquid chromatography electrospray ionization mass spectrometry (nano-LC-ESI-MS) as two complementary techniques, we characterized H1 histones isolated from rat testis. Without any pre-separation of the perchloric acid extraction, a total of 70 different modified peptides, including 50 phosphopeptides, were identified in the rat linker histones H1.0, H1a-H1e, and H1t. Out of the 70 modified H1 histone peptides, 27 peptides could be identified with CESI-MS only, and 11 solely with LC-ESI-MS. Immobilized metal-affinity chromatography enrichment prior to MS analysis yielded a total of 55 phosphopeptides; 22 of these peptides could be identified only by CESI-MS, and 19 only by LC-ESI-MS, showing the complementarity of the two techniques. We mapped 42 H1 modification sites, including 31 phosphorylation sites, of which 8 were novel sites. For the analysis of core histones, we chose a different strategy. In a first step, the sulfuric-acid-extracted core histones were pre-separated using reverse-phase high-performance liquid chromatography. Individual rat testis core histone fractions obtained in this way were digested and analyzed via bottom-up CESI-MS. This approach yielded the identification of 42 different modification sites including acetylation (lysine and N(α)-terminal); mono-, di-, and trimethylation; and phosphorylation. When we applied CESI-MS for the analysis of intact core histone subtypes from butyrate-treated mouse tumor cells, we were able to rapidly detect their degree of modification, and we found this method very useful for the separation of isobaric trimethyl and acetyl modifications. Taken together, our results highlight the need for additional techniques for the comprehensive analysis of post-translational modifications. CESI-MS is a promising new proteomics tool as demonstrated by this, the first comprehensive analysis of histone modifications, using rat testis as an example.

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Analysis of samples stored as individual plugs in a capillary by electrospray ionization mass spectrometry.

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Analysis of samples stored as individual plugs in a capillary by electrospray ionization mass spectrometry.

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