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Enhancing Performance of Liquid Sample Desorption Electrospray Ionization Mass Spectrometry Using Trap and Capillary Columns.

ABSTRACT: Desorption electrospray ionization mass spectrometry (DESI-MS) is a recent and important advance in the field that has extensive applications in surface analysis of solid samples but has also been extended to analysis of liquid samples. The liquid sample DESI typically employs a piece of fused silica capillary to transfer liquid sample for ionization. In this study, we present the improvement of liquid sample DESI-MS by replacing the sample transfer silica capillary with a trap column filled with chromatographic stationary phase materials (e.g., C4, C18). This type of trap column/liquid sample DESI can be used for trace analysis of organics and biomolecules such as proteins/peptides (in nM concentration) in high salt content matrices. Furthermore, when the sample transfer capillary is modified with enzyme covalently bound on its inside capillary wall, fast digestion (< 6 min) of proteins such as phosphoproteins can be achieved and the online digested proteins can be directly ionized using DESI with high sensitivity. The latter is ascribed to the freedom to select favorable spray solvent for the DESI analysis. Our data shows that liquid sample DESI-MS with a modified sample transfer capillary has significantly expanded its utility in bioanalysis.

SUBMITTER: Cheng S

PROVIDER: S-EPMC4878830 | biostudies-other | 2015 Dec

REPOSITORIES: biostudies-other

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Enhancing Performance of Liquid Sample Desorption Electrospray Ionization Mass Spectrometry Using Trap and Capillary Columns.

Cheng Si S Wang Jun J Cai Yi Y Loo Joseph A JA Chen Hao H

International journal of mass spectrometry 20151201

Desorption electrospray ionization mass spectrometry (DESI-MS) is a recent and important advance in the field that has extensive applications in surface analysis of solid samples but has also been extended to analysis of liquid samples. The liquid sample DESI typically employs a piece of fused silica capillary to transfer liquid sample for ionization. In this study, we present the improvement of liquid sample DESI-MS by replacing the sample transfer silica capillary with a trap column filled wit ...[more]

PMID: 27239159

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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.

Project description:We recently reported the use of desorption electrospray ionization (DESI) as a novel interface to couple high-performance liquid chromatography (HPLC) with mass spectrometry (MS) (Chem. Commun. 2011, 47, 4171). One of the benefits of such an interface is that post-column derivatization of separated analytes can be integrated with ionization via a "reactive" DESI approach in which a derivatizing reagent is doped into the spray solvent. The reactive DESI interface allows analyte desorption/ionization from the end of the chromatographic column with prompt MS detection; a short time delay of ~20 ms was demonstrated. In this study, we extended this application by "supercharging" proteins following HPLC separation using a DESI spray solvent containing supercharging reagents, m-nitrobenzyl alcohol (m-NBA) or sulfolane. Proteins (insulin, ubiquitin, lysozyme and α-lactalbumin) eluted out of the LC column can be supercharged with the protein charge state distributions (CSDs) significantly increased (to higher charge), which would be advantageous for subsequent top-down MS analysis of proteins. Interestingly, supercharging combined with reactive DESI enhances tolerance towards trifluoroacetic acid (TFA), which is known to be a superior additive in the mobile phase for premium peptide/protein chromatographic separation but has severe signal suppression effects for conventional electrospray ionization (ESI). In comparison to electrosonic spray ionization (ESSI), a variant form of ESI, the sensitivity of protein analysis using LC/DESI-MS with the mobile phase containing TFA can be improved by up to 70-fold for lysozyme and α-lactalbumin by including m-NBA in the DESI spray solvent. Presumably, by reducing TFA dissociation in the droplet, supercharging agents lower trifluoroacetate anion concentrations and concomitantly reduce ion pairing to analyte cationic sites. The reduced ion pairing therefore decreases the TFA signal suppression effect. The supercharging capability and the reduction of TFA signal suppression suggest that LC/DESI-MS is a valuable method for protein analysis.

Dataset Information

Enhancing Performance of Liquid Sample Desorption Electrospray Ionization Mass Spectrometry Using Trap and Capillary Columns.

Publications

Enhancing Performance of Liquid Sample Desorption Electrospray Ionization Mass Spectrometry Using Trap and Capillary Columns.

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