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Issue 5, 2012
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Gas-phase basicity of several common MALDI matrices measured by a simple experimental approach

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Abstract

We present a combined experimental and theoretical study to determine the gas-phase basicity of several relatively small organic molecules that are used as matrices in MALDI: alpha-cyano-4-hydroxycynnamic acid (αCHCA), ferulic acid (FA), 3-hydroxypicolinic acid (HPA), sinapinic acid (SA), and 2,4,6-trihydroxyacetophenone (THAP). Our simple and fast experimental approach utilizes the ability of an electrosonic spray ionization (ESSI) source to produce high densities of gas-phase ions at ambient conditions, so that their gas-phase thermochemical properties can be probed in a bracketing-like experiment at atmospheric pressure, with no need for high vacuum. The reaction between the analyte and reference bases is monitored by a commercial mass spectrometer. We determined the following GB values of the MALDI matrices studied: 908.1 ± 0.8 (αCHCA), 863.8 ± 8.0 (FA), 876.3 ± 10.2 (HPA), 867.4 ± 1.4 (SA), and 864.2 ± 7.6 (THAP) kJ mol−1. A good agreement between the experimentally measured and computationally predicted (DFT-B3LYP, G4MP2) gas-phase basicities for the studied compounds is found, except for αCHCA for which the calculations resulted in approximately 80 kJ mol−1 lower GB. We attribute the observed discrepancy between the measured and calculated values to a gas-phase rearrangement of αCHCA into a heterocyclic aromatic isomer, 7-hydroxyquinoline-3-carboxylic acid (HQA). HQA is thermodynamically more stable and features higher GB than that of αCHCA (calculated at approximately 920 kJ mol−1). The gas-phase basicity values of THAP and HPA are reported for the first time.

Graphical abstract: Gas-phase basicity of several common MALDI matrices measured by a simple experimental approach

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Publication details

The article was received on 17 Nov 2011, accepted on 18 Nov 2011 and first published on 06 Jan 2012


Article type: Paper
DOI: 10.1039/C1RA01117K
Citation: RSC Adv., 2012,2, 1962-1969
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    Gas-phase basicity of several common MALDI matrices measured by a simple experimental approach

    K. Barylyuk, L. Fritsche, R. M. Balabin, R. Nieckarz and R. Zenobi, RSC Adv., 2012, 2, 1962
    DOI: 10.1039/C1RA01117K

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