The role of free electrons in MALDI: electron capture by molecules of α-cyano-4-hydroxycinnamic acid

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Eur. J. Mass Spectrom. DOI: 10.1255/ejms.650

The role of free electrons in MALDI: electron capture by molecules of α-cyano-4-hydroxycinnamic acid

S.A. Pshenichnyuk^* and N.L. Asfandiarov
Institute of Physics of Molecules and Crystals, Ufa Research Center, Russian Academy of Sciences, October Avenue 151, 450075 Ufa, Russia. E-mail:

ABSTRACT:

Low energy (012 eV) electron attachment to molecule of typical matrix substance used for Matrix Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI MS), namely α-cyano-4-hydroxicynnamic acid, has been investigated in the gas phase at different temperatures in the range from 140°C to 260°C by means of Negative Ion Electron Capture Mass Spectrometry (ECNI MS). The yield of negative ions, formed by electron capture, was measured as a function of incident electron energy for four different temperatures. The long-lived parent molecular anion [M] (M/Z 189) was observed in negative ion mass spectra of the substance under investigation. Its autodetachment lifetime was estimated to approximately 600 µs. It was found that at 140°C the main decay channel of the long-lived temporary molecular anion of α-cyano-4-hydroxicynnamic acid is a formation of [MCOOH] fragment negative ion (M/Z 144) with intensity 37.2% in percentage terms with respect to the total anion current. Also there are [MH], [MCO₂] and [CN] fragments in the spectra with intensities of about 7.7%, 21.6% and 3.1% at 140°C. It was shown that escape of CO₂ molecule from the parent molecular anion is a slow process. It takes [M] of about 10 µs to decay on molecule of carbon dioxide and [MCO₂] fragment anion. Increasing of temperature of the target molecule alters significantly the negative ion mass spectra of α-cyano-4-hydroxicynnamic acid. A possible role of the findings in typical MALDI MS experiments is discussed.

Keywords: MALDI, negative ions, free electrons, low energy electron attachment, temperature effect

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