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The effect of electrospray solvent composition on desorption electrospray ionisation (DESI) efficiency and spatial resolution.

Green, F M; Salter, T S; Gilmore, I S; Stokes, P*; O'Connor, G* (2010) The effect of electrospray solvent composition on desorption electrospray ionisation (DESI) efficiency and spatial resolution. Analyst, 135 (4). pp. 731-737.

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Abstract

This study shows that the parameters contact angle, solubility and solvent properties are all important for improving the spot size and efficiency of DESI. Model amino acid systems were studied to explore different factors affecting the efficiency of desorption electrospray ionisation (DESI), E. when changing the solvent composition. A model system of phenylalanine, evaporated on to glass, uv/ozone treated glass and PTFE substrates were studied with different electrospray solvent compositions of ACN:H2O, MeOH:H2O, EtOH:H2O and IPA2:H2O with varying fractions of organic solvent. This showed that a greater fraction of organic solvent could reduce the DESI spot size by up to a factor 4 times than the traditioanlly used 0.5 fraction. The wettability of the substrate surface is shown to have a weak effect on DESI spot size, with low wettabilities and solubilities causing greater spreading and distribution of droplets and hence larger DESI spot sizes.

Different amino acids were studied with a constant electrospray solvent composition, to distinguish the effects of solubility and solvent properties. This shows that E is linearly dependent on analyte solubility. However, this does not account for the large improvements in E by increased electrospray organic solvent fraction. On the phenylalanine system, an increase in protonated [M+H]+ intensity means a times 35 enhancement in E when moving from a 0.5 to a 0.9 organic solvent fraction. This study shows that these enhacements are due to smaller electrospray droplets rather than changes in solubility or ionisation. This study allowed the effects of different chemical, surface and ionisation mechanisms to be understood individually, leading to better optimisation and understanding of DESI.

Item Type: Article
Keywords: DESI, ambient mass spectrometry, direct analysis, solvent composition
Subjects: Nanoscience
Nanoscience > Surface and Nanoanalysis
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/4611

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