Comparisons of ambient spray ionization imaging methods

Ambient ionization methods allow for the examination of surfaces in their native conditions at atmospheric pressure with minimal or no preparation. Spray-based ambient ionization methods such as desorption electrospray ionization (DESI) and easy ambient sonic-spray ionization (EASI) have been successfully applied to imaging mass spectrometry. In 2012, a comparative study between DESI and EASI on spatial resolution and sensitivity was published by Janfelt and Norgaard (J. Am. Soc. Mass Spectrom., 23 (2012) 1670-1678). We expand on that work by comparing DESI and EASI techniques for the assessment of the limit of detection (LOD) of several drugs on a PTFE surface and for the determination of the spray spot size varying flow rate and solvent composition for imaging purposes. MS/MS imaging was also done with both methods for performance comparison. The results showed that good ion images can be obtained by both techniques in the MS or MS/MS mode. No significant difference was observed in the spray spot size produced by DESI and EASI. DESI was found to have similar or higher sensitivity than EASI depending on the analyte interrogated. (C) 2014 Elsevier B.V. All rights reserved.