Fig. 1. Design and optimization of MCAEF. (a) A photograph of the MCAEF set-up inside an electronic matrix sprayer. (b) Schematic diagram of MCAEF mechanism. (c) Effect of electric field intensity (E) on S/Ns of six lipids detected by positive-ion (+) MALDI-FTICR MS. The error bars reflect nine mass spectra acquired from triplicate tissue slides that were mounted on three ITO-coated microscopic glass slides. (d) (+) MALDI-FTICR mass spectra of lipids detected on rat liver tissue sections without MCAEF. (e) (+) MALDI-FTICR mass spectra of lipids detected from rat liver tissue sections with (+) MCAEF. (f) (+) MALDI-FTICR mass spectra of lipids detected from rat liver tissue sections with (–) MCAEF. Two ESI generated ions from the Agilent “ESI tuning mix” solution (i.e., m/z 622.029 and m/z 922.010), were used as the controls and are labelled with black asterisks. The m/z 922.010 ion was used for peak intensity normalization. The matrix-related ions are labeled “▲”, including m/z 303.050 [quercetin + H]⁺, m/z 341.006 [quercetin + K]⁺, and m/z 643.048 [2quercetin + K]⁺. (g) Overlay of mass spectra of the “ESI tuning mix” peaks of m/z 622.029 and m/z 922.010, and PC(38 : 4) of m/z 848.557 with and without MCAEF.