Lateral resolution of desorption nanoelectrospray: a nanospray tip without nebulizing gas as a source of primary charged droplets

Desorption nanoelectrospray (nanoDESI) was described in 2007 and it represents a miniaturized version of desorption electrospray without the assistance of the nebulizing gas. Compared to DESI, a nanoelectrospray tip (2 ± 1 μm I.D.) generates primary charged droplets of smaller sizes and lower spray liquid flow rates. This is the first report on utilization of nanoDESI for mass spectrometry imaging (MSI). Its new coupling with a Q-TOF instrument allowed faster mass spectra acquisition (4 Hz) essential for MSI of fine surface details. To evaluate nanoDESI potential for mass spectrometry imaging, etched glass substrates with Rhodamine B patterns of different dimensions were prepared. The Rhodamine B lines were analysed in 1D scanning mode and their width was determined experimentally by nanoDESI measurement. The experimental data revealed that the lateral resolution of nanoDESI is close to 30 μm along the x-axis (orthogonal to the inlet). 2D scanning mode confirmed good resolution along both axes as dye squares with dimensions about 60 μm × 60 μm were easily distinguished. The low flow rate of the spray liquid reduced undesirable analyte washing effects, which allowed repeated scanning analysis of the surface. The presented results demonstrate the applicability of nanoDESI for high surface resolution mass spectrometry imaging.