Desorption electrospray ionisation
Desorption electrospray ionisation (DESI) has recently developed into a powerful method for rapid imaging of a wide range of analytes under ambient conditions.
In desorption electrospray ionisation, a focused electrospray of a volatile solvent is directed at the sample surface, dissolving molecular constituents of the surface which become encapsulated in ejected secondary droplets. As the solvent in the secondary droplets evaporates, surface-originating species are ionised and enter the inlet of the mass spectrometer.
Desorption electrospray ionisation can provide ambient, label-free imaging with no sample modification. Its relatively soft analysation may lead to low analyte fragmentation and easier identification. By rastering the sample stage, images with a pixel size of 20-100 µm may be achieved. Through optimisation of solvent system and spray parameters, desorption electrospray ionisation may enable the detection and localisation of many analyte classes including drugs, lipids, metabolites, peptides, proteins, glycans, isomers, polymers and processing contaminants.
NPL has a strong background in understanding the fundamentals behind DESI, enabling reliable and reproducible measurements. We continue to advance the use of DESI for tissue imaging, pharmaceutical development and analysis of medical devices.
Liquid extraction for surface analysis
Liquid extraction for surface analysis decouples the sampling and ionisation events, enabling analysis of diverse analytes and complex geometries from selected spatial locations. Using a robotic pipette, a solvent droplet is brought into contact with the sample surface. Analytes are dissolved into the solvent, which is reaspirated before being transferred for nanoelectrospray ionisation through a nanoESI chip.
Work at NPL has explored the use of liquid extraction for surface analysis for analysis of medical devices and wound dressings, and its multimodal use with other MSI techniques. We work closely with stakeholders interested in the application of liquid extraction for surface analysis in forensics and spatial profiling of proteins.