National Physical Laboratory

Ambient mass spectrometry

Ambient mass spectrometry techniques enable analysis of diverse samples with minimal sample preparation and without exposure to the vacuum required by other MSI techniques.

Desorption electrospray ionisation (DESI)

Desorption electrospray ionisation (DESI) was first described in 2004 by Graham Cook's group, and has rapidly developed into a powerful method for rapid imaging of a wide range of analytes under ambient conditions.

In DESI, 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.

DESI 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, DESI 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 (LESA)

LESA 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 LESA 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 LESA in forensics and spatial profiling of proteins.

Instrumentation

Waters Synapt G2-Si

  • High-resolution hybrid Q-TOF mass spectrometer with ion mobility
  • Waters/Prosolia DESI source
  • Travelling wave ion mobility provides separation by collisional cross-sectional area, as well as mass-to-charge ratio
  • ESI source
Waters Synapt G2-Si with DESI source
Waters Synapt G2-Si with DESI source


Thermo LTQ Orbitrap Velos mass spectrometer

  • Advion Triversa Nanomate source with liquid extraction for surface analysis (LESA) capability
  • Prosolia DESI 2D source
  • Developmental atmospheric pressure, transmission mode MALDI source (AP-TM-MALDI)

Selected publications

Measurement services

If you are interested in accessing the techniques and expertise available at NiCE-MSI and NPL, there are many ways of working with us.

Contact

Josephine Bunch

Last Updated: 30 Oct 2017
Created: 16 Nov 2016

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