Simplest ambient ionisation method yet for mass spec?

The novel ambient ionisation technique dubbed matrix-assisted ionization vacuum (MAIV) was introduced at the end of 2012 as an especially soft ionisation method in which ions were produced simply by exposing a matrix solution of the analyte to the vacuum in the mass spectrometer. There is no need for applied voltages, heat, or a laser beam. The pressure differential between the atmosphere and the inlet is sufficient to produce ions.

Those initial experiments were carried out using mass spectrometers with closed vacuum systems incorporating either electrospray ionisation or matrix-assisted laser desorption/ionisation. Now, Sarah Trimpin and Ellen Inutan from Wayne State University have simplified their method even further by modifying the ion sources so that they are partially open to atmospheric pressure, as described in Analytical Chemistry. The principle advantage of this change is to allow for the quick interchange of samples, leading to high-throughput analyses.

The best matrix they found to date was 3-nitrobenzyl alcohol and it was used to analyse different types of compounds from a variety of substrates. The drugs LSD and clozapine, the proteins carbonic anhydrase, ubiquitin and myoglobin, the peptide angiotensin I and the lipid sphingomyelin were analysed as matrix solutions on glass plates, wipes, foil, filter paper, PCR tubes and caps, and 96 and 384 well plates. Good spectra were obtained in all cases, ionisation being promoted simply by the difference in pressure at the interface.

This method suggests "a very simple approach to high throughput analyses for small and large nonvolatile molecules. Such an approach would not need an ion source and could use rolls of ribbon or paper as the matrix:analyte substrate. It could be useful in many areas where simplicity, sensitivity, and throughput are important such as blood spot analyses, portable mass spectrometers, and production control," said Trimpin.