Electrospray ionisation is the most commonly used method for mass spectrometry analysis in the department. It is quick and easy to run, and usually results in the molecule of interest being ionised as a molecular ion adduct. Samples can be recorded in positive or negative mode, identifying either cations or anions.

Positive mode

The molecular ion adduct formed is usually a protonated (M+H⁺), sodiated (M+Na⁺) or potassiated (M+K⁺) species. Peaks in the resulting spectrum therefore correspond to the molecular mass plus 1 for H, 23 for Na or 39 for K.

Negative mode

The molecular ion adduct formed

When analysing a mass spectrum to confirm the presence of a species in ESI mass spectrometry, the following should both be met:

• A close correlation between the calculated and observed mass (typically <5 ppm) for the identified molecular ion adduct(s)

• The isotope pattern for molecular ion adduct(s) matching the predicted isotope abundance

ESI as a technique can confirm the presence of a compound, but the technique provides no information on the purity of a sample. The abundance of different ESI peak groups does not correlate with the quantities of different components in the analysed sample.

This page provides information on the analysis of ESI mass spectra which have been collected. For information on sample submission and recording of data, see the instrumentation pages for mass spectrometry.