Historically, the majority of benchtop GC-MS users have concentrated on Electron Impact ionisation as the primary mode of operation. This stems from the relative simplicity of the technique together with its powerful ability to confirm unknown compounds via library searching of the acquired EI spectra.

Conversely, the complimentary techniques of CI+ and especially CI- have been viewed more as 'research' modes and their use has largely been confined to the larger, non bench-top instruments.

However, recent advances in bench-top MS systems have permitted some instrument manufacturers to offer negative ion Cl on a compact mass analyser. This presentation will consider the relative advantages and disadvantages of using CI- on a range of 'ECD-type' compounds, both for GC-MS and LC-MS.