Modification of a gas chromatography/atmospheric pressure chemical ionisation time-of-flight mass spectrometer as an alternative to automated atmospheric pressure solids analysis probe.

Abstract

The atmospheric pressure solids analysis probe (ASAP) has been successfully introduced into laboratories as a routine analytical tool but the technique is labour-intensive and is not easily automated. This paper describes the modifications made to an existing atmospheric pressure gas chromatography (APGC) system to enable the automated analysis of samples that would have otherwise been analysed by ASAP. Liquid samples were injected into a 1 m piece of fused silica guard column using a standard split/splitless gas chromatography (GC) inlet, oven and autosampler. A novel timing delay circuit was developed and integrated into the system to control acquisition start times and a bespoke heating block/calibrant delivery system was used to transport either the calibration or reference compound into the ionisation source. The modified system has allowed the successful analysis of those samples requiring ASAP to be carried out in a fully automated manner using APGc. The analysis is rapid and can be carried out in less than 2 min. The results obtained are directly comparable with those obtained by ASAP. A typical mass accuracy of better than 5 mm/z units was achieved, allowing the molecules to be identified based on their elemental formulae. An existing APGC system has been successfully modified and is suitable for the automatic analysis of samples normally analysed by ASAP. The APGC instrument incorporates the use of a novel reference compound and delivery system which allows accurate mass measurements to be performed. This and the other modifications described have allowed the technique to be incorporated into an existing suite of mass spectrometry-based experiments for use in the characterisation of organic molecules.