Increasing analytical space in gas chromatography-differential mobility spectrometry with dispersion field amplitude programming

Enhancing the analytical space of differential mobility spectrometry with dispersion field amplitude programming was proposed. Six volatile organic compound candidate breath markers, 1,3-butanediol, butanone, ethylbenzene, heptan-2-one, nonanal, and o-xylene were used to characterise the effect of programming the amplitude of the dispersion field on the sensitivity, and resolution of the responses observed. Sensitivity followed two patterns of behaviour. Sensitivity to heptan-2-one and 1,3-butanediol increased to a maximum at approximately 20 kV cm−1, attributed to dissociative ionisation effects. The remaining four compounds’ responses were dominated by wall-loss phenomena resulting in a constant reduction in sensitivity as dispersion field amplitude was increased. The effect of the dispersion field on analytical space was pronounced. At a field strength of 18 kV cm−1 protonated monomers and proton-bound dimers could be observed within the chromatographic responses for the carbonyl compounds. Dissociative ionisation products were also discerned for 1,3-butanediol and butanone. The ion chemistry of the two hydrocarbons was not affected by the dispersion field amplitude. Resolution of the product ions and their separation from the reactant ion peaks increased significantly with increasing dispersion field amplitude. With a range of behaviours observed. Peak resolutions increased from the range 0 to 1.2 to 1.2 to 7, while resolving power increased from 0 (at low dispersion field amplitudes) to the range 0.2–6 at 20–24 kV cm−1. The effect of programming the dispersion field amplitude on a “real-life” application was demonstrated with replicate breath samples obtained from a subject with chronic obstructive pulmonary disease.