Fast quantitative characterisation of differential mobility responses

Abstract

A chromatography-based method for producing mass flux-response surfaces for differential mobility spectrometers is described as a replacement for exponential dilution and mixing approaches. An exponential dilution or mixing experiment typically takes 150 min; while the exponential function in the Gaussian elution profile obtained from linear chromatography may be exploited in approximately 10 s. The approach was demonstrated with a gas chromatograph-mass spectrometer and the correlation of the calibration results to nominal on-column masses was within experimental error for 19 separate analyses. The method was then applied to a gas chromatographic (10.6 eV UV) differential mobility spectrometer. Mass fluxes in the range 10 pg s⁻¹ to 250 ng s⁻¹ were generated over the 5 s to 10 s associated with the elution of a chromatographic peak. The characterisations were repeated for a range of electrical field strengths from 10 kV cm⁻¹ to 30 kV cm⁻¹. Triplicate runs indicated that the approach was reproducible and that response surfaces could be generated rapidly from chromatographic data. The effects of trace impurities associated with the chromatographic eluent on the relationship between compensation voltage and electrical field strength was observed. This emphasised the importance of managing this aspect of the operation if reliable estimates of alpha functions for the compounds under study were to be obtained. Application of this approach to other detection systems with an 85% reduction in the analytical operations required to produce a reliable calibration function was also noted.