Accurate Drift Time Determination by Traveling Wave Ion Mobility Spectrometry: The Concept of the Diffusion Calibration

Abstract

Ion mobility spectrometry (IMS) is a gas phase separation technique, which relies on differences in collision cross section (CCS) of ions. Ionic clouds of unresolved conformers overlap if the CCS difference is below the instrumental resolution expressed as CCS/ΔCCS. The experimental arrival time distribution (ATD) peak is then a superimposition of the various contributions weighted by their relative intensities. This paper introduces a strategy for accurate drift time determination using traveling wave ion mobility spectrometry (TWIMS) of poorly resolved or unresolved conformers. This method implements through a calibration procedure the link between the peak full width at half-maximum (fwhm) and the drift time of model compounds for wide range of settings for wave heights and velocities. We modified a Gaussian equation, which achieves the deconvolution of ATD peaks where the fwhm is fixed according to our calibration procedure. The new fitting Gaussian equation only depends on two parameters: The apex of the peak (A) and the mean drift time value (μ). The standard deviation parameter (correlated to fwhm) becomes a function of the drift time. This correlation function between μ and fwhm is obtained using the TWIMS calibration procedure which determines the maximum instrumental ion beam diffusion under limited and controlled space charge effect using ionic compounds which are detected as single conformers in the gas phase. This deconvolution process has been used to highlight the presence of poorly resolved conformers of crown ether complexes and peptides leading to more accurate CCS determinations in better agreement with quantum chemistry predictions.

Recommendations for reporting ion mobility Mass Spectrometry measurements

“…For a homogeneous population of ions, the width of ATD is primarily controlled by ion diffusion, Coulomb repulsion (space charge), the (temporal or spatial) width of ion injection pulse, the (temporal or spatial) width of detector acquisition window, and electric field homogeneity. This nominal width can be predicted theoretically (Siems et al, ; Wyttenbach, Von Helden, & Bowers, ; May et al, ), or determined experimentally from structurally rigid (e.g., C 60 ) or homogeneous ions (Jeanne Dit Fouque et al, ; Kune, Far, & De Pauw, ), although this can be hard to achieve for large ions. However, the experimental ATD can be broader than predicted.…”

High‐resolution ion mobility spectrometry‐mass spectrometry of isomeric/isobaric ribonucleotide variants

“…This, in turn, would explain the small systematic differences in the apparent R values between nucleotides. Although necessitating a further detailed study, measurements of the apparent R could be used to assess the intrinsic structure dynamics of nucleotide isomers, which may contribute to the diversity of conformations included in the corresponding ion population …”

“…Although necessitating a further detailed study, measurements of the apparent R could be used to assess the intrinsic structure dynamics of nucleotide isomers, which may contribute to the diversity of conformations included in the corresponding ion population. 48 F I G U R E 1 Ion mobility mass spectrometry data obtained from canonical ribonucleotides on the linear TW device (A) and the cyclic ion mobility (cIM) device after one pass (B), two passes (C), and three passes (D) these types of experiments tend to afford a modest 2% loss of ion current per pass. 47 In our experiments, no signs of fragmentation events were detected during methyl-cytidine analysis.…”

Effectiveness and Limitations of Computational Chemistry and Mass Spectrometry in the Rational Design of Target‐specific Shift Reagents for Ion Mobility Spectrometry

“…IMMS data (IMS ATD and MS spectra) were reprocessed using Waters MassLynx 4.1. PeakFit v4.11 was used for ATD peak deconvolution using the diffusion calibration strategy for helping the Gaussian fitting process.…”

“…[58] IMMS data (IMS ATD and MS spectra) were reprocessed using Waters MassLynx 4.1. PeakFit v4.11 was used for ATD peak deconvolution using the diffusion calibration strategy [38] for helping the Gaussian fitting process . 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57…”