TY - JOUR

T1 - Kinetics in DMS

T2 - Modeling Clustering and Declustering Reactions

AU - Haack, Alexander

AU - Hopkins, W. Scott

N1 - Funding Information: The authors would like to acknowledge the high-performance computing support from the Digital Research Alliance of Canada. W.S.H. would like to acknowledge the financial support provided by the Natural Sciences and Engineering Research Council (NSERC) of Canada in the form of Discovery and Alliance grants as well as the government of Ontario for an Ontario Early Researcher Award. A.H. gratefully acknowledges this work being funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, 449651261).

PY - 2022/12/7

Y1 - 2022/12/7

N2 - Differential mobility spectrometry (DMS) uses high-frequency oscillating electrical fields to harness the differential mobility of ions for separating complex sample mixtures prior to detection. To increase the resolving power, a dynamic microsolvation environment is often created by introducing solvent vapors. Here, relatively large clusters are formed at low-field conditions which then evaporate to form smaller clusters at high-field conditions. The kinetics of these processes as the electrical field strength oscillates are not well studied. Here, we develop a computational framework to investigate how the different reactions (cluster association, cluster dissociation, and fast conformational changes) behave at different field strengths. We aim to better understand these processes, their effect on experimental outcomes, and whether DMS model accuracy is improved via incorporating their description. We find that cluster association and dissociation reactions for typical ion-solvent pairs are fast compared to the time scale of the varying separation fields usually used. However, low solvent concentration, small dipole moments, and strong ion-solvent binding can result in reaction rates small enough that a lag is observed in the ion's DMS response. This can yield differences of several volts in the compensation voltages required to correct ion trajectories for optimal transmission. We also find that the proposed kinetic approach yields generally better agreement with experiment than using a modified Boltzmann weighting scheme. Thus, this work provides insights into the chemical dynamics occurring within the DMS cell while also increasing the accuracy of dispersion plot predictions.

AB - Differential mobility spectrometry (DMS) uses high-frequency oscillating electrical fields to harness the differential mobility of ions for separating complex sample mixtures prior to detection. To increase the resolving power, a dynamic microsolvation environment is often created by introducing solvent vapors. Here, relatively large clusters are formed at low-field conditions which then evaporate to form smaller clusters at high-field conditions. The kinetics of these processes as the electrical field strength oscillates are not well studied. Here, we develop a computational framework to investigate how the different reactions (cluster association, cluster dissociation, and fast conformational changes) behave at different field strengths. We aim to better understand these processes, their effect on experimental outcomes, and whether DMS model accuracy is improved via incorporating their description. We find that cluster association and dissociation reactions for typical ion-solvent pairs are fast compared to the time scale of the varying separation fields usually used. However, low solvent concentration, small dipole moments, and strong ion-solvent binding can result in reaction rates small enough that a lag is observed in the ion's DMS response. This can yield differences of several volts in the compensation voltages required to correct ion trajectories for optimal transmission. We also find that the proposed kinetic approach yields generally better agreement with experiment than using a modified Boltzmann weighting scheme. Thus, this work provides insights into the chemical dynamics occurring within the DMS cell while also increasing the accuracy of dispersion plot predictions.

KW - collision cross section

KW - density functional theory

KW - differential ion mobility

KW - ion-solvent cluster

KW - kinetics

KW - reaction rates

UR - http://www.scopus.com/inward/record.url?scp=85141691659&partnerID=8YFLogxK

U2 - 10.1021/jasms.2c00224

DO - 10.1021/jasms.2c00224

M3 - Article

C2 - 36331115

AN - SCOPUS:85141691659

VL - 33

SP - 2250

EP - 2262

JO - Journal of the American Society for Mass Spectrometry

JF - Journal of the American Society for Mass Spectrometry

SN - 1044-0305

IS - 12

ER -