Chiral Separation By Ion Mobility Spectrometry

1. D S- and R-Atenolol with drift times of 24.61ms and 25.04ms respectively Sodium adducts of D- and L- Methyl-a-glucopyranoside with drift times of 25.24ms and 25.76ms respectively; m/z 217 amu D Mixture of Sodium adducts of D- and L-Methyl-a-glucopyranoside with drift times of 25.33ms and 25.87ms respectively; m/z 217 amu Mixture of S- and R-Atenolol with drift times of 24.66ms and 25.06ms respectively Department of Chemistry Hill Research Group Ion Mobility Spectrometry Chiral Separation By Ion Mobility Spectrometry Herbert H. Hill Jr1., Prabha Dwivedi1, and Ching Wu2 1 Department of Chemistry & Center for Multiphase Environmental Research, Washington State University, Pullman, WA 99164 2 Excellims Corporation; 6 Westside Drive; Acton, MA 01720 RESULT SUMMARY OVERVIEW Purpose: Gas Phase Separation of Chiral Ions Method: Ion Mobility Mass Spectrometry Results: Enantiomers interact differently with addedchiral modifiers in ion mobility drift cell resulting in gas phase chiral discrimination Chiral Gas Chiral analyte A schematic illustration of 3-point-rule “Pirkle Rule” required for chiral recognition. CIMS separation utilizes stereo- chemically different non-covalent interactions between the enantiomers (pink shaded) and the chiral drift gas (blue shaded). Photograph and schematic diagram of the ESI-APIMS-qMS. The IMS cell was divided into a desolvation region (7.5 cm) and a drift region (25 cm) by a Bradbury-Nielsen ion gate which was used to pulse ion packets into the drift region with a pulse width of 0.1 milliseconds. The qMS was operated in the single ion monitoring mode to monitor the arrival time distributions of mass selected ions. INTRODUCTION Similarity of enantiomers in their chemical and physical properties makes their separation and detection difficult. Recently several MS methods have been reported which produce rapid, universal and reproducible enantiomer discrimination without extensive sample preparation and method development. However, these approaches often require complex data analysis of fragmentation patterns and ion-molecule reactions to occur between a chiral selector and the ion of interest. Ion mobility spectrometry separates ions in gas phase within seconds based on differences in ion-neutral collision dynamics. Addition of chiral modifiers into the drift gas provides an environment for preferential weak gas phase interactions with the chiral modifier, producing mobility differences between enantiomeric ions and effecting their gas phase separation. Superimposed IM spectra of racemic mixtures of valinol, threonine, penicillamine, tryptophan, methyl-α-D-glucopyranoside and atenolol with nitrogen as the drift gas. Single IMS peaks were observed for each racemic mixture. Enantiomers could not be separated in the pure nitrogen drift gas. CONCLUSIONS Gas phase separation and resolution of enantiomers is possible when the drift gas of an ion mobility spectrometer is modified with a chiral vapor. Selective interactions occur between the enantiomers and the chiral modifier such that the individual enantiomers have different gas phase ion mobilities through the spectrometer and can be separated in time. In all cases the addition of the chiral modifier to the drift gas reduced the mobilities of the enantiomers but the one mobility of one enantiomer was always reduced more than the other. With a relative limited set of experiments, un-optimized experimental parameters and a single chiral drift gas modifier, separations of multiple pairs of enantiomers from four different classes of compounds were achieved. CIMS separation of atenolol enantiomers Top: IMS spectra of individual enantiomers Bottom: IMS spectra showing CIMS separation of enantiomers from their racemic mixture EXPERIMENTAL IMS designed and constructed at WSU was interfaced to a model 150-QC ABB Extrel quadrupole MS via a 40-µm pinhole interface. The IMS was operated at a temperature of 200oC and an electric field of 432 V/cm (N: number density = 1.43*1019, E/N = 3.02 Townsend) Nitrogen used as the drift gas was doped with chiral modifiers and arrival times of enantiomers monitored while operating the IMS-qMS in single ion monitoring mode. Chiral modifiers (S-(+)-2-butanol and R-(-)-2-butanol) were infused by a syringe pump into a silica capillary which was connected to the heated nitrogen drift gas line using a T-junction. Ions were produced by ESI at a potential of 15.00 kV. ACKNOWLEDGEMENTS Effect of chiral modifier introduction rate on arrival times of the methionine enantiomers. Greater preferential shift in ion mobility of enantiomers was observed with S-(+)-2-butanol compared to R-(-)-2-butanol. CIMS separation of sugar enantiomers Top: IMS spectra of individual enantiomers Bottom: IMS spectra showing CIMS separation of enantiomers from their racemic mixture The authors thank Dr. Issik Kanic of the Jet Propulsion Laboratory (California Institute of Technology, Pasadena, California 91109-8099 USA) for providing initial funding for this project. In addition this project was partially supported by a Road Map Grant from the National Institutes of Health (R21 DK 070274).