Chiral Separation By Ion Mobility SpectrometryChiral Separation By Ion Mobility SpectrometryHerbert H. Hill JrHerbert H. Hill Jr11., Prabha Dwivedi., Prabha Dwivedi11, and Ching Wu, and Ching Wu2 2

11 Department of Chemistry & Center for Multiphase Environmental Research, Washington State University, Pullman, WA 99164 Department of Chemistry & Center for Multiphase Environmental Research, Washington State University, Pullman, WA 9916422 Excellims Corporation; 6 Westside Drive; Acton, MA 01720 Excellims Corporation; 6 Westside Drive; Acton, MA 01720

CONCLUSIONS

INTRODUCTION

RESULT SUMMARY

Purpose: Gas Phase Separation of Chiral Ions

Method: Ion Mobility Mass Spectrometry

Results: Enantiomers interact differently with added chiral modifiers in ion mobility drift cell resulting in gas phase chiral discrimination

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.

EXPERIMENTAL

ACKNOWLEDGEMENTS

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.

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 atenolol enantiomersTop: IMS spectra of individual enantiomersBottom: IMS spectra showing CIMS separation of enantiomers from their racemic mixture

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.

OVERVIEW

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.

Extent of preferential shift in mobility of methionine with chiral modifier concentration in drift gas

21.00

21.50

22.00

22.50

23.00

23.50

24.00

24.50

0 10 20 30 40 50 60 70

Chiral Modifier (micro L/hr)

Dri

ft T

ime

(ms)

D-Methionine

L-Methionine

D-methionine

L-Methionine

R-(-)-2-Butanol

S-(+)-2-Butanol

160

120

80

40

0

IMS

Re

spo

ns

e

403530252015105

Drift Time (ms)

A

B

C D

E

F

A ValinolB ThreonineC PenicillamineD TryptophanE Methyl glucopyranosideF Atenolol

140

120

100

80

60

40

20

0

-20

IMS

Re

sp

on

se

3530252015

Drift Time (ms)

100

80

60

40

20

0

-20

IMS

Re

sp

on

se

3530252015

Drift Time (ms)

Mixture of S- and R-Atenolol with drift times of 24.66ms and 25.06ms respectively

S- and R-Atenolol with drift times of 24.61ms and 25.04ms respectively

(R)-(+)-AtenololO

NH2

O(R)

HOHN

(S)-(-)-Atenolol

O

NH2

O(S)

HOHN

80

60

40

20

0

IMS

Res

po

nse

3530252015

Drift Time (ms)

Methyl--L-glucopyranoside

O

(R)

(S)

OH(R)

OH

(R)

HO

(S)

OHO

Methyl--D-glucopyranoside

O

(S)

(R)

OH(S)

OH

(S)

HO

(R)

OHO

Sodium adducts of D- and L- Methyl-a-glucopyranoside with drift times of 25.24ms and 25.76ms respectively; m/z 217 amu

60

50

40

30

20

10

0

-10

IMS

Re

sp

on

se

3530252015

Drift Time (ms)

70

60

50

40

30

20

10

0

-10

IMS

Re

sp

on

se

3530252015

Drift Time (ms)

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

CIMS separation of sugar enantiomersTop: IMS spectra of individual enantiomersBottom: IMS spectra showing CIMS separation of enantiomers from their racemic mixture

1.521.551.731.73(L), 19.11±0.05

(D), 18.72±0.04(L), 16.83±0.04

(D), 16.82±0.03

D and L-serine106 (M+H)+

1.281.311.451.45(L), 22.61±0.05

(D), 22.22±0.03(D), 20.05±0.04

(L), 20.07±0.04

D and L-phenylalanine

166 (M+H)+

1.601.621.741.74(D), 18.26±0.04

(L), 17.84±0.04(D), 16.75±0.03

(L), 16.72±0.04

D and L-valinol104 (M+H)+

1.401.421.531.53(L), 20.78±0.04

(D), 20.48±0.03(L), 18.92±0.05

(D), 18.94±0.03

D- and L-penicillamine

150 (M+H)+

1.211.23 1.301.30(L), 23.98±0.04

(D), 23.61±0.05(L), 22.32±0.03

(D), 22.35±0.04

D- and L-methyl-a-glucose

203 (M+Na)+

1.121.15 1.301.30(L), 25.87±0.07

(D), 25.33±0.08(L), 22.40±0.05

(D), 22.42±0.05

D- and L-methyl-a-glucopyranoside

217 (M+Na)+

1.481.511.691.69(L), 19.61±0.05

(D), 19.22±0.05(L), 17.20±0.04

(D), 17.22±0.03

D and L-threonine

120 (M+H)+

1.221.231.561.56(L), 23.83±0.06

(D), 23.59±0.04(L), 18.66±0.04

(D), 18.61±0.04

D and L-methionine

150 (M+H)+

1.231.251.321.32(L), 23.63±0.05

(D), 23.22±0.05(L), 21.99±0.04

(D), 22.02±0.03

D and L-tryptophan

205 (M+H)+

1.161.181.181.18(R), 25.06±0.05

(S), 24.66±0.04(R), 24.51±0.03

(S), 24.56±0.03

R and S-atenolol267 (M+H)+

Ko of enantiomers in S-(+)-2-butanol

Ko enantiomers in N2

Chirality and td, of enantiomers in S-(+)-2-butanol

Chirality and td, of enantiomers in N2

Test compoundsMolecular weight of ion

654321

1.521.551.731.73(L), 19.11±0.05

(D), 18.72±0.04(L), 16.83±0.04

(D), 16.82±0.03

D and L-serine106 (M+H)+

1.281.311.451.45(L), 22.61±0.05

(D), 22.22±0.03(D), 20.05±0.04

(L), 20.07±0.04

D and L-phenylalanine

166 (M+H)+

1.601.621.741.74(D), 18.26±0.04

(L), 17.84±0.04(D), 16.75±0.03

(L), 16.72±0.04

D and L-valinol104 (M+H)+

1.401.421.531.53(L), 20.78±0.04

(D), 20.48±0.03(L), 18.92±0.05

(D), 18.94±0.03

D- and L-penicillamine

150 (M+H)+

1.211.23 1.301.30(L), 23.98±0.04

(D), 23.61±0.05(L), 22.32±0.03

(D), 22.35±0.04

D- and L-methyl-a-glucose

203 (M+Na)+

1.121.15 1.301.30(L), 25.87±0.07

(D), 25.33±0.08(L), 22.40±0.05

(D), 22.42±0.05

D- and L-methyl-a-glucopyranoside

217 (M+Na)+

1.481.511.691.69(L), 19.61±0.05

(D), 19.22±0.05(L), 17.20±0.04

(D), 17.22±0.03

D and L-threonine

120 (M+H)+

1.221.231.561.56(L), 23.83±0.06

(D), 23.59±0.04(L), 18.66±0.04

(D), 18.61±0.04

D and L-methionine

150 (M+H)+

1.231.251.321.32(L), 23.63±0.05

(D), 23.22±0.05(L), 21.99±0.04

(D), 22.02±0.03

D and L-tryptophan

205 (M+H)+

1.161.181.181.18(R), 25.06±0.05

(S), 24.66±0.04(R), 24.51±0.03

(S), 24.56±0.03

R and S-atenolol267 (M+H)+

Ko of enantiomers in S-(+)-2-butanol

Ko enantiomers in N2

Chirality and td, of enantiomers in S-(+)-2-butanol

Chirality and td, of enantiomers in N2

Test compoundsMolecular weight of ion

654321

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.

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).

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).

Chiral analyteChiral Gas

C

A

B

C

A

BC'

D'

B'

A'

D'

C'

B'

A'

C

A

B

C

A

BC'

D'

B'

A'

D'

C'

B'

A'

D

D

Department of Chemistry

Hill Research Group Ion Mobility

Spectrometry