study of ion confinement, transport and heating effects in ... · contact: sandilya garimella,...

• Experimental Setup:

• Computational Models:Study of ion trajectories in SIMION 8.1:

Ion Kinetic Energies and Ion Temperatures3: (at 2.5 torr)

Modeling Ion Structural Changes during Gas Phase Transport in Devices: The Teff determines the ion structure. The evolution of ion trajectories of Substance P and the potential for unfolding due to TW and RF fields were modeled in SIMION 8.1

Study of Ion Confinement, Transport and Heating Effects in Traveling Wave DevicesSandilya V.B. Garimella, Yehia M. Ibrahim, Roza Wojcik, Ian K. Webb and Richard D. SmithBiological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA

Introduction

Overview Methods Results

AcknowledgementsThis project was partially supported by the U.S. Department of Energy (DOE) Office of Biological and Environmental Research (OBER) Pan-omics program at Pacific Northwest National Laboratory (PNNL) and MOBILIon Systems Inc. and performed in the Environmental Molecular Sciences Laboratory, a DOE OBER national scientific user facility on the PNNL campus. PNNL is a multiprogram national laboratory operated by Battelle for the DOE under contract DE-AC05-76RL01830.

References1.) Deng, L., Webb, I.K., et al.: Serpentine ultralong path with extendedrouting (SUPER) high resolution traveling wave ion mobility-MS usingstructures for lossless ion manipulations. Anal. Chem. 89(8), 4628-4634, (2017)

2.) Ibrahim, Y.M., et al.: New frontiers for mass spectrometry basedupon structures for lossless ion manipulations. Analyst, 142(7), 1010-1021, (2017)

3.) Tolmachev et al : Collisional activation of ions in RF ion traps andion guides: The effective ion temperature treatment. JASMS 15(11)1616-1628, (2004)

Future and Conclusions

CONTACT: Sandilya Garimella, Ph.D.Biological Sciences DivisionPacific Northwest National LaboratoryE-mail: Sandilya.garimella@pnnl.gov

• Traveling Wave (TW) based ion mobility(IM) combined with mass spectrometry(MS) is being increasingly adopted forbiological analysis

• Confinement and separations of ionstructures in TW-SLIM devices havebeen extensively studied1 , 2

• Applications benefit from gentle iontransport with minimal ion heatingeffects

• Herein we present a study of relative ionheating effects in TW devices throughcomputations and experiments

• A computational model that tracks evolving ion temperature (and ion structure) as it travels through an ion transport device operating at a few torr pressure has been built and validated for Substance P 3+.

• The model has been applied to study the relative heating effects during operation of SLIM

• Computational model of ion heating was used to study different arrangements of electrodes in circular conduits.

• A quadrupolar/Octopolar shape to the confinement potential provided practically no ion heating compared to other geometry arrangements investigated.

• Traveling wave ion guides provide IMSseparations, but the relative heatingeffects under different configurations arenot characterized

• SLIM experimental parameters (geometry,electric fields) were varied to studyrelative heating effects on specificthermometer molecules (exampleSubstance P)

• Ion effective temperatures werecalculated based on ion kinetic energiesextracted from SIMION

• A SIMION model was used to calculatethe extent of ion population that changedconformation due to heating in SLIM andSynapt platform

• Different ion guide geometries are studiedand characterized

www.omics.pnl.govCareer Opportunities: For potential openings in Integrative Omics Group at PNNL please visit http://omics.pnl.gov/careers

Comparison of Different Cylindrical Ion Guides

13 m SLIM module4 RF strips 3 TW Path length 1mSquare TW profile

The cross-section is symmetric about the axis (similar to a circularly arranged SLIM device)The electric fields provide gentle confinement and transport as evidenced from 19% surviving compact conformer

Axial confinement (i.e. adjacent electrode rings have RF with opposite polarity in addition to opposite polarity within a segmented ring structure) results in excessive ion heating

Octopolar confinement is gentle and no ion activation is seen

Geometry “a” on the left has been adapted into a planar version in SLIM devices. Geometry “c” has been adapted into planar SLIM for dual polarity confinement and separations (see poster WP 392)

Structural Changes of SubstanceP in SLIM

𝑛𝑛𝑝𝑝 = 𝑛𝑛𝑜𝑜 𝑒𝑒− ∫0𝑡𝑡 𝐴𝐴𝑒𝑒

− 𝐸𝐸𝑎𝑎𝑘𝑘𝐵𝐵 𝑇𝑇𝑒𝑒𝑒𝑒𝑒𝑒(𝐾𝐾𝑖𝑖)𝑑𝑑𝑑𝑑

Arrhenius Parameters: A = 6.3 x 1011 (1/s) Ea = 1.5 (eV)Initial Population Distribution: 30% compact and 70% unfolded conformerRF: 300 Vpp, 1 MHz, TW 20 Vpp, 60 kHz

np – concentration of unfolded conformer no – concentration of folded conformerEa - Activation energy , A – Pre-exponential factor

Ki changes with applied voltages Ti (t) = Teff(Ki) at low E/N

Confinement becomes narrow at higher guard biasesNo Heating Some Heating Complete Unfolding

1 mtorr 1 torr

0 2 4 6 8 10300

325

350Teff = 350 K

ion

Tem

pera

ture

(K)

time (µs)

@1 torr Ti(t) = Teff

0.0 0.5 1.0 1.5 2.00.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

Tim

e

Ion Kinetic Energy (eV)

3 Volts7 Volts12 Volts

Ion Kinetic Energy (Ki) distributions (SIMION simulations in SLIM at 2.5 torr) can be modulated with applied voltages,

which effect the distribution of Teff

Time for ion to reach an equilibrium temperature is instantaneous at 2.5 torr

and above

Initial Population Distribution: 25% compact and 75% unfolded conformer

a)

b)

c)

Effect of TW amplitude and speed in Synapt TW Ion Guide30 V, 1000 m/s 30 V, 500 m/s(separation) (surfing/snow plow)

Synapt G2: TW superimposedAdjacent ring electrodes have opposite RF phase

0 5 100

50

100

150

200

Cou

nts

Arrival Time (ms)

30 V

0 5 10

20 V

0 5 10

10 V

1000 m/s 500 m/s 200 m/s

At similar average axial ion speed, higher TW amplitude causes more heating

to MS