Analytical1), Physical & Theoretical2) Chemistry University of Wuppertal, Germany

Institute for Pure and Applied Mass Spectrometry

Results

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Distribution of Ion Acceptance in a Fluid-dynamically Optimized Multi-purpose Ion Source

Matthias Lorenz2), Klaus J. Brockmann2), Walter Wißdorf2), Dennis Klink1), Oliver J. Schmitz1), Thorsten Benter2)

Description of displayed data

� DIA plots for both MPIS configurations (cf. Fig. 6) show a strong dependence on electricalfields (voltages) + fluid-dynamics (gas flows)

� Increasing the fluid-dynamical impact of theAEF unit (balanced, 0.1 L/min, 1.2 L/min active

gas removal, cf. Fig. 2-4 and 11-13) causesincreasing sensitivity loss which is evident in theDIA data

� Significantly changed DIA for AEF equipped ionsource (cf. Fig. 1+10 vs. 2+11) is mainly due to

changed fluid-dynamics, not to electrical fields(data not shown)

� Successive reduction of LC peak tailing withincreasing fluid-dynamical impact of AEF unit

(cf. Fig. 5, 7-9; laser beam positions as indica-ted)

Figure 10

c d

a b

Figure 11

c d

a b

Figure 12

c d

a b

Figure 13

c d

a b

Figure 1

c d

a b

Figure 2

c d

a b

Figure 3

c d

a b

Figure 4

c d

a b

Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

MPIS AEF 0 L/min AEF 0.1 L/min AEF 1.2 L/min- 500 V

Sp

ray

sh

ield

at

0 V

-25 V

Sp

ray

sh

ield

at

-50 V

120

L/h

240

L/h

- 1500 VCapillary voltage - 500 V - 1500 VCapillary voltage - 500 V - 1500 VCapillary voltage - 500 V - 1500 VCapillary voltage

120

L/h

240

L/h

Dry

ga

s flo

wD

ryg

as

flo

w

Results

AEF-equipped MPIS (right panel)

� AEF drain located opposite to

vaporizer (active gas removal,original drain opening forsheath gas inlet purging source)

� Analyte sampled from straight flowpenetrating ion source

MPIS (left panel)

� Analyte path not directed; long ion dwell time at AP

� Ion source as flow systemwith unfavorably located

drain position

� Ion source buffersanalyte (molecular

+ ionic species) due to unfavora-

ble fluid dynamics

� Significant differen-

ces in transporttimes for analytes

Sampling

Vap

ori

zati

on

Vap

ori

zati

on

Dwell

Dra

in

Introduction Conclusions

Methods

AcknowledgementFinancial support is gratefully acknowledged:

Bruker Daltonics GmbH, Bremen, Germany

Literature1) Constapel, M.; Schellenträger, M.; Schmitz, O.J.; Gäb, S.; Brockmann, K.J.;

Giese, R.; Benter T. Atmospheric pressure laser ionization: a novel ionization method for liquid chromatography/mass spectrometry. Rapid Commun. Mass Spectrom. 2005, 19, 326-336.

2) Benter, T.; Schmitz, O.J. Atmospheric Pressure Laser Ionization. In Advances in LC-MS instrumentation, Journal of Chromatography Library 72, Cappiello, A. Ed. 2007.

3) Benter, T. Atmospheric Pressure Laser Ionization. In The Encyclopedia of Mass Spectrometry, Gross, M.L., Caprioli, R.N., Eds., 1st ed.; Elsevier: Oxford, U.K., 2007.

4) Schiewek, R.; Lorenz., M.; Giese, R.; Brockmann, K.J.; Benter, T.; Gäb, S.; Schmitz, O.J. Development of a multipurpose ion source for LC-MS and GC-API MS. Anal. Bioanal. Chem. 2008, 392, 87-96.

5) Lorenz, M.; Schiewek, R.; Brockmann, K.J.; Schmitz, O.J.; Gäb, S.; Benter, T. The Distribution of Ion Acceptance in Atmospheric Pressure Ion Sources: Spatially resolved APLI Measurements. J. Am. Soc. Mass Spectrom. 2008, 19, 400-410.

6) Lorenz, M.; Wissdorf, W.; Klee, S.; Kersten, H.; Brockmann, K.J.; Benter, T. Spatially and temporally resolved atmospheric pressure laser ionization as a powerful tool for the characterization of ion sources: An overview. Proceedings of the 58th ASMS Conference on Mass Spectrometry and Allied Topics; Salt Lake City, UT, 2010.

7) Lorenz, M. Räumlich und zeitlich aufgelöste Photoionisierung als Werkzeug zurCharakterisiterung von Atmosphärendruckionenquellen in derMassenspektrometrie. Dissertation, University of Wuppertal, Wuppertal, Germany, 2010.

8) Wissdorf, W.; Lorenz, M.; Benter, T. Numerical Simulation of the Distribution of Ion Acceptance (DIA) in a Commercial API Source. Presented at ASMS Conference on Mass Spectrometry and Allied Topics; Denver, CO, 2011.

Experimental setup

MS: Bruker micrOTOF

Ion source: Multi-purpose ion source (MPIS) [4],

optionally with AEF unit (cf. Fig. 6)

Light source: ATL ATLex 300 KrF* laser (λ = 248 nm),

CryLas DPSS (λ = 266 nm)

HPLC: Halo C18, 4.6 x 30 mm, 2.7 µm,

MeOH/H2O (90/10), 1 mL/min,

20 µL 1 µmol/L pyrene in MeOH/H2O (95/5)

DIA measurements

Light source: ATL ATLex 300 KrF* laser, 50 Hz, 5 mJ

Analyte: 0.1 µmol/L pyrene in MeOH,

100 µL/min liquid flow introduction

Gas flows: 120…240 L/h dry gas @ 200°C,

3 bar nebulizer pressure @ 320°C,

Dry nitrogen (gas cylinders)

DIA: Principle and spatial arrangement

Distribution of ion acceptance

� Significant changes of sensitivity distribution in MPIS with altered fluid-dynamical conditions (cf. Fig. 1,10 vs. 2…4,11…13)

� Significant reduction of absolute sensitivity due to the removal of any analyte not directly sampled (as expected)

LC application of AEF

� LC peak width reduction already for passive operation / changed position of drain opening (data not shown)

� Stable operation of AEF-equipped ion source with active exhaust (set-up shown in Fig. 6) for a wide range of gas + liquid flows

� Moderate sensitivity reduction in temporally resolved LC data (cf. Fig. 5, 7-9) as compared to significant drop in intensity for integral data on sensitivity distribution (cf. Fig. 1…4, 10…13)

Interpretation

� AEF equipped MPIS reduces the signal contri-bution of analyte species with long dwell times within the AP ion source reservoir; the effect increases up to a considerable gas removal from the ion source (ion source purged with additional sheath gas, cf. Fig. 6)

� Temporal variability of analyte (ions + mole-cules) transport mechanisms is avoided, stable conditions are indicated by narrow (also for equally sized, cf. inlay in Fig. 9) LC peaks

� MPIS geometry equipped with AEF represents flow system with orthogonal MS sampling

� AEF equipped ion source prevents analyte buffering and enables fast online analysis

Outlook

� Since reduced sensitivity is due to incomplete analyte ionization and ion sampling processes within the ion source, further research will be focused on these aspects

ASMS 2011

Vaporization stage

Spray shield (attractive electrode)

Transfer capillary(attractive electrode)

DIA

AP ion source

time (a.u.)

sig

na

l(a

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X (mm)

Y (

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x (mm)

Y (

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Data on the distribution of ion acceptance (DIA)

as gathered from spatially resolved atmospheric

pressure laser ionization (APLI, [1-3]) measurements

have previously been reported [5-7]. In particular

the combination with temporally resolved photo-

ionization experiments have provided deep insight

into the analytical limitations due to fluid-dynami-

cal drawbacks of current atmospheric pressure

(AP) ion source designs [6-8]. A pronounced ana-

lyte dwell time in the ion source and a broad distri-

bution of ion storage times foster memory effects

and chromatographic peak broadening, particu-

larly in LC hyphenation.

The analytical limitations result from unfavorable

transport conditions within the ion source. Long

analyte dwell times and thus long trajectories for

ionic [6,7] and molecular species cause the “buf-

fering nature” of the ion source. One approach

toward a fluid-dynamical optimization is to design

the ion source as a true “flow system” with ortho-

gonal MS sampling, i.e. with up- and downstream

flow control. Such an “Active Elevated Floor” (AEF)

unit is capable of preventing a large-volume ana-

lyte distribution and a broad distribution of transfer

times – important origins of memory effects and

broad chromatographic peaks.

180

L/h

���� 4 cm i.d. ����

Drain

Air (Bernoulli)

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Sampling

Sheath

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