sample from GC

make-up gas inlet

to MS radiation source

GC-transfer line

Kai Kroll; Walter Wissdorf; Hendrik Kersten; Thorsten BenterPhysical & Theoretical Chemistry

Wuppertal, Germany

Institute for Pure and Applied Mass Spectrometry

Experimental SetupIntroduction

Development of a dual-mode laminar flow ion source for APPI-

and APLI-GC-MS

Methods

Conclusions

Acknowledgement

Literature

• 24/7 heating of all setups at 300 °C for several

weeks without loss of performance

• GC measurements reveal a high level of linearity

in the pg on-column range

• Transfer of the analytes into the MS without

significant loss of separation performance

Peak widths down to 0.7 s (FWHM)

• Simple variation of geometric parameters

• Ion source is interfaced to MS control software

APLI Mode:

• As expected, a larger inner diameter and a longer

dwell time leads to a better ionization efficiency

and gain in sensitivity

• Limit of detection for PAHs down to the fg range

APPI Mode:

• Setup 1 shows a significant decrease in sensitivity

compared to setup 2. The longer tube length

presumably leads to more pronounced ion-wall

losses

• Gain of sensitivity with longer dwell times in the

conical ionization inlet (vortex)

• The simulations show a longer residence time in

the cone with 5 mm tube diameter. These results

are in accordance with the measurements

• A GC column position slightly off axis leads to an

increased ionization efficiency

Table 1: Overview of the different setup modifications; ion

dwell times calculated from make-up gas volume flow

SetupLength

[mm]

Inner

diameter

[mm]

Ion dwell time

[ms]

1 150 5 240

2 85 5 140

3 150 2.5 70

4 85 2.5 50

APLI APPIPeak width

(FWHM)

[s]

Limit of

Detection*

[pg/µL]

Slope

Linear

range**

[pg/µL]

Setup

Linear

range**

[pg/µL]

Slope

Limit of

Detection*

[pg/µL]

Peak width

(FWHM)

[s]

0.8 – 1 0.6 34119 0.8 – 100 1 10 – 100 113 8 1 – 1.3

0.7 – 1.1 6 35 10 – 100 2 10 – 100 265 6 0.8 – 1.1

0.8 – 1.3 3 2797 6 – 600 3 100 – 600 16 60 0.8 – 1.3

0.8 – 1.3 40 65 60 – 600 4 100 – 600 12 80 0.7 – 1.3

Figure 1a: The custom dual-mode laminar flow ion source setup

• S/N = 3 ** for a dilution series of Naphthalene in n-hexane

Table 2: Analytical performance of the four laminar flow ion source versions for APLI- and APPI-GC-MS.

Performance

Crucial design aspects

• Tightly sealed ionization volume

• Chemically and photo-physically

inert matrix gas

• Conical ionization volume inlet

• Asymmetrical make-up gas inlet

Vortex inside ionization volume

for higher ionization efficiency

• Injection of the GC flow into the

major make-up gas flow

(The concept of the ionization

volume inlet is based on the GC-APPI

source presented by Kersten et al. in

2014 [3])

• Use of non outgassing materials

• Controlled operation temperature

up to 300 °C

Figure 3e: Determination of the linear ranges of the four

versions of the laminar flow ion source setup, APPI, for

naphthalene (m/z 128)

Figure 3a: Linear ranges for the four modifications of the

laminar flow ion source setup in APLI mode for naphthalene

(m/z 128).

Figure 3b: Dilution series of naphthalene 0.8 –

1000 pg/µL (m/z 128). Setup 1, APLI

Figure 3d: Dilution series of naphthalene 0.8 –

1000 pg/µL (m/z 128). Setup 1, APPI

Figure 3c: Chromatogram of the EPA 8270 LCS Mix 1

(100 pg/µL). Ion source setup 3, APLI mode.

Figure 3f: Chromatogram of the EPA 8270 LCS Mix 1

(100 pg/µL). Setup 1, APPI mode.

Note: The pronounced signal deviation around 200 pg/µL is observed in all four setups and for both ionization

methods. The reasons for this behavior are yet unknown and subject to current investigations.

CFD Simulations

Figure 2a: CFD simulation of the ionization volume inlet. Make-up gas flow 760

mL/min; GC column flow 2 mL/min. The red flow lines indicate the make up gas

flow, the yellow flow lines indicate the GC column effluent

make-up gasmake-up gas

make-up gas

sample from GC sample from GC

sample from GC sample from GC

make-up gas

Figure 2b: Variation of GC

column position for setup 1,

APPI. 100 pg/µL naphthalene

GC column on-axisGC column 1 mm off-axisAt the annual ASMS meeting in 2010, we introduced

a novel laminar flow ion source (LFIS) for API-MS [1].

In the following years, we presented the capabilities

of the LFIS with the analysis of in-situ samples from

atmospheric smog chamber experiments [2]. Based

on the original LFIS, we designed a novel interface

for GC-API-MS.

Challenges:

• Design of a novel GC-MS interface, suitable for

atmospheric pressure photoionization (APPI) and

atmospheric pressure laser ionization (APLI)

• Design with sustained chromatographic fidelity

→ Prevention of cold spots

→ Prevention of dead volumes

• Swift change between APPI and APLI operation

• Variable ionization chamber volume (length and

inner diameter) to optimize for the ionization

efficiency and ion transport in APPI and APLI

• Controllable via MS-software

iGenTraX UG, Haan, Germany

Bruker Daltonics GmbH, Bremen, Germany

5 m

m t

ub

e2

.5 m

m t

ub

e

[1] Barnes, I.; Kersten, H.; Wissdorf, W.; Pöhler, T.; Hönen, H.; Klee, S.; Brockmann, K. J.; Benter, T., Novel laminar flow ion sources for LC- and GC-API MS, 58th ASMS Conference on Mass Spectrometry and allied topics, Salt Lake City, UT, USA (2010)

[2] Barnes, I.; Kersten, H.; Bejan, J.; Benter, T., In- situ MS monitoring of atmospheric degradation product studies of aromatic hydrocarbons with APPI and APLI, 59th ASMS Conference on Mass Spectrometry and allied topics, Denver, CO, USA (2011)

[3] Kersten, H.; Haberer, K.; Kroll, K.; Benter, T., Progress in the development of a GC-APPI source with femtogram sensitivity, 62nd ASMS Conference on Mass Spectrometry and allied topics, Baltimore MD, USA (2014)

MS

Ion Source

Radiation

Source

GC

Transfer

Line

Samples

GC

injection

Make-up

gas

CFD

simulations

amaZon speed ETD, Bruker Daltonik

GmbH

Custom-made dual-mode laminar

flow ion source

APPI: VUV Kr discharge RF lamp

emitting 10.0 and 10.6 eV photons

(Syagen, Morfo)

APLI: ATL Atlex KrF*-excimer laser

(248 nm, 5 mJ, 50 Hz)

GC 7890 A, Agilent Technologies Inc.

Custom temperature-controlled GC-

transfer line

EPA 8270 LCS Mix 1, Supelco

78 compounds

Dilutions: 1 fg/µL – 100 pg/µL

Naphthalene diluted in n-hexane

Dilutions: 10 fg/µL – 1 ng/µL

Split ratio 1/100 (already included in

the concentration values)

Injection volume 1 µL

Nitrogen 5.0, Messer Industriegase

GmbH

Flow rate: 760 mL/min

Comsol Multiphysics 4.4

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

0 2 4 6 8 10 12 14

inte

nsi

ty [

a.

u.]

retention time [min]

y = 113.21x + 1011.7

R² = 0.9945

y = 265.93x – 1257.2

R² = 0.9992

y = 16.013x + 436.48

R² = 0.9999

y = 12.068x – 3.7542

R² = 0.9964

0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

2.5E+04

3.0E+04

0 100 200 300 400 500 600 700

pe

ak a

rea

[a

. u

.]

concentration [pg/µL]

Setup 1 Setup 2 Setup 3 Setup 4

0.0E+00

2.0E+04

4.0E+04

6.0E+04

8.0E+04

1.0E+05

1.2E+05

0 200 400 600 800 1000 1200

pe

ak a

rea

[a

. u

.]

concentration [pg/µL]

Setup 2

0.0E+00

2.0E+06

4.0E+06

6.0E+06

8.0E+06

1.0E+07

1.2E+07

1.4E+07

1.6E+07

0 200 400 600 800 1000 1200

pe

ak a

rea

[a

. u

.]

concentration [pg/µL]

Setup 1

y = 34119x + 31893

R² = 0.9991

y = 352.27x + 1296.5

R² = 0.9964

y = 2796.7x – 1165.3

R² = 0.9993

y = 65.173x – 831.11

R² = 0.9974

0.0E+00

5.0E+05

1.0E+06

1.5E+06

2.0E+06

2.5E+06

3.0E+06

3.5E+06

4.0E+06

0 100 200 300 400 500 600 700

pe

ak a

rea

[a.

u.]

concentration [pg/µL]

Setup 1 Setup 2 Setup 3 Setup 4

0.0E+00

1.0E+07

2.0E+07

3.0E+07

4.0E+07

5.0E+07

6.0E+07

0 2 4 6 8 10 12 14

inte

nsi

ty [

a.

u.]

retention time [min.]

0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

2.5E+04

off axis on axis

pe

ak a

rea

[a

. u

.]

GC column position