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Soft Ionization (Li Ion/ QTOF) Achim M. Trimborn, John T. Jayne, Jesse Kroll, Douglas R. Worsnop Aerodyne Research, Inc. Jan Niklas Schaper, Thorsten Hoffmann University of Mainz
Soft Ionization (Li Ion/ QTOF)
Achim M. Trimborn, John T. Jayne, Jesse Kroll, Douglas R. Worsnop Aerodyne Research, Inc.
Jan Niklas Schaper, Thorsten Hoffmann University of Mainz
Motivationmolecular information on organic aerosollittle or no fragmentation
high sensitivity
compatible to standard AMS
A+ + M + N [A-M]+ + NLi+ + M + N [Li-M]+ + N
Li+
Li+
Li+Li+
Li+
[Li-M]+
Ionization
Source provides Li ion current of ~10 µA -> 6*1013 ions per second
Why Lithium ion attachment?
0.12
0.10
0.08
0.06
0.04
0.02
0.00fra
ctio
n of
tota
l sig
nal
120100806040200m/z
0.20
0.15
0.10
0.05
0.00
cont
ribut
ion
to to
tal s
igna
l
200180160140120100m/z
electronimpact
Li+ ionattachment
29 60 (C2H4O2)
73 (C3H5O2)
57
168 (M+6)102
Ion blanking with quad
0.20
0.15
0.10
0.05
0.00
cont
ribut
ion
to to
tal s
igna
l
200180160140120100m/z
Fragmentation due to Li+ ionization
Oleic acid
Phthalsaeuredipropylester
Fragmentation (quantification)
Properties that influence the ionization efficiency ofLi ion attachment
PolarizationNot known for many compounds Refractive index a measure for polarization
gas phase acidityUnknown for most of the compounds
normalized ionization efficiency( refractive index used as measure for polarization)
Valve open
Valve closed
Pressure dependence of the ionization
Comparison of ACPI and Li ion atachment ( �-pinene and ozone)
APCI + ionizes mainly ketones and aldehydes
ACPI - ionizes mainly acids and carboxylic groups
Li ion attachment sees most of the tested componentsLower sensitivity
15
10
5
0
Li i
on s
igna
l / H
z
200150100500CPC mass /µg m-3
m/z=81 r2=0.997
m/z=102 r2=0.984
m/z=168 r2=0.992
Quantification
Signal linear with mass loading ( or a given compound)
Comparison to filter samples
35
30
25
20
15
10
5
0
Li_A
MS
m/z
168
sig
nal (
Hz)
20151050filter sample levoglucosan (ug/m3)
Summary
Li ion attachment ionization results in spectra showing less or no fragmentationquadrupol allows clean blanking of ions up to m/z=24mass resolution is the same as in EI ionizationsensitivity is some µg m-3 in 10ssignal is linear with mass loading -> allows for quantification of known compounds
Quadrupol blanking can also be use to blank electrons in negative ion mode
build easy to use quadrupol electronicsmeasure more standardsbetter understanding of ionization mechanism
Todo
Thanks to Niklas Schaper for the good characterization of the Li-ion-AMS
