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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

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

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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

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cont

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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