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Development of an atmospheric pressure ionization source for in situ monitoring of degradation products of atmospherically relevant volatile organic c [...] / submitted by Hendrik Kersten. 2011
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Table of Contents
Notation and Terminology
1 Introduction
1.1 Atmospheric Chemistry
1.1.1 Laboratory studies
1.2 Mass Spectrometry
1.2.1 Atmospheric Pressure Ionization (API)
1.2.1.1 Atmospheric Pressure Laser Ionization (APLI)
1.2.1.2 Atmospheric Pressure Photo Ionization (APPI)
1.2.1.3 Negative Ion Formation (NIF)
1.2.1.4 Ion Transformation Processes (ITP)
2 Goals
3 Experimental
3.1 Mass Spectrometer
a) Storing mass range capability.
b) Mass discrimination
c) Mass analysis
d) Mass resolution
e) Mass accuracy
f) Switching positive-negative modus
g) Resonant excitation
h) Ion isolation
i) CID
j) Msn experiments
k) Duty cycle
l) Chromatogram mode
m) Software
3.1.1 Laser Systems
3.1.2 Common API Source
3.1.3 Novel Laminar-Flow Ion Source (LFIS)
3.1.4 Novel APPI Setup
3.1.4.1 Setup for Characterization of Transfer Capillaries
3.1.4.2 Characterization of the Discharge Lamp
3.1.3 Setup for Neutral Radical Induced ITP Studies [82]
3.3 Photoreactor
3.3.1 Procedure of Atmospheric Degradation Studies
3.3.2 FT-IR-setup
3.3.3 MS Sampling Unit
3.3.4 MS Ionization Unit
3.4 Chemicals
3.5 Computational Investigations
4 Results and Discussion
4.1 Common API sources
4.1.1 Distribution of Ion Acceptance (DIA) Studies
4.1.2 Fluid Dynamical Behavior
4.1.3 H2O and O2 Background Concentrations [82]
4.2 Development of a Novel API Approach
4.2.1 LFIS - Preliminary Experiments
a) Rough determination of the flow characteristics
b) Ion transmission efficiencies
c) Different behavior of quartz and metal tubes
d) Impact of the laser frequency in coaxial configuration
e) Suggestive estimate of coaxial sensitivity
4.2.2 LFIS - Realization
4.2.2.1 LFIS - Fluid Dynamical Simulations
a) Flow characteristic
b) Diffusion along the flow propagation
4.2.2.2 LFIS – APLI
a) Choice of laser system
b) Laser beam expansion.
c) Interaction laser radiation → metal surface
4.2.2.3 LFIS – APPI
a) Implementation
b) Transit time.
4.2.3 Development of APPI on Transfer Capillaries
4.2.3.1 Characterization of Transfer Capillaries
a) Comparison of original and home–made capillary
b) Adaptability of fluid dynamic equations - laminar or turbulent
c) Critical and static pressure, velocity distribution, and transit times
d) Upstream pressure variation
4.2.3.2 First APPI on Capillary Approach
4.2.3.3 Development of Miniature VUV Spark Discharge Lamps
a) In general
b) High voltage-power supplies
c) APPI with or without window
d) Balanced pressure separation
e) Lamp design 1
f) Lamp design 2
g) Lamp design 3
h) Operating stability tests
i) Determination of lower detection limits (LODs)
j) Experimental sparking characteristics of design 3 with the DD20_10 C-Lader
k) Theoretical considerations on the spark characteristics
l) Optical emission spectroscopy (OES)
m) VUV emission efficiency in comparison to the commercially available APPI lamp
n) VUV emission spectroscopy below 105 nm
4.2.3.4 Impact of Different Ionization Positions on MS Spectra
a) Impact on negative ion mode
b) Impact on positive ion mode
4.3 Ion Transformation Processes (ITP)
4.3.1 Unintended Collision Induced ITP
4.3.2 Neutral Radical Induced ITP (NRITP) [82]5F
4.3.2.1 Evidence for Ion-Neutral Radical Chemistry
4.3.2.2 Oxidation of the Pyrene Radical Cation - Feasible Pathways
a) Oxidation via direct addition of O(3P) and OH
b) Oxidation via the pyrenyl cation [M-H]+
4.3.2.3 Oxidation of the Pyrene Radical Cation - Kinetic Investigations
a) Impact of O2, O(3P), and O3 on the ion distribution
b) Impact of H2O, OH, and H on the ion distribution
c) Impact of Cl, ClO, and ClOO on the ion distribution
4.3.2.4 Consequences for Degradation Studies with APPI-MS
4.3.3 ITP via Chemical Ionization
4.3.3.1 APPI/APLI-Positive Ion Chemical Ionization (PICI)
4.3.3.2 APPI/APLI-Negative Ion Chemical Ionization (NICI)
4.4 Degradation Studies
4.4.1 Features and limitations of the MS setup
4.4.2 Exemplary Degradation Study
4.4.2.1 Blank test without p-xylene present in the reactor
a) Signals of protonated water clusters
b) Signals of NOx, HNOx and HNOx∙NOx
c) Signals of Ox
d) Signals of CH3ONO and its degradation products
4.4.2.2 Degradation Study with p-xylene
a) Initial step I: H-atom abstraction from methyl group
b) Initial step II: OH-addition to the aromatic ring
5 Summary and Conclusion
a) Investigations on the commercially available API source
b) Development of a laminar flow ion source with a laminar sampling unit
c) Novel APPI approach with home-built miniature spark discharge lamps
d) Ion transformation processes
e) Exemplary degradation study of p-xylene
6 Indexes
6.1 List of Figures
6.2 List of Tables
6.3 References