On the Mechanism of Electrospray Ionization and Electrospray-based Ambient Ionization Methods

186 Pages·2011·5.23 MB·English

ETH Library
On the mechanism of electrospray
ionization and electrospray-based
ambient ionization methods
Doctoral Thesis
Author(s):
Wang, Rui
Publication date:
2011
Permanent link:
https://doi.org/10.3929/ethz-a-006657051
Rights / license:
In Copyright - Non-Commercial Use Permitted
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DISS. ETH NO. 19962

On the Mechanism of Electrospray Ionization and
Electrospray-based Ambient Ionization Methods

A dissertation submitted to
ETH ZURICH

for the degree of
Doctor of Sciences

presented by
Rui WANG
M. Sc. in Chemistry, Tsinghua University, China
Born November 24th, 1981
Shanghai, China P. R.
Citizen of China

Accepted on the recommendation of
Prof. Dr. Renato Zenobi, examiner
Prof. Dr. Kelsey D. Cook, co-examiner
Prof. Dr. Wendelin Jan Stark, co-examiner

Zurich, 2011

This dissertation is dedicated to my parents and husband,
for their endless love and support

Acknowledgements
First, I would like to sincerely express my gratitude to my supervisor, Prof. Dr. Renato
Zenobi. Four years ago, I knew almost nothing about electrospray ionization and mass
spectrometry, and he took the risk to accept me as a Ph.D. student. He was always patient for
my basic questions and slow progress at the starting time. In four years, I have learned not
only abundant professional knowledge of ESI and MS, but also how to manage a scientific
project from him. In addition to science, he also helps me a lot in improving my English, the
pronunciation and writing skills. I am really grateful for his guidance, insightful comments,
and the freedom he has given me in conducting my research.
I would also like to acknowledge my co-examiners, Prof. Dr. Kelsey D. Cook and Prof.
Dr. Wendelin Jan Stark, who have taken the time to read my thesis and helped improve it with
their insightful comments and suggestions.
Theoretically, my project was a kind of 'solo' project. However, I have never been involved
in this project alone, which is owed to the people I cooperated with: Mr. Arto Juhani Gröhn,
Dr. Waisiang Law, Dr. Liang Zhu, Dr. Rolf Dietiker, Dr. Thomas schmid, Prof. Huanwen
Chen, Dr. Maxim Yulikov, and Dr. Karl Ulrich Krieger. Many thanks are due to them for
sharing their time in the laboratory and great discussions of scientific results. I also would like
to thank the students, who worked with me: Mr. Pavel Sagulenko, Mr. Yury Kostyukevich,
Mr. Pitt Allmendinger and Mr. Zhiyi Yang. This project would not be able to have these
fruitful results without their work.
I sincerely thank Mr. Heinz Benz who helped me tirelessly with all the electronics in my
project. I am indebted to the people in the mechanical shop for manufacturing various sources,
fiber holders, vacuum systems and so on, especially Mr. René Dreier, Mr. Christoph André
Bärtschi, and Mr. Kurt Baumgartner.
It is a special pleasure to mention my previous and current colleagues in Prof. Zenobi's
group. I am grateful to have worked with them for four years in such a relaxing and enjoyable
atmosphere. I owe my deepest gratitude to all of them for exchanging the scientific ideas,
sharing the lunch time and traveling time together. Especially, many thanks are due to Dr.
Rob Nieckarz, Dr. Liang Zhu and Mr. Lukas Meier for proofreading my thesis and Mr. Stefan
Schmid for translating the summary. I highly appreciate the great help of Dr. Arno Wortmann
and Maarten Heringa when I just started the project. I also owe special thanks to our group
secretary, Ms. Brigitte Bräm, for her help in countless issues especially related to German
documents and her nice desserts and smiles. Many thanks go to the FT-ICR team for sharing
the time in the team meeting and my officemates, Dr. Vladimir Frankevich, Dr. Thomas
Schmitz and Miss Fan Chen for sharing the most office time together.
Last, but not least, no words can sufficiently express my gratitude towards my entire
family and close friends, in particular my parents, Mrs. Genli Chen and Mr. Chengliang Wang,
and my husband, Dr. Weihua Zhang. Without their unconditional love, support and patience, I
could not achieve the success I have today.
Contents
Summary ................................................................................................................................................. I
List of abbreviations ............................................................................................................................. V
Chapter 1: Electrospray ionization (ESI): history, evolution, and current developments ............. 1
1.1 General introduction ...................................................................................................................... 3
1.2 History of electrospray ionization ................................................................................................. 9
1.3 Evolution of the direct electrospray ionization method ............................................................... 10
1.3.1 Nanoelectrospray Ionization (NanoESI) .............................................................................. 10
1.3.2 Subambient pressure ESI (SPIN) ......................................................................................... 12
1.3.3 Pneumatic electrospray ionization (Pneumatic ESI) ............................................................ 13
1.3.4 Techniques that generate an electrospray from a Probe/Paper ............................................. 17
1.4 Development of electrospray-based ambient post-ionization methods ....................................... 18
1.4.1 Sample introduction via a gas/liquid flow (GC-ESI, SESI, EESI, FD-ESI) ........................ 19
1.4.2 Sample introduction via desorption using ESI/SSI/gas (DESI, EASI, ND-EESI) ............... 23
1.4.3 Sample introduction via desorption using other techniques ................................................. 26
1.5 Outline of this thesis .................................................................................................................... 27
Chapter 2: Mechanism of the electrospray process ......................................................................... 31
2.1 Overview of electrospray process ............................................................................................... 33
2.2 Electrochemistry inside the ESI capillary ................................................................................... 34
2.2.1 Electrochemical reactions in the ESI capillary ..................................................................... 34
2.2.2 Influence of electrochemical reactions on ESI-MS measurements ...................................... 36
2.3 Onset and emission of an electrospray ........................................................................................ 37
2.3.1 Electric field, current and voltage of the electrospray .......................................................... 37
2.3.2 Spray modes of the electrospray ........................................................................................... 39
2.3.3 Influence of various spray modes on ESI-MS measurements .............................................. 42
2.3.4 Spray modes of nanoESI ...................................................................................................... 42
2.4 Shrinking process of droplets in the electrospray ........................................................................ 43
2.4.1 Size and charge of initial droplets ........................................................................................ 43
2.4.2 Solvent evaporation and coulombic fission of droplets in the electrospray ......................... 43
2.5 Evolution of the conformation and concentration of analytes in the electrospray plume ........... 46
2.5.1 Solvent evaporation .............................................................................................................. 46
2.5.2 Droplet fission and partitioning effects ................................................................................ 48
2.6 Formation of gas-phase ions from droplets ................................................................................. 50
2.6.1 Ion evaporation model (IEM) ............................................................................................... 50
2.6.2. Charged residue model (CRM) ........................................................................................... 53
Chapter 3: Instrumental ..................................................................................................................... 55
3.1 Optical Methods .......................................................................................................................... 57
3.1.1 Laser induced fluorescence (LIF) ......................................................................................... 57
3.1.2 Infrared spectroscopy (IR) .................................................................................................... 61
3.2 ESI quadrupole time-of-flight (QTOF) mass spectrometry (MS) ............................................... 63
3.3 Phase Doppler Anemometry (PDA) ............................................................................................ 66
Chapter 4: Mechanistic studies of ESI using in-situ optical methods ............................................ 71
4.1 Evolution of solvent polarity in the electrospray plume .............................................................. 73
4.1.1 Abstract ................................................................................................................................ 73
4.1.2 Introduction .......................................................................................................................... 73
4.1.3 Experimental and methods ................................................................................................... 75
4.1.4 Results and discussion .......................................................................................................... 77
4.1.5 Conclusions .......................................................................................................................... 86
4.2 Behavior of noncovalent complexes in the electrospray plume .................................................. 87
4.3 Investigation of the electrospray plume by infrared spectroscopy .............................................. 91
Chapter 5: Mechanistic studies of electrosonic spray ionization using mass spectrometry and
numerical simulations ......................................................................................................................... 95
5.1 Abstract ....................................................................................................................................... 97
5.2 Introduction ................................................................................................................................. 97
5.3 Experimental and Methods .......................................................................................................... 98
5.4 Result and discussion ................................................................................................................ 100
5.5 Conclusions ............................................................................................................................... 110
Chapter 6: Mechanistic studies of extractive electrospray ionization using laser-induced
fluorescence and mass spectrometry ............................................................................................... 111
6.1 Abstract ..................................................................................................................................... 113
6.2 Introduction ............................................................................................................................... 113
6.3 Experimental Methods .............................................................................................................. 115
6.4 Results and Discussion .............................................................................................................. 118
6.5 Conclusions ............................................................................................................................... 125
Chapter 7: Mechanistic studies of extractive electrospray ionization using Phase Doppler
Anemometry and numerical simulations ........................................................................................ 127
7.1 Abstract ..................................................................................................................................... 129
7.2 Introduction ............................................................................................................................... 129
7.3 Experimental and methods ........................................................................................................ 131
7.4 Results and discussion ............................................................................................................... 132
7.5 Conclusions ............................................................................................................................... 143
Chapter 8: Conclusions and Outlook .............................................................................................. 145
Bibliography ...................................................................................................................................... 153