Comparison of Different Types of Ion Mobility Mass ...Comparison of Di erent Types of Ion Mobility...

Universiteit van Amsterdam

Literature Thesis

Comparison of Different Types of IonMobility Mass Spectrometry for the

Analysis of Synthetic & Bio -Macromolecules

Author:

Dennis R. Drost

Supervisors:

Prof. Dr. M. Honing

Dr. W.T. Kok

A thesis submitted in fulfilment of the requirements

for the degree of Master of Science

Van ’t Hoff Institute for Molecular Sciences

June 2014

http://www.uva.nl

Research Group Web Site URL Here (include http://)

Department or School Web Site URL Here (include http://hims.uva.nl/)

“Science is to see what everyone else has seen, but think what no one else has thought."

Albert Szent-Gyorgyi

UNIVERSITEIT VAN AMSTERDAM

AbstractFaculty of Science

Van ’t Hoff Institute for Molecular Sciences

Master of Science

Comparison of Different Types of Ion Mobility Mass Spectrometry for the Analysis of

Synthetic & Bio - Macromolecules

by Dennis R. Drost

In this thesis different types of commercially available ion mobility mass spectrometers are com-

pared on a fundamental level. Applications, advantages and disadvantages of different types

of ion mobility mass spectrometry systems are studied to see which system or combination of

systems gives the best results for different types of analysis. The combination of ion mobility

spectrometry with mass spectrometry is often vital for the complete analysis of both synthetic

and bio-macromolecules, since this combination provides information about the chemical struc-

ture, building blocks and conformation of the molecule. It is shown that high-field asymmetric

waveform ion mobility spectrometry coupled to a mass spectrometer gives the highest orthog-

onality of the two techniques, but lacks the possibility to determine the collision cross section.

Since ion mobility analysis uses a continuous stream of ions, its duty cycle and flexibility are

increased compared to traveling wave ion mobility where ions are inserted in packages into the

drift region. However, traveling wave ion mobility spectrometry has a much higher resolving

power compared to high-field asymmetric waveform ion mobility. A downside of both high-field

asymmetric ion mobility and traveling wave ion mobility is that field heating effects can occur,

potentially distorting or fragmenting the molecular structure of the analyte.

http://www.uva.nl

Faculty Web Site URL Here (include http://)

Department or School Web Site URL Here (include http://hims.uva.nl/)

Contents

Abstract iii

List of Figures vii

List of Tables ix

1 Introduction 11.1 Goal of this literature thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 Challenges concerning macromolecules . . . . . . . . . . . . . . . . . . . . . . . 21.3 Ion mobility mass spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.4 Different ways of commercially available IM-MS . . . . . . . . . . . . . . . . . . 5

1.4.1 Drift tube ion mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.4.2 Travelling wave ion mobility . . . . . . . . . . . . . . . . . . . . . . . . . 61.4.3 High-field asymmetric waveform IMS . . . . . . . . . . . . . . . . . . . . 71.4.4 Customized IM-MS instruments . . . . . . . . . . . . . . . . . . . . . . . 9

2 The technology behind IMS and its coupling with MS 112.1 Traveling wave ion mobility spectrometry . . . . . . . . . . . . . . . . . . . . . . 12

2.1.1 The Wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.1.1.1 Triangular waveform . . . . . . . . . . . . . . . . . . . . . . . 142.1.1.2 Half-sinusoidal waveform . . . . . . . . . . . . . . . . . . . . . 15

2.1.2 Advantages and disadvantages of traveling wave IMS . . . . . . . . . . . 162.1.3 Best applications for traveling wave IMS . . . . . . . . . . . . . . . . . . 16

2.2 High-field asymmetric waveform ion mobility spectrometry . . . . . . . . . . . . 162.2.1 Different designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.2.1.1 Cylindrical electrode design . . . . . . . . . . . . . . . . . . . 182.2.1.2 Dome electrode design . . . . . . . . . . . . . . . . . . . . . . 192.2.1.3 Cube electrode design . . . . . . . . . . . . . . . . . . . . . . . 20

2.2.2 Advantages and disadvantages of FAIMS . . . . . . . . . . . . . . . . . . 202.2.3 Best applications for FAIMS . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.3 Ionization sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.3.1 Radioactive ionization sources . . . . . . . . . . . . . . . . . . . . . . . . 222.3.2 Electro spray ionization . . . . . . . . . . . . . . . . . . . . . . . . . . . 222.3.3 Secondary electro-spray ionization . . . . . . . . . . . . . . . . . . . . . 23

v

Contents Literature Thesis

2.3.4 Corona-spray and corona-discharge ionization . . . . . . . . . . . . . . 232.3.5 Matrix-assisted laser desorption ionization . . . . . . . . . . . . . . . . . 232.3.6 Photo-ionization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3 Applications and discussion 253.1 Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.1.1 Cyclic polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263.2 Proteomics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273.4 Comparison with other techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.4.1 Liquid chromatography-mass spectrometry . . . . . . . . . . . . . . . . 29

4 Conclusion 31

Bibliography 35

vi

List of Figures

1.1 Number of publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Placing of FAIMS device before MS . . . . . . . . . . . . . . . . . . . . . . . . . 41.3 Ion separation in DT-IMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.4 Traveling wave TW IMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.5 Ion motion between two flat plate electrodes in FAIMS . . . . . . . . . . . . . . 7

2.1 Modeled traveling wave profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . 142.2 FAIMS properties described . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.3 Cylindrical FAIMS electrode design . . . . . . . . . . . . . . . . . . . . . . . . . 192.4 Cube FAIMS electrode design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.5 ESI evaporation principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.1 Separation of PEG polymer comparison . . . . . . . . . . . . . . . . . . . . . . . 28

vii

List of Tables

1.1 Customizable IM-MS companies . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1 Applications of ESI-FAIMS-MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.1 Specific advantages and disadvantages of the common IM-MS systems . . . . . 334.2 Main advantages and disadvantages of IMS . . . . . . . . . . . . . . . . . . . . 34

ix

Chapter 1

Introduction

The synthesis and characterization of one-, two-, and three dimensional synthetic and bio-macromolecules has been a rapidly growing area [1]. However, the scientists’ need to knowof ever increasingly complex polymers and biomolecules, especially about the detailed threedimensional structure of macromolecules, creates problems for analysts since the properties ofcomplex polymer mixtures and biomolecule mixtures tend to be difficult to determine. Sinceabout 1990, research has been started in to coupling ion mobility spectrometry to a massspectrometer, to combine their strengths to gain information about not only the compositionof a molecule but also its three dimensional structure. Figure 1.1 shows the rising interest inthis technique and that many believe it holds a lot of potential to overcome current analyticalchallenges when dealing with large biomolecules and polymers. [1]

Figure 1.1: Number of publications about ion mobility mass spectrometry published per yearfrom the years 1990 to 2013 [2]

1

Chapter 1. Introduction Literature Thesis

1.1 Goal of this literature thesis

In this thesis ion mobility mass spectrometry (IM-MS) and its underlying physics is investi-gated, focusing on the differences in ion mobility spectrometry between commercially availablesystems. This understanding will be used to screen a variety of current applications, evaluatepossible future applications and study the power of IM-MS. Finally the strength of IM-MS andwhat additional information it has to offer will be discussed, concluding with an analysis onwhat type of IM-MS system best suites of analyzes.

1.2 Challenges concerning macromolecules

Recently there has been a trend towards the synthesis of larger and more complex mixtures ofmacromolecules. Sometimes, in addition to the complexity of the mixtures, the macromoleculesare present in very low concentrations, this causes problems for most analytical techniqueseither due to their low resolution when dealing with large molecules or due to the limitationof an upper mass limit. Adding to this problem is the fact that nowadays not just the buildingblocks and the length of the polymer play a part, but also the specific three dimensionalstructure and inter polymer network [1]. The same goes for bio-macromolecules like proteins,where for example the same molecule can have a lot of different properties depending on itsthree dimensional structure. A large field of research, called proteomics, is specialized in theworkings of proteins and their conformation [3].

For some time now it has been possible to get the total mass of a macromolecule and its lengthcan be determined. Even the building blocks and some information about the order of thoseblocks has been available to analysts. For a long time this was enough information, but recentlythe deeper understanding of polymers and biomolecules combined with more computing powerhas enabled scientists to create models capable of predicting chemical properties of molecules,like strength and hydrofobicity, based on other properties such as length, mass, building blocksand its three dimensional structure. With these models, all kinds of new materials can bestudied and made and the properties of polymers and biomolecules can be linked to theirchemical structure [4]. To create such a model, these properties first have to be known for ahigh number of different molecules, but often only parts of the required data can be found.

In essence there are only two fundamental characteristics of macro molecules, their chemicalstructure and their molecular weight distribution (MWD). Unfortunately these properties are themost challenging for condensed-phase techniques to determine [4, 5]. The chemical structureof a polymer comprises:

• The nature of the repeating units

• The nature of the end groups

2

Literature Thesis Chapter 1. Introduction

• The composition of possible branches and cross links

• The nature of defects in the structural sequence

The MWD gives information about the average molecular size and describes how evenly themolecular size is distributed. This property depends on the synthesis of the polymer and mayvary greatly. When these two characteristics are fully known the properties of a polymer likeits strength, functioning and heat resistance can be derived and optimized to create a polymerbest suited for a certain application.

The chemical structure of a macro molecule almost always causes it to fold in a certain way,causing the molecule to have a certain size and shape. These properties cause the molecule tohave more or less resistance in an ion mobility spectrometer due to collisions with the carriergas, and therefore it is one of the main separation bases in ion mobility spectrometry. Thisproperty is called the collision cross section (CCS). The importance of the CCS is that withit, a lot of different properties of a molecule can be determined like its folding, which is avery important variable in proteomics. Combined with other techniques also the density andother properties of the molecule can be found. Depending on the IMS techniques used, theCCS can be calculated in advance and by comparing these with their experimental values anunderstanding and models can be gained of different properties of macro molecules [6? ]. TheCCS is also dependent on the carrier gas used, and different properties can be found usingdifferent types and mixtures of carrier gases [7].

The same goes for biomolecules, the need for structural information is growing because asingle protein can have many different functions and properties depending on the way it isfolded. Also, a lot of medicines and antibiotics interact with the structure of a molecule andtherefore can be made more effective if the structure of the molecule targeted by this medicineis known.

1.3 Ion mobility mass spectrometry

There are various analytical methods available for the characterization of polymers, but almostall of them have great disadvantages. For example, they can only measure the overall averagefeatures of the polymer, like nuclear magnetic resonance, instead of the individual molecularstructure [8]. Often information about for example the end groups or byproducts is lost in thenoise because these molecules have a weak signal and/or are present in too low concentrationrange compared to the measured polymer [9]. Since the development of ion sources that are ca-pable of producing intact macromolecular ions, mass spectrometry (MS) based methods for de-termining molecular weights and sequencing have become routinely applied to macromoleculeproblems [10]. With mass spectrometry detailed structural information can be acquired, espe-cially when using soft ionization methods. However MS is not the best option when analyzingpolymers containing oligomers of differing structures, but rather isobaric molecular weights.

3


Recently it has been found that coupling ion mobility spectrometry to mass spectrometry (IM-MS) has the ability to capture subtle differences at the molecular level in complex polymermixtures nearly instantaneously. Therefore it shows great potential for rapid, high-resolutionseparations of analytes based on structure and mass-to-charge ratios [11, 12]. This gives a lot ofpossibilities for many different industries in which polymers of all kinds are used, such as drugdelivery, food storage, industrial lubricants, space flight, nano-particles, the possibility to dointernal calibration and many more [13–15]. With ion mobility spectrometry (IMS) it is possibleto separate by a molecule’s structure and combining this with the weight of a molecule even thediffer between oligomers can be seen. When combining IMS with MS, the IMS device is mainlyused to separate the ions prior to their introduction into the vacuum chamber of the MS [16].This means that, as can be seen in figure 1.2, the IMS device is placed after the atmosphericpressure ion source and before the inlet of the mass spectrometer.

Ion mobility spectrometry is an analytical technique that separates ions in the gas phase underatmospheric pressure by their size and shape [17, 18]. These ions are then extracted from thereactor by an electric field and introduced into a drift tube in which they are pushed towardan ion collector by an electric field for detection. This electric field can have many differentproperties and forms but often consists of some sort of wave form. Depending on the typeof IMS used, the ions are separated depending on their mobility through the drift tube witha certain form of resistance. The ion detector of an IMS system can be replaced by a massspectrometer to add a dimension of orthogonality. This adds orthogonality because with IMSthe separation is based on the collision cross section of an ion and with MS the separation isbased on the mass to charge ratio (m/z) [19]. So ion mobility adds a degree of orthogonality tomass spectrometry due to the ion’s interactions with a neutral target or buffer gas. Combiningthese two techniques gives a lot of possibilities to not only measure the mass of molecules but,also their shape.

Due to the fact that not only the mass of a molecule, but also its shape can be determinedusing ion mobility mass spectroscopy, it has been applied to the analysis of biomolecules. Forexample by using electro spray ionization (ESI) and MALDI sources, combining them withmass spectrometry to create a powerful tool in the analysis of proteins, peptides and syntheticpolymers [18–22].

Figure 1.2: ESI-FAIMS-MS device with a dome electrode placed before the MS inlet. Theasymmetric waveform and the compensation voltage are applied to the inner electrode [16, 23].

4


When IMS was first coupled to MS, researchers had to build the instruments themselves, whichlimited the field to specialists. Their work was largely focused on atomic clusters. Later, aroundthe 1990’s, it was demonstrated that this technique could be used to larger and more complexmolecules, for example biological molecules and polymers [24]. This all changed when in 2006Waters Corporation brought their first commercial IM-MS system on the market. Not muchlater Thermo Fischer Scientific followed with their version of IM-MS, namely FAIMS, whichstands for high-field asymmetric waveform IMS.

1.4 Different ways of commercially available IM-MS

There are two types of ion mobility mass spectrometry (IM-MS) instruments commerciallyavailable. Waters has the SYNAPT High Definitions MS (HDMS). Thermo Fisher offers itssystem, based on high-field asymmetric waveform IMS (FAIMS) as a pre selection step for itsquadrupole and ion trap mass spectrometers [25]. The SYNAPT from Waters uses a form of IMScalled traveling wave IMS (TWIMS or T-wave IMS). Waters coupled this type of IMS to a Timeof Flight (TOF) mass spectrometer, which has the advantage of a high speed of measurement.An IMS instrument can scan about 50 spectra per second, while TOF-MS can get up to 50,000spectra each second, this means that it is possible to get a full mass spectrum of each part ofthe IMS spectrum [24].

Recently Bruker corporation has also started manufacturing commercial ion mobility massspectrometry systems, but no data has been published yet using this machine so it will not bediscussed in this thesis.

1.4.1 Drift tube ion mobility

All ion mobility spectrometry techniques are based on the first type of ion mobility tube used,which was the drift tube (DT-IMS). It is not used often anymore since the commercial systems donot use it, however it has relatively the easiest physics behind it, so IMS itself will be introducedwith DT-IMS and after that the type of systems used by the commercial available machines isdiscussed. Although it is barely used by the IM-MS system manufacturers it is still consideredone of the three main IMS techniques because of its relative simplicity in both the setup usedand the theory behind it.

In DT-IMS ions move in a linear drift tube through a homogeneous, continuous electric field ofintensity E filled with a neutral gas. When these ions move trough a gas under the influenceof an electric field, the combination of acceleration due to the field and deceleration due tocollisions with the gas lead very quickly to a average thermal velocity va and dependent on themobility K and E with [26–28]:

va = KE (1.1)

5


Figure 1.3: A bundle of ions enters the drift tube, where they are propelled by the electric field,and descelerated by the drift gas getting to a thermal velocity characteristic for each molecule

[26].

which causes different molecules to travel through the tube in different times, as is illustratedin figure 1.3, and this time is directly proportional to the space they occupy [29, 30]. Thefundamentals of DT-IMS are so well known that from the average velocity, the average collisioncross section of an ion can be calculated down to a few angstroms.

1.4.2 Travelling wave ion mobility

Travelling wave ion mobility spectrometry is used by Waters in their Synapt IM-MS. In thistechnique the separation parameter is the ion transit time [29]. A sequence of symmetricpotential waves continually propagating through a tube propels ions along with their velocitydepending on the mobility (K) (figure 1.4). Different species transit the tube in unequal times.Commonly smaller molecules collide less frequently with the carrier gas and make it to the MSfirst [30].

Figure 1.4: Ions propelled by traveling wave in TW IMS [29].

Using a soft ionization method, including an IMS dimension is highly complementary to MSfor the analysis of polymeric systems [31]. Using this combination, ions tend to fall in familiesdepending upon their charge and size. One of the ways this can be done is by having acontinuous beam of ions, ionized using ESI, accumulating in an ion funnel. These accumulated

6


ions periodically enter the drift region when an electrostatic gate at the end of the funnel.Generally, for ions with a relative small collision cross section, the smaller ions will have ahigher mobility than larger ones if they have the same charge state. After exiting the IMS,the ions are focused and are then send to a mass analyzer to detect the ions. Most massanalyzers have a shorter duty cycle than an IMS so data can be recorded in a nested fashion[32]. A downside is that so far the theory behind this technique is not yet fully understood andtherefore it is not yet possible to calculate the shape of an ion on the basis of the time it takesto travel through the drift tube [30].

1.4.3 High-field asymmetric waveform IMS

A downside of most IMS techniques is that they provide ion mobility values in the limit of EN ,

where E is the field strength and N is the gas density number [33]. Most are not designed tooperate at higher E

N values in which the ion mobility deviates measurably form the low-fieldlimit. This means that you would need very high field, or very low gas density. High fieldsare limited by the safety and technologie and decreasing the gas density to much will reducethe number of collisions, nullifying the gas principle behind IMS. However, a lot of importantinformation can be gained when operating at higher E

N values, for example about the ion-neutral interaction potential. With new technologies a non-uniform electric field can be createdwhich can operate at high E

N values [34]. This is high-field asymmetric waveform ion mobilityspectrometry (FAIMS), it was first described in 1993 by Buryakov et al [35].

Figure 1.5: Ion motion between two flat plate electrodes in FAIMS for an ion that has a increasedmobility in higher field strength so that one hits the lower electrode, while the one with a moreconstant mobility in both the high and low field will continue to the detector. The electrodesare approximately 2mm apart and an asymmetric square waveform is applied to the upper

electrode. The gas flow is from left to right [36].

In high-field asymmetric waveform IMS, just as in most IMS techniques, ions are driven througha carrier gas by electric fields [37]. Differences however, are significant when comparing FAIMS

7


with traditional DT-IMS. In FAIMS, the ions are separated while they are carried by a flow ofgas between closely spaced electrodes. In DT-IMS, on the other hand a discrete pulse of ionsdrifts from an inlet gate to a collector electrodes. This means that where in DT-IMS the carriergas generates the separtion by resistence, while in FAIMS the carrier gas pushes the ions troughthe drift region while the field generatios the ion seletion [16]. In figures 1.3 and 1.5 can beseen that in DT-IMS all the ions flow to the detector, just all with different velocities, while inFAIMS depending on their differences in velocity in the high and low field not all ions get tothe detector, and those who get there might differ in their mobility and therefore the time thatit takes them to hit the detector. So in FAIMS the ions pass through in a continuous stream,whereas the ions separated by DT-IMS are detected as discrete pulses of ion current as theycollide with the collector electrode. In a way you can compare FAIMS to a quadrupole analyzer,where ions are selected based on their behavior in the field region, and compare DT-IMS to atime of flight analyzer, where all ions go to the detector but the measurement is based on thetime it takes to get there.

Another big difference is that FAIMS uses an asymmetric electric field instead of a homoge-neous field or wave along the whole drift tube [30]. This causes some differences with other,traditional, IMS methods. In FAIMS the electric field oscillates so that only certain ions cantravel down the drift tube, while others hit the wall. This causes FAIMS to not separate ionslinearly in time but to act more like a ion filter instead of a mobility analyzer.

In a FAIMS device, ions are separated by the difference in their mobility in a high and low elec-tric field. In the strong field the ions are driven forward faster, thereby increasing the collisionenergy of the ions and the carrier gas compared to the thermal collision energy undergone atthe weak field. Subtle effects on the mobility arise from these changes in the collision energy[16, 38]. However, the mobility of different ions is affected differently by this difference in energy.Some ions gain a higher and some a lower mobility undergoing the higher collision energy. Thechange in mobility is a combined result of both the ion and the carrier gas and is tabulatedfor many small ions and various carrier gases. The strong field is achieved by applying thepeak voltage of the asymmetric waveform. The weak field, of opposite polarity, is often appliedlonger than the high field, therefore it is named asymmetric waveform.

How the change in mobility can affect the transition time of an ion in FAIMS can be seen infigure 1.5. The mobility in the weak field is about equal for most ions, but the mobility in thestrong field varies a lot and can even be negative (in comparison with the carrier gas), thisdifference in mobility is determining the ions transition time. Because of the higher mobility inthe high field, the ion is repelled more by the upper plate than it is attracted in the weak field,thereby reducing its distance to the lower electrode. After a number of cycles of the asymmetricwaveform, the ion will collide with the lower electrode. To transport the ion successfully betweenthe electrodes, a weak electric field can be superimposed to compensate for its drift therebypreventing the ion of interest from colliding with the wall and enabling the user to select certainions [16].

8


1.4.4 Customized IM-MS instruments

There are companies that provide customized IM-MS systems, these are not the somewhatadaptable one size fits all instruments that Waters and Thermo Fisher Scientific offer but cos-tumer specific designed instruments. In table 1.1 can be seen what kind of instruments can beprovided by some companies.

Company Excellims Corp Ionwerks Tofwerks AGTypical costof service

Contact vendor for quote $750,000 $350,000

Type of massspectrometerused

Standard used isquadrupole, but otherconfigurations areavailable by agreement

Orthogonal TOF hihg resolution or com-pact version orthogonalTOF

Type of ionmobilityspectrometerused

Standard IMS; High Reso-lution IMS; Chiral IMS

standard IMS (periodicfocusing at 2-10 Torr He)

Standard IMS; High-resolution IMS; Atmo-spheric pressure IMS

AdditionalInformation

Standard is ESI andambient pressure; High-resolution IMS areinterfaced to a quadrupolemass spectrometer througha linear interface; Optionalorthogonal ion extractioninterface available forsuperior ion transportationefficiency Also offers anovel chiral ion mobilityspectrometer/quadrupolemass spectrometer for arapid separation and iden-tification of ennantiomers

Instruments are speciallydesigned for MALDI andMALDI/IMS imaging

Can be coupled to LC;Ion sources can be electro-spray or corona discharge;Ion mobility spectrometersare resistive glass tubesfrom photonis with resolu-tion of 100-120

Table 1.1: Companies that provide customized IMS/MS instruments [24].

9

Chapter 2

The technology behind IMS and itscoupling with MS

Problems regarding the analysis of large molecules such as polymers is not restricted to thesynthesis of polymers, but also occur in areas of research involving large biomolecules suchas proteins. For instance to assess the function of a protein, a critical step is to determine itsstructure. This is challenging because many of these proteins only exist in low concentrationswithin cells and may not interact often and only for a short time. This makes analysis usingclassical structural biology tools like X-ray crystallography and NMR problematic, because theyneed quite high amounts of almost pure protein to work. This is why current methods foranalyzing protein mixtures are often based on 2D gel electrophoresis separation, after whicheach individual spot is analyzed by matrix assisted laser desorption ionization coupled to amass spectrometer (MALDI-MS) [39]. For some time now IM-MS has been an establishedtechnique for studying shape and conformation of small molecules and individual proteins inthe gas phase, but only recently IM-MS has been used to analyze intact protein complexes andmixtures of proteins to, for example, create proteome maps [40–42]

The mobility, K , of an ion in an electric field can be described by equation 2.1, in which Kh isthe ion mobility at high field, K0 is the mobility at the low field and f (E) is a function whichdescribes the electric field strength [23, 38]. This means that the movement of the ion dependson the type of electric field that is used and the strength of that field, this is what differentiatesthe types of IMS from each other. When the type of electric field is known, this equation canbe rewritten to more specific forms but the basic idea of all IMS systems is described by thisequation.

Kh(E) = K0[1 + f (E)] (2.1)

11

Chapter 2. The technology behind IMS and its coupling with MS Literature Thesis

Often however, not the mobility of a molecule but its velocity is measured. With this velocityand equation 1.1, or a more technique specific formula, this velocity can be translated to amobility which is characteristic for a specific molecule.

In this chapter the two techniques used by the commercially available instruments will bediscussed. These techniques are traveling wave ion mobility spectrometry and high-field asym-metric waveform ion mobility spectrometry.

2.1 Traveling wave ion mobility spectrometry

Traveling wave ion mobility spectrometry (TW-IMS) is used in the Synapt High DefinitionsMS from Waters [25]. It is a relatively new IMS method, and for quite some time the factorsgoverning the separation, the ion transit time, and the resolution were not fully understood[29].

Generally, large ions experience more collisions with neutrals and thus take more time (tD) toexit the drift region than smaller ions. This means that the ions will migrate through the neutralgas and separate according to their collision cross section. Additionally, ions with a highercharge will experience greater field strengths and exit the drift region faster [18, 22, 29, 38].

From the drift time, the collision cross section (Ω) can be calculated using the Mason-Schampequation [43]

Ω =3e16N

√2πµkbT

1K

(2.2)

where N is the drift-gas number density, µ is the reduced mass of the ion and drift gas, kb isthe Boltzmann constant, and T is the drift-gas temperature. From the Mason-Schamp equation,equation 2.3 can be derived which gives the interaction between the ion and the neutral driftgas molecules [6, 22, 44].

Ω =

√18π16

ze√kbT

[1mI

+1mN

] 12 tDEL

760P

T273.2

1N

(2.3)

Here z is the ion charge, e is the elementary charge, mI is the mass of the ion and mN is themass of the neutral gas, E is the electric field strength, L is the length of the drift region, Pis the drift gas pressure and N is the neutral gas number density. In most experiments a lotof variables belonging to the IMS machine are constant so, when combining equation 2.3 andequation 2.4 equation 2.5 can be derived in which B is a correction factor resulting from thetime-varying electric field present in the TW-IMS separation device and can be experimentallydetermined [44].

12

Literature Thesis Chapter 2. The technology behind IMS and its coupling with MS

µ =mNmImN +mI

(2.4)

Ω = kb1

µ12

tBdZ (2.5)

If the mass of the carrier gas is much smaller than the mass of the analyte ions µ remains fairlyconstant, this together with the assumption of singly charged ions, which is true for certainionization techniques, and the fact that k is constant the equation can be simplified further into equation 2.6. Which can be turned in to equation 2.7 by derivatization of both sides by mass.

Ω = k′btBd (2.6)

∆Ω

∆m= k′b

∆tBd∆m

(2.7)

This last equation, equation 2.7, suggests that in a mass-mobility plot,∆tBd∆m

, the slope is pro-

portional to the change of the CCS in a given mass difference,∆Ω

∆m, and can therefore be

used as an indication of a structural relationship between both. In fact in both DT-IMS-MSand TW-IMS-MS slopes in mass-mobility plots have been used to compare structurally relatedcompounds.

In some cases the gas purity, pressure or temperature cannot be measured accurately, calibrationof the drift tube using ions of known collision cross-section is preferable [22]. This also is thecase when using a traveling wave that uses time varying electric fields [45]. When the collisioncross-section as well as the mass information is known, a fit with computational models can beattempted to determine the structure of the original molecule.

2.1.1 The Wave

The traveling wave, TW, is an identical symmetric oscillation which is set up along a stackedring ion guide (SRIG). This is achieved by raising the voltages of selected electrodes spacedby fixed intervals. The speed, s, at which the wave moves is set by switching those electrodes[29]. The waves produced by TW IMS push all ions along but the motion, c, depends on themaximum voltage, v, at the front relative to the speed of the wave as follows from equation 2.8.

c =KEmaxs

(2.8)

13


This is a critical parameter in TW IMS, because it influences how and how much ions interactwith the traveling wave, if c 1, the wave passes underneath the ions so the ions only "bump"with slight axial displacement. On the other hand ions are "shoved" ahead of the lead wave. Ifc > 1. In the last case where c ≈ 1 the ions "surf" the wave, traveling with a mean velocity closeto speed of the wave but occasionally falling over tops.

As shown in figure 2.1, the wave can be described with a peak potential U , a maximum E ofEmax, a baseline width b and wavelength p. With these parameters a fundamental understand-ing of the waves used in TW-IMS can be gained, for this we will first look at the simplest waveprofile which is of a triangular waveform as seen in figure 2.1a.

Figure 2.1: Modeled traveling wave profiles: (a) triangular, (b) bi-triangular, (c) half-sinusoidal[29].

2.1.1.1 Triangular waveform

The triangular waveform, seen in figure 2.1a, is the simplest wave profile because it has the leastdifferent shapes in it and therefore can be described with less and easier formula’s compared tothe later given waveforms. The potential of this wave can be described by E = 2U

E [29]. Thisgives the ions an average velocity over the total wave cycle of:

14


v =dtC

=bs(KE)2

ps2 − (p − b)(KE)2(2.9)

The formula for the transit time through the TW-IMS of length L with this waveform can bederived and is given by:

tt =Lv=L[ps2 − (p − b)(KE)2]

bs(KE)2(2.10)

It can be seen from equation 2.10 that the traveling time depends on K2 instead of linear K asis the case in drift tube ion mobility spectrometry.

2.1.1.2 Half-sinusoidal waveform

While the triangular waveform has some relatively easy mathematics, it is not the most cor-rect form. This because an electric field in space must be continuous [29], which a triangularwaveform is not. This means that it is in a superposition with contributions of multiple elec-trodes producing a smooth axial potential, called a bi-triangular waveform. An example of abi-triangular waveform can be seen in figure 2.1b, but they can be composed of more than twotriangular waves and in different combinations. But this is still not the "best" representation ofa realistic waveform. Realistic waveforms are closer to a smooth half-sinusoidal wave profile asin figure 2.1c [29].

With this kind of gradually varying functions, the summation is replaced by integration and thepotential becomes a function of the axial coordinate x, E(x), for the average velocity this leadsto:

v =K2

s

∫ b0

E2(x)dxs2 −K2E2(x)∫ b

0

dx

s2 −K2E2(x)

(2.11)

When the mobility, K , is much smaller than time over Emax (K s sEmax

) equation 2.11 can besimplified to [29]:

v =K2

bs

∫ b

0E2(x)dx =

K2E2

s(2.12)

15


2.1.2 Advantages and disadvantages of traveling wave IMS

TW-IMS is a very moderate technique overall; it has no real major disadvantages, but neitherhas it big advantages. One of the disadvantage TW-IMS has however, is that it is harder todetermine the collision cross-section compared with conventional DT-IMS. This is due to theboth temporally and spatially changing electrical field [46, 47]. The result being that it is veryhard to derive the theoretical relation between the CCS and the drift time. In practice however,often this is overcome by calibrating the TW-IMS by molecules with known CCS, but someimportant factors always need to be considered in any TW-IMS experiment with respect toCCS calibration, carrier gas composition and the calculation of theoretical CCS from knownstructures [48]. A full survey of the advantages and disadvantages of TW-IMS can be found inthe conclusion in table 4.1.

2.1.3 Best applications for traveling wave IMS

TW-IMS is especially suited to study the CCS of macro molecules with the only downside beingthat the instrument needs to be calibrated first [28, 47]. It has been shown that TW-IMW can beused to investigate the three dimensional structure of proteins and the stability of that structurewithin the gas phase [49]. The TW-IMS is especially suited for this because it can operate atbiologically relevant sample concentrations and its speed facilitates its use in an automatedfashion. That TW-IMS is very suited vor protein analysis can also be seen in the wide usage inthis field of research already shortly after the release of this technique by Waters and therebyalso the rise in publications using TW-IMS [50].

2.2 High-field asymmetric waveform ion mobility spectrom-etry

A basic high-field asymmetric waveform ion mobility spectrometry (FAIMS) consists of twoelectrodes (often plates) of which one held at ground potential and the other has a changingpotential. This generates an electric field with an asymmetric waveform between these twoplates. As seen in figure 2.2 the low field of the asymmetric waveform is almost always turnedon longer than the high field.

It can be seen that, when not compensated, ions with a higher mobility at the high field thanin the low field will, at average, move toward the 0V plate and collide with it, while ions with alower mobility in the high field will move to the electric field generating plate and collide withit over time. To prevent the ions from colliding with the walls, a compensating electric field canbe used. With this you can prevent certain ions from hitting the wall, which also enables you toselect specific ions.

16


Figure 2.2: All properties of FAIMS described. Ions with increasing(purple), constant(blue) anddecreasing(yellow) mobility in high field. The lower plate is generating the asymmetric electric

field and the upper field is at constant voltage of 0V [51]

There is a problem with the waves described in figure 1.5 and 2.2, namely, it has very high powerrequirements which makes it a costly form of IMS and introduces a potential safety concern[16]. Because of this reason, a combination of a sine wave and its harmonic is used, this type ofwave can be described by:

V (t) =23Dsin(ωt) +

13Dsin(2θωt −φ) (2.13)

Where D is the peak voltage, DV , ω the waveform frequency in radians per second and φ isa phase shift of π2 radians. The energy consumption is minimized by using inductor-capacitortuned electronic circuits.

The separation in high-field asymmetric waveform ion mobility spectrometry (FAIMS) is basedon the mobility difference between the high and low electric field. At low field the mobility isoften determined by the thermal collision energy between the ions and the carrier gas. However,depending on the ions and the carrier gas mixture, a lot of interaction can happen influencingthe mobility of the ions [16, 38]. For example, complexes can be formed between the carriergas and the ions, thereby changing the mobility of the ions. This complex forming effect canbe enhanced by adding 10-10,000 ppm of water to the carrier gas. The complexes formed alsoinfluence the compensation voltages used to get the desired ions to the detector.

17


Area of Interest Analytes FAIMS electrode designSeparation of iso-mers and isobaricpeaks

Leucine enkaphalin clusters Cylindrical

Leucine/isoleucine CylindricalOrtho-, meta-,para-phthalic acids DomeMicrocystin DomeDisaccharides DomeNapthenic acids DomeUnderivatized amino acids DomePoly(ethylene glycol) isomers DomeLiposaccharides Dome

Protein conformeridentification

Bovine ubiquitin Cylindrical/Dome

Bradykinin DomeGramicidin S DomeCytochrome c DomeBeta-microglobulin CubeProstanoids CubeBradykinin Planar FAIMSUbiquitin DomeLysozyme, PEG ions Dome

Tryptic peptides Pig hemoglobin peptides Cylindrical/DomeEnolase I tryptic peptides DomeComplex tryptic digets, various proteins Dome

Table 2.1: Most suited electrode for different applications of ESI-FAIMS-MS [23].

2.2.1 Different designs

There are different types of FAIMS drift tubes, namely planar, dome, cube and cylindrical[23, 52]. All will be explained here and in the advantages and disadvantages of FAIMS sectiontheir specific advantages and disadvantages will be named. A guide to common used elektrodedesings for some different types of analytes can be found in table 2.1.

2.2.1.1 Cylindrical electrode design

The first generations of FAIMS devices used the cylindrical electrode design and were usedalmost exclusively until about 2000 [23]. The design, as is shown in figure 2.3, consists oftwo small inner electrodes and one long outer electrode. The inner electrodes are concentriccylinders held about 5 mm apart. These two inner cylinders are surrounded by a long outerelectrode. Ion separation occurs in the 2 mm space between the long inner electrode and the

18


Figure 2.3: Schematic view of the cylindrical electrode design. (a) 3D view and (b) cross-sectionalview. [23].

outer electrode. A dispersion voltage is applied to the outer electrode. As shown there aretwo places where the gasses enter the device, namely the carrier inlet and or the sample inletsand two exits; the carrier gas out and the sample gas out. The sample inlet is often usedfor introduction of volatile species or for ESI generated ions. The charged particles will travelthrough the device and exit to the electrometer, while neutral molecules will exit through thesample gas out.

2.2.1.2 Dome electrode design

The dome electrode design is shown in figure 1.2 and has some resemblance to the cylindricaldesign; both have an inner and outer electrode. One of the biggest differences is that in thedome electrode the inner electrode has a semi-spherical end and the outer electrode has a flatend and that the ions enter the IMS perpendicular to the MS. The annular space between thetwo electrodes ranges from 1.7 to 2.7 mm. The size of the annular region impacts both theresolution and the transmission efficiency of the FAIMS device, and can be optimized based onthe needs of the assay [23]. This electrode design is particularly well-suited to the separation ofprotein conformers and tryptic peptides as well as other applications where low flow rates, of5µL min−1 or less, can be used. Together with the cube electrode the dome electrode belongsto the coaxial type of electrodes [23].

19


2.2.1.3 Cube electrode design

In this design, the outer electrode is a 2.5 cm by 2.5 cm cube into which a hole is drilled.This hole accommodates the inner electrode. The annular space between the inner and outerelectrodes is fixed [23]. The ions are introduced parallel to the orifice of the mass spectrometer.This design was most useful for applications with high flow rates.

Figure 2.4: Schematic of the Thermo Fisher cube electrode design [53].

This type of electrode can also be used in a heated fashion, heated cube electrode, in whichalmost the whole systems is made of metal. One of the big differences is that air is introducedcontinually, also functioning as a cooling gas to maintain a constant temperature, while theinner and outer electrode can be heated independently which is particularly useful when usingheated MS ionization sources. Together with the dome electrode the cube electrode belongs tothe coaxial type of electrodes [23].

2.2.2 Advantages and disadvantages of FAIMS

While FAIMS is a technologically advanced technique, highly orthogonal to MS, with a lot ofpossibilities, one of the biggest disadvantages of FAIMS is that it is not possible to derive thecollision cross section with it [47]. With more complex setups however, it is possible to derivethe CCS with FAIMS but this is not possible with an ordinary FAIMS-MS setup [54]. The mainadvantage of FAIMS however is that it allows ions to be analyzed as a continuous stream insteadof a pulsed experiment. Combined with the ability of FAIMS to act as an ion filter, it producesa continuous beam of a subset of ions resulting in a simplified spectrum, which can be neededfor some difficult problems often occurring when analyzing macro molecules [55]. When usingFAIMS it is also important to know what type of electrode design you are using. The advantagesand disadvantages of both types, planar and coaxial, are listed here [23, 52];

20


• A coaxial design, either a dome or cube electrode, has generally a much longer ionresidence time, resulting in slower detector response.

• When the focusing conditions are met, the coefficient of ion transition in coaxial FAIMSbecomes more than those in planar FAIMS and vice versa.

• The focusing conditions in coaxial FAIMS cannot be met simultaneously for all sorts ofions.

• Planar FAIMS separates ll types of ions without discrimination in the features of α-dependence of ion polarity.

A full survey of the advantages and disadvantages of FAIMS can be found in the conclusion intable 4.1.

2.2.3 Best applications for FAIMS

Due to the non-uniform field, higher EN values can be used which enables a wider range of

mobility values [33]. With new sensors and equipment FAIMS is very suited for detecting lowmolecular weight compounds (such as SO2 and HCN, which are of interest in the militarysphere) in high-voltage systems with a detection at about 10-20 ppb [56]. Also for highermolecular weight compounds like DMMP end DEEP, both phosphonate stimulants, have beenmeasured with sensitivities up to 0.25 ppb.

2.3 Ionization sources

Prior to the 1980’s there where only ionization techniques limited to electron and chemicalimpact capable of ionizing low molecular wight, volatile and thermally stable compounds [57].Since then, a lot of different techniques have been developed that use softer ionization methodsso that bigger and less stable molecules can be ionized and analyzed with the mass spectrometeras well. In 2002 John Fenn and Koichi Tanaka even were awarded the Nobel prize for chemistryfor their development of soft desorption ionization methods for mass spectrometric analysisof biological macromolecules. Today scientists have a lot of different ionization sources tochoose from, all with different advantages and disadvantages. In this section the properties andcharacteristics of different ionization methods will be shown and research will be done to seewhich one is best suited to measure polymers.

21


2.3.1 Radioactive ionization sources

With radioactive ionization sources the ionization in the source is produced by the mission ofelectrons radiated from the radioactive source [18]. The ionization energy depends on the typeof radioactive source used, but has an average energy of 19 KeV . The radiated electrons collidewith neutral molecules of the analyte or the drift gas where they are ionized by a series of chargetransfer reactions. One of the downsides of this ionization method is that, together with othercharge transfer methods, there is the possibility of interfering reactions with contaminationcompounds which depletes the reactant ions, thereby decreasing the response to the compoundof interest [58]. Another disadvantage is the requirement to supply the sample in the vaporphase, which makes this technique disadvantageous for polymers because they often are notvolatile. An advantage however is that this ionization source does not need a power supplybecause it is continuous, therefore it is especially suited for portable and miniaturized devices.

2.3.2 Electro spray ionization

When Electro-spray ionization (ESI) was first developed, it greatly expanded the range of com-pounds that could be analyzed by IMS. This increase in application range was achieved becausewith ESI it is possible to ionize molecules still dissolved in small solvent droplets, allowing eas-ier sample intake, combining with techniques like liquid chromatography, and the possibilityto analyze [18]. It is becoming of even more use recently, because ESI is being optimized toionize bigger and bigger molecules [59]. In the ESI process, a high electric potential is appliedto the sample injection syringe, which then creates electric charges. This causes the sample tobe drawn to the target electrode, which is held at a lower voltage, by the coulomb force. Unlikemost ionization methods, ESI takes places at atmospheric pressure with the analytes dissolvedin a volatile solvent [57]. The solvent slowly evaporates as it travels towards the target elec-trode, which is the system inlet, shown in figure 2.5. This evaporation causes the charge on thedroplets to increase, which then "explode" due to coulombic repulsion. This process continuesto decrease the size of the droplets, ideally culminating in molecular ions.

Figure 2.5: Principle of evaporation and coulombic repulsion of droplets created with electronspray [60]

22


ESI is a soft ionization source especially suited for liquid samples and non volatile high molec-ular weight analytes such as polymers so that they also can be analyzed in the gas phase [18].With ESI you get simpler spectra with almost no fragmentation, so the molecular weight caneasily be determined. A problem of ESI however is that mass spectra of mixtures or samplescontaining impurities can be difficult to interpret because of the multiple charging phenomenon[10]. This causes a charge-state distribution for individual components of mixtures often to oc-cur over the same narrow mass to charge range which causes the peaks to, partly, overlap. Thisproblem can of course be overcome by adding a separation prior to detection, for example IMS.

2.3.3 Secondary electro-spray ionization

Where in ESI only the ions directly coming from the inlet jet are picked up by a probe, insecondary electro-spray ionization (SESI) a second probe is present to pick up secondary ions,ions generated by bombarding with ions [18, 61]. This is especially useful for analyzing specificsites and difficult to access surfaces, for example organelles on a cell and image surfaces. Thejet used in SESI exerts negligible damage so it is very useful to analyze valuable objects since itis semi non-destructive.

2.3.4 Corona-spray and corona-discharge ionization

In corona-spray ionization the bath gas around the inlet needle is ionized with a high electricfield that is applied around the tip [18]. Neutral molecules can evaporate from the needleand the ionized bath gas react with them to ionize the sample. This technique is used asan alternative for radioactive ionization, but especially corona-discharge ionization has a highpower consumption and therefore loses its usefulness in miniaturization and portable IMS.

2.3.5 Matrix-assisted laser desorption ionization

Matrix-assisted laser desorption ionization (MALDI) is especially suited for macromoleculeslike DNA, proteins and polymers because it does not fragment them in the protonation process,witch also makes the determination of the molecular weight easier. The analyte is dissolved in amatrix solution of small organic molecules which is then dried on a target plate [18]. The matrixabsorbs the applied laser pulse and sublimes carrying some of the analyte which is protonatedin the process. All molecules are singly protonated which simplifies the analysis and makes itmore sensitive. Overall, MALDI is very suited for analysis of polymers and coupling to IMSand MS and the mass range of molecules that can be ionized using MALDI is still growing [62].

23


2.3.6 Photo-ionization

Photo-ionization is achieved by using light with a short wavelength, from a lamp or laser, toexcite the electrons in a molecule and ionize it [18]. Advantages of this technique are thatyou can selectively ionize compounds by adjusting the wavelength of the light source, lamp orlaser. Disadvantages of especially UV lamps can be the moderate energy output which limitsthe ionization and the types of compounds that can be analyzed.

24

Chapter 3

Applications and discussion

IM-MS is a relatively new technique, but it has been shown that it can be used to do orimprove a lot of new and previously challenging analysis. Examples are differentiating betweena protein in its native folded state and its intact but denatured analogue [63]. In the case ofsynthetic polymers, IMS has been used to detect low abundance [31], to differentiate betweenend groups [8], to analyze different side chain isomers [11], to elucidate different block copolymerratios and to separate polymer blends. Linear and cyclic hexacadmium complexes can also bedistinguished, offering precedence for distinguishing these macromolecular architectures [64].

With IM-MS it is possible to separate based on size and mass, it allows for the separation ofisomers or conformers of different compounds [24]. This allows for a lot of applications inbiological and pharmaceutical area’s where isomers and conformers can make the differencebetween, for example a working medicine or a potential health risk. When a IMS is coupledwith a TOF, mass-resolved ion mobility distributions for a distribution of ions can be obtainedsimultaneously [65]. This results in some distinct advantages, including an improved efficiencyin recording collision cross sections for many different species in the distribution of ion systems,a nett improvement in the ability to resolve different peaks, when compared to the individualmobility separation or m/z dispersion, and allows for direct measurements of distributions ofions. This is all accomplished by recording the flight times of the TOF within the individualdrift time windows of the IMS [32].

One of the applications IM-MS is the analysis of polymers like polyethylene glycol (PEG),which is a polymer that gets attached to biotherapeutics to increase the stability of the activecompounds in vivo [24]. But so far it has been challenging to do the actual characterizationof PEG due to the many ways in which it polymerizes with varying lengths and branches. IM-MS has proven to get more detailed information in the characterization of PEG and therebycontributing to the understanding of how and why they work and how they can be improved.

Polar polymers give a lot of problems in normal MS. This is due to the high number of chargeson the ions, which makes it impossible to resolve the individual peaks for polymers above a

25

Chapter 3. Applications and discussion Literature Thesis

mass of 20-40 kDa [66]. This is even true if a resolving power of over 10,000 is achieved. IM-MS resolves this problem by separating the ions by their mobility K and take an m/z spectraof every K. This means that the spectra will be less crowded, that the different polymers anddifferent configurations will not be shown in the same m/z spectra and most importantly that alot more information and differences can be seen between polymer mixtures.

Not only the extra information that can be gained from IM-MS is an advantage, also thesubstitution of chromatographic separations by IMS has a lot to offer. While more samplepreparation might be needed [11], a lot of time can be gained in the separation step becauseIMS is often a lot faster than a chromatographic separation step.

3.1 Polymers

3.1.1 Cyclic polymers

Cyclic polymers inhibit unique behavior, especially their degradation behavior. cyclic polymershave a lot of interesting properties, for example, increased glass transition temperature, asmaller hydrodynamic volume, and a lower intrinsic viscosity when compared to their linearanalogues [67]. One of the most promising and intriguing potential applications of cyclicpolymers is the encapsulation and targeted delivery of drugs in the human body [68, 69].Despite this, cyclic polymers are one of the least studied polymers because most reactionsgiving cyclic polymers are susceptible to the generation of linear byproducts with the samemass or rings that are slightly bigger or smaller [70]. It is found challenging to characterize thepurity of cyclic polymers and to confirm that there are no trace amounts of linear polymerspresent, which can greatly influence the behavior of the total polymer. So because it is veryhard to get reliable data of a cyclic polymer, not a lot of studies have been done on them andtheir potential in a lot of different areas still is unknown.

IM-MS is the first technique to successfully evaluate the architectural purity of (cyclic) polymers[70]. In contrast to techniques like NMR or IR, IM-MS can find trace impurities of polymersbecause the signal of the backbone of the polymer is not overwhelming that of the end groupsand the small differences between chain length, which is the case in NMR and IR where you canonly measure the average structural features of a polymer [11, 70, 71]. Size exclusion chromatog-raphy (SEC) can be used to confirm the architecture of cyclic polymers but the low resolvingpower of this technique often impedes the analysis of the purity of the polymers. MS cangive complementary information such as accurate mass measurements of each unique polymerchain length [72]. Size exclusion chromatography coupled to MS (SEC-MS) can therefore giveinformation about the impurities of cyclic polymers, but IMS offers a better and mostly fasterseparation of the different polymers so this still is the better choice.

26

Literature Thesis Chapter 3. Applications and discussion

3.2 Proteomics

It has been shown that a combination of IMS with MS has a lot of possibilities in the fieldof proteomics, especially when analyzing mixtures of proteins. For example IM-MS data ofpeptide mass mapping indicates that a greater number of proteolytically derived peptides areobserved by using IMS separation prior to MS rather than by for example MALDI-MS alone[12, 15].

IM-MS is a very promising technique for proteomics because it allows for a high throughput ofsamples which is preferable for proteomic questions due to the high number of measurementsneeded to get all the wanted information [73]. Other requirements are a low limit of detection, ahigh sensitivity and a wide dynamic range, all of which mass spectrometry offers. Ion mobilityspectrometry however suffers from poor sensitivity and a low limit of detection (nmol-pmol)[12]. Still a lot of effort is being put into overcoming those challenges because of the uniquecapabilities IM-MS has to offer, for example suppression or elimination of chemical noise, rapid(µs-ms) separation of complex mixtures and nearly simultaneous (bio)polymer sequencing.

3.3 Limitations

A few of the most important IM-MS limitations are depending on the ionization method usedfor the experiment. With most ionization methods it is hard to ionize for example hydrophobicmembranes [22]. Also the interpretation possibilities, given interpretable MS data, the structuralinformation provided by IM-MS is limited by the IMS resolution for the ion of interest whichcan be poor [12]. High resolutions, above 10-15, is not often found for large complexes, howevermuch higher values have been reported for smaller molecules [74, 75].

Two serious challenges of IM-MS are its poor sensitivity compared to other techniques and itslimited peak capacity relative to alternative multidimensional separation approaches.

The calibration of IM-MS is often based on the use of calibration ions, this means that thecalibration is limited by the available calibration ions [22]. Sometimes calibrations can be doneusing equations like equation 2.3 but this is only the case if all parameters can be measuredaccurately.

3.4 Comparison with other techniques

For synthetic and biomacromolecules IMS is not the only option to get accurate weight distri-butions and absolute concentrations of mixtures of these molecules. SEC-MS is a techniquesimilar to IM-MS in that both SEC and IMS separate molecules based on their size/cross sec-tion but both techniques do this in different ways [76]. Using ESI-SEC-MS for example, it has

27


been shown that molecules with a molecular weight up to 10 kDa can be analyzed regardlessof the monomer class of the polymers and without external calibration or additional modelassumptions.

There are a lot of different techniques that can be used to separate and analyze polymers andbig biomolecules and all of them have different possibilities and limitations. In this sectionsome of these techniques will be compared with IM-MS.

Figure 3.1: Separation with different polymer analyzing methods of two different PEG sampleswhich vary slightly in molecular composition. Sample 1 (green) is 4250 Da and sample 2 (blue)is PEG 3400 Da. (A) is a SEC analysis and determines the bulk composition. (B) is a MALDI-MS of both samples doped with Cs+. (C) are 3D IM-MS images color coded, were red is mostto blue is least abundant. Samples where doped with cesium chloride and analyzed in a 3 m

drift tube instrument [11]

28

Literature Thesis Chapter 3. Applications and discussion

An example of a comparison of the different abilities of SEC, MALDI-MS and IM-MS can beseen in figure 3.1. In this application, a PEG polymer is analyzed first using SEC figure 3.1A,which gives the bulk composition and evidence of a high-mass tail for sample 2. With MALDI-MS, figure 3.1 B.1 and B.2, more information can already be gathered. The singly chargedoligomer chains of similar ion intensity permit end group analysis. However, the high-mass tailof sample 2 cannot be detected. Also, the only real difference between the oligomers is thespread and place of the individual chains. IM-MS however provides a direct measure of allionized sample components. Using the 3D images gained from IM-MS, figure 3.1C, multiplecharge state families can be found and the high mass tail can be analyzed. It can be seen thatwith IM-MS more than just a difference in the mass of the chains can be found, also manycharacteristics to the shape of these ions can be extracted on an closer inspection of this data.

A lot of information can be found from the IM-MS combination that the two techniques sepa-rately, or other techniques could not have shown. For example it can be seen in figure 3.1 C.2that with increasing polymer chain length more and more folding transitions (marked with a T)occur, some even undergo collapsing transitions (for example the +4 charged ion at T4) untila structural density is reached where these polymer ions drift in the IMS dimension similar toproteins(this is true for +3 charged ion when m/z > 1500 and for +4 charged ions when m/z >2000) [11, 77]. This is the kind of information you do not get from other techniques. As shownin figure 3.1 B.1 and B.2, with MS alone you can see that there is a difference between the twosamples and some information about the individual oligomer chains can be gained. But whenIMS is added to MS as seen in figure 3.1 C.1 and C.2 you also get the otherwise lost informationabout the different ways in which these molecules fold and orientate them selfs which for a lotof research is an important property.

Over all, the strength of IM-MS is not its peak capacity or sensitivity, but its superior peakcapacity production rate [12]. This high peak production rate is due to the low analysis time(µs-ms) and allows users of these instruments to get the needed results a lot faster. This isespecially preferable in the industrial and medical area where time can make the differencebetween wasting whole batches of product or even life and death.

3.4.1 Liquid chromatography-mass spectrometry

Liquid Chromatography-mass spectrometry (LC-MS) on complex biological mixtures has ad-dressed several of the analytical challenges encountered in proteomics, for example by theability to increase the dynamic range of the analysis by attenuating chemical noise or instru-mental background [78, 79]. A downside of this technique however is that there are significantlimitations on both the experimental design and independent optimization of the LC and MSseparation conditions and there is a large disparity in the timescales of the two analyte disper-sive dimensions [12]. Compared to IM-MS, LC-MS has a very low throughput, this is due to theoften slow LC separations which can require minutes up to hours. The primary advantages of

29


IM-MS over LC-MS are a significant reduction of separation times and post ionization separa-tion by the IMS provides information on the products of the ionization rather than both neutraland ionic species which are separated in liquid chromatography. Where the strength of LC-MSis the orthogonality of the two separation dimensions, IM-MS relies on the correlation betweenthe two separation dimensions for different chemical classes or conformational classes, addinga dimension of information not present in conventional liquid phase separations [80].

30

Chapter 4

Conclusion

The interplay between IM and MS data is often vital for the complete analysis and utility ofthe information gained from the two dimensions [22]. MS data is used to define the charge andcomposition of the observed ions and without this information it is often difficult to interpretIM data correctly. In many cases trends in the drift time versus mass to charge ratio (m/z)plots reveal information that can indicate for example the charge state or molecular class of theobserved ions [15].

With IM-MS, or even IMS-IM-MS, you can acquire signature spectra of subtle structural char-acteristics of polymers like weight, end groups, conformation and conformational changes [11].These permit almost instantaneous recognition of sample differences even from a quantitativeperspective. The 3D analyses are simple, fast, sensitive and cost effective technique to provideinformation about molecular shape and size with the possibility to predict physical propertiesof polymers.

Using a combination of IMS and MS, good separation of isobaric oligomers can be achieved[8]. Even mixtures that are not separable with MS-MS experiments can be separated usingan IM-MS device. However, the resolving power of IM-MS/MS degrades at high molecularweight. For example, limited separation is observed in oligomers with precursor ion resolutionof >10000 Dalton. IM-MS-MS enables full structural characterization of polymers, identifyingdifferent end groups. Overall IMS provides an extra dimension of fast, sensitive ion separationto MS enabling isobaric synthetic polymers to be differentiated by their size, shape and charge.

Another strong point of IM-MS is that some limitations like the sensitivity and dynamic rangecan be significantly improved by using multiplex data acquisition methods and position sensitivedetection strategies [81]. Even the throughput can be enhanced further by multiplexing the ioninjection into the drift cell for example by using MALDI or ESI [12].

The introduction of ion mobility separation prior to MS, results in a significant reduction inspectral congestion as compared to ESI-MS alone and allows many features associated with arange of different sizes and charge states to be resolved [32]. The traditionally frequently used

31

Chapter 4. Conclusion Literature Thesis

techniques to characterize polymers often describe the sample as a bulk system and are mostlyrelatively insensitive. This makes it difficult to pick up on small differences or impurities suchas the distribution of oligomers which can be observed more clearly by a IM-MS combination.

Overall IM-MS offers some great possibilities such as; fast 2D separations (µs-ms) in compari-son with LC or CE-MS, reduction of chemical noise and ion suppression effects, fast separationof molecules of different molecular and/ or conformational class and nearly simultaneous ac-quisition of both parent and fragment spectra [12].

The specific advantages and disadvantages are given in table 4.1 and a summary of the mainadvantages and disadvantages of IMS in general are given in table 4.2.

Overall, when speed is of importance or MS is not fully suited for sample analysis, FAIMS isthe best technique. It analyses ions as a continuous beam and has the highest orthogonality toMS compared to DT-IMS and TW-IMS. Combined with its high sensitivity and superior linearrange, FAIMS is suited for a wide range of applications in the industrial and medical world.However, determining the CCS is not possible using FAIMS. For research purposes TW-IMS isa better suited technique than FAIMS. After calibration TW-IMS is able to determine the CCS.The high resolving power and good sensitivity combined with generally more possibilities tofine tune the experiment make TW-IMS a more versatile technique than FAIMS, which is oftenpreferred by scientists who do not perform routine tests.

32

Literature Thesis Chapter 4. Conclusion

Technology DT-IMS Traveling wave IMS FAIMSCollisioncross sectionmeasure-ment(CCS)

Possible to do directCCS measurementbased on low-fieldmobility

Requires system cal-ibration with ideallychemical and physi-cally equivalent cali-brant with known CCS

CCS cannot be deter-mined

Orthogonalityof separation

Poor orthogonality.Larger ions have largerm/z values

Large ions also havelarger m/z value sopoor orthogonality

Highly orthogonal toMS

Linear dy-namic range

Limit to size of ionpacket in pulse wichlimits linear dynamicrange, can be improvedby staggered pulsing

Limit to size of pulse ofions which limits lineardynamic range, stag-gered pulsing can im-prove this

Superior linear dy-namic range, usesstream of ions insteadof pulses

Duty cycle Relative to other tech-niques a poor duty cy-cle

Better duty cycle thanDT-IMS but still notvery good

Ions are analyzed asa continues beam, sofastest µ, duty cylebut when using scan-ning mode, becomesthe slowest

Physical ef-fects on ionstructure

Ambient conditions forions

Field heating effects,potentially distorts orfragments molecularstructure

Field heating effects,potentially distorts orfragments molecularstructure

Resolvingpower

Highest resolvingpower

High resolving power,generally lower thenDT-IMS

Less resolving powerbut high separation se-lectivity by fine tun-ing experimental con-ditions

Sensitivity Low sensitivity Higher sensitivity Highest sensitivityOther advan-tages

Can be used to separatespecies of very similarmobility

Can be used for mo-bility separation of ionseither generated by col-lision induces dissoci-ation or by electrontransfer dissociation

Relatively easy to trans-fer the ion mobility de-vice between differentmass spectrometers

Other Disad-vantages

Gating type instru-ments are susceptibleto ion losses when ionstravel from atmosphericpressure in the IMS tovacuum in the MS

The geometric config-uration of the FAIMS-MS instrument allows itonly to analyze ions im-mediately after ioniza-tion

Table 4.1: Specific advantages and disadvantages of the three main ion mobility mass spectrom-etry systems, color indicating the relative ranking of the techniques on that criteria [28, 47]. Thecolor indicatios the relative ranking, where green indicates best, yellow indicates mediocore and

red indicates worst.

33

Chapter 4. Conclusion Literature Thesis

Advantages / characteristics Disadvantages CommentsAtmospheric pressure opera-tion

Contamination by atmosphericvapors

Simple and inexpensive due tothe absence of vacuum pumps

Efficient vapor-phase ionizationof organic and/ or inorganicparticles

Complex spectra and interfer-ence due to widespread ioniza-tion

Almost a universal technique

Selectivity based on protonaffinity or ionization potentialof analytes

Low proton affinity or ioniza-tion potential coumpounds arehard to detect

Many available sources allowionization of different analytes

Gas-phase ion separation Not suitable for non volatile an-alytes

Separation based on collisioncross-sections

Size and shape are not specificqualities

Can be used as second dimen-sion of separation techniquessuch as mass spectrometry

Portability, miniturization andmechanical robustness

Field and harsh environmentsapplications

Fast and sensitive analyses (mil-lisecond time range)

Fast electronics are required Monitoring of reactions andproduction and the detection ofexplosives, drugs etc. in air-ports and customs

Low aquisition and operatingcostsIMS protects the MS interface Noise is reduced by limiting the

material that enters the massspectrometer

Limited linear range Sample size must be carefullymanaged to avoid saturation

Possibility to increase sensitiv-ity by use of fourier transformIMS

Short duty cycle due to pulsingions into the drift tube, 1% orless of the analysis time

Sensitivity could be higherwithout pulsing

Overlapping analytes can beseparated changing the buffer-gas or solvent

Different responses with variousbuffer gasses and with samplesolvents

Experimental conditions mustbe carefully reproduced to re-peat experiments

Reproducibility of reduced mo-bilities within 1-2 %

Table 4.2: Main advantages and disadvantages of IMS [18].

34

Bibliography

[1] Susumu Kitagawa, Ryo Kitaura, and Shin-ichiro Noro. Functional porous coordinationpolymers. Angewandte Chemie International Edition, 43(18):2334–2375, 2004.

[2] Google scholar www.scholar.google.com searching for ion mobility mass spectrometry andsorting for year of publication.

[3] Mike Tyers and Matthias Mann. From genomics to proteomics. Nature, 422(6928):193–197,2003.

[4] Dirk Willem Van Krevelen and Klaas Te Nijenhuis. Properties of polymers: their correlationwith chemical structure; their numerical estimation and prediction from additive group contri-butions. Access Online via Elsevier, 2009.

[5] Charlotte Uetrecht, Rebecca J Rose, Esther van Duijn, Kristina Lorenzen, and Albert JRHeck. Ion mobility mass spectrometry of proteins and protein assemblies. Chemical SocietyReviews, 39(5):1633–1655, 2010.

[6] Matthew F Bush, Zoe Hall, Kevin Giles, John Hoyes, Carol V Robinson, and Brandon TRuotolo. Collision cross sections of proteins and their complexes: a calibration frameworkand database for gas-phase structural biology. Analytical chemistry, 82(22):9557–9565,2010.

[7] Gary Alan Eiceman, Zeev Karpas, and Herbert H Hill Jr. Ion mobility spectrometry. CRCpress, 2013.

[8] Gillian R. Hilton, Anthony T. Jackson, Konstantinos Thalassinos, and James H. Scrivens.Structural analysis of synthetic polymer mixtures using ion mobility and tandem massspectrometry. Analytical Chemistry, 80(24):9720–9725, 2008.

[9] Anthony P. Gies, Michal Kliman, John A. McLean, and David M. Hercules. Characteriza-tion of branching in aramid polymers studied by maldiâ^’ ion mobility/mass spectrometry.Macromolecules, 41(22):8299–8301, 2008.

[10] Sheila C Henderson, Stephen J Valentine, Anne E Counterman, and David E Clemmer.Esi/ion trap/ion mobility/time-of-flight mass spectrometry for rapid and sensitive analysisof biomolecular mixtures. Analytical chemistry, 71(2):291–301, 1999.

35

Bibliography Literature Thesis

[11] Sarah Trimpin and David E Clemmer. Ion mobility spectrometry/mass spectrometry snap-shots for assessing the molecular compositions of complex polymeric systems. Analyticalchemistry, 80(23):9073–9083, 2008.

[12] John A McLean, Brandon T Ruotolo, Kent J Gillig, and David H Russell. Ion mobility–massspectrometry: a new paradigm for proteomics. International Journal of Mass Spectrometry,240(3):301–315, 2005.

[13] Theresa M Allen and Pieter R Cullis. Drug delivery systems: entering the mainstream.Science, 303(5665):1818–1822, 2004.

[14] Andre Nel, Tian Xia, Lutz Mädler, and Ning Li. Toxic potential of materials at thenanolevel. Science, 311(5761):622–627, 2006.

[15] Brandon T Ruotolo, Kent J Gillig, Earle G Stone, David H Russell, Katrin Fuhrer, Marc Go-nin, and J Albert Schultz. Analysis of protein mixtures by matrix-assisted laser desorptionionization-ion mobility-orthogonal-time-of-flight mass spectrometry. International Journalof Mass Spectrometry, 219(1):253–267, 2002.

[16] Roger Guevremont. High-field asymmetric waveform ion mobility spectrometry: A newtool for mass spectrometry. Journal of Chromatography A, 1058(1):3–19, 2004.

[17] Glenn E. Spangler. Theory and technique for measuring mobility using ion mobility spec-trometry. Analytical Chemistry, 65(21):3010–3014, 1993.

[18] Roberto FernÃ¡ndez-Maestre. Ion mobility spectrometry: History, characteristics and ap-plications.

[19] GF Verbeck, B. Ruotolo, H. Sawyer, K. Gillig, and D. Russell. A fundamental introductionto ion mobility mass spectrometry applied to the analysis of biomolecules. Journal ofbiomolecular techniques: JBT, 13(2):56, 2002.

[20] Amina S. Woods, Michael Ugarov, Tom Egan, John Koomen, Kent J. Gillig, Katrin Fuhrer,Marc Gonin, and J. Albert Schultz. Lipid/peptide/nucleotide separation with maldi-ionmobility-tof ms. Analytical Chemistry, 76(8):2187–2195, 2004.

[21] Thomas Wyttenbach, Paul R. Kemper, and Michael T. Bowers. Design of a new electrosprayion mobility mass spectrometer. International Journal of Mass Spectrometry, 212(1):13–23,2001.

[22] Brandon T Ruotolo, Justin LP Benesch, Alan M Sandercock, Suk-Joon Hyung, and Carol VRobinson. Ion mobility–mass spectrometry analysis of large protein complexes. Natureprotocols, 3(7):1139–1152, 2008.

[23] Beata M Kolakowski and Zoltán Mester. Review of applications of high-field asymmetricwaveform ion mobility spectrometry (faims) and differential mobility spectrometry (dms).Analyst, 132(9):842–864, 2007.

36

Literature Thesis Bibliography

[24] Rajendrani Mukhopadhyay. Ims/ms: its time has come. Analytical Chemistry, 80(21):7918–7920, 2008.

[25] Celia Henry Arnaud. Ion mobility-mass spec combo. Chem.Eng.News, 86:11, 2008.

[26] JI Baumbach. Process analysis using ion mobility spectrometry. Analytical and bioanalyticalchemistry, 384(5):1059–1070, 2006.

[27] Gushinder Kaur-Atwal, Gavin O’Connor, Alexander A Aksenov, Victor Bocos-Bintintan,CL Paul Thomas, and Colin S Creaser. Chemical standards for ion mobility spectrometry:a review. International Journal for Ion Mobility Spectrometry, 12(1):1–14, 2009.

[28] IM-MS system manufacturer Owlstone. A comparison of the 3 main forms of ion mobilityspectrometry.

[29] Alexandre A. Shvartsburg and Richard D. Smith. Fundamentals of traveling wave ionmobility spectrometry. Analytical Chemistry, 80(24):9689–9699, 2008.

[30] Herbert H. Hill Jr, William F. Siems, and Robert H. St. Louis. Ion mobility spectrometry.Analytical Chemistry, 62(23):1201A–1209A, 1990.

[31] Sarah Trimpin, Manolo Plasencia, Dragan Isailovic, and David E. Clemmer. Resolvingoligomers from fully grown polymers with ims-ms. Analytical Chemistry, 79(21):7965–7974,2007.

[32] Cherokee S. Hoaglund-Hyzer, Young Jin Lee, Anne E. Counterman, and David E. Clemmer.Coupling ion mobility separations, collisional activation techniques, and multiple stages ofms for analysis of complex peptide mixtures. Analytical Chemistry, 74(5):992–1006, 2002.

[33] Larry A Viehland, Roger Guevremontb, Randy W Purves, and David A Barnett. Compari-son of high-field ion mobility obtained from drift tubes and a faims apparatus. InternationalJournal of Mass Spectrometry, 197(1):123–130, 2000.

[34] Randy W Purves and Roger Guevremont. Electrospray ionization high-field asymmetricwaveform ion mobility spectrometry-mass spectrometry. Analytical chemistry, 71(13):2346–2357, 1999.

[35] IA Buryakov, EV Krylov, EG Nazarov, and U Kh Rasulev. A new method of separation ofmulti-atomic ions by mobility at atmospheric pressure using a high-frequency amplitude-asymmetric strong electric field. International journal of mass spectrometry and ion processes,128(3):143–148, 1993.

[36] Yuriy Zrodnikov and Cristina E Davis. The highs and lows of faims: predictions andfuture trends for high field asymmetric waveform ion mobility spectrometry. Journal ofnanomedicine & nanotechnology, 3(5):109e, 2012.

[37] Gary Alan Eiceman and Zeev Karpas. Ion mobility spectrometry. CRC Press Boca Raton,FL, 1994.

37


[38] Edward A. Mason and Earl W. McDaniel. Transport properties of ions in gases. NASASTI/Recon Technical Report A, 89:15174, 1988.

[39] Ole N Jensen, Matthias Wilm, Andrej Shevchenko, and Matthias Mann. Sample preparationmethods for mass spectrometric peptide mapping directly from 2-de gels. In 2-D ProteomeAnalysis Protocols, pages 513–530. Springer, 1999.

[40] Martin F Jarrold. Peptides and proteins in the vapor phase. Annual review of physicalchemistry, 51(1):179–207, 2000.

[41] Joseph A Loo, Beniam Berhane, Catherine S Kaddis, Kerry M Wooding, Yongming Xie,Stanley L Kaufman, and Igor V Chernushevich. Electrospray ionization mass spectrometryand ion mobility analysis of the 20s proteasome complex. Journal of the American Societyfor Mass Spectrometry, 16(7):998–1008, 2005.

[42] Xiaoyun Liu, Stephen J Valentine, Manolo D Plasencia, Sarah Trimpin, Stephen Naylor,and David E Clemmer. Mapping the human plasma proteome by scx-lc-ims-ms. Journal ofthe American Society for Mass Spectrometry, 18(7):1249–1264, 2007.

[43] Arif Ahmed, Yun Ju Cho, Myoung-han No, Jaesuk Koh, Nicholas Tomczyk, Kevin Giles,Jong Shin Yoo, and Sunghwan Kim. Application of the mason- schamp equation andion mobility mass spectrometry to identify structurally related compounds in crude oil.Analytical chemistry, 83(1):77–83, 2010.

[44] David P Smith, Tom W Knapman, Iain Campuzano, Richard W Malham, Joshua T Berry-man, Sheena E Radforda, and Alison E Ashcrofta. Deciphering drift time measurementsfrom travelling wave ion mobility spectrometry-mass spectrometry studies. cell [Equation(1)], 12(13):13, 2009.

[45] Kevin Giles, Steven D Pringle, Kenneth R Worthington, David Little, Jason L Wildgoose,and Robert H Bateman. Applications of a travelling wave-based radio-frequency-onlystacked ring ion guide. Rapid Communications in Mass Spectrometry, 18(20):2401–2414, 2004.

[46] Tom W Knapman, Joshua T Berryman, Iain Campuzano, Sarah A Harris, and Alison EAshcroft. Considerations in experimental and theoretical collision cross-section measure-ments of small molecules using travelling wave ion mobility spectrometry-mass spectrom-etry. International Journal of Mass Spectrometry, 298(1):17–23, 2010.

[47] Francesco Lanucara, Stephen W Holman, Christopher J Gray, and Claire E Eyers. Thepower of ion mobility-mass spectrometry for structural characterization and the study ofconformational dynamics. Nature chemistry, 6(4):281–294, 2014.

[48] Tom W Knapman, Joshua T Berryman, Iain Campuzano, Sarah A Harris, and Alison EAshcroft. Considerations in experimental and theoretical collision cross-section measure-ments of small molecules using travelling wave ion mobility spectrometry-mass spectrom-etry. International Journal of Mass Spectrometry, 298(1):17–23, 2010.

38


[49] Charlotte A Scarff, Konstantinos Thalassinos, Gillian R Hilton, and James H Scrivens.Travelling wave ion mobility mass spectrometry studies of protein structure: biological sig-nificance and comparison with x-ray crystallography and nuclear magnetic resonance spec-troscopy measurements. Rapid Communications in Mass Spectrometry, 22(20):3297–3304,2008.

[50] Ewa Jurneczko and Perdita E Barran. How useful is ion mobility mass spectrometry forstructural biology? the relationship between protein crystal structures and their collisioncross sections in the gas phase. Analyst, 136(1):20–28, 2011.

[51] AA Shvartsburg and GA Eiceman RD Smith. Faims website www.faims.com, 2013.

[52] EV Krylov. Comparison of the planar and coaxial field asymmetrical waveform ion mobilityspectrometer (faims). International Journal of Mass Spectrometry, 225(1):39–51, 2003.

[53] Thermo Fisher Corporation. Thermo fisher faims tm operator’s manual. Revision A, pages70111–97134, 2006.

[54] Randy W Purves, David A Barnett, Barbara Ells, and Roger Guevremont. Elongated con-formers of charge states+ 11 to+ 15 of bovine ubiquitin studied using esi-faims-ms. Journalof the American Society for Mass Spectrometry, 12(8):894–901, 2001.

[55] Randy W Purves. Enhancement of biological mass spectrometry by using separationsbased on changes in ion mobility (faims and dms). Analytical and bioanalytical chemistry,405(1):35–42, 2013.

[56] MA Rush. Applications for a mems fabricated faims device. Int J Ion Mobil Spectrom, 10:15–17, 2007.

[57] Susan E Slade. Application of label-free mass spectrometry-based proteomics to biomarker dis-covery. PhD thesis, University of Warwick, 2013.

[58] Samar K. Guharay, Prabha Dwivedi, and Herbert H. Hill. Ion mobility spectrometry: Ionsource development and applications in physical and biological sciences. Plasma Science,IEEE Transactions on, 36(4):1458–1470, 2008.

[59] John B Fenn. Electrospray wings for molecular elephants (nobel lecture). AngewandteChemie International Edition, 42(33):3871–3894, 2003.

[60] University of bristol education material http://www.chm.bris.ac.uk/ms/newversion/esi-ionisation.htm.

[61] RFK Herzog and FP Viehböck. Ion source for mass spectrography. Physical Review, 76(6):855, 1949.

[62] Michael Karas and Franz Hillenkamp. Laser desorption ionization of proteins with molec-ular masses exceeding 10,000 daltons. Analytical chemistry, 60(20):2299–2301, 1988.

39


[63] Robert R Hudgins, Yi Mao, Mark A Ratner, and Martin F Jarrold. Conformations of glynh + and alan h + peptides in the gas phase. Biophysical journal, 76(3):1591–1597, 1999.

[64] Yi-Tsu Chan, Xiaopeng Li, Monica Soler, Jin-Liang Wang, Chrys Wesdemiotis, andGeorge R Newkome. Self-assembly and traveling wave ion mobility mass spectrometryanalysis of hexacadmium macrocycles. Journal of the American Chemical Society, 131(45):16395–16397, 2009.

[65] Cherokee S Hoaglund, Stephen J Valentine, C Ray Sporleder, James P Reilly, and David EClemmer. Three-dimensional ion mobility/tofms analysis of electrosprayed biomolecules.Analytical chemistry, 70(11):2236–2242, 1998.

[66] APIMS Preexisting. The differential mobility analyzer (dma). Ion Mobility Spectrometry-MassSpectrometry: Theory and Applications, page 105, 2011.

[67] J Anthony Semlyen and ER Semlyen. Cyclic polymers. Springer, 2001.

[68] Jessica N Hoskins and Scott M Grayson. Cyclic polyesters: synthetic approaches andpotential applications. Polymer Chemistry, 2(2):289–299, 2011.

[69] Bo Chen, Katherine Jerger, Jean MJ Fréchet, and Francis C Szoka Jr. The influence ofpolymer topology on pharmacokinetics: differences between cyclic and linear pegylatedpoly (acrylic acid) comb polymers. Journal of Controlled Release, 140(3):203–209, 2009.

[70] Jessica N Hoskins, Sarah Trimpin, and Scott M Grayson. Architectural differentiationof linear and cyclic polymeric isomers by ion mobility spectrometry-mass spectrometry.Macromolecules, 44(17):6915–6918, 2011.

[71] Yueyang Zhong, Suk-Joon Hyung, and Brandon T Ruotolo. Ion mobility–mass spectrometryfor structural proteomics. Expert Review of Proteomics, 9(1):47–58, 2012.

[72] Steffen MWeidner and Sarah Trimpin. Mass spectrometry of synthetic polymers. Analyticalchemistry, 82(12):4811–4829, 2010.

[73] Claire O’Donovan, Rolf Apweiler, and Amos Bairoch. The human proteomics initiative(hpi). Trends in biotechnology, 19(5):178–181, 2001.

[74] Catherine S Kaddis, Shirley H Lomeli, Sheng Yin, Beniam Berhane, Marcin I Apostol,Valerie A Kickhoefer, Leonard H Rome, and Joseph A Loo. Sizing large proteins andprotein complexes by electrospray ionization mass spectrometry and ion mobility. Journalof the American Society for Mass Spectrometry, 18(7):1206–1216, 2007.

[75] Ph Dugourd, RR Hudgins, DE Clemmer, and MF Jarrold. High-resolution ion mobilitymeasurements. Review of scientific instruments, 68(2):1122–1129, 1997.

40


[76] Till Gruendling, Michael Guilhaus, and Christopher Barner-Kowollik. Fast and accuratedetermination of absolute individual molecular weight distributions from mixtures of poly-mers via size exclusion chromatography- electrospray ionization mass spectrometry. Macro-molecules, 42(17):6366–6374, 2009.

[77] Stormy L Koeniger, Samuel I Merenbloom, and David E Clemmer. Evidence for many re-solvable structures within conformation types of electrosprayed ubiquitin ions. The Journalof Physical Chemistry B, 110(13):7017–7021, 2006.

[78] Rainer Bischoff. Recent developments in proteomics. Analytical and bioanalytical chemistry,376(3):289–291, 2003.

[79] Wenjun Mo and Barry L Karger. Analytical aspects of mass spectrometry and proteomics.Current opinion in chemical biology, 6(5):666–675, 2002.

[80] Amina S Woods, Michael Ugarov, Tom Egan, John Koomen, Kent J Gillig, Katrin Fuhrer,Marc Gonin, and J Albert Schultz. Lipid/peptide/nucleotide separation with maldi-ionmobility-tof ms. Analytical chemistry, 76(8):2187–2195, 2004.

[81] Brandon T Ruotolo, John A McLean, Kent J Gillig, and David H Russell. Peak capacityof ion mobility mass spectrometry: the utility of varying drift gas polarizability for theseparation of tryptic peptides. Journal of mass spectrometry, 39(4):361–367, 2004.

41

Comparison of Different Types of Ion Mobility Mass ...Comparison of Di erent Types of Ion Mobility...

Documents

Transcript of Comparison of Different Types of Ion Mobility Mass ...Comparison of Di erent Types of Ion Mobility...