Development of a Novel Mass Spectrometric ... - Jacobs University
Development of a Novel Mass Spectrometric ... - Jacobs University Development of a Novel Mass Spectrometric ... - Jacobs University
Introduction an ionisation technique of choice for the analysis of medium to less polar, small and thermally relative stable analytes. It is a form of CI which takes place at atmospheric pressure. APCI was first introduced by Horning in 1973 for the analysis of volatile compounds. 43 However APCI wasn’t spread until the commercialisation of ESI after Fenn’s work in 1985. 98 Contrary to ESI, APCI has the capability to vaporise higher boiling point analytes which resist volatilisation. Figure 1-5 Schematic description of the atmospheric pressure chemical ionisation (APCI) interface and the mechanism of ion formation in the corona discharge region Ionisation inside APCI is separated from solvent evaporation. After the mobile phase is introduced into a pneumatic nebuliser, it is heated to high temperatures (400-450 °C) inside a heated quartz tube and sprayed with high flow of nebulizer gas (nitrogen gas). Ionisation occurs in gas phase, in contrast to ESI, by subjecting the vaporised neutral analytes and reagent gas molecules (N 2 , H 2 O, O 2 ) to corona discharge needle that creates the ions. It is emphasized that the corona discharge needle is used as an electron source to ionise gas phase molecules such as molecules of N 2 (commonly used as sheath gas) and molecules of the solvent (commonly used methanol/water) forming radical cation in positive ion-mode. These ions collide with the neutral analytes resulting in the creation of ions. The high frequency of collisions results in high ionisation efficiency and thermalisation of the analyte ions. These ions enter pumping and focusing stages within mass 21
Introduction spectrometry in as much as with other ionisation techniques like ESI. The APCI techniques generally produce pseudo-molecular ions depending on many factors such as the chemical properties of the analytes, the polarity of electrospray voltage, the nature of the matrix and the solvent composition. It is not always easy to predict whether positive or negative ions will be preferentially produced. Overall protonation of the analyte is usually observed in positive-mode APCI. Other molecular ions and fragments like (M-H) + can also be formed. 76,99 Research efforts have focused to control ion generation in APCI by selecting a convenient sheath gas or a proper solvent. Many types of ions are still produced for each analyte. This phenomenon can complicate the analysis of complex mixtures. This happens when solvent molecules engage in the generation of the radical cations that collide with the neutral analytes ions. Ionisation upon APCI with no liquid reagent can be most likely attributed to N 2 molecular ions N +• +• 2 . N 2 ions are thought to be responsible for production of molecular ions by electron abstraction. The A significant advantage of APCI is the ability to introduce nonpolar solvent instead of polar solvents and to handle higher flow rate in the range of 1ml/min commonly applied in high performance liquid chromatography (HPLC). This allows the analysis of nonpolar species which otherwise can’t be analysed under ESI conditions. APCI is known to be a less ‘soft’ ionisation technique than ESI by causing fragmentation compared to ESI ionisation. A schematic description of an APCI-interface and the mechanism of APCI is given in Figure 1-5. 1.3.9 Petroleomics Global energy challenges have impelled chemical analysis towards better understanding of petroleum composition. The chemical composition of crude oil is so complex in terms of the number of chemically distinct constituents in an abundance range 10 000-100 000. Petroleum distillates are complex mixture of aliphatic, naphthenic and polaromatic hydrocarbons including various heteroatom (e.g. N, O) hydrocarbons. Olefins are found in the cracked petroleum streams. 41 22
- Page 1 and 2: Development of a Novel Mass Spectro
- Page 3 and 4: Declaration of Authorship I ,Nadim
- Page 5 and 6: This work has been carried out unde
- Page 7 and 8: Contents Contents Declaration of Au
- Page 9 and 10: List of Figures List of Figures Fig
- Page 11 and 12: List of Figures Figure 3-39 MS 2 fr
- Page 13 and 14: List of Tables List of Tables Table
- Page 15 and 16: Abbreviations Abbreviations APCI AP
- Page 17 and 18: Abbreviations UV VGOs VOCs VRs ultr
- Page 19 and 20: Introduction Analytical chemistry h
- Page 21 and 22: Introduction 1.2 Presence and Fate
- Page 23 and 24: Introduction aliphatic hydrocarbons
- Page 25 and 26: Introduction Figure 1-1 Examples of
- Page 27 and 28: Introduction Figure 1-2 Range of io
- Page 29 and 30: Introduction fractions. 42 Another
- Page 31 and 32: Introduction 1.3.5 APLI Other crude
- Page 33 and 34: Introduction products). Other molec
- Page 35 and 36: Introduction Other studies performe
- Page 37: Introduction APLI-FT ICR-MS Crude o
- Page 41 and 42: Introduction catalytic processing t
- Page 43 and 44: Introduction Figure 1-6 Kendrick ma
- Page 45 and 46: Introduction including determinatio
- Page 47 and 48: Introduction 1.5 Scope and Signific
- Page 49 and 50: Experimental e) Other model mixture
- Page 51 and 52: Experimental 2.2.2 Preparation of O
- Page 53 and 54: Experimental 2.4 Graphical Presenta
- Page 55 and 56: Results and Discussion experiment.
- Page 57 and 58: Results and Discussion Intens. [%]
- Page 59 and 60: Results and Discussion common featu
- Page 61 and 62: Results and Discussion 3.2 APCI-TOF
- Page 63 and 64: Results and Discussion These compou
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- Page 67 and 68: Results and Discussion Ions were pr
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- Page 71 and 72: Results and Discussion procedure ba
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- Page 75 and 76: Results and Discussion to produce m
- Page 77 and 78: Results and Discussion 519.5863 519
- Page 79 and 80: Results and Discussion Higher mass
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Introduction<br />
spectrometry in as much as with other ionisation techniques like ESI. The APCI<br />
techniques generally produce pseudo-molecular ions depending on many factors<br />
such as the chemical properties <strong>of</strong> the analytes, the polarity <strong>of</strong> electrospray voltage,<br />
the nature <strong>of</strong> the matrix and the solvent composition. It is not always easy to<br />
predict whether positive or negative ions will be preferentially produced. Overall<br />
protonation <strong>of</strong> the analyte is usually observed in positive-mode APCI. Other<br />
molecular ions and fragments like (M-H) + can also be formed. 76,99<br />
Research efforts have focused to control ion generation in APCI by selecting a<br />
convenient sheath gas or a proper solvent. Many types <strong>of</strong> ions are still produced for<br />
each analyte. This phenomenon can complicate the analysis <strong>of</strong> complex mixtures.<br />
This happens when solvent molecules engage in the generation <strong>of</strong> the radical<br />
cations that collide with the neutral analytes ions.<br />
Ionisation upon APCI with no liquid reagent can be most likely attributed to N 2<br />
molecular ions N +• +•<br />
2 . N 2 ions are thought to be responsible for production <strong>of</strong><br />
molecular ions by electron abstraction. The A significant advantage <strong>of</strong> APCI is<br />
the ability to introduce nonpolar solvent instead <strong>of</strong> polar solvents and to handle<br />
higher flow rate in the range <strong>of</strong> 1ml/min commonly applied in high performance<br />
liquid chromatography (HPLC). This allows the analysis <strong>of</strong> nonpolar species<br />
which otherwise can’t be analysed under ESI conditions. APCI is known to be a<br />
less ‘s<strong>of</strong>t’ ionisation technique than ESI by causing fragmentation compared to ESI<br />
ionisation. A schematic description <strong>of</strong> an APCI-interface and the mechanism <strong>of</strong><br />
APCI is given in Figure 1-5.<br />
1.3.9 Petroleomics<br />
Global energy challenges have impelled chemical analysis towards better<br />
understanding <strong>of</strong> petroleum composition. The chemical composition <strong>of</strong> crude oil is<br />
so complex in terms <strong>of</strong> the number <strong>of</strong> chemically distinct constituents in an<br />
abundance range 10 000-100 000. Petroleum distillates are complex mixture <strong>of</strong><br />
aliphatic, naphthenic and polaromatic hydrocarbons including various heteroatom<br />
(e.g. N, O) hydrocarbons. Olefins are found in the cracked petroleum streams. 41<br />
22
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