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 alkene compounds under investigation. 43 On contrast the alkane derivatives like 5- α-cholestane, squalane and hentriacontane studied under the same conditions produced different product ions accompanied with notorious fragmentation. In addition to that changing APCI reagent to MeOH/H 2 O, only few of the tested analytes were detected where fragmentation was observed for most of them. It was clear that this study facilitated to a certain extent the analysis of petroleum cuts through understanding the behaviour of model compounds structurally similar to those in petroleum. Although the above reported APCI methodology has established a stable corresponding ion for few hydrocarbon analytes, it failed to achieve a successful ionisation of saturated aliphatic hydrocarbons. In fact another similar study performed by the group of Kenttamaa didn’t even yield any detectable ions for saturated cyclic hydrocarbon 5-α-cholestane under different APCI conditions. 96 1.3.7 Summary In summary to this part, nonpolar hydrocarbons that form 90% of the petroleum composition were examined by different mass spectrometries coupled to different ionisation technologies mostly assisted by various chemical modification processes. EI and CI are not ideal for high MW hydrocarbon analysis because they produce extensive fragmentation. 28 In the analysis of complex mixture, fragmentation is deleterious, because the production of more than one signal per analyte complicates an already crowded mass spectrum and thus makes it difficult to identify parent ion. On the other hand ESI was found capable of ionising only polar hydrocarbons. Further studies employing DESI, MALDI, APPI and APLI were found rather selective for certain types of nonpolar hydrocarbons. Using FD and FI suffers from low ionisation efficiency, varied response factors of hydrocarbons of different types of MW (affecting quantification) and fragmentation of molecular ions due to heating of analytes. 28 17
Introduction Other studies performed using APCI have attributed hydrocarbon ionisation to the chemistry of this methodology. 2 For example, failure to control ion generation in APCI restricts the production of lone intact gas phase hydrocarbon ions in mass spectrometry. Tuning APCI conditions can to some extent control gas phase reactions. However, certain analytes still produce significant abundant ions or fragments which can consequently complicate a real life sample containing thousands of hydrocarbons. 43 Specifically, failure to produce intact, high mass alkane gas phase ions has been preventing mass spectrometric analysis of saturated hydrocarbons as well limiting its application towards petroleum industry. Furthermore all studies carried out using APCI-MS focused on model system and pure reference compounds rather than achieving any analysis of n-alkanes within real life samples of complex mixtures. It is well demonstrated that the aforementioned studies have lacked a “universal” soft ionisation method that simultaneously can ionise both saturate (i.e. paraffins, cyclic paraffins) and aromatic petroleum molecules (alkylated benzenes, alkylated polynuclear aromatics, alkylated thiophenoaromatics, etc). A summary of most significant studies performed for model or complex hydrocarbon mixtures is given in Table 1. As understood from the above reporting, an ideal mass spectrometric method capable of desorping intact hydrocarbons into the gas phase and ionising all hydrocarbon analytes, including saturated and unsaturated analytes, to yield intact molecular or pseudomolecular ions that are representative of neutral hydrocarbon molecular weight (MW) without fragmentation and while avoiding any derivatisation or adduct chemistry would be an intriguing novel approach. Such approach should accordingly infer product ions can be subjected to controlled fragmentation using tandem MS. Acquisition of qualitative and quantitative data from complex hydrocarbon mixture can be then greatly facilitated as ionisation of all components becomes uniform. In other words the first step in characterization of organics in petroleum is to define the molecular mass distribution and proceed with elemental composition assignment from efficiently accurate mass 18
- 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: Introduction products). Other molec
- Page 37 and 38: Introduction APLI-FT ICR-MS Crude o
- Page 39 and 40: Introduction spectrometry in as muc
- 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
- Page 65 and 66: Results and Discussion Intens. [%]
- Page 67 and 68: Results and Discussion Ions were pr
- Page 69 and 70: Results and Discussion Intens. [%]
- Page 71 and 72: Results and Discussion procedure ba
- Page 73 and 74: Results and Discussion Intens. [%]
- 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 />
alkene compounds under investigation. 43 On contrast the alkane derivatives like 5-<br />
α-cholestane, squalane and hentriacontane studied under the same conditions<br />
produced different product ions accompanied with notorious fragmentation. In<br />
addition to that changing APCI reagent to MeOH/H 2 O, only few <strong>of</strong> the tested<br />
analytes were detected where fragmentation was observed for most <strong>of</strong> them. It was<br />
clear that this study facilitated to a certain extent the analysis <strong>of</strong> petroleum cuts<br />
through understanding the behaviour <strong>of</strong> model compounds structurally similar to<br />
those in petroleum.<br />
Although the above reported APCI methodology has established a stable<br />
corresponding ion for few hydrocarbon analytes, it failed to achieve a successful<br />
ionisation <strong>of</strong> saturated aliphatic hydrocarbons. In fact another similar study<br />
performed by the group <strong>of</strong> Kenttamaa didn’t even yield any detectable ions for<br />
saturated cyclic hydrocarbon 5-α-cholestane under different APCI conditions. 96<br />
1.3.7 Summary<br />
In summary to this part, nonpolar hydrocarbons that form 90% <strong>of</strong> the petroleum<br />
composition were examined by different mass spectrometries coupled to different<br />
ionisation technologies mostly assisted by various chemical modification<br />
processes.<br />
EI and CI are not ideal for high MW hydrocarbon analysis because they produce<br />
extensive fragmentation. 28 In the analysis <strong>of</strong> complex mixture, fragmentation is<br />
deleterious, because the production <strong>of</strong> more than one signal per analyte<br />
complicates an already crowded mass spectrum and thus makes it difficult to<br />
identify parent ion. On the other hand ESI was found capable <strong>of</strong> ionising only<br />
polar hydrocarbons. Further studies employing DESI, MALDI, APPI and APLI<br />
were found rather selective for certain types <strong>of</strong> nonpolar hydrocarbons. Using FD<br />
and FI suffers from low ionisation efficiency, varied response factors <strong>of</strong><br />
hydrocarbons <strong>of</strong> different types <strong>of</strong> MW (affecting quantification) and<br />
fragmentation <strong>of</strong> molecular ions due to heating <strong>of</strong> analytes. 28<br />
17
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