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| Author(s): |
Jose Geraldo Alves Brito Neto
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2002-10-29 |
| Examining board members: |
Claudimir Lucio do Lago;
Roy Edward Bruns;
Manoel Tiago Freitas da Cruz;
Marcos Nogueira Eberlin;
Jose Manuel Riveros Nigra
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| Advisor: | Claudimir Lucio do Lago |
| Abstract | |
Several articles can be found in the literature describing methods forthe determination of isotopic ratios through the various modalities ofmass spectrometry. However, almost all of them have a commonrestriction on the type of molecular ion that can be employed in thesedeterminations: they must be either elemental ions, or polyatomic ionswhose sole polyisotopic element is the one being analysed. This isusually achieved through the destruction of the molecules, or throughcomplex synthetic procedures. In this work, a mathematical methodcapable of deconvolving the isotopomeric pattern of a molecular ion,i.e., calculating the isotopic pattern of its constituent atoms givenits formula and its mass spectrum, has been developed. The maincontribution of such a method to the field is the broadening of therange of acceptable chemical species for isotopic analyses. Thedeveloped algorithm was characterized by applying it to a large numberof simulated spectra with the objective of modelling its response tosome experimental imperfections common to mass spectrometry andrelevant for isotopic analyses, such as noise, instrumental massdiscrimination, detection non-linearity, lack of resolution and badbaseline compensation. The results allowed us to conclude that, inspite of whatever commonsense might suggest, isotopic analysescarried out through the polyatomic approaches can, in many cases, bemore exact and precise than those performed through conventionalapproaches. It could also be concluded that, in general, the largerthe number of instances of the element of interest in the formula ofthe chosen ion, the better the results become. Also as part of theproject, the viability of employing polyols as probes for thehydrogen/deuterium ratio in aquous samples in equilibration methodsand electrospray mass spectrometry has been studied. The studiedpolyols were: manitol, gluconic acid, glucosamine and N-metilglucamine(through its complex with boric acid). The obtained results showedsome systematic errors that suggest that there might be a partialexchange of non-labile hydrogen atoms during the electrosprayphenomenon. Alternative probes are proposed. (AU) | |