No / This article reports on the use of comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–TOFMS) for forensic geotaphonomy application. Gravesoil samples were collected at various depths and analyzed for their volatile organic compound (VOC) profile. A data processing procedure was developed to highlight potential candidate marker molecules related to the decomposition process that could be isolated from the soil matrix. Some 20 specific compounds were specifically found in the soil sample taken below the carcass and 34 other compounds were found at all depths of the gravesoil samples. The group of the 20 compounds consisted of ketones, nitriles, sulfurs, heterocyclic compounds, and benzene derivatives like aldehydes, alcohols, ketones, ethers and nitriles. The group of the 34 compounds consisted of methyl-branched alkane isomers including methyl-, dimethyl-, trimethyl-, tetramethyl-, and heptamethyl-isomers ranging from C12 to C16. A trend in the relative presence of these alkanes over the various layers of soils was observed, with an increase in the amount of the specific alkanes when coming from the carcass to the surface. Based on the specific presence of these methyl-branched alkanes in gravesoils, we created a processing method that applies a specific script to search raw data for characteristic mass spectral features related to recognizable mass fragmentation pattern. Such screening of soil samples for cadaveric decomposition signature was successfully applied on two gravesoil sites and clearly differentiates soils at proximity of buried decaying pig carcasses from control soils.

Orientador: Fabio Augusto / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-19T18:08:24Z (GMT). No. of bitstreams: 1 Marques_SandraReginaRivellino_D.pdf: 2317302 bytes, checksum: fe68941a7328088e8aaba96b46928a24 (MD5) Previous issue date: 2011 / Resumo: A técnica de microextração em fase sólida através do headspace (HS-SPME) combinada com a cromatografia gasosa bidimensional abrangente e detecção por ionização em chama (GCxGCxFID) foi empregada para detectar artefatos formados durante o preparo da amostra de méis, que poderiam ser prejudiciais ao processo de identificação de sua origem floral. O método foi otimizado utilizando-se planejamento multivariado. Para isso, uma mistura de diferentes tipos de méis brasileiros foi usada como modelo. Os artefatos de extração identificados foram classificados como resultantes da manipulação através do HS. A influência da temperatura e do tempo de exposição ao tratamento térmico também foi avaliada. A identificação da fração volátil da mistura de mel foi realizada por GCxGCxFID e cromatografia gasosa acoplada à espectrometria de massas com analisador quadrupolar (GC-QMS) comparando-se o índice de retenção linear com programação de temperatura obtido na primeira dimensão (D-LTPRI), calculado a partir dos cromatogramas obtidos por GCxGCxFID, e os índices obtidos por GC-QMS para as mesmas amostras. Esta identificação foi confirmada por cromatografia gasosa bidimensional abrangente combinada a um espectrômetro de massas por tempo de vôo (GCxGCxTOFMS). Portanto, a identificação e detecção de artefatos de extração previamente desconhecidos é atribuída às vantagens da GCxGC. A GCxGCxFID combinada com ferramentas quimiométricas foi empregada para classificar algumas amostras de méis de diferentes origens do Piauí-Brasil. A GCxGCxQMS foi empregada para identificação dos voláteis de algumas destas amostras. A combinação de HS-SPME - (GCxGC ou GC) com o poder de identificação do detector MS, juntamente com índices de retenção e de métodos quimiométricos forneceram informações valiosas sobre a classificação química dos méis / Abstract: Solid phase microextraction through headspace (HS-SPME) was otimizated by a multivariate design. This technique combined with comprehensive two-dimensional gas chromatography with flame ionization detection (GCxGC-FID) was employed to detect potential artifacts formed during preparation of honey samples, that could possibly be relevant to the identification of its floral origin. A mixture of different types of brazilian honeys was used as the model sample. The extraction artifacts identified were classified as resulting from HS manipulation. The influence of temperature and time exposure of the thermal treatment was also evaluated. The identification of the volatile fraction of the honey blend was performed through combination of GCxGC-FID and GC coupled to quadrupole mass spectrometry (GC-QMS) by comparing the one dimensional linear temperature programmed retention index (D-LTPRI) calculated from GCxGCxFID chromatograms to that of chromatograms of the same samples obtained on GC-QMS. This identification was confirmed by GCxGC combined with a time-of-flight mass analyzer (GCxGC-TOFMS). Therefore, the identification and detection of previously unknown extraction artifacts is attributed to advantages of GCxGC. GCxGCxFID in combination with chemometric tools was employed to classify some honey samples from different origins from Piauí-Brazil. GCxGCxQMS was employed for the identification of the volatiles from some one of these samples. The combination of HS-SPME - (GCxGC or GC) and the qualitative information of MS, retention index and chemometric methods may be able to provide valuable information on the chemical classification of honeys / Doutorado / Quimica Analitica / Doutor em Ciências

A novel chromatographic method was devised that makes use of the superb group separation power of normal phase supercritical fluid chromatography (SFC) combined with a fast second separation by a resistively heated gas chromatograph (GC). The SFC was operated isothermally with stopped flow to provide the time required for the GC analysis. The GC analysis had a typical cycle time of 1 minute. During this time the GC column was independently heated at a rate of 450°C/min to 250°C and actively cooled down again to -50°C before the next GC injection takes place. This was achieved with an in-house designed, resistively heated, temperature programmable gas chromatograph. Various temperature measurement circuits were also evaluated. An interface was developed that allows transfer between the SFC and the GC in such a way that the entire eluent from the first separation is analysed by the second separator. Chromatographic resolution was not lost during the transfer process from the first to the second separation stages. The interface also allows for the exchange of the carrier gas used in the second gas chromatographic separation to provide for the maximum separation speed. In the first separation, a silica gel packed column and the novel application of a silica gel porous layer open tubular capillary column was used for SFC group separation. The SFCxGCftp was applied to petrochemical samples and essential oils and the results were compared to that obtained with a commercially available GCxGC system. / Thesis (PhD)--University of Pretoria, 2003. / Chemistry / unrestricted