Nitrogen-specific gas chromatographic detection by atomic plasma spectral emission. Analytical gas chromatography-mass spectrometry studies of subsurface biomarkers.

摘要

Analysis of nitrogen containing compounds by gas chromatography with atomic emission detection has always been problematic. Nitrogen detection has been customarily done using the 174.53 and 174.27 nm atomic lines, with very limited selectivity and sensitivity. Nitrogen can also be detected using the cyanogen (CN) molecular emission bands at 388 nm. It has been reported that a 100-fold improvement in the selectivity using this line can be reached. Therefore, in the present work, the instrument available in the laboratory was modified to allow the use of the 388 nm line for the nitrogen detection.;The modification of the instrument involved the use of a mixture of reagent gases that were optimized to produce the best nitrogen emission using the 388 nm line. Figures of merit of the detection using this line, were evaluated and compared with the commonly used nitrogen line (174 nm) and the carbon detection (193 nm).;The dependence of the GC-AED response with the molecular structure of the analyte, and its application in the determination of empirical formula was also evaluated, and its application for analysis of petroleum products.;The second part of the present work studied the biomarkers in deep subsurface samples and their relationship with the microbial activity.;Little is known of microbial community characteristics at depths larger than 50 m below surface, information that is crucial for the clean up of contaminated underground environments. The use of classical approaches to identify microbiota, often results in the characterization of less than 10% of the biota present when analyzing deep subsurface samples, therefore, the analysis of lipid content in the samples have been proposed. Microorganisms use lipids as constituent of their cell walls or as nutritional sources. Monitoring lipids can be used to develop a picture of how, when, where and under which conditions microbes are active in the subsurface.;This research was focussed in the biomarker study of a shale and sandstone from Cerro Negro, New Mexico. Biomarkers were determined to study distribution, concentration and availability of resources that support life and microbial activity and their relationship with geochemical parameters.