Evaluation of a pulsed glow discharge time-of-flight mass spectrometer as a detector for gas chromatography and the influence of the glow discharge source parameters on the information volume in chemical speciation analysis

The figures of merit of a pulsed glow discharge time-of-flight mass spectrometer (GD-TOFMS) as a detector for gas chromatography (GC) analysis were evaluated. The mass resolution for the GD-TOFMS was determined on FWHM in the high mass range (208Pb+) as high as 5,500. Precision of 400 subsequent analyses was calculated on 63Cu+ to be better than 1% RSD with no significant drift over the time of the analysis. Isotope precision based on the 63Cu+/65Cu+ ratio over 400 analyses was 1.5% RSD. The limits of detection for gaseous analytes (toluene in methanol as solvent) were determined to be as low as several hundred ppb or several hundred pg absolute without using any pre-concentration technique. Furthermore, the different GD source parameters like capillary distance, cathode-anode spacing, and GD source pressure with regards to the accessible elemental, structural, and molecular information were evaluated. It was demonstrated that each of these parameters has severe influence on the ratio of elemental, structural, and parent molecular information in chemical speciation analysi

Evaluation of a pulsed glow discharge time-of-flight mass spectrometer as a detector for gas chromatography and the influence of the glow discharge source parameters on the information volume in chemical speciation analysis

ISSN:1618-2650ISSN:1618-264

Mineral-templated growth of natural graphite films

International audienceOrganic material in sediments is progressively altered during diagenesis and metamorphism, leading to the formation of kerogen and ultimately crystalline graphite. Bulk carbonaceous material in metamorphic terrains typically has attained an overall degree of structural order that is in line with peak metamorphic temperature. On a micron- to nano-scale, however, carbonaceous material can display strong structural variation. The main factor that drives this variation is the chemical and molecular heterogeneity of the precursor biologic material. Specific conditions during metamorphism, however, can also play a role in shaping the microstructure of carbonaceous material. Here we describe the structural variation of carbonaceous material in rocks of the 2.0 Ga Zaonega Formation, Karelia, Russia. Raman spectroscopy indicates that bulk carbonaceous matter in these rocks has experienced peak temperatures between 350 and 400 °C consistent with greenschist-facies metamorphism. On a nano-scale, however, a strong structural heterogeneity is observed. Transmission electron microscopy (TEM) reveals the occurrence of thin films of highly ordered graphitic carbon at mineral surfaces. These graphite films - consisting of 20-100 individual layers - completely envelop quartz crystals and occur on specific crystal surfaces of chlorite. It is proposed that minerals can act as templates for the parallel ordering of carbon crystallites causing enhanced graphitization within narrow zones at mineral surfaces. Alternatively, oriented organic precursor molecules could have been adsorbed onto charged mineral surfaces, leading to thin graphitic films during later metamorphic heating episodes. Overall the presented observations demonstrate that mineral surfaces can initiate and accelerate localized graphitization of sedimentary organic material during metamorphism, and therefore cause distinct nano-scale variation in structural order