G. Alexander

Method for preparing glass capillary columns for gas chromatography

Abstract A method is given to prepare glass capillary columns with almost any stationary phase. The method is based on etching the soda-lime glass capillary tubing by dry gaseous hydrochloric acid. Coating the columns by the static method resultsin high-performance apolar and polar columns. The polar columns can be used even for the analysis of highly polar solutes. Studying the etched surface of soda-lime glass, the presence of a uniform layer of microcrystalline NaCl was found.

Surface chracteristics of treated glasses for the preparation of glass capillary columns in gas-liquid chromatography

The wettabilit of borosilicate and soda-lime soft glasss was studied by measuring critical surface tensions (CST) of the glasses and taking scanning electron micrographs (SEM) before and after various treatments: etching with hydrogen chloride gas, silanization, impregnation with surface-active agents, and combinations of these. Considerable increase in CST values ws found after the etching of the soda-lime glass, and this effect could be explained by a geometrical model of the surface. The CST values, togetther with the surface tensions of a serires of gas chromatographic stationary phases, can help in the preparation of glass capillary columns, as ws illustrated by SEM micrographs of coated internal surfaces of capillary columns.

Occurrence and transformation of phyllocladanes in brown coals from Nograd Basin, Hungary

Abstract Phyllodactanes are the major components of the lipid extracts of two series of brown coals from the Nograd Basin (Northern Hungary). In this basin coalification was induced by thermal stress of volcanic origin which determined the isomeric composition of these compounds. Depending on the degree of maturation the 16α(H)-isomer decreases in abundance relative to the more geochemically stable 16β(H)-isomer, the presumed equilibrium ratio being 0.3. Laboratory thermal degradation experiments have confirmed the feasibility of this transformation, showing that phyllocladene and isophyllocladene are intermediate products of the process. Variable amounts of retene and simonellite are also found, but no evidence is obtained of abietane-type precursors. Nevertheless, a close relationship of the retene-phyllocladane ratio with maturity, represented by the H C ratio, is observed. As an explanation, it is suggested the thermally induced formation of retene from phyllocladanes, simonellite being an intermediate of the proposed reaction. Further evidence for this hypothesis has been obtained from laboratory simulation experiments. Finally, the presumed isomerization and aromatization rates of these diterpenoids have been compared for the series of samples, pointing to a promising tool for assessing the geochemical history of coal basins.

Investigation of hydrocarbon constituents of a young sub-bituminous coal by gas chromatography-mass spectrometry

Abstract Hydrocarbon fractions were obtained from a coal extract by open-column chromatographic methods. Compounds amenable to gas chromatography were investigated by computerized gas chromatography-mass spectrometry. Several aliphatic and hydroaromatic biomarkers were observed. Monoaromatic compounds not previously reported in the literature were also detected. They are believed to be intermediates of diagenetic aromatization reactions. The retention indices for several pentacyclic hydroaromatic hydrocarbons are reported.

Study of aromatic biomarkers in brown coal extracts

Abstract Gas Chromatographic mass spectrometric (g.c.-m.s.) analysis or aromatic hydrocarbon fractions of 10 brown coal samples has shown the predominance of pentacyclic compounds. Some tetracyclic compounds were also detected. They appeared to be diagenetically related to triterpenoids naturally occurring in the biosphere. Diagenetic aromatization of triterpenoids having a six-membered E ring mainly follow a pathway in which dehydrogenation proceeds from ring A to E. A set of reactions involving C ring cleavage is also an omnipresent process. Aromatization including an A ring cleavage played a minor role.

Predominance of even carbon-numbered n-alkanes in coal seam samples of Nograd Basin (Hungary)

n-Alkanes are ubiquitous in sedimentary samples, often exhibiting distributions with odd carbon-number predominances which are lost during the maturation of the organic matter [1]. Distributions with even carbonnumber preferences are also found although less frequently, n-Alkane profiles with slight even carbon-number predominances in the C2a-C3o range have been associated with highly saline, carbonate environments where bacterial activity has developed on the remains of algal communities [2]. On the other hand, n-alkane distributions maximizing at Ca6 or C18 have been found in anoxic marine environments or areas where a postdepositional reduction of algal fatty acids was suggested to occur [3]. However, very recently we found, for the first time, such distributions in surface sediments of a well-oxygenated estuarine system (Shatt-al-Arab, Iraq), thus pointing to an autochthonous, possibly bacterial, source [4]. These distributions occurred in sediments underlying fresh (river), brackish (estuary) and marine (open sea) waters. Then, another paper was published [5] concerning the lipid composition of sediments taken in the Gulf of Mexico, giving additional support to the bacterial source hypothesis. In the present paper the occurrence of striking predominance of even carbonnumbered n-alkanes in the C~4-C2o range is extended to some coal samples from seams of Nograd Basin (northern Hungary), representing, to the best of our knowledge, the oldest geologic samples (lower Miocene) in which this type of distribution has been described. Brown coal series in the Nograd Basin (Nograd region, northern Hungary) were formed during the lower Miocene in a paralic (coastal swamp) environment. Three coal seams of this basin were selected for this study: Szorospatak (Sz), Menkes (Ms) and Kanyas (Ks). There, two layers have been classified according to the depositional conditions (see Table 1) [6], layer I (1.5-2.4 m thick) corresponding to peat formation under marine water and layer II (1.2-2.5 m thick) corresponding to brackish water sedimentation. According to the Van Krevelen classification, the elemental composition of these coals correspond to type III kerogens (terrestrial) having undergone a variable degree of diagenesis. In fact, volcanism in the southern part of the basin accelerated the coalification process in mines Sz and Ms. In this sense, coals from mine Ms reflect the highest degree of thermal maturation (lowest O/C ratios). On the other hand, mine Ks in the north was not affected. The maceral composition is dominated by huminites with no major quantitative difference among the three seams [7]. The vitrinite reflectance ranges between 0.39 and 0.65%. The lowest values cluster near 0.41+_0.02% and correspond to Ks, the seam not affected by volcanism, whereas the highest values (0.62_+ 0.02%) correspond to Ms reflecting the coal rank increase by volcanic heating [8]. The thermal effect was moderate but enough for many samples to pass the boundary between brown and hard coals (Ro=0.50%, [1]). n-Alkane distributions having strong C14-C22 even carbon-number and C23-C35 odd carbon-number predominances occurred in coals, rocky coals and adjacent sediments of Ks and Sz seams. In contrast to this, unimodal distributions with no carbon-number preference below n-C22 and low oddto-even carbon-number predominance between n-C23 and n-C35 were found in Ms. In Fig. I several of these profiles are shown. The corresponding carbon preference indices (CPI) for all samples as well as the relative abundances of the two n-alkane ranges are listed in Table 1. The n-alkane profiles depicted in Fig. I show a variety of even n-alkane distributions. In some samples nC16 predominates (SD), but in general n-Cls is the most abundant homolog (KH, SC, SM, SK). These profiles constitute representative examples of the whole set of samples and generally do not parallel the well-known and rather constant distribution of sedimentary fatty acids in marine environments [9]. Therefore, the hypothesis of the reductive process previously mentioned appears unlikely in the present case. Alternatively, direct biogenic contributions are suggested for the occurrence of these n-alkane profiles with even carbon-number predominance. Several examples show that bacterial production of n-alkane distributions in the C~4-C22 range with strong maxima of one or two n-paraffins is relatively common [10-13]. Furthermore, fungi [14] and yeast [12] have also been reported to biosynthesize such n-alkanes. This is especially relevant for the present coal seam samples because of the recognized importance of these microorganisms in peat formation [15]. On these grounds, instead of reductive processes, particular environmental conditions or substrate variations, leading to preferential growth of different populations of these microorganisms may account for such even n-alkane occurrences with even carbon-number predominance. An interesting feature observed in the composition of the less matured samples (Ks) is the inverse relationship be-

Identification of aliphatic biological markers in brown coals

Abstract Ten coal samples were subjected to solvent extraction and aliphatic hydrocarbon fractions were obtained by open column chromatography. The fractions were analysed by gas chromatography-mass spectrometry : nalkanes, di- and triterpenoid hydrocarbons and (in lesser amounts) sterenes were found. The distribution of the biological markers found indicated the low rank of the samples, but contradictions in the composition of hopanoids were observed. Some compounds not previously reported in the literature were also present.

Chromatographic Fingerprinting of coal extracts

Abstract Seven Hungarian coal samples of different ranks were examined by solvent extraction, liquid chromatographic (LC) separation of the extracts and analysis of the aliphatic and aromatic hydrocarbon LC fractions by high-resolution gas chromatography. The LC fraction distribution is characteristic of the coal. The gas chromatograms of the two hydrocarbon LC fractions show strong similarities for related samples and can server as “fingerprints” of the coals. For the n-alkanes, parameters such as “carbon preference index” can be calculated. For other aliphatic and aromatic hydrocarbons, respectively, the retention and “PAH indices” are presented.

Investigation of a hydrothermally treated brown coal by i.r. and Chromatographic methods

Abstract I.r. spectra of a brown coal (Merseburg, GDR) and two hydrothermally treated samples, and their solvent extracts, were studied. Difference spectra showed a significant increase in the aliphatic absorptions, a decrease in hydroxy groups and changes in the carbonyl, carboxylate and carbonate group contents as a consequence of the treatment. Eight fractions of each extract separated by column chromatography were also investigated, the hydrocarbon fractions by gas chromatography and the other fractions by i.r. spectroscopy. The non-uniform distribution of n -alkanes in the original sample became uniform after the treatment.

Occurrence and transformation of tricyclic aromatic hydrocarbons in low rank coals

Abstract Aromatic components of extracts obtained from four low rank coal samples were investigated by gas chromatography-mass spectrometry. A number of compounds were observed for the first time. The tricyclic aromatic hydrocarbons were investigated in detail. They show close similarities in structure to those reported to be formed in laboratory dehydrogenation experiments. The co-occurrence of molecules in the same samples containing additional unsaturation as well as the aromatic ring(s), offers strong support for the hypothesis of progressive aromatization of diterpenoids. A hypothetical diagenetic pathway is proposed to explain the generation of many of the compounds present. In the pathway the following reactions were considered: aromatization (i.e. dehydrogenation), elimination of substituents, methyl shift, isomerization and side chain shortening of fully aromatized species.