Pristane/phytane

Of particnlar significance in the study of petroleum weathering are the biomarker molecules (e.g., pristane, phytane, the hopanes and steranes). Historically, the biomarkers have been employed as crude oil signatures in prospecting and characterization. More recently, such molecules have also been employed in the environmental field, both for the determination of pollutant source and estimation of the degree of weathering. 

The degradation of sulfur heterocycles in Prudhoe Bay crude oil by aerobic enrichment cultures of marine and soil microorganisms was studies by Fedorak and Westlake (22,22). Figure 4 shows typical results obtained when the aromatic fraction of the oil was analyzed by capillary GC with a sulfur-specific detector. The mixed microbial populations in these enrichments were able to degrade the n-alkanes, pristane, phytane and a number of polycyclic aromatics in this oil (21, 22). There were some similarities between the biodegradability of the sulfur heterocycles in Figure 4 and that of the aromatic hydrocarbons reported by Fedorak and Westlake (21,22). For example, although cultures without N and P addition were able to remove a number of the sulfur heterocycles from the oil, the addition... 

A number of selected molecular parameters obtained from analysis of immature crude oils and sediment extracts are evaluated as indicators of palaeosalinity. The nature of these parameters is discussed taking into account the role of intermolecular and intramolecular incorporation of sulfur into specific functionalized lipids. Specific distribution patterns of methylated chromans and C20 isoprenoid thiophenes and the relative abundance of gammacerane are excellent indicators for palaeosalinity, whilst other parameters such as 14< (H),17a(H)/140(H),170(H) -sterane ratios, the pristane/phytane ratio, the even-over-odd carbon number predominance of n-alkanes and the relative abundance of C35 hopanes and/or hopenes may indicate palaeohypersalinity but are affected by environmental factors other than hypersalinity and by diagenesis. 

The importance of these depositional environments makes it desirable that studies concerned with the reconstruction of palaeoenvironments from sediments or source rocks of oils also establish molecular parameters for palaeohypersalinity. Recently, ten Haven et al. (7-9) have summarized a number of "organic geochemical phenomena" related to hypersaline depositional environments. In addition to previously known parameters, such as an even-over-odd carbon number predominance of n-alkanes and a low pristane/ phytane ratio (<0.5), several new parameters were suggested. These parameters, however, are mainly based on empirical relations. 

A more critical evaluation of the above mentioned ratios and phenomena reveals the usefulness of the various palaeosalinity indicators. Distribution patterns of methylated chromans and the relative abundance of gammacerane are not influenced by sulfur incorporation reactions and may directly reflect species distributions in the palaeoenvironment. To some extent this holds for 14a(H),17a(H)/140(H),170(H)-steraneratios as well, although incorporation of sulfur may influence this ratio and original A7/A5-sterol ratios do not always correlate with hypersaline environments. The isoprenoid thiophene ratio is highly useful as a palaeosalinity indicator since the distribution of the C20 isoprenoid thiophenes directly reflects the distribution of their substrates. The other parameters (pristane/phytane ratio, odd-over-even carbon number predominance of n-alkanes, relative abundance of C35 hopanes and/or hopenes) should be used with caution because they obviously depend on the quenching by sulfur of specific lipids, a process which is not restricted to hypersaline environments. 

Gas chromatograms of three saturated hydrocarbon fractions, roughly representing the different facies (Figure 2), show that some relative and absolute variations exist between the three facies. n-Alkanes, pristane, phytane and the extended hop-17(21)-enes are indicated. The most prominent changes within different compound classes in the saturated hydrocarbon fraction are highlighted below. 

The pristane/phytane ratio (Figure 3d) also shows a trend which is apparently influenced by the three facies types. This ratio is thought to reflect changes in anoxicity and/or salinity (30-32). 

Figure 10. Variation of 63AS with Pristane/Phytane. There are only data for three Miocene reservoirs, because the oils in other Miocene reservoirs are highly degraded, therefore pristane and phytane are absent.

Liquid hydrocarbons derived from coal have a composition that is somewhat distinctive, and that distinguishes them from oils derived from algal-dominated type I and II source rocks. For example, petroleum derived from coal tends to have high pristane/phytane ratios a ratio >4 is... 

The basic fish oil (27) also included a generous amount of saturated fatty acids. As can be seen from Figure 5 and Table 1, the saturated fatty acids are dominated by the 16 0 (palmitic acid), usually accompanied by about half as much or less of 14 0 (myristic acid) and much less of 18 0 (stearic acid). Usually the saturated fatty acid totals are at least 20%, especially as the odd chain (15 0, 17 0) and methyl-branched (iso, anteiso, pristanic, phytanic) fatty acids (compare Figure 4) are sam-rated and will total around 2-3%. An unsaturated peak that is often observed is 17 ln-8, which is roughly equal to 17 0. The details of these peaks are discussed in other publications, but those researchers attempting modern open-tubular gas chromatography analyses should be aware of their presence and influence on peak identification and quantitation. As can be seen from Figure 6, there is an... 

D.W. Johnson, M.-U. Trinh, T. Oe, Measurement of plasma pristanic, phytanic and very long chain fatty acids by LC-ESI-MS-MS for the diagnosis of peroxisomal disorders, J. Chromatogr. B, 798 (2003) 159. 

Pristane/Phytane Index. The data obtained for the stratigra-phic column CERI-1 (33) say that the ratio pristane/phytane varies froml.l (at the topof thelst layer) to 2.0 (2m below the previous point). It keeps approximately constant at 1.5 for therest of the col umn. Carvalhaes (23) found the value 1.94 for a sample of the same formation. In all samples so far analysed from the Irati F. the ratio is greater than one. 

Bitumens, were separated by chromatography, urea clathration and 5A molecular sieve occlusion before and after analyses of many of the aliphatic sub-fractions by GC and gas chromatography-mass spectrometry (GC-MS). Experimental details are noted in a previous publication (16) in which the distribution of cyclic alkanes in two lacustrine deposits of Devonian (N.E. Scotland) and Permian (Autun, France) age, (the D and C series samples) were discussed, Chromatographic separation into aliphatic, aromatic and polar compounds of the bitumens extracted from the shales gave the results shown in Table VI. Carbon Preference Indices and pristane/phytane ratios were measured in this work space limitations precluded... 

Most of the alphatic fractions were separated into normal and branched alkane fractions after the removal of unsaturated hydrocarbon. Most of these subfractions were analysed by GO to give fingerprint chromatograms. These analyses were used to provide data that allowed carbon preference indices, pristane/phytane ratios etc. to be measured. Also, the relative amounts of (17 H, 21/ H 17/3 H, 21 oCH and 17 H, 21(3 H) hopanes, steranes, 4-methyl steranes, carotenoid and other related compounds were assessed from gas chromatograms and reconstructed ion chromatograms. A large number of Kovats Retention Indices (0V-101) were measured and tabulated for these compounds also (10). 

Al-Dirbashi, O.Y. et al., Rapid UPLC-MS/MS method for routine analysis of plasma pristanic, phytanic, and very long chain fatty acid markers of peroxisomal disorders, J. Lipid Res., 49(8), 1855, 2008. 

The ratio of the isoprenoids pristane (Ci9) and phytane (C2o). When these compounds are resolved from the normal C17 and Cig peaks with which they are closely associated in the chromatogram, their ratio (if near one) is diagnostic for petroleum, or (if pristane > > phytane) for biogenic sources. Pristane is common in plankton (cope-pods) and various marine animals phytane has only rarely been reported except as a component of petroleum (30). 

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