Carbon preference indices

Previous studies on heavy hydrocarbon content of young sediments showed that they contained all the n-paraffin series, but that those containing paraffins with odd numbers of carbon atoms were several times as abundant as those containing even numbers of carbon atoms. Bray and Evans (7) defined a ratio of odd to even paraffins as a carbon preference index (CPI). In Recent sediments (mostly from nearshore environments) the CPI varied from 2.5 to 5.5. Crude oils and extracts from ancient shales exhibited little odd-carbon preference. The CPI for ancient shales varied from 0.9 to 2.3 and that for crude oils from 0.6 to 2.2... 

At this point it should be remarked that multivariate regression with latent variables is a useful tool for describing the relationship between complex processes and/or features in the environment. A specific example is the prediction of the relationship between the hydrocarbon profile in samples of airborne particulate matter and other variables, e.g. extractable organic material, carbon preference index of the n-alkane homologous series, and particularly mutagenicity. The predictive power was between 68% and 81% [ARMANINO et al., 1993]. VONG [1993] describes a similar example in which the method of PLS regression was used to compare rainwater data with different emission source profiles. 

The carbon preference index (CPI) (1) for fatty acids in the coal samples examined has been calculated see Table VI). The CPI is a... 

Table VI. Carbon Preference Index (CPI) for Monofatty Acids Sample Free Bound Total...

Carbon Preference Index (32). This index, devised by Bray and Evans to be used as a maturity index decreases as the sediment increases maturation to a limit of one. Carvalhaes C28) showed that an Irati sample submitted to a maximum of 509C in its thermal history, presented a CPI of 1.58 indicating it to be a reasonably mature sediment. Nooner Oro (29) gave the values of 1.05 for this Formation. 

The carbon preference index (CPI) is a numerical means of representing the odd-over-even predominance in -alkanes in a particular carbon-number range. It is often used as a maturity measurement where... 

Marzi R.,TorkelsonB.E., Olson R.K. (1993) A revised carbon preference index. Org. Geochem. 20,1303—6. 

Figure 5. Three-dimensional diagram showing the distribution of selected aromatic hydrocarbons in samples from the North Atlantic OCS areas. I, Biphenyl 2, C2-naphthalenes 3, Cs-naphthalenes 4, Crphe-nanthrenenes 5, fluoranthene 6, pyrene 7, C20H12 CPI, Carbon Preference Index (n-C20 to n-CS1) Pr., pristane Ph., phytane.

Table 2. Variation in pristane to phytane (PrfPhJ. prisiane to n-Cn and n-C[j and the carbon preference index (CPI) in Smorbukk. Maturity and phase fractionation are the main factors responsible for the variation...

G.C.-M.S, analysis. The n-alkane distribution is distinctive, with a marked preference of odd over even carbon number (carbon preference index, 1.9, as in low-rank coals) in the range above C25 but with a smooth, nearly Gaussian, distribution for the lower range (peaked at Cie or C17) also, the pristane/phytane ratio is high (U.5), as in sediments of marine origin. 

Analysis results of n-alkanes, fatty acids, PAH. Also given are CPI (Carbon Preference Index) of alkanes, the ratios C17/C31 (indicating short-chain to long-chain alkanes), and (indicating short-chain to long-chain fatty acids). Included are phenantrene to anthracene ratios (PHN/ANT) and of fluoranthene to pyrene (FLO/PYR) with the selected compounds retene and perylene added in separate columns. 

The identification of the homologous n-alkanes in the aliphatic hydrocarbon fractions for most leachates allowed the determination of the carbon preference index (CPI, ratio no. 1), which provides supportive evidence for the relative incorporation of different aliphatic hydrocarbon sources. 

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