N-Alkane extract

Figure 3. Comparison of n-alkane extract distribution for Wyodak subbituminous coal, O, and n-alkane distribution from CPU bottoms recycle product, (Wyodak subbituminous coal).

Pristane percentages increase with rank lignite contained small or non-detectable amounts. There was no apparent correlation between wt % n-alkanes extracted and rank. The distribution maximum chain... 

Nepeta (Lamiaceae) is a genus of perennial or annual herbs found in Asia, Europe and North Africa. About 250 species of Nepeta are reported of which, 67 species are present in Iran. Some species of this genus are important medicinal plants and their extracts have been used for medicinal purposes. Aerial parts of Nepeta sintenisii Bornm. was subjected to hydrodistillation and the chemical composition of isolated essential oil has been analyzed by GC/MS method for first time. Identification of components of the volatile oil was based on retention indices relative to n-alkanes and computer matching with the Wiley275.L library, as well as by comparison of the fragmentation patterns of the mass spectra with those reported in the literature. 

GC-C-IRMS instrumentation enables the compound-specific isotope analysis of individual organic compounds, for example, n-alkanes, fatty acids, sterols and amino acids, extracted and purified from bulk organic materials. The principle caveat of compound-specific work is the requirement for chemical modification, or derivatisation, of compounds containing polar functional groups primarily to enhance their volatility prior to introduction to the GC-C-IRMS instrument. Figure 14.7 summarises the most commonly employed procedures for derivatisation of polar, nonvolatile compounds for compound-specific stable isotope analysis using GC-C-IRMS. 

The identification of all chemicals within the extracts were unknown, therefore accurate quantifications were not performed for all chemicals. As a preliminary investigation, approximate amounts were calculated using the following method. A 1 (tL injection of 100 ng pL-1 solution of n-alkanes (C7-25) in hexane was analysed by GC on an HP1 column. The approximate amounts of chemicals within the extract were calculated using the following equation ... 

Yang et al. [2] have compared sorbent trapping with solvent trapping after the supercritical fluid extraction of volatile petroleum hydrocarbons in soil. Sorbent trapping yielded quantitative collections of n-alkanes as volatile as n-hexane, while solvent trapping effectively collected w-alkanes as volatile as n-octane. 

Figure G1.3.1 Determination of the retention index (Rl) of an unknown compound C in an aroma extract (A) by comparing with a series on n-alkanes (B) analyzed under the same GC-conditions. 

The method of analysis involves extraction of 1 L of aqueous sample (liquid-liquid extraction) or 25 g of soil (sonication or Soxhlett extraction or supercritical fluid extraction) or an appropriate amount of the sample with methylene chloride. The extract is dried, concentrated to a volume of 1 mL, and injected into a capillary GC column for separation and detection by FID. For quantitation, the area or height response of all peaks eluting between C-10 and C-28 are summed and compared against the chromatographic response of the same peaks in a 2 Fuel or Diesel Oil standard. A 10-component n-alkanes mixture containing even numbered alkanes ranging between 10 and 28 C atoms has been recommended as an alternative calibration standard. These alkanes occur in all types of diesel oils, and each compound constitutes approximately a 1% total mass of diesel fuel, i.e., 1 g of diesel fuel contains about 10 mg each of any of the above alkanes. Therefore, when using the latter as a calibration standard, the result must be multiplied appropriately by 100. 

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 distribution of n-alkanes, isoprenoids and other branched hydrocarbons in the saturated/unsaturated hydrocarbons fraction of the modem microbial mat ranges mostly between C14 and C21, in extracts and pyrolysates (Figure 5A and 6C). It is similar to the distribution of the hydrocarbons described in the "top mat" of the Gavish sabkha in Israel (17). The main differences are the presence, in the extract of... 

The Paleosoil of Mangrove. The GC trace of the saturated/unsaturated hydrocarbons of the extract from the buried soil of mangrove is dominated by odd n-alkanes probably derived from cuticular waxes (Figure 6A). The "intermediate" fraction of the same extract is poor in sulfur compounds (Figure 6B) only a C29 sterane thiol previously identified in the Rozel Point oil (18). and by a C30 n-alkylthiophene. The former compound might be related to the C29 sterene dominantly present in the saturated/unsaturated fraction (Figure 6A). 

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 n-alkanes are an interesting homologous series because they display great regularity in their behavior. Many of their fluid phase properties, for example, can be correlated with the number of carbon atoms in the molecules ( 1, 2 ). In order to develop general relations for supercritical extraction, therefore, we have stud.ied the solubilities of solid n-alkanes containing 28 to 33 carbon atoms in supercritical ethane. 

As shown in Fig. 9.1.2, the phenolic fraction of a bleach plant E, effluent contains not only chlorinated phenols but also fatty acids and their esters, and even n-alkanes. The latter two classes of compounds probably are carry-over extractives from the wood during pulping or, in part, originate from defoaming agents added to the pulping liquor. 

Results from Irradiation in n-Alkane Solutions To obtain useful kinetic information based upon the detailed mechanism outlined in Scheme 13.5 is a daunting task. By simplifying it, useful kinetic data can be extracted from irradiations of (R)-3b in polymer films. Before doing so, information obtained in isotropic media, -alkanes of differing viscosities, will be analyzed. ... 

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