Equivalent carbon number

TAGs are abbreviated as Tx where x is relative to the Equivalent Carbon Number (ECN) that corresponds to the number of carbon atoms of all the acyl moieties of the TAG. 

Another approach is to consider petroleum constituents in terms of transportable materials, the character of which is determined by several chemical and physical properties (i.e., solubility, vapor pressure, and propensity to bind with soil and organic particles). These properties are the basis of measures of teachability and volatility of individual hydrocarbons. Thus, petroleum transport fractions can be considered by equivalent carbon number to be grouped into 13 different fractions. The analytical fractions are then set to match these transport... 

An important feature of the analytical methods for the total petroleum hydrocarbons is the use of an equivalent carbon number index (EC). This index represents equivalent boiling points for hydrocarbons and is the physical characteristic that is the basis for separating petroleum (and other) components in chemical analysis. 

Two methods can be used to obtain the equivalent carbon number nx of compound X ... 

Figure 2.15—Graphical measurement of Kovats index (/ = lOO/jj) on a column in the isothermal mode.The equivalent carbon number nx is obtained using the logarithm of the corrected retention time tLX). When using a temperature program, a linear relationship can be obtained using a corrected formula. However, this is achieved with a lower precision.

The first problem in the HPLC analysis of TGs is the identification of the individual TGs. Planner et al. (90) observed that under isocratic conditions the logarithm of the elution volume of a triacylglycerol is directly proportional to the total number of carbon atoms (CN) and inversely proportional to the total number of double bonds (X) in the three fatty acyl chains. This elution behavior is controlled by the equivalent carbon number (ECN) of a triacylglycerol, which may be defined as... 

Critical pairs have been defined as those structures with an equivalent carbon number (ECN). This includes critical pairs that contain one or more critical acyl groups on the glycerol,... 

Triglycerides in vegetable oils are separated according to their equivalent carbon number by reversed-phase liquid chromatography and detected by differential refractometry. Quantitation is by area normalization. Elution order is determined by calculating the equivalent carbon numbers, ECNs, often defined (as we said before) as CN — 2n, where CN is the carbon number and n is the number of double bonds. To calculate ECNs more accurately, the origin of the double bond is taken into account ... 

Ruiz-Sala et al. (129) described a reversed-phase HPLC method with a light-scattering detector for the analysis of TGs in milk fat. The identification of TGs was carried out by a combination of HPLC and gas-liquid chromatography (GLC), and was based on the equivalent carbon numbers and retention times of different standard TGs. Finally, quantitation of peak areas from HPLC chromatograms was carried out after applying a deconvolution program to the parts of chromatograms with poor resolution. 

They studied the effect of the mass detectors drift tube temperature on the low-molecular-mass TGs. Solutions of 10 mg/ml of tributyrin, tricaproin, tricaprylin, tricaprin, and trilaurin were injected twice at each of the following drift tube temperatures 20,25, 30,45, and 60°C. Five replications of the HPLC analysis were performed for one sample of ewe s milk fat to determine the reproducibility of the HPLC method. The TG composition was estimated in accordance with the method based on the calculation of the equivalent carbon numbers (ECNs) of the HPLC chromatographic peaks and in the molar composition in fatty acids, analyzed by GLC, collected at the HPLC chromatograph outlet. The HPLC fractions were collected every 40 s at the outlet of the column after 14 min there were no peaks before that time. 

Fig. 7 Correlation between the logarithm of the retention time of the 3,5-dinitrobenzoyl derivatives of PG molecular species expressed in min (log RT) and the corrected equivalent carbon number ECN. (Reprinted from Ref. 89 with the permission of the American Oil Chemists Society.)...

Absolute Difference Between Found and Theoretical Equivalent Carbon Number (ECN) 42 (Trilinolein) Values. The triglyceride composition of the oil is determined by high-performance liquid chromatography (HPLC) (74). (A chromatogram of an olive oil sample (ECN 42, 0.8%) is shown in Figure 10.) The theoretical triglyceride composition is calculated with a Lotus 123 program provided by the lOOC. The maximum difference of theoretical ECN 42 vs. ECN 42 found is calculated. (ECN = CN-2u, where CN is the carbon number and n is the number of double bonds.) The maximum difference between the real and theoretical ECN content... 

For purposes of this section, the chemical-specific parameters for the petroleum hydrocarbon fractions are based on selecting a midpoint for the fraction, based on empirical data unified by equivalent carbon number (EC). The fractions labeled as C5-C7 and >C7-C8 are characterized by one compound only, benzene and toluene, respectively. Remaining fractions are characterized by multiple compounds, as described in TPHCWG (1997b). Representative physical parameters for TPH fractions are presented in Table 5-7. 

Noncarcinogenic Effects. These effects are assessed only if the carcinogenic indicator compounds are not detected or are below regulatory criteria. The following petroleum hydrocarbon fractions, minus the carcinogenic indicator compounds, were selected as representing compounds with similar transport properties. Toxicity values for constituents of the fraction or for a similar mixture were selected to represent the toxicity of the fraction. Aromatic and aliphatic hydrocarbons are considered separately and further subdivided on the basis of equivalent carbon number index (EC). This index is equivalent to the retention time of the compounds on a boiling point GC column (non-polar capillary column), normalized to the //-alkanes. Physical and chemical properties of hydrocarbons that are... 

EC = Equivalent Carbon Number Index MRL = minimal risk level... 

C = carbon number EC = Equivalent Carbon Number Index MRL = minimal risk level NA = not applicable WOE = weight-of-evidence classification for carcinogenicity... 

C = carbon number EC = Equivalent Carbon Number Index MRL = minimal risk level NA = not applicable NV = not verifiable the health effects data for this compound were reviewed by the EPA RfD/RfC Work Group and determined to be inadequate for the derivation of an RfC (EPA 1998b) WOE = weight-of-evidence classification for carcinogenicity... 

Equivalent Carbon Number Index—an index based on the boiling point of a chemical normalized to the boiling point of n-alkanes or its retention time in a boiling point gas chromatographic column (GC). 

---