Equivalent carbon number index

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. 

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). 

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 MADEP (1997) has published a draft report for public comment regarding implementation of their approach. This report references the TPHCWG (1997a, 1997b, 1997c) approach (below), particularly in defining fractions with regard to transport properties, which are related to the equivalent (or relative) carbon number indexes for the compounds. 

Without changing the tuning of the instrument, a compound X is now injected onto the column. The new chromatogram obtained allows the calculation of the Kovats retention index of X on the specific column used. This index is obtained by multiplying the equivalent alkane carbon number that has the same retention time as X by 100. 

Figure 2.22 Graphical measurement of Kovats retention index (/= lOOn ) on a column in the isothermal mode. The number of equivalent carbons n, is found from the logarithm of the adjusted retention time t of X. The chromatogram corresponds to the injection of a mixture of 4 n-alkanes and two aromatic hydrocarbons. The values in italics match the retention times given in seconds. By injecting periodically this mixture the modifications to the Kovats indexes of these hydrocarbons permits the following of the column s performance. The calculations for retention indexes imply that the measurements were effected under isothermal conditions. With temperature programming they yield good results to the condition to adopt an adjusted formula, though this entails a reduction in precision.

In order to get some insight on how ELF works, we will analyse a number of parent molecules CeHsX (X = H, OH, F, Cl, Br and I). Their localization domains are displayed in Figure 14. Except for the substituent itself, all these molecules have 6 V(C, C), 5 V(C, H) and one V(C, X) basins. The differences are to be found in the hierarchy of the V(C, C) basins which is ruled by the nature of the substituent. In benzene, all the V(C, C) basins are equivalent and therefore the six critical points of index 1 between these basins have the same value, i.e. rj(rc) = 0.659. In the phenyl halides where the molecular symmetry is lowered from D h to C2v, the former critical points are then distributed in four sets according to the common carbon position ipso, ortho, meta and para. In phenol with a Cj symmetry, the two ortho and the two meta positions are not totally equivalent. In all studied molecules, the r) rc) values are enhanced in the ipso, ortho and para positions and decreased in the meta position. It has been remarked that the electrophilic substitution sites correspond to the carbon for which r) rc) is enhanced. Moreover, it is worthwhile to introduce electrophilic substitution positional indices defined by equation 26,... 

SAMPLE SOLUTION (a) The molecular formula CiqHis contains four fewer hydrogens than the alkane having the same number of carbon atoms (Q qH22)-Therefore, the index of hydrogen deficiency of this compound is 2. Since it consumes two molar equivalents of hydrogen on catalytic hydrogenation, it must have two double bonds and no rings. 

A compound (X) is now injected onto the column without changing the tuning of the instrument. The resulting chromatogram will enable 4, the Kovats retention index, to be calculated for X and the specific column employed this is equal to 100 times the equivalent number of carbon atoms of the theoretical alkane having the same adjusted retention time than X. Two methods can be used to find... 

Isotopically labelled compounds. In this index, deuterium and tritium are given as D and T respectively and treated as heteroatoms for the purpose of indexing. Carbon-13 compounds are listed as though they contained carbon-12 and oxygen-17 and oxygen-18 compounds treated as though they contained the equivalent number of oxygen-16 atoms. 

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