Kovats Retention

Elution volume, exclusion chromatography Flow rate, column Gas/liquid volume ratio Inner column volume Interstitial (outer) volume Kovats retention indices Matrix volume Net retention volume Obstruction factor Packing uniformity factor Particle diameter Partition coefficient Partition ratio Peak asymmetry factor Peak resolution Plate height Plate number Porosity, column Pressure, column inlet Presure, column outlet Pressure drop... 

Kovats retention indices RI Mass transfer coefficient h... 

GC-EAD Gas chromatography combined with an EAG detector GC-MS Gas chromatography combined with mass spectrometry HPLC High performance liquid chromatography KI Kovats retention index... 

Jalali-Heravi, M., Fatemi, M. H. J. Chromatogr. A 915, 2001, 177-183. Artificial neural network modeling of Kovats retention indices for noncyclic and monocyclic terpenes. 

Equation 4.1 describes the Rohrschneider-McReynolds system in terms of the five probes and their corresponding phase constants namely, benzene (X ), butanol (Y ), 2-pentanone (Z ), nitropropane (U ), and pyridine (S ) with the overall difference in the Kovats retention index (AI). 

The aids to chromatography include a) resolution calculations on chromatograms of standard mixtures to monitor column performance, b) calculation of Kovats retention index for help in identifying peaks, and (c) multiple point calibration curves for improved quantitation. The file searching routines access two sets of data. Information (such as molecular formula, molecular weight) is stored on 3100 compounds from the Arctander data( ). This allows a quick computer search through the data which is difficult... 

Retention time Kovats retention indices a) R1 SE54 1029, b) RIsP2100 1020... 

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. 

The Kovats retention index, /, for a linear alkane equals 100 times the number of carbon atoms. For octane, / = 800 and for nonane, 1 = 900. A compound eluted between octane and nonane (Figure 23-7) has a retention index between 800 and 900 computed by the formula... 

The molecular weight and the Kovats retention index can then be combined to aid in the identification of the component. A linear relationship exists between the molecular weight and retention index for a homologous series of compounds. The relationship varies for each class of compound thus, a clue can be obtained regarding the type of compound present which can be verified by some other technique. 

Tx = retention time of a peak (x) to be indexed T = retention time of the paraffin that immediately precedes x T +i = retention time of the paraffin that immediately follows x RI = Kovats retention index of x... 

Pyrido[l,2-a]pyrimidin-4-one, its 6,7,8,9-tetrahydro derivatives, and their monomethylated derivatives were characterized by gas-chromatographic (GC) retention indices measured on apolar and medium-polar stationary phases (91MI4). Kovats retention indices of alkyl-substituted 4//-pyrido[ 1,2-a]pyrimidines-4-ones and some 6,7,8,9-tetrahydro... 

Spieksma, W., Luijk, R., Govers, H.A.J. (1994) Determination of the liquid vapour pressure of low-volatility compounds from the Kovats retention index. J. Chromatogr. A, 672, 141-148. 

Table II lists some furan and thiophene components substituted with sulfur at the three position on both heterocyclic rings generated in one reaction system. Also included are Kovats retention index data and references reporting the occurrence in foods or model systems.

Keesom forces, 43, 44 Kinetics of chromatography, 53 Kovats retention index, 78... 

Peak identification based on both experimental and published Kovats retention indices. Courtesy ofJasbir Chana, Phoenix Natural Products Ltd. 

A most important contribution to the above means of identification is the Kovats retention index system [28]. The Kovats retention index of a compound is 100 times the number of carbon atoms in a hypothetical n-alkane that would display in the given system the same retention as the compound in question. Hence, the retention index system essentially is also based on the regularities between the retention data and number of carbon atoms in homologous compounds. The concept of the Kovats retention index system is illustrated by the model in Fig. 3.7, which shows a plot of log A) values for homologous compounds of the type CH3(CH2) X and for n-alkanes against carbon number. It is apparent that the retention index of, e.g., C2H5X is 560, i.e., 7(C2HSX) = 200 +... 

Fig. 3.7. Schematic representation of the concept of Kovats retention indices.

De Beer et al. [501] reported an extensive comparative study of the chromatographic behaviour of methyl esters and pentafluorobenzyl esters of these substances. They correlated retention data (Kovats retention indices) on nine stationary phases with the structure of the derivatives and with the polarity of the stationary phases with the aim of utilizing these dependences for identification purposes. However, much more significant is the better separation obtained with pentafluorobenzyl esters and the possibility of increasing the sensitivity of the analysis. 

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