INDEX temperature-programed

Van Den Dool, H. and P.D. Kratz (1963), Generalization of the retention index system including linear temperature programmed gas-liquid partition chromatography . J. Chromatogr, Vol. 11, p. 463. 

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 results of the evaluation showed the RIs to vary only slightly with the different operator, the different instrument of the same manufacturer with the same column in one or several laboratories, column individuals of the same manufacturer, solvents (diethyl ether, acetone, and ethyl acetate), and use of a multistep temperature program. There were no significant differences in the reproducibility of RIs determined using different index standard series. M-standards are relatively nonpolar and differ little in their behavior from C-standards on a nonpolar SE-54 phase. When the number of index standard components was reduced, the RI values... 

Hale MD, Hileman FD, Mazer T, Shell TL, Noble RW, Brooks JJ (1985), Anal. Chem. 57 640-648.. .Mathematical modeling of temperature programmed capillary gas chromatographic retention indexes for polychlorinated dibenzofurans"... 

The hydrothermal deactivation of Y zeolite containing 0, 4, 7 and 12 wt.% of REO and its effects on catalytic activity, stability and selectivity were investigated. The Y zeolites were hydrothermally deactivated at 788°C in three consecutive cycles of two hours each. The fresh and deactivated zeolites were characterized by measuring Unit Cell Size (UCS) and surface area. The acidic properties were measured by the Temperature Programmed Desorption (TPD) of ammonia and IR-pyridine desorption. In order to correlate structural, textural and acid properties with catalytic behavior, the zeolites were evaluated in the conversion of cyclohexane. The Hydrogen Transfer Index (HTI) measured as a ratio of paraffins to olefins is a parameter of the selectivity. It was found that the REO was incorporated into zeolite structure up to high concentrations modifying to some extent XRD deflection, the acidic properties and the HTI ratio. After deactivation, the acidity and HTI were diminished and the Lewis/Bronsted acid ratio was modified. HTI decreased as REO concentration increased. 

Retention index There are two types of retention index, namely the isothermal retention and the hnear temperature programming index. Both indices express the retention characteristics of a chemical compound analysed by GC to the retention of the homologous series of normal ahphatic hydrocarbons analysed under identical conditions. Under both retention index systems, a chemical compound is bracketed by two ahphatic hydrocarbons that are assigned a retention index value corresponding to the number of carbon atoms in the hydrocarbon molecule multiphed by 100. The isothermal retention index, RL, is defined as a logarithmic interpolation between two successive ahphatic hydrocarbons eluted just prior to and just after the compound A under the isothermal GC conditions, and is calculated for compoxmd A as follows ... 

The retention time of the non-retained hydrocarbon methane is represented as tcH4. Similarly, the temperature programming index, Rip is experimentally determined by equation (23) ... 

There are many books and other sources that discuss the retention index from theoretical and practical aspects. One comprehensive book is "The Sadtler Standard Gas Chromatography Retention Index Library" [15]. This series of book (from Volume 1 to Volvune 4) provides detailed data on the retention indices for more than 2,000 compoimds under varying isothermal and temperature programming GC conditions for the purpose of the general identification of unknown compoimds. 

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.

The Kovats retention index [137], using n-alkanes as a series, is most commonly used for both internal and external data comparisons. With certain precautions in mind, this retention system is usable for temperature-programmed runs. Within the field of biological investigations, fatty acid esters [133] and steroidal hydrocarbons [134] were also used to standardize the retention data within a compound class. However, the use of the so-called methylene units [135] is basically identical with the Kov its system. 

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