Retention index table

The HcReynolds abroach, which was based on earlier theoretical considerations proposed by Rohrschneider, is formulated on the assumption that intermolecular forces are additive and their Individual contributions to retention can be evaluated from differences between the retention index values for a series of test solutes measured on the liquid phase to be characterized and squalane at a fixed temperature of 120 C. The test solutes. Table 2.12, were selected to express dominant Intermolecular interactions. HcReynolds suggested that ten solutes were needed for this purpose. This included the original five test solutes proposed by Rohrschneider or higher molecular weight homologs of those test solutes to improve the accuracy of the retention index measurements. The number of test solutes required to adequately characterize the solvent properties of a stationary phase has remained controversial but in conventional practice the first five solutes in Table 2.12, identified by symbols x through s have been the most widely used [6). It was further assumed that for each type of intermolecular interaction, the interaction energy is proportional to a value a, b, c, d, or e, etc., characteristic of each test solute and proportional to its susceptibility for a particular interaction, and to a value x, X, Z, U, s, etc., characteristic of the capacity of the liquid phase... 

McReynolds used the retention index of certain solutes to compare different stationary phases and to assess their selectivity compared with a reference liquid phase, squalane. Squalane is considered to be non-polar and any increase in the retention index of the selected solute on the test column compared to squalane may be considered to be due to the greater polarity of that solvent. McReynolds constants have been determined for all stationary phases using a range of solutes of varying polarity (Table 3.8) and may be used to assist in selecting an appropriate stationary phase. 

The retention index of a compound obtained on a given stationary phase under given experimental conditions constitutes worthwhile information. However, if several indices of the same compound obtained on different stationary phases are available, better identification of this compound can be made. Because of the excellent reproducibility of retention times on modern chromatographs, this method is reliable for known control compounds. While obtaining retention indices does not constitute absolute identification of a compound, this method can be quite useful to identify unknowns if the proper retention indices tables are available on the most common stationary phases (Squalane, Apiezon, SE30, Carbowax 20M). However, the use of retention indices is now of lesser interest because of capillary columns that involve new stationary phases. This limits the information that can be obtained from the retention indices. Hyphenated techniques are currently more popular. They represent excellent methods for compound identification but depend on instruments that are more complex and more expensive. 

The retention index of 657 for benzene on poly(dimethylsiloxane) in Table 24-3 means that benzene is eluted between hexane (7 = 600) and heptane (7 = 700) from this nonpolar station-aiy phase. Nitropropane is eluted just after heptane on the same column. As we go down the table, the stationary phases become more polar. For (biscyanopropyl)09(cyanopropylphenyl)0l-polysiloxane at the bottom of the table, benzene is eluted after decane, and nitropropane is eluted after -Cl4H30. 

C. (a) In Table 24-3.2-pentanone has a retention index of 987 on a polyethylene glycol) column (also called Carbowax). Between which two straight-chain hydrocarbons is 2-pentanone eluted ... 

Table I. Identification of Unknown Mixture Using Both Molecular Weight and Retention Index...

Verification requires sniffing an authentic standard to verify that the component and the standard have the same retention index and odor quality. Table G 1.8.1 shows the result obtained when sniffing the sample used in Figure Gl.8.4. 

The McReynolds constants listed are differences in retention index units between die reference compound run on squalane and on die other phases listed. The last entry in the table shows die absolute retention indices for the reference compounds on squalane. Reference compounds are (1) benzene, (2) 1-butanol, (3) 2-pentanone, (4) 1 nitropropane, and (5) pyridine. (Note that Rohrschneider s constants are based on these reference compounds and may differ slightly from the McReynolds constants. The reference compounds for Rohrschneider s constants are (1) benzene, (2) ethanol, (3) 2-butanone, (4) nitromethane, and (5) pyridine.) The minimum temperature is that at which normal gas-liquid chromatography (GLC) behavior is expected. Below that temperature, die phase will be a solid or an extremely viscous gum. The maximum temperature is that above which die bleed rate will be excessive. 

Table n. Physical Properties, SFC Capacity Factors, and GLC Retention Indexes for the PAHs Studied... 

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.

To get the polarity constants for the other stationary phases, each solute in Table 13 was run on squalane and on the liquid phase of interest at 100°C and 20% liquid loading. The retention index I was determined for each analyte, and the difference between the two values on the two phases (A/) was obtained. The A/ summed for all five probes is given as... 

Both of these approaches used in the characterization of stationary liquid-phase polarities by means of retention indices have been further explored and expanded [104, 259-261]. For a review on the characterization of solvent properties of phases used in gas-liquid chromatography by means of the retention index system, see reference [344]. Similar methods for the characterization of solvent polarity in liquid-liquid and liquid-solid chromatography can be found in references [105-107] cf also Section A-7 and Tables A-10 and A-11 in the Appendix. 

The assignment of each alcohol residue, however, was checked by synthesis starting from the lactone of 2-hydroxyglutaric acid with a two step esterification. Table 1 shows a collection of our results concerning GC-0 evaluation together with retention index and mass spectral data. The sensory properties of compoimd 1 are described as weak, fatty, lactone-like. 

The irradiated membranes were then tested in a pilot plant with a plate-and-frame module with capacity for two membranes with an effective area of 90 cm each. Permselective results of irradiated membranes were compared to those of nonirradiated membranes [3]. It was observed that the performance of the samples irradiated with electronic or gamma radiation was very similar to that of the nonirradiated membranes. Tables 32.1 and 32.2 show the results of permeate flux and retention index for gamma- and electron-irradiated membranes, respectively. 

The introduction of GC as an analytical technique has had a profound impact on both qualitative and quantitative analysis of organic compounds. Identification of compounds by GC can be accomplished by their retention times on the column as compared to known reference standards, by inference from sample treatment prior to chromatography, " or by the concept of retention index. " The latter method and tables of retention indices " with associated conditions have been reported. " Although qualitative data and analytical techniques for identification of compounds are well-established " and relative retention data for over 600 substances also have been published, " the main utility of GC undoubtedly lies in its powerful combination of separation and quantitative capabilities. Use in quantitative analysis involves the implementation of two techniques being performed concurrently, i.e., separation of components and subsequent quantitative measurement. 

A neat reference mixture was prepared that contained 17 pure NHCs plus pyridine and quinoline as retention index markers (Table 1 Fig. 2). Relative amounts were adjusted to give approximately equal peak sizes. Triplicate analyses were performed on the 65 °C headspace above this mixture and above several wastewaters. To minimize any effect of column aging on peak retention times, the reference and wastewater replicates in each test series were alternated. Reproducibilities were excellent with standard deviations averaging 0.12 retention units overall and 0.05 retention units for the reference mixture. Reference-peak to sample-peak correlations were performed by a variety of statistical procedures including z tests. Student-t tests and, later, the procedure described in Section 3.2. 

Extensions of the definition of a retention index were done by choosing gradient temperature conditions [42] or methyl esters as standards instead of normal hydrocarbons. Tables for retention indexes of certain substances have been published [43]. However, the retention index system has limited utility for the GC analysis of pyrolysates due to the complexity of such samples. 

Every reagent in Table 1 is characterized, not only by its own retention index but also by retention index (RI) values of principal by-products of the reaction. This permits us to predict the possible overlapping of their chromatographic peaks with signals of derivatives of target compounds. 

Weckwerth solute descriptors (Table LI) are five solute parameters based on —> Kovats retention index on seven of GC stationary phases for 53 compounds [Weckwerth, Vitha et al, 2001]. 

These parameters must be quoted for a particular solvent, as the solvent as well as the intrinsic nature of the polymer will determine what interactions occur. Selected data on conducting polymer phases obtained using this series are shown in Table 1.6, where they are compared with a conventional hydrophobic material, carbon (C18 alkyl chains)-coated silica. The retention index obtained using toluene indicates that the conducting polymers are capable of nonpolar interactions. The high reten-... 

There are tables of retention indexes of compounds currently in general use on the most common stationary phases. If several retention indexes of the same compound obtained on different stationary phases are available, then this unique collection of values could then characterize the compound more precisely. Identification by retention index is not as reliable as using more popular hyphenated techniques as GC/MS (cf. Section 2.8.2), but it requires a not inconsiderable material investment. 

What would be the Kovats retention index for a compound that had a retention time of 5.3 minutes using the data in Table 20-4, p. 232 ... 

A summary of the retention indices of more than 80 alkyl nitrates has been reported. In general, the separation of the alkyl nitrates follows the order of boiling points in Table 19.8. The 1-n-alkyl nitrate is always the last member of each group to elute. Thus, it can be used as a window marker or retention index marker compound. The most abundant alkyl nitrates found in atmospheric samples are typically the secondary nitrates. For this reason, the 2-Cs and 2-Cio alkyl nitrates have also been suggested as marker compounds. ... 

Peak numbers correspond to those in Figures i and 2 and Table II. RI, retention index. Average relative conccniratiop t. standard deviation (n=I2). SDE, simultaneous steam distillation-solvent extraction. DE, direct solvent extraction. Compound tentatively identified by comparing its mass spectrum to Wiley 13SK mass spectral database, Compound not previously identified in saffron. Compound positively identified as described in materials and methods. V trace. Compound tentatively identified by comparing its mass spectrum with published literature (II). nd. not detected. I.S., internal standard, N/A, not available, peak could not be resolved. 

Not only variations in the pressure at constant temperature influence column-to-column retention data the role of the column hold-up volume as well as the mass of stationary phase present in the column is also important. The net retention volume caleulated from the adjusted retention volume corrects for the column hold-up volume (see Table 1.2). The specific retention volume corrects for the different amount of stationary phase present in individual colunms by referencing the net retention volume to unit mass of stationary phase. Further correction to a standard temperature of 0°C is discouraged [16-19]. Such calculations to a standard temperature significantly distort the actual relationship between the retention volumes measured at different temperatures. Specific retention volumes exhibit less variability between laboratories than other absolute measures of retention. They are not sufficiently accurate for solute identification purposes, however, owing to the accumulation of multiple experimental errors in their determination. Relative retention measurements, such as the retention index scale (section 2.4.4) are generally used for this purpose. The specific retention volume is commonly used in the determination of physicochemical properties by gas chromatography (see section 1.4.2). 

Rohrschneider s approach is able to predict retention index values for solute s with known solute constants (a, through e) [283,288]. These are determined from AI values for the solute on at least five phases of known phase constants and solving the series of linear equations. The retention index of the solute on any phase of known phase constants (X through S ) can then be calculated from Eq. (2.8). The theoretical defects of the method for assigning intermolecular interactions do not apply to the prediction of retention index values. A mean error of about 6 index units was indicated in some calculations. The retention or retention index values for thousands of compounds can be calculated from literature compilations of solute descriptors and the system constants summarized in Tables 2.6 and 2.8 using the solvation parameter model [103]. The field of structure-driven prediction of retention in gas chromatography is not well developed at present and new approaches will likely emerge in the future. 

As can be seen from Table 8-3, the calculated retention indices mostly correspond well with the values given in the literature. Discrepancies greater than 50 retention index units are rare. We could not confirm the literature value of the retention index for MDMA with our measurements. Every laboratory when validating methods for calculating retention indices should compare with results from the literature in order to be able to use retention indices from the literature to confirm its own measurement results. The choice and optimization of the sample preparation method is also part of the method validation of drug screening. This procedure has already been described in Chapter 7. 

A simple rule for predicting the possibility of GC analysis of organic compounds is based on the reference data on their boiling points. If any compound can be distilled without decomposition at pressures ranging from atmospheric to 0.01-0.1 Torr, it can be subjected to GC analysis at least on standard non-polar polydimethyl siloxane stationary phases. Thus, most of the monofunctional hydroxy compounds, as well as their S -analogues (thiols, thiophenols) can be analyzed directly. The confirmation of chromatographic properties of any analyte should not only be verbal (at the binary yes/no level) but also indicate its GC retention index (RI) as the most objective criteria, as illustrated in Table 1. 

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