McReynolds Constants Research Articles

Preparation and gas chromatographic characterisation of 3-bromo-4-(4-methylbenzyloxy)azobenzene stationary phase

The synthesis of 3-bromo-4-(4-methylbenzyloxy)azobenzene (BMBOA) and its use as a stationary phase in packed columns are described. Chromatographic characteristics such as column efficiency, polarity (McReynolds constants) and operating temperature range were studied. Retention factors, specific retention volumes and activity coefficients for alcohols, esters, ketones, aromatic hydrocarbons andn-alkanes were determined. Phenols and 2,3, and 4-chlorobenzyl chlorides were separated on the new phase. Based on experimental data some assumptions were made on the possible types of intermolecular forces between solute and solvent.

Preparation of 4-vinylpyridine and divinylbenzene porous-layer open tubular columns by in situ copolymerization

A new type of polar porous polymer glass capillary column, named OPPLOT-S, was prepared by in situ copolymerization of 4-vinylpyridine and divinylbenzene. Its chemical composition was found to be similar to that of Porapak S. The OPPLOT-S columns performed very efficiently in analysing alcohols, hydrocarbons, nitriles, amines, polar and apolar mixtures and permanent gases. They can provide good separations of NH 3H 2O, CH 3OHH 2O and COCH 4CO 2 in a relatively short time under general conditions. The polarities of capillary columns were evaluated by using the Rohrshneider and McReynolds constants.

Characterization of some silica-based reversed-phase liquid chromatographic columns based on linear salvation energy relationships

The characterization of six silica-based reversed-phase liquid chromatographic columns was attempted by calculating characteristic interaction constants for the stationary phases based on linear solvation energy relationships. Four interaction properties of the stationary phase, m (the cavity formation/dispersive interaction strength), s (dipolarity/polarizability), b (hydrogen bond donating acidity) and a (hydrogen bond accepting basicity), are readily determined by multiple regression analyses of logarithmic capacity factors ( k′) for a set of test solutes measured on it in an aqueous mobile phase of a given organic content versus the solute properties represented by the Van der Waals molar volume, Kamlet-Taft dipolarity/polarizability, π*, hydrogen bond accepting basicity, β, and hydrogen bond donating acidity, α. The magnitudes of the four constants vary with the type of bonded ligand and with brand in the case of stationary phases having the same ligand, while they generally decrease in the order m > b > a > s, regardless of the type of the organic modifier in the mobile phase for all six columns. Although the four interaction strength constants are not as general as the widely used Rohrschneider and McReynolds constants for GLC stationary phases, it is believed that they will be useful in choosing the best column for a given separation among a number of nominally equivalent columns and columns with different bonded functionality.

The effect of the trifluoropropyl group in polysiloxane stationary phases used for capillary gas chromatography

AbstractFour poly(methyl 3,3,3‐trifluoropropyl siloxanes) with trifluoro‐propyl group content (group substitution) between 8 and 35 percent have been synthesized and characterized as stationary phases for gas chromatography in borosilicate glass capillary columns. Results are compared with those from two commercial stationary phases–a polydimethylsiloxane and a poly(methyl 3,3,3‐trifluoropropyl siloxane) with a fifty percent trifluoropropyl group content (group substitution).Retention index values, McReynolds constants, polarity (as defined by McReynolds) and retention polarity (as defined by Takács) increase regularly with the trifluoropropyl group content of the stationary phase. The temperature coefficient of the retention indices of the McReynolds probes, and that of the polarities, have been determined at temperatures between 60 and 180 °C. Specific retention volumes do not follow the linear dependence on trifluoropropyl group content observed for retention indices or polarities. Substances with electron‐donor groups show maximum retention for a trifluoropropyl group content of ca 30%, whereas the retention of hydrocarbons, halogenated compounds, and alcohols decreases as the degree of trifluoropropyl group substitution increases from 0 to 50%. It is felt that a polysiloxane with a trifluoropropyl group content of ca 30 to 35% would be the best choice for the separation of ketones, nitro compounds or amines.

The gas—liquid chromatographic stationary phase properties of liquid organic salts: Anomalous selectivity variation when employing the Rohrschneider/McReynolds system

The liquid organic salts studied here have wide stable liquid temperature ranges and act as efficient, highly selective gas—liquid chromatographic stationary phases. The effect of carbon number on the gas liquid chromatographic stationary phase properties of this series of tetra- n-butylammonium n-alkylsulfonate salts was evaluated by the well-known Rohrschneider/McReynolds system. Several problems arose when attempting to characterize these polar liquid organic salts employing this system. The specific retention volumes for the polar selectivity probes were generally not affected by an increase in the carbon number for the series studied here. However, the specific retention volumes for the n-alkane retention index markers increased dramatically as the anion carbon number was increased. The overall effect was a net decrease in the calculated McReynolds constants with increasing carbon number, although the true selectivity of the different stationary phases remained constant. Additionally, the specific retention volumes of the basic test probe, pyridine, showed large erratic variations and, in some cases, was not recovered from the columns. The results suggest the possibility of on-column chemical reactions occurring with some of these salts, and an alternative test probe, 2,6-dimethylpyridine (lutidine) is proposed to eliminate this problem. As McReynolds constants are presently the most commonly used parameters for predicting retention and gas chromatographic stationary phase selection, it is important that workers are aware of the inherent limitations of this scheme.

Evaluation of the polarity of packed and capillary columns by different classification methods

The behaviour of packed gas chromatographic columns filled with 30 different stationary phases was compared by using various polarity indicators: the difference in apparent carbon number of linear alkanes and alcohols with the same retention time, Δ C , the sum of the first five McReynolds constants,Σ MR 5 , Snyder's selectivity parameters, the Kováts coefficient, K c , and the retention polarity, RP . The correlation between these different systems for polarity evaluation is discussed. The polarity of some wide-and narrow-bore capillary columns, filled with non-polar, polar and modified carbon layer phases, was also evaluated as a function of temperature, in the range 60–120°C for Σ MR 5 and selectivity parameters and in the range 60–190°C for Δ C .

Potential ambiguities in the use of mcreynolds constants: Apparent differences in stationary phase selectivities exclusively attributable to the hydrocarbon index standards

Potential ambiguities in the use of mcreynolds constants: Apparent differences in stationary phase selectivities exclusively attributable to the hydrocarbon index standards

Analysis of haloalkanes on wide-bore capillary columns of different polarity connected in series

Thirty chloro-, bromo- and iodo-methanes, -ethanes and -ethenes, with one or more identical or different halogen atoms in the molecule, that can be present as contaminants in polluted surface or underground water were separated by using non-polar (SPB-1) and polar (Supelcowax-10) wide-bore capillary columns connected in series. Retention times and indices were measured at different temperatures and carrier gas flow-rates. The most efficient combination was obtained by connecting the two columns in the order non-polar + polar, which permitted the complete resolution of 26 compounds, while two were partially separated and two were co-eluted. The non-polar column alone co-eluted nine, the polar column eight and the polar + non-polar arrangement four compounds. The polarity of the coupled columns system was evaluated by using Rohrschneider and McReynolds constants with respect to various polarity probes, and by comparison of the slopes and intercept values of the straight lines obtained by plotting the retention values of various homologous series of compounds as a function of the number of carbon atoms in the molecule.

Polarity of Nonionic Surfactants as Determined by Gas Chromatography

Abstract The use of gas chromatography to determine the polarity of model and commercial surface active agents is discussed. Various polarity parameters are presented, and their positive and negative features are discussed. Effects of chromatographic conditions upon these polarity parameters are presented. The use of the polarity index and the retention index of ethanol and methanol, and the sum of the first five McReynolds constants is favorable. Relationships between various polarity parameters and between these parameters and the hydrophile lipophile balance (HLB) are discussed. The effect of surfactant structures upon their polarity parameters is presented. Polarity parameters can be used to estimate the HLB of surfactants and they can be used as analytical coefficients to characterize the average structure of nonionic surfactants. Some properties of nonionic surfactants can be predicted from their polarity parameters. They can be also used to predict and interpret the behavior of extractants and surf...

Correlation of Retention Indices with Resolution and Selectivity in Reversed-Phase HPLC and GC

The solvent selectivity triangle concept for characterizing high-performance liquid chromatographic (HPLC) mobile phase liquids consistently fails to group solvents according to selectivity for resolving aromatic compounds in reversed-phase HPLC. Selectivity differences between solvents classified in the same group often exceed those for solvents classified in different groups. Nevertheless, solvents characterized by simple relationships between resolution and 2-keto alkane retention indices correlate accurately with experimental resolution for 16 aromatic compounds with 12 reversed-phase solvents in binary mixtures with water. Also, by adjusting for the relative slopes of the 2-keto alkane retention index standards in HPLC or n-alkane standards in gas chromatography (GC), retention index differences are directly correlated with resolution, whereas nonadjusted retention index differences fail to correlate with resolution. Anomolies in McReynolds constants used in the classification of GC liquid phases are eliminated by adjustment for relative slope differences for the n-alkane standards that occur with the various phases.

Stationary phase for gas chromatography I polychlorinated kerosene (PCK) phase

The polychlorinated kerosene (PCK) is a useful medium-polar staticnary phase with a usable temperature range from <^ 40°to 150° and imparts an unusually high degree of support deactivation enabling nitro compounds, aldehydes, carboxylic acids to be analyzed at low con- centrations. McReynolds constants are given

Characterization of gas chromatographic liquid phases using McReynolds constants: An experiment for instrumental analysis laboratory.

This paper describes an experiment that is designed to aid in the development of an understanding of the fundamental processes involved in gas chromatographic separations by introducing the student to the Kovats retention index system.

Soviet polysiloxane stationary phases for gas chromatography

Polysiloxane stationary phases developed and used in the Soviet Union are described in detail, probably for the first time in the Western literature. Materials comparable to those produced by Western specialty chromatographic suppliers are included; polysiloxanes particularly suitable for high-temperature use are available in the Soviet Union and comparable materials are not available elsewhere. The effect of adsorption on the determination of McReynolds constants of stationary phases is discussed.

Studies of chromatographic packings consisting of porous polymers : III. Influence of silanization of polichrom a on the separation of short-chain free fatty acids by gas chromatography

A previously described cross-linked porous styrene polymer has been used for the separation of aqueous solutions of short-chain free fatty acids (SFFA) at low concentrations by gas chromatography. The unmodified polymer Polichrom A can separate C 2-C 7 SFFA in samples containing up to 1 μq of each component with considerable tailing, but the peaks tend to disappear at the 10 ng level. Silanization of Polichrom A with dimethyldichlorosilane (DMCS) allows the separation of SFFA at the 10 ng level without tailing. Secondary silanization with hexamethyldisilazane (HMDS) worsens the chromatographic separation. McReynolds constants, the number of theoretical plates and the resolutions obtained with unsilanized and silanized samples of Polichrom A and Chromosorb 101 are compared.

Correlation of two criteria of polarity for stationary phases in gas-liquid chromatography

Linear relationships between the partial molar excess Gibbs function of a solute methylene group, Δ G E(CH 2), and the average McReynolds constant, ΔI, and between Δ G E(CH 2) and the individual McReynolds constants were determined for a set of 55 liquid stationary phases. All these relationships were identical at the given level of statistical significance. An analysis of the relationships indicates that Δ G E(CH 2) and ΔI are equivalent criteria of polarity for liquid stationary phases and that polarity can adequately be characterized by a single criterion.

Universal system for liquid stationary phase classification on the basis of thermodynamical data

Equations modifying Rohrschneider's relationship between ΔI and thermodynamical characteristics values are derived. Polarity in chromatography is discussed as a possibility of stationary phases or absorbents to enter into intermolecular interactions and is determined on the basis of the partial molar free energies of solution (ΔG) of six test substances. A simple method for the calculation of stationary phase polarity in terms of ΔG from retention indices and McReynolds constants is given. Equations are presented for the calculation of stationary phase selectivity utilizing ΔG data tabulated for selected test substances. The thermodynamical basis of selecting a reference phase for a unified system expressing the selectivity of stationary phases which can also be applied for adsorbents is suggested. The energy equivalent to an index unit, ΔGi.u., is discussed.

Comparativ study of the gas—liquid chromatographic behavior of the pentalfuorobenzyl esters and the methyl esters of ten chlorophenoxyalkyl acids

The gas—liquid chromatographic (GLC) behaviour of the pentafluorobenzyl and methyl esters of ten structurally related chlorophenoxyalkyl acids was studied by comparing their retention indices on nine frequently used liquid phases with increasing McReynolds constants. The resolution of each liquid phase is different for the pentafluorobenzyl and the methyl ester derivatives. However, using an apolar and a polar phase, a graph of the retention index ( I) on the polar phase against the difference in retention indices (Δ I) between the polar and the non-polar phase shows a good correlation between structure and retention in gas—liquid chromatography. The graphs constructed for the pentafluorobenzyl and for the methyl esters have the same structure—retention correlations.

Stationary phase polarity classification at high temperature

The Rohrschneider classification system for stationary phase polarity has been extended t high-temperature evaluation at 180°. This is made possible by the use of a new non-pllar reference phase, hydrogenated Apiezon M, and a set of high-temperature probes consisting of n-butylbenzene, octanol, 2-octanone, 1-nitrohexane and collidine. The system has been tested using six stationary phases and a method of transposing the data obtained at 180° into McReynolds constants for phase classification is given.

Tailoring porous polymer gas chromatographic packings

The synthesis, thermal stabilities, B.E.T. surface areas and amxima of the pore radii distributions of some porous polymers were studied. The specific retention volumes of selectged compounds were measured and McReynolds constants were calculated, providing a classification of polymers for gas chromatographic purposes. The effects of the chemical nature, surface area and porous structure of the polymers on teh retentions of solutes with diffeent polarities were determined. Examples of the practical analytical utilization of these stationary phases are presented.

Use of 24,24-diethyl-19,29-dioctadecylheptatetracontane (C 87H 176) as a non-polar base stationary phase in Rohrschneider-McReynolds type schemes

An examination of the hydrocarbon C 87H 176 (24,24-diethyl-19,29-dioctadecylheptatetracontane) developed by Kováts as a standard stationary phase is reported. The hydrocarbon is compared with squalane and dimethylpolysiloxane and a thermal stability equal to that of the siloxane is apparent at both 120° and 180° determined by repetitive measurement of McReynolds constants. Some discussion is also included of a further recently described hydrocarbon produced by exhaustive hydrogenation of Apiezon M, which exhibits McReynolds constants substantially identical to those of squalane, is apparently thermal stable to 200° and may well be of lower cost.