Medium-polar Phases Research Articles

First deep eutectic solvent-based (DES) stationary phase for gas chromatography and future perspectives for DES application in separation techniques

The paper presents the first application of deep eutectic solvents (DES) as stationary phases for gas chromatography. DES obtained by mixing tetrabutylammonium chloride (TBAC) as a hydrogen bond acceptor (HBA) with heptadecanoic acid being a hydrogen bond donor (HBD) in a mole ratio of HBA:HBD equal to 1:2 was characterized by its ability to separate volatile organic compounds (VOCs). The Rohrschneider – McReynolds constants determined reveal that the synthesized DES is a stationary phase of medium polarity. A detailed retention characteristic was determined for a number of groups of chemical compounds, including aromatic hydrocarbons, alcohols, ketones, sulfides and thiophene derivatives. The synthesized DES was found to have a high selectivity towards alcohols. At the same time, the investigated stationary phase was found to have specific interactions with some analytes. For example, a stronger retention was observed for 1-hexanol and 1-heptanol compared to other alcohols. Retention times of these two alcohols are longer by 191% and 300%, respectively, relative to the expected value based on their boiling point. Such an increased retention is caused by a synergistic effect of various kinds of interactions – the possibility of formation of hydrogen bonds between the DES and the hydroxyl group of alcohols and hydrophobic interactions of alkyl chains of the DES with the alkyl chain of alcohols. The ability to modify properties of DESs by replacement of HBA or HBD with a different chemical compound or by dissolving in DES macromolecular substances makes the proposed stationary phase highly flexible. In addition to using the developed DES in chromatographic techniques, the retention data collected indicate the possibility of its application to other separation techniques, i.e. extractive distillation.

Experimental evaluation of solvent elution strength in reversed-phase TLC on medium polarity phases

Seven chromatographic grade solvents miscible with water (acetone, acetonitrile, dioxane, ethanol, isopropanol, methanol, tetrahydrofuran), as well as water itself were investigated in the context of their eluotropic strength in reversed-phase chromatography on four medium-polar adsorbents (cellulose, CN, NH2 and DIOL). The test set for this research consisted of 35 model compounds. A modern chemometric mixture design concept allowed to estimate each solvent effect separately with a relatively small error (about 0.05 of RM value for all adsorbents). The solvent effects were analyzed chemometrically in multivariate manner and a final model was fitted to achieve the solvent strength. The estimation error was computed both from regression and bootstrap approach.

Intermolecular interactions between polyarylenephthalides surface and organic compounds of different nature by inverse gas chromatography data

Polyarylenephthalides are a promising class of polymeric materials. They are soluble in organic solvents, but remain resistant to water, as well as to acids and bases. All this makes polyarylenphthalide promising materials for the formation of films on surfaces. However, for this it is necessary to first study the ability of polyarylenephthalides to different intermolecular interactions, as well as the polarity of their surface.Therefore, it is of interest to use the inverse gas chromatography method for studying the adsorption properties of the surface of polyarylenephthalates, as well as the evaluation of its conditional polarity. Two polymers of the class of polyarylenephthalides were used as the studied samples: chlorinated (in position 4) poly phthalidylidenefluorene) (OPS-236) and poly (phthalidylidene diphenyl) (PE-259). They are distinguished by the presence of a methylene group between two benzene rings. Inert solid support Chromaton NAW was used as a solid substrate for the deposition of polyarylenphthalide films. The application was carried out from chloroform by evaporation of the solvent at a temperature of 40 ° C. The amount of the applied polymer was 1% by weight of the inert carrier. The study was conducted by the method of inverse gas chromatography. Samples were introduced as diluted vapor-air mixtures at the limit of the detector sensitivity. This made it possible to measure the retention parameters in the Henry region and consider the interactions between sorbate molecules to be negligible. The relative conditional polarity of the surface and the contributions of various intermolecular interactionsto adsorption free energy were estimated by the method of linear free energy relationship (LFER). From the obtained LFER-coefficients, the contributions of intermolecular interactions to the adsorption energy were calculated, and the relative conditional polarity of the surface was also estimated. The dispersion and specific component of the Helmholtz free energy of adsorption was calculated by the Dong method. It has been established that adsorbents based on polyarylenephthalides are able to act as stationary phases for chromatography. It is shown that polyarylenephthalide films are capable of both dispersion and various specific interactions with organic molecules. The surface of polyarylenephthalides can be attributed to stationary phases of medium polarity, more polar than porous polymers based on styrene and divinylbenzene and less polar than silica gels.

Novel stationary phases based on asphaltenes for gas chromatography.

We present the results of investigations on the possibility of the application of the asphaltene fraction isolated from the oxidized residue from vacuum distillation of crude oil as a stationary phase for gas chromatography. The results of the investigation revealed that the asphaltene stationary phases can find use for the separation of a wide range of volatile organic compounds. The experimental values of Rohrschneider/McReynolds constants characterize the asphaltenes as stationary phases of medium polarity and selectivity similar to commercially available phases based on alkyl phthalates. Isolation of asphaltenes from the material obtained under controlled process conditions allows the production of a stationary phase having reproducible sorption properties and chromatographic columns having the same selectivity. Unique selectivity and high thermal stability make asphaltenes attractive as a material for stationary phases for gas chromatography. A low production cost from a readily available raw material (oxidized petroleum bitumens) is an important economic factor in case of application of the asphaltene stationary phases for preparative and process separations.

How do you make the best Caipirinha?

Recently we discovered through metabolomics a novel type of solvents, which we called Natural Deep Eutectic Solvents (NADES). They are formed by mixtures of sugars, amino acids, organic acids and bases in certain molar ratios, e.g. malic acid and choline like well known synthetic ionic liquids. Also two neutral solids may form a deep eutectic solvent at room temperature. So we discovered that various sugars with e.g. choline or malic acid form such liquids. These NADES are medium polar like ethanol, and proved to be excellent solvents for most natural products, including proteins, DNA, RNA and polysaccharides, often with orders of magnitude higher solubility than in water. Do they occur in nature? Nectar is an example of a NADES, but we believe that NADES play an important role in nature as a third liquid phase of medium polarity between water and lipids. In resurrection plants, cacti, seeds all ingredients of NADES present, and also cold and drought resistant plants are rich in NADES ingredients. The occurrence of NADES in cells would explain how water insoluble compounds like terpenoids can be biosynthesized, as well as very high levels of flavonoids and derivatives occur in flowers in a liquid state. NADES ingredients are found in all pro- and eukaryotic cells. When you start thinking about possible roles of NADES in nature, the possibilities are almost infinite!

Characterization of organic pollutants in industrial effluents by high-temperature gas chromatography–mass spectrometry

The characterization of complex mixtures of organic contaminants present in industrial effluents is a well-known problem. The determination of individual target analytes depends very much on the analytical method used. In this article, the possibilities of using high-temperature gas chromatography–mass spectrometry (HT-GC–MS) are explored. In HT-GC–MS non-polar and medium-polarity phases can be operated at temperatures up to 370–420°C, allowing the analysis of high-molecular-weight compounds. So far, the applications of HT-GC have included the analysis of hydrocarbons up to C-100, lipids, sugars, and polyglycerols, but no data have been reported on the characterization of organic pollutants present in industrial effluents. The general sample handling approach reported here is based either on a sequential solid-phase extraction (SSPE) procedure, with a change of solvent composition in the elution from two different cartridges (C18 and Lichrolut EN), or on a toxicological fractionation. Effluent samples from tanneries, petrochemical plants, and textile industries are characterized, and the levels of the main organic pollutants identified are indicated. More than 50 compounds, including n-alkanes, phthalates, esters, acids, and phenols, were identified in the effluents studied.

Thermodynamic properties of alkylbenzenes from retention-boiling point correlations in gas chromatography

A thermodynamic interpretation of the empirical correlation between retention and boiling point for alkylbenzenes in stationary phases of low and medium polarity has been found. The transfer of molecules between the liquid and mobile phases was assumed to be similar to, although not identical with, vaporization of any given pure liquid and characterized using the Trouton's rule. The two equations developed relate relative retentions to solute boiling point and two systems constants under a given set of conditions. The first equation was found to give a better description since it involves fewer assumptions and approximations. Validity of the model was confirmed by agreement between theoretical and experimental values for equation constants although the agreement becomes poorer as the stationary phase polarity increases. The relationships discussed are applicable to all congeneric solutes of low polarity in stationary phases of medium polarity.

Enantiomeric resolution of persistent compounds of technical toxaphene (CTTs) on t-butyldimethylsilylated β-cyclodextrin phases

Eight of the most important single compounds of technical toxaphene were separated on t-butyldimethylsilylated β-cyclodextrin (β-BSCD) diluted in a medium polar phase using gas chromatography with electron capture detectors (GC-ECD). The enantiomeric resolution of all compounds was obtained in one GC run. The β-BSCD phase also separated the enantiomers of oxychlordane, cis- and trans-chlordane as well as α-HCH. Problems in the enantioselective determination of CTTs in biological samples are discussed. Finally, the enantioselective determination of the two most recalcitrant CTTs in biological samples was achieved using electron capture negative ionization mass spectrometry (GC-ECNI-MS) in the single ion monitoring (SIM) mode.

New liquid crystalline stationary phase for capillary gas chromatography

In the last few years the use of capillary columns with liquid crystalline stationary phases has increased. In general, liquid crystals are stationary phases of medium polarity, therefore a mixed retention mechanism is expected]. It is known that the surface of the support affects the orientation of the molecules of the liquid crystalline stationary phase and that this effect is greater than with conventional stationary phase+. Recently we have systematically studied the influence of the film thickness and the surface quality on the properties of selected liquid crystalline stationary phases coated on glass capillary columns, and on the retention data of compounds having different structures and polarities3. The aim of this work was the introduction of a new, more polar, liquid crystalline stationary phase and to compare its properties in capillary columns with that of comparable structure.

Preparation of inert and high‐temperature stable apolar and medium polar glass‐capillary columns using OH‐terminated polysiloxane stationary phases

AbstractCoating intensively leached silica surfaces with OH‐terminated phases provides a new way of producing, by simple means, columns with substantially increased inertness and thermostability. In addition, their separation efficiency is found to be typically higher than that of columns with traditional coatings. The underlying basic effect is a condensation process between terminal silanol groups of the phase and residual silanols, of the glass surface, thus producing the mentioned inertness. Moreover, the surface‐bonded molecules are immobilized without addition of a radical generator. If required, crosslinking can also be effected using a volatile azo compound. No vinyl groups are required for this additional immobilization process. The paper discusses all processes involved, and gives detailed working directions for the following medium polar phases. OV‐1701‐OH, OV‐31‐OH (new, 17% cyanopropyl), OV‐61‐OH, and OV‐17‐OH, and the apolar phases PS‐347.5 and PS‐086. There is no doubt so far that the principle of terminal silanol groups is applicable to all silicone phases, and may replace the traditional endcapped stationary phases in the future.

A cold silanization method for preparation of medium polarity capillary columns

AbstractSilane‐coupling agents, commonly used for fiberglass reinforced plastics (FRP), were applied for deactivation of silanol sites in glass capillary columns prior to coating with mediumpolarity phases such as Carbowax and Superox. The columns, prepared in a two‐stage process in the case of glass (acidic leaching and drying, dynamic cold silanization followed by static coating with the phase) or a one stage process in the case of fused silica, gave the best results when deactivation and hence wettability were induced by glycidoxypropyltrimethoxy silane.

The gas chromatographic characterization of 2-thiaadamantane derivatives

The Kováts indices of 2-thiaadamantane and its 4-mono- and 4,8-disubstituted homologues were determined at 190, 200 and 210° for all of the solutes used. Capillary columns with Apiezon L (non-polar phase) and polyphenyl ether 6 P5E (medium polar phase) were used.