Polymeric Ionic Liquids Derived from L-Valine for the Preparation of Highly Selective Silica-Supported Stationary Phases in Gas Chromatography.

A series of silica-supported polymeric ionic liquid (PIL)-based stationary phases derived from a vinylic L-valine ionic liquid monomer and divinylbenzene (DVB) as the crosslinking agent have been prepared and studied as gas chromatographic stationary phases. These coated gas chromatographic columns exhibited good thermal stabilities (230-300 °C) and high efficiencies (1700-2700 plates/m), and were characterized using a linear solvation parameter model in order to understand the effects of the amount of DVB on the features of the resulting composite systems. Their retention behavior and separation efficiencies were demonstrated using the Grob test. By tuning the crosslinking degree for the IL-derived stationary phase, the separation selectivity and resolution of different compounds were improved. The different retention behaviors observed for many analytes indicate that these stationary phases may be applicable as new types of GC stationary phases.

Determination of volatile compounds in cider apple juices using a covalently bonded ionic liquid coating as the stationary phase in gas chromatography.

A chromatographic method for the separation of volatile compounds in Asturian cider apple juices has been developed. For this separation purpose, a monocationic imidazolium-based ionic liquid bearing a reactive terminal iodine atom was synthesized by a quaternization-anion exchange chemical sequence. Next, the gas chromatography (GC) stationary phase was prepared by covalently linking the imidazolium monolith to the reactive silanol groups of the inner capillary wall at 70 °C. This coated GC column exhibited good thermal stability (290 °C), as well as good efficiency (2000 plates/m) in the separation of volatile compounds from Asturian apple cider juices, and was characterized using the Abraham solvation parameter model. The intra-day and inter-day precision of the chromatographic method was evaluated, obtaining relative standard deviations from 3.7 to 12.9% and from 7.4 to 18.0%, respectively. Furthermore, recoveries from 82.5 to 122% were achieved. Graphical Abstract Covalent bonding of an ionic liquid to inner column wall led to a great improvement of the separation efficiencies of stationary phases in gas chromatography.

Gas chromatographic analysis of fatty acid methyl esters of milk fat by an ionic liquid derived from L-phenylalanine as the stationary phase.

A Gas Chromatography (GC) method has been developed for the separation and characterization of the different fatty acids in anhydrous milk fat (AMF) by means of an ionic liquid stationary phase, characterized by a monocationic imidazolium salt derived from L-phenylalanine. The inner surface of a fused silica capillary column was modified using this ionic liquid functionality and 3-aminopropyldiethoxymethyl silane. This coated GC column, which exhibited good thermal stability (270°C) and good efficiency (2700 plates/m), has been characterized using the Abraham solvation parameter model. The intra-day and inter-day precision of the method have been evaluated, obtaining relative standard deviations (RSD) from 0.99% to 4.0% and from 2.8% to 9.2%, respectively. Furthermore, recoveries from 90% and 99% have been achieved.

A chemometric approach to characterization of ionic liquids for gas chromatography.

A chemometric study was carried out to characterize three ionic liquid types (ILs) with hexacationic imidazolium, polymeric imidazolium, and phosphonium cationic cores, using a range of contra-anions such as halogens, thiocyanate, boron anions, triflate, and bistriflimide. The solvation parameter model developed by Abraham et al., unsupervised techniques as cluster analysis (CA), and supervised techniques as linear discriminant analysis (LDA), step-LDA, quadratic discriminant analysis (QDA), and multivariate regression techniques as discriminant partial least squares (D-PLS), or multiple linear regression (MLR) were used to characterize the functionalized ILs above. CA established two main groups of phases, those with an acidic H-bond and those with basic ones. Once detected, the two natural groups, a linear and quadratic delimiters with good classification (>96 %) and prediction (>92 %) capacities were computed. The use of step-LDA technique allowed us to establish that a, b, and s solvation parameters were the most discriminant variables. These variables were used for modeling purposes, and a D-PLS and MLR models were constructed using a binary response. The explained variance of categorical variable by the model validated by cross-validation was 65 %, and 94.5 % of ILs were correctly predicted. IL characterization carried out would allow the appropriate selection of phases for gas chromatography (GC).

Polymeric imidazolium ionic liquids as valuable stationary phases in gas chromatography: chemical synthesis and full characterization.

Seven new functionalized polymerizable ionic liquids were chemically prepared, and later applied for the preparation of polymeric stationary phases in gas chromatography. These coated GC columns, which exhibited good thermal stabilities (240-300°C) and very high efficiencies (3120-4200 plates/m), have been characterized using the Abraham solvation parameter model. The chromatographic behavior of these polymeric IL columns has been deeply studied observing excellent selectivities in the separation of many organic substances such as alkanes, ketones, alcohols, amines or esters in mixtures of polar and non polar solvents or fragrances. Remarkably, the challenging separation of xylene isomers has been possible using a bis(trifluoromethylsulfonyl)amide based imidazolium IL coated column as a gas chromatography stationary phase.

Characterization of hexacationic imidazolium ionic liquids as effective and highly stable gas chromatography stationary phases.

Polycationic ionic liquids (ILs) are an attractive class of ILs with great potential applicability as gas chromatography stationary phases. A family of hexacationic imidazolium ILs derived from the cycloalkanol family was chemically first prepared in a straightforward manner and then applied for analytical separation purposes. Four tuneable engineering vectors, namely cation ring size structure, anion nature, spatial disposition of cycloalkanol substituents and O-substitution, were considered as experimental parameters for the design of the desired ionic liquids. A total number of five new phases based on a common benzene core respectively exhibited column efficiencies around to 2500 plates/m, broad operating temperature ranges and also, even more importantly, good thermal stabilities (bleeding temperature between 260 and 365°C), finding variations in the selectivity and analytes elution orders depending on the IL structures. Their solvation characteristics were evaluated using the Abraham solvation parameter model, establishing clear correlations between their cation structure and retention capability with respect to certain analytes. The study of relationships between the ILs structure and solvation parameters gives us an idea of the IL stationary phase to be used for specific separations.

Evaluation of new ionic liquids as high stability selective stationary phases in gas chromatography.

Two ionic liquids (ILs), namely (S,S)-1-butyl-3-(2'-hydroxy-cyclohexyl)-3H-imidazol-1-ium tetrafluoroborate and (S,S)-1-butyl-3-(2'-acetyl-cyclohexyl)-3H-imidazol-1-ium tetrafluoroborate have been employed as stationary phases in capillary gas chromatography. These new phases exhibit a column efficiency of 1,600 and 2,100 plates m(-1) for IL 1 and IL 2, respectively, a wide operating temperature range and good thermal stability (bleeding temperature of 250 °C for IL 1 and 160 °C for IL 2). Inverse gas chromatography (GC) analyses were used to study the solvation properties of these ILs through a linear solvation energy model. The application of these ILs as new GC stationary phases was studied. These stationary phases exhibited unique selectivity for many organic substances, such as alkanes, ketones, esters, and aromatic compounds. The efficient separation of several mixtures containing compounds of different polarities and the good separation of fatty acid methyl esters (FAMEs) and cis/trans isomers indicate that these ILs may be applicable as a new type of GC stationary phases.