Stable room-temperature ionic liquids (RTILs) have been used as novel reaction solvents. They can solubilize complex polar molecules such as cyclodextrins and glycopeptides. Their wetting ability and viscosity allow them to be coated onto fused silica capillaries. Thus, 1-butyl-3-methylimidazolium hexafluorophosphate and the analogous chloride salt can be used as stationary phases for gas chromatography (GC). Using inverse GC, one can examine the nature of these ionic liquids via their interactions with a variety of compounds. The Rohrschneider-McReynolds constants were determined for both ionic liquids and a popular commercial polysiloxane stationary phase. Ionic liquid stationary phases seem to have a dual nature. They appear to act as a low-polarity stationary phase to nonpolar compounds. However, molecules with strong proton donor groups, in particular, are tenaciously retained. The nature of the anion can have a significant effect on both the solubilizing ability and the selectivity of ionic liquid s...

Examination of ionic liquids and their interaction with molecules, when used as stationary phases in gas chromatography.

Metal–organic frameworks (MOFs) have received great attention because of their fascinating structures and intriguing applications in hydrogen storage, gas separation, catalysis, chiral separation, sensing, and imaging. Recently, MOFs such as MOF-508, MIL-47, and MIL53 have been shown to be promising as stationary phases for gas chromatography (GC) and liquid chromatography. 11] All these pioneering works on the utilization of MOFs as stationary phases in chromatography were performed on packed columns. However, packed columns usually result in low resolution as a result of peak broadening, which impairs the separation efficiency of MOFs. Moreover, gram-scale MOFs are needed for packed columns, leading to high-cost applications of MOFs as stationary phases in chromatographic separation. In contrast, capillary columns, either wall-coated open tubular (WCOT) columns or porous layer open tube (PLOT) columns, involve a thin film of MOFs coated on their inner walls, and thus improve the resolving power of MOFs and reduce the amount of MOFs required for GC applications. However, to the best of our knowledge, no work on the utilization of MOFs as stationary phases for high-resolution capillary GC separation has been reported so far. Herein we show the first fabrication of the MOF-coated capillary column for high-resolution GC separation. For a proof-of-concept demonstration, we choose MIL-101 as the stationary phase and xylene isomers and ethylbenzene (EB) as the targets for separation. Xylene isomers and EB are important raw chemicals in industry; in particular, p-xylene is used in the manufacture of terephthalic acid for the polyester industry. The separation and detection of individual xylene isomers and EB are also of environmental concern, and of great practical interest in air monitoring and blood analysis. For these reasons, numerous stationary phases have been developed for GC separation of xylene isomers and EB, for example, 7,8benzoquinoline, tetrachlorophthalate, 1,8-diaminonaphthalene, modified organo-clays Bentone-34, liquid-crystalline compounds, b-cyclodextrin derivatives, poly(ethylene glycol), and MIL-47. However, long analysis time (27–90 min) or temperature programming is often needed. MIL-101 is a chromium terephthalate MOF with coordinatively unsaturated sites (CUS). We utilized MIL-101 as the stationary phase because of its high surface area, large pores (2.9–3.4 nm), accessible CUS, and excellent chemical and thermal stability, which make it an attractive candidate for isomer separation. However, MIL-101 has never been explored as the stationary phase for chromatographic separation before, even though the tiny crystal size characteristic of MIL-101 is beneficial to the fabrication of MIL-101 coated capillary columns by a dynamic coating method. In this work, we prepared the MIL-101 coated capillary column and achieved a baseline separation of p-xylene, oxylene, m-xylene, and EB on the fabricated MOF coated capillary column by GC within 1.6 min without the need for temperature programming (Figure 1).

Metal–Organic Framework MIL-101 for High-Resolution Gas-Chromatographic Separation of Xylene Isomers and Ethylbenzene

Covalent organic frameworks (COFs) are a novel class of porous materials, and offer great potential for various applications. However, the applications of COFs in chiral separation and chiral catalysis are largely underexplored due to the very limited chiral COFs available and their challenging synthesis. Here we show a bottom-up strategy to construct chiral COFs and an in situ growth approach to fabricate chiral COF-bound capillary columns for chiral gas chromatography. We incorporate the chiral centres into one of the organic ligands for the synthesis of the chiral COFs. We subsequently in situ prepare the COF-bound capillary columns. The prepared chiral COFs and their bound capillary columns give high resolution for the separation of enantiomers with excellent repeatability and reproducibility. The proposed strategy provides a promising platform for the synthesis of chiral COFs and their chiral separation application.

/pdf/bottom-up-synthesis-of-chiral-covalent-organic-frameworks-49pgfr423p.pdf

Bottom-up synthesis of chiral covalent organic frameworks and their bound capillaries for chiral separation

Cyclodextrins: a versatile tool in separation science

Facile room-temperature solution-phase synthesis of a spherical covalent organic framework for high-resolution chromatographic separation

The overall polarity of 22 chiral stationary phases (CSPs) used in capillary open tubular gas chromatography columns was estimated using the first five Rohrschneider-McReynolds constants. Most of the columns (i.e., 18) were wall-coated, and four were of the wall-immobilized or of the so-called "bonded" type. A wall-coated capillary squalane column was specially prepared as a polarity reference column. All but two of the CSPs were based on derivatized cyclodextrins (CDs) of different sizes. The overall properties of the CSPs are discussed in terms of the five Rohrschneider-McReynolds constants and their average values. It was found that the derivatized cyclodextrin CSP polarity increased with the CD ring size. The bonded CSPs were significantly less polar than their coated homologues due to the apolar polymer used to immobilize the CD rings. The retention behavior of 14 compounds was studied at 100 degrees C on the capillary columns. Retention parameters are clearly related to the McReynolds constants. Conversely, the enantiomeric resolution capability of a given stationary phase is not related to the constants. The enantioselective resolution mechanism critically depends on the solute structure and on the nature of the CSP.

Determination and use of Rohrschneider-McReynolds constants for chiral stationary phases used in capillary gas chromatography.

Adsorptive bubble separation methods are known to be useful for processing large amounts of material at a relatively low cost. These techniques have been used to enrich components from both heterogeneous and homogeneous solutions. There is a need for economical process-scale enantiomeric separations. Thus far there has been little evidence to support the feasibility of 2using an adsorptive bubble process to enrich enantiomers. We demonstrate that foam-forming chiral collectors can be used in conjunction with an inexpensive glass device to enantiomerically enrich some pharmaceutically important compounds as well as derivatized and underivatized amino acids. Factors that appeared to affect this water-based separation include the following: (a) column length, (b) column geometry and packing, (c) gas flow rate, (d) concentration of the collector and the racemate, (e) nature of the collector, (f) temperature, (g) pH, (h) reflux time, (i) foam dryness, and (j) the presence of other materials in the sample (e.g., miscible organic solvents, salts, etc.). The chiral collectors used in this study are known to be able to associate with analytes via ligand exchange interactions, hydrophobic inclusion complexation, and hydrogen-bonding interactions among others. 28 refs., 5 figs., 5 tabs.

Foam Flotation Enrichment of Enantiomers

Gas-solid chromatographic analysis of automobile tailpipe emissions as a function of different engine and exhaust system modifications

Activating Pyruvate Kinase Improves Red Blood Cell Integrity By Reducing Band3 Tyrosine Phosphorylation

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Determination and use of Rohrschneider-McReynolds constants for chiral stationary phases used in capillary gas chromatography.

Foam Flotation Enrichment of Enantiomers

Gas-solid chromatographic analysis of automobile tailpipe emissions as a function of different engine and exhaust system modifications

Activating Pyruvate Kinase Improves Red Blood Cell Integrity By Reducing Band3 Tyrosine Phosphorylation