A stamped aluminium gas chromatographic column disk employing directly grown anodic aluminium oxide stationary phase for the separation of aromatic and chlorinated compounds

In this study, mesoporous anodic aluminium oxide (AAO) with moderate polarity was used as a GC stationary phase to demonstrate the applicability to various compound species. The fluidic channel measured 6 meters in length and had a cross-section area of 0.127 mm2. The column disk measured 6.2 cm in diameter and was fabricated through a stamping process on an aluminium substrate. The AAO stationary phase was directly grown on the aluminium substrate through an anodization process using oxalic acid as the electrolyte. The pore size of the AAO stationary phase was approximately 50-70 nm, with film thicknesses ranging from 6-20 μm. AAO based on oxalic acid exhibited significantly reduced surface polarity, making it suitable for separating polarizable and slightly polar compounds. The theoretical plate number for benzene had reached 1800 plates per meter, and for n-butane, it had reached 2500 plates per meter. A complex mixture of 16 compounds spanning alkanes, olefins, aromatics, and chlorinated hydrocarbons was effectively separated in 8 minutes with the temperature programmed to 200 °C.

Homochiral Metallacycle Used as a Stationary Phase for Capillary Gas Chromatographic Separation of Chiral and Achiral Compounds

Metallacycles are a novel class of supramolecular materials with circular structures, internal cavities, and abundant host-guest chemical properties that have exhibited good application prospects in many fields. However, to the best of our knowledge, no research on the use of metallacycles as stationary phases for gas chromatographic (GC) separations has been published yet. In this work, we report for the first time the use of a homochiral metallacycle, [ZnCl2L]2, as a stationary phase for GC separations. [ZnCl2L]2 was synthesized by reaction of (S)-(1-isonicotinoylpyrrolidin-2-yl)methyl-isonicotinate (L) with ZnCl2 via coordination-driven self-assembly. The [ZnCl2L]2-coated column displayed an excellent separation performance not only of organic isomers but also of racemic compounds. Sixteen racemates (including alcohols, esters, amino acid derivatives, ethers, organic acids, and epoxides) and 21 isomeric compounds (including positional, structural, and cis/trans-isomers) were well separated on the [ZnCl2L]2-coated column. Impressively, some racemates were resolved with high resolution values (Rs), including 1,2-butanediol diacetate (Rs = 25.86), ethyl 3-hydroxybutyrate (Rs = 20.97), 1,3-butanediol diacetate (Rs = 18.09), and threonine derivative (Rs = 18.61). Compared with the commercial β-DEX 120 column for separation of the tested racemates, the [ZnCl2L]2-coated column exhibited good enantioseparation complementarity, enabling separation of some racemates that could not be separated, or were not well resolved, by the β-DEX 120 column. In addition, many organic mixtures, such as n-alkanes, alkylbenzenes, n-alcohols, and a Grob test mixture, were also well separated on the [ZnCl2L]2-coated column. The column also has good reproducibility and thermal stability on separation. This work not only reveals the great potential of metallacycles for GC separations but also opens up a new application of metallacycles in separation science.

Recognition in the Domain of Molecular Chirality: From Noncovalent Interactions to Separation of Enantiomers

It is not a coincidence that both chirality and noncovalent interactions are ubiquitous in nature and synthetic molecular systems. Noncovalent interactivity between chiral molecules underlies enantioselective recognition as a fundamental phenomenon regulating life and human activities. Thus, noncovalent interactions represent the narrative thread of a fascinating story which goes across several disciplines of medical, chemical, physical, biological, and other natural sciences. This review has been conceived with the awareness that a modern attitude toward molecular chirality and its consequences needs to be founded on multidisciplinary approaches to disclose the molecular basis of essential enantioselective phenomena in the domain of chemical, physical, and life sciences. With the primary aim of discussing this topic in an integrated way, a comprehensive pool of rational and systematic multidisciplinary information is provided, which concerns the fundamentals of chirality, a description of noncovalent interactions, and their implications in enantioselective processes occurring in different contexts. A specific focus is devoted to enantioselection in chromatography and electromigration techniques because of their unique feature as "multistep" processes. A second motivation for writing this review is to make a clear statement about the state of the art, the tools we have at our disposal, and what is still missing to fully understand the mechanisms underlying enantioselective recognition.

Chiral stationary phases and applications in gas chromatography

Chiral compounds are ubiquitous in nature and play a pivotal role in biochemical processes, in chiroptical materials and applications, and as chiral drugs. The analysis and determination of the enantiomeric ratio (er) of chiral compounds is of enormous scientific, industrial, and economic importance. Chiral separation techniques and methods have become indispensable tools to separate chiral compounds into their enantiomers on an analytical as well on a preparative level to obtain enantiopure compounds. Chiral gas chromatography and high-performance liquid chromatography have paved the way and fostered several research areas, that is, asymmetric synthesis and catalysis in organic, medicinal, pharmaceutical, and supramolecular chemistry. The development of highly enantioselective chiral stationary phases was essential. In particular, the elucidation and understanding of the underlying enantioselective supramolecular separation mechanisms led to the design of new chiral stationary phases. This review article focuses on the development of chiral stationary phases for gas chromatography. The fundamental mechanisms of the recognition and separation of enantiomers and the selectors and chiral stationary phases used in chiral gas chromatography are presented. An overview over syntheses and applications of these chiral stationary phases is presented as a practical guidance for enantioselective separation of chiral compound classes and substances by gas chromatography.

Cyclofructans as Chiral Selectors: An Overview

Cyclofructans are cyclic oligosaccharides made of β-2,1-linked fructofuranose units. They have been utilized as chiral selectors, usually after derivatization, with high-performance liquid chromatography (HPLC), gas chromatography (GC), capillary electrophoresis (CE), and supercritical fluid chromatography (SFC). The focus herein will be directed to their development and applications as chiral selectors in various chiral separation techniques. Discussion of their use in hydrophilic liquid interaction chromatography (HILIC) will be limited. Their use in liquid chromatography, especially their improvements with the use of superficially porous particles (SPPs) will be emphasized. Method parameters and future directions are also discussed.