Separation performance of p-tert-butyl(tetradecyloxy)calix[6]arene as a stationary phase for capillary gas chromatography

Separation performance of the calix[8]arene functionalized with polyethylene glycol units for capillary gas chromatography

In this paper, an amphiphilic calix[8]arene with polyethylene glycol unit branches (C8A-PEG) was synthesized and applied for capillary gas chromatography (GC). The C8A-PEG was coated on the inner wall of a capillary column by a static method with the column efficiency of 3165 plates/m and polar nature. As demonstrated, the C8A-PEG column has excellent physicochemical properties and separation performance since it has π-electron-rich 3D cavity which combines with polar PEG units. Compared with two columns corresponding to the construction units C8A and PEG, the C8A-PEG column shows distinctly advantageous performance for the mixture of 22 components with diverse types. Impressively, it shows satisfactory resolution for positional isomers and cis-/trans- isomers, especially the challenging isomers of toluidine and dimethylaniline. The outstanding distinguishing capability of the C8A-PEG stationary phase is mainly attributed to the abundant molecular recognition interactions, including van der Waals, dipole-dipole, H-bonding and π-π stacking interactions. This work has proved that the new GC stationary phases constructed by different units can complement each other's advantages, improve their physicochemical properties and separation performance, and have broad application prospects in chromatographic analysis.

A New Capillary Gas Chromatography Column Based on Poly(ethylene glycol) Methyl Ether-Functionalized Calix[4]arene

In this work, a novel capillary column (C4A-mPEG) with a calixarene-based polymer stationary phase (poly(ethylene glycol) methyl ether-functionalized 4-tert-butylcalix[4]arene) was designed and used for gas chromatographic (GC) separations. The C4A-mPEG capillary column, prepared by the static coating method, showed moderate polarity and a column efficiency of 2332 plates/m, determined by 1-octanol at 120 °C. The separation features of C4A-mPEG stationary phase, resulting from its unique structure and multiple molecular recognition processes with analytes, including π-π, H-bonding, dipole-dipole, and van der Waals interactions, allowed to obtain high-resolution performances for a wide range of compounds and their isomers, especially benzaldehydes, phenols, and anilines. Moreover, compared with 4-tertbutyl calix[4]arene (C4A) and polyethylene glycol (PEG) stationary phases, a higher resolving capability was also observed for the separation of toluidine and xylidine isomers.

Performance and selectivity of amphiphilic pillar[5]arene as stationary phase for capillary gas chromatography

Pillar[n]arenes possess highly symmetrical and rigid pillar-shaped architecture with π-electron rich cavity that afford their reliable host-guest recognition interactions towards matched guests. In this work, a novel amphiphilic pillar[5]arene (P5A-C10-2NH₂) was designed, synthesized and employed as the stationary phase for capillary gas chromatography. To date, they have not been reported in the field of chromatography. The P5A-C10-2NH₂ capillary column (10 m × 0.25 mm i.d.) was prepared by static coating method. Its capillary column exhibited moderate polarity and column efficiency of 2265 plates/m determined by naphthalene at 120 °C. As evidenced, the P5A-C10-2NH₂ column achieved advantageous separation performance for a mixture of 24 analytes of diverse types and exhibited different chromatographic selectivity from two pillar[5]arene derivatives columns and commercial HP-35 column with 35%-phenyl-methylpolysiloxane. Moreover, the P5A-C10-2NH₂ column baseline resolved more than a dozen positional and cis-trans isomers. Furthermore, the separation mechanism of P5A-C10-2NH₂ column was discussed by quantum chemical calculations. In addition, the P5A-C10-2NH₂ column had high thermal stability and excellent separation repeatability 0.01-0.04% for run-to-run, 0.03-0.17% for day-to-day and 3.2-3.9% for column-to-column. The special amphiphilic structure and high resolution for various analytes reveal the good potential of pillararenes as a new class of stationary phases for chromatographic analyses. Moreover, the TPG column achieved improved thermal stability over the GIL column and excellent repeatability.