Post-modification of covalent organic framework for gas chromatographic separation of isomers

Separation of isomers is important in diverse areas such as life science, chemical industry, pharmaceutical and environmental science, but still challenging due to their similar physicochemical properties. Development of new stationary phases is an effective way to improve the performance of chromatography for the separation of isomers. Here, we report the post-modification of a new hydroxyl-functionalized covalent organic framework (COF) TzDHNDA with [(1-phenylethyl)amino]acetic acid (PEAA) via esterification reaction to construct PEAA functionalized COF (TzDHNDA-PEAA). The prepared TzDHNDA-PEAA was stable up to 380 °C and used as stationary phase to make TzDHNDA-PEAA coated capillary column for gas chromatographic separation of isomers. The TzDHNDA-PEAA coated capillary column showed a high column efficiency for n-dodecane (12417 plates m^-1, 120 °C) and high resolution separation of the isomers of fluoroaniline (R_m-/o-=3.2, R_p-/m-=2.4), chloroaniline (R_m-/o-=5.7, R_p-/m-=1.8), nitrotoluene (R_p-/o-=2.2, R_m-/p-=1.7), pinene (R_β-/α-=2.4), ionone (R_β-/α-=4.8) and 1,3-dichloropropene (R_E-/Z-=2.0). The fabricated column offered better separation of chloroaniline isomers than commercial capillary columns InertCap WAX, InertCap 1701 and InertCap 5. The introduced benzene ring, secondary amine and carbonyl groups of PEAA into the COF TzDHNDA significantly improved the resolution of isomers due to the enhanced hydrogen-bonding and π-π interactions. This work shows that post-modification strategy is an effective way to prepare novel COFs for chromatographic separation of isomers.