CROWN ETHERS AS STATIONARY PHASES IN GAS-CHROMATOGRAPHY - COMPARISON BETWEEN DIBENZO-18-CROWN-6, DIBENZO-24-CROWN-8 AND DICYCLOHEXANO-24-CROWN-8 WITH RESPECT TO POLARITY, SELECTIVITY AND STABILITY

Chromatographic characteristics, including thermal stability, polarity and selectivity, of dibenzo-18-crown-6 (DB18C6), dibenzo-24-crown-8 (DB24C8) and dicyclohexano-24-crown-8 (DCH24C8) were compared. Phase transition studies were carried out by plotting graphs of log(specific retention volume) against the inverse of absolute temperature. Nitrochlorobenzene, nitrophenol, nitroaniline, chloroaniline, cresol, chlorophenol and dimethylphenol isomers were injected onto these crown ether stationary phases at 3%, 10% and 20% loadings. Dimethylphenol and nitrochlorobenzene isomers were separated well on 10% DB24CB and 10% DCH24C8 columns. DB18C6 is useful for the direct analysis of nitrophenol and nitroaniline isomers without any derivatization.