Retention Behavior of Aromatic Compounds on a Poly(butylene terephthalate) Stationary Phase: Effect of Mobile Phase Composition

A poly(butylene terephthalate) (PBT)-coated silica gel particle was introduced as a stationary phase in liquid chromatography, and the retention mechanism of the PBT stationary phase was investigated by measuring the retention of various aromatic and polar compounds including nucleosides under various types of mobile phase conditions. The retention of aromatic compounds with alkyl functional group(s) in the chemical structure was studied using methanol or acetonitrile as the mobile phase component. Even in the acetonitrile/water mobile phase, where π–π interactions were normally suppressed, the retention trend based on the typical hydrophobic behavior was found, confirming that π–π interactions could play a small role in the specific retention behavior. In the retention tendency for disubstituted benzenes using acetonitrile/water mobile phases with different water contents, the mobile phase composition could have a minimal effect on the selectivity for these isomers. However, for the separation of nitrotoluene, an excellent selectivity was observed when acetonitrile/water = 50/50 was used as the mobile phase. This is presumably because nitrotoluene, which has a high dipole moment, has a large contribution from dipole-dipole interactions on the PBT stationary phase. Comparing the retention of nucleoside on the PBT and typical octadecylsilica stationary phases, it was shown that a larger retention for these analytes on the PBT stationary phase. The retention mechanism of the PBT stationary phase could include a dipole-dipole interaction in addition to a hydrophobic interaction, resulting in a unique retention trend of various isomeric aromatic compounds on the PBT phase.