Chromatographic Behavior of Polar Compounds With Liquid vs. Supercritical Fluid Mobile Phases

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Abstract
Aromatic amines and azaarenes are successfully separated on both analytical scale and microbore packed columns via supercritical fluid chromatography (SFC). Because microbore columns can be used with commercial instruments that have density and pressure programming capability, higher sensitivity and resolution are obtained. Separation is compared with both reversed-phase and normal-phase high-performance liquid chromatography (HPLC). The SFC separation has a much higher degree of resolution, and method development is easier than with HPLC modes. Flame-ionization (FID), ultraviolet (UV), and Fourier transform infrared (FTIR) on-line detectors are used for detection and identification. A comparison of restrictors indicates that an optimized separation also requires an optimized restrictor size because different restrictor sizes have different linear velocities. A retention mechanism study for these nitrogen-containing compounds with SFC shows that the elution order not only depends on basicity and steric hindrance, but also on the solubility of the solute in CO2. The results show that lower density solubility is a major factor in elution order; however, at higher density, basicity and steric hindrance are more important.

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