Inverse gas chromatography

Analytical gas chromatography A (top) compared with inverse gas chromatography B (bottom). While in gas chromatography a sample containing multiple species is separated into its components on a stationary phase, Inverse gas chromatography uses injection of a single species to probe the characteristics of a stationary phase sample.

Inverse gas chromatography is a physical characterization analytical technique that is used in the analysis of the surfaces of solids.^[1]

Inverse gas chromatography or IGC is a highly sensitive and versatile gas phase technique developed over 40 years ago to study the surface and bulk properties of particulate and fibrous materials. In IGC the roles of the stationary (solid) and mobile (gas or vapor) phases are inverted from traditional analytical gas chromatography (GC); IGC is considered a materials characterization technique (of the solid) rather than an analytical technique (of a gas mixture). In GC, a standard column is used to separate and characterize a mixture of several gases or vapors. In IGC, a single standard gas or vapor (probe molecule) is injected into a column packed with the solid sample under investigation.

During an IGC experiment a pulse or constant concentration of a known gas or vapor (probe molecule) is injected down the column at a fixed carrier gas flow rate. The retention time of the probe molecule is then measured by traditional GC detectors (i.e. flame ionization detector or thermal conductivity detector). Measuring how the retention time changes as a function of probe molecule chemistry, probe molecule size, probe molecule concentration, column temperature, or carrier gas flow rate can elucidate a wide range of physico-chemical properties of the solid under investigation. Several in depth reviews of IGC have been published previously.^[2][3]

IGC experiments are typically carried out at "infinite dilution", where only small amounts of probe molecule are injected. This region is also called Henry's law region or linear region of the sorption isotherm. At infinite dilution probe-probe interactions are assumed negligible and any retention is only due to probe-solid interactions. The resulting retention volume, V_R^o, is given by the following equation:

${\displaystyle V_{R}^{\circ }={\frac {j}{m}}F(t_{R}-t_{o}){\frac {T}{273.15}}}$

where j is the James–Martin pressure drop correction, m is the sample mass, F is the carrier gas flow rate at standard temperature and pressure, t_R is the gross retention time for the injected probe, t_o is the retention time for a non-interaction probe (i.e. dead-time), and T is the absolute temperature.