Inverse Size Exclusion Chromatography (SEC) is a liquid chromatogrpahy method to investigate pores in a porous material under normal operating conditions. It relies on the permeation of test molecules into the porous material and relating sample retention to pore size using chromatographic separation theory developed by Cassasa and Gorbunov. The best and most widely available instrument for running the analysis is a conventional LC instrument, which is present in most labs. Basic GPC/SEC equipment can be used to perform the measurements.
The main difference to traditional GPC/SEC is that, the unknown sample, the porous material to be characterized, is not dissolved in the mobile phase and injected, but packed into a chromatography column which is then installed into the GPC/SEC system. Several samples or probe molecule, consisting of molecules of different and known sizes/molar masses and dissolved in the mobile phase, are then injected onto the column. The retention volume or retione time is the measured, all results are retrieved from a table relating molecular size to chromatographic retention.
Detailed analysis of pore accessibility yields a multitude of analytical results, which can be derived from the pore size distribution; therefore the following results are accessible with this technique:
- average pore size
- dispersity of pore sizes
- pore size distribution
- pore volume
- specific surface area
- optimum size of guest molecule
- selectivity parameters
Results can be presented in many ways (differential or cumulative representation, volume or surface distribution).