High Temperature HPLC has become recently available for the analysis of polyolefins, field where it is better known under the name of Interaction Chromatography. It was first used in Solvent Gradient Interaction Chromatography mode (SGIC) and it is today extended with the use of a thermal gradient instead, also known as Thermal Gradient Interaction Chromatography (TGIC).
The TGIC technique using carbon based adsorbents was developed by The Dow Chemical Company to characterize the composition distribution in polyethylene copolymers. This technique requires a cooling (adsorption) and a heating (desorption) step. Elution of the sample takes place in that last heating step, observing a linear dependence of comonomer content to desorption temperatures in a similar manner to TREF and CEF, and being molar mass independent above 20,000 Da. TGIC will adsorb polymer molecules by the level of molecular surface in contact with the surface of the adsorbent, thus it may discriminate polymers by the level of irregularities in the chain, in a similar approach to crystallization techniques. TGIC, however separates by adsorption and no co-elution is expected.
Resolution in TGIC is lower than in crystallization techniques but it has the possibility to extend the range of polymers to be analyzed towards the amorphous region which is limited by crystallization techniques. Then, the analyses of elastomers and other amorphous polyolefins are the main application of TGIC. TGIC is performed with a single solvent, typically o-DCB or 1, 2, 4 TCB in a Crystallization Elution Fractionation instrument (CEF) with the standard autosampler, injection system and an infrared detector, only requiring to replace the TREF column by a TGIC column.