In some complex resins, a fractionation by TREF may not render the expected results, while CRYSTAF mode will do it properly. The analyst should select the preferred method by performing TREF and CRYSTAF analysis on the parent sample.
In this fractionation method, the sample is dissolved and then the desired fractions are crystallized by programming decreasing temperature steps. At each temperature step, part of the sample will crystallize corresponding to the fraction at this cut, while the rest will remain in solution. The crystallized part will be separated from the solution, re-dissolved and finally it will be filtrated and collected as the corresponding temperature cut fraction. The remaining solution will repeat the same steps for each following temperature cut.
This fractionation method is more time consuming than the TREF mode because of the re-dissolution and crystallization steps, which need to be performed for each fraction.