**4. Conclusion**

None of the three columns tested offers a complete separation of the injected PAH and methyl-PAH isomers. On the SLB-ILPAH column 22, isomers overlapped at more than 50% of the peak height. The phenyl arylene column showed an overlap of 19 isomers and the 50% phenyl-polysiloxane phase of 13 isomers. Also, none of the columns was able to totally resolve all 16 EPA PAHs. The 50% phenyl-polysiloxane column showed the best overall resolving power and is, therefore, currently considered the best option for the PAH and methyl-PAH analysis.

However, the SLB-ILPAH column is interesting because of a strongly deviating elution pattern, which is due to the different type of interactions between the analytes and the stationary phase. That makes the ionic liquid column interesting for specific separations that cannot be obtained on one of the other two columns or possibly on other traditional phases. A huge advantage of the ionic liquid column is, for example, the total separation of chrysene from triphenylene. An additional advantage is that using this ionic liquid phase, together with e.g. the 50% phenyl-polysiloxane phase, may result in a (semi-)orthogonal separation of PAHs and methyl PAHs in one GC×GC run.

The ionic liquid SLB-ILPAH column and the high phenyl content 50% phenyl-polysiloxane column both show better thermal stability with less bleeding compared to that of the phenyl arylene "low bleed" column. This low bleeding is an asset for GC×GC because often, more polar columns are used, which show higher bleeding.

**Author Contributions:** Conceptualization, J.B. and E.S.; methodology, J.B. and E.S.; validation, J.B. and E.S.; formal analysis, E.S.; investigation, E.S.; resources, J.B.; data curation, E.S.; writing—original draft preparation, E.S.; writing—review and editing, J.B. and E.S.; visualization, E.S.; supervision, J.B.

**Funding:** The research received no external funding.

**Acknowledgments:** The authors thank Sigma-Aldrich for making the ionic liquid column available.

**Conflicts of Interest:** The authors declare no conflict of interests.
