**5. Conclusions**

Gas chromatography is a well-established technique for the determination of TCAs in biological matrices. GC methods are considered rapid, simple, accurate, e fficient and robust. In recent years, a lot of progress has been made in the field of sample preparation to replace the conventional techniques (protein precipitation, SPE, and LLE). For this purpose, various microextraction techniques such as LPME, SPME, MSPE, etc. have been implemented. These techniques are in compliance with the principles of "green chemistry". Moreover, novel materials have been synthesized and used to enhance preconcentration factors and to develop accurate methods with low limits of detection, which together with high recovery values can be achieved by GC, while sensitivity and selectivity can be higher than those of HPLC. However, a wide variety of materials such as metal–organic frameworks, graphene-oxide nanoparticles, etc. can be tested for such purposes. Additionally, recently developed microextraction techniques such as fabric phase microextraction and capsule phase microextraction can be also tested [82,83].

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

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