**4. Discussion**

A lot of progress was made in this scientific field during 1980–2000. Both packed columns and capillary columns were used for this purpose. Moreover, various detection systems such as NPD, FID, SID, MS, were adopted. Liquid–liquid extraction was the most frequent sample preparation technique, while various solvents were tested. Derivatization with various reagents, resulting in di fferent trifluoroacetyl, heptafluorobutyryl or carbethoxyhexafluorobutyryl, were also employed. Other conventional sample preparation techniques including protein precipitation and solid phase extraction have also been used.

However, due to the rapid development of high-performance liquid chromatography, the application of gas chromatography was significantly reduced after 2000. This can be attributed to the fact that HPLC, especially when coupled with mass spectrometry, can provide highly sensitive methods and extremely low limits of detection. Until today, HPLC is a well-established technique for the determination of various drugs (antidepressants, antipsychotics, antiepileptics, etc.).

The recent advances in the use of gas chromatography for the determination of TCAs in biofluids focus on the implementation of novel sample preparation techniques, such as LPME, SPME, EME, etc. Additionally, novel materials have been synthesized and tested for the extraction of tricyclic antidepressants from biofluids. These techniques follow the principles of "green chemistry" and have numerous advantages compared to conventional sample preparation methods.

The reported GC methods can be classified into the more sensitive GC-MS methods and the GC methods coupled with other detection systems (mostly ECD, NPD, and FID). The GC-MS methods combine the resolution ability of gas chromatography with the highly sensitive detection ability of mass spectrometry. Therefore, highly sensitive methods can be developed and low LODs can be obtained. Satisfactory LOQ values can be obtained both with GC-FID and with GC-NPD techniques. As shown in Table 1, by using a preconcentration method in combination with GC-MS, limits of quantification can be reduced to 0.2 ng/mL, while, with GC-FID and GC-NPD, they are more than 0.5 ng/mL and 44 ng/mL, respectively. This is of high importance especially for forensic toxicology applications in which highly sensitive and specific GC-MS (or LC-MS, LC-MS/MS) are required.
