## 4 Discussion
However, the best results were obtained at almost neutral pH, suggesting that an equilibrium between neutral and ionized forms of the compounds are favored to the microextraction process. This may be attributed to the lipophilic-hydrophilic nature of Straa-X. Finally, since the target SCs presented mostly non-polar characteristics, with log \(p\) values between 2.99 and 3.36, it was expected that the addition of salt or an organic modifier would not increase the overall efficiency [22]. It must be emphasized that the back-extraction stage and the overall analytical process uses only 100 \(\mu\)L of organic solvent per sample (MeOH/ACN, 1/1, \(v/v\)). This represents a 16 or 15-fold decrease when compared to analytical methodologies that employed dispersive liquid-liquid microextraction [13] or solid-phase extraction [17], respectively, without significant loss in efficiency. Additionally, the proposed methodology is absent of memory effects since BA\(\mu\)E devices are designed to be used only once because they are very cheap, as well as easy and simple to prepare in a lab. This is a great advantage over other microextraction devices such as microextraction by packed sorbent [11], which has a limited number of applications before exhibiting a decrease in efficiency. Furthermore, these devices always need additional cleaning and washing steps after being used. To the best of our knowledge, this is the first work that combines a microextraction sorption-based technique followed by GC-MS analysis for screening traces of \(\alpha\)-PVP, \(\alpha\)-PVT, and MDPV in oral fluid samples. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/analytica3010002/s1](https://www.mdpi.com/article/10.3390/analytica3010002/s1)]([https://www.mdpi.com/article/10.3390/analytica3010002/s1](https://www.mdpi.com/article/10.3390/analytica3010002/s1)), Figure S1: Mass spectra of \(\alpha\)-PVP, \(\alpha\)-PVT and MDPV obtained by GC-MS under full-scan mode; Figure S2: Effect of the back-extraction solvent (a) time (b) on the microextraction of the three SCs in aqueous media, obtained by BA\(\mu\)E-\(\mu\)LD/GC-MS(SIM). The error bars represent the standard deviation of three replicates; Figure S3: Effect of stirring rate on the microextraction of the three SCs in aqueous media, obtained by BA\(\mu\)E-\(\mu\)LD/GC-MS(SIM). The error bars represent the standard deviation of three replicates; Figure S4: Effect matrix pH on the microextraction of the three SCs in aqueous media, obtained by BA\(\mu\)E-\(\mu\)LD/GC-MS(SIM). The error bars represent the standard deviation of three replicates; Figure S5: Effect of matrix MeOH (a) and NaCl (b) content on the microextraction of the three SCs in aqueous media, obtained by BA\(\mu\)E-\(\mu\)LD/GC-MS(SIM). The error bars represent the standard deviation of three replicates. **Author Contributions:** Conceptualization, S.M.A. and H.G. ; methodology, A.M.S. and M.M.M.-S.; validation, S.M.A., N.R.N. and H.G. ; formal analysis, A.M.S., S.M.A. and H.G. ; investigation, A.M.S. and M.M.M.-S.; writing--original draft preparation, A.M.S. and S.M.A. ; writing--review and editing, N.R.N., H.G. and J.M.F.N. ; supervision, N.R.N., H.G. and J.M.F.N. ; funding acquisition, H.G. and J.M.F.N. All authors have read and agreed to the published version of the manuscript. **Funding:** The authors thank Fundacao para a Ciencia e a Tecnologia (Portugal) for financial support for the projects UIDB/00100/2020 and UIDP/00100/2020 granted to CQE (Centro de Quimica Estrutural), UID/04292/2020 granted to MARE (Marine and Environmental Sciences Centre), UIDP/04046/2020 and UIDB/04046/2020 granted to BioISI (BioSystems and Integrative Sciences Institute), and the Ph.D. grant (SFRH/BD/107892/2015) and for the contract established from DL 57/2016. **Data Availability Statement:** All relevant data are within the manuscript.