## 1 Introduction  
According to the United Nations Office on Drugs and Crime (UNDOC), new psychoactive substances (NPS) are \"new narcotic or psychotropic drugs that are not listed in the Single Convention on Narcotic Drugs of 1961 or the Convention on Psychotropic Substances of 1971, but which may pose a public health threat comparable to that posed by substances listed in those conventions\" [1]. These compounds have become an alternative to classic drugs, such as cocaine, ecstasy, heroin, or cannabis. By 2020, several hundreds of NPS have been detected and around 830 are now being monitored by the European Monitoring Centre for Drug and Drug Addition (EMCDDA). Synthetic cathinones (SC) are the second largest class of NPS being monitored by the EU Early Warning System (19%), after synthetic cannabinoids (24%) [2]. Cathinone is the main active compound present in the _Catha edulis_ (Khat) plant. The use of this plant for its stimulant effects similar to amphetamine and methamphetamine goes back hundreds of years and is still extensively used by many people, mainly in East Africa and in the Arabic Peninsula [3]. Similarly, SC intends to mimic these effects. Since its first appearance in drug markets in the mid 2000s, many SCs have been identified, e.g., 4-methylmethachathione (mephedrone), 3,4-methylenedioxypyrovalerone, n-phyrone, 3,4-methylenedioxypyrovalerone (MDPV), \(\alpha\)-pyrrolidinopentiophenone (\(\alpha\)-PVP), 3,4-Methylenedioxy-\(\alpha\)-pyrrolidinopropiopiophenone (MDPPP), methylene, butylone, 4-methylethethionine, 4-fluoromethathinone, \(\alpha\)-pyrrolidinopentiothiophene (\(\alpha\)-PVT), and 4'-methylenedioxy-\(\alpha\)-pyrrolidinobutiophenone (MDPBP), among many others [2]. Global seizures of SCs have steadily increased until it peaked in 2017. Nevertheless, the number of countries and quantities have increased, and SCs represented 8% of the global seizures of synthetic NPS (excluding ketamine) by weight in 2019 [1]. SCs are a particular toxic class of NPS, where several effects have been associated with its consumption, including nausea, hallucination, high blood pressure, and even death [4; 5; 6; 7]. For these reasons, there is a need for innovative analytical methodologies that enable its screening in many types of biological matrices, especially via non-invasive approaches (e.g., oral fluids). Other advantages of using this biological matrix as an analysis medium are its fast sampling time, its difficulty to adulterate, its minimum or zero health hazards to the subject, and its representing of the free fraction of a drug [8; 9]. Furthermore, it has already been shown that oral fluids can be used to monitor SCs since MDPV and \(\alpha\)-PVP have already been detected in the ranges of 20.5-831.7 and 81.9-935.0 \(\mu\)g L\({}^{-1}\), respectively [10]. Several analytical methodologies have been proposed for the determination of SCs in oral fluids, such as gas chromatography (GC) or high-performance liquid chromatography (HPLC) hyphenated to mass spectrometry systems (GC-MS and LC-MS or LC-MS/MS) [9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. These methodologies always include a previous enrichment step. Nowadays, the most popular miniaturized sorption-based extraction methods are solid-phase microextraction (SPME) and stir bar sorptive extraction (SBSE) [19]. However, other static microextraction techniques such as absorptive microextraction (BA\(\mu\)E) have already proven to be suitable for the trace analysis of polar to non-polar analytes in aqueous media, including the analysis of legal and illegal drugs in several types of biological matrices [20; 21; 22; 23; 24]. It must be emphasized that although SCs suffer partial thermal degradation during GC-MS analysis [25; 26], it is pertinent to develop methodologies without derivatization since they provide more comprehensive and faster results.