## 5 Bar Adsorptive Microextraction  
Bar-adsorptive microextraction (BA\(\upmu\)E) was firstly introduced by [PERSON] et al. in 2010 [77]. Theoretical aspects on BA\(\upmu\)E were described in the research work of [PERSON] et al. [78]. It is a significant sorption-based micro-technique designed to address certain limitations of stir-bar sorptive extraction. This technique enables the extraction of polar and non-polar compounds by utilizing alternative materials as sorbent phases. In its most widely recognized configuration, BA\(\upmu\)E employs polypropylene cylindrical bars (15 mm in length and 3 mm in diameter), with the sorbent phase affixed using an adhesive film. A key advantage of the BA\(\upmu\)E technique is the possibility of using various sorbent phases that enhance the extraction selectivity for specific analytes. Additionally, it supports the use of environmentally friendly sorbent materials with notable physicochemical properties, ensuring efficient extraction performance.  
A high-throughput BA\(\upmu\)E and microliquid desorption was proposed by [PERSON] for the determination of ketamine and worketamine in urine samples [79]. Since both analytes present a weak basic character, the urine samples were initially basified at pH 11 and then extracted using NVP-DVB sorbent for 30 min at 1800 rpm. The desorption was carried out through cavitation for 15 min using 100 uL methanol. The authors used a similar apparatus to the one described in their previous study [80]. According to the authors, this apparatus presented remarkable effectiveness as a rapid tool for the simultaneous microextraction of up to 100 samples. Matrix-matched calibration curves were constructedin the range of 5-1000 \(\upmu\)g/L with \(r^{2}>\) 0.999. No matrix effects were observed, as the recoveries were acceptable, being in the range of \(-\)9.1-9.0. One year later, the same group of authors utilized the same microextraction technique to determine six tricyclic antidepressants (namely amitriptyline, dinarserin, trimipramine, inipramine, mirtazapine, and dosulepin) in urine using large-volume injection GC-MS [81]. One-variable-at-a-time was used for the optimization of the BA\(\upmu\)E procedure. Six different polymer coatings were studied, and it was found that C\({}_{18}\) and Strata-cyano materials provided the best selectivity. These polymers differ significantly, as the C\({}_{18}\) polymer contains a long aliphatic chain that facilitates strong hydrophobic interactions with the aliphatic chains in the molecular structures of the target drugs. On the other hand, a cyano-based polymer enables dipole-dipole interactions via its cyano group and the electronegative elements (N and/or S) within the chemical structures of the six drugs. For the analyte elution, an ultrasonic irradiation (100 W) was applied to the sorbent coatings for 15-30 min, while methanol was employed as the elution solvent. More recently, [PERSON] et al., inspired by the previous work of [PERSON] [81], developed a BA\(\upmu\)E protocol for the isolation of alkylamine stimulants (1,3-dimethylbutylamine, 1,4-dimethylpentylamine, heptaminol, isometheptene, 1,5-dimethylhexylamine, and tuaminoheptane) from human urine matrixes [82]. The identification of the analytes was carried out in SCAN mode in the range of 70-600 \(m/z\). The analytes were derivatized with \(N\)-methyl-N-trimethylsilyl-trifluoracetamide at 80 \({}^{\circ}\)C for 10 min in order to increase their volatility. A temperature gradient from 90 \({}^{\circ}\)C to 300 \({}^{\circ}\)C at a rate of 20 \({}^{\circ}\)C/min was followed to separate the analytes. As the sample pH is a crucial parameter that can influence the extraction recovery of the analytes, this value was studied in the range of 2-11. The stability of the target analytes in the final extract prior to GC-MS analysis was examined up to 144 h after preparation. The methodology proved to be an excellent alternative, as it is cost-effective, user- and eco-friendly, and requires only a small volume of urine sample (1 mL).