## 2 Biosorbent-Based Extraction Phases
### Cork as a Biosorbent
SPME—solid phase microextraction; TAME—thin film microextraction; BAuE—bar-adsorptive microextraction; SPE—solid-phase extraction. When used for OCP determination [15] the extraction efficiency of the cork fiber was attributed mostly to dipole-dipole interactions with the analytes. The authors also reported the occurrence of hydrogen bonds with the compounds containing oxygen atoms. In the work of [PERSON] et al. [16], the cork fiber extraction efficiency for 4-MCB and OD-PABA was compared with PDMS/DVB and PDMS fibers, and the results showed a better extraction efficiency when the cork fiber was used, for both analytes. Cork has also been used with thin film microextraction (TFME) [17]. TFME comprises a new geometry for SPME, aiming to provide more sensitivity for this technique. The device used in TFME consists of a support coated with a thin layer of a sorbent phase that can be used in headspace or immersion mode. Moreover, this technique has been designed to fit a commercially available 96-well plate system providing high-throughput analyses. To date, there has been only one study published using cork with TFME, by [PERSON] et al. in 2017 [17]. The TFME cork coating coupled with 96-well plate system was used as a high-throughput method for the extraction of emerging contaminants in a water sample by high-performance liquid chromatography-diode-array detector HPLC-DAD (Table 1). In this work, analytes with the log K\({}_{\text{ow}}\) ranging from 2.49 to 5.92 were successfully extracted by the cork sorbent phase. Another microextraction technique that used cork as the sorbent phase is called bar-adsorptive microextraction (BA\(\upmu\)E) [18]. The BA\(\upmu\)E device consists of a finely divided powder (up to 5 mg) fixed with suitable adhesives in polypropylene supports with cylindrical bar format. In the experimental procedure, the adsorbing bars are placed in direct contact with the sample, under constant stirring. Due to the low density of the polypropylene support, this floats just below the vortex formed by agitation, preventing direct contact of the bar with the flask's walls containing the sample, thus increasing the useful life of the device. After extraction, the desorption step consists of completely inserting the bar into vials containing a few microliters of a suitable extraction solvent. Cork biosorbent has been used twice with BA\(\upmu\)E. It was first used in 2015 for determination of polar and intermediate polarity compounds (parabens, benzophenone and triclocarban) in water samples by HPLC-DAD [18]. In this study, bars of 7.5 and 15 mm in length were used. Hollow cylindrical polypropylene tubes (15 mm length and 3 mm diameter) were coated with adhesive films followed by a layer of the cork powder (200 mesh). Before use, the bars were conditioned under ultrasound agitation with 250 \(\upmu\)L of acetonitrile (ACN) for 15 min. The half bars (length of 7.5 mm) were obtained by cutting the 15 mm length bar in half. As shown in Table 1, the quantification limits ranged from 1.6 to 20 \(\upmu\)g L\({}^{-1}\) using a bar of 15 mm and 0.64 to 8 \(\upmu\)g L\({}^{-1}\) using a bar of 7.5 mm. The second study was published in 2017. At this time, the use of cork BA\(\upmu\)E bars was extended to biological samples for determination of two potential lung cancer biomarkers (hexanal and heptanal) in human urine by HPLC-DAD [19]. In this study, the adsorptive bar surface was impregnated with 2,4-dinitrophenylhydrazine (DNPH) so that derivatization and extraction were accomplished simultaneously on the surface of the bar under acidic conditions. Relative recoveries in urine samples varied from 88 to 111% (Table 1). Figure 1 illustrates a scheme of the biobased BA\(\upmu\)E procedure used. According to the authors, one of the main advantages was the low cost of the method, since polypropylene tubes, adhesive and cork obtained from cork stoppers were used to produce the devices.