## 3 Materials and Methods
### Experimental Set-Up
#### 3.2.2 Experimental Optimization Conditions (HS-SPME and HS-BA\(\mu\)E Assays)  
To optimize the HS-SPME experimental conditions, 1 \(\upmu\)L of a mix solution of the five selected BVOCs (100.0 mg L\({}^{-1}\)) and IS (20.0 mg L\({}^{-1}\)) was spiked at the bottom of 40 mL glass flasks, which resulted in final masses of 100 and 20 ng for each VOC and IS, respectively. The flasks were then closed with septum caps suitable for the HS analysis and preconditioned in a thermostatic sand bath (30 min) at the selected temperature. The microextraction was performed by exposing the SPME fiber to the HS of the flasks (Figure 2a). After the microextraction, the SPME fiber was collected in the device and removed from the sample flasks, it being immediately inserted into and exposed to the GC-MS injection port for the thermal desorption (TD) and direct analysis of the extracted BVOCs. All analyses were performed in triplicate. Blank assays without spiking were also performed to assess the absence of analyte transference and possible carry-over. The approach used for the optimization of the diverse experimental parameters consisted in a one-variable-at-a-time (OVAT) strategy; while the study of the behavior of one variable was being performed, all the remaining were fixed. The selected parameters for the optimization process of the HS-SPME methodology were SPME fiber material (PDMS, PDMS/DVB, CAR/PDMS and DVB/CAR/PDMS), thermal desorption time (1, 2, 3, 4 and 5 min), equilibrium time (5, 10, 15, 30, 45 and 60 min) and thermostatization temperature (30, 40 and 50 \({}^{\circ}\)C), in accordance with previous reports [7; 9; 10; 13; 14; 20; 22].  
For the optimization of the HS-BA\(\mu\)E experimental conditions, 100 \(\upmu\)L of a mix solution containing the five selected BVOCs (5.0 mg L\({}^{-1}\)) was spiked at the bottom of 5 mL glass flasks, which corresponds to a total of 500 ng of each. The previously conditioned BA\(\mu\)E devices were placed into the HS of the flasks (Figure 2b), which were immediately closed up and placed in a thermostatic sand bath for the enrichment step. After the microextraction, the BA\(\mu\)E devices were removed from the glass flasks with clean tweezers and transferred into glass vials with inserts containing 90 \(\mu\)L of an organic solvent; then, they were subjected to an ultrasonic treatment (Branson 3510 E-DTH, 42 +/ - 2.5 kHz, 100 W, Switzerland) for liquid desorption (LD). Subsequently, 10 \(\mu\)L of a 20 mg L\({}^{-1}\) IS solution was added into the glass inserts, resulting in a final concentration of 2 mg L\({}^{-1}\). Finally, the BA\(\mu\)E devices were removed from the vial, which were sealed for GC-MS analysis. Each assay and blank were performed in triplicate. The optimization of each experimental parameter was performed in a similar manner as the HS-SPME optimization, i.e., a one-variable-at-a-time (OVAT) strategy. The selected parameters for the optimization process of the HS-BA\(\mu\)E were the sorbent coating material (ACs: CA1, CN1, SX PLUS and R; Ps: S-X, S-DVB, S-CN and HLB), desorption solvent (\(n\)-C\({}_{6}\), DCM, MeOH and ACN), desorption time (15, 30, 45 and 60 min), equilibrium time (0.5, 1, 2, 3 and 16 h) and thermostatization temperature (20, 30 and 40 \({}^{\circ}\)C), according to previous works [5; 13; 18; 19; 23; 24]. The data obtained by the HS-BA\(\mu\)E/GC-MS studies were determined by comparing the signal areas with the standard solutions from all five target BVOCs.