## 3 Materials and Methods
### Experimental Set-Up
#### 3.2.3 Validation Assays  
For validation purposes, several assays were performed for both analytical methodologies under optimized experimental conditions. Two experimental configurations were adopted; for the HS-SPME(PDMS/DVB)/GC-MS, 1 \(\mu\)L of the BVOCs mix solution (with the desired concentration) and IS (20.0 mg L\({}^{-1}\)) were added into 40 mL glass flasks; for the HS-BA\(\mu\)E(R)/GC-MS, 100 \(\mu\)L of the BVOCs mix solution was spiked into 5 mL glass flasks, using the same procedures as in the previous section. The validation process of both methodologies involved the assessment of several parameters, including linearity, sensitivity, selectivity, accuracy and precision, according to previous studies [5; 7; 9; 13; 14; 18; 19; 23; 24; 25]. Initially, the selectivity of both analytical methodologies was evaluated by verifying the absence of interfering compounds with identical retention times for each analyte, performed by means of both HS-SPME/GC-MS and HS-BA\(\mu\)E/GC-MS analyses of blank assays. Afterwards, calibration curves were plotted by analyzing the calibration standards of the five BVOCs in concentrations ranging from 20.0 to 700.0 mg L\({}^{-1}\) for HS-SPME(PDMS/DVB)/GC-MS (equivalent to total masses of 20 and 700 ng, respectively) and between 1.0 and 5.0 mg L\({}^{-1}\) for HS-BA\(\mu\)E(R)/GC-MS (equivalent to total masses of 100 and 500 ng, respectively). The linearity was then assessed through the lack-of-fit test, as well as the verification of the residual dispersion and determination coefficient (\(r^{2}\)) of each calibration plot [26]. The sensitivity of both methodologies was evaluated by determining the limit of detection (LOD), limit of quantification (LOQ) and lower limit of quantification (LLOQ). The LOD and LOQ correspond to signal-to-noise (S/N) values of 3/1 and 10/1, respectively, while the LLOQ is the lower concentration, which is measurable according to accuracy and precision acceptance criteria and usually used as the first point of the calibration plot. To assess intra-day (\(n\) = 6) as well as inter-day (\(n\) = 6, during 3 consecutive days) accuracy and precision, assays were performed under optimized conditions for the analysis of the HS of the glass flasks after spiking with the five BVOCs and the IS mix solution. For the HS-SPME(PDMS/DVB)/GC-MS analytical approach, the IS concentration was maintained at 20 mg L\({}^{-1}\) (equivalent to 20 ng); meanwhile, four spiking levels of the analyte were evaluated: the LLOQ, followed by a low, medium and high concentration, equivalent to masses of 20, 100, 400 and 700 ng, respectively, from each VOC; for the HS-BA\(\mu\)E(R)/GC-MS assays, the IS concentration was 2 mg L\({}^{-1}\) (equivalent to 20 ng); meanwhile, the selected four concentrations for the BVOCs mix were equivalent to 100, 200, 300 and 500 ng. The acceptance criteria used for accuracy and precision were the percentage of the relative error (%RE) and the relative standard deviations (RSDs), which were \(\leq\)15% for all spiking levels, except at the LLOQ, where values of RSD and RE \(\leq\) 20% were accepted [13; 26]. Whenever indicated, all validation assays were performed in triplicate.