## 2 Results and Discussion
### Optimization of the BA\(\mu\)E-\(\mu\)LD Efficiency
#### 2.2.2 Microextraction Parameters
However, above 5% of NaCl, the \"salting-in\" effect can also occur, where the analytes can interact with the salt ions through electrostatic interactions and decreasing the recovery, in agreement with previous reports [41]. The equilibrium time was the next parameter to be optimized, since in equilibrium conditions the maximum sensitivity and precision are achieved [8]. In Figure 4d, it is possible to observe that the best results are achieved when the equilibrium time lasts for 16 h, in agreement with previous reports, where a comparable behavior was observed [23]. Even so, despite the substantial time involved, the analytical process can be performed overnight without any special requirement. It is noteworthy that 16 h are needed to achieve maximum recovery yields, although we can greatly reduce the equilibrium time and still obtain efficiencies of about 65% by using only 1 h.  
Finally, the effect of the sample dilution was also studied and, as expected, by keeping the amount of the sorbent phase fixed and decreasing the sample volume, the recovery yields increase due to the increase in the concentration factor. Thus, with a larger sample volume, an instrumental response should increase due to the greater enrichment of the extracted analytes, with the consequence of an increase in the equilibrium time [8; 42; 43; 44]. In this sense, the variation of the sample volume was evaluated for five different levels (1.5, 5.0, 10.0, 25.0 and 40.0 mL), with the results (data not shown) showing that the best response was obtained with the use of only 5 mL of aqueous solution. From the beginning, the BA\(\mu\)E devices used in this work were prepared with PP subtracts. Nevertheless, to make them more compatible with the instrumental systems, as well as to improve the routine work, new generation devices were already proposed using nylon subtracts [23]. They are much smaller, more flexible, user-friendly, allows the back-extraction stage in an only single step and compatible with the injection operation of the conventional instrumental systems. So far, these devices had only been combined with HPLC systems. In this work, we decided to combine, for the first time, the new generation BA\(\mu\)E devices with a GC-MS system. For this purpose we decided to compare the performance of the conventional devices with the new generation ones, as depicted in Figure 5. From the data obtained, very similar performances are achieved between both devices. Therefore, given the advantages of the nylon subtracts, these were adopted for the validation and application sections. At the end of the optimization procedure, the attained recovery yields were between 80.5 and 99.6% for the six target TCAs (RSD < 12.1%), under the following experimental conditions; extraction stage: 5 mL of ultrapure water spiked with 100 \(\mu\)L of TCAs mix solution (500.0 \(\mu\)g L\({}^{-1}\)), pH 12, 5% NaCl, 3 h (990 rpm); back-extraction stage: 90 \(\mu\)L MeOH/ACN (50:50), 30 min under ultrasonic treatment (42 \(\pm\) 2.5 kHz, 100 W). Figure 5: Effect of substrate type on the microextraction efficiency for the six TCAs in aqueous media by BA\(\mu\)E(C18)-\(\mu\)LD/LVI-GC-MS(SIM). The error bars represent the standard deviation of three replicates.