## 3 Results and Discussion
### Method Validation  
The optimized experimental conditions achieved for monitoring the UV filters in aqueous media were as follows; microextraction stage: PS-DVB phase, 16 h (750 rpm), pH 2.0, and 20% of NaCl; back-extraction stage: mobile phase (100 \(\upmu\)L), 10 min under sonication. In order to validate the proposed methodology, assays were performed on 25 mL of ultra-pure water samples spiked with the target compounds at concentrations ranging from 0.16 to 16.0 \(\upmu\) L\({}^{-1}\) for PBS and 0.80 to 80.0 \(\upmu\) L\({}^{-1}\) for BZ4. The analytical limits were also evaluated and calculated, with S/N of 3 and 10, respectively. Table 2 summarizes the average extraction efficiency (61.8 \(\pm\) 9.1% for PBS and 69.5 \(\pm\) 4.8% for BZ4), LODs (0.04 \(\upmu\)g L\({}^{-1}\) for PBS and 0.20 \(\upmu\)g L\({}^{-1}\) for BZ4), LOQs (0.16 \(\upmu\)g L\({}^{-1}\) for PBS and 0.80 \(\upmu\)g L\({}^{-1}\) for BZ4), and determination coefficients (0.9985 for PBS and 0.9993 for BZ4) obtained for the proposed methodology to monitor the two UV filters, under optimized experimental conditions. Repeatability studies were then evaluated in terms of interday (three replicates a day in three consecutive days) and intraday (five replicates performed in the same day) assays, in which the data obtained showed RSD below 12%. From the validation data, the proposed methodology performed by BA\(\upmu\)E(PS-DVB)-\(\upmu\)LD/HPLC-DAD showed remarkable analytical performance for trace analysis of the two UV filters under study.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**UV Filter**} & **Extraction** & \multirow{2}{*}{**LOD**} & \multirow{2}{*}{**LOQ**} & \multirow{2}{*}{**Dynamic**} & \multirow{2}{*}{**Range**} & \multirow{2}{*}{**Slope**} \\  & **Efficiency** & & & & & \\  & **(\%)** & & & & & \\ \hline
**PBS** & 61.8 \(\pm\) 9.1 & 0.04 & 0.16 & 0.16–16.0 & 0.9985 & 9.25 \\ \hline
**BZ4** & 69.5 \(\pm\) 4.8 & 0.20 & 0.80 & 0.80–80.0 & 0.9993 & 2.47 \\ \hline \end{tabular}
\end{table}
Table 2: Average recoveries, LODs (limits of detection), LOQs (limits of quantification), linear dynamic ranges, determination coefficients (\(r^{2}\)), and slopes obtained for the two UV filters by BA\(\upmu\)E(PS-DVB)-\(\upmu\)LD/HPLC-DAD, under optimized experimental conditions.  
Figure 2: Effect of pH (**a**), equilibrium time (**b**), ionic strength (**c**), and matrix polarity (**d**) on the microextraction efficiency for both UV filters in ultra-pure water. The error bars represent the standard deviation of three replicates.  
By comparing the proposed methodology with other passive sampling approaches, such as stir bar sorptive-dispersive microextraction (SBSDME; recoveries yields of \(58\pm 2\) and \(55\pm 5\%\) and LODs of \(2.8\)\(\mathrm{\SIUnitSymbolMicro}\)\(\mathrm{L}^{-1}\) and \(1.6\)\(\mathrm{\SIUnitSymbolMicro}\)\(\mathrm{L}^{-1}\) for PBS and BZ4, respectively) [14], BA\(\mathrm{\SIUnitSymbolMicro}\)E presented much higher extraction efficiency and lower LODs, being an effective analytical alternative for monitoring both UV filters in aqueous media.  
The presence of the sulfonic groups in the chemical structure of both target analytes makes them highly soluble, hindering the corresponding microextraction. Consequently, few studies are reported in the literature regarding the analysis of very hydrophilic UV filters, and most of them use SPE as sample enrichment, which is more expensive, requires larger sample volumes, and is not eco-friendly. In short, the methodology proposed herein is a remarkable contribution as an alternative analytical methodology for monitoring trace levels of polar UV filters in aqueous media, besides being eco-friendly, user-friendly, very cost-effective and in compliance with the routine work.