## 3 Results and Discussion
Electroanalytical measurements confirmed the statistical significance of the linear regression model, as the calculated F-value (F\({}_{\rm cal}\)) of 314.70 exceeded the tabulated F-value (F\({}_{\rm 5\%}\) (1.80)) of 238.90. Similarly, chromatographic results reinforced this finding, with an F\({}_{\rm cal}\) of 1136.00 surpassing the F\({}_{\rm 5\%}\) (1.50) of 230.20. Additionally, both methods yielded an F ratio greater than 1.00, indicating strong statistical reliability. The regression model accounted for 99.64% of OC concentration variations in chromatography and 97.52% in electroanalysis, demonstrating the accuracy of both approaches. Comparison Between Electroanalytic and Chromatographic Approaches for Quantifying OC in Different Sunscreen Samples Using the Standard Additions Method  
As described earlier, all samples (NaCl solutions and swimming pool water) with a known amount of OC were analyzed using both HPLC and electroanalytic methods. The samples were prepared to achieve a concentration of 0.4 mg L\({}^{-1}\), which is within established environmental limits and falls within the linear range of both methods [3; 32; 33]. The OC concentrations provided by the manufacturers of the sunscreens were compared with those determined through electroanalytical and chromatographic methods, as shown in Figure 5. It is worth noting that, while the sunscreen labels indicated the presence of OC, they did not provide quantitative information on its concentration. The amount of OC added to the solutions confirmed that it made up less than 10% of the total formulation. From an experimental perspective, the standard addition method effectively minimized matrix effects for both HPLC and electroanalysis. For HPLC, an increase in peak height was observed with rising OC concentration in sunscreens, consistent with previous studies [7; 14; 15; 34]. In the case of electroanalysis using the GCS, the current response  
\begin{table} \begin{tabular}{c c c c c c} \hline
**Electrode** & **Method** & \begin{tabular}{c} **Linear Range** \\ **(mg L\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **LOD** \\ **(mg L\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **LOQ** \\ **(mg L\({}^{-1}\))** \\ \end{tabular} & **Ref.** \\ \hline Screen-Printed Carbon & DPAdSV & 4.00–108.00 & 1.50 & 4.70 & [30] \\ Carbon Nanofibers Modified & DPAdSV & 17.00–90.00 & 2.20 & 7.60 & [30] \\ Screen-Printed & SWV & \(7\times 10^{-3}\)–0.18 & \(1.2\times 10^{-3}\) & \(3.9\times 10^{-3}\) & [31] \\ Hanging Mercury Drop & SWV & 1.80–25.00 & 1.00 & 3.20 & [26] \\ GCS & DPV & 0.09–1.08 & \(0.11\pm 0.01\) & \(0.86\pm 0.04\) & This work \\ \hline \end{tabular} 
\begin{tabular}{c c c c c} \hline
**DPAdSV–differential pulse adsorptive stripping voltammetry; SWV—square wave voltammetry; DPV—differential pulse voltammetry. ** & **increased proportionally with OC concentration, unaffected by the sample composition. A statistical comparison of both methods revealed no significant differences at the 95% confidence level, confirming the reliability of both approaches [35; 36; 37; 38; 39]. When a real water matrix was used, no significant variations were found, indicating that the GCS could serve as an effective measuring tool. As shown in Figure 5, OC concentration values obtained from both chromatographic and electroanalytic methods were closely aligned, demonstrating that there were no discernible differences in their applicability for detecting and quantifying OC in sunscreen formulations. Based on these results, DPV analysis with the GCS proves to be a suitable method for determining OC concentration in swimming pool water. Applicability of Electroanalysis and Chromatography for Determining OC Concentration During the Electrochemical Treatment of Different Water Matrices  
Figure 6a,b illustrate the OC concentration decay over time during the electrochemical treatment of swimming pool water and NaCl solutions (0.002 M), respectively, using a BDD anode at current densities of 5 and 10 mA cm\({}^{-2}\).