## 3 Results and Discussion  
The sensitivity of the GCS was evaluated using differential pulse voltammetry (DPV) by recording both anodic and cathodic scans. Due to the chemical structure of OC, its functional groups can undergo oxidation or reduction. However, the anodic DPV profile showed no significant voltammetric current signal. In contrast, the cathodic scan revealed a prominent current peak at \(-1.13\) V, indicating a strong reductive interaction between OC and the GCS surface (Figure 3). This behavior aligns with findings from previous studies [25; 26]. To assess the dynamic and linear ranges, calibration plots were generated over a broad concentration range using DPV and HPLC methods (Figure 4). The data clearly showed that the slope gradually decreased until reaching an asymptotic value, following the expected linear trend at lower concentration levels. For electroanalysis, the calibration plot was linear between 0.09 \(\pm\) 0.01 and 1.08 \(\pm\) 0.06 mg L\({}^{-1}\) (Figure 4a), while for chromatography, it was linear between 1.00 and 5.00 mg L\({}^{-1}\) (Figure 4b). However, repeatability decreased at lower concentration levels. Figure 3: DPV profile recorded in BR buffer (0.04 M, pH 6.0): (black line) blank; (pink line) \(1.00\pm 0.15\) mg L\({}^{-1}\) of OC in BR buffer. Experimental conditions as described in the experimental section. Using the GCS, multiple analytical curves were constructed, with peak intensity measured as a function of analyte concentration. The electroanalysis results yielded the following calibration equation (Equation (1)):  
\[\mathrm{i/\mu A}=(31.77\pm 4.13)\times[\mathrm{OC}]\;\mathrm{mg}\;\mathrm{L^{-1}}-(1.84\pm 1.83) \tag{1}\]  
(n = 10, R\({}^{2}\) = 0.9952, P = 95%) as shown in the inset of Figure 4a. Similarly, the chromatography data produced the following calibration equation (Equation (2)):  
\[\mathrm{i/\mu A}=(0.83\pm 0.06)\times[\mathrm{OC}]\;\mathrm{mg}\;\mathrm{L^{-1}}-(0.14\pm 0.19) \tag{2}\]  
(n = 7, R\({}^{2}\) = 0.9964, P = 95%) as shown in Figure 4b. Furthermore, the regression residuals (Figure 4c,d) displayed a random distribution around zero, visually confirming the absence of significant nonlinearity in either method. Notably, the calibration curves remained consistent across different days, demonstrating their reproducibility. Additionally, the regression standard deviation method [27] was used to determine the limit of detection (LOD), following Equation (3):  
\[\mathrm{LOD}=3\times S_{\mathrm{y/x}}/b \tag{3}\]  
Figure 4: OC calibration curves: **(a)** DPV profiles recorded in BR buffer (0.04 M, pH 6.0) for various OC concentrations: 0.00; 0.09; 0.18; 0.27; 0.36; 0.63; 0.81; 0.90; 0.99, and 1.08 mg L\({}^{-1}\); inset: current peak intensity as a function of OC concentration; **(b)** chromatographic responses recorded in BR buffer (0.04 M, pH 6.0) for OC concentrations: 0.00; 1.00; 1.50; 2.50; 3.00; 4.00, and 6.00 mg L\({}^{-1}\); **(c)** weighted residuals from electroanalytic measurements; **(d)** weighted residuals from chromatographic responses. where \(b\) represents the slope of the calibration plot, and \(S_{\rm y/x}\) is the residual standard deviation. This approach minimizes false positive and false negative errors (\(\alpha\) = \(\beta\) = 0.05) in line with IUPAC recommendations [28] and prior research [27; 28; 29]. The LOD values were 0.11 \(\pm\) 0.01 mg L\({}^{-1}\) for electroanalysis and 0.86 \(\pm\) 0.04 mg L\({}^{-1}\) for HPLC. Similarly, the limit of quantification (LOQ) was estimated using Equation (4):  
\[\rm{LOQ}=10\times S_{\rm y/x}/b \tag{4}\]  
The LOQ values were 0.35 \(\pm\) 0.02 mg L\({}^{-1}\) for electroanalysis and 2.86 \(\pm\) 0.12 mg L\({}^{-1}\) for HPLC. These results indicate that the electroanalytic approach was more sensitive than HPLC, as it achieved LOD and LOQ values. Furthermore, when comparing the electroanalytical method's performance with previously published studies (Table 1), the GCS demonstrated high accuracy and confidence in detecting and quantifying similar organic compounds in aqueous solutions.