As can be seen from Fig. 4A, the DPV signal was enhanced along with the increasing concentration of BPR. Fig. 4B demonstrates the linear relationship between concentrations of BPR and the DPV current responses of the electrode in the presence of 0.24 mM SDS under the optimized instrument parameters and experimental conditions. The peak current increased linearly against the concentration of BPR on the two ranging from 4.00 nM to 0.126 μM (R2 = 0.9985) and from 0.126 to 0.317 μM (R2 = 0.9560). The detection limit for BPR was calculated to be 1.33 nM based on S/N = 3. A low detection limit and wide linear range were obtained at CPE in the presence of SDS compared to the other reports (Table 2).