In acidic

solutions, the current decreased with a decrease in the pH solution. This behaviour can be attributed to the protonation of complexation sites present in the modified material, preventing the Cu(II) accumulation at the CPE-CTS. Thus, acetate buffer solution (0.1 mol L−1, Pifithrin-�� price pH 6.0) was selected as the supporting electrolyte in further studies. The effect of the CTS percentage (10–30% w/w) in the CPE on the voltammetric response of the sensor was evaluated. The maximum anodic current peak was obtained with 15% (w/w) of CTS in the paste and a 5.0 × 10−5 mol L−1 Cu(II) solution. For lower Cu(II) concentrations, a decrease in the current was observed, which can be attributed to the low amount of CTS available for the Cu(II) complexation. On the other hand, the current decrease observed when the CTS concentration in the paste was higher than 15% can be explained by the decrease in the electronic conductivity of the modified CPE, since CTS shows poor conductivity which can not be supplied by the low concentration of graphite.

Consequently, the composition of 15:20:65% (w/w/w) CTS:Nujol:graphite powder, respectively, PF-02341066 manufacturer was used in the construction of the CPE-CTS. In stripping voltammetry the analyte pre-concentration from the solution to the electrode surface is a critical step. In most cases, a pre-concentration potential (Epc) is applied for a preset time (tpc) and both of these parameters exert a strong influence on the electrode voltammetric response. The effect of the Epc from −0.1 to −0.7 V and a pre-concentration step carried out at open circuit potential on the anodic current peak obtained by cyclic voltammetry employing the CPE-CTS in a 5.0 × 10−5 mol L−1 Cu(II) solution were evaluated. At open circuit potential the pre-concentration was poor. Better results were obtained at controlled-potential, particularly at −0.4 V, which was the potential chosen to be employed in the subsequent tests. Another important parameter that must be precisely controlled in the experiments is the pre-concentration time. Increased tpc resulted in increasing anodic currents. A linear relationship was

observed over 90 s, but with increasing wideness in the anodic current peak, causing a L-NAME HCl considerable loss of resolution. Therefore, the tpc that provided the best relationship between voltammetric profile and current magnitude was 180 s, which was used in further experiments. Ensuring a clean electrode after the stripping is important in order to achieve reproducible results. Thus, the conditioning potential (0.1–0.7 V) and time (0–120 s) of the anodic current supplied by the CPE-CTS were studied. The cleaning step removes adsorbed impurities and copper that remain on the electrode surface after the stripping. The studies showed that a potential of 0.5 V applied for 30 s after each experiment is sufficient to clean the electrode surface. These conditioning parameters were therefore used in all subsequent experiments.