# Development of Heavy Metal Potentiostat for
## 2 Methodology
### Detection of Heavy Metal Using Square Wave Anodic Stripping Voltammetry Method  
In this study, the capability of the HMstat to detect heavy metal elements was demonstrated. The working solution of 10 ppm of Pb and Cd was prepared by diluting a standard solution of Pb and Cd (1000 ppm) in 0.1 M acetate buffer. The screen-printed gold electrodes (SPGEs) were purchased from DropSens (Spain). Each strip contained three electrodes printed on the same planar platform. The three electrodes were a 4 mm diameter gold disk-shaped working electrode (WE), a gold counter electrode (CE), and a silver pseudo-reference electrode (RE). All detection was performed by placing  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type of \(V_{ap}\)** & \(V_{ap}\) **(V)** & **Test Part** & **Parameter** & **HMstat** & **Rodeostat** \\ \hline \multirow{4}{*}{Constant} & \(-0.5\) & PCP & \(V_{in}\) & \(\surd\) & \(\times\) \\  & & CMP & \(I_{out}\) & \(\surd\) & \(\surd\) \\ \cline{2-6}  & \(+0.5\) & PCP & \(V_{in}\) & \(\surd\) & \(\times\) \\  & & CMP & \(I_{out}\) & \(\surd\) & \(\surd\) \\ \hline \multirow{2}{*}{Ramp} & \(-1\) to \(+1\) & PCP & \(V_{in}\) & \(\surd\) & \(\times\) \\  & & CMP & \(I_{out}\) & \(\surd\) & \(\surd\) \\ \hline \multirow{2}{*}{SWV} & \(-1\) to \(+1\) & PCP & \(V_{in}\) & \(\surd\) & \(\times\) \\  & & CMP & \(I_{out}\) & \(\surd\) & \(\times\) \\ \hline \multicolumn{6}{c}{\(\surd\) tested; \(\times\) not tested due to the data unavailability.} \\ \end{tabular}
\end{table}
Table 1: Type of potential applied to the HMstat and Rstat.  
100 \(\upmu\)L solution on the three-electrode strip. It is to be noted that all the potential applied throughout this work refers to silver pseudo-RE.  
The experiment was conducted using a square wave anodic stripping voltammetry method (SWASV), in which the SWASV signal was generated by the CSC. There were two main steps in the SWASV method. First was the deposition step and second was the stripping step. The mechanism of the heavy metal ion during the deposition and stripping steps was illustrated in Figure 4. The deposition step is where the negative potential is applied to the WE. The purpose of the deposition step was to reduce the heavy metal ion in the working solution onto the electrode surface. The reduction will occur if the applied deposition potential is more negative than the reduction potential of heavy metal [32]. This step was followed by the stripping step. In the stripping step, the deposited heavy metal ion on the electrode surface is reoxidized and dissolved into the working solution [32]. The reoxidation tends to occur when the applied potential matches the oxidation potential of each heavy metal, so that the measured current indicates a different peak for each heavy metal species [16]. The details of the parameters used in the steps for heavy metal ion detection were listed in Table 2.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Deposition Step** & \\ \hline Potential & \(-\)0.9 V \\ Time & 120 s \\ \hline Stripping Step & \\ \hline Initial potential & \(-\)0.7 V \\ Final potential & 0.0 V \\ Modulation amplitude & 50 mV \\ Step amplitude & 50 mV \\ frequency & 10 Hz \\ \hline \hline \end{tabular}
\end{table}
Table 2: Experimental parameters.  
Figure 4: Heavy metal (HM) ion during (1) deposition and (2) stripping step on screen-printed gold electrode (SPGE) connected to potentiostat read-out circuit component (PRCC). RE, WE, and CE are reference electrode, working electrode, and counter electrode, respectively.