Theory:

Heavy metal ions are one of the primary source of water pollution, as they are non-biodegradable and contaminate most of the natural resources occurring in the environment. With the increasing demand for heavy metal detection, electrochemical detection is favorable because of its high sensitivity and efficiency.The experiment is performed using a potentiostat, an electrochemical instrument that precisely controls the applied potential and records the resulting current in a three-electrode system. The resulting current–potential plot, known as a voltammogram, exhibits distinct oxidation or reduction peaks corresponding to specific heavy metals. In such measurements, the peak current is directly proportional to the analyte concentration, enabling accurate quantitative analysis. The following figure illustrates a voltammogram for further explanation.

There are a variety of electrochemical methods that can be used for the detection of heavy metal ions. Amongst various techniques, differential pulse voltammetry (DPV) and square wave voltammetry (SWV) are the most effective methods. DPV is a technique that involves applying amplitude potential pulses on a linear ramp potential. In this technique, a base potential value is chosen at which there is no faradaic reaction and applies to the electrode. The base potential is increased between pulses with equal increments. Along with DPV, one more powerful electroanalytical technique is square-wave voltammetry (SWV). It is a large amplitude differential technique in which a waveform composed of a symmetrical square wave, superimposed on a base staircase potential, is applied to the working electrode. The main difference between DPV and SWV methods can be attributed to the type of excitation signal. In DPV, a constant but small amplitude potential pulse superimposed on a DC potential ramp is applied during the lifetime of the drop. However, SWV has a higher sensitivity than a differential pulse that does not involve reverse current. The boron-doped diamond (BDD) electrode is used as a working electrode as it has a large potential window and good electrochemical stability in heavy metal ion detection.