**6.4 pH (buffer capacity) of medium**

The pH-value have significant influence onto the size of the square wave voltammetric peaks and also assists in the hydrolysis of metal ions, therefore, it is crucial to choose a suitable pH-value for the sensing of metal ions. At the high concentration of hydrogen ion, the intensity of peak current is reduced due to protonation of hydrophilic groups on the surface of sensing material which leads to the decrease in the attachment sites for the adsorption of the heavy metal ions. Proper pH maintains originality of electron rich functional group over the sensing integrity.

### **6.5 Supporting electrolyte**

Supporting electrolytes are introduced to purge off the electro-migration effect. Therefore, the stripping voltammetric response of the peaks of current for the metal ions determination was also assessed by varying the nature of the stripping medium.
