Development of an Electrochemical Sensor for the Detection and Quantification of Pb(II) and Cu(II) in Aqueous Solutions Using Carbon Paste Electrodes Modified with Glutathione
Authors: Balderas Patricia , Castañeda Josue , Roa Gabriela , Amaya Araceli 
Published: February 2020

An efficient and environmentally friendly electrochemical sensor was developed to determine and quantify heavy metals such as lead and copper at trace concentrations present in water by voltammetric techniques[1]. The obteined information allows be able to give an adequate treatment avoiding harmful effects to the ecosystem and human society.
Carbon paste electrodes modified with glutathione were used since they are capable of forming complexes with the heavy metal ions. The metal ions are fixed on the surface of the working electrode obtaining important information for the study.
The presence of heavy metals in wastewater may have different reasons, is important to control the contamination due to its high toxicity and its high capacity of permanence in the media and of accumulation in living organisms. Within this perspective, it is important to monitor these metals in water, using simple, fast and reliable techniques. [2]
In the experimental part was revelant the development of carbon paste electrodes were made weighing 0.475 g of graphite powder, 0.025 g of glutathione, and 0.45 g of mineral oil and were mixed. The paste obtained; which was used to fill 1mL insulin syringe. Subsequently, a cut was made to measure the desired length of the electrode. This cut was connected to a piece of copper wire with a part immersed inside the electrode and another making the electrical contact with the caiman.

The Solutions of copper sulphate and lead nitrate were prepared at a concentration of 0.1 M that served as study analytes and a solution of HClO4 1 M that served as a supporting electrolyte.
For the analyzes of cyclic voltammetry and anodic redissolution, a Basi brand Epsilon EC-2000-XP potentiostat was used. Adapting a glass cell and the use of three electrodes: the modified carbon paste electrode as working electrode, an Ag/AgCl as reference electrode and a graphite as counter electrode.
The cyclic voltammetric analysis was performed adding 10 mL of the HClO4 solution to the electrochemical cell and 10 μL of solution of the lead solution was added, obtaining the respective voltammogram; subsequently, the copper solution was analyzed following the same procedure. With the voltammograms obtained it was possible to know parameters required for the performance of the anodic redisolution voltammetry (ARV).
The (ARV) started fixing the respective parameters for the lead solution in the potensiostat with an initial volume of 10 mL of HClO4, and then 10 μL of lead nitrate solution was added and mixed with a stir bar, consecutively until reaching 100 μL. For each addition or concentration, the respective voltammogram was obtained. The same procedure was made for the copper solution.The voltammograms showed information as the current intensity and area under the curve. This data points were used for the preparation of the calibration curve for both metals.
In the analysis of results we can mention that with the cyclic voltamperomatrics it was possible to detect and characterize the metals under study.

The oxidation potential served as a parameter to perform the (ARV), obtaining voltamrograms when modifying the concentration. Data such as the potential, area under the curve and current intensity were obtained.
With this data points were obtained with which a calibration curve for lead and another for copper can be drawn. And in this way have a reference to quantify the amount of metal in a water sample.
The lowest concentration for the detection and quantification of both metals was given for values of 10-10 M. The electrode of carbon paste modified with glutathione detected lower concentrations compared with studies already made to the electrodes of carbon paste modified with other substances.

A conclusion of the study is that when adding the glutathione molecule to the paste, it has a thiol group capable of complexing and attracting ions such as lead and copper and other metals with valence (II), thus allowing detection and later quantification.
Comparing previous studies to modified carbon paste electrodes with the modification made with glutathione, the limits of detection and sensitivity were improved.

REFERENCES

[1] Koirala, Kisan, et al. (2016) "Chemically modified carbon paste electrode for the detection of lead, cadmium and zinc ions." Sensor Review 36.4: 339-346.
[2] Fu Fenglian, Wang Qi (2011) “Removal of heavy metal ions from wastewaters: A review” Journal of Environmental Management, 92,407- 418