On Site Determination of Heavy Metal Ions with Portable Electrochemical Instrument Based on Smartphone
Authors: Lin Wencheng , Sun Xianyou , Zhou Shuqi , Liang Tao , Kirsanov Dmitry , Legin Andrey , Wan Hao , Wang Ping 
Published: July 2021

Introduction

Most heavy metal ions are harmful to human body and may cause a variety of diseases, among which chromium(VI), cadmium, arsenic and their compounds are classified as Group 1 (human carcinogen) by IARC [1]. Heavy metal ions can enter the human body through direct drinking and the enrichment of food chain. Therefore, the allowed concentration of heavy metal ions are recommend by WHO, which are 50 μg/L for chromium(VI), 3 μg/L for cadmium, 10 μg/L for arsenic, respectively [2].
Compared with other methods, electrochemical method is gaining wide recognition and has the advantages of fast speed, simple operation and possibility of use in portable detection on site [3]. Therefore, a portable electrochemical instrument based on smartphone was designed, in order to detect the concentration of heavy metal ions in the field.

Method

A block diagram of the portable electrochemical instrument is shown in Fig. (a). The instruction of controlling electrochemical process is sent out by MCU and executed by potentiostat. The electrochemical signal obtained is simply processed and returned to MCU. The communication between MCU and smartphone software based on Android system is realized through Bluetooth. The completed printed circuit board (PCB) of the instrument is shown in Fig. (b).
The determination of chromium(VI) is realized by gold nanoparticles modified gold electrode, in order to obtain a larger electrochemical response. The gold nanoparticle modification was achieved by applying a potential of -0.3 V for 120 seconds with stirring in 0.2 mmol/L chloroauric acid with 0.5 mol/L sulphuric acid, which is simple, stable and repeatable for on site determination. As shown in Fig. (c), the increase of electrode surface area can be observed by Atomic Force Microscope (AFM).
After parameters optimization, the detection of Chromium(VI) was carried out in 0.3 mol/L nitric acid by linear sweep voltammetry (LSV) with a potential range of 0.8 V to 0.2 V. There is no accumulation process during detection, so it takes less than 10 seconds.

Results and Conclusions

The linear sweep voltammograms in chromium(VI) concentration range of 10 μg/L to 100 μg/L with a step of 10 μg/L are shown in Fig. (d). The standard curve of Cr(VI) is shown in Fig. (e), where it shows a linear relationship with the correlation coefficient of 0.98. A detection limit of 6.4 μg/L can be calculated, suggesting the sensitivity of the method for Cr(VI) detection. These results indicate that the portable electrochemical instrument based on smartphone can be a promising alternative for heavy metal ions detection on site.

References

International Agency for Research on Cancer. (2020). Agents classified by the IARC Monographs, volumes 1-128. http://monographs. iarc. fr/ENG/Classification/index. php.

Edition, F. (2011). Guidelines for drinking-water quality. WHO chronicle, 38(4), 104-8.

Holmes, J. , Pathirathna, P. , & Hashemi, P. . (2019). Novel frontiers in voltammetric trace metal analysis: towards real time, on-site, in situ measurements. TrAC Trends in Analytical Chemistry, 111, 206-219.

Figure 1