(231h) Portable and Low-Cost Potentiostat System for Quantification of Cadmium in Wastewaters

The incessant growth of human activities has been accompanied by a constantly increasing release of pollutants to the environment, some of which tend to accumulate in air, water, and land to levels that pose a risk several living organisms and fragile ecosystems. One of such compounds is Cadmium, which is a relatively scarce metal usually found in the earth's crust and is also the inevitable byproduct of the extraction processes of zinc, lead and copper [1]. Even at very low concentrations, Cadmium is cytotoxic and carcinogenic to humans and due to its marked tendency to accumulate in kidneys, bones and the respiratory system [2][3]. Cadmium dissolves easily in polluted waters with low pH levels and can be transported to fresh superficial waters for human consumption. Furthermore, it could reach soil or fertilizers from which plants might absorb it to finally end up in food sources [4].

Cadmium in water sources is usually quantified via atomic absorption spectroscopy [5] and inductively coupled plasma atomic emission spectroscopy [6][7]. These two analytical methods are approved by federal agencies and organizations such as the US-EPA [8]. Additional analytical approaches based on electrochemical measurements are quite precise and include anodic stripping voltammetry [9], adsorptive cathodic stripping voltammetry [10], and potentiometric stripping analysis [8]. Main drawbacks of these methods include the pre-treatment of samples prior to measurements via tedious and lengthy protocols, and the need for expensive and large devices that limit in-situ and real-time monitoring [11]. Accordingly, there is a need for high sensitivity methods to detect and quantify cadmium in a simple, rapid, and inexpensive manner. An interesting avenue to respond to this challenge is to manufacture a portable device that also incorporates the sensitivity of electrochemical reactions. Such a device is known as a potentiostat and mainly consist of a stepped triangular signal generator, a transimpedance amplifier and a voltage follower. Here we benchmark our recently developed potentiostat with a commercially available potentiostat. Our manufacturing strategy allowed us to prepare a low-cost potentiostat. Details of the protocols can be found elsewhere [12]. Briefly, the portable device is assembled in an electronic PCB which have a composite material known as FR4 as substrate, and two coper layers on each side, it has dimensions of 5,34 cm x 4,45 cm and is capable of generating stepped voltage signals to conduct electrochemical measurements. Also, the device accuracy is of 0.8mV in the generated signal and is able to capture currents in the range of nA. The development was enabled by an ultra-low-power microcontroller from Texas Instruments (USA).

Cells of three electrodes were fabricated for measuring cadmium in water with both devices via cyclic voltammetry (CV). Measurements were successfully conducted with an exceedingly low sample volume of less than 300 µL. Materials such as copper (Cu) and Gold (Au) served as primary components for the developed cells and in some cases 4-Aminothiophenol (4-ATP) was covalently conjugated to the metal surface to increase the Cadmium chelation efficiency. Previous work with a commercial potentiostat demonstrated that sensors based on Cu, Au/Cu and Au/Cu modified with 4-ATP were able to measure Cadmium in aqueous solutions ranging from 13 Cd mg/mL to 0,786 Cd mg/mL. To carry out the tests, one cycle of CV between –1 V to 0 V was applied, which resulted in an anodic peak of cadmium oxidation between –0.5V and –0.4V. Current at this peak was directly proportional to the amount of substrate present in the sample. Different cell architectures will be tested to establish the detection limit of the device, which is expected to be in close proximity to the maximum allowable cadmium concentration in water for human consumption. Accordingly, our sensing technology appears suitable to monitor wastewater and water sources in a rapid, inexpensive, and portable manner. Moreover, the device is user-friendly and requires a low level of training for operation. We expect to develop avenues to use the device with samples of challenging physicochemical properties such as food, urine, saliva and blood.

REFERENCES

1] Lenntech. Cadmium (Cd), Chemical properties of cadmium - Health effects of cadmium - Environmental effects of cadmium. https://www.lenntech.com/periodic/elements/cd.htm#ixzz5CYn8XMpv . [Accessed: 14-Dec-2017]. 2017

[2] WHO. Exposure to cadmium: A major public health concern. http://www.who.int/ipcs/features/cadmium.pdf. [Accessed: 12-Apr-2018]. 2010.

[3] J. Godt, F. Scheidig, C. Grosse-Siestrup, V. Esche, P. Brandenburg, A. Reich, and D. A. Groneberg, “The toxicity of cadmium and resulting hazards for human health.,” J. Occup. Med. Toxicol., vol. 1, p. 22, Sep. 2006. DOI: 10.1186/1745-6673-1-22

[4] WHO. Cadmium in Drinking-water Background document for development of WHO Guidelines for Drinking-water Quality. http://www.who.int/water_sanitation_health/dwq/chemicals/cadmium.pdf [Accessed: 12-Apr-2018]. 2011.

[5] R. Golbedaghi, S. Jafari, M. R. Yaftian, R. Azadbakht, S. Salehzadeh, and B. Jaleh, “Determination of cadmium(II) ion by atomic absorption spectrometry after cloud point extraction,” J. Iran. Chem. Soc., vol. 9, no. 3, pp. 251–256, Jun. 2012. https://doi.org/10.1007/s13738-011-0018-7

[6] J. M. E. Almendro, C. B. Ojeda, A. G. De Torres, and J. M. C. Pavon, “Determination of Cadmium in Biological Samples by Inductively Coupled Plasma Atomic Emission Spectrometry After Extraction With,” Elements, vol. 117, no. November, pp. 1749–1751, 1992.

[7] T. Daşbaşı, Ş. Saçmacı, A. Ülgen, and Ş. Kartal, “A solid phase extraction procedure for the determination of Cd(II) and Pb(II) ions in food and water samples by flame atomic absorption spectrometry,” Food Chem., vol. 174, pp. 591–596, May 2015. https://doi.org/10.1016/j.foodchem.2014.11.049

[8] Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile for Cadmium. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service. 2012.

[9] Rajawat, D.S., Kumar, N. & Satsangee, S.P. J Anal Sci Technol (2014) 5: 19. https://doi.org/10.1186/s40543-014-0019-0

[10] Deswati D, Pardi H, Suyani H, Zein R. Adsorptive Cathodic Stripping Voltammetric Methodwith Alizarin for the Simultaneous Determination of Cadmium, and Zinc in Water Samples. Orient J Chem 2016;32(6). Available from: http://www.orientjchem.org/?p=25331

[11] Zohreh Dahaghin, Paul A. Kilmartin, Hassan Zavvar Mousavi, Simultaneous determination of lead(II) and cadmium(II) at a glassy carbon electrode modified with GO@Fe3O4@benzothiazole-2-carboxaldehyde using square wave anodic stripping voltammetry, Journal of Molecular Liquids, Volume 249, 2018, Pages 1125-1132

[12] Segura CC, Osma JF (2017) Miniaturization of Cyclic Voltammetry Electronic Systems for Remote Biosensing. Int J Biosen Bioelectron 3(3): 00068. DOI: 10.15406/ijbsbe.2017.03.00068