Improved Anodic Stripping Voltammetric Determination of Arsenic Using Nanoporous Gold Microelectrode

Arsenic is a highly toxic element and a relatively widespread water pollutant which is thought to be poisoning significant amount of people in various developing countries [1]. Exposure to arsenic can cause a variety of adverse health effects, including dermal changes and respiratory, cardiovascular, gastrointestinal, genotoxic, mutagenic, and carcinogenic effects. Contamination of groundwater by arsenic has been reported in 20 countries where arsenic levels in drinking water are above the World Health Organization’s arsenic guide line value of 10 mg L^-1. Many detection methods have been developed for determination of such levels of arsenic. These include inductively coupled plasma mass spectrometry (ICPMS), graphite furnace atomic absorption spectrometry, and high-performance liquid chromatography with ICPMS. However, the most reliable techniques are more suitable for laboratory conditions only and are time-consuming. They cannot thus be used for routine in-field monitoring of a large number of samples. Electrochemical techniques provide a possible means to this end since they are both rapid and portable.

We have developed a fast and convenient electrochemical alloying-dealloying approach to fabricate a range of nanoporous microelectrodes of noble metals by applying modulated potential to their corresponding disk microelectrodes in an ionic liquid electrolyte bath comprising of ZnCl₂ and 1-ethyl-3-methylimidazolium chloride [3]. The resulted nanoporous microelectrodes have high surface area and retain diffusional properties typical of a regular microelectrode. In this work, we fabricated nanoporous gold (NPG) microelectrodes by the electrochemical alloying-dealloying method and investigated their electrochemical responses to arsenic (III) in acidic media using anodic stripping voltammetry. Figure 1(A) shows the image of surface layers of the NPG microelectrode which was measured using field-emission environmental scanning electron microscope (SEM). Regular nanopores (black regions) and ligament spacings (white regions) were observed.  To examine the ability of the NPG microelectrode as a tool in arsenic detection in water, linear sweep voltammetry and 0.1 M HNO₃ as supporting electrolyte were used. Deposition of As(III) onto the NPG and an Au-disk microelectrodes was carried out at deposition time of 120 s from the electrolyte solution containing As(III) during anodic stripping voltammetric measurements.  Figure 1(B) shows that the stripping peak measured is considerably higher than on the NPG microelectrode than the Au-disk microelectrode of the same geometric diameter. We further measured the limit of detection (LOD) for both the NPG and Au-disk microelectrodes. Their LOD values are around 2 mg L^-1, lower than the he WHO recommended level 10 mg L^-1.

Insert Figure 1

Figure 1. (A) SEM image of nanoporous gold layer. (B) Anodic stripping voltammograms measured at 100 mV s^-1 after deposition of 120 s at -0.40 V vs Ag/AgCl from 0.1 M HNO₃containing As(III) for the NPG (blue) and Au-disk (red) microelectrodes.

References

[1] US Environmental Protection Agency, www.epa.gov/safewater/arsenic .html.

[2] D. Yamada, T. Ivandini, et al., J. Electroananl. Chem. 615(2008) 145-153.

[3] J. Jiang, X. Wang, L. Zhang, Electrochim. Acta 111 (2013) 114-119.