Abstract
Trace minerals play an essential role in methane production via anaerobic digestion (AD). It is important to monitor Ni(II) and Co(II) concentrations and the Ni/Co concentration ratio for the rapid diagnosis of the ecological status or activity of methanogens in AD. Electrochemical detection of Ni(II) and Co(II) was investigated by coating the Bi-chitosan nanocomposite on a glassy carbon electrode (GCE) via the electrodeposition technique. A square-wave adsorptive cathodic stripping voltammetry technique (SWAdCSV) was applied and optimized when dimethylglyoxime (DMG) was used as the chelating agent for Ni(II) and Co(II) measurements. The SWAdCSV results showed that the current peaks for Co(II) detection are 6.1 times greater than the current peaks for Ni(II) measurements, probably due to the different affinity of DMG molecules between Ni(II) and Co(II). DMG molecules demonstrated higher selectivity toward Co(II) cations compared to Ni(II). The modified Bi-chitosan GCE developed in this study showed a relatively wide range of the Ni(II) and Co(II) concentrations (2–100 µg L−1) with a limit of detection of 3.6 µg L−1 for Ni(II) and 2.4 µg L−1 for Co(II), respectively. The developed sensor was applied to Ni(II) and Co(II) spiked natural water samples and showed good performance of detection with 12 consecutive measurements. Overall, the fabricated sensor showed excellent sensitivity toward Ni(II) and Co(II) in natural water samples.
Highlights
Ni and Co are well-known essential trace minerals for methane production in anaerobic digestion (AD)
There was no stripping current peak observed with nioxime as a chelating agent, and this study focused on the optimization of Ni(II) and Co(II) detection using
limit of detection (LOD) was calculated using the following Equation (1) [41]: CL = 3 × SB /b where CL is the detection limit, SB signifies the standard deviation of blank signals, and b is the slope of the calibration curves, which is known as the sensor sensitivity (μA−1 )
Summary
Ni and Co are well-known essential trace minerals for methane production in anaerobic digestion (AD). The ASV technique relies on the formation of amalgams of heavy metal ions on the surface of a working electrode at a certain negative deposition potential. The adsorptive cathodic stripping voltammetry technique (AdCSV) can be an alternative approach to detecting heavy metal ions which rely on the formation of target metal complexes with a chelating agent on the surface of the working electrode [20,21]. During the stripping voltammetry measurements, the complexes are accumulated onto the surface of the working electrode Several metal ions, such as vanadium [22], molybdenum [23], nickel, and cobalt [24] have been successfully detected by the AdCSV technique. Measurements in real AD samples to further assess the microbial activity of methanogens in AD
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