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Due to the toxicity and the detrimental effects of nickel and cobalt on human health, their concentrations in drinking water must be controlled. Therefore, EU the legislation specifies 20 µg/L as the limit value for nickel in drinking water. The current provisional guideline value for Ni in the World Health Organization’s «Guidelines for Drinking-water Quality» is set to a maximum concentration of 70 µg/L. To monitor the concentrations of Ni and Co with the 884 Professional VA, a method for simultaneous determination on the glassy carbon electrode (GC-RDE) modified with a Bi film is used.

The simplicity of the bismuth film preparation step allows quick and easy regeneration of the sensing layer. The determination is based on adsorptive stripping voltammetry of both elements using dimethylglyoxime (DMG) as a complexing agent. This method results in excellent performance in terms of sensitivity, reaching a limit of detection of 0.05 μg/L for Ni and 0.03 μg/L for Co. This non-toxic method is best suited for both manual and automated systems, allowing the determination in sample series with low to medium number of samples.

Drinking water, mineral water, sea water

Prior to the first determination, an ex-situ bismuth film is deposited from a bismuth solution. In the next step, the electrodes are cleaned with ultrapure water and the bismuth solution is removed. The water sample is placed into the measuring vessel. Ammonium buffer together with the complexing agent (DMG) are added, and the simultaneous determination of nickel and cobalt is carried out with the 884 Professional VA using the parameters specified in Table 1. The concentration is determined by two additions of a nickel and cobalt standard addition solution.

Figure 1. 884 Professional VA fully automated for VA
Table 1. Parameters
Parameter Setting
Mode DP – Differential Pulse
Deposition potential -0.8 V
Deposition time 30 s
Start potential -0.85 V
End potential -1.25 V
Peak potential Ni -0.97 V
Peak potential Co -1.12 V
  • Working electrode: Glassy carbon (GC-RDE)
  • Reference electrode: Ag/AgCl/KCl (3 mol/L)
  • Auxiliary electrode: Glassy carbon rod

With a 30 s deposition time, this method is suitable for the determination of both nickel and cobalt in water samples in concentrations from β(Ni) = 0.2–8 µg/L and β(Co) = 0.1–10 µg/L. Using a 90 s deposition time, the limit of detection can be lowered to approximately 0.05 µg/L for nickel and 0.03 µg/L for cobalt.

Figure 2. Determination of nickel and cobalt in tap water (30 s deposition time)
Table 2. Result
Sample Ni (μg/L) Co (μg/L)
Tap water 0.34 < LOD
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Metrohm Siam

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Internal reference: AW VA CH4-0589-122019