The nature of voltammetric waves of copper complexes with dimethylglyoxime in ammonia and borate buffer solutions

Low-Cost Reusable Sensor for Cobalt and Nickel Detection in Aerosols Using Adsorptive Cathodic Square-Wave Stripping Voltammetry

A low-cost electrochemical sensor with Nafion/Bi modification using adsorptive stripping voltammetry for Co and Ni determination in airborne particulate matter and welding fume samples is described. Carbon stencil-printed electrodes (CSPEs) manufactured on low-cost PET films were utilized. Dimethylglyoxime (DMG) was used as a Co(II) and Ni(II) chelator with selective chemical precipitation for trace electrochemical analysis. Electrochemical studies of the Nafion/Bi-modified CSPE indicated a diffusion-controlled redox reaction for Co and Ni measurements. The Nafion coating decreased the background current and enhanced the measured peak current. Repeatability tests based on changes in percent relative standard deviation (RSD) of peak current showed the electrode could be used at least 15 times before the RSD exceeded 15% (the reported value of acceptable repeatability from Association of Official Analytical Chemists (AOAC)) due to deterioration of electrode surface. Limits of detection were 1 μg L^-1 and 5 μg L^-1 for Co and Ni, respectively, which were comparable to electrochemical sensors requiring more complicated modification procedures. The sensor produced a working range of 1-250 and 5-175 μg L^-1 for Co and Ni, respectively. Interference studies showed no other metal species interfered with Co and Ni measurements using the optimized conditions. Finally, the developed sensors were applied for Co and Ni determination in aerosol samples generated from Co rods and a certified welding-fume reference material, respectively. Validation with ICP-MS showed no statistically different results with 95% confidence between sensor and the ICP methods.

Electrochemical and spectroscopic investigation of the reduction of dimethylglyoxime at mercury electrodes in the presence of cobalt and nickel

Voltammograms (polarograms) obtained from solutions of cobalt and nickel containing dimethylglyoxime (dmgH(2)) are widely used for the trace determination of these metals. Detailed electrochemical and spectroscopic studies on the reduction process observed in the analytically important ammonia buffer media at mercury dropping, hanging, and pool electrodes are all consistent with an overall 10-electron reduction process, in which both the dmgH(2) ligand and cobalt ions are reduced in the adsorbed state:  Co(II) + 2dmgH(2) ⇌ (solution) [Co(II)(dmgH)(2)] + 2H(+); [Co(II)(dmgH)(2)] + Hg ⇌ (electrode) [Co(II)(dmgH)(2)](ads)Hg; and [Co(II)(dmgH)(2)](ads)Hg + 10e(-) + 10H(+) → Co(Hg) + 2[2,3-bis(hydroxylamino)butane]. The limited solubility of the nickel complex in aqueous media restricts the range of studies that can be undertaken with this system, but an analogous mechanism is believed to occur. Low-temperature voltammetric studies in dichloromethane at a frozen hanging mercury drop electrode and in situ electron spin resonance electrochemical measurements on more soluble analogues of the dimethylglyoxime complexes are consistent with an initial one-electron reduction step being available in the absence of water. Deliberate addition of water to acetone solutions enables the influence of the aqueous environment on voltammograms and polarograms to be examined. The results of the present study are compared with the wide range of mechanisms proposed in other studies.