Mercury ions, glassy carbon electrode

These workers used a radiometer ISS 820 ion-scanning system [101,321-323] equipped with a glassy carbon electrode to determine copper at the 2-200 xg/l level in nitrogen-purged 0.45 pm Millipore-filtered seawater to which had been added 5 ppm mercury. 

Using a glassy carbon electrode modified with a mercury film, Weber et al. [66] measured the association and dissociation rate constants for the complex formed between Pb + and the 18-crown-6 ether. It was found that Pb + forms a complex with 18-crown-6 with a stoichiometiy of 1 1 in both nitrate and perchlorate media. The formation constant, for the nitrate and perchlorate systems are (3.82 0.89) X 10 and (5.92 1.97) x lO mol Ls , respectively. The dissociation rate constants, are (2.83 0.66) x 10 with nitrate and (2.64 0.88) x 10 s with perchlorate as counter ion. In addition, the binding of Pb + with benzo-18-crown-6 embedded in a polymerized ciystalline colloidal array hydrogel has been also analyzed [67]. 

Fig. 8.7 Cyclic voltammograms of cobalticinium ion in 1 mM (tj-C5H5)2CoPF6-0.1 M Bu4NBF4-AN [30a]. Recorded using a hanging mercury drop electrode (a) and a glassy carbon electrode (b) at 100 mVs-1 and at 25 °C.

Lead and mercury are deposited as micron-sized clusters, predominantly at intercrystallite boundaries [105] so does lithium from the polyethylene oxide solid electrolyte. What is more, Li intercalates into the sp2-carbon [22, 138], Thus, observations on the Li intercalation and deintercalation enable one to detect non-diamond carbon on the diamond film surface. Copper is difficult to plate on diamond [139], There is indirect evidence that Cu electrodeposition, whose early stages proceed as underpotential deposition, also involves the intercrystallite boundaries [140], We note that diamond electrodes seem to be an appropriate tool for use in the well-known electroanalytical method of detection of traces of metal ions in solutions by their cathodic accumulation followed by anodic stripping. The same holds for anodic deposition, e.g. of, Pb as PbCh with subsequent cathodic reduction [141, 142], Figure 30 shows the voltammograms of anodic dissolution of Cd and Pb cathodically predeposited from their salt mixtures on diamond and glassy carbon electrodes. We see that the dissolution peaks are clearly resolved. The detection limit for Zn, Cd, and Pb is as low as a few ppb [143]. 

Solid electrodes are used for the analysis of metal ions that cannot be determined on mercury electrodes with reasonable efficiency, or not at all. Some examples are listed in Table II.7.3. They are representatives of two groups of ions. The stripping peak potentials of deposits of the first group are higher, or close to, the stripping potential of mercury. For instance, the concentration of bismuth ions cannot be measured on mercury electrodes below 5 x 10 mol/L, but on a glassy carbon electrode, these ions can be determined at the concentration level of 10 mol/L... 

Mercury ions can be detected on a glassy carbon electrode in a concentration as low as 5 X 10 mol/L [16], The atoms of the second group are poorly soluble in mercury (Sb, Co, Ni, Fe). Besides, the reduction of some of these ions and the oxidation of their atoms are both kinetically controlled processes on mercury electrodes [1],... 

Rajabi HR, Roushani M, Shamsipur M. Development of a highly selective voltammetric sensor for nanomolar detection of mercury ions using glassy carbon electrode modified with a novel ion imprinted polymeric nanobeads and multi-wall carbon nanotubes. J Electroanal Chem 2013 693 16-22. 

During potentiometric stripping analysis (PSA), trace elements or ions are pre-concentrated by potentiostatic deposition on an electrode (e.g., mercury film on a glassy-carbon electrode). In contrast to DPASV, PSA is not subject to background... 

The conditions for reliable cyclic voltametry determination of trace Sn concentrations in sea water were investigated. All organotin compounds should be converted to Sn(II) by UV-photolysis adsorption on mercury drop in the presence of 40 pM of tropolone (1) cyclic voltametry stripping shows two cathodic peaks, corresponding to the two-step process Sn(IV) — Sn(II) -> Sn(0)29. A complex of Sn ions with catechol can be accumulated in a glassy carbon mercury film electrode, followed by stripping voltametry measurement in the cathodic direction, at pH 4.2-4.7. Interference occurs when Cu, Cd and Cr are present LOD 0.5 pg/L for 300 s accumulation30. 

Stripping voltammetry or stripping analysis has a special place in electrochemistry because of its extensive application in trace metal analysis. Stripping voltammetry (SV) is a two-step process as shown schematically in Fig. 18b. 12. In the first step, the metal ion is reduced to metal on a mercury electrode (thin mercury film on glassy carbon or a HMDE) as amalgam. 

The mercury electrode used in stripping analysis is either a conventional HMDE or a mercury film electrode (MFE). In current practice, the MFE is typically deposited onto a rotating glassy carbon or wax-impregnated graphite disk. One usually adds mercuric ion... 

The same solution gives a peak current of 25 jjiA at a 100-A thick mercury film electrode on glassy carbon when the deposition time is 1 min, the electrode rotation rate is 2000 rpm, and the sweep rate is 50 mV/s. What currents would be observed for sweep rates of 25 and 100 mV/s under otherwise unchanged conditions Compare this situation to the one observed for a deposition time of 1 min, a sweep rate of 50 mV/s, and a rotation rate of 4000 rpm Suppose the film thickness were varied by the use of different concentrations of mercuric ion in the analyte. What effect would one see on the peak current under otherwise constant conditions ... 

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