Stripping voltammetry has recently enjoyed a popular renaissance in trace element detection applications, although these techniques have always been regarded as some of the most sensitive available for trace metals detection.

The sensitivity of voltammetric methods is due to the use of a pre-concentration, or accumulation, step in which the analyte is accumulated at the electrode by either a faradaic (anodic or cathodic stripping) or non-faradaic (absorptive) process.  The analytical signal is then generated by the subsequent voltammetric stripping step, where the voltage is swept, or stepped, so as to remove the adsorbed analyte from the electrode.  The current during this process is recorded, usually as a function of voltage (for a voltage sweep) or time (for a voltage step), and the area of the current wave produced (proportional to the charge passed) is measured.  Quantification is then performed by calibration, usually by a sequential standard addition methodology, where known quantities of a standard solution are added to the same analysis vessel.  Whilst stripping voltammetry is essentially a non-destructive analytical process, the calibration procedure removes the possibility of re-analysis.  Mercury is most commonly used as an electrode for these determinations.

We have developed this technique to perform the analysis of the soluble fraction of metallic compounds in deposited dust.  This has allowed the accurate measurement of trace metals in environmental samples at mass fractions less than 10^-9 kg/kg.  Results from a six-month study of metallic compounds in deposited dust in Teddington are shown in the figure below.

The total deposition fluxes of Ni, Cd, Pb and Zn measured by
stripping voltammetry during the 6-month field measurement campaign.
Measurement uncertainties are quoted at the 95% confidence level

More recently we have proposed that stripping voltammetry could be used as a possible primary method for amount of substance measurement, by using hemispherical mercury microelectrodes of known size to perform the stripping analysis.  This is because it can be shown that under special circumstances, for hemispherical mercury micro-electrodes on a glassy carbon substrate (as shown in the figure below), the operation of this technique for the measurement of electro-active ions in solution, can be fully described and understood by a series of measurement equations.

The sphere-cap family of hemi-spheroidal microelectrodes in cross section which
could be used as a possible primary method for amount of substance measurement,
on a conducting basal plane with radius a, and height b above the basal plane.
Common dimensions for these electrodes will be of the order of 10 microns

References

• Brown, R J C, Roberts, M R, Milton, M J T, “Systematic error arising from ‘Sequential’ Standard Addition Calibrations: Quantificationand correction”, Anal. Chim. Acta (2007), doi:10.1016/j.aca.2007.01.064
• Brown, R J C, Shaw, M C, Roberts, M R, “Practical methodology for the solubility speciation analysis of ambient dust deposits for heavy metals: application to a 6-month measurement campaign”, Int. J. Environ. Anal. Chem., 2006, 86, (6), 453-460.
• Brown, R J C, Milton, M J T, “Stripping voltammetry as a possible primary method for amount of substance”, IEEE Trans. Instrum. Meas., 2007, DOI 10.1109/TIM.2007.891159