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Anodic Stripping Voltammetry

Introduction

Anodic stripping voltammetry is an electrolytic method in which a mercury electrode is held at a negative potential to reduce metal ions in solution and form an amalgam with the electrode. The solution is stirred to carry as much of the analyte metal(s) to the electrode as possible for concentration into the amalgam. After reducing and accumulating the analyte for some period of time, the potential on the electrode is increased to reoxidize the analyte and generate a current signal. The ramped potential usually uses a step function, such as in normal-pulse polarography (NPP) or differential-pulse polarography (DPP).

The concentration of the analyte in the Hg electrode, CHg, is given by:

       il td
CHg = -------
      n F VHg
where il is the limiting current during reduction of the metal, td is the duration of accumulation, n is the number of moles of electrons transferred in the half reaction, F is the Faraday constant (96,487 coulombs/mole of e-), and VHg is the volume of the electrode. The expression for current produced by anodic stripping depends on the particular type of Hg electrode, but is directly proportional to the concentration of analyte concentrated into the electrode. The main advantage of stripping analysis is the preconcentration of the analyte into the electrode before making the actual current measurement. Anodic stripping can achieve detection of concentrations as low as 10-10 M.


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