Potentiostat Sample Results
Below are just a few examples of the types of experiment that one can perform using a potentiostat. Detailed descriptions of some laboratory-based electroanalytical experiments to determine trace heavy metals at the ppb level can be found on the Potentiostat page here.
Cyclic Voltammetry on Pt in Sulphuric AcidIn this experiment a Pt working electrode is used. In the "forward" sweep, adsorbed H atoms (Hads) are oxidised to H+ ions. Thereafter, is a quiet "double layer" region, following which Pt is oxidised to Pt oxides. At the highest positive potentials O2 evolution occurs.
In the reverse sweep, the Pt oxides are reduced back to Pt, and then H+ are reduced to Hads. This latter process occurs in the "hydrogen region". Once a monolayer of adsorbed H atoms has formed, these atoms associate , becoming adsorbed H2 molecules that can aggregate into bubbles of H2 gas. That process is occurring at the very left edge of the CV trace shown here.
Potentiometric Stripping Analysis (PSA)
In PSA the WE is initially held at a negative potential (as in ASV), causing metal cations from solution to plate as the respective metals into a film that has previously been deposited on the working electrode.
After the deposition period the potentiostat control system is disconnected from the CE and the potential difference between the WE and the RE is monitored as a function of time.
Oxidants in solution (including dissolved oxygen) that migrate to the film cause oxidative “stripping” of metals that have previously plated in the film, giving rise to a series of “waves” in the potential vs. time trace, as shown opposite.
PSA makes use of potential measurements as opposed to current measurement. The potentiostats described here can both be conveniently operated in this "galvanostat" mode.
Potentiometric Stripping Analysis
In the data shown here, a technique known as histogram binning has been used to count the number of points falling within each potential window so as to construct a stripping trace from the potential vs time trace displayed in the figure above.
Plateaus in the stripping trace (corresponding to oxidation of each metal species present) become peaks after this processing step.
More information about this process can be found by visiting the Galvanostat page.
Square Wave Stripping Voltammetry - Zn, Cd, PbIn stripping analysis metal cations in solution are first deposited onto the working electrode in an initial reduction step.
This is followed by an oxidation step in which the elements come back into solution. During this step characteristic peaks for each metal appear at predictable potentials (using the electrochemical series).
Stripping voltammetry is useful for quantitative analysis because the areas of these peaks can be related to the chemical amounts of each element deposited.
Pulsed Amperometric Detection - Glucose
At left are some results in a flow system demonstrating electrochemical detection of glucose at a gold (Au) working electrode. Here, 4 x 50 μl injections of a 0.1M glucose solution were made.
The sugar reduction was carried out at -0.8V for 600 ms, followed by detection at -0.35V for 250 ms (purple trace) and at +0.40V for 250 msec (red trace), after which an oxidative cleaning step occurred for 600 msec before repeating the cycle.
In these results the vertical axis is relative current and the horizontal axis time.