pulsed amperometric detectors

[chembot]

With regards to pulsed electrochemical detection waveform optimization....

These waveforms obviously vary depending on the type of analytes in question but typically waveforms contain 5-8 parameters (time and potential parameters). Does anyone believe it is absolutely necessary when creating hydrodynamic voltammograms or optimizing pulsed waveforms for multiple analytes (1-5 analytes) after they've been resolved by HPLC to remove the working electrode and polish it after each time or potential parameter change? To me, this sounds rather cumbersome but is there really any advantage to doing this?

For hydrodynamic voltammetry, one can used DC amperometry and just change the potential for a series of separations to observe peak height/area versus applied potential response. I wonder if it is necessary to remove and polish the working electrode for each potential change.

Any thoughts?

[Chris Pohl]

chembot,

The only case where polishing would be advisable between each change in waveform parameters is when the analyte is known to be unusually prone to electrode fouling reactions during the detection process. An example of this would be detection of phenols under conditions where they undergo a polymerization reaction. In this case, you would need to polish the electrode (or substitute a fresh, clean disposable electrode) as part of the optimization process. But in general, it is actually a bad idea to polish the electrode repeatedly during the optimization process. Depending on the polishing technique, the polishing materials, the type of electrode and the detection operating mode, it can take literally hours for the electrode to stabilize after each polishing step! Generally, my rule of thumb is to polish only as a last resort, certainly not after every minor change in the waveform! Of course, using a different disposable electrode for every optimization step would get around the long stabilization times associated with polishing but this approach could be relatively expensive.

Actually, a more crucial element of waveform optimization is making sure that the effects of the waveform change have stabilized before moving on to different conditions. For example, if one increases the duration of the negative cleaning potential, the effect on the first injection after this change might well be an increase in signal to noise ratio whereas after three or four additional injections the stable signal-to-noise ratio might actually be less than the starting point.