Anodic stripping voltammetry linear sweep rate?

I am using an PSoCStat potentiostat to measure Pb, with a Pt counter electrode, a pencil lead working electrode and an Ag/AgCl reference electrode. This device doesn't not support Square Wave Voltammetry. Adding Bi(III) and some Pb shows the peaks as expected.


The problem is that the PSoCStat paper demonstrates Pb detection using a linear sweep rate of 0.1V/S. This results is a very weak peak in my experimental setup. Increasing the sweep rate to 10 V/S results in a very large peak. This is 100X the sweep rate used by the PSoCStat example and other LSASV examples I see on the web. I read that the faster scan rates do indeed increase the current.


The question I have is why is the LSASV examples using such slow rates which appear to decrease sensitivity? It is because slower rates allow narrower peaks which allow simultaneous Cd and Pb detection?




I am not a voltammetry expert (aside of Czech chemists are supposed to be as followers of the founder of polarometry/voltammetry Jaroslav Heyrovský), so just pointing out general electrochemical principles:


If there are multiple redox systems in a sample, slower rate may improve selectivity. As at fast rates, redox systems are far from equilibrium state, with reaction kinetics and diffusion playing bigger role.


Hypothetically, one redox system can have its stripping preferred thermodynamically, while other one kinetically, so the latter can start forming its peak while the former is not finished yet (but would be already at slow rate).


As consequence, fast rates kinetically broaden peaks due kinetic overpotentials. Additionally, there can be more significant transient capacitance or double layer change effects.


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