Any experts with square wave voltammetry or screen printed electrodes?
Does anyone know what could cause high baseline current from SWV testing of a redox probe in Tris HCl buffer? I've been testing various disposable screen-printed electrodes (SPEs) and some produce good SWV response with ~1 uA baseline current, while others produce very bad data with 50 uA baseline or higher. The SWV conditions are: 1 mV step & 25 mV amplitude. The high baseline appears to be frequency dependent: 18 uA @ 100 Hz, 54 uA @ 200 Hz and 215 uA @ 400 Hz.
SPEs on ceramic substrates seem more susceptible to this error than SPEs on plastic substrates. The worst case occurred after conditioning the Au WE by running CV -0.4 to +1.4 V in acid one afternoon then running SWV on the redox probe in buffer on the following day. Could this be due to the acid (0.5 M H2SO4) diffusing into the ceramic substrate?
Also, a high baseline current was not observed in CV scans of the bad electrodes. CV double layer was centered on 0 A indicating no underlying anodic reaction to produce the + i baseline in SWV.
(I'm not concerned with the drift in redox peak potential, fairly certain this is due to variation in potential of screen printed AgCl RE &/or variation in actual E(0) of SAM-tethered redox probe)
Could you, please, remake a new (time[1]Tn) series of the SWV testing (for the case of the ceramic substrates) ?
So you will have the (baseline) current drift ind vs. time Tn.
1. Notation for the time Tn = total time in the acid (0.5M H2SO4) for diffusion into the ceramic substrate: [n=1,3,2,...N].
Professor Samaras, I agree that a plot of SWV response as a function of soak time in electrolyte would be useful, unfortunately I do not have this data. The red and green data in the attached plot are for two different electrodes, both conditioned the day before (and then rinsed with H2O). The red data is for an electrode which exhibits 7-8X higher electro-active surface area than the electrode which produced the green data (540 uC Au red'n peak vs. 70 uC peak area). The different EASA is due to different processing conditions from the manufacturer.
Furthermore, the red data was collected at 400 Hz, while the green data was at 200 Hz. At 400 Hz, the electrode which produced the green plot exhibited a baseline SWV current ~240 uA (and thus was not plotted due to scaling issues for the figure).
I think that it could be a side effect due to the acid retention into the ceramic substrate. If so, a "new" (parallel background) electrode is forming. This side effect should increase the (baseline) current drift id over (the soaking) time.
Hi Make,
You can run your SWV experiment with normal gold electrodes and check if still you have a high baseline.
''The high baseline appears to be frequency dependent: 18 uA @ 100 Hz, 54 uA @ 200 Hz and 215 uA @ 400 Hz''. This is normal since the influence of capacitive current (charging/discharging) is larger at high frequencies. So, it will be better if you can work at low frequencies (10-50Hz).
Which workstation are you using for your experiments?
Regards
Thanks for your response Dr. Tlili. For these measurements we used a VersaStat3. The high baseline was not typical for most screen printed electrodes, just aged SPEs on ceramic substrate. However, as I now recall some of the SPEs on plastic substrates had similar high baseline after aging. Seems to be some deficiency in the disposable electrodes - not intended for long shelf-life &/or storage in liquid electrolyte.
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