I am trying to run DPVs using a GCE/glassy carbon working electrode on Ruthenium in 0.2 M acetate buffer (Pt CE & Ag/Agcl RE). When I try using a lower surface area electrode I see that noise during the whole DPV scan or the background noise increases.
Is there a correlation between surface area and electrochemical noise for a given material? Also would a faster scan mean lower noise? How do you go about reducing background noise (I am using a faraday cage)?
To eliminate Background noise, besides using a Faraday cage we use Isolators to reduce AC signal and in some cases even run the whole system including Laptop on DC Power (ie. Car Batteries).
How are you making the electrode? I've never personally worked with DPV, but with other electrochemical techniques, if noise is increasing with decreasing electrode surface area, something about the way you're making the electrode might be increasing the level of surface irregularities. Otherwise, noise should decrease with decreasing surface area (Cottrell equation). In cyclic voltammetry, faster scan rates increase noise, so I wouldn't recommend increasing scan rate to decrease noise, though you're welcome to try it out. You might try increasing the time of the scan to decrease noise, but without knowing what kind of analyte/system you're trying to measure, I don't know what to suggest.
I am using a glassy carbon electrode/GCe as working electrode (of different diameters). That's a commercial off the shelf GCE with 0.2 M acetate buffer as electrolyte with Ruthenium in it (mM range). When I say noise I mean signal/current-noise per unit area not absolute noise....I'm normalizing current/signal per unit area to make comparison.
i = n x F x A x v (i = current; n = number of electrons; F = Farady constant; A = electrode area; v = scanrate).
With a smaller area (A) the measured current (i) is less so the signal/noise ratio (if the noise strenght is constant) is increased..... You can run your experiment with a higher scanrate to increase the current. The current depends also on the concentration of the analyte (Cottrell).....
Other "hint": Have you polished the electrode before? (maybe you can decrease the noise by cleaning the electrode surface)
other effects which raise the noise are impurity of solvent and supporting electrolyt. Have you cleaned your electrodes/solvent electrochemically? Scan in solvent and supporting electrolyt (background), with a really slow rate (5-10 mV/sec) in the electrochemical window. IR-compensation off?
(additionally: contacts of electrodes and the potentiosat and maybe (but not fully sure) the distance between CE and WE or Ref and WE/CE can effect the backround noises)
in addition to Ralph Huebners comments above (I fully agree!), if you have the chance to rotate the electrode, this may also reduce noise. Noise (or current irregularities) may also occur if gas evolution takes place on your WE: The gas bubbles shield the electrode surface from the electrolyte, and this leads to a decrease in current, if the bubble looses contact, the area as well as the current increase again, and so on. Rotation may prevent the formation of larger bubbles, thereby decreasing the "noise".
Good luck, and try out if you can!
reduce noise is often a nice problem ! However if you use larger electrodes you get higher signal and higher noise ! This is a golden rule !!
However in your case , if I understand well you have the contrary! , then probably other problems arise ! First could be the definition of the electrodic area ; The electrodic area should be well defined and very often with small electrodes this is the major problems , Solution can enter into a poor definition of the electrodic area , it will not change and continue to give a lot of problems of noise ! Then be sure to define as much as possible the electrodic area .. eliminate possible infiltration of the solution and undesired contacts !
If the current are in the picoamperes you can think to a better screen of the cables . use grounded cables can sometime decrease the noise eliminatong the stry current in the circuit.
The kind of surface can vary the noise .. If the surface is porous you can have a higher noise relative to the current values ! therefore try to use non porous material as possible !
Glassy carbon electrode is very good material but you should take care how to define the electrode area , how to eliminate possible intrusion of the solution along the side wall of the material!
Finally I would like remind an electrochemical pretreatment of the electrode is often a good solution to decrease the electrodic noise ! In this way we can eliminate absorbed material of previous use of the electrode ! The electrochemical pretreatment can be done by cycling the electrode up to1.6 V several times in buffer solutions !
If all mentioned things won`t help you can also check if your CE has appropriate surface area (it should be quite big according to the WE).
- a Faraday cage,
- cleaning correctly the surface of working electrode
- increasing the concentration of analayte and/or
- increasing surface area of WE
will give you a reduction of noise current.
good luck!
Dear Harikrishna, What is your noise mean value of? I think it is acceptalbe up to 5mVolts. We had faced a similar problem with polymeric coting surface in NaoH electrolyte.
The noise could also be related to the potentiostat that you are using. What is the lowest current range of the potentiostat in relation to the current that you are trying to measure?
To eliminate Background noise, besides using a Faraday cage we use Isolators to reduce AC signal and in some cases even run the whole system including Laptop on DC Power (ie. Car Batteries).
I kinnda of figured out it was the maximum current settings in the Gamry potentiostat that I use. When I reduced the value from 300 mA to 0.3 mA I get a very good peak and lower noise? Did I do something fundamentally wrong in setting this value?
I found a few pointers to my problem. Here's some online link to few things to fix it-http://www.gamry.com/service-support/resources/fixed-vs-autoranging/
We (the ECG-Comon group) study electrochemically produced noise as a method to try to understand corrosion processes, and have undertaken a number of round-robin experiments to look at the reliability of such measurements. Hopefully our experimental results will be submitted shortly. I'll make a couple of points based on our work, and our current understanding of electrochemical noise:
1. Electrode area does affect the relative magnitude of the noise for several reasons. Purely electrochemical noise (i.e. noise generated by natural fluctuations in the rates of the anodic and cathodic reactions, which we can define as the standard deviation of a notionally constant potential or current ) usually goes down relative to the measured signal in inverse proportion to the square root of the area. Instrument noise may be affected by the impedance of the electrode, and hence its area, but it will typically be relatively constant, and hence less important for larger electrodes. Thus if, unlike us, you don't want to study the noise it's best to use large electrodes.
2. Modern digital instruments vary considerably in their quality, and two important errors can occur during the conversion of the analogue signal to the digital domain; quantization (steps due to the limited resolution of the analogue to digital converter) and aliasing ( transformation of high frequency noise to a lower frequency by the sampling process - look the terms up on Wikipedia for details). We have found commercial potentiostats to be rather variable in their susceptibility to these forms of noise. In order to minimize these and other types of instrument noise, you should, in general, use the most sensitive current and potential ranges that do not result in overloading (as you have found). You should also use anti-aliasing filters to remove high frequency noise prior to the analogue to digital conversion process - especially if the sampling rate is less than 50 Hz - good instruments should incorporate these, but not all do (or at least they don't all match the filter characteristics to the sampling rate).
For a review of work on electrochemical noise prior to 2001 (but the basic theory is still reasonably valid) see “The Interpretation of Electrochemical Noise Data”, R.A. Cottis, Corrosion, 27, 3, 265-285 (2001).
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