Frequently Asked Questions Electrodes

When do Electrodes require cleaning?

See the application note Cleaning and Polishing Voltammetric Electrodes

ANSWER

1. If they look dirty they probably are and cleaning should be done.

2. If the electrochemistry reaction produces any sort of insoluble material (including any sort of electrodeposition or electropolymerization reaction) then cleaning of the working electrode (and maybe also the auxiliary electrode) will be required.

3. If you get strange peaks in a cyclic voltammogram run when the the electrodes are placed in fresh solvent/electrolyte then (assuming the electrolyte solution is pure) then the working electrode surface should be cleaned.

4. If the current is unexpectedly small then the working (or auxiliary) electrode surface may be coated with a non conductive material. Although by this stage it would normally be visibly fouled.

5. If you get the expected voltammetric peaks but at wrong E values then the reference electrode may be exhausted and need regenerating or replacement.

6. If you get oscillations/noise in starting a volumetric experiment then the reference electrode may be clogged or broken giving an open circuit. If this is suspected then repeat the experiment without the reference electrode attached. If you get a similar result then the reference electrode needs cleaning or replacement.

Our ET030 Electrode Polishing Kit is useful for cleaning electrodes.

Effect of high pH values on ET072 Leakless Miniature Ag/AgCl Reference Electrode

QUESTION

A customer would like to know if the ET072 Leakless Miniature Ag/AgCl Reference Electrode is stable in extreme pH-conditions. It would be used for several weeks in pH 12-13 environments. Would that be a problem you think ?

ANSWER

The LF electrodes were kept in 5 M potassium hydroxide for few days and in 3 M in sodium hydroxide for over a year. No junction damage occurred. A little shift in potential might occur, but the electrode functions well

ET072 Leakless Miniature Ag/AgCl Reference Electrode Extreme operating conditions

QUESTION

A customer would like to know if the ET072 Leakless Miniature Ag/AgCl Reference Electrode will endure 1M KOH solution @ 80°C conditions ?

ANSWER

ET072 was boiled in KOH for 15 min then left it to cool down for one hour in KOH. There were no apparent change in conductivity or potential.

Soaked one ET072 in 5 M KOH at room temperature for weeks. There was no damage.

This is an important advantage, since researchers use toxic mercury/mercury oxide electrodes with porous junctions because normal Ag/AgCl electrodes are not stable due to the formation of Ag(OH) which is converted to Ag2O. So our ET072 electrode can be used in extreme acid or extreme base. These electrodes have been soaked for long periods >300days and even boiled in 100g/l Sulfuric acid without damage.

Measuring Sugars using Zensor Electrodes

QUESTION

Customer asked about measuring total carbohydrates (Sugars in sweet beverages)

ANSWER

Copper-plated Zensor electrodes have been used to detect various sugars (which is the type of carbohydrates I guess your customers are interested in). See the Zen2005 paper "An electrochemical cell coupled with disposable screen-printed electrodes for use in flow injection analysis". Copper plating of carbon Zensor electrode (eg ET083) is also described in this paper. These electrodes can be used with the Zensor Flow cell or the customer might be able to build their own flow cell.

Since then Zensor also produce a 'copper nanoparticle' electrode that is suited for sugar detection, see their 'NCSE' series screen printed working electrodes, (brochure enclosed, in traditional Chinese File:Ncse.pdf). We don't stock the electrodes but when we last enquired about them they sold in a pack of 8 for the same price as charged for a pack of 40 of the carbon electrodes (ie five times more expensive than ET083).

Instructions in using Leak-Free Electrodes

QUESTION

Customer asked for instruction regarding use of ET072 electrodes

ANSWER ET072 PLEASE DO NOT APPLY TOO MUCH PRESSURE ON THE CONNECTOR. REMOVE THE CAP PROTECTING THE TIP BEFORE USE. ET072 was developed with the use of conventional reference electrodes. ET072 utilizes a unique junction which is robust and highly conductive but not porous. ET072 junction is resistant to most commonly used organic solvents. It is not affected by hydrofluoric acid and common dilute acids and bases. Please contact us for further information. There is no need to store LF-2 in concentrated chloride solution. If the electrode is left to dry for a very long period of time, it should be immersed in water for a few hours. If using the electrode in solutions containing ions that form precipitates with chloride and potassium ions, we DO NOT recommend storing the electrode in potassium chloride solution. If using the electrode in dry organic solvent, the electrode should be washed with solvent or acetone to remove water. The electrode should be stored in aqueous solution NOT the organic solvent.

High resistance of ET072 Leakless Miniature Ag/AgCl Reference Electrode

QUESTION

I recently purchased a miniature leakless Ag/AgCl reference electrode from eDAQ, and I am trying to use it for cyclic voltammetry in a rotating disk electrode setup. I am getting very bizarre results and my potentiostat is having trouble giving me a quality uncompensated resistance value for the cell (gives high phase error). I did not have this problem when working with an Ag/AgCl with a porous junction. Is the resistance of these leakless electrodes necessarily higher than that of those with porous frits? Is there a difference in experimental applications between your miniature leakless electrodes and regular-sized ones (i.e., is there a range of suitable currents for the smaller electrode vs. the larger one)?

ANSWER

The ET072 has an internal resistance (impedance) of less than 10 kohm. In most cases this will not present a problem for the potentiostat however in some cases large electrode impedance (depending on factors such as choice of electrolyte solution, distances between working, reference, and auxiliary electrodes, etc) may cause potentiostat instability, especially if positive feedback iR compensation is being used.

In such cases it may be necessary to:

1. run the potentiostat in 'high stability' mode (refer to the potentiostat manual)

2. select a different reference electrode with lower impedance. The 'leakier' the electrode the less resistance/impedance it will have.

3. change the electrochemical cell design and especially bring the electrodes closer together,

4. increase the concentration of the background electrolyte, or

5. introduce a capacitor of appropriate size between the reference and auxiliary electrode.

O-Rings used by eDAQ

QUESTION

What is the O-ring material used by eDAQ on various electrodes.

ANSWER

Nitrile/NBR a synthetic rubber used in many critical applications. https://en.wikipedia.org/wiki/Nitrile_rubber

Calomel Electrodes

QUESTION

Does eDAQ sell Calomel electrodes? For information on calomel electrodes check out our web page at

https://www.edaq.com/wiki/Reference_Electrode_Potentials#The_Calomel_.28Hg.2FHg2Cl2.29_Electrode

ANSWER

No we don't. Because of the many restrictions on selling and shipping mercury containing products (calomel is a mixture of mercury and mercurous chloride) we refer our customers to one of these sellers.

Commercial calomel electrodes are available from:

 Koslow Scientific (USA) http://www.koslow.com
 ALS Co. Ltd (Japan) https://www.als-japan.com/1390.html
 Ionode Pty Ltd (Australia) http://www.ionode.com

The real question is why anyone would want to use a calomel electrode in the first place? If the answer is that they have always done (they were once considered easy to make by the user) then the obvious question is why can't they use a silver/silver chloride electrode.

There may be some technical reason that precludes the use of a silver/silver chloride electrode, and this may need to be verified. But otherwise why not use an off-the-shelf silver/silver chloride electrode, including our leakless reference electrodes - they are usually cheaper and come in a greater variety of shapes and sizes.

Use of ET072 and ET069 in Ionic Liquids

QUESTION

Can ET069 and ET072 leakless ref electrodes be used in ionic liquids (RTILs Room Temperature Ionic Liquids)?

ANSWER

These electrodes should be OK to use in most ionic liquids. However the potentials under these conditions are not established standards and it would be best at the end of the experiment to use a cyclic voltammogram of ferrocene in the ionic liquid to determine reportable values. Ferrocene is also often used as a reference for volumetric experiments in organic solvents.

Use of ET072 and ET069 in aggressive solvents

QUESTION

Can the above leakless electrodes be used in organic solvents, perchlorate and silver salts solutions, or Hydrofluoric acids?

ANSWER

Our leakless electrodes ET072 and ET069 enable you to perform your experiments in organic solvents, perchlorate and silver salts solutions, or Hydrofluoric acids without being worried about clogging or degradation! It can also be used for long term experiments without the worry that the filling electrolyte be diluted or run out. This leakless reference electrode uses our newly developed conductive junction. The filling electrolyte is confined to the barrel and will not leak at all (zero leakage). The junction has very high conductivity with resistance under 10 kohm. It has exceptional mechanical stability, zero swelling, resistance to organic solvents, and is robust. The junction potential is independent of the sample nature or ionic strength. The electrode body is constructed from PEEK for superior chemical resistance. The filling electrolyte (3.4 M KCl) does not leak through the junction which prevents sample contamination with chloride and potassium ions. This means no clogging and no need for double junction. Since the electrode construction does not involve any glass, it can be used in hydrofluoric acid solutions.

Use of HydroFlex Hydrogen Electrodes

QUESTION

We have some laboratory electrochemical test cells that need a good reversible hydrogen electrode. The working electrolyte for these cells is 32% caustic soda at 90 degrees C. Will the Hydroflex electrode hold up well in these conditions?

ANSWER

Hydroflex is usable as a Reversible, Standard and Normal Hydrogen Electrode (RHE SHE, NHE).

The most common use of HydroFlex in the daily lab routine certainly is the application as RHE. You simply dip HydroFlex into your solution, directly. The advantages are obvious. You don't need a liquid junction, you don't have diffusion potentials and you don't contaminate your solution by ions flowing out of your reference system. As HydroFlex needs no maintenance except the regular exchange of the H2-Cartridge every 6 months, it is very well applicable for long-term tests.

Hydroflex is particularly suitable as a reference electrode in aqueous acid or alkali solutions, and can be used at pressures up to 10 bar and temperatures of up to 210 °C. pH range -2 to pH 16

ET903 Conductivity Probe loses its black plating

ET903 Conductivity Probe loses its black plating

QUESTION

Please see the photo of ET903 electrode. When we first delivered the electrode to our user, the red marked platinum plate was plated by some black substance. But now the black substance peels off from the platinum plate.

Please advise us whether we can use the electrode continuously or not.

ANSWER

These electrodes or probes use platinum which is platinised. See this Wikipedia explanation

After platinization, the electrode should be rinsed and stored in distilled water. The electrode loses its catalytic properties on prolonged exposure to air and becomes more likely to damage.

If some of the platinum black has been removed, the K value will change, but can be adjusted for by calibration. If most has been removed, it will require to be re-platinised (instructions included above).

Platinum black on the surface of the electrode is fragile and can be shaken off or damaged and may need recoating. These electrodes are suitable for continuous use in a stable environment. The length of continuous use may depend on the exact conditions of flow/ temperature and mechanical conditions.

The above is relevant for the ET901, ET902 and ET903 conductivity probes.

Leakless Reference Electrodes general questions

> 1. what is the resistance of the leakless ref electrode ?

less than 10 kohm

> 2. is there a difference between the miniature and the larger LF electrodes (aside from the size) ?

No.

> 3. is there any experience with use of these LF electrodes used over months or even years (drift of potential due to ions intruding from the electrolyte?)

Depending on conditions (solvents, temperature, etc) and frequency of use you can usually expect months to years of use.

> 4. what is the pin material ?

gold plated

Please remember these electrodes are designed primarily for ease of use, and generally need to be replaced when they begin to show excessive drift. See information sheet at

https://www.edaq.com/product_sheets/transducers/ET072_Leakless_Miniature_Ag-AgCl_Reference_Electrode.pdf. for Maintenance details.