Hello Gehan,

Providing more information would be helpful - are you applying electrical stimulation to a saline bath (solution tank) with live brain tissue?

Those kinds of experiments are fairly standard for neurophysiologists, but I've never come across concerns that the electrical stimulation alters the perfusing saline. I realize that the properties of buffer saline solution can be altered by running electrical current through it, as would be the case during gel electrophoresis, but that's only because the magnitude of the current typically applied during electrophoresis is much greater than would be used for typical physiology experiments, and also during most physiology experiments, the currents are typically applied only very briefly and intermittently, unlike the case with electrophoresis.

More detail on what it is exactly you're trying to perform would help.

Best,

Thank you very much for your answer. No, there is no brain tissue. I was trying to measure the contact impedance of the electrode by applying a battery (3.3)in parallel to them and a resistance(10Kohm). I think you may be right. May be I should use much smaller current. Instead of applying a battery, may be it would be better to use something like LM334Z. Also I would like to point out how I prepare the solution. I use 1 cup of sea water (its conductivity is 5 S/m) and 14 cup of distilled water. This gives conductivity 0.33 similar to that of gray matter. I didn't add salt to distilled water directly because the amount of salt to be added is difficult to adjust accurately( about 0.25 teaspoon of salt per litre of distilled water). Could this be the cause? If so, I could give it a second try with direct salt adding. 

I agree with the remarks Haider. Why do not try to use chemical compounds known to induce LTP in steps separated by washout ,  and record electrical signals generated ?

It sounds like Gehan is trying to characterize electrodes to be used in vivo, similar to these studies. Hope these links help. 

I agree with Haider that what you'd like to do is better accomplished with smaller, more physiological currents. The math should stay the same. 

Philippe, read carefully, Gehan just wants to measure properties of the electrodes during stimulation. There is no biology or tissue at this stage of his experiment. And even down the line it seems he needs to administer precise stimulation. Not sure where chemical LTP would help him. 

PS -  I recommend you stop using sea water and instead make something like aCSF, from scratch using distilled/deionized water and lab grade chemicals. You can then adjust the conductivity using more water or electrolytes. I don't know what you mean by saline being hard to make. With a reasonably good scale and graduated cylinder,  you should be able to reproducibly make any solution you want. 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3066196/

http://www.sciencedirect.com/science/article/pii/S1297956205001178

Thank you all for your replies. I will consider them in my future experiments

Agreed on 5 S/m conductivity of sea water. However, it varies depending on where, how and when you get it. Did you actually check the salinity of seawater? Did you purify it to ensure there are no contaminants? What is the unit of 0.33 in battery and also the solution you made? Surely 12 cups of seawater and 1 cup of "distilled" water (what is the need? you are adding it to seawater anyway!) will give you WAY much saline solution than that of gray mater. Also, 0.25 teaspoon = (5*0.25=)1.25 gm of salt. This will give you 0.125% w/v NaCl solution, which is not normal salinity (0.9% w/v) or that of gray mater. What is your source of information? 

It's the other way around 14 cup of distilled water vs only one cup of sea water. Thank you for pointing out this mistake. Any way I repeated the experiment with distilled water and salt and a lower current and got reasonable results for various electrode types.

In a paper 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3651514/

They took gray matter conductivity to be 0.33. That's why 5/15=0.33 (14 dist.wat+1 sea water)

The salt to be added to one litre of distilled water to get 0.333 S/m conductivity is from here: Figure 3 in:

http://www.angelfire.com/ab6/hershey/saec.pdf

I am very well aware of the 0.9% matter but I have some personal family reasons that makes it difficult to go to college for experiments.. so I am trying to make use of this time by experimenting at home

Any way for now, thank God and thanks to colleagues advice, I have some reasonable results for a start.

Having to work with applied mathematics is a bit distracting as you work in different fields ..never get time to be an expert in any single field