urgent. large voltage offset & drifting

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pangeng
pangeng's picture
urgent. large voltage offset & drifting

Hi everyone,

I am in urgent knowing what is wrong with my amplifier (HEKA EPC 10 USB). So thankful if you guys could give me a hand.
I met a problem when using a HEKA EPC 10 USB (with patchmaster) which belonged to another staff in the lab previously.

using test pulse (default setting), when the pipet of the probe dipping into the bath solution, the voltage offset increased a lot (even over 200mV).
If configuring the Gain below 0.02mV/pA, I may see the current signal. I use the "auto" button of the voltage offset section, patchmaster keeps voltage offset as 0mV. I have to manually configure that. In addition, the signal drift randomly up and down.
All setting of patchmaster is default.

However, if I use the model circuit/model cell, there is no any problem. amplifier is grounded, microscope is grounded.

what I tried
re-prepare fresh agar bridge
re-coat silver ware
filter bath solution
use bath solution as pipet solution
directly dip reference wire into the bath solution without using agar bridge
re-instal patchmaster
without using glass pipette, directly dip silver wire into the bathsolution

May I ask what is the potential problem that I did not check?

thx!!!

BigPharmBoy
BigPharmBoy's picture
Using the model cells was an

Using the model cells was an excellent idea. You said that the model cell works just fine. This suggests that there isn't anything wrong with your headstage or amplifier.

There seems to be a huge junctional potential problem here. But it doesn't seem to be a result of your solutions because you still have the problem when you substitute bath solution for the pipette solution.

The only other things I can think of is that there might be some residue buildup inside your pipette electrode holder. So you will have to disassemble the holder and rinse it thoroughly with distilled H2O. The other things is that there may not be a sufficient connection between the headstage and the reference electrode in the bath. You may need to replace the wire that connects those two components.

wantapi
wantapi's picture
Hi!

Hi!
It is definitlely not the amplifier.

There might be a very small leak in your bath chamber, creating a current between the bath and the microscope. Check by putting the pipette and the earth into solution in something that is clearly tight, such as a cell culture dish. Disconnect the perfusion for this test.

Secondly, you might not have  a real silver wire. If you are using wires that only have a silver coating but are not silver throughout, you will not be able to coat the wire properly and drift will be the result.

Regards, wantapi