Peter is right. It can happen.

Do you do the experiments with patch-clamp technique? Are you using virtual ground mode for recordings of ionic currents? Have you tried to un-couple the vacuum pump circuit from the suction line from the chamber by introducing a separating container?

It is a quite common source of noise. To break this suction effect, we put a small piece of paper just below the suction pipette. Microscope lens cleaning paper (really thin) works perfectly. You slightly pull back the suction pipette, the paper will make a "bridge" of recording solution. This breaks the biggest of the suction effect.

You describe it as "irregular spike noise". Do these spikes coincide with droplets being sucked down the aspiration line? I had my share of issues with that, particularly if the suction line ran parallel to a ground wire or was close to the headstage.

Another common issue with the aspiration causing noise is if a continuous liquid column protrudes out of the Faraday cage, towards the waste reservoir. In that case you would be more likely to see line frequency hum, though.

With both scenarios, I achieved improvement by inserting a dripping chamber into the suction line and/or using large-diameter tubing as much as possible. Both measures interrupt a continuous liquid column and prevent the formation of droplets that close off the cross section of the tube.

Thank you all so much for the helpful answers. I have tried some of your suggestions.. but they do not seem to work.

In particular, using broader tubes or inserting a needle in the suction tube (and ground) or using a drip chamber do not help. The problem is that anytime liquid is taken irregularly, there is noise. Indeed, if I suction with a syringe or even using a plastic Pasteur pipette, I still see the spikes.

At the end, I avoid this problem partially following Peter's suggestion. I couldn´t reduce the vacuum intensity... but I basically disconnect the vacuum pump and now I extract the liquid using the same peristaltic pump that I use to add the solution into the bath... because the exchange of liquid is slow and with same intensity in the inlet and outlet... the noise is much reduced (although it still happens some times... but nothing that disturbs my recordings).

I know this is not a solution for the original problem but at least I can go on with my experiments.

Thank you for your contributions!

Best regards,

Diego

Diego, what is the material the suction outlet tube is made of? Is it plastic, metal or glass tube? In my rig the suction outlet was a piece of glass tube that had conical tip (partly pulled glass capillary about 2-3 mm of initial diameter). So, the tip had the size of 1-1.5 mm and it was sharpened at an angle of 45o by a diamond file. So, the suction of solution in the chamber and air occurred simultaneously and continuously. It may need to somewhat regulate the strength of suction to get smooth continuous suction. If you have virtual ground configuration you should not use direct grounding

Try to break the suction tubing by cutting the tube and introduce a piece of metal grounded tube between the two parts of the suction tube. Both measures disrupt the liquid column which works as an antenna. Hope it works