MC Gradient Valve

[hplcnewuser1]

Hi, I noticed air bubbles in the thin tube going from MCGV into inlet active valve. The degaser is down but there is no bubbles in chan A and B going into MCGV. What is causing these bubbles and is this a problem for downstream, like pump or column? Also I have noticed noisy baseline only when running gradient. I'm not looking for perfect chromatography so not worried about retention shift or such. How can I avoid these bubbles without having a working degaser.
I am new to HPLC thanks for any help

[tom jupille]

How can I avoid these bubbles without having a working degaser.

The short answer is "you can't". The degasser is there for a purpose.

I'm assuming your mobile phase involves some blend of water (or a buffer) with acetonitrile or methanol. The problem is that those binary mixtures of water + polar organic solvent are very much non-ideal, in the sense that the properties of the mixture are not the average of the properties of the pure solvents. In particular, the solubility of air can be much lower than the solubililty of air in the pure solvents. When you mix the solvents, that excess air comes out as bubbles.

You can try degassing off-line using an aspirator and ultrasonic bath, but as soon as you put the reservoirs on the system, they start to reequilibrate with the atmosphere.

[tkubowicz]

Hello

I agree with with Tom, what you see is probably air from water:organic solvent mixture.
First of all you should always use degasser (or degas mobile phase).
What you can try is instead of pure water use water:ACN 95:5 (when it is mixed with 100% ACN you won't see air bubbles - air will have different solubility). Of course your method (gradient profile) will be slightly different
It is nice trick however it is not ideal solution for your problem.

Regards

Tomasz Kubowicz

[Kreall]

unfortunately Tom is right. The degasser has its purpose. But if I would be in this situation and samples are really important and there is no other HPLC system I would improvise.

As Tom said as soon as you stop degassing mobile phase it equilibrate with atmosphere. So I would try constatnt degassing by sparkling the mobile phase with helium for whole analysis.
But this could not solve the problem, very expensive solution. One word describing it - crazy.