Chromatography Forum

How can we know the air bubble's presence in column and how can we remove them ?

there is no such thing as air bubble in column (assuming we are talking about HPLC column). You might have no solvent ion column because you did not use end plugs. As soon as you start pumping solvent through column you will fill it with solvent.

Actually, I've seen trapped air in columns take a while to redissolve and work its way out. The symptom with optical detectors has been spiking of the baseline as the air comes out of solution at the entrance to the detector. In my experience, the spiking decreases in frequency and eventually disappears once all the air has been removed. I've seen it take anywhere from a few minutes to a couple of hours (depending on how badly the column was dried out).

I disagree with that. Spikes are related to air trapped in detector cell, if you remove column, use by-pass and apply higher flow rate you will flash air bubble from the cell. This happened when your detector cell accumulates some dirt and air bubble "hangs" to the wall. Usually higher organic wash solves this problem.
In my opinion, geometry of the column, presence of small particles of silica and flow/pressure in the column should eliminate air in column after passing 1-2 column volumes.

There is absolutely no doubt that columns can harbor air bubbles. I have used a N2 presure system (instead of piston pumps) and carelessness have caused N2 to be blown through the column. It takes a long time to get all the gas out, using pure organic can speed this up. One can see air bubbles, even foam, come out of the column if a teflon tube is used for the connection to the detector.

If you do inadvertantly end up with air in a column, it helps to connect either a backpressure restrictor after your detector cell or a long length of narrow bore tubing to generate some back pressure across the detector cell. This holds the outlet of the column at a higher pressure than in normal operation which helps solubalise residual gases, and also holds the detector cell at an elevated pressure which helps prevent outgassing in the flow cell.

In my opinion, geometry of the column, presence of small particles of silica and flow/pressure in the column should eliminate air in column after passing 1-2 column volumes.

I wish my columns had known your opinion ahead of time, they might have behaved better!

All joking aside, though, we have to disagree on this one.

To parallel Hans' experience, I have had columns that were improperly capped for storage and had at least partially dried out. When first hooked up (no detector) we could see visible bubbles coming out the end. When we hooked up the detector, the baseline spiked like mad, then the spikes gradually became less frequent and finally went away (presumably as the air dissolved). We could see bubbles in the teflon tubing coming out of the detector.

Air trapped in column= overrated.

Ive seen pleanty of people remove the air after several CV's and have no problem with their columns...

of course my next question is how did it get there! Youre fired!

warranting no backpressure, frit is still in place...
Just kidding...flush re equil...and run

So if I find a column that was inadvertantly stored without caps, it might still be OK? I have always heard that it was trash after it dried.

What about collapse due to using inadequate organic. Can that be regenerated?

Ron J.

So if I find a column that was inadvertantly stored without caps, it might still be OK? I have always heard that it was trash after it dried.

It might and it might not. Depends on what was in it and how thoroughly it dried out. If you're lucky, you'll get a bunch of air bubbles out; the bubbles will gradually get less frequent as trapped air dissolved and the column will be OK.

If you're unlucky, you'll get the air bubbles out, but the column will not perform correctly (high pressure, peak shape issues, selectivity changes, etc.). If you had buffer salts in there, for example, and they dried out/crystallized/precipitated inside the pores you may not be able to revive the column.

If you don't have a backup column handy and you need to get up and running, attempted resuscitation may be your only choice. Otherwise, you have to weigh the value of your time against the cost of a replacement column ("Columns are cheap; your time is valuable!").

What about collapse due to using inadequate organic. Can that be regenerated?

To be nit-picky, "dewetting" is probably a better explanation than "phase collapse" for what happens to some columns with very-low-organic mobile phase (hey, picking nits is what I do!); it *is* (usually) reversible, but it can take quite a long time for the inside of the pores to re-wet. Higher flow rate (actually, higher back pressure) helps, as does using a high % of organic solvent.