Chromatography Forum

Hi,

We have an LC system coupled to a QTOF mass spectrometer. Few days ago the column got jammed and the pressure started building beyond the max pressure limit. I tried washing the column with 95% and 100% acetonitrile... after that it seemed okay.. but even then the pressure was higher than usual.

Last week I was washing the column with 95% ACN, suddenly an error showed... "Compressor limit of the pump exceeded". I Googled it and got the suggestion to purge the pump. After purging, when I closed the purge valve, I got no pressure. Certainly, somewhere it is leaking. Then I saw a point on the sample loop is bulged up and solvent is leaking from there. I have attached the picture for your reference.

My question is should I just change the sample loop and the column? Or there is a serious need for a more in depth inspection? The company people are asking for huge amount of money for inspection. We don't have an AMC also.

I am also curious about what made this loop rupture happen, so that I can avoid it in future.

If I just go for a sample loop what should be the pore size of the loop? And also, We run various types of sample, from peptides to small molecules. What pore size column should I go for such a general purpose use?

Thanks in advance

Arnab

Hi Arnab,

I'd say, replace the sample loop with a sample loop having the same part number as the original one--keep things simple. Do you have a record of the volume of the loop and its material of construction? Ah yes, from the photo, it looks like a 50 microliter loop made of PEEK. Not too expensive to replace. If you're running THF as a solvent, I'd consider replacing this plumbing material with stainless steel.

Don't know the ID of sample loops off-hand, I think the ID is likely standard (say 0.17 mm ID), it is the length that is the more important parameter.

Hard to give advice on particle size without knowing more about how speedy you want to perform your separations and things along this line.

Let us see how others weigh in and thank you!

For a simple replacement , take a 0.5mm ID peek tubing and cut 25cm , this makes very close to 50ul loop.

Remove the peek nuts from the damaged loop and replace with the new loop.
Then test the system again to see if any more leak.

I agree with Matt. Peek tubing is good but with organic solvents it can swell and if pressure is too high the fitting cannot stay at his place. Just get a new 50µl sample loop. More interesting is why your column showed such a high back pressure, what happened there. Can you tell us the column and the chromatographic conditions?

Thank you so much guys. First I'll answer why the column showed huge pressure.

I realized later, before the incident I ran a mixture of ammonium formate and acetonitrile and then the LC was idle for few days. I should have washed off all the buffer out of the system by running water. When I detached the back end of the column there were white fine residues, probably salt precipitation.

In high concentrations of ACN they got precipitated, I guess. Even the PEEK tubing connecting the guard column to the column also got blocked and I could see white deposition in the pore.

mattmullaney, yes it was a 50 uL. For time being, I cut the loop and am using a half of it just to flush the system. I got a PEEK tube with the same pore size with 50 uL volume.

I washed the column by fitting in reverse in a different HPLC and washed with water, looks like the salt has been washed off. Now I'll check by attaching to my LC system.