After we transfered our HPLC in another room and reinstaled it, problems obtaining proper peaks occured. We can't get proper baseline and after injection of the sample in the column, pressure drop occurs.
Is it possible that air entered in the system?
I tried removing it by flushing the system with 10ml/min flow, but it didn't help.
Could someone suggest anything?
Thanks.

Hi Majad,

We did encounter pressure drop in our HPLC before. Usually the reason is due to air in the system. What we usually do is detach the guard column, analytical coulm and detector, leaving only the pump and injector/autosampler. We then attach a syringe to the draw off valve of the pump, draw out some of the mobile phase and then, without removing the syringe, we open the flow of up to 4 ml/min. While maintaining at this flow, we manually purge any air bubble in the system by pushing hard on the syringe and observe the pressure drop while doing this. You can close the draw off valve from time to time to check if a steady pressure can be maintained. If the fluctuations in the flow still remains, we would continue on the manual purging step until a steady pressure is achieved.

I assumed that you have degassed your mobile phase prior to using it, so I am only recommending the above procedure. Some solvents if left standing for long period of time absorbs gases too and this also causes pressure fluctuation in the system.

Good Luck

Thank you Anonymous.
Meanwhile I tried the procedure with the syringe, but nothing gets better.
Actualy, the pressure drop is not very severe (from 2000psi to 1600psi, then continuosly until 1400psi and here is stabilized), but is evident that occurs after injection.
The problem is I can't get any peak in my chromatogram, only noise is registered.

Hello MajaD,
Is it possible the connections to injection device are reversed?How is the sample injected?

Thank you all for the suggestions.
We solved the problem, which showed to be combined.
The pressure drop was due to air in the system. After repeated operation with the syringe(1/2 hour), the pressure was stabilized.
The other problem was that detector was badly conected i.e. channel B was conected instead channel A. That's why we didn't get any peak (it wasn't registerd by the detector), since we normaly work on channel A.
It wasn't a big deal, but it gave me a full day troubleshooting and all this because of transfering the device in another room.(:-))

Hi MajaD,

Glad to be of help. Half an hour sure is a long time to do the trick when you purge the system manually with the syringe. The hands of the person who did the purging must be sore for a while afterwards. But like the saying goes...."all's well that ends well" (smile)

Pet