Pressure leaps from run to run

[phongp]

Hello everyboby.
This is my first time posting. I hope anyone can help me. My problem is i ran a serie of injections and the pressure raises from 1 injection to the next and drop back to normal again on the third. The pressure profiles look similar on all three except the second one is raised by 3 bar. A couples of injections later it happened again the pressure raised and turn back to normal on the next injection.

My conditions are

FLow: 1,000 ml/min
MP A: MeOH/ 28mM tertbutylammonium acetate 70/30(v/v)
MP B: MeOH
gradient
0 min 85% B
8 min 85% B
10 min 95% B
11 min 85% B
18 min 85% B

Anyone have an idea on what might cause this?

Thanks

[Gerhard Kratz]

What is your reequilibration time between 2 runs? What kind of RP column you are using?

[phongp]

i am using a C-8, 150x4.6 mm with 3.5µm particles. 7mins at the end of the gradient is to reequillibrate the column. is it insufficient?

[Gerhard Kratz]

7 min for reequilibration at 1ml per min flow should be ok. Could be that your injection valve or your pump, the valves of A or B makes the troubble. If you use an autosampler please check if you have a leackage. Second, please check the flow of each valve A and B to see if both valves are working ok and each A and B has the exact flow. Please check also your flow rate while you get back pressure changes.

[phongp]

I dont suspect the pumpvalves because the retention time for my two peaks are the same on all injections. I dont see any leaks at the injectionvalve. Right now im running another established method with different column and mobilephase. I will check the precision and see if the pressure leaps on this method aswell.

[phongp]

I´ve checked the flowrate from chanel A then B with a 10 ml volumetric flask. at 1 ml/min it took 10min and 10min 1 sec to fill the flask from chanel A recpective B. i injected a sample six times with the established method and the precision is fine (rsd=0,7%). No pressure leaps even thought i did 18 injections.

im suspecting the methanol, i dont filter it because its of HPLC grade. I saw some dust in the mobile phase B container. I´ll filter it from now on and see if the problem returns.