Chromatography Forum

Please help--Agilent 1100 binary pump--pressure fluctuating from 10 bars--80 bars (2 line solvents mixed-72:28 ,1.2ml/min)--if single line A or B used, pressure was pretty stable whatever solvent used (pure A or B or even premixed A/B--72:28).
Thanks
solvent used: A--Ethyl Acetate B--Hexanes
100% A---pressure stable
100% B---pres. stable
premixed solvent(A:B--28:72) by one channel--Pres. stable--I had to use this way to finish analysis , not like before we used 2 channels (A2 & B1)
28% E.A. in channel A2 & 72% Hex. in channel B1--Press. 10-70+ bars ---fluctuating

---During next few days we always use 1 channel running this HPLC, and the back-pressures were pretty stable even sometimes we also switch between RP and NP.

---one week later, we use 2 channels (A2 & B1) to run this instrument with E.A. & Hex. (same solvents as last week),the pressure are back to normal.So i guess there was air bubbles in the system last week.

I really appreciate all your feed-backs.

Thanks

Thanks again

What solvent do you use? Do you use column or zero dead volume? With ZDV, 80 bar is to high, check frit in purge valve, disconnect capillary from sampler and then check the pressure.
If you use column in most cases 20 bar is to low, if there is no visible leak, there is probably internal leak. Firstly do for A channel: Run 100% A, pull out tube A from mobile faze, so you grab air bubble in tube. Put tube back in mobile phase, and observe the travel of the air through system. Does the air move up and down (problem with AIV), or bobble run smoothly towards degasser. Repeat for B channel. Do you use solvent selection valve?

Hi
If you try to do a gradient, where you use 100% organic i A, and some buffer solution i B, you often see this problem, do to checkvalves. this is fixed by adding some water to bottle A, so you thereby gets 95% wather instead 100%. It might be a good idea to rinse the system with: water-10% HNO3-water-isopropanol just remember to remove collum.

BR

Maybe degassing your solvents in ultrasonic-bath and using vaccum will help?

The compressibility factors for the two pumps is correctly set?

I'd second Klaus.

I'd also recommend you to check your outlet ball valves. In binary pumps, they must be in better shape than in isocratic/quaternary systems.