By Anonymous on Tuesday, February 11, 2003 - 07:15 am:
I have a Perkin Elmer Series 200 pump (quatenary).With 50/50 methanol water, from A and B bottles,at 1.0 ml per minute the pressure is 1300 psi (Zorbax C8 15 cm ambient). However, when using the eluent from D bottle which contains 50% methanol, 40% water and 10% 0.50 Molar sodium acetate buffer, the pressure increase to 3600 psi.I tried removing the filter inside bottle D to see if that is clogged but pressure is still 3600 psi. Could buffers elevate pressure this much? Or is this a equipment problem?
By readski on Wednesday, February 12, 2003 - 12:38 am:
Questions: Will the pressure return to 1300 if you switch back to MeOH/H2O mix? Will this phenomenon occur if you switch B and D bottles? Do you filter your buffer after making?
By Anonymous on Wednesday, February 12, 2003 - 07:07 am:
Readski:
Thanks for the reply. I tried using all ports ABCD with the eluent containing 50MM sodium acetate buffer and the pressure were all high still. I did an experiment by lowering the buffer concentration to 25 MM and the pressure dropped from 3600 to 1400 psi.Though I am aware that adding buffer can increase the viscosity of an eluent I am surprised that it could have such a significant effect on the system pressure. Is my experience a common knowlege? Can anyone scientifically predict pressure changes based on buffer concentration? Original Anonymous.
By Chris Pohl on Wednesday, February 12, 2003 - 10:08 am:
I'm afraid that prediction of pressure changes with composition of buffer is not something that can be readily accomplished without collecting a great deal of data. Qualitatively, it is definitely well known that at concentrations of 0.5 molar and above, the effect of ionic strength on viscosity can be significant. But typically at 50 mM the effect of ionic strength on viscosity is minimal. So, at first glance experience would seem to be a bit surprising. The caveat, however, is that the effect of ionic strength on viscosity is intimately related to how close you are to the solubility limit of the electrolyte in the solvent-water mixture. As you approach this point, the viscosity effect should be greatest. Still, the pressure rise you describe seems abnormal. Are you sure there aren't impurities in the sodium acetate which aren't soluble in the mobile phase? Have you tried making up the sodium acetate from acetic acid and 50% sodium hydroxide?
By Anonymous on Wednesday, February 12, 2003 - 03:27 pm:
Chris Pohl:
Thank you for your insight into this incident. My solvent is filtered after the pump and before it reaches the autosampler. Even if the sodium acetate may have undissolved crystals it is caught in the filter. I have not tried using sodium hydroxide and acetic acid as my buffer but I shall try as you suggested. Thanks for you posts. I learn a lot from you. Original Anonymous.
By Anonymous on Wednesday, February 12, 2003 - 03:35 pm:
Readski:
Yes, the pressure goes down when the solvent goes back to 50/50 methanol water. And my mobile phase is filtered with 0.45 um filter. Original Anon.
By readski on Thursday, February 13, 2003 - 04:40 am:
What is the pressure if you ran 50/50 MeOH/H2O from the same bottle? Is this different from your original 1300psi from 2 bottles?
I like Chris' idea make your buffer with NaOH/acetic acid. Or just H20/acetic acid if you can work in a lower pH range.
By Anonymous on Friday, February 14, 2003 - 12:50 pm:
Readski and all:
Reading your posts made me feel that the problem I am having with high pressure on using eluent with buffer and lower without it could be a pump problem. I did experiments with just menthanol and water using a combination of ports and here are the results with 50% from each port:
Methanol Water Pressure
A B 1600
A D 2450
A C 2380
B A 2390
C A 1450
D A 1600
I called Technical support at Perkin Elmer and the engineer thinks the proportioning valve at B is faulty. It is giving less than 50%. So in the first test there was less than 50% water and more menthanol and resulted in lower pressure - 1600 psi. But when the ports were reversed, 4th test,there was less methanol in the mix and resulted ih higher pressure: 2390 psi.
The recommendation was to run 20% nitric through port B at 2 ml/min,for 15 minutes, rinse, 10% ammonium hydroxide for 15 minutes and rinse. Will post the results later. Original Anonymous.
By readski on Saturday, February 15, 2003 - 12:27 pm:
Pressure from AB should =BA.... if this is true
then AC should =CA and AD=DA but your chart does not reflect this. I suspect you have more than just a faulty B valve.
I am not familiar with PE valves but Agilent systems use a magnetic control and typically when they fail we have to replace the unit.
Good luck...