Most likely you have a reasonable pressure differential in some spot - somewhere in the system air bubbles get compressed (and dissolved) under high pressure, then the pressure drops as you reach the column, and the bubbles re-form. This may not happen with water due to lower viscosity or perhaps less initial bubbles. Moving the flow restrictor (backpressure generator) may have something to do with this.
Solutions - try adjusting the backpressure valve to a considerably lower value and move it back where it belongs. Check your system for kinks in the tubing, clogged tubes, or user-installed thin tubes where the system design calls for thicker ones. Artem -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Ailong Ke Sent: Thursday, July 03, 2008 5:13 PM To: [email protected] Subject: [ccp4bb] air bubbles in the Bio-Rad Duoflow system Hello All, I own a Bio-Rad Duoflow system for almost a year. The machine lived up to some of the recommendations I saw on this board. However, there is this annoying problem with air bubbles entering columns and I cannot figure out the source. The system would be free of any air bubbles in the beginning, and performs fine when water is loaded using needle/syringe into the 5ml superloop and then injected into the column. When protein samples are injected the same way, a lot of air bubbles would appear and get trapped inside the ion exchange column, leaving yellowish marks on the Uno columns and eventually reducing their performance. I've been a FLC/AKTA user for about ten years and have never seen such problems. I doubt it is due to a faulty injection valve because we recently had it replaced for other reasons. We did move a backpressure generator (a little black piece) from post-column position to before-column, otherwise we cannot run sizing columns in a reasonable flow rate. I'd like to hear if you have similar experiences and how you fixed the problem. Thanks a lot! Ailong --
