by
Slammy1 » Fri May 30, 2008 5:10 pm
First, these low volume degassers will typically have some issues with wide gradients, especially with methanol which is hard to degas. I had nightmares running wide methanol gradients in early method development on the 1100's. If possible, pre-mix as much as you can as outgassing can occur dropping an organic into aqueous even with passing through the degasser. The 2695's have a lot of issues with outgassing if they're allowed to stand very long, in my experience. Plus, the default prime flow rate is 7.5 mL/min x 3 min, I drop it to 5 x 5 for routine application to give it more residence time in the degasser. One way to ensure you don't have an air bubble at the start of the run is to pull with the dry prime function, close the valves, and (with the column disconnected) force some MP through the pumps. Often, you can disconnect the SUS-pipes (do they still call them that? - the tubing running into the check valves) and verify you have flow when running at 0.2 mL/min. It's a good way to rid yourself of stubborn bubbles. On the older Waters systems, if I took over from someone who let the system run dry I'd tranistion water to IPA and be done with it (methanol works too, it's easier to clean but not as effective). Could be a seal issue too, though I'd hold judgment on that until you're sure it's not just a stubborn bubble.