Chromatography Forum

HELLO,

I am currently using an old Varian 3400 ECD. The detector is configured with one injection port terminating into 2 ECDs. I am using an RTx-5 and RTx-1701 (30 meters) and a guard column connected using a Restek universal tightfight y connector. My carrier gas is helium (6 mL/min) and I am using a temperature program. I am in the splitless mode. My front detector goes negative during the temperature program. When I look at the voltage on sceen it drops of to 0. This is a very old GC and it it not capable of reading the back pressure. I would think if I had a leak my baseline and signal would increase. Does anyone have any suggestions.

Thanks in advance.

Ms. Odonnell,

Some things to look at. First, most obvious, ensure you don't have a leak at the Y fittings when the oven is cool. Second, assuming it is affecting only one channel, swap the column ends and see if the problem stays put. If problem stays with the detector, then detector issue, if problem moves, column or injector. Third, swap the electrometers (or just the cables.) If problem stays with the detector, likely your detector needs cleaning. If problem moves, your electrometer is probably bad. One of the really nifty things about GC's configured this way.

Divide and conquer.

Best regards.

Thanks a lot for your response. I like that-divide and conquer. Here is the latest, I had already tried swiching the boards, as well as, the detector before I posted this message and to no avail. I did try your idea about switching the detector column ends. Guess what? Neither detector has gone negative. It has only been several hours but the voltage has not dropped off. I should know more tomorrow with an overnight run. Most of the instruments I use are Agilent 7890's. I would have gotten a shutdown message or could look on the screen and see an elevated pressure if I had a leak or some other problem. With this old Varian I have to measure the flow from the detector and I have no idea what the back pressure is. The "Y" connector I sealed with a resin to minimize leaks. I know the split when I read it out the side is around 20. I thought you were on to something when you said to switch the detector ends-this is really crazy. I need to complete a project on this instrument so I can not retire it yet. Let me know if you think of anything else. I value your opinion.