Atmospheric Pressure Interference with TCD Use

[bgrasmeder]

We seem to be getting a lot of interference on our Agilent 7820 TCD due to atmospheric pressure changes. Simply opening a door near the lab will cause a spike in the baseline which can be a big problem if it comes near a component of interest. If it is a windy day, the baseline is very unstable and we can not get precise measurements. I have seen similar behavior on a TCD installed on an Agilent 6890

Has anyone seen this behavior and if so, what did you do to overcome this? Any information would be helpful.

Thank you.

[GasMan]

Just connect a few feet of 1/8 inch plastic tubing to the TCD exit.

Gasman

[bgrasmeder]

I will give that a try. Thank you!

[bgrasmeder]

Gave it a try but didn't have much success. I am completely amazed it is so sensitive. The instrument sits inside a room which is inside a very large room (30 x 50) with very tall ceilings. It is attached to the main production facilility and has a very large opening between the two areas. If I open a door, fully 30 feet away and around a corner in the main facility, I will see a disruption in my baseline.

[Johnny Rod]

Might sound like a silly question but what column, flows/pressure are you using? What TCD parameters? I take it you've isolated this problem from anything else the instrument/gas piping is doing? On ours we see loss of precision when doors slam around the time of injection but the chromatography looks okay. I had to turn off the inlet/column auto flow zero as it was making baseline bumps at the end of each run though.

[bgrasmeder]

Our column is a 2 meter packed Haysep S, column temp is 40 degrees C and flow is set to 20. There is no question this is a pressure phenomenon. If you open and close a door, there is an immediate baseline disruption. There is a vent in the room which is pretty strong which may be enhancing the affect. We're going to try turning that off to see if we get the same affect. Agilent suggested adding tubing to the outlet as well, but they suggested 10 feet or more. The tubing we put on last week was only a foot or two. Hopefully the tubing will make a difference.

[Johnny Rod]

Do you see any fluctuation in head pressure when you are getting the bumps? I'm running out of ideas a bit!

[bgrasmeder]

OK, now I am confused. The head pressure of what? I'm not sure where you read the head pressure, sorry.

Yeah, this is weird.

[Johnny Rod]

Column head pressure, you can get it on the display or using the software keypad on the PC (I presume you have this installed? Looks like a 6890 keypad). As these things seem to fixed in flow control mode, the setpoint for pressure is usually zero but the actual pressure will be there.