Method for adding a guard column to a column in GC-MS

Hi everyone, I’m trying to add a guard column to our 7200B GC/Q-TOFMS, fitted with a multi-mode inlet. I connected a 30 cm x 0.32 mm deactivated silica column to a 30 m x 0.25 mm x 0.25 um column using Pressfit connectors. There were no leaks and the system seemed fine, but I consistently got a very noisy baseline in the GC trace in the standard runs. The baseline for the MS, in addition, was not noisy but was always above 0 on the y-axis (see image). Does anybody have any advice on this? In particular I have two questions: 1) Does anybody know whether the guard column should be included in the method in the software (Agilent MassHunter)? I believe it should but we could not figure out how to do so. Especially as I used a guard column of a wider diameter than the column. For my next try I will use one of the same diameter, but I would still like to know how to include this in the method. 2) Are Pressfit connectors suitable for this use? I have heard contrasting opinions, and I’m wondering whether siltite micro (or mini) unions are better, even though they seem more fiddly. I would be very grateful for any information on this! Thank you. Eugenia

Parents Reply
  • Thank you for your help Paul. We leak checked all GC connections with a Restek leak detector, including the connection to the transfer line. I think my colleague did the tune report and said it was fine (I don't have it as I'm away for a couple of weeks). I can try to get it for you though by asking my colleague.

    When we changed it back to the previous setup (no guard, different column), the system was working as usual.

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