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

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