8 Replies Latest reply on Jan 16, 2019 5:24 AM by james_jenkins

    Increasing FID response over time (GC 7890a)


      Hello Guys,


      I am using Agilent 7890a GC with an FID detector. I using this GC in online mode to analyze reactor exit gases. I am currently studying the dehydrogenation of Methylcyclohexane over Pt catalyst. Recently I noticed that the FID response is gradually increasing over time (ref. to the attached PDF, FYI its over 12 hours time). Then I tried dosing just Methylcyclohexane alone over the by pass without catalyst (so no reaction expected). Even in this case FID response is showing same trend.


      Details of my set up and GC is give below:


      I am using Helium as the make up gas in the GC and more over I use Helium as carrier gas in the reactor. The line from the Reactor exit to GC inlet is heating to 200 C. The gas sampling valve is at 150 C, the front injection port is at 250 C, split ratio of 100, the column (capillary) method runs from 50 C to 250 C and FID is operating at 300 C.


      Is this increasing response due to different injection volume or due to malfunctioning of FID itself ?


      Thank you in advance!