Moisture in our detector fuel line?

 We are trying to validate a new method, and our area counts are low and inconsistent. Our Hydrogen is from a generator and goes through an indicating filter. I replaced said filter recently, and am seeing it respond to moisture fairly quickly. How often should I really need to replace this filter in order to protect my gas supply? Bear in mind that this same hydrogen is also being used as carrier on some instruments, so I'm trying to protect columns as well. Is it possible that enough moisture is still in the line, even after filtration, to affect the FID response?


Thanks again

Jason in TX

  • Hi Jason,


    which filter do you use? Just give me the part number and I can check the capacity for moisture. Also the type of hydrogen (99.9999%, 99.999% or 99.996%) helps in the calculation.


    On the other hand, even with those gas qualities mentioned above and thinking about the fuel line only, it won't affect the function of the FID.


    If your area counts vary that much it is normally a sign that you loose analytes in the injection system, maybe by leakage or septum purge.


    Best regards,



  • It's not just the variability. To be honest, the problem is ultimately low counts. Other locations have reported area counts of around 200, whereas we are seeing mostly 50-80. We do get occasional outliers as high as 120, and some as low as in the 30s. but most of them are in the 50-80 range. When they're that low, any deviation makes it hard to maintain <2% RSD.


    The general setup: New 8890 running with the Openlab CDS 3.2.

    Column is DB-624 (30 x 0.53 x 3.00) plumbed with He carrier and makeup from cylinder, air from local compressor with filters at the compressor, and H2 for the fuel gas from bench top generator (99.9999% according to manufacturer's site). 

    The H2 filter is a Gas Clean CP17973.


    The method runs on Split injection, 10:1 with 25.0 mL/min flow at 250 C. Carrier(He) set to 2.5 mL/min

    column flow is 2.5 mL/min run under constant pressure

    Oven ramps from 70-150 C over 5 minutes

    FID set at 300 C constant column+makeup flow

    H2 40 mL/Min

    Air 400

    makeup (He) set to 25.0 


    The samples are all clean, dry solvents at this point. 


    I should mention that we have other instruments on these same gas lines which have not seen much use. Our older 6890 which runs our regular headspace samples is on the same lines, with the H2 as carrier. THAT's the column (an HQ-PLOT) that I know has been affected by wet gas in the past. We are currently seeing issues on that now too, but I think that stems from an earlier filter being saturated and not changed early enough. I wanted to make sure we weren't still seeing too much moisture get past the new filter before replacing that again, though.


    I'm thinking of putting one of these Gas Clean filters on the incoming air line inside the lab as well. If nothing else, it will prove whether the air might still have moisture in it as well.


    We are also thinking about trying the run on another inlet. Maybe moving the column entirely. We are kind of at our wits end, to tell the truth.

  • FYI: We found the problem. There is something wrong with the inlet/split vent system somewhere. We tried looking for any leaks, and couldn't find any. The instrument diagnostic tests even came back clean. But when we went from the front inlet to the rear, the area counts came all the way into the expected range, and our %RSD was fine. We will call to have the system given another once-over by the tech.


    Jason Minter

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