Consistent step in baseline on GC/MS

[ERA_Erin]

Hi,

I am new to running the GC/MS. I am running EPA method 8260 for Volitale compounds in wastewater. I have noticed that we have a consistent step in our chromatograph around the 5-6 min mark. it is only elevated 60000 response counts, but this seems to be enough to be altering our data for our early eluting compounds. I have attached an image and can provide more if needed. Please let me know if you have a suggestion as to why this is occurring and how I can correct it. Also, I hope I posted this in the correct board. Thanks

[Chroman]

That should be water peak. You can reduce it by shorting your desorb time, if your method allows for it, but all your compounds will be affected as well. If it´s not posing a major interference I would ignore it...

[AICMM]

ERA_Erin,

At 4-6 minutes, the peak suggests you have about a 3 minute desorb? Shortening the desorb could help. However, you should not be scanning so low that you would see water or even CO2 for that matter. So the first question is, what is your scan range? Can you post a spectrum of that "peak". Also, you seem to have a fairly high noise level relative to the internal standard peaks. Your scan range is a factor here as well but so is your split ratio. Can you post that as well?

Best regards,

AICMM