7890B GC: D5580B Quantification

I’m running ASTM D5580 on a 7890B GC set up with open lab software. A few months ago we needed to replace the TCEP column as we lacked a gas filter and result in damage to the TCEP column which affected quantification. The column was successfully replaced, installed, instrument adjustments and calibrations were made and was back up running in no time. It was passing when running a certified quality control sample.


A couple of problems have arose recently.

First probllem, I noticed on D5580A for Benzene and Toluene determination, Toluene content is coming out higher when testing tests with known values. What would cause this to occur for this compound if there was no obvious issue during set up?

(Internal standard is 2-Hexanone, wash solution is iso-octane)z


Second problem, over the last two weeks, Running D5580B for determination of ethylbenzene, o,m, p xylenes and C9+ aromatics, the ethylbenzene content has steadily been decreasing and when compared to a certified reference material, the content that is tested is well below the expected value (10% of what it should be from the looks of it).

What could be causing my ethylbenzene to come up short and how could I address this issue?

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