Dear all,

we observe a strange behaviour for some substances in our GC-C system. While measurements of amino acids, PFLA and amino sugars run smoothly (most of the time...), we have problems with the peak heights of several derivatives of polyhydroxybutyrate. We tried several compounds and found either no peak in IRMS (while there is no problem in GC-FID) for crotonic acid ethyl ester, or a linear relationship between sample amount and peak height that intersects the x-axis at (for example) 70g/L, i.e. no peaks for lower concentrations but a nice linear, reproducible relationship above that threshold for crotonic acis and ethyl-3-hydroxybutyrate.
Apparently some part of the GC-C system eats parts (or all) of the substances. But why does this not happen for GC-FID, where the same setup (although on a different GC with different inlet) is used?

Did anyone experience this kind of behaviour or has any idea what the reason might be?

Best,
Jens