Chromatography Forum

I wonder if anyone can suggest what is wrong.

I am analysing 16 PAHs by GCMS using a method we have been using unmodified for some time now. In our latest run I noticed that the peak areas of my standard were decreasing from run to run. also the retention time of the first couple of compounds shifts about 5 seconds over the course of 11 injections of the same standard (different vials) although the latter peak times don't shift at all.

Can anyone think of a reason?

Thanks in anticipation of a reply.

A decrease in area with a longer retention time is usually a sign of a leak in the inlet system. This affects early eluting compounds more than late eluters, but usually all retention times are affected to some extent.

A decrease in area with a longer retention time is usually a sign of a leak in the inlet system. This affects early eluting compounds more than late eluters, but usually all retention times are affected to some extent.

Thanks for that, we've done an air-water check but no evidence of a leak, however, I know how fiddly these inlets are,I 've inherited three septumless head, cryo-cooled PTV injectors and I've still to get used to them.