Chromatography Forum

Happy new year to everyone!

I faced an issue recently . When running GCMS Tuning standard on the GCMS using EPA8270E, the benzidine peak has became so small till 20000 in abundance only for a 50ppm mix! It used to be a relatively sharp peak with abundance 2million!

It is really a weird thing as I had changed to a new column, used a new liner and septa and changed to a new gold seal, changed ferrules and trimmed columns and washed the ion source and did a dftpp tuning! But the issue cannot be resolved !

Can someone please advise?

Thank you.

I'd try a standard of a different chemical, one that you are familiar with.

You need to first isolate whether this is a GC issue or an MSD issue.

How does the pentachlorophenol peak look?

Normal tuning shot includes pentachlorophenol to check for breakdown and tailing of the acid analytes, benzidine to check for breakdown and tailing of the basic analytes and DDT for breakdown of the more fragile analytes and DFTPP to check the mass ratios.

If pentachlorophenol is good and benzidine is bad then you probably injected something very acidic or there are high boiling compounds as residue somewhere. Since you changed the column and cleaned the source the it is most likely in the inlet. One place to check that most often miss is the split vent line. If there are high boiling components that have built up in the port or the line itself, then it needs to be cleaned out. If it is an Agilent with the copper split vent line the just replace with new copper line and use a pipe cleaner to clean the port from where the line attached into the injection port itself.