Amphetamines by GCMS

[chemboy831]

Morning everyone,
I'm running a GCMS assay quantifying amphetamine, methamphetamine, and the designer amphetamines mda, mdma, and mdea with an Agilent 5973 MSD. I've been derivatizing my samples with TFAA to improve chromatographic performance, and all has been running smoothly for over a year. Lately, the quality of the assay has been terrible, especially with the designer amphetamines. Severe tailing, and loss of abundance. All recommended maintenance is performed regularly (inlet liners once a week, clipped column and gold seal change 1 month ago, source clean about 2 months ago.) All my other assays on that particular instrument are working perfectly, so I'm at a loss as to what could be going wrong. Anyone see anything like this? I just purchased fresh TFAA yesterday to try out, but the stock i'm working from now isn't that old. Recommend other derivatizing agents? HFBA, PFPA?
Thanks for any help you can suggest.

[Peter Apps]

Try a new column - after a years work the one that you have is probably seriously tired.

Peter

[mty]

If your instrument is working well, and it sounds like it is, consider the humidity of your lab. Perhaps this is an obvious thing you've already checked, but we've had derivatizations go kerflooey just because the air handling in the lab went south in the summer.

[ods-at-pacific]

You do not say anything about the quality of the mass spectra at the apex of the chromatographic peaks. Has this changed? Are there mass spectral peaks present that were not there before? What about your filters on the carrier gas, when were they last changed? What is the m/z range you are using for the acquisition? Does this range allow you to see air (m/z 28 and 32) and water (m/z 18 ) peaks in the mass spectrum? If it does not do an acquisition so that you can see if this is a potential problem. What type of septum are you using? How often do you change it? What type of injection split or spiltless? What type of result do you get if you run the acquisition method with no injection?

Another consideration is the carrier gas. High purity helium can contain argon. Does your spectrum show peaks at m/z 40?

[Bigbear]

How old is the injection port. Injected samples "see" the portion outside the liner during injection. You may need to solvent wash the injector shell using a brass brush. There are instructions on the Agilent web site, search for injecton port maintenance.