Chromatography Forum

I work in a toxicology lab, and our opiate method is an SPE extraction (with MO TMS derivatives) with GCMS (EI) analysis. Without going into all the specifics of the SPE steps and GC method, I was wondering if anyone had experience with dropping abundance of the MO drugs (hydrocodone especially, hydromorphone, oxycodone, oxymorphone) throughout a single run. Basically, our first positive controls looks fine after a new liner is installed, but by the end of a sequence the last positive control is failing primarily due to these MO drugs. Changing the liner will increase the abundance from the same final control that had been failing, so we were wondering if it was an inlet/liner problem. The large drop off seems to be a fairly new problem in the last 6 moths, however the drop off has always been there a little bit.

We have tried many liners with similar results, so then we figured it was the inlet getting "gunked up". We are currently trying to clean/bake the inlet, but I worry that it's a problem with the extraction itself. I can list out the steps if necessary, but really hoping someone has identified a critical step in the process that impacts these drugs. Thanks!

Is this a glass or metal liner ?

In either case, were the "good" liners silanized & have you tried silanization to passivate the current liners ?

Have you changed supplier of the liners ?

The liner is glass. The one we have been running routinely for our methods is Agilent Ultra Inert Liner item 5190-3167. Splitless, single taper with wool. They are deactivated. We have been using this one for a while, so there hasn't been a vendor change.