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- Posts: 25
- Joined: Sat Apr 09, 2022 4:08 pm
I've just started working on developing a splitless method using an Agilent 7000 GC-MS/MS equipped with a DB5MS-UI (Agilent) 30m 0.25/0.25 column using a mixture of 4 analytes dissolved in IPA (starting initially) at 10 PPM.
A couple of runs into the work, a bunch of peaks (mostly cyclic siloxane derivatives) began to appear in the chromatogram which to my eye at least appeared to be most likely to have come from the septum and became progressively worse as more samples were run. Fairly obviously I changed the septum, but as the peaks were still present, I figured that perhaps the liner had become contaminated with septum particles, so I swapped it out for a new one expecting to see a beautiful baseline. I was much disappointed when I saw nothing but a very clean liner and contaminant peaks that were still of a similar height to one of my analyte peaks!
I did a 300C ‘bakeout’ of the injector (as recommended) which reduced the peak sizes temporarily, but they came back with a vengeance fairly rapidly. To my mind, the peaks are most likely to be from a septum (injection port or vial) so my plan over the next few days is to try to determine this by doing some blank runs without an injection, to see if the problem is injector based, then try runs without a vial septum to see if that is the problem as well as checking the needle for any snags. I have to admit that I have done a few runs taking sample from the same vial multiple times over a couple of days (not great practise), but IPA is pretty innocuous stuff, so I can’t imagine that it’s breaking down the material (Silicone/PTFE) and causing issues.
Before I start going mad and changing out the gold seal and everything else I can think of, does anyone have any further suggestions please?