Thanks to a nightshift of a colleague of mine, the GC-MS is up and running again. The baseline is still pretty elevated (4x as high as before), but that could also be due to the inefficiency of the previous filament. Anyway, the baseline seems to be fine.
But the column bleeding is not. I have made some tests, as a performance check:
1 – Instrument background, no injection
2- Fiber backgrounds (PDMS/DVB and Polyacrylate fibers) after conditioning
3- MilliQ blanks with both fibers
… and I have found a lot (read: too much) of bleeding in all of them. I am working in splitless mode and I purge after 3 min with 50 mL/min.
For comparison reasons, I have also tried to work in split mode (ratio 10:1, otherwise identical conditions) for one of my samples. This reduces the column bleeding significantly (to an acceptable level), but also it also reduces the sensitivty too much in order to detect compounds that I see in splitless mode *sigh*.
Finally, I ended up changing/checking the liner – and this was good, there was already quite a bit of junk accumulated. I have also moved the glasswool packing a bit towards the end in order to avoid any contact with the fiber. Additionally, I can now place the fiber more centrally in the liner during desorption – placing it closer to the column and near the temperture optimum. Ultimately, I would like to use a liner that is better suited for SPME usage with splitless injection (smaller volume and narrower bore) in order to optimise the focusing of desorbed compounds.
Some first experiments with the blank fiber showed significant improvements, most of the bleeding is gone – even in splitless mode . Let’s see, if that continues, when used with samples – I am hopeful.
