One of my major problems with the SPME-GC/MS measurements was the amount of water that entered the GC-MS via the SPME fiber. After dipping the fiber into the sample solution, the amount of water remaining on the fiber after the adsorption process was finished was quite substantial causing a trail of water in the chromatogram and increased column bleeding.
Since the very beginning I have removed the drop that usually hangs on the protective needle, which covers the fiber during transfer and storage – removal with a lint-free tissue was fine. In order to reduce the water content further I have experimented with drying the fiber in a dry N2 stream. For that purpose I have used a glass vial with a septum port (for the fiber) and gas-tight in-/outlets for N2.
While exposing the fiber for drying I noticed that a second drop of water is always hidden in the needle and only removed by evaporation in the injector port (thus increasing the water load on the column). As a result I am now removing this second drop too. I have also dropped the idea of drying the fiber, because it does not remove any additional water (once the second drop is removed) and I am too afraid anyway to loose compounds through volatilisation in the N2-stream.
By removing both drops of water, my baseline is considerably better and column bleeding was significantly reduced. I am surprised that I have never read about this problem in any of the SPME papers that deal with water analysis, although the problem is a faulty construction of the fiber and the protective needle.
