A dirty syringe needle is a very common cause of poor repeatability. If you are performing manual injections, wipe the needle with a clean, lint-free cloth or tissue dampened with your solvent before loading the syringe. Wipe off excess solvent after loading the syringe.
Leaks in the septum, injection port seal, and column nut allow sample to escape. Tighten fittings or replace injection port components as necessary.
If the injection expands to a volume greater than the volume of the liner, it can skew the peak to the left (peak tailing) or right (peak fronting). Decrease the injection size.
Make sure the connections at both ends of the column are secure. Heating and cooling of the GC oven can cause the column nuts to loosen.
WARNING! The GC oven and the column nuts are often very hot. Make sure they have cooled before handling them.
Keep the foreline pump and diffusion pump serviced. Make sure the carrier gas supply is steady and well-regulated. Avoid large changes in the ambient temperature. Keep the MSD out of drafts and direct sunlight.
Vent the MSD.
Open the vacuum manifold.
Check the internal analyzer wiring connections. Correct any loose connections.
Close the vacuum manifold.
Make sure all cables to the side board are securely fastened.
See the MSD maintenance documentation for instructions for opening the vacuum manifold.
The grounds for the detector and GC power sources may be at different potentials. This creates a current path (ground loop) through the detector interface and analyzer. Make sure the grounds for the power sources are at the same potential.
WARNING! Checking for a ground loop should be done by a qualified electrician.