These can frequently be identified by an intense peak at 207 m/z (dimethylpolysiloxane). Non cross-linked capillary columns are a major cause. High-bleed septa are also a common cause. We recommend cross-linked capillary columns for almost all applications. We also recommend low-bleed septa such as the Agilent Technologies “red” septa (5181-3383).
A simple test to detect column bleed is to increase the GC oven temperature 20 or 30 degrees C. A corresponding increase in background indicates column bleed. Column bleed can be prevented or minimized by conditioning the column.
See the MSD maintenance documentation for instructions for conditioning columns and septa.