Graphite ferrules

Left to right three vespel ferrules for different size connectors, one graphite ferrule, and a blended vespel ferrule. Graphite is extremely soft and deforms well to create a leakproof union. It typically cannot be resealed. Vespel is a hard material that often can be reseated. 

Figure 20-24. Graphite ferrules (Courtesy - Alltech Associates Inc., Deerfield, IL)...

The connections of the capillary to the detector, injector and the insert are additional and frequent trouble spots. Injeetion of 2 mL of dichloromethane into the closed oven is a useful overall leak test. A rapid response of the detector (10-20 s) indicates a leak near the detector, a signal delayed by the residence time in the column (eg., 60s for a 30m column length) indicates a leak near the injector. The more specific signal test is then applied as discussed above. Ferrules for the capillary are frequent sources of problems with some equipment. Graphite or vespel ferrules must have a 0.5 mm bore for a 0.32 mm i.d. column. 

Ferrules for capillary columns are usually fabricated from graphite and Vespel/graphite composites. Graphite ferrules are easy to use and have a higher... 

Always cut the ends of a capillary column after insertion through graphite ferrules. 

Retightening of graphite/vespel ferrules by to turn after the first two or three temperature-programmed runs is strongly recommended. 

Always use graphite/vespel ferrules when connecting a column to a gas chromatography-mass spectrometry interface. 

Graphite-Vespel (15% 85%) 350°C upper temperature limit general-purpose use in capillary columns recommended for MS or oxygen-sensitive detectors, also compatible with other detectors, such as FID and NPD most reliable leak-free connection proper installation requires a finger-tight turn on the nut, then an additional quarter-turn with a wrench the ferrule hole must match the column o.d. exactly to ensure a leak-free seal not reusable. 

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