Columns and Fittings
Fittings
Graphite O•ringsor ferrules have excellent sealing quality and long service life, can be used continuously to 400 C, and are generally recommended for most applications, particularly capillary and glass columns. They are also recommended for inlet and detector liners, and for split/splitless capillary inlet inserts.
Since they do not adhere permanently to glass or metal, they can be removed easily without damage to the column, tubing, liner, or insert. A rear metal ferrule may be needed if recommended by the manufacturer.
Commonly used with metal columns and tubing, brass nuts and ferrules on the column prevent damage to inlet and detector liners, but may develop leaks above 250 C or with temperature programming.
Also commonly used with metal columns and tubing, stainless steel fittings minimize possibility of leakage at high temperature, but require care in installing columns; overtightening may damage the column end or inlet/detector fitting.
Teflon ferrules may be used to 250 C but are recommended only for isothermal work, because they develop leaks when temperature•programmed.
Commonly used with glass columns, Vespel (or graphite•filledVespel) ferrules are reusable and work well to 350 C. These ferrules may leak or crack if tightened when cold.
Glass columns can be installed using silicone O•rings. For O•ring installation, a back metal ferrule, reversed, is necessary to provide a flat surface to seal against.
Silicone O•ringsare useful to about 250 C, but, due to bleed, interfere in high•sensitivitywork. They also gradually lose elasticity and crack, so they must be replaced fairly often.
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