A chromatographic device comprises a chromatographic tube, a chromatographic
medium,
a piston assembly, an elongate rod, and a threaded member. The piston assembly
is within the tube and is positioned generally between a first end of the tube
and the chromatographic medium. The chromatographic medium is generally between
the piston assembly and a second end of the tube. The elongate rod extends partially
into the chromatographic tube such that the piston assembly is between the elongate
rod and the second end of the chromatographic tube. The elongate rod has a threaded
outer surface. The threaded member is threaded to the threaded outer surface of
the elongate rod. The treaded member is operatively secured to the chromatographic tube.