PURPOSE: To prevent mixing of a sample liquid with a solvent of a lower inner tube, by loading an outer tube with the bottom inner surface thereof being projected with a lower inner tube with the upper and lower ends stopped while a tiny hole is formed at the lower end thereof and a bottomed upper inner tube.

CONSTITUTION: When a lower inner tube 2 filled with a solvent 5 through a tiny hole 10 is put into an empty outer tube 1, a rim part of the tiny hole 10 of the lower inner tube 2 abuts a protrusion 11 of the bottom of an outer tube 1 at the bottom thereof 1 to cover the tiny hole 10. Under such a condition, a sample liquid 4 is injected into the outer tube 1 and moreover, an upper inner tube 3 with a solvent 6 injected thereinto is inserted into the outer tube. With such an arrangement, the protrusion 11 formed at the bottom of the outer tube 1 functions as a plug for the tiny hole 10 of the lower inner tube 2 thereby enabling preventing mixing of the sample liquid 4 with the solvent 5 in the lower inner tube 2 even under a long-time use.