PURPOSE: To concentrate easily a sample and to enable quick analysis of a low concn. of the sample with high accuracy by passing a specified amt. of the sample into a drying tube then cooling the sample and dissolving again the intended element accumulated on the inside wall of the tube in a dissolving liquid.

CONSTITUTION: A drying tube 4 is heated to 80W150°C by a heater 5 and a sample 1 is fed to said tube by a constant volume feed pump 3. After the sample is thoroughly dried in the tube, the sample 1 is removed and the heater 5 is deenergized to allow the tube 4 to cool. A dissolving liquid 2 is introduced by the pump 3 into the tube 4 and the intended element accumulated on the inside wall is again dissolved and is collected in a collecting vessel 8. The degree of concentration of the concd. liquid is determined by the ratio between the amt. of the sample 1 fed to the tube and the amt. of the liquid 2. The analysis of the sample of the concn. lower than in the prior art is made possible quickly with high accuracy.