PURPOSE: To separate and sample quickly and exactly the satd. component, olefinic component and arom. component in a sample hydrocarbon oil, by providing metallic columns, a pump, etc. which withstand respectively high pressures and determining the partition points of the three components by using an indicator added to the sample or silica gel.

CONSTITUTION: A sample hydrocarbon oil is drawn by an injection cylinder 8 into a sample loop 7, and a displacement solvent such as isopropyl alcohol or the like is fed from a vessel 1 through a high pressure-resistant pump 2, a three-way valve 5, and a six-way valve 6 to the loop 7 where the sample is passed through high pressure-resistant metallic columns 11 packed with silica gel to a flow cell 14 arranged to avoid the incorporation of foam. A small column 16 contg. a fluorescent indicator (JIS K 2536) or the like for analyzing the compsn. of petroleum products, i.e., hydrocarbons which is incorporated in a silica gel is placed in front of the inlet of the columns 11, and the point where the absorbancy increases sharply at each partition point of the components which are separated in order of the satd. component, the olefinic component, the aromatic component and the displacement component is detected with an autograph UV visible spectrophotometer 13, whereby the respective components are quickly and exactly separated and drawn. The three components contg. no displacement solvent are thus separated with high purity.