PURPOSE:To decrease the secondary mixing of separated components in eluate by vertically arranging an enriching rod whose surface has a smooth conical shape and end part at the large-diameter side has a protruding shape with the large-diameter side upward, and supplying the eluate from the upper part. CONSTITUTION:An enriching rod 10 whose surface has a smooth conical shape and end part on the large-diameter side has a protruding shape is vertically arranged with the large-diameter side upward. Eluate from the column of high performance liquid chromatograph is supplied through a supply tube 24. Then, the eluate wets the entire surface of the rod and flows down by its own weight. At this time, solvent is evaporated. When the eluate is enriched and the enriched eluate reaches the lower end of the rod 10, a liquid droplet 40 is formed. When the droplet 40 becomes the adequate size, it falls down. The amount of the falling liquid droplet 40 is determined by the physical properties such as viscos ity or surface tension and the like and the diameter of the lower end of the rod 10. Infrared rays are projected on the fallen liquid droplet 40 from a spectro scope 44, and infrared spectroscopic measurement is performed. Thus the secon dary mixing of the separated components in the eluate can be decreased.