PURPOSE: To realize a direct interface between a liquid chromatograph and a particle collector, and an infrared or a Raman spectrometer by supplying a liquid jet flow into a specific space and dispersing the liquid jet flow by a speed gas.

CONSTITUTION: A liquid flowing out from a chromatograph column is fed by means of a pump 10 through lines 11, 13, a filter 16 and a line 17 and jetted into a monodispersive aerosol generator 18. It is then entrained by a high speed jet flow of inert gas from a thin tube 19 into a space 20 and diluted with a gas from a line 21 in order to evaporate a volatile solvent. Subsequently, it is passed through pressure reducing chambers 28, 29 coupled through an outlet pipe 26 with pumps 30, 31 in order to remove the dispersion gas and the solvent. A beam of aerosol dispersed with a sample substance can be collected as a small spot by a collecting plate 50 or a particle beam is led to a cell 52 and irradiated with an infrared beam 55 to produce an infrared spectrum which can be introduced to a mass spectrometer M. Alternatively, a solvent is introduced by means of the pump 10 and a sample can be injected using a syringe 15.