PURPOSE: To selectively and highly sensitively detect a macrolide antibiotic by applying a surface ionization detector to supercritical fluid chromatography and, at the same time, using an inactive column filler.

CONSTITUTION: A gas introducing section 13 is composed of, for example, a reduced-pressure flowing passage for supercritical fluid-gas transformation constituted by inserting and fixing a fused-silica capillary tube 7 having an inside diameter of about 57μm and length of about 20mm into and to the through holes of heating blocks 9a and 9B. A ring-like base electrode 2 is provided at the end section of the tube 7 and a voltage of, for example, about 200V is applied across the electrode 2 from an external power source. When the component flowing out from a column is introduced into a supercritical fluid chromatographic detector 1 through the tube 7, the fluid is transformed into a gas and the liquification of the sample is prevented by heating. The tertiary amine contained in the sample is easily ionized on an emitter electrode 3, because its ionization potential is low. Therefore, such a compound as a macrolide antibiotic can be selectively and highly sensitively detected.