a method for detection of capillary gas chromatographic (c-gc) effluent using supersonic jet spectroscopy is described. a novel concept is introduced which overcomes four major obstacles' high temperature of the gc: low gc flow rate: low dead volume requirement: and duty factor mismatch to a pulsed laser. the effluent from the c-gc flows into a low dead volume antechamber into which a pulsed valve, operating at 5 hz, discharges high-pressure inert gas for 600 mus. the antechamber feeds through a small orifice into a high-vacuum chamber: here an isentropic expansion takes place which causes marked cooling of the gc effluent. the fluorescence of the effluent is then excited by a synchronously pulsed dye laser with iodine vapor in helium (2 ml/min) modeling the gc effluent, the fluorescence of the cooled molecules is monitored with different delay times between opening of the pulsed valve and firing of the laser. with a glass wool plug inserted in the antechamber to promote mixing between the high-pressure pulse gas and the iodine, the observed pressure variation with time follows a simple gas-dynamic model. operating in this pulsed mode it is found that the effluent concentration increases by a factor of 7 while the rotational temperature drops from 373 to 7k. the overall fluorescence intensity actually increases nearly 30-fold because the temperature drop narrows the absorption bands. tests on acenaphthene chromatographed on a 15-m capillary column show that the antechamber does not degrade resolution and that the high-pressure puls