PURPOSE: To extend life of a capillary tube by decreasing a temperature of a reactor, and reduce rhodium content of an alloy constituting the capillary tube to reduce cost by a method wherein a catalyzer of which a base is paralldium is sealed in the capillary tube of a cracking reactor.

CONSTITUTION: A device 8 containing catalyzer hydrogenating microreactor and a hydrogen flame ionizing detector and a cracking reactor 6 are arranged on a downstream side of a capillary column 5, an injector 4 is arranged on an upstream side, these devices are coupled via a pipe line 25 for supplying an air, a pipe line 26 for supplying carrier gas and a pipe line 27 for supplying auxiliary gas. A capillary tube 9 made of a platinum/rhodium alloy heated at a high temperature is incorporated in the reactor 6. A filament 24 of palladium is inserted into this tube 9, an operation temperature and a stand-by temperature of the reactor 6 are decreased by catalyzer actions of metal palladium, and further the content of expensive rhodium can be decreased.