A completely a utomatic apparatus h as been develop ed for t he prepa rative-scale p urification of compo unds by gas-liquid chromatograph y. A clock timer periodically activates a pump t hat injects a sample into the column . The recording potentiometer o n which t he chromatogra m is t raced has a swit ch m oun ted at t he upper margin. Collection of t he p urified main component occurs when t he recorder p en goes to t he end of the scale and t rips t he swi tch . The sensitivity of the detector bridge circuit is adj usted so that only t he t race caused by t he major component will activate the collection process.T oluene, ethylbenzene, and mesitylene were purified wit h the apparatus. Best results were obtained with tolucne. In one pass t hrough t he apparatus, 92 percen t of the impurities were removed fro m the toluene and t he p urified product was collected at a rate of 25 ml of liquid per day.