Abstract: A method and apparatus are described for the isolation and purification of a solute prior to carrying the solute by means of a carrier gas into analytical instruments such as gas chromatographs. The apparatus is comprised of a serial differential trapping arrangement. The method provides for increasing the ratio of solute to carrier gas in a gaseous stream containing a carrier gas and a sample comprising solute. This is accomplished by forming a first gaseous stream comprising the sample, passing the first gaseous stream into a first adsorbent-containing trap and therein trapping said solute; and, thereafter simultaneously heating and backflushing said first trap with a first carrier gas to form a second gaseous stream comprising first carrier gas and the solute. The second gaseous stream derived from the first trap is passed to a second adsorbent-containing trap and solute is trapped therein.