This article presents a new method for selective preconcentration of target species and the elimination of unwanted ones from a sample mixture. In this approach, the temperature and flow direction of two microfabricated preconcentrators connected in series are controlled according to the boiling points of target species. Each micro preconcentrator consists of embedded high-aspect-ratio pillars coated with Tenax TA as the adsorbent polymer. The results showed successful concentration of propofol, a drug used for general anesthesia, from a mixture containing several volatile organic compounds found in breath. Measurements showed increase in relative concentration of propofol to C 14 by 99.8% and elimination of water-like solvent by 99.9%.