In the field of analytical techniques, the preprocessing of the gases is generally a very important step, especially to get a preconcentration effect in order to increase the limit of detection. Concentrations ranges to detect are often lower than detection limit of many analyzers, leading to the needs of preconcentration devices. A gas mixture can flow through a microreactor and can be accumulated during a certain time thanks to a sorbent, and can be desorbed by a temperature pulse and brought to the detector. The current development of micro chromatograph needs a step of preconcentration. Microfabricated technology allows fabrication of miniaturized preconcentrator for this analytical detection system for in situ chemical analyzes. Main part of the device is a silicon microreactor (20*8,5mm², thickness 500μm) with a micro structuration made by deep reactive ion etching (DRIE) leading to a chamber with a volume of 14 µl. This device is usually filled with carbon powder as the adsorbent. The interaction between the sorbent and the gas is a physisorption reaction in order to not affect the analyte chemical structure. The adsorbent can also be the bulk like Porous Silicon (PS) which presents a high surface area and consequently interesting properties for the gas adsorption with weaker interactions, but lower desorption temperatures. A comparison between these two sorbent types is interesting in order to estimate their efficiency. A platinum resistance is screen printed on the back side of the silicon plate to act as a heater for the control of desorption temperature with a heating rate of 40°C/s. This allows adsorbed molecules to be released with a high concentration. An application for VOC is related to analysis in chemical plants. Experiments conducted with a carbon nanopowder preconcentrator associated to a micro chromatograph (μGC) with SRA Instruments Company have allowed to obtain preconcentration factors (ratio of outlet to inlet concentration) close to 800 with 50 ppb of toluene.