A continuously operating pre-concentrator for trace gas analysis includes a flow channel, a pumping chamber, and a separation membrane between the flow channel and the pumping chamber. The flow channel has a width that decreases from the inlet to the outlet in such a way that the trace gas and the carrier gas maintain a substantially constant flow speed through the flow channel. The separation membrane is configured to allow preferential removal of molecules of the carrier gas from the flow channel, as the gas sample flows from the inlet to the outlet, thereby increasing concentration of the trace gas in the gas sample. The separation membrane includes a substantially non-adsorbing material that allows the gas sample to flow substantially continuously through the flow channel, so that a variation in concentration of the trace gas can be detected in substantial real time.