Abstract: An apparatus for sampling a gas stream and concentrating selected constituents found therein. The apparatus includes a collection chamber into which a gas stream is drawn and a nozzle which sprays charged droplets of a collection fluid countercurrent to the gas stream. The charged droplets, now containing the selected constituents, are propelled to the wall under the influence of an electrostatic force and collected in a collection well at the bottom of the collection chamber. The apparatus can include a cyclonic flow inducer which imparts a circumferential component to the gas stream velocity, thereby enhancing collection efficiency by increasing the residency time of the gas stream within the collection chamber.