Abstract This work describes a device that permits the use of a small glass impinger for the automatic sampling and enrichment of air pollutants “on-line” with high-performance liquid chromatographic separation. The impinger is mounted in a modified autoinjector instead of in the vial rack which, using appropriately modified software, permits the automatic sampling of the pollutants by bubbling air through an adequate reaction solution. This solution with the trapped/reacted compounds is then transferred by the autosampler syringe from the impinger to a high-performance liquid chromatography (HPLC) column. After several steps to clean the impinger, using the mobile phase or a specially chosen solvent, the impinger is ready for a new analysis. With a tandem configuration, which allows the first sample to be analysed during the sampling of a second one, a higher analysis frequency is obtained. The technique was tested by determining ng/l concentrations of aldehydes and ketones in an urban environment, sucking air through solutions of 2,4-dinitrophenylhydrazine (DNPH) and phosphoric acid in triethylphosphate. The resulting DNP-hydrazones were injected automatically into a 250×4.6 mm I.D. reversed-phase C 18 HPLC column (3 μm) and were separated using an isocratic acetonitrile-water (70:30, v/v) mobile phase and then they were detected with a UV monitor at 360 nm. All sampling parameters, such as DNPH and acid concentrations, impinger air flow, sampling time, derivatization speed, blank values, etc., are discussed.