Abstract: The present invention is related to a method to detect and speciate short-lived chemical substances such as organic radicals in natural and artificial gaseous environments. In short, positive charged reagent ions (AH+) are created in a soft ionization unit (9) and then accelerated into a so called drift chamber (2), where they collide with injected radical molecules (RO2), after which the newly born product ions (RO2H++A) are detected and spectated in a sensitive mass spectrometer (4) according to their masses. The main field of application of the invention would be the detection of gas-phase organic radicals in ambient air, for research activities on air chemistry, air quality, and medical investigation of the impact of air pollution on human health, as well as for routine monitoring activities in the same fields of indoor and outdoor environment monitoring, health monitoring.