Process and device for detecting measured substances in an ambient substance. especially for detecting gaseous warfare agents in ambient air A process and a device are used to detect measured substances (A, B) in an ambient substance, especially to detect gaseous warfare agents in ambient air. First, light reaction ions (O2-, H+ with H2O clusters) are generated from a reaction substance (ambient air, H2O), and are added to the mixture (32) of measured substance (A, B) and ambient substance. Reaction ions (O2-,H+ with H2O clusters) thereby attach themselves, in spatially inhomogeneous distribution in a measurement chamber (10), to heavy molecules (MA, MB) of the measured substance (A, B), forming quasi-molecular ions (MA-, MB+). An electric field of a predefined basic frequency and amplitude which varies over time and alternates about a zero line is generated in the measurement chamber (10). The quasi-molecular ion current resulting from the electric field is measured and the measured signal is analyzed. To differentiate a first measured substance (A) from a second measured substance (B) present simultaneously in the ambient substance, first, in a preliminary test for a defined measurement chamber (10), the correlation between the quasi-molecular ion current and the basic frequency, the amplitude, and one asymmetry in the change over time in the electric field strength with respect to the zero line are determined, each time in isolation for the first (A) and for the second (B) measured substance. Then a first measurement is made of the mixture (32) with a first asymmetry, followed by a second measurement of the mixture (32) with a second asymmetry. The measured signals of the two measurements are logically correlated (Figure 2).
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