Odor detection of single chemicals and binary mixtures.

The investigation explored the olfactory detectability of two chemically and structurally similar esters, ethyl propanoate and ethyl heptanoate, presented singly and in mixtures. Initially, we measured concentration-detection (i.e., psychometric) functions for the odor of ethyl propanoate and ethyl heptanoate presented singly. Using this information, we prepared binary mixtures of the two chemicals in varying complementary proportions and, also, selected concentrations of the single compounds, such that, if a rule of response-addition (i.e., independence of detection) were to hold, the stimuli (mixed and single) should approximate equal detection. Next, we measured the actual detectability of these stimuli within the same experiment. The results were analyzed in terms of response-addition (or -additivity) and of dose-addition (or -additivity). The outcome revealed that at low levels of detectability the mixtures approximate response-addition, that is, independence of detection, whereas at high levels of detectability they approximate dose-addition. In the light of previous findings for the olfactory detection of the more dissimilar chemical pairs 1-butanol/2-heptanone and butyl acetate/toluene, we conclude that the described outcome generalizes across a variety of chemical pairs.