Experimental secondary reference odour mass (SROM) measurement for selected four odorants

Abstract Background The selection of panellists in dynamic olfactometry traditionally relies on their sensitivity to n-Butanol. The introduction of secondary reference odour mass (SROM), as proposed in the updated standard EN 13725:2022, offers a potential improvement in the selection process and, consequently, in odour quantification accuracy. This study was conducted at the Laboratorio Olfattometrico of Politecnico di Milano, using the new standardized procedure outlined in EN 13725:2022. This study measured and calculated the SROM values for four odorants (dimethyl sulphide, toluene, methanethiol and acetaldehyde), comparing the results with odour thresholds available in the literature. Results The research’s findings show that sulphur-containing compounds, such as dimethyl sulphide and methanethiol, have lower SROM values, respectively 0.0015 and 0.000066 µmol/mol, indicating higher odour potency compared to the other tested substances (SROM toluene = 0.77 µmol/mol and SROM acetaldehyde = 0.024 µmol/mol). Focusing on the examiners' response, a slight correlation between their response to investigated odorants and n-Butanol is found. In addition, the response of examiners to odorants is generally found to be less variable compared to their response to n-Butanol under the test conditions. A different trend emerges when comparing the panellists' responses to n-Butanol and acetaldehyde: the variability between individual responses is higher for acetaldehyde, and there is a slight negative correlation between the responses to the two substances. Conclusions This study provides specific SROM values and experimental evidence supporting the integration of odorant-specific reference materials into panel selection procedures, with the aim of enhancing the reliability of dynamic olfactometry.