Feasibility of membrane inlet mass spectrometry for on-site screening of volatile monoterpenes and monoterpene alcohols in forest soil atmosphere

Volatile monoterpenes and monoterpene alcohols exist in the forest soil atmosphere and they may play an important role in controlling microbial processes related to C and N cycling in boreal forest soils. Therefore, information is needed about their actual concentrations in the soil atmosphere. Here, we developed and applied membrane inlet mass spectrometry (MIMS) with a simple sampling probe for an on-site determination of the most common monoterpenes and monoterpene alcohols in the forest soil atmosphere. The MIMS method was also compared with a chamber method for collection samples into sorbent tubes and an off-line static headspace GC-FID analysis. The sampling principles of the methods are different: the chamber method measures a bulk concentration of a 3-liter sample whereas with MIMS it was possible to measure smaller sample volumes at more localized sites. The chamber method gave higher concentrations than MIMS did, partly due to a fact that roots, cut during the installation of the chamber into the soil, could increase the concentrations of monoterpenes in the soil atmosphere and partly due to a possible interference of ambient air with MIMS measurements. The MIMS method can reliably give only the total concentrations of monoterpenes and monoterpene alcohols. On the other hand, the MIMS method is very rapid and easy to use and can provide analytical tools for direct on-site screening.