The research at the Environmental Physics Laboratory has been focused on the on-line VOCs measurements using Proton Transfer Reaction Mass Spectrometer (PTR-MS) - Ionicon Analytik, Innsbruck, Austria. This instrument allows real-time measurements with a high sensitivity and a fast time response. The air to be analyzed is continuously pumped through a drift tube reactor where the fraction of VOCs is ionized in proton-transfer reactions with hydronium ions (H3O+) - the soft ionization method, that generally does not lead to fragmentation of the product ions what simplifies the interpretation and the quantification of the mass spectra.
Monitoring ambient VOC concentrations in a semi-urban area of Belgrade represents the main activity of our laboratory. In addition to that, instrument has been used in biological research under in vitro conditions, and there is some effort to apply PTR-MS device in breath analyses to provide noninvasive diagnostics of diabetes.
Monitoring ambient VOC concentrations in a semi-urban area of Belgrade
Atmospheric residence time of VOCs is short – from few hours to months – hence, their direct impact on radiative forcing is relatively small, but their indirect impact due to their involvement in atmospheric photochemistry i.e. production of ozone in presence of NOx and light, impact on OH radical concentrations and the production of photochemical oxidants as well as production of secondary aerosols (SOAs) is quite significant. They play an important role in determining tropospheric chemistry, aerosol burden and oxidizing capacity of the atmosphere, global carbon cycle and global climate. There is evidence, as well, that some VOCs may cause harmful health effects.
In a semi-urban area of Belgrade the concentrations of VOCs are episodically measured. Receptor models are used for discernment of potential sources. The transport pathways and potential source regions are investigated based on backward trajectories and computed using HYSPLIT model. Potential Source Contribution Function (PSCF) and Concentration weighted trajectory hybrid receptor models are used for identification of source regions. Further more, the US EPA health risk assessment model is being applied to measured VOC concentrations for assessment of health risk due to exposure to them through inhalation.
The essential oils are usually accumulated in glandular trichoms on the leaf surface of plants, from where they can be released like volatile organic compounds (VOCs) into external media. Plants release VOCs into the atmosphere in response to various biotic and abiotic stresses. PTR-MS device offers the possibility of sensitive VOC detection without sample preparation or chromatography, and is therefore a suitable tool for following the dynamics of VOC emission under in vitro conditions.
Iridoid monoterpenoid, nepetalactone, the dominant compound in essential oils of majority medicinal and aromatic Nepeta species (fam. Lamiaceae), is the compound of interest in our research. PTR-MS device is used for the measurements of nepetalactone content in the atmosphere of glass jars. The effect of different carbohydrate sources (sucrose, fructose and glucose) in culture medium on the accumulation of nepetalactone in shoot cultures has been investigated. There is, also, the possibility to investigate the allelopathic potential of nepetalactone.
Further research is aimed at determining various biological activities of nepetalactone, but of other VOCs under in vitro conditions, as well.
The exhaled human breath contains the natural constituents of air as well as a variety of endogenous volatile organic compounds. The most abundant of these are acetone, methanol, ethanol, propanol and isoprene. To achieve direct breath analysis in real time, the dynamic response of the instrument or technique must be appropriate. The 90% response time should be less than 10% of the total duration of an exhalation to measure the analyte concentration accurately. The response time is relevant to real-time techniques (e.g. PTR-MS). The time resolved analysis of exhaled breath gas is, also, of high capability and significance for different applications.
In collaboration with Institute of Endocrinology, Diabetes and Metabolic Diseases levels of acetone were measured with PTR-MS device in breath of diagnosed diabetics and compared to breathe gas of healthy individuals. Persons with diabetes can exhibit a broad range of acetone in their breath, but still increased comparing to healthy ones. As such, its concentration levels in breath can be indirectly represented as the metabolic products of diabetes.