Sorption and Subsequent Chromatographic Determination of Volatile Organic Compounds in Soil Air with the Use of an Exfoliated Graphite-Based Carbon Monolith

This paper discusses the possibility of using a new graphene-based monolith material developed at the Department of Chemistry, Moscow State University, for the identification of new oil deposits or offshoots adjacent to already registered oil fields in the course of areal geochemical surveys. Sorption of volatile organic compounds (VOCs) from soil air within an oil field was performed using two sorbents (Tenax-TA traditionally used in such analytical tests and a carbon adsorbent) with subsequent gas chromatographic determination involving mass spectrometric detection and thermal desorption as a way of sample injection (TD/GC/MS). The new material absorbs more hydrocarbons ( n -alkanes and monoaromatics) in the C 8 –C 16 range than Tenax-TA, and its chromatographic peaks are more intense. The irreversible sorption phenomenon is observed for VOCs starting from C 17 and higher; however, the concentrations of such substances in soil air are low owing to the low pressure of their saturated vapors under normal conditions. Overall, chromatograms obtained using the carbon monolith reflect the oilfield characteristics better compared to Tenax-TA. To enhance the sensitivity of determination, the thermal desorption conditions were optimized: the helium flow rate through the sorbent sample and the compound desorption time were adjusted to ensure the maximum peak area. The regeneration procedure was applied to the sorbent samples with the purpose of reusing them. Unlike the carbon monolith, Tenax-TA cannot be completely purified since it decomposes into its components at lower temperatures that the carbon monolith. Overall, the new graphene-based sorbent is not only reusable but also much cheaper than the imported polymer Tenax-TA since it is produced using only domestic materials.