Determination of volatile organic compounds: allowable storage times for sorption tubes after sampling

Abstract

Introduction. Monitoring and control of priority chemicals presented in the emissions in cities of Lipetsk, Omsk, Cherepovets, Novokuznetsk, participating in «The Clean Air» Federal project, require frequent sampling of air samples, their transportation and storage prior to analysis. Since most samples are not analyzed immediately after sampling, correct quantitative results can only be obtained if there is verified data on the long-term stability of volatile organic compounds (VOCs) collected on sorption tubes. The purpose of this work is to obtain up-to-date, experimentally substantiated data on the stability of various VOCs during storage of exposed sorption tubes in laboratory conditions. Materials and methods. Several groups of VOCs have been selected as the most common air pollutants. VOC stability tests during storage up to 5 months were carried out on model samples using sorption tubes filled with Tenax TA sorbent. The VOC content was determined by thermal desorption (TD) and gas chromatographic analysis using mass spectrometric detection (GC-MS). Results. When stored under laboratory conditions at a temperature of (20 ± 5)°C and humidity in the range of 33-65% in hermetically sealed containers or a glass desiccator, there was shown the stability of 28 VOCs, taken on tubes filled with Tenax TA sorbent: trichloromethane, carbon tetrachloride, trichlorethylene, tetrachlorethylene, benzene, o-xylene, the sum of isomers of m-xylene and p-xylene, ethylbenzene, n-octane, toluene, n-butanol, n-heptane, 1,2-dichloroethane, n-hexane, dichloromethane, ethyl acetate, n-butyl acetate, chlorobenzene, isopropylbenzene, α-pinene, n-propylbenzene, α-methylstyrene, 2-butoxyethanol, styrene up to 5 months; for 5 VOCs: phenol, pentanal (valeric aldehyde), hexanal (caproic aldehyde), n-nonane and n-decane - no more than 4 weeks. Limitations. The stability of the investigated VOCs was not studied at low (less than 15 °C) and high (more than 25 °C) temperatures, as well as high humidity (more than 65 %). Conclusion. The results obtained allow planning the frequency and period of air sampling and the time of their storage in the form of exposed tubes before transfer to the laboratory, as well as the time of preparation and storage, taking into account the throughput of the equipment during their analysis in the laboratory.