环境中挥发性有机物监测及分析方法

挥发性有机物(VOCs)是一类重要的环境污染物,严重威胁着环境和人类健康。随着VOCs问题的日趋突出,关于VOCs监测技术的研究也越来越多,检测技术逐渐完善。本文对大气中VOCs的监测技术进行了详细的综述,重点介绍了气相色谱-质谱、高效液相色谱等离线检测方法和质子转移反应质谱法在线监测方法。此外,本文分析了各种采样方法及仪器检测技术的优势与不足,旨在为大气VOCs的监测与研究起到一定的指导作用。

The monitoring and analysis methods of volatile organic compounds in the ambient air

Background, aim, scope Volatile organic compounds (VOCs) are a series of important pollutants which have strong impacts to environment and human health. They are the direct precursors of surface ozone and secondary organic aerosol from photochemical and atmospheric reactions. There is thus an urgent need for accurate and precise measurement of VOCs. This paper reviews and compares those updated VOCs monitoring technologies. Proper parameters and conditions for sample collections and analytical methods for the widely-used off-line and on-line measurements have been discussed and proposed. Materials and methods In this study, we reviewed the achievement on VOCs sampling and analysis based on researches published in the recent decades. Results Off-line monitoring requires collection of airs into a container (e.g., canister) or onto sampling matrix (i.e., absorbent), which could be divided into non-selective and selective collection. For the non-selective air sampling, stainless steel canister and polymer bags (e.g., Tedlar or Teflon) are widely used. Selective air collection allows the target compounds to be enriched onto the absorbent by either active sampling or passive diffusion. Absorbent tube is typical media which is more convenient to be carried and offers a lower cost than the canister or sampling bag methods. In addition, the tubes can be reused at least 100 times before the absorbent to be replaced. Instrumental analysis is an important sector in the VOCs measurement. Laboratory-based capillary gas chromatography (GC) coupled with a mass spectrometry detector (MSD), flame ionization detector (FID), electron capture detector (ECD), or photoionization detector (PID) is a typical instrument to analyze either canister/sampling bag or absorbent tube loaded samples. MSD is able to detect and identify a wide range of VOCs. ECD is more sensitive on detection of halogen and nitro-compounds, while FID is suitable to measure high carbon-fraction compounds such as alkanes and alkenes. PID offers high sensitivity and fast response in characterizations of aromatic compounds (e.g., benzene). Discussion Such entire air collection has advantages on reconstructing the whole air compositions in real environment and needless of complicated operation techniques. However, few drawbacks include that the containers are too bulky to be transported and active compounds are easily lost from the inner wall. Compared with the active methods, passive air sampling methods do not require multiple equipments and units (e.g., no electricity supply is needed) and results in a low operation cost. However, the measurement can be highly interfered by external factors such as air velocity. Compare with the off-line monitoring, on-line methods avoid complicated post-sampling procedures. However, current on-line monitoring limit on detection of single or multiple compounds with high abundances only. In addition, the instruments are often costly. Conclusions Both off-line and on-line VOCs monitoring technologies have their own advantages and short-comings. Selection of a proper or combination monitoring methods is critical to achieve the goals of researches and sampling campaigns. Recommendations and perspectives Cost and operation techniques are considerations as well. All operators and technicians must be well-trained and all of the QA/QC procedures should be followed. In addition, further works on method development and advancements is necessary to obtain a more accurate, precise and sensitive measurement on VOCs.