Vapors Generation of Volatile Organic Compounds (VOCs) From Pure Liquids

Background and aims: Production of fixed concentration of vapors from pure liquid has many applications in laboratory and field studies of occupational health and toxicological research and also in calibration of air pollutant measurement devices of the workplaces. In this study, the advantages and disadvantages of different concentration generation methods were discussed. In addition two selected methods were compared and the factors that influence the generated concentration were identified. Methods: In order to make certain concentrations of styrene, evaporation and injection methods were used. In evaporation system air was blown in a 250 (ml) midget impinger in two modes (close to the liquid surface and inside the liquid). For injection system a syringe pump (3100 Graseby, Smiths Co) was used. Affecting factors on concentration stability like temperature, flow rate, position of nozzles have been investigated. Results: To produce 300(ppm) of styrene vapor concentrations in RH=19%, coefficient of variation (C . V) of the concentrations generated in bubbler and syringe pump systems were 2.86 and 2.01 percent respectively. Syringe pump system reached to the equilibrium approximately in 60 (min), while for the evaporative systemit took 105 (min).When the nozzle of the bubbler was placed close to the liquid surface, the coefficient of variation was 1.97% , however, when it was placed inside the liquid, the C.V was 2.52% . Conclusions: Controlling the influencing factors like temperature and flow rate are most important points for the generation of constant concentrations. The low coefficient of variation in the syringe pump system proved the better capability and functionality of this system compared to bubbler system. One advantage of the syringe pump system is that it is not dependent on liquid level of the container.