[Preparation of standard mixture of volatile organic compounds]

This article presented a simple, convenient and flexible device for the preparation of standard mixtures of VOCs. By the aid of a constant pressure on the surface of a liquid with specific composition of VOCs, the liquid passed through a long capillary tube at a definite flow rate. A standard VOCs source was thus formed. The mean relative standard deviation (RSD) of flow rate was 3%. As the outlet of capillary tube inserted in a stream of zero air, the components of liquid vaporized and eventually became a homogeneous gas mixture. The concentration of VOCs in the mixture varied with the pressure applied and the flow rate of dilution air. The mean RSD of concentration of total VOCs in the standard mixture determined by GC method was 5.7%, and the absolute error was 8%. No significient difference was found between the determined and calculated concentrations of the mixture. This method is suitable for preparation of standard mixtures of VOCs with boiling points lower than 150 degrees C.