Dynamic calibration method for reactive gases

In this study an evaporation method is applied to dynamically generate reference gas mixtures with an accurately known concentration of reactive compounds. As a representative application, the method is used to generate several reference gas mixtures for oxidized mercury. The reliability of online monitoring of gases is dependent on the availability of accurate and metrologically traceable calibration standards. For reactive gases this is a challenge since these sticky gases easily adsorb to surfaces, which complicates and can even prevent the use of traditional static tools. In the evaporation method, a solution with well-known concentration is dosed using, e.g. an automatic syringe pump or a peristaltic pump, and mixed with the carrier gas flow. Mixing and evaporation are key parts of this process, along with temperatures and materials in different parts of the system and gas flow rate, which play an important role in the response time optimization. To estimate the applicability of this method we test its operation in the case of oxidized mercury by investigating the key operational parameters: calibrator response time and stability, possible non-linear behaviour of selected molecules, and also sensitivity to interference caused by other reactive gas compounds. We also compare its outcome to a traceable source for Hg0. Based on the achieved results the evaporation method technique is both a potential and feasible tool for the dynamic preparation of calibration gas mixtures for reactive components, in both laboratory and field conditions.