Traceability of real-time reference gas generation for reactive gaseous compounds

For reactive gaseous compounds, limited availability of bottled standard gases often limits their measurement accuracy and comparability. Typically, an available reference gas concentration range for the specific compounds may be limited to even orders of magnitude higher than the levels normally measured at atmospheric measurements and most often only dry reference gases in inert matrices, typically nitrogen, are available. This means that when applying test gases from cylinders humidity in measurement system may cause significantly longer measurement response than in normal operation.

 

A real-time reference gas generation is an effective method to circumvent these obstacles. Controlled evaporation of the reference solution enables flexible and reliable generation of test gases in wide concentration and flow ranges as well as in different gas matrices. The method is useable in field conditions and it may provide cost savings since necessary consumables include solely pure carrier gas and solution of the studied chemical with know concentration.

 

We validate this method for different reactive gaseous compounds and key impurities. For mercury chloride, the most typical form of oxidised mercury in process emissions and atmosphere, reference gas with concentration ranging from sub-ng/m³ to tens of µg/m³ is generated. In case of typical base and acid trace impurities, ammonia, hydrogen chloride and hydrogen fluoride, the reference gases are generated in (bio-) methane and air matrices. In all cases studied, the stabilization time of generating gas flow is no longer, than some minutes. Accuracy and traceability of the generated gas concentration are estimated based on full uncertainty calculation as well as comparison with traceable reference gas standards.