Uncertainty evaluation for nine VOC gas certified reference materials used for indoor air testing

Abstract

9 kinds of volatile organic compounds (VOC) gas certified reference materials (CRM) for indoor air quality testing were developed at nominal 1 µmol/mol in nitrogen. The property value was assigned gravimetrically and its uncertainty was evaluated by combining different contributions to uncertainty. The resources of uncertainty were discerned as the preparation process, homogeneity and stability and the evaluation method of each uncertainty component was proposed, especially the uncertainty calculation method of raw material’s purity encountered with “interference impurity” was discussed. The relative expanded uncertainties (k = 2) of the nine VOC CRM were in the range from 1.63 % to 2.32 %. The experimental results show: (1) the uncertainty component has basically the similar contribution to the gross uncertainty of its property value; (2) the uncertainty associated with the mass weighing of nine VOC mixed intermediate liquid has the greatest influence on the uncertainty caused by the preparation process; (3) the nine VOC CRM was stable for minimum 12 month with pressure above 2 MPa but their uncertainties should be assessed and combined; (4) more attention should be attached to the uncertainly connected with stability to study its long-time stability.