Reference Gas Mixtures of Formaldehyde in Nitrogen: Preparation by a Dynamic Gravimetric Method

The preparation of formaldehyde gas mixtures required for metrological assurance of air pollution control is an urgent task. Methods for the preparation of gas mixtures of formaldehyde for metrological purposes are considered. The 2 μmol/mol-level gas mixtures of formaldehyde in nitrogen have been obtained by a dynamic-gravimetric method with the depolymerization of trioxane vapor. The efficiency of the trioxane conversion process was experimentally studied. The sources of uncertainty are analyzed in detail. The reference gas mixtures obtained were used for the formaldehyde mole fraction measurements during the CCQM-K90 key comparison. The relative expanded uncertainty of the measurement U = 3.3% was achieved, confi rmed by the comparison results.