Preparation of calibration standard gas mixtures by primary gravimetric method: a case study on 960 μmol/mol of carbon dioxide in a nitrogen matrix

Abstract

Calibration standard gas mixtures (CSGMs) are important reference standards that are necessary to achieve traceability for accurate and reliable gas measurement results. The CSGM of ~960 μmol/mol carbon dioxide (CO2) in a nitrogen (N2) matrix as the target concentration were prepared using a gravimetric method according to ISO 6142 with one dilution step. The CSGMs of ~2.8 % mol/mol CO2 in N2 were prepared and used as pre-mixtures. Verification of the CSGMs (pre-mixtures and target concentration) was conducted using a gas chromatographic thermal conductivity detector (GC-TCD). The results indicated that both the gravimetrical value and the analyzed value of CO2 concentration where in good agreement. Excellent stability of the ~960 μmol/mol of CO2 in N2 CSGMs was shown during storage for a specified time. Such stability was characterized by a relative low uncertainty (0.177%) that was less than the required target uncertainty (0.250%). Additionally, determination of CO2 concentration in a working standard (WS) gas mixture was done using two-point calibration and it generated higher precision than other methods. This implies that two-point calibration (bracketing technique) approach is a promising method that can be applied for quantification of the concentrations of sample gas mixtures in an international laboratory comparison held by the Asia Pacific Metrology Programme (APMP-QM-S15), and for certification of a WS.