Alternative Methods for Determination of Certified Value and its Uncertainty: Case Study of Using the Gravimetric Method for Preparation of Gaseous Primary Reference Material of Ethanol in Nitrogen at the Slovak Institute of Metrology

Resumo

Gaseous mixtures of ethanol in nitrogen are prepared by the gravimetric method according to ISO 6142. The liquid component, ethanol, is added into the cylinder by the gas tight syringe. The exact amount of added liquid is determined by weighing the syringes. The exact amount of ethanol is calculated before starting filling the cylinder in accordance with the concentration of the final mixture. This calculated amount of liquid is filled into the syringe. The same type and volume of the empty syringe is used as a reference syringe. Before filling, the full syringe is weighed vs. the reference syringe. After filling, the empty syringe is weighed vs. the reference syringe. This procedure and the determination of the uncertainty of the weighing have a considerable influence on the certified value of the final mixture. Here, based on this simple experiment, we present the approach for uncertainty analysis used at the Slovak Institute of Metrology and compare it with different approaches, which includes the GUM uncertainty framework, the Monte Carlo method, and the characteristic function approach.