Estimation of uncertainty at reference buffer solution certification

Abstract

The national standard of the pH scale is the primary standard of the Republic of Kazakhstan, which confirmed its equivalence with international comparisons, namely, key comparisons of APMP QM-R19 (2014) and pilot comparisons of COOMET 655/EN/15 (2017). The standard implements the primary method of pH measurements using cells without transfer (Harned cells) with hydrogen and silver chloride electrodes. This cell is characterized by high reproducibility of measurement results. The state reference materials (SRM), which are widely used by laboratories at verification of measuring instruments and internal quality control, are certified with this standard. SRM of pH are the accurate samples of chemicals dissolved in 1 kg of bidistilled deionized water with a specific electrical conductivity of not more than 2•10–4 Cm/m at a temperature of 20 °C. The paper presents an estimation of uncertainty of certified pH values of CRM-standard buffer solutions in the range 9.010–9.280 pH. Determination of the pH of solutions is an indirect type of measurement. The reference pH value is determined from the results of measurements of electromotive force, temperature, pressure and other parameters.