Comparison of the primary methods for pH measurement of the VNIIFTRI and the PTB

A comparison of the primary methods for pH measurement of Russia and German y was carried out. Three buffer solutions: potassium tetraoxalate, 0.05 mol /kg, potassium hydrogen phthalate, 0.05 mol/kg and disodium tetraborate dec ahydrate, 0.01 mol/kg, prepared from materials of the All-Russian Research Institute for Physical, Technical and Radio-Technical Measurements (VNIIFTR I) and Merck KGaA, Germany, were used. The pH values obtained at 25 degrees C in this comparison agree within an expanded uncertainty of 0.004 for the berate and oxalate buffers and 0.005 for the phthalate buffer (k = 2).