Accuracy of pH standard solutions

Abstract

High purity reagents for the pH standard solutions are needed to secure the reliability of the pH values. The reagents of potassium hydrogen phthalate, potassium dihydrogen phosphate, disodium hydrogen phosphate and sodium tetraborate were prepared by recrystallization of commercial reagents using deionized water. Impurities (Na, K, Ca, etc, ) in the reagents were compared with those in the NBS and commercial reagents. The purities of the primary reagents were higher than those of other reagents. The performance of a high sensitive pH measurement system which permits measurements at 0.0001 pH level was evaluated. The standard deviation of the pH values of the pH standard solutions prepared from the reagents was below 0.001 pH. The pH value of the pH buffer solution prepared from commercial phosphate reagents differed from those of the pH standard solutions.