Borax buffer solution for pH measurement: Homogeneity and stability studies and its application in the proficiency testing program

This paper describes the preparation of borax buffer solution and its application as proficiency testing (PT) test samples in a PT scheme. The test samples were made gravimetrically from 0.01 M sodium tetraborate decahydrate and pH of the test samples were measured by using a differential potentiometric cell. Homogeneity and stability of test samples were evaluated in accordance to ISO13528:2015. The results obtained revealed that test samples met the PT requirement criteria in terms of stability and homogeneity. The prepared PT test samples were used in the 2016 PT scheme. From the results received from 50 participants, it was found that about 44 % of participants achieved satisfactory results, 38 % achieved unsatisfactory results, while the remaining participants (about 18 %) showed a questionable result.