Standardization of the Boehm titration. Part I. CO2 expulsion and endpoint determination

The various steps required in the Boehm titration (CO2 removal, agitation method, endpoint determination, etc.) are carried out in different ways by different research groups, making a comparison of the results between these groups difficult. Herein, the methods of CO2 expulsion and endpoint determination for the Boehm titration were standardized. Blank samples of the three Boehm reaction bases, NaHCO3, Na2CO3 and NaOH, were examined for complete CO2 expulsion through sparging with an inert gas (N2 or Ar), heating, or utilizing a N2-filled glove box. Boehm titrations using NaOH as the reaction base were studied through direct titration and back-titration. It was found that to minimize errors both the NaOH titrant and HCl should be standardized prior to titration and that a back-titration is preferable for all three reaction bases. Additionally, the titration should be performed immediately after degassing for 2 h with N2 or Ar, and degassing should continue during the titration. This is found to be particularly true of the NaOH reaction base, where the effects of dissolved CO2 are the most noticeable and persistent. With sufficient CO2 removal, there is no significant difference between pH electrode or colour indication endpoint determination, and either is satisfactory.