D664_9 (17a) 04-2014

Determination of meter readings for the aqueous buffer solutions. To ensure comparable selection of endpoints when definite inflection points are not obtained in the titration curve, determine daily for each electrode pair, the meter readings obtained with aqueous acidic and basic buffer solutions. The response of different glass electrodes to hydrogen ion activity is not the same. Therefore, it is necessary to establish regularly for each electrode system the meter readings corresponding to the buffer solutions arbitrarily selected to represent acidic or basic endpoints. Immerse the electrodes in the pH 4 and the pH 11 aqueous buffers, and stir each of them for approximately five minutes, maintaining the temperature of the buffer solution at a temperature within 2 degrees Celsius of that at which the titrations are to be made. Read the cell voltage for each of them. The readings so obtained are taken as the endpoints in titration curves having no inflection points.