How does the inflection point method handle “ties”?
If more than one pair of data points produces the same maximum change in pH per unit of acid added in the region of an expected endpoint, the endpoint is calculated as the average titrant volume of the first and last such points, and the endpoint pH at that titrant volume is interpolated. Note that the change in pH is associated with the mean titrant volume between the two data points that produces the pH change. For example, the change in pH between titrant volumes of 40 and 44 counts (or mL) is associated with a titrant volume of 42 counts (or mL). So, a “tie” between two pH changes produced between (a) counts 40 and 42 and (b) counts 42 and 46 is determined by averaging the average of 40 and 42 with the average of 42 and 46, resulting in an assignment of the endpoint to a titrant volume of 42.5 counts (the average of 41 and 44).
