Of the following, the incorrect option related to the determination of the isoelectric point of amino acids and proteins:
a. In proteins you can estimate why when they reach the isoelectric point they precipitate.
b. It requires amino acids to be protonated, which is why they are prepared in acid.
c. It is not necessary for the potentiometers to be calibrated as the value is not altered.
d. It is required to add the slow titrating agent so as not to exceed the pH.