Now, of course, this method is not very useful if these three proteins have the same combination, have the same number of these ionizable amino acids, because what that means is these three proteins will have the same exact value for the isoelectric point. So they have to have a different isoelric point value for this technique to actually be useful in separating our proteins. Now, the question is, how exactly do you determine what your pi value is for a specific polypeptide? Now, before we determine what the pi value of specific proteins is, let's ask the following question. How do you determine what the pi value is of a single amino acid? So let's take a look at the following four cases.