The pKa values for H2dipic had previously been reported [22] and the following average values equal to 2.2 and 4.6 were obtained for pKa1 and pKa2, respectively, documenting that in neutral and alkaline solutions H2dipic exists as dianion dipic2−. Investigations on electrochemical
behavior of pyridine-2,6-dicarboxylic acid on hanging mercury drop electrode (HMDE) showed that
H2dipic is strongly adsorbed on the mercury electrode only in acidic solutions, i.e., double deprotonated anion dipic2− does not adsorb on Hg