Ions can migrate in an electric field. If the buffered solution used in gel electrophoresis were set at pH 9.0, vasopressin would migrate toward the: ANSWER: negatively charged cathode. supplementary information: Vasopressin. The pKa of the N-terminus is 8.0, the phenolic hydroxyl is 10.0, and the guanidino group is 12.5. tbr cbt explanation: First, we must determine the charge on vasopressin when the pH of the surrounding solution is 9.0. A pH of 9.0 is about halfway between a pH of 8.0 (vasopressin has a pKa = 8.0) and a pH of 10.0 (vasopressin has a pKa = 10.0). The charge on vasopressin at pH 9.0 is therefore +1 (given that it carries a +0.5 charge at pH = 8.0 and +1.5 charge at pH = 10.0). This means that vasopressin is a cation at a pH of 9.0. In biology, a positively charged cation is attracted to the cathode, so the cathode must be negatively charged. The best answer is D. I understand that the cathode is connected to the Negative terminal of the batter so that's why a positive charge would move towards a cathode but I'm having trouble understanding how they figured out that at a ph of 9 vasopressin was positively charged +1. please help.