Best to know your own market value and argue for that. Know how much you make and net for the company will give you an idea of your own value.
If your plan to increase your rate of pay is to whine that someone else has more or is more valuable, your argument will fall on deaf ears. Deaf fairly.
Go in and say "I'm worth this much, and it is because i make the company this much money and deserve this share of it" instead of "I'm worth this much because this other person is"
Almost no one who has ever demanded a raise because their colleague makes more than them has ever gotten that raise.