Is it appropriate to ask for a pay raise as an adjunct professor with a Master's degree?
There are myriad factors that go into pay rates, but the bottom line with this or any job is your pay should reflect what you bring to the table.  Sounds to me like you have a rarified skill that is in demand in this specific instance so yes, absolutely, ask for a pay increase.  Politely, sweetly, and prepared to hear "no."