So the game is, unique ways to determine concentration? OK, I'll play. Can you evaporate a known volume, and mass? Or evaporate, roast to NaO, and then mass, and calculate backwards?
Using a pH meter, on this solution, won't give you a useful answer, do you know why? *Hint* Can you figure out the pH of a 2 M, 2.5 M, 2.25 M, and 1.13 M, or 1.0, or 0.98 M NaOH solution. How can you fix it so you can get useful info from a pH meter?
Notice, you still haven't answered my question, how accurately do you need the answer. What is the likely value -- 2, 2.25, 2.5, or is it far away like 3 or 1.1. And do you need the answer as -- 2, 2.2, 2.20, or 2.213 M. This is info you need to know first.