please add a water -> oxygen , hydrogen , deuterium recipe to the mass spectrometer
can be in the realistic relation of
3200mb water -> 1600mb oxygen , 3199mb water , 1mb deuterium

Sure

Wouldn't this result in a hydrogen -> deuterium converter as you could just take the hydrogen and oxygen and recombine them into water and send the water back through?

I thought about it and yes this would convert hydrogen to deuterium but it really doesn't matter because by default water is infinite and is already an infinite source of deuterium.

Added for 1.3
Recipe: 1000mb Water -> 990 mb Hydrogen, 10 mB Deuterium, 500 mB Oxygen
This is inline with the current centrifuge recipe 10,000 mb Water -> 100 mB Heavy Water