Girdler sulfide process The Girdler sulfide (GS) process, also known as the Geib–Spevack (GS) process, [1] is an industrial production method for filtering out of natural water the heavy water ( deuterium oxide = D 2 O) which is used in particle research, in Deuterium NMR spectroscopy, deuterated solvents for proton NMR spectroscopy, in heavy water nuclear reactors (as a coolant and ...