How are ortho-hydrogen and para-hydrogen separated?

Ortho-hydrogen and para-hydrogen are two distinct modifications of molecular hydrogen that differ based on the relative spin alignments of their protons. Because these forms exhibit slightly different physical properties, such as varying vapor pressures, they can be separated using low-temperature gas chromatography.1

Additionally, while these forms do not typically interconvert, equilibrium between them can be established through specific methods, such as applying an electrical discharge, heating the gas to high temperatures, or using catalysts like activated charcoal or paramagnetic substances. Notably, essentially pure para-hydrogen can be produced by exposing a hydrogen mixture to charcoal at the temperature of liquid hydrogen, which facilitates the conversion of all ortho-hydrogen into para-hydrogen. Conversely, it is not possible to prepare pure ortho-hydrogen directly from a mixture because the concentration of para-hydrogen never drops below 25 percent.1