Abbo

High purity oxygen is made by cryogenic fractional distillation - splitting air by the boiling points of its constituents. Nitrogen boils at -195.79 degrees C, Argon at -185.85 degrees and Oxygen at -182.95 degrees. The main impurity would be Argon, as the constituent of air with the boiling point closest to Oxygen.

Pressure Swing Adsorption sieves out the nitrogen, so it leaves behind the argon that makes up 0.93% of air.

Either way you're stuck with narcotic argon.

Incidentally, in PSA, the nitrogen is not absorbed by the zeolite but sticks to it and is released periodically, so the process is called adsorption.