Help How do I know if this is 99.9% Helium?

[dogemn]

This is a brand of helium tanks that is sold where I live but how can I know if it contains 99.9% pure Helium and no oxygen?

 

[LaVieEnRose]

If it is for balloons I think you can count on it not being pure enough.it's

 

[ipmanwc0]

helium is pretty rare now so unless it says differently it's probably 20% air