Freezing clean piss?

I froze some clean piss and it has a bright yellow ring around the top of the ice.

its in a mason jar, just tossed into the freezer after a good long drain.

is it normal to have that yellow ring?

also, i have been reading alot about microwaves to bring piss up to temps.

a car heater works much much better. plus, u usually DRIVE to a drug test right? so ya...

i'd say that would probably work freezing your pee quickly after whipping it out...its not like the test for freezerburn

freezing pee works. so i've heard.

problem is finding clean pee...