B:
To a solution of 10 mg in 2 mL of water add 1 drop of ferric chloride TS: an intensely green color develops.
C:
To 10 mL of a solution (1 in 10,000) add 1.0 mL of 0.10 N iodine. Allow to stand for 5 minutes, and add 2.0 mL of 0.10 N sodium thiosulfate: the solution is colorless or has at most a slight pink or slight violet color (epinephrine and isoproterenol at the same pH, about 3.5, give a strong red-brown or violet color).
Limit of arterenone
Its absorptivity (see Spectrophotometry and Light-scattering 851) at 310 nm, determined in a solution containing 2 mg per mL, is not more than 0.2.
Assay
Dissolve about 500 mg of Norepinephrine Bitartrate, accurately weighed, in 20 mL of glacial acetic acid, warming slightly if necessary to effect solution. Add 2 drops of crystal violet TS, and titrate with 0.1 N perchloric acid VS. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 31.93 mg of C8H11NO3·C4H6O6.