A: To 2mLof Injection add 3mLof water,and mix.Add 10mLof cupric sulfate TS:a bluish-gray precipitate is formed.

B: To 2mLof Injection add 3mLof water,and mix.Add 2mLof 3Nsodium hydroxide and 2drops of sodium nitroferricyanide solution (1in 20):a red-purple color is produced,and it rapidly changes to yellow.

Standard solution— Dissolve an accurately weighed quantity of USPL-Cysteine Hydrochloride RSin nitrogen-saturated water to obtain a solution having a known concentration of about 1mg per mL.

Standard preparation— Transfer 20.0mLof Standard solutionto a 200-mLvolumetric flask,dilute with nitrogen-saturated 1.0Nsodium hydroxide to volume,and mix.

Assay preparation— Dilute an accurately measured volume of Injection,equivalent to about 250mg of cysteine hydrochloride,quantitatively and stepwise with nitrogen-saturated 1.0Nsodium hydroxide,to obtain a solution having a concentration of about 0.1mg per mL.

Procedure— Transfer a suitable amount of Standard preparationto a polarographic cell.With mercury dropping from the electrode,lower the dropping mercury electrode of a polarograph so that the end is submerged in the liquid.Bubble oxygen-free,water-saturated nitrogen through the liquid for 15minutes.Record the polarogram from -0.2volt to -1.10volts,using a saturated calomel electrode as the reference electrode.In a similar manner,record the polarograms obtained using portions of the Assay preparationand of the nitrogen-saturated 1.0Nsodium hydroxide.Determine the height of the diffusion current wave at -0.4volt.Calculate the quantity,in mg,of C3H7NO2S·HCl·H2Oin each mLof the Injection taken by the formula: in which Cis the concentration,in mg per mL,of USPL-Cysteine Hydrochloride RS.In the Standard preparation,Vis the volume,in mL,of Injection taken;and (id)Uand (id)Sare the observed diffusion currents,corrected for the diffusion current of the 0.1Nsodium hydroxide,of the Assay preparationand the Standard preparation,respectively.