Medium: 0.1 N hydrochloric acid; 750 mL.

Apparatus 1: 100 rpm.

Time: 60 minutes.

Procedure— Determine the amount of C10H13NO3 dissolved from UV absorbances at the wavelength of maximum absorbance at about 274 nm of filtered portions of the solution under test, suitably diluted with Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Metyrosine RS in the same medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C10H13NO3 is dissolved in 60 minutes.

Standard preparation— Dissolve a suitable quantity of USP Metyrosine RS, accurately weighed, in dilute hydrochloric acid (1 in 100) to obtain a solution having a known concentration of about 100 µg per mL.

Assay preparation— Combine the contents of not less than 20 Capsules, and transfer an accurately weighed portion of the combined contents, equivalent to about 100 mg of metyrosine, to a 100-mL volumetric flask. Add 50 mL of dilute hydrochloric acid (1 in 100), shake by mechanical means for 45 minutes, dilute with dilute hydrochloric acid (1 in 100) to volume, mix, and filter. Transfer 10.0 mL of the filtrate to a 100-mL volumetric flask, dilute with dilute hydrochloric acid solution (1 in 100) to volume, and mix. Concomitantly determine the absorbances of this solution and the Standard preparation at the wavelength of maximum absorbance at about 274 nm, with a suitable spectrophotometer, using dilute hydrochloric acid solution (1 in 100) as the blank. Calculate the quantity, in mg, of metyrosine (C10H13NO3) in the portion of Capsules taken by the formula: in which C is the concentration, in µg per mL, of USP Metyrosine RS in the Standard preparation, and AU and AS are the absorbances of the solutions obtained from the Assay preparation and the Standard preparation, respectively.