Reagent preparation— Dissolve 250mg of p-dimethylaminobenzaldehyde in a cooled mixture of 130mLof sulfuric acid and 70mLof water,and add 0.40mLof ferric chloride solution (1in 20).

Standard preparation— Dissolve in tartaric acid solution (1in 100)a suitable quantity of USP Dihydroergotamine Mesylate RS,accurately weighed,and dilute quantitatively and stepwise with the same solvent to obtain a solution having a known concentration of about 50µg per mL.

Assay preparation— Transfer an accurately measured volume of Injection,equivalent to about 5mg of dihydroergotamine mesylate,to a 100-mLvolumetric flask,dilute with tartaric acid solution (1in 100)to volume,and mix.

Procedure— Transfer 5.0mLeach of the Standard preparation,the Assay preparation,and tartaric acid solution (1in 100)to provide the blank,to separate 50-mLconical flasks.Add 10.0mLof the Reagent preparationto each,shake,and allow to stand for 30minutes.Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 585nm,with a suitable spectrophotometer,using the blank to set the instrument.Calculate the quantity,in mg,of C33H37N5O5·CH4O3Sin each mLof the Injection taken by the formula: in which Cis the concentration,in µg per mL,of USP Dihydroergotamine Mesylate RSin the Standard preparation,Vis the volume,in mL,of Injection taken,and AUand ASare the absorbances of the solutions from the Assay preparationand the Standard preparation,respectively.