Patent ID: 8921116

Claim:
A method comprising: (a) providing a sample of a composition comprising a copolymer of Glu, Ala, Lys, and Tyr; (b) determining, in the sample of the composition, the amount of polypeptides having a having a diethylamide-modified C-terminal amino acid, wherein the determining step comprises: fragmenting the copolymer, and measuring the level of diethylamide in the fragmented copolymer by detecting diethylamide; and (c) preparing a pharmaceutical composition comprising glatiramer acetate using at least a portion of the composition comprising the copolymer of Glu, Ala, Lys, and Tyr if the amount of polypeptides in the sample having a diethylamide-modified C-terminal amino acid is about 7 mol % to about 20 mol %.