Patent ID: 8202732

Claim:
A chemical analysis method for the determination of RO(CH 2 CH 2 O) n H, RO(C 2 H 4 O) n A, and AO(C 2 H 4 O) n A in a mixture thereof, wherein R is an alkyl group, A is a functional group for coupling with a surface or a biologically active material or other thing of use and n is an integer greater than 100, comprising the steps of: (a) derivatizing the A groups of the mixture with a derivatizing agent to form a derivatized mixture comprising RO(CH 2 CH 2 O) n H, RO(C 2 H 4 O) n AD, and DAO(C 2 H 4 O) n AD, wherein AD is the derivatized A group; and (b) chromatographing a sample of the derivatized mixture by reverse phase liquid chromatography under critical conditions to determine the relative amounts of RO(CH 2 CH 2 O) n H, RO(C 2 H 4 O) n AD, and DAO(C 2 H 4 O) n AD in the derivatized mixture.