A chemical analysis method for the determination of RO(CH2CH2O)nH, RO(C2H4O)nA, and AO(C2H4O)nA 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 another thing of use and n is an integer greater than 10. The method includes the step of chromatographing a sample of the mixture by liquid chromatography under critical conditions to determine the relative amounts of RO(CH2CH2O)n H, RO(C2H4O)nA, and AO(C2H4O)nA in the mixture. In addition a chemical analysis method for the determination of RO(CH2CH2O)nH, RO(C2H4O)nA, and AO(C2H4O)nA in a mixture thereof, wherein R is an alkyl group, A is a functional group for coupling with a biologically active material and n is an integer greater than 10. The method includes two steps. The first step is derivatizing the A groups of the mixture with a derivatizing agent to form a derivatized mixture comprising RO(CH2CH2O)nH, RO(C2H4O)nAD, and DAO(C2H4O)nAD, wherein AD is the derivatized A group. The second step is chromatographing a sample of the derivatized mixture by liquid chromatography under critical conditions to determine the relative amounts of RO(CH2CH2O)nH, RO(C2H4O)nAD, and DAO(C2H4O)nAD in the derivatized mixture.