Figure 6

Response plots of absorbance at 420 nm to quantities of NHS esters. Reaction between NHS esters and ethanolamine continued for 15 min at 25°C; reaction between ethanolamine and TNBS continued for 15 min at 55°C; absorbance was measured after cooling of reaction mixture with tap water. The response equations were as follows. (1) NHS − SC − mPEG5k : A₄₂₀ = − 0.0006 × C + 0.7548, R² = 0.9911; (2) NHS − CB − mPEG5k : A₄₂₀ = − 0.0009 × C + 0.7834, R² = 0.9970; (3) NHS − AC : A₄₂₀ = − 0.0010 × C + 0.7272, R² = 0.9978.