Modification of the Stewart biphasic colorimetric assay for stable and accurate quantitative determination of Pluronic and Tetronic block copolymers for application in biological systems.

Block copolymers are increasingly being applied in areas such as transfection, membrane sealing, site-specific targeting, and bionanoengineering yet there is a relative paucity of assays available for simple, stable and reproducible colorimetric determination of copolymer concentration in solution. We have focused on improving the accuracy and reproducibility of a modified version of the Stewart biphasic colorimetric assay for quantitative determination of Pluronic (poloxamer) and Tetronic (poloxamine) macromolecules. The optimized assay achieved linear response ranges in chloroform for commonly used copolymers such as poloxamine 904 (20-300 microg/ml), poloxamine 908 (10-400 microg/ml), poloxamer 402 (20-400 microg/ml), and poloxamer 407 (10-400 microg/ml).