Specific Refractive Index Increment Measurements on Macromolecules Using a Waters R401 Differential Refractometer

An accurate and simple method for determining the specific refractive index increment, dn/dc, of synthetic polymers during size-exclusion chromatography has been developed using a modified Waters R401 differential refractive index (DRI) detector. The only modification required on the R401 involved the replacement of the standard white light source with a monochromatic source. The use of this instrument offers a number of advantages over more classical instruments and procedures normally employed in evaluating this parameter. The only requirement which must be met in order to successfully measure this parameter is the conservation of mass (in terms of the amount of polymer injected on to the columm and which passes through the DRI detector). However, in some cases, even this requirement may be relaxed. The application of this procedure will be demonstrated for several synthetic polymers in mixed and single solvent systems.