Chemical composition characterization of blends formed by styrene-acrylonitrile (SAN), ethylene-propylenediene (EPDM) and EPDM-g-SAN copolymer molecules has been performed with size-exclusion chromatography with DRI and UV detectors. With proper detector calibration reliable average composition results were obtained, whereas it has been found that the composition distributions calculated from the chromatogram fractions are affected by large experimental errors. The blend components were successfully separated with precipitation-redissolution liquid chromatography, and an evaporative light scattering detector was found suitable for eliminating baseline drifts in the chromatograms, due to the eluent gradients which had to be employed. The application of evaporative detectors for quantitative measurements, however, appears questionable.