It has been found that isosorbide provided by commercial suppliers contains sorbitol which is likely present due to the incomplete conversion to isosorbide. As described herein, it is believed that sorbitol reacts to form sorbitol-derived color bodies at elevated temperatures and extended reaction times leading to poor color properties of the resulting isosorbide-containing polycarbonate. In one embodiment, the isosorbide monomer is tested for the presence of sorbitol and treated to reduce the concentration of sorbitol prior to polymerization. In another embodiment, the isosorbide is simply treated to reduce the concentration of sorbitol regardless of whether it is present or not. Where isosorbide is tested for the presence of sorbitol, the sorbitol content in isosorbide can be measured by an organic purity measurement method such as chromatographic methods including Gas Chromatography (GC) and High Performance Liquid Chromatography (HPLC). A calibration curve may be generated in these chromatographic methods by analyzing prepared standard solutions having various concentrations of high purity reagent or analytical grade sorbitol. In a preferred embodiment sorbitol content is determined by HPLC.