Pharmaceutical grade chondroitin sulfate: Structural analysis and identification of contaminants in different commercial preparations

•Sixteen chondroitin sulfate (CS) preparations were analyzed for purity and CS structure.•Eleven (out of 16) samples were less than 15% CS.•Maltodextrin was the main contaminant in nine, and lactose in two of these samples.•Five samples were more than 90% CS, but their structures varied, concerning size and sulfation. The aim of the present study was to characterize 16 pharmaceutical grade chondroitin sulfate (CS) samples, concerning the structure and presence of contaminants, in comparison to USP and analytical grade CS. Agarose gel electrophoresis has shown that only 5 samples were >90% CS, while 11 contained less than 15% CS. FACE (fluorophore-assisted carbohydrate electrophoresis) revealed that maltodextrin was the main contaminant in nine of them, and lactose in two. Raman spectroscopy corroborated these results. Concerning the structure of the CS present in the five CS-rich samples, the ratios 4-sulfated:6-sulfated disaccharides varied from 0.9 to 1.7, and their modal molecular weight was 20–29kDa. Also, they were all contaminated by small amounts of keratan sulfate (