Sulphur dioxide (SO2) proved to increase absorbance at 280 nm of grape skin and seed extracts containing it, diluted with ethanol-HCl to assess total flavonoids and anthocyanins in the same analysis. Additional absorbance at 280 nm was also observed in acetone:H2O extracts, if the acetone had not completely evaporated before the extracts were diluted with a solvent. Flavonoids were correctly quantified in the extracts when SO2 or acetone were removed by solid-phase extraction with a C18 RP as sorbent and methanol as eluting solvent.
Keywords: Anthocyanins; Anthocyanins (PubChem CID: 5318979); Flavonoids; Polyphenols; Proanthocyanidins; Proanthocyanidins (PubChem CID: 108065); Sulphur dioxide; Sulphur dioxide (PubChem CID: 1119).
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