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Typical chromatograms of PETRA using HA as internal standard. (A) From a standard solution (450 µg/mL PETRA) by GC–MS; (B) from a sample solution of residual PETRA extracted from PEO film using GC–MS; (C) from a standard solution (450 µg/mL PETRA) using GC–FID; and (D) from a sample solution of residual PETRA extracted from PEO film using GC–FID.
