Five mg of CWR were digested with 2.6 mL of 25% acetyl bromide in glacial acetic acid for 2 h at 50 °C using a HACH LT200 system. Samples were cooled on ice and transferred into 10 mL of 2 M NaOH plus 12 mL glacial acetic acid. The reaction tube was rinsed with glacial acetic acid and 1.75 mL of 0.5 M hydroxylammonium chloride was added. Each volume was adjusted to 30 mL with glacial acetic acid, centrifuged (3000 g, 15 min) and lignin content was measured spectrophotometrically (280 nm, extinction coefficient ε = 22.9 g− 1 L cm− 1).
Lignin was characterized following the nitrobenzene oxidation method previously described [69 (link), 78 (link)]. The products after nitrobenzene oxidation of ten mg of CWR were derivatized with Bis(trimethylsilyl)trifluoroacetamide and analysed by gas chromatography coupled to mass spectrometry (GC-MS). A HP-5MS column (30 m × 0.25 mm, 0.25 μm, Agilent) was used on a 7890B-5977A GC-MS system (Agilent). Salicylic acid-D4 was used as internal standard.
Lignin was characterized following the nitrobenzene oxidation method previously described [69 (link), 78 (link)]. The products after nitrobenzene oxidation of ten mg of CWR were derivatized with Bis(trimethylsilyl)trifluoroacetamide and analysed by gas chromatography coupled to mass spectrometry (GC-MS). A HP-5MS column (30 m × 0.25 mm, 0.25 μm, Agilent) was used on a 7890B-5977A GC-MS system (Agilent). Salicylic acid-D4 was used as internal standard.
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