Syringaldehyde

The alkaline nitrobenzene oxidation (NBO) method was used to analyze the monolignin proportion as described by Wu et al. [53 (link)]. HPLC (Waters e2695 Alliance) with a column of Kromat Universil C₁₈ (4.6 mm × 250 mm, 5 μm) was used to analyze the lignin monomers using p-Hydroxybenzaldehyde (H), Vanillin (G) and Syringaldehyde (S) (purchased from Sinopharm Chemical Reagent Co., Ltd.) as standard chemicals and ethyl vanillin as the internal standard material. The column was operated at 30°C with a CH₃OH : H₂O : CH₃COOH (23 : 76 : 2, v / v / v) carrier liquid at a flow rate of 1.0 mL/min. The calibration curves of all analytes routinely yielded correlation coefficients 0.999 or higher.

The protocols were described by Xu et al. [12] (link) with minor modification. Standard chemicals included p-Hydroxybenzaldehyde(H), vanillin(G) and syringaldehyde (S) (from Sinopharm Chemical Reagent Co., Ltd.), Acetovanillone (AV) and acetosyringone (AS) (from Biosharp Co., Ltd.), trans-p-CA (pCA) and trans-FA (FA) (purchased from Sigma-Aldrich Co. LLC.).
The crude cell wall residues (0.05 g) were added with 10.0 mL 4 M NaOH containing 1.0 mg/mL NaHSO₃ and stirred at 170 °C for 2 h in a 25 mL Teflon gasket sealed in a stainless steel bomb at 20 rpm. After transferred to a triangular flask, the lysate was acidified to pH 2.0 with 6 M HCl, the acidified solution was extracted with chloroform (3×10.0 mL), and the combined organic extracts were evaporated to dryness under reduced pressure at 40 °C. The extracts were re-dissolved with 2.0 mL elution phase, filtered by 0.22 µm membrane for total phenolics analysis.