C18 silica

[β-¹³C]-Ferulic acid was prepared from vanillin and [2-¹³C]-malonic acid via Knoevenagel condensation with anhydrous pyridine and aniline, following a published method,^{23,24 (link)} in 86% yield. ¹H NMR data were identical with unlabelled ferulic acid; δ_C (100 MHz, CD₃OD) 115.8 ppm; ESI m/z 193.0 (MH⁻). [β-¹³C]-Ferulic acid was converted to [β-¹³C]-coniferyl alcohol using the method of Tramontina et al.,^{25 (link)} using E. coli cells overexpressing Nocardia iowensis carboxylic acid reductase (NiCAR) and Coptotermes gestroi aldo–keto reductase (CgAKR-1). The [β-¹³C]-coniferyl alcohol product was purified using solid phase extraction. A column (2 × 30 cm) containing 10 g of C₁₈ silica (Agilent) was conditioned using methanol (30 mL) followed by water (30 mL). Samples were applied into the column at a flow rate of 15 mL min⁻¹; which was washed with water (30 mL); then coniferyl alcohol was eluted using methanol (30 mL). Yield 70%. ¹H NMR spectral data were identical to unlabelled coniferyl alcohol,^{23,24 (link)} and matched literature data for [β-¹³C]-coniferyl alcohol.^{15,24 (link)}δ_C (100 MHz, CD₃OD) 125.6 ppm; ESI m/z 179.0 (MH⁻).

Standard solutions of five polycyclic musks, namely, celestolide (ADBI), phantolide (AHMI), traseolide (ATII), galaxolide (HHCB), and tonalide (AHTN), with concentrations of 10 mg/L were obtained from Dr. Ehrenstorfer (Augsburg, Germany). The internal standard, ¹³C₆-labeled hexachlorobenzene (¹³C₆-HCB, 100 mg/L), was obtained from Cambridge Isotope Laboratories (Andover, MA, USA). Pesticide-grade n-hexane, dichloromethane (DCM), acetone, and chromatography-grade ethyl acetate were supplied by Fisher Scientific (J.T. Baker, Pittsburgh, PA, USA). N,N′-Dicyclohexylcarbodiimide (DCC) was obtained from Alfa Aesar (Ward Hill, MA, USA). Hydrazine hydrate (85%) was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Analytical-grade N,N-dimethylformamide (DMF) was obtained from J&K Scientific Ltd. (Beijing, China).
Graphene oxides (GOs) were purchased from Nanjing XFNANO Materials Tech (Nanjing, China). Aminosilica and C18 silica were obtained from Agilent (Santa Clara, CA, USA). N-Vinylpyrrolidone polymeric cartridges (Oasis HLB) were obtained from Waters (Milford, MA, USA).