Natfa

Sodium trifluoroacetate (Na-TFA, Sigma-Aldrich, Gillingham, United Kingdom) was prepared at 0.1 mg mL⁻¹ in methanol and used as an external calibrant. An additional internal calibration was performed in DataAnalysis 5.3 with a calibration list containing abundant homologous alkylated compounds corresponding to protonated molecular compositions containing 2, 5, and 7 oxygen atoms (O₂[H], O₅[H] and O₇[H], respectively). The samples were assigned using Composer 1.5.6 (Sierra Analytics, CA, USA) with molecular assignments corresponding to C_4–100H_4–1000O_0–20N_0–2S_0–4 with up to 0.8 ppm error in both protonated (“H”) or molecular ion form. Double bond equivalents (DBE), are calculated according to eqn (2) where c, h and n are the number of carbon, hydrogen, and nitrogen atoms, respectively. KairosMS and custom R scripts were used for data visualization.^{28 (link)} Density diagrams, plotted using VKSim,²⁹ were used to visualise the distribution of molecules according to their H/C and O/C-values. The total number of compositions are reported including isotopic compositions unless otherwise specified. The intensity-weighted mean of the oxygenated heteroatomic classes, O_o, is calculated using eqn (3)³⁰