4 ethyl 2 methoxyphenol

2,6-dimethylpyrazine, nonanal, (E)-2-octenal, 2,3-dimethylpyrazine, 3-ethyl-2-methylpyrazine, 2,3,5-trimethylpyrazine, 2-ethyl-3,5-dimethylpyrazine, benzaldehyde, (E)-2-nonanal, β-caryophyllene, γ-butyrolactone, phenylacetaldehyde, furfuryl alcohol, 2,4-decadienal, geranyl acetone, guaiacol, 4-ethyl-2-methoxyphenol, γ-nonanolactone, 2-methoxy-4-vinylphenol, hexanal, 2-phenyl-2-butenal (all of them are chromatographic purity with at least 97% purity, J&K Scientific Ltd.). A C7−C30 n-alkane mixture was purchased from J&K Scientific Ltd., Beijing, China. The internal standard 2-octanol (chromatographic purity with 98.0% purity), anhydrous ethanol (chromatography grade), and sodium chloride (analytical purity) were purchased from China National Pharmaceutical Group Corp. (Shanghai, China). High purity helium (99.999%) was purchased from Beijing Yanglilai Chemical Gas Co., Ltd. (Beijing, China).

A total of 32 different kinds of soy sauce, coded as XH1, XH2, XH3, XH4, XH5, XH6, XH7, XH8, YZ, HT1, HT2, HT3, HT4, JJ1, LJJ2, LJJ3, LJJ4, LJJ5, CB1, CB2, CB3, CB4, JJ1, JJ2, LCC1, LCC2, LCC3, BT1, BT2, HJ, WZ, and MG were used in this work. All samples were purchased from a local supermarket. All samples were stored in their original containers and sealed at room temperature (25 °C) prior to analyzsise.
Chromatographic grade methanol (99.9%) was purchased from Merck Chemical Company (Shanghai, China). 2-Methyl-3-heptanone (99.9%), and 5-ethyl-4-hydroxy-2-methyl-3(2H)furanone (99.9%) were purchased from Macklin Biochemical Company (Shanghai, China). 2,5-Dimethyl-4hydroxy-3(2H)-furanone (99.9%) was purchased from Sigma-Aldrich (Steinheim, Germany). Ethyl acetate (99.9%), 4-ethyl-2-methoxyphenol (99.9%), and 3-methylbutanal (99.9%) were purchased from J&K Scientific (Beijing, China). C₆–C₂₈ n-alkanes standard mixtures (≥97%) were purchased from Sigma Aldrich (Steinheim, Germany). Purified water was purchased from Hangzhou Wahaha Co., Ltd., Hangzhou, China.