Carbonyl Compound Analysis via DNPH Derivatization

2,4-Dinitrophenylhydrazine (DNPH) was purchased from Rhawn (Shanghai, China), with purity ≥ 99%. Methanol and acetonitrile of liquid chromatographic grade (purity ≥ 98%) were purchased from Sigma-Aldrich (Shanghai, China). Hydrochloric acid and silica gel powder of 300–400 mesh were acquired from Sinopharm Chemical Reagent (Beijing, China). The standard solution was composed of: 2-butanone-DNPH, butyraldehyde-DNPH, pentanal-DNPH, pentanone-DNPH, acrolein-DNPH, acetaldehyde-DNPH, butenal-DNPH, furfural-DNPH, formaldehyde-DNPH, hexaldehyde-DNPH, benzaldehyde-DNPH, 2-crotonaldehyde-DNPH, formylofuran-DNPH, heptanal-DNPH, octanal-DNPH, nonanal-DNPH, decanal-DNPH, and cyclohexanone-DNPH, which were purchased from A Chemtek; additionally, acetoin-DNPH, 2-pentanone-DNPH, and 4-heptanone-DNPH, with a purity of above 98%, were acquired from TanMo Quality Testing Co., Ltd. (Beijing, China). A blank solid-phase extraction (SPE) column without any other filler applied was purchased from Biocomma Limited Co., Ltd. (Shenzhen, China). A 5 L Tedlar bag was purchased from Sigma-Aldrich (Shanghai, China), and prior to their use, bags were cleaned with N₂ at a high temperature (80 °C) until carbonyl compounds were free. Ultrapure water was used for all aqueous solution preparation. A detailed procedure for the solid phase column extraction is presented in Supplementary material.