title: Simultaneous sampling of volatile and non-volatile analytes in beer for fast fingerprinting by extractive electrospray ionization mass spectrometry.
abstract: By gently bubbling nitrogen gas through beer, an effervescent beverage, both volatile and non-volatile compounds can be simultaneously sampled in the form of aerosol. This allows for fast (within seconds) fingerprinting by extractive electrospray ionization mass spectrometry (EESI-MS) in both negative and positive ion mode, without the need for any sample pre-treatment such as degassing and dilution. Trace analytes such as volatile esters (e.g., ethyl acetate and isoamyl acetate), free fatty acids (e.g., caproic acid, caprylic acid, and capric acid), semi/non-volatile organic/inorganic acids (e.g., lactic acid), and various amino acids, commonly present in beer at the low parts per million or at sub-ppm levels, were detected and identified based on tandem MS data. Furthermore, the appearance of solvent cluster ions in the mass spectra gives insight into the sampling and ionization mechanisms: aerosol droplets containing semi/non-volatile substances are thought to be generated via bubble bursting at the surface of the liquid; these neutral aerosol droplets then collide with the charged primary electrospray ionization droplets, followed by analyte extraction, desolvation, ionization, and MS detection. With principal component analysis, several beer samples were successfully differentiated. Therefore, the present study successfully extends the applicability of EESI-MS to the direct analysis of complex liquid samples with high gas content.
authors.affiliation: Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhu
authors.forename: Zhong
authors.initials: Z
authors.lastname: Hu
authors.forename: Gerardo
authors.initials: G
authors.lastname: Gamez
authors.forename: Wai Siang
authors.initials: WS
authors.lastname: Law
authors.forename: HuanWen
authors.initials: H
authors.lastname: Chen
authors.forename: ShuiPing
authors.initials: S
authors.lastname: Yang
authors.forename: Konstantin
authors.initials: K
authors.lastname: Chingin
authors.forename: Roman M
authors.initials: RM
authors.lastname: Balabin
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: TingTing
authors.initials: T
authors.lastname: Zhang
authors.forename: Renato
authors.initials: R
authors.lastname: Zenobi