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.

Online molecular characterisation of organic aerosols in an atmospheric chamber using extractive electrospray ionisation mass spectrometry

“…In this paper, we focus on the application of one such approach to organic aerosol analysis, namely extractive electrospray ionisation (EESI) MS. The EESI process predominantly forms molecular ions ([M + H] + and [M − H] − ) and is able to efficiently ionise organic analytes even in complex sample matrices such as urine (Devenport et al, 2014), beer (Zhu et al, 2010) and olive oil . Doezema et al (2012) demonstrated an initial application of EESI-MS to organic aerosols, identifying a number of products formed from α-pinene ozonolysis in positive ion mode.…”

Distillation of fermented sugarcane juice: fractions characterized by electrospray ionization mass spectrometry and multivariate data treatment

“…These assumptions were corroborated by high‐resolution mass measurements: a maximum error of 4.33 ppm between the experimental and theoretical exact masses expected for these compounds (C 6 H 12 O 2 , C 8 H 16 O 2 , C 10 H 20 O 2 and C 12 H 24 O 2 ) was noticed. Furthermore, several authors have previously reported the presence of some of these acids in fermentation processes to produce wine, beer and even rum . Finally, note that only subtle changes in the relative intensities of these anions can be observed in these mass spectra.…”

New trends in beer flavour compound analysis

“…Gas chromatography–flame ionization detection (GC‐FID) or gas chromatography–mass spectrometry (GC‐MS) is currently used to measure volatile compound concentrations in beer. Mass spectrometers with electron impact ionization (EI) and quadrupole or ion trap analysers are used by a number of research groups, but electrospray ionization (ESI) coupled to time‐of‐flight (ToF) mass spectrometers has also been used . Ethers, esters, acids, aldehydes, ketones, alcohols, sulfur compounds, hydrocarbon compounds, alicyclic compounds, heterocyclic compounds and aromatic compounds can be measured simultaneously using GC‐MS methods .…”