Modified proton transfer reaction mass spectrometry (PTR‐MS) operating conditions for in vitro and in vivo analysis of wine aroma

Abstract

With proton transfer reaction-mass spectrometry standard operating conditions, analysis of alcoholic beverages is an analytical challenge. Ethanol reacts with the primary ion H 3 O + leading to its depletion and to formation of ethanol-related ions and clusters, resulting in unstable ionization and in significant fragmentation of analytes. Different methods were proposed but generally resulted in lowering the sensitivity and/or complicating the mass spectra. The aim of the present study was to propose a simple, sensitive, and reliable method with fragmentation as low as possible, linearity within a realistic range of volatile organic compounds concentrations, and applicability to in vivo dynamic aroma release (nosespace) studies of wines.For in vitro analyses, a reference flask containing a hydro-alcoholic solution (10% ethanol) was permanently connected to the PTR-MS inlet in order to establish ethanol chemical ionization conditions. A low electric field strength to number density ratio E/N (80 Td) was used in the drifttube. A stable reagent ion distribution was obtained with the primary protonated ethanol ion C 2 H 5 OH 2 + accounting for more than 80% of the ionized species. The ethanol dimer (C 2 H 5 OH) 2 H + accounted for only 10%. Fragmentation of some aroma molecules important for white wine flavor (various esters, linalool, cis-rose oxide, 2-methylpropan-1-ol, 3-methylbutan-1-ol, and 2-phenylethanol) was studied from same ethanol content solutions connected alternatively with the reference solution to the instrument inlet. Linear dynamic range and limit of detection (LOD) were determined for ethyl hexanoate. Fragmentation of the protonated analytes was limited to a few ions of low intensity, or to specific fragment ions with no further fragmentation. Association and/or ligand switching reactions from ethanol clusters were only significant for the primary alcohols. Interpretation of the mass spectra was straightforward with easy detec- To overcome this problem, the protonated ethanol ion and its dimer have been used as reagent ions in the characterization of wine using direct headspace analysis and mass spectral fingerprints. 9 To achieve operational conditions with stable reagent ions signal and distribution, a flow of ethanol-saturated nitrogen was continuously added to the wine headspace and admitted into the ethanol/nitrogen main stream directed towards the drift-tube of a PTR-MS. Stable reagent ions signals were obtained and were not affected by changes in ethanol content of the wine samples. However, the procedure resulted in a 10-fold dilution of the wine headspace into the ethanol-saturated nitrogen main flow, affecting significantly the sensitivity of the method, which can be detrimental for the detection of low-concentration compounds potentially of oenological importance. were investigated, dilution of the samples headspace occurred. If the method was alleged to be superior to the previous ones, reduction of ethanol effects was obtained still with a certain loss of sensitivity, and t...

Volatile compounds profiling by using proton transfer reaction‐time of flight‐mass spectrometry (PTR‐ToF‐MS). The case study of dark chocolates organoleptic differences

“…As the water dimer PA (808 kJ.mol −1 ) is lower than many VOCs PA, the first hydronium/water ion cluster (H 2 O) H 3 O + should be generally considered as another primary ion for quantification purpose. The ion clusters (H 2 O) n H 3 O + are implied in ligand‐switching reactions that complicate data interpretation, although compared with SIFT, formation of adducts in the drift‐tube is limited due to the non‐thermal conditions induced by the electric field and the operating temperature in the drift‐tube …”

Assessment Wine Aroma Persistence by Using an in Vivo PTR-ToF-MS Approach and Its Relationship with Salivary Parameters

“…Nevertheless, the measurement of ethanolic solutions by these techniques present technical difficulties since changing the ethanol concentration in the source made reliable measurements difficult. Very recently, a new methodology has been developed by Semon and collaborators [17] in which the parameters of the PTR/MS instrument has been adjusted to allow ethanol chemical ionization conditions while minimizing the protonated molecule fragmentation of the volatiles with no compromise in sensitivity for in vivo applications. This methodology has been successfully employed by Arvisenet and collaborators [18] to evaluate the effect of sugar and acid composition on in vivo aroma release in model wines.…”

Development of an in-mouth headspace sorptive extraction method (HSSE) for oral aroma monitoring and application to wines of different chemical composition

“…The presence of a relative and variable amount of ethanol in the wine also compromises discrimination ability, quantification, and spectra interpretation (Spitaler, et al, 2007). Recently, a smart modification of an in vivo-PTR-ToF-MS method was proposed for wine aroma analysis (Sémon, Arvisenet, Guichard, & Le Quéré, 2018). However, this method was carried out using synthetic wines with no matrix effect and aromatized with nine selected aroma compounds, which do not represent wine aroma complexity.…”