Time-resolved quantification of volatile aroma compound formation during heat treatment of tobacco leafs: method development and application using PTR-ToF-MS Marco Wellinger a *, Sergio Petrozzi a, Jean-Marc Renaud b, Monika Christlbauer b , Chahan Yeretzian a a Zurich University of Applied Sciences, Institute of Chemistry and Biological Chemistry, 8820 Wädenswil, Switzerland. b Philip Morris International, Product Development, Phillip Morris Products SA, Quai Jeanrenaud 3, 2000 Neuchâtel, Switzerland *[email protected] Introduction / m/z Figure 1: Transmission curve of the PTR-ToF-MS Eq 1 Experimental Figure 2: Sampling and gas dilution setup / ppm / ppm A method for the on-line quantification of aroma compounds in the processing air of a laboratoryscale tobacco dryer was developed, based on ProtonTransfer-Reaction Time-of-Flight Mass-Spectrometry (PTR-ToF-MS). A major advantage of PTR-ToF-MS, compared with PTR-Quadrupole-MS, is the high time resolution (in the range of seconds) that can be achieved while scanning the complete spectrum (i.e., from 0-200 m/z) with a mass resolution (m/Δm) of up to 5,500. A soft ionization takes place by charge transfer from a hydronium ion leading to very limited fragmentation. The development of the quantification method comprised three experimental steps. First, a specific sampling setup was designed that allowed continuous dilution of up to 300-fold. Secondly, the instrument-specific mass discrimination effect was determined by the measurement of known concentrations of a commercially available gas standard. In the third step, the fragmentation patterns for 11 out of 27 aroma substances, for which no literature data on fragmentation was available, were determined using either pure substances or solutions in ethanol. The ion selection for the quantification was made according to the ion abundance and the specificity of the ion for the target compound. TrRH+ = −3.88 10−5 𝑚2 𝑚 −2 + 1.493 10 − 0.1571 𝑧 𝑧 / ppb Heat treatment/ toasting of tobacco is part of the cigarette manufacturing process, whereby some flavor compounds are formed through, e.g. Maillard reactions between nitrogenous compounds and endogenous or added sugars. By studying the absolute contents and evolution of aroma compounds in tobacco during heat treatment, we aim at better understanding the chemical and kinetic process underlying aroma formation, and explore their dependence on process and product parameters. / min / min Figure 3: Time concentration profiles with PTR-ToF-MS (five replicates) – 100 g tobacco - laboratory tray dryer Substance name and attributed mass (m/z) Average of the relative standard deviations [%] N=11 - (Std. dev. - 1σ) Acetic acid (13C) m/z 62.032 5.9 (0.1) Diacetyl m/z 87.044 6.0 (0.1) 2-phenylethanol / 3-ethylphenol m/z 123.08 5.9 (0.2) 1-octen-3-one m/z 127.112 6.1 (0.1) (Z) / (E)-2-nonenal m/z 141.127 7.3 (0.1) Ethylcinnamate m/z 177.091 5.7 (0.1) Beta-damascenone m/z 191.143 7.4 (0.3) Table 1: Substance specific precision of PTR-ToF-MS determined with five replicate measurements Results The method allowed the quantification of 27 aroma compounds in the processing air with a precision (RSD, n=5) of 5 to 8 %. The measured levels of aroma compounds ranged from 2 to 30’700 ppb. The limit of quantification (approximated by the 10-fold standard deviation of the blank) was in the single digit ppb range for almost all compound. Except for ammonia, acetic acid and nicotine which were present between 4860 ppb and 630’000 ppb. The evolution of the concentration of the 27 compounds in the processing air could be quantified with a time resolution of 10 seconds. Conclusion The developed methodology proved suitable for the assessment of specific processing parameters on the extent and kinetics of the release of aroma compounds during tobacco processing. The results of such measurements are a basis for the optimization of the processing conditions towards tobacco flavor enhancement. Figure 4: Time concentration profiles during toasting of tobacco with PTR-ToF-MS – 1 kg tobacco – small industrial tray dryer Substance name and attributed mass (m/z) LOQ ppb (STD DEV x10) Acetic acid (13C) m/z 62.032 54.8 Diacetyl m/z 87.044 2.6 2-phenylethanol / 3-ethylphenol m/z 123.08 0.6 1-octen-3-one m/z 127.112 0.6 (Z) / (E)-2-nonenal m/z 141.127 1.0 Ethylcinnamate m/z 177.091 1.2 Beta-damascenone m/z 191.143 0.5 Table 2: Limit of quantification during online PTR-ToF-MS measurements (13 values of 10 second each)