IOFI recommended practice for the use of predicted relative-response factors for the rapid quantification of volatile flavouring compounds by GC-FID T. Cachet,* H. Brevard, A. Chaintreau, J. Demyttenaere, L. French, K. Gassenmeier, D. Joulain, T. Koenig, H. Leijs, P. Liddle, G. Loesing, M. Marchant, Ph. Merle, K. Saito, C. Schippa, F. Sekiya and T. Smith Abstract: This recommended practice enables the quantification of volatile compounds in flavourings to be made by gas chromatography with flame-ionization detection, without having authentic compounds available, and also in many cases it can avoid time-consuming calibration procedures. The relative-response factors (RRF) can be predicted from the molecular formula of the compound, and this approach can be applied to compounds containing the atoms C, H, O, N, S, F, Cl, Br, I, and Si, providing that the molecular formula and number of benzene rings in the analytes are known. The purity of chemically- defined flavouring substances or chromatographic standards can also be estimated using these predicted RRF, and this proce- dure can also be used to quantify (poly)hydroxylated compounds, after their derivatization into trimethylsilyl ethers or esters. Copyright © 2016 John Wiley & Sons, Ltd. Additional supporting information may be found in the online version of this article at the publisher’s web site. Keywords: flavourings; quantitative analysis; GC-FID; predicted relative response factors Introduction The Working Group on Methods of Analysis (WGMA) of the International Organization of the Flavor Industry (IOFI) has previously published a recommended practice for the quantitative determination of specific volatile substances in flavourings and other complex mixtures such as essential oils, using gas chromatography with flame-ionization detection (GC-FID). [1] In the scientific literature on flavours, fragrances, and essential oils, the raw percentages of peak areas are often used as such, or in association with that of an internal standard (ISTD), assuming that all response factors are equal to unity - a practical approach but one that has been shown to lead to poor accuracy. [2] On the other hand, quantifying by rigorous methods (internal standardization, internal normalization) is accurate but time- consuming, because it requires the establishment of calibration curves, or the experimental determination of response factors relative to a given ISTD). [1] Even this does not solve the challenge of compounds that are not available in the pure state to be used as standards, or those that are not stable enough to be stored before use for the determination of their relative-response fac- tors (RRF). The present technique enables the quantification of volatile compounds in flavourings to be made by GC-FID, without having authentic compounds available, and also in many cases it can avoid time-consuming calibration procedures. The relative- response factors can be predicted from the molecular formula of the compound, and this approach can be applied to compounds containing the atoms C, H, O, N, S, F, Cl, Br, I, and Si, providing that the molecular formula and number of benzene rings in the analytes are known. This procedure also makes it possible to quan- tify (poly)hydroxylated compounds, after their derivatization into trimethylsilyl ethers or esters. This technique, described in a number of publications, [2–5] with applications reported in the flavour, fragrance, and other domains, [6–12] can also be used to estimate the purity of chemically-defined flavouring substances or chromatographic standards using these predicted RRF. Principle The flavouring or individual compound (as such or after derivatiza- tion) is injected together with an internal standard, and their responses are corrected using their predicted RRF. The value of the latter is calculated from the molecular formula and the number of benzene rings in the analytes. * Correspondence to: Dr. T. Cachet, IOFI, 6 Avenue des Arts, 1210 Brussels, Belgium. E-mail: tcachet@iofiorg.org IOFI (International Organization of the Flavor Industry), Working Group on Methods of Analysis Flavour Fragr. J. 2016, 31, 191–194 Copyright © 2016 John Wiley & Sons, Ltd. Recommended practices Received: 15 December 2015, Accepted: 16 December 2015 Published online in Wiley Online Library: 2 February 2016 (wileyonlinelibrary.com) DOI 10.1002/ffj.3311 191