This article provides a critical overview of current methods to quantify essential oil components. The fields of application and limits of the most popular approaches, in particular relative percentage abundance, normalized percentage abundance, concentration and true amount determination via calibration curves, are discussed in detail. A specific paragraph is dedicated to the correct use of the most widely used detectors and to analyte response factors. A set of applications for each approach is also included to illustrate the considerations.of linalool, linalyl acetate, β-pinene, sabinene, limonene and α-terpineol. 9 Figure 3 reports the enantioselective-gas chromatography-total ion mass spectrometry (ES-GC-SCAN-MS) profile of an adulterated bergamot EO together with those of linalool and linalyl acetate and α-terpineol in enantioselective-gas chromatographyselected ion monitoring mass spectrometry (ES-GC-SIM-MS) and their enantiomeric ratios.Normalized % abundance can be assumed to be a 'quantitative' comparison of GC profiles, but for some applications it is not sufficient to satisfy all quantitation Figure 3. ES-GC-TIC-MS profile of bergamot EO. (A) Peak identification: 1, α-pinene; 2, β-pinene; 3, sabinene; 4, limonene; 5, linalool; 6, linalyl acetate; 7, α-terpineol; a, (R) enantiomer; b, (S) enantiomer. ES-GC-SIM-MS profiles and enantiomeric ratios of (B) linalool and linalyl acetate (80, 93, 121 m/z) and (C) α-terpineol (59, 93, 136 m/z). Analysis conditions: column, heptakis-2,3-di-O-ethyl-6-O-t-butyldimethylsilyl-β-CD, 30% in PS086 (Megadex, Mega ® ), 25 m × 0.25 mm i.d., 0.25 μm film thickness; temperature programme, 50°C, rising at 2°C/min to 200°C, then held for 5 min; injection mode, split (ratio 1:50); injector temperature, 220°C; EI mode, 70 eV; ion source temperature, 230°C; carrier, helium; flow rate, 1.0 ml/min in constant flow mode. Full scan mode: scan range, 35-350 m/z; SIM mode: dwell time, 0.2 sFigure 4. GC profile of peppermint EO. Analysis conditions: Megawax (60 m × 0.25 mm i.d., 0.25 μm film thickness); temperature programme, 75°C for 8 min, rising at 4°C/min to 220°C, then held for 5 min; injection mode, split (ratio 1:100); injector temperature, 230°C; detector (FID) temperature, 250°C; carrier, H 2 ; flow rate, 1.5 ml/min in constant flow mode
