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

This article is a short overview of the state of the art in essential oil analysis. Several aspects of the analysis of essential oils and volatile fraction of vegetable matrices are here critically discussed. The following topics are dealt with: steam distillation, hydrodistillation and headspace sampling for sample preparation, and fast-GC, fast-GC-qMS analysis, enantioselective GC, multidimensional GC techniques and GC-isotopic ratio mass spectrometry (GC-IRMS) for analysis and quantitation.

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High concentration capacity headspace techniques (headspace solid-phase microextraction (HS-SPME) and headspace sorptive extraction (HSSE)) are a bridge between static and dynamic headspace, since they give high concentration factors as does dynamic headspace (D-HS), and are as easy to apply and as reproducible as static headspace (S-HS). In 2000, Chromtech (Idstein, Germany) introduced an inside-needle technique for vapour and liquid sampling, solid-phase dynamic extraction (SPDE), also known as "the magic needle". In SPDE, analytes are concentrated on a 50 m film of polydimethylsiloxane (PDMS) and activated carbon (10%) coated onto the inside wall of the stainless steel needle (5 cm) of a 2.5 ml gas tight syringe. When SPDE is used for headspace sampling (HS-SPDE), a fixed volume of the headspace of the sample under investigation is sucked up an appropriate number of times with the gas tight syringe and an analyte amount suitable for a reliable GC or GC-MS analysis accumulates in the polymer coating the needle wall. This article describes the preliminary results of both a study on the optimisation of sampling parameters conditioning HS-SPDE recovery, through the analysis of a standard mixture of highly volatile compounds (␤-pinene, isoamyl acetate and linalool) and of the HS-SPDE-GC-MS analyses of aromatic plants and food matrices. This study shows that HS-SPDE is a successful technique for HS-sampling with high concentration capability, good repeatability and intermediate precision, also when it is compared to HS-SPME.

The present study examines the ability of targeted and non-targeted methods to provide specific and complementary information on groups of samples on the basis of their component distribution on the two-dimensional gas chromatography (GCxGC) plane. The volatile fraction of Arabica green and roasted coffee samples differing in geographical origins and roasting treatments and the volatile fraction from juniper needles, sampled by headspace-solid phase microextraction, were analyzed by GCxGC-qMS and sample profiles processed by different approaches. In the target analysis profiling, samples submitted to different roasting cycles and/or differing in origin and post-harvest treatment are characterized on the basis of known constituents (botanical, technological, and/or aromatic markers). This approach provides highly reliable results on quali-quantitative compositional differences because of the authentic standard confirmation, extending and improving the specificity of the comparative procedure to trace and minor components. On the other hand, non-targeted data-processing methods (e.g., direct image comparison and template-based fingerprinting) include in the sample comparisons and correlations all detected sample components, offering an increased discrimination potential by identifying compounds that are comparatively significant but not known targets. Results demonstrate the ability of GCxGC to explore in depth the complexity of samples and emphasize the advantages of a comprehensive and multidisciplinary approach to improve the level of information provided by GCxGC separation.