Peels of four local Citrus species (Citrus sinensis L. Obsbeck, Citrus reticulata Blanco, Citrus maxima Burm. and Citrus aurantifolia christm.) grown in a same locality under the same climatic conditions were subjected to steam distillation. The essential oils and floral waters obtained were analyzed by gas chromatography coupled with a flame ionization detector (CPG-FID) and by gas chromatography coupled to a mass spectrometer (CPG-MS). The essential oils yields were ranged between 0.2 and

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... . The qualitative and quantitative analyses show 74 compounds in all oils samples. The oils were largely dominated by hydrocarbon monoterpenes with limonene as major compound (91.5-94.0%; 90.4-93.4%; 77.7-93.7% and 34.8-51.2%) in oils from Citrus sinensis, Citrus reticulata, Citrus maxima and Citrus aurantifolia, respectively. In addition to limonene, oils of Citrus aurantifolia contained high amounts of β-pinene (6.8-14.4%), p-cymene (5.8-12.2%), γ-terpinene (0.3 -7.4%), neral (1.5-9.4%), geraniol (1.9-12.7%). Although presenting the same major compound (limonene), the oils had compositions that were qualitatively and quantitatively different. The enantiomeric analyses showed that the chiral major compounds were (R) -(+)limonene, (S) -(-)limonene, (1S) -(-) -β-pinene, (1R)-(+)-β-pinene and (S) -(+) -carvone. The hydrosols analyzed were composed of oxygenated compounds and did not have the same major compound. A qualitative and quantitative difference in chemical composition was noted between the Hydrosols. GC-MS The gas chromatograph (AGILENT 6890-USA) equipped with MS (AGILENT 5973 NETWORK mass selective detector) in the electron impact mode (70 eV) source and quadrupole temperatures were of 280°C and 150°C respectively. The scanned mass range was fixed at 35 to 350 amu. The column was the same than GC-FID. The oven temperature was 6 programmed as follows: isotherm of 5 min at 40 °C then a progression of 8°C/min up to 280°C with a final hold of 5 minutes at 280°C. The injector, used in splitless mode, was at 240 °C. The carrier gas was Helium (He) with a constant flow rate of 1.1 mL/min. The identification of the compounds was made using data of computer library (Wiley 275L) connected to the GC-MS and retention indices of components calculated using retention times of n-alkanes compared with those of the literature 9-10 . Whenever possible, the identifications were confirmed by comparison of the recorded retention data with those of pure standard compounds injected in the same conditions. CPG-FID equipped with a chiral column The gas chromatograph (K0733B) is equipped with a silica-type chiral capillary column (Beta Dex TM 110), 30m Long 0.25mm diameter and 0.25μm film thickness. The oven temperature was programmed as follows: initial oven temperature was held at 40°C for 2 min, then increases from 2 °C/min to 220 °C (4 min). Helium was used as the carrier gas at a constant flow rate of 1.1 ml/min. Injector (splitless mode) and flame ionization detector temperatures were set at 220°C and 230°C, respectively. The flow rate of the hydrogen is 35 ml / mm and that of the air 350 ml / min. A series of n-alkanes (C 7 -C 30 ) is injected for the calculation of the retention indices. The identification of the compounds is made by referring to the retention indices of standard compounds injected in the same conditions and by superposing the chromatograms of standards compounds and of the essential oils ( Figures: 2 and 3) . The standard compounds used, racemic limonene, (1S)-(-)-β-pinene (99%) (S)-(+)-carvone (98.5%) were purchased from Sigma-Aldrish (Boornem, Belgium). RESULTS AND DISCUSSION Results Essential oil yields