.3. GC-FID and GC-MS
The CPLO was injected into a GC 6890 (Agilent) equipped with a double injector and two DB-1 capillary columns (60 m × 0.25 mm, film thickness 0.25 μm, J&W 122-1062). One column was connected to an MS 5973N (Agilent) for identification, and the other to an FID for quantitation. The temperature programme was as follows: 50 °C for 5 min, increased to 120 °C at a rate of 3 °C/min, then increased to 250 °C at a rate of 5 °C/min, 5 min isothermal, then increased to 300 °C at a rate of 15 °C/min, and then 20 min isothermal; split ratio, 1:50; injection volume, 0.2 μl; injector and detector temperatures, both 250 °C; carrier gas, helium at constant flow rates of 1.8 ml/min and 2.1 ml/min, respectively. The CPLO was diluted 1:10 in dichloromethane before being submitted to GC-FID-MS analysis. For all GC-MS analyses, mass spectra were generated by EI at 70eV at a scan ranging from m/z: 29-250 during the first 20 min and then at a scan ranging from m/z: 29-450.
Compounds were identified by analyzing and comparing mass spectra and linear retention indices obtained with pure references. Linear retention indices (LRIs) were determined after injection of a series of n-alkanes (C5-C31) under similar conditions. GC-MS peaks were identified and integrated using HP Chemstation software and MS and LRI library (internal, Wiley and Nist05).
Quantitative analysis was performed using methyl octanoate as internal standard and the response factor of each compound. Their percentages were obtained from the FID area corrected with the use of the response factors, previously measured with pure analytes under the same conditions or calculated according to de Saint Laumer, Cicchetti, Merle, Egger, and Chaintreau (2010). The relative response factors (RRFs) were calculated as follows: RRF = (mcompound × areaISTD)/(mISTD × areacompound), where mcompound and areacompound are the mass and corresponding GC peak area of the analyte and mISTD and areaISTD are the mass and GC peak area of the internal standard.