2.4. GC-MS

Samples were diluted with methanol at a 1:10 ratio and they were analyzed in a gas chromatograph (Agilent 7890B, Agilent Technologies Inc., Santa Clara, CA, USA) and a mass spectrometer (Agilent 5977A). An Agilent HP-5 silica capillary column (30 m × 0.25 mm, film thickness 0.25 µm) was used. Split injection in a 1:20 ratio was used and the injector temperature was 250 °C. The temperature program was 40 °C, hold for 8 min, increase 5 °C/min to 180 °C and then increase 10 °C/min to the final temperature of 250 °C, maintained for 20 min. Helium was used as the carrier gas. The SCAN method was used with an atomic mass unit from 33 to 400. The identification of compounds was accomplished by retention times and GC-MS data library (NIST02, National Institute of Standards and Technology, Gaithersburg, MD, USA). The relative abundance of the total ion chromatogram areas of the compounds was calculated. The method was used for quick screening of the distillates and to support the other analytical methods used in the study.