The GC oven was programmed to increase from 60 C (held for 1 min) to 220 C at 10 C/min, after
which 220 C was held for 3 min. The gas flow to the detector contained H2 (40 mL/min) and air (450 mL/min), the detector temperature was 300 C, the injection port temperature was 260 C and the 1-lL samples were loaded with an auto-sampler in the splitless mode.