d HP-5MS capillary column
(30 m × 0.25 mm, film thickness 0.25 m; Agilent-Technologies,
Little Falls, CA, USA). Temperatures of injector and detector were
set respectively at 220 ◦C and 290 ◦C. The temperature of column
was programmed from 80 ◦C to 220 ◦C at a rate of 4 ◦C/min, with
the lower and upper temperatures being held for 3 and 10 min,
respectively.