Chromatographic separations were acquired using a polyethylene
glycol capillary column (60 m 0.53 mm ID df 0.25 mm)
(Agilent Co., St Louis, USA) with a 0.25 mm ID 0.5 m guard
column connected w/union. Carrier gas was nitrogen (Tsingtao
Chemical Co., Shanghai, China), and its purity was >99.999%.