2.1　Chemicals

Compounds and reagents were all of analytical grade and purchased from Sigma，except where stated otherwise.N，O bis(Trimethylsilyl)trifluoroacetamide(BSTFA)and 1%trimethylchlorosilane(TMCS)were purchased from Tokyo Chemical Industry(Tokyo，Japan).O-Methoxyamine hydrochloride and pyridine(silylation-grade)were obtained from Aladdin Chemistry(Shanghai，China).Acetonitrile(HPLC-grade)was from Sinopharm Chemic Reagent(Shanghai，China).Ultrapure water was produced by a Milli-Q Reagent Water System(Millipore，USA).(https://www.daowen.com)