1. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510 640, China
2. University of Chinese Academy of Sciences, Beijing 10069, China
3. Institute of Mass Spectrometry and Atmospheric Environment, Jinan University, Guangzhou 510632, China
4. Dipartimento di Chimica, Università di Torino, Via Pietro Giuria 5, Torino 10125, Italy