1. a State Key Laboratory of Organic Geochemistry , Guangzhou Institute of Geochemistry, Chinese Academy of Sciences , Guangzhou 510640 , China
2. b Department of Chemical Sciences , Redeemer's University , Klm 46/48 Lagos-Ibadan Expressway, Redemption , Nigeria
3. c Petroleum and Environmental Geochemistry Research Group, Chemistry Department, University of Ibadan , Ibadan , Nigeria