The main impurities in octylferrocene were its three isomers including(2-octyl)-ferrocene,(3-octyl)-ferrocene and(4-octyl)-ferrocene,which derived from the preparation of industrial product octylferrocene by separation.It is difficult to assess the purity of the isomers with high precision as the related reference materials for metal organic compounds are still in shortage at home and abroad.In this paper,gas chromatography was firstly employed to investigate the homogeneity and stability of the isomers prepared in laboratory,then the kinds of impurities in them were determined,and the mass balance approach was utilized to estimate the purity of the candidates.The purity assessment on organic impurities was mainly studied,and the uncertainty for the results were evaluated in the end.This may lay a foundation for the application of related substances in high-tech field.