Purity analysis of polyhedral oligomeric octa (nitrophenyl) silsesquioxane

The purity of polyhedral oligomeric octa(nitrophenyl)silsesquioxane (ONPS) was analyzed using high performance liquid chromatography/ESI-Q-TOF MS (HPLC-ESI-Q-TOF MS). The peaks of ONPS and impurities could be distinguished and the purity of ONPS could be calculated. The impurity peaks of HPLC were separated completely through changing the analytical conditions. The best HPLC conditions in the testing were obtained. The analytical time under these conditions was longer than under others. It was obtained that nitrophenylsilsesquioxane (NPS) was in 97.55 wt%. According to the analytical results from MS and the extracted ion chromatogram (EIC) HPLC-MS for ONPS, it could be found that in ONPS there is a little of nonanitro-octaphenylsilsesquioxane (9-NPS), but no 7-NPS and 10-NPS. It was supposed that ONPS and 9-NPS had the same ionization degree because of their very similar chemical structures. It was obtained that ONPS was in a purity of 92.42%, while the 9-NPS was in an amount of 5.13%, and impurities were in 2.45%. It was confirmed that nitro groups on the phenyl groups were at either para-or meta-position in ONPS according to the results of HPLC and the polarity analysis of different isomers. Compared to centrosymmetric structure of octaphenylsilsesquioxane (OPS), ONPS could be non-centrosymmetric due to difference of-NO2 substitution position on the phenyl groups. All of the possible polarity distributions were analyzed for the ONPS. It was pointed that there are seven kinds of different polarity distributions on ONPS molecules, and they are correspondent to the particular peaks of HPLC results, respectively. As well, the purity of ONPS was analyzed using ultra performance liquid chromatography (UPLC) and it provided consistent results with HPLC in high separation efficiency. It is suggested that the HPLC-ESI-Q-TOF MS method can be used to analyze the purity of ONPS.