1998 年 33 巻 1 号 p. 17-24
Impurities were analyzed in the benzene synthesized from an environmental sample for 14C measurement and influence of the impurities on 14C activity measurement was examined. Chloride, nitrite, nitrate, phosphate, sulfate ions were observed in the benzene. Contamination of inner glass surface of the synthesis line, especially traps, was found to be a source for these impurities. Toluene, ethyl benzene, o-xylene and grease which was used for connections and cocks in the line were detected. The amount of benzene-derivatives was small and did not act as quenchers in 14C measurement. On the other hand, a large amount of grease (DOW CORNING HIGH VACUUM SILICONE GREASE) was observed in the synthesized benzene, resulting in underestimation of 14C activity. Alternative grease (Shin-Etsu Co., Ltd.; FG-721) is insoluble to benzene. 14C concentration of NBS RM49 showed in good agreement with the recommended value when FG-721 was used, suggesting a suitability for the benzene synthesis.