| Popis: |
A procedure for the determination of the cerium isotopic ratio by thermal ionization mass spectrometry of the Ce+ ion has been investigated. The intensity of the Ce+ ion emitted from Ce(NO3)3 was considerably enhanced by the addition of graphite to the filament substrate during loading. Interferences from the impurities of barium and lanthanum can be overlooked because the Ba+ peak disappeared at the normal temperature for emitting the Ce+ ion and the 138La+ intensity was too weak (10−17A). The interference of 142Nd with 142Ce can be calibrated by using a 142Nd/143Nd ratio of 2.2274. The 136Ce/140Ce, 138Ce/140Ce and 142Ce/140Ce ratios in five chemical reagents with different origins have been measured as 0.002122 ± 0.000004, 0.002865 ± 0.000005 and 0.125201 ± 0.000055 (SD) in average value, corresponding to the percentage abundances of 0.1878(4), 0.2535(5), 88.4808(50) and 11.0779(44) for 136Ce, 138Ce, 140Ce and 142Ce, respectively. Based on these ratios, the atomic weight of cerium was calculated to be 140.1148(1) (SD), which is more precise than the cerium atomic weight of 140.115(4), recommended by IUPAC. |
