Examination on simultaneous multi-element isotope ratio measurement by inductively coupled plasma time of flight mass spectrometry

Abstract

The simultaneous multi-element isotope ratio measurement by inductively coupled plasma time of flight mass spectrometry (ICP-TOFMS) was examined to evaluate the possibility of simultaneous multi-element determination by isotope dilution mass spectrometry (IDMS). Output from the two different ICP-TOFMS instruments (icpTOF and Optimass 9500) were examined and the figures of merit between them were determined from the analytical results of intensity ratios as isotope ratio measurements for 10 elements (137Ba/135Ba, 111Cd/112Cd, 63Cu/65Cu, 69Ga/71Ga, 60Ni/62Ni, 208Pb/206Pb, 107Ag/109Ag, 205Tl/203Tl, 238U/235U and 66Zn/68Zn). For the results, linear calibration curves for all elements, except for 235U obtained by icpTOF, with coefficient of determination (r2) of more than 0.999 could be obtained for both ICP-TOFMS instruments in the range of concentration from 1 ng mL−1 to 100 ng mL−1, even though the sensitivities of elements were slightly different. However, the trends of intensity ratios of elements observed were different between two ICP-TOFMS instruments, especially for heavier elements such as Pb, Tl and U. The icpTOF provided consistent isotope ratios at the concentrations from 1 ng mL−1 to 100 ng mL−1 for most of elements examined, although Optimass 9500 did not provide consistent isotope ratios except for Ba, Ga and Ag. From these analytical results, icpTOF appears to be the better instrument for simultaneous multi-element determination by IDMS compared to Optimass 9500. Consequently, the simultaneous IDMS of Cd, Hg and Pb by icpTOF was demonstrated to examine the possibility of simultaneous multi-element IDMS by ICP-TOFMS and the consistent analytical results with respect to the certified values could be obtained. From these results, it was expected that icpTOF could be used for simultaneous multi-element IDMS to obtain accurate and precise analytical results since it provided consistent isotope ratios of elements.