1992 Volume 41 Issue 4 Pages 185-192
The direct determination of rare earth elements, Th and U in fresh water was still difficult because of the lack of sensitivity, although such high sensitive methods as inductively coupled plasma mass spectrometry (ICP MS-quadrupole type) and activation analysis have been introduced. Recently, double focusing and high resolution ICP MS has been developed to allow the separation of overlapped ions (polyatomic ions and analyte ions at the same nominal mass) . This instrument also has a greater sensitivity and lower background as compared to those of the conventional quadrupole type ICP MS. In this study, a double-focusing and high resolution ICP MS with an ultrasonic nebulizer which gives increased sensitivity was used. This combination enabled the direct determination of the rare earth elements, Th and U in fresh water without pre-concentration. In the analysis of ultra trace level of elements, interferences from overlapped ions become a serious problem. In fresh water, however, it is found that high resolution measurement is not necessary to analyze the above elements, except Sc. Excellent detection limits of the order of 0.5-11.6 pg/l were achieved for these elements, with the exception of Sc (92 pg/l) . Although the concentrations of these elements in fresh water were as low as ng/l-pg/l, it was possible to determine the elements by this direct method. The concentrations of the rare earth elements, Th and U in 86 samples of fresh water collected from various places in Japan were measured by this method. The concentrations were in the range of 0.6 ng/l (Tm) -38.2 ng/l (Y) on average, and span a wide range (e.g., 0.9-199 ng/l U) . The mean concetrations of these elements in river waters were slightly higher than those of lake waters.
