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Four series of experiments had been carried out for correct ytterbium isotope ratios measurements (IRM).(1) For erbium IRM, 167 Er/ 166 Er ~0.682 60, derived from recently published thermal ionization mass spectrometry (TIMS) measurements, was applied as an internal normalization factor. (2) Ytterbium has no calibrated isotope ratio values. In an erbium-ytterbium-hafnium mixture solution we determined ( 171 Yb/ 172 Yb) Er-corr ~0.653 436(4) using the above 167 Er/ 166 Er ratio as external normalization factor. In the same mixture we also determined ( 171 Yb/ 172 Yb) Hf-corr ~0.653 297(25) using the well-known IUPAC value for the ratio 179 Hf/ 177 Hf ~0.732 50 as external normalization factor. In these measurements no atomic isobaric interference exists at the corresponding mass numbers. (3) These two 171 Yb/ 172 Yb ratios, derived with data at mass intervals 166-167 and y178, were interpolated to mass interval 171-172, applying linear and slightly curved (exponential) line interpolations. 171 Yb/ 172 Yb ~0.653 367 and 0.653 344 are the linear and curved line interpolated values, respectively. Then, all ytterbium isotope ratios were measured in pure ytterbium solutions and internally corrected with each of the two 171 Yb/ 172 Yb ratios. ( 4) Using the literature value for 178 Hf/ 177 Hf ~1.467 290, we obtained 179 Hf/ 177 Hf ~0.732 49(2), which is in very good agreement with the above mentioned IUPAC value. The exponential correction equation was applied in this work. The mean Er ratio values are in good agreement with literature, except for the 162 Er/ 166 Er ratio, which is 2.19% lower than the reported absolute TIMS value. The mean Yb ratio values obtained in this work are in fair agreement with data reported in the last 25 years. We believe that they are the closest to the true values. The precision (2s) is at least 3-8 times better comparing to the measured TIMS precision.

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An analytical method for the determination of plutonium concentration and its isotope ratio at ultratrace level in natural water by inductively coupled plasma mass spectrometry (ICP-MS) is proposed. In order to preconcentrate Pu and to avoid matrix effects and clogging effects on the cones during the mass spectrometric measurements, an effective Pu separation procedure (on TEVA resin) from the matrix was applied. Studies of the separation procedure for 2.1 pg of 242 Pu spiked into 100 L of lake water from the Sea of Galilee result in a recovery of 62%. The detection limits of 239 Pu in 100 L lake water were determined as 1 6 10 219 g mL 21 and 3 6 10 220 g mL 21 using ICP-SFMS and MC-ICP-MS, respectively. 239 Pu was detected in the Sea of Galilee at a concentration level of about 3.6 6 10 219 g mL 21 with a 240 Pu/ 239 Pu isotope ratio of 0.17. This measured plutonium isotope ratio is the most probable evidence of plutonium contamination of the Sea of Galilee as a result of global nuclear fallout after the nuclear weapons tests in the sixties. This paper discusses applications of double-focusing sector field ICP-MS with single and multiple ion collection for the quantitative determination of plutonium and its isotope ratio at the 10 219 g mL 21 level in natural water.

The capability of a second-generation Nu Instruments multiple collector inductively coupled plasma mass spectrometer (MC-ICP-MS) has been evaluated for precise and accurate isotope-ratio determinations of lead. Essentially the mass spectrometer is a double-focusing instrument of Nier-Johnson analyzer geometry equipped with a newly designed variable-dispersion ion optical device, enabling the measured ion beams to be focused into a fixed array of Faraday collectors and an ion-counting assembly. NIST SRM Pb 981, 982, and 983 isotopic standards were used. Addition of thallium to the lead standards and subsequent simultaneous measurement of the thallium and lead isotopes enabled correction for mass discrimination, by use of the exponential correction law and 205Tl/203Tl = 2.3875. Six measurements of SRM Pb-982 furnished the results 206Pb/204Pb = 36.7326(68), 207Pb/204Pb = 17.1543(30), 208Pb/204Pb = 36.7249(69), 207Pb/206Pb = 0.46700(1), and 208Pb/206Pb = 0.99979(2); the NIST-certified values were 36.738(37), 17.159(25), 36.744(50), 0.46707(20), and 1.00016(36), respectively. Direct isotope lead analysis in silicates can be performed without any chemical separation. NIST SRM 610 glass was dissolved and introduced into the MC-ICP-MS by means of a micro concentric nebulizer. The ratios observed were in excellent agreement with previously reported data obtained by TIMS and laser ablation MC-ICP-MS, despite the high Ca/Pb concentration ratio (200/1) and the presence of many other elements at levels comparable with that of lead. Approximately 0.2 microg lead are sufficient for isotope analysis with ratio uncertainties between 240 and 530 ppm.

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