Application of isotope-dilution laser ablation ICP?MS for direct determination of Pu concentrations in soils at pg�g?1 levels

Abstract

The methods available for determination of environmental contamination by plutonium at ultra-trace levels require labor-consuming sample preparation including matrix removal and plutonium extraction in both nuclear spectroscopy and mass spectrometry. In this work, laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied for direct analysis of Pu in soil and sediment samples. Application of a LINA-Spark-Atomizer system (a modified laser ablation system providing high ablation rates) coupled with a sector-field ICP-MS resulted in detection limits as low as 3x10(-13) g g(-1) for Pu isotopes in soil samples containing uranium at a concentration of a few microg g(-1). The isotope dilution (ID) technique was used for quantification, which compensated for matrix effects in LA-ICP-MS. Interferences by UH+ and PbO2+ ions and by the peak tail of 238U+ ions were reduced or separated by use of dry plasma conditions and a mass resolution of 4000, respectively. No other effects affecting measurement accuracy, except sample inhomogeneity, were revealed. Comparison of results obtained for three contaminated soil samples by use of alpha-spectrometry, ICP-MS with sample decomposition, and LA-ICP-IDMS showed, in general, satisfactory agreement of the different methods. The specific activity of (239+240)Pu (9.8 +/- 3.0 mBq g(-1)) calculated from LA-ICP-IDMS analysis of SRM NIST 4357 coincided well with the certified value of 10.4 +/- 0.2 mBq g(-1). However, the precision of LA-ICP-MS for determination of plutonium in inhomogeneous samples, i.e. if "hot" particles are present, is limited. As far as we are aware this paper reports the lowest detection limits and element concentrations yet measured in direct LA-ICP-MS analysis of environmental samples.

Spatially resolved analysis of plutonium isotopic signatures in environmental particle samples by laser ablation-MC-ICP-MS

“…In contrast to other studies (e.g. [ 42 – 44 ]), where ultra-trace concentration levels of Pu isotopes in environmental samples had been determined by applying a single collector ICP-MS, a multi-collector-ICP-MS instrument was applied here, especially following the need that the isotope ratio has to be determined on short transient signals to not compromise measurement precision and accuracy of Pu isotope ratio measurements. Similar to a previous study on U, Nd and Ru/(Ru + Tc) isotope ratios [ 18 ], the standard collector block of the Nu Plasma HR multi-collector was modified for measuring 239 Pu + , 240 Pu + and 242 Pu + simultaneously with three SEMs (Fig.…”

Progress of the Analytical Methods and Application of Plutonium Isotopes in the Environment

“…Another commonly used instrument is LA-ICP-MS, which can directly analyze solid samples without dissolution. For example, Boulyga, S. F., et al [102] developed a LA-ICP-MS method to directly analyze the concentration of plutonium isotopes in soils at the pg g −1 level. The uranium hydride ion was significantly suppressed with the application of laser ablation, and a UH + /U + ratio of 1.1 × 10 −6 was obtained.…”

Combining standard addition and isotope dilution in order to improve SI traceable LA-ICP-MS measurements

“…Additionally, uniformitythe prerequisite for mutual recognitioncan be ensured. 12,13 Besides internal standardization, [14][15][16][17] solid certied reference materials (CRMs) can be used to quantify element contents in the sample. To represent the sample as good as possible, it is necessary to use a matrix matched CRM.…”