RESUMO
Long-lived high abundance radionuclides are of increasing interest with regard to decommissioning of nuclear sites and longer term nuclear waste storage and disposal. In many cases, no routine technique is available for their measurement in nuclear waste and low-level (ng kg-1) environmental samples. Recent advances in ICP-MS technology offer attractive features for the selective and sensitive determination of a wide range of long-lived radionuclides. In this work, inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS)-based methodology, suitable for accurate routine determinations of 93Zr at very low (ng kg-1) levels in the presence of high levels (µg kg-1) of the isobaric interferents 93Nb and 93Mo (often present in nuclear waste samples), is reported for the first time. Additionally, a novel and systematic strategy for method development based on the use of non-radioactive isotopes is proposed. It relies on gas-phase chemical reactions for different molecular ion formation to achieve isobaric interference removal. Using cell gas mixtures of NH3/He/H2 or H2/O2, and suitable mass shifts, the signal from the 93Nb and 93Mo isobaric interferences on 93Zr were suppressed by up to 5 orders of magnitude. The achieved limit of detection for 93Zr was 1.3 × 10-5 Bq g-1 (equivalent to 0.14 ng kg-1). The sample analysis time is 2 min, which represents a significant improvement in terms of sample throughput, compared to liquid scintillation counting methods. The method described here can be used for routine measurements of 93Zr at environmentally relevant levels. It can also be combined with radiometric techniques for use towards the standardisation of 93Zr measurements. Graphical abstract Interference-free determination of 93Zr in the presence of high concentrations of isobaric 93Mo and 93Nb by ICP-MS/MS.
RESUMO
In recent years, laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) has gained increasing importance for biological analysis, where ultratrace imaging at micrometer resolution is required. However, while undoubtedly a valuable research tool, the washout times and sensitivity of current technology have restricted its routine and clinical application. Long periods between sampling points are required to maintain adequate spatial resolution. Additionally, temporal signal dispersion reduces the signal-to-noise ratio, which is a particular concern when analyzing discrete samples, such as individual particles or cells. This paper describes a novel, two-volume laser ablation cell and integrated ICP torch designed to minimize aerosol dispersion for fast, efficient sample transport. The holistic design utilizes a short, continuous diameter fused silica conduit, which extends from the point of ablation, through the ICP torch, and into the base of the plasma. This arrangement removes the requirement for a dispersive component for argon addition, and helps to keep the sample on axis with the ICP cone orifice. Hence, deposition of sample on the cones is theoretically reduced with a resulting improvement in the absolute sensitivity (counts per unit mole). The system described here achieved washouts of 1.5, 3.2, and 4.9 ms for NIST 612 glass, at full width half, 10%, and 1% maximum, respectively, with an 8-14-fold improvement in absolute sensitivity, compared to a single volume ablation cell. To illustrate the benefits of this performance, the system was applied to a contemporary bioanalytical challenge, specifically the analysis of individual biological cells, demonstrating similar improvements in performance.
