Bolometers are among the most promising nuclear detectors for next-generation double beta decay search. A bolometer consists of an energy absorber connected to a temperature sensor. The signal is collected at extremely low temperatures (usually below 20 mK for large bolometers) and manifests as a thermal pulse recorded by the sensor, which can be made of a small semiconductor crystal, a thin superconducting film, or a metallic magnetic thermometer. Several compounds can be used as detectors for bolometers, including Li2MoO4 (LMO) crystals which are grown starting from Li2CO3 (lithium carbonate) and MoO3 (molybdenum trioxide) high purity powders.

The main challenge of future double beta decay searches is the reduction of radioactive background. In this context, the radiopurity of the detector materials is of great concern. One of the techniques widely used to certify the radiopurity of materials is Inductively Coupled Plasma Mass Spectrometry (ICPMS). In this talk I will discuss the application of this technique to the measurement of thorium (²³²Th) and uranium (²³⁸U) concentration in Li2CO3 and MoO3.

To solubilize Li₂CO₃, an acid solution was employed, while MoO₃ was dissolved in an alkaline solution due to its distinct chemical properties. Ultra-pure reagents were utilized throughout the procedures, and all equipment was preconditioned and verified by ICP-MS monitoring to ensure minimal background contamination. Matrix separation was achieved using chromatographic resins specifically designed for transuranic elements (TRU), which facilitated the removal of the matrix and enhanced measurement accuracy. The quantification of ²³²Th and ²³⁸U in each sample batch involved chemical characterization of the initial powders and crystals, with analysis performed using High-Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICPMS). Both low and medium resolution settings were applied to minimize interference due to presence of Mo during measurements.