Simple strategy to suppress the thermal effect for multi-element analysis in sulfide minerals by LA-ICP-MS with a cryogenic ablation cell

Abstract

A simple method is presented to suppress the thermal effect for the accurate determination of multi-elements in sulfide minerals using laser ablation inductively coupled plasma mass spectrometry with a cryogenic ablation cell (CLA-ICP-MS). The sulfide mineral samples were frozen (−30 °C) using a specifically designed Peltier-cooled ablation cell and analyzed directly using LA-ICP-MS. The ablation morphologies were investigated using scanning electron microscopy (SEM) images and microphotographs to compare the laser ablation behavior. A reduction in the melting, vapor redeposition, and heat-affected zone were observed at low temperature, which may be attributed to the effective suppression of the thermal effects caused by the laser ablation process. Ablated aerosol collection experiments indicated significant variations in particle size at low temperature (−30 °C) and room temperature (20 °C). The mean values of the ablated aerosol particle size of pyrite, chalcopyrite, and galena were 62 nm, 78 nm, and 146 nm at 20 °C and 51 nm, 35 nm, and 48 nm at −30 °C, respectively. The thermal effect on different sulfide minerals varied depending on the depth of thermal penetration, with the degree of impact being influenced by the sample's thermal diffusivity. A higher thermal diffusivity in sulfides resulted in a reduced magnitude of the thermal effect during ablation. Comparing the precision of the time-resolved signal during laser ablation between the two temperatures, the signal precision was significantly improved and the relative standard deviation (RSD) was improved from 28–39% to 11–24%. The signal intensity was enhanced by an additional 5–70% for different elements. The proposed method demonstrated lower deviation between the found values and the reference values, falling within 7% when analyzing natural sulfide minerals, including pyrite, chalcopyrite, and galena. The findings consistently demonstrated that CLA-ICP-MS can offer more dependable insights into the distribution of elements in sulfide minerals.