Multi-element imaging of urinary stones by LA-ICP-MS with a homogeneous co-precipitation CaC2O4-matrix calibration standard.

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) studies on trace element concentration and their spatial distribution in CaC2O4-matrix urinary stones are important but powerfully rely on matrix-matched external calibration. In this work, CaC2O4 precipitate CaOx-1 which was doped with Mg, Cr, Mn, Fe, Co, Cu, Zn, and Sr was prepared by the homogeneous co-precipitation method. It had a homogeneous distribution of major (RSD of 0.46%) and trace elements (RSD of 1.83-6.92%) due to the negligible concentration difference compared with that prepared by the heterogeneous co-precipitation method. Based on this, an analytical method for quantitative determination of elemental concentration in CaC2O4-matrix samples was established using CaOx-1 as a calibration standard, and the accuracy of this method was assessed by calibrating the elemental concentration in another synthetic CaC2O4 precipitate CaOx-2 with relative deviation (Dr) from - 11.43% (Mn) to 9.76% (Mg). Finally, a methodology for quantitative imaging of Mg, Cr, Mn, Fe, Co, Cu, Zn, and Sr in urinary stones via LA-ICP-MS was developed. From the elemental distributional maps, an annular texture can be found for Mg, Cu, Zn, and Sr, which corresponds to the annular white and brown texture in the real urinary stone. A homogeneous distribution of Fe and low concentrations of Cr and Co were found throughout the stone, while Mn was highly concentrated in the margin of the stone. All these results demonstrate that quantitative distribution patterns of Mg, Cr, Mn, Fe, Co, Cu, Zn, and Sr can be obtained by LA-ICP-MS using CaOx-1 as a calibration standard, which can provide potential evidence for urological and other medical studies.

Preparation of REE-doped NaY(WO4)2 single crystals for quantitative determination of rare earth elements in REE:NaY(WO4)2 laser crystals by LA-ICP-MS.

In REE:NaY(WO4)2 laser crystals, optical properties like laser conversion efficiency are dependent on the doped rare earth element (REE) concentration, which necessitates the importance for accurate determination of the REE concentration in these precious samples. However, in situ microanalysis of these samples by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is often hampered by the lack of matrix-matched reference materials. In this work, a REE-doped NaY(WO4)2 single crystal (NaYW-500) that has a nominal REE concentration of 500 µg g-1 was synthesized and employed as a candidate reference material. Its homogeneity (1 RSD of elemental concentration or 89Y-normalized signal intensity) was measured by electron probe microanalysis (EPMA) and LA-ICP-MS to be less than 2% for major elements and mainly <3% for REEs, respectively. Then, an LA-ICP-MS analytical method was developed by using 89Y as the internal standard and using NaYW-500 as the external calibrator under the optimal operating conditions. Quantitative determination of the REE concentration in the other two REE:NaY(WO4)2 single crystals NaYW-50 and NaYW-5000 show that these samples can be accurately measured with relative deviations (Dr) of -6.00 to 12.33% and -9.86 to 6.94%, respectively. Further application of the proposed analytical method to quantitative determination of the Ho concentration in a Ho:NaY(WO4)2 laser crystal shows that desirable accuracy was obtained with a Dr of 4.62%. It demonstrates that the proposed method by preparing REE-doped NaY(WO4)2 single crystals for quantitative determination of the REE concentration in NaY(WO4)2 laser crystals is valid and robust.