Quantitative determination of rare earth elements in scheelite via LA-ICP-MS using REE-doped tungstate single crystals as calibration standards

A green and facile direct ink writing technique for preparation calibration standards in laser ablation inductively coupled plasma mass spectrometry analysis

BACKGROUND

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a powerful tool for microanalysis of solid materials. Nevertheless, one limitation of the method is the lack of well-characterized homogeneous reference materials (RMs), such as BaF2 crystal and BaCO3 ceramics samples, making direct quantification difficult. This work presents a novel Direct Ink Writing (DIW) method to produce RMs for microanalysis. The Mg, Cr, Fe, Co, Ni, Cu, Y, Mo, Pr, Gd, Dy, Ho, Er, Tm, Yb, and Lu solutions were gravimetrically doped into BaCO3 by mixing with the dispersant and then cured with DIW techniques. (94) RESULTS: BaCO3 powder was combined with a dopant analyte to produce a printable slurry, aided by the use of a dispersant and cellulose. The resulting mixture was then printed using DIW equipment. The retention rates of the doped elements were investigated by internal and external standard method, and the results showed that they were completely dispersed in the solid material. After further optimization, it was found that there was no significant heterogeneity among the printed samples. LA-ICP-MS was used to analyze printed samples, to evaluate micro-scale homogeneity. The mass concentration of the doped element was determined by ICP-MS, verify its move closer to nominal value. Compared with the traditional reference materials preparation methods, the DIW technology greatly increased the sample homogeneity and the accuracy of the desired concentration. (132) SIGNIFICANCE: As far as we know, there are few reports on the application of DIW method to prepare calibration standards. In brief, it is proved that the proposed method of preparing calibration standard by DIW technique to quantify analytes is valid and robust. This procedure provides great potential for LA-ICP-MS in-situ analysis in the field of well-prepared products, such as ceramic and crystal samples.(63).

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 (D_r) 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 (D_r) 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 D_r 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.

Calcium fluoride as a dominating matrix for quantitative analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS): A feasibility study

Calcium fluoride formed by the reaction between ammonium bifluoride and calcium chloride was investigated as a dominating matrix for quantitative analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Transformation from a solid sample to the calcium fluoride-based matrix permitted quantitative analysis based on calibration standards made from elemental standards. A low abundance stable calcium isotope, i.e. ⁴⁴Ca⁺, was monitored as the internal standard for quantitative analysis by LA-ICP-MS. Correlation coefficient factors for multiple elements were obtained with values over 0.999. The results for multiple elements in a certified reference material of soil (NIST SRM 2710a) agreed with the certified values in the range of expanded uncertainty, indicating the present method was valid for quantitation of elements in solid samples.