Elemental Analysis of Solid Food Materials Using a Reliable Laser Ablation Inductively Coupled Plasma Mass Spectrometry Method

Investigation on effects of TiO2 on cucumber seedlings using ICP-OES and LA-ICP-MS

With the expansion of TiO2 applications in various fields, TiO2 inevitably enters the soil, increasing the possibility of plant roots being exposed to high concentrations of TiO2. Therefore, it is important to study plant growth under TiO2 exposure conditions. In this study, the combination method of inductively coupled plasma emission spectroscopy (ICP-OES) and laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) was used to evaluate the effect of TiO2 on the content and distribution of nutrient elements in different parts of cucumber seedlings. The results showed that the low concentrations (50 mg/L, 100 mg/L and 200 mg/L) of TiO2 had gradually enhanced the growth of cucumber seedlings, while the high concentration (500 mg/L) of TiO2 had a significant inhibitory effect on the plant. The contents of elements (Ti, K, Ca, Mg, Mn, Fe, Zn, and Cu) in cucumber seedling roots, stems and leaves incubated with 200 mg/L TiO2 were determined by ICP-OES, and the results showed that the uptake of TiO2 increased the content of nutrient elements in the plant. High-resolution imaging of Ti, Ca, Mg, Mn, Fe, Zn, and Cu in roots, stems, and leaves using LA-ICP-MS showed that Ti accumulated mainly at the margins of the leaves. Ca, Mg, Mn, Fe, Zn, and Cu in the leaves were mainly concentrated in the main veins and lateral veins. By evaluating the content and distribution of elements in the plant with ICP-OES and LA-ICP-MS, it provides a new idea to study the mechanism of nanoparticles in the plant. It provides a theoretical basis for the correct use of nanomaterials, which is of great significance in promoting the sustainable development of agriculture.

A frozen suspension external calibration strategy for elemental quantitative imaging of fresh plant soft tissues by LA-ICP-MS with cryogenic ablation cell

A simple and reliable external calibration strategy of LA-ICP-MS for fresh plant soft tissues was developed. The prepared plant suspension was frozen by the designed cryogenic ablation cell and used as external standard for quantitative elemental imaging analysis of fresh plant tissues. The controllable water content of the prepared external standards provides a similar matrix with fresh soft tissues, and a homogeneous elemental distribution could be ensured due to the fine grinding particle sizes. More interestingly, the presence of water increased the signal intensity produced by the suspension by a factor of 1.6 (Pb) to 66.6 (La) compared to that of the pressed cake. The excellent dispersing property and advantage of long-term use were achieved owing to the employment of 0.1% PAANa as suspending agent. A series of plant reference materials were analyzed, and the relative errors of most elements were less than 10 %, indicating that there is a reliable accuracy of the proposed method. The limits of detection (LODs) ranged from 0.1 ng·g-1 (La) to 1279 ng·g-1 (S). This method was used for elemental imaging analysis in rice leaves under arsenic stress, and the results were consistent with previous studies, which mean that the proposed method could provide technical support for researchers in the fields of agriculture and environment.

In-situ elemental quantitative imaging in plant leaves by LA-ICP-MS with matrix-matching external calibration

Due to the enormous interest in plants related to bioscience, environmental and toxicological research, analytical methods are expected with the ability of getting information on elemental transfer, distribution and contents in plants. In this work, a mixture of gelatin (GA) and hydroxypropyl methyl cellulose (HPMC) was prepared to simulate plant matrix, a method based on laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with matrix-matching external calibration was proposed for direct quantification of multiple elements in plants. The composition of GA&HPMC substrate was optimized, such as the concentration of spiked nitric acid, the mass fraction of both GA and HPMC in the substrate and the mass ratio of GA: HPMC. After spiking elemental solution, coating the mixture onto a glass slide and drying overnight at room temperature, GA&HPMC substrate was obtained. The substrate obtained with GA: HPMC of 8: 2 was used to fabricate the standard series, which exhibited good elemental homogeneity and similar elemental signal intensities in LA-ICP-MS detection to that obtained for plant Certified Reference Material (CRM). CRMs of different plants including Citrus leaf (GBW10019), Tea (GBW07605), Beans (GBW10021) and Scallions (GBW10049) were further pressed into pellets and subjected to the proposed method, and the quantification accuracy was demonstrated. The limits of detections of this method were found to be 0.003 (Ce)-104 (Ca) μg g-1, with a wide linear range (0.01-10000 μg g-1) for 17 target elements. The application potential of the method was further demonstrated by performing elemental imaging in Trigonotis peduncularis leaves. Rapid in-situ quantitative imaging of Zn, Cu, Sr and Mn was achieved, and the elemental quantitative distributions were discussed. The constructed substrate helped direct elemental quantification in plants. It provided a powerful and efficient tool for the investigation of the distribution and transfer of elements in plants, favoring further exploration of elemental bioavailability, transport and toxicity mechanisms.

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.

Uptake, transformation, and environmental impact of zinc oxide nanoparticles in a soil-wheat system

Zinc oxide nanoparticles (ZnO-NPs) are metal-based nanomaterials, but their long-term effects on plant growth and the soil environment in the field remain unclear with most previous studies using short-term laboratory and glasshouse studies. In this study, we used a field experiment to examine the long-term effects of ZnO-NPs in a soil-wheat (Triticum aestivum) system. It was found that although ZnO-NPs had no significant effect on either yield or the concentration of other nutrients within the grain, the application of ZnO-NPs significantly increased Zn concentrations. Indeed, for grain, the application of ZnO-NPs to both the soil and foliage (SFZnO) (average of 33.1 mg/kg) significantly increased grain Zn concentrations compared to the the control treatment (21.7 mg/kg). Using in situ analyses, nutrients were found to accumulate primarily in the crease tissue and the aleurone layer of the grain, regardless of treatment. Specifically, the concentration of Zn in the aleurone layer for the SFZnO treatment was 2-3 times higher than that in the control, being >300 mg/kg, whilst the Zn concentration in the crease tissue was ca. 600 mg/kg in the SFZnO treatment, being two times higher than for the control. Although the application of ZnO-NPs increased the total Zn within the grain, it did not accumulate within the grain as ZnO-NPs with this being important for food safety, but rather mainly as Zn-phytate, with the remainder of the Zn complexed with either cysteine or phosphate. Finally, we also observed that ZnO-NPs caused fewer changes to the soil bacterial community structure and that it had no nano-specific toxicity.

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.