The fundamentals of laser ablation and elemental analysis shall be discussed in this article to inform readers regarding the principles, applications, and latest research.
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What is Elemental Analysis?
Elemental analysis is a procedure used in materials science and analytical chemistry to determine the element makeup of a material specimen such as water, mineral deposits, or bodily fluids. The type of elemental analysis could be subdivided into two types, termed qualitative and quantitative. Qualitative analysis is performed to determine the type of element while quantitative analysis ascertains the level/number of elements.
There are several techniques of elemental analysis including inductively Coupled Plasma Mass Spectrometry (ICP-MS), X-ray fluorescence, scanning electron microscopy, etc. ICP-MS is an elemental analysis method capable of detecting several components from the periodic table at milligram to nanogram levels per liter.
A very precise mass spectroscopy monitor is combined with inductive reasoning linked plasma-focused beam source in this approach. Elemental analysis is useful for elements like oxygen, nitrogen, halogens, etc. It is used in a variety of sectors, including geological testing, mining, environmental sensing, biopharmaceutical assessment, and medical trials. Through combustion analysis, the elemental analysis may be performed to identify the amounts of numerous gases.
Introduction to Laser Ablation
Laser ablation is a process utilized for creating micro patterns that involve the elimination (ablation) of small percentages of a substrate surface using a focused pulsating laser beam. It is a difficult but advantageous procedure. The laser impulse frequency, laser wavelength, and the refractive index of the substrate are major factors affecting laser ablation.
In analytical chemistry, laser ablation has become a dominating tool for direct solid samples and elemental analysis. Its benefits include direct spectroscopy and analysis of solid particles, no synthetic methods for disintegration, diminished contamination or specimen damage, evaluation of compact specimens that are not distinguishable for solution analysis, and perseverance of spatial heterogeneity of elemental composition.
Laser Ablation Systems for Elemental Analysis
A laser, an ablation stage, and a monitoring technique are typical components of a laser irradiation device. Most typically, pulsating lasers are employed to generate light energy for ablation. Typically, the samples are put on a manually controlled ablation platform. Detection systems are frequently LP-ICP-MS or ICP-AES.
Argon or other inert gases are frequently used to transport the ablated material into the ICP. Shorter emission wavelengths, in general, provide greater photon energy for effective cleavage of bonds and ionization of the substrate material. Furthermore, keeping in view the operational wavelength, ablation may include thermally operated and/or non-thermal processes.
Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS)
Owing to its resolution, accuracy, and theoretical accessibility, LA-ICP-MS is regarded as among the most adaptable technologies for the elemental study of solid objects. Ever since its emergence, the abilities of LA-ICP-MS in terms of precision, resolution, and consistency have risen steadily, mainly due to experimental developments and the development of clever adjustment and validation procedures.
As a result, LA-ICP-MS has become a widely used approach for element and hydrocarbon studies of diverse materials. It is quite an efficient technique that is advantageous in offering spatial as well as structural data regarding the compositional distribution of elements in biological specimens. Its widespread advantages over conventional techniques have also led to its rapid utilization in the elemental analysis of solid substances as well its utilization in forensic sciences and soil analysis.
This technique involves the usage of only a pulsed laser, optimization apparatus, transport line, air-sealed specimen housing, and an inductively coupled plasma mass sensor. The laser ablation technique, being implemented along with the physicochemical state of the specimen, causes a variable combination of groups, nanoparticles, and clumps emitted during the annealing process, resulting in 'nonrepresentative' samples occasionally.
Limitations of LA-ICPMS
LA-ICPMS is a very powerful elemental analysis and solid analytical method that provides excellent resolving power as well as simple sample processing. Even though LA-ICP-MS has significant promise for depth profiles, it is currently not viable compared to classic procedures such as X-Ray Photoelectron Spectroscopy (XPS), Ion Mass Spectroscopy, and so on.
Furthermore, non-uniform elimination operations and matrix-sensitive ablation events occurring during the engagement of the laser light with the substance may have an impact on the depth resolution that can be achieved. Femtosecond (fs)-LA systems can decrease heat impacts during elimination, however, the Gaussian beam profiles produced by current fs-laser systems generate pyramidal crater forms that compromise depth resolution. The penetration depth per laser beam is another important factor influencing LA depth resolution.
Latest Research
The latest article by Mr. Hirata and his team published in Analytical Sciences is focused on enhancing the resolution of laser ablation ICP-MS. To increase resolving power, image analysis was performed in this work with the combination of a low volume unit with an offset laser ablation methodology.
The integration of a completely redesigned small volume cell and in-torch gaseous blending methods resulted in a quicker data saturation time. This is critical for increasing spatial resolution in a laser scanner's direction. Furthermore, the coupling of small distances between laser lines (laser pitching spacing) and selective and complete combustion of only living clinical specimens put on glass surfaces led to laser ablation of regions smaller than the diameter of the laser ablation crater.
Scanning characterization of Gd-ethylenediamine tetra-methylene phosphonate acid-doped mouse bone was performed to illustrate the realistic application of the current approach. The current approach revealed a more pronounced favored concentration of Gd near the anatase cell's edge. They were able to increase the resolving power of the chemical photography acquired with the LA-ICPMS technology by combining a shortened rinsing system configuration with a shave treatment strategy.
In short, laser ablation has proved to be a successful technique for elemental analysis, and further research is needed to overcome its limitations.
References and Further Reading
Tanaka, Eisei, et al. 2022. Improvement of spatial resolution of elemental imaging using laser ablation-ICP-mass spectrometry. Analytical Sciences. 1-8. Available at: https://link.springer.com/article/10.1007/s44211-022-00085-8
Suski, Kaitlyn J., et al. 2021. Real-time characterization of particles produced by laser ablation for analysis by inductively coupled plasma mass spectrometry. Spectrochimica Acta Part B: Atomic Spectroscopy 179. 106092. Available at: https://www.sciencedirect.com/science/article/pii/S0584854721000367?via%3Dihub
Oelze, Marcus, Daniel A. Frick, and Sarah A. Gleeson. 2021. Laser ablation split stream for in situ sulfur isotope and elemental analysis. Journal of Analytical Atomic Spectrometry 36(6). 1118-1124. Available at: https://pubs.rsc.org/en/content/articlelanding/2021/JA/D1JA00083G
Liao, Xiuhong, et al. 2021. Isotopic Analysis by Laser Ablation Solution Sampling MC-ICP-MS─ An Example of Boron. Analytical Chemistry. Available at:
https://pubs.acs.org/doi/10.1021/acs.analchem.1c04497
Arrowsmith, Peter. 1987. Laser ablation of solids for elemental analysis by inductively coupled plasma mass spectrometry. Analytical Chemistry 59(10). 1437-1444. Available at: https://pubs.acs.org/doi/abs/10.1021/ac00137a014
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