Glow discharge optical emission spectrometry is a technology that is used primarily to study the elemental composition of materials. It has many applications in the material manufacturing industries, where it can be used to tell if there is any oxidation, surface treatment, or contaminants present in or on a sample.
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In this article, we discuss the principle behind the functioning of glow discharge optical emission spectrometry, some of its practical applications as well as studies that have used the technology in innovative ways. Finally, we look at some disadvantages worth noting when considering the technology in a workflow.
How Does Glow Discharge Optical Emission Spectrometry Work?
Glow discharge is plasma that forms when an electric current is passed through a gas. It is produced when voltage is applied between a cathode and an anode in a glass tube containing a low-pressure gas like helium. This ionizes the gas such that the tube lights up with a bright light, which can be maintained when the voltage applied exceeds the striking voltage. The color of the light produced is specific to the type of gas used in the tube.
The excited atoms and ions in the discharge plasma produce a distinct emission spectrum for each element, and a single element can produce multiple distinct emission spectral lines which is what makes up the light generated by the discharge.
A glow discharge optical emission spectrometer is composed of a discharge lamp, an optical spectrometer, and a data detection and analysis system. The optical spectrometer is used to analyze the emission spectrum of the gas while the data detection and analysis system allows for qualitative and quantitative analysis of the interactions in the gas.
Magnetron discharge and radiofrequency discharge are the two most common glow discharge plasma generators.
What are the Applications and Practical Uses of Glow Discharge Optical Emission Spectrometry?
If an elemental composition depth profile of a sample of up to 150 µm is needed, glow discharge optical emission spectroscopy is the technique to use. This is especially desirable for metals and insulators. It provides rapid elemental analysis, making it essential for quality control in steelmaking and aluminum metallurgy processes.
In the steel industry, for example, the applications of glow discharge optical emission spectrometry have been reviewed. Processes such as passivation of stainless steel, phosphatization on electro-galvanized steel substrate, comparison of two paint layers on a hot-dip galvanized substrate, quantitative carbon analysis of steel sheet, aluminum surface segregation in aluminum transformation induced plasticity steel material, mini spangle formation on aluminum-zinc coatings, and investigating surface coloration.
Using this technology, it is possible to know the elements present in a sample and their concentration, and the composition of a sample with depth, which can help to tell if there is any oxidation, surface treatments, or contaminants present in or on the sample.
What are Some Advantages of Glow Discharge Optical Emission Spectrometry?
The advantages that stand out with this method include the possibility to analyze both surfaces and the bulk of the sample with considerable depths. The method can analyze up to 43 elements simultaneously, which includes all metals, sulfur, carbon, oxygen, chloride, and hydrogen. This range is generally from hydrogen to uranium, although this is largely dependent on the configuration of the instrument, a detection limit of parts per million (ppm), and depth profiles ranging from a hundred nanometres to 150 µm.
It can be used to analyze both insulators and conductors, there is a high detection sensitivity, and the quantification is direct and simple with appropriate standards.
Examples of Use of Glow Discharge Optical Emission Spectrometry
Ghanbari et al., in a study published in the journal ECS Electrochemistry Letters, used glow discharge optical emission spectrometry to detect lithium deposition as a function of depth in graphite electrodes in a post-mortem analysis, as lithium deposition reduces cell safety by causing rapid capacity decay.
Lithium plating was achieved by cycling commercial cells with graphite anodes at 5°C. After formation, graphite electrodes with solid electrolyte interphases were compared. Oxygen, lithium, and carbon depth profiles revealed varied surface impacts in terms of thickness and lithium content, with lithium deposition having a substantially greater lithium concentration.
Using depth profiling, glow discharge optical emission spectrometry was able to demonstrate lithium deposition on graphite anodes of the Li-ion batteries.
Researchers have also sought to improve the technology to widen its use. In a study published in the Journal of Analytical Atomic Spectrometry, the researchers developed a battery-operated miniaturized glow discharge optical emission spectrometry device to measure metals in water samples. There was no need for pre-treatment of the water samples, and this made it an environmentally friendly approach.
The device could simultaneously test Cd, Hg, and Pb without separation or enrichment, with detection limits of 33–253 g/L (flow injection mode) and 7–92 g/L /(continuous flow mode). The calibration curves for Cd, Hg, and Pb were linear for concentrations in the range of 2–50 g m/L. Certified reference materials, tap water, and ocean samples were all tested successfully with good accuracy.
What are Some of the Limitations of Glow Discharge Optical Emission Spectrometry?
Glow discharge optical emission spectrometry is highly efficient in providing important information that helps in the processing of metals and insulators. However, it has a couple of disadvantages.
The method is destructive, especially for soft materials like polymers and biomaterials, as it requires vaporizing the sample. As well as this, the configuration of the instrument can limit the number of detectable elements, it doesn’t provide imaging, and there is still a need to provide adequate standards. Furthermore, the instrument is limited to atomic information and the samples have to be flat and vacuum compatible.
To summarize, glow discharge optical emission spectrometry provides a fast and reliable way to qualitatively and quantitatively analyze elements in samples. It provides high-quality data that can be used to improve the materials manufacturing process. Despite its limitations, avenues for innovative use and improvement of its capabilities exist.
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References and Further Reading
Azom. (2018). What is Optical Emission Spectroscopy (OES)? [Online]. AZoM.com. Available at: https://www.azom.com/article.aspx?ArticleID=15632
Ghanbari, N., Waldmann, T., Kasper, M., Axmann, P. and Wohlfahrt-Mehrens, M. (2015). Detection of Li deposition by glow discharge optical emission spectroscopy in post-mortem analysis. ECS Electrochemistry Letters, 4(9), p.A100. https://doi.org/10.1149/2.0041509eel
Peng, X., Guo, X., Ge, F. and Wang, Z. (2019). Battery-operated portable high-throughput solution cathode glow discharge optical emission spectrometry for environmental metal detection. Journal of Analytical Atomic Spectrometry, 34(2), pp.394-400. https://doi.org/10.1039/C8JA00369F
Xhoffer, C. and Dillen, H. (2003). Application of glow discharge optical emission spectrometry in the steel industry. Journal of Analytical Atomic Spectrometry, 18(6), pp.576-583. https://doi.org/10.1039/B212750B