Analytical Glow Discharges in Argon Lead
To better understand the mechanics behind charge transfer reactions, Zdeněk Weiss, head of the laboratory at the Institute of Physics of the Czech Academy of Sciences in the Czech Republic, conducted a study to explain why argon ions and analyte ions react more strongly in analytical glow discharges than in other similar plasmas (1).
Zdeněk Weiss | Image Credit: © Zdeněk Weiss
Glow discharge (GD) spectroscopy is a well-established method in the elemental analysis of metals, coatings, and surface-modified materials. Examples of GD spectroscopy include glow discharge optical emission spectroscopy (GDOES) and glow discharge mass spectrometry (GDMS). GDOES is powered by Grimm-type lamps, which are light sources meant for “emission spectroscopic routine investigations of solid planar samples” (2).
Excitation and ionization of analyte atoms usually happens independent of analyzed matrices. This is because the process usually happens in an argon plasma which strongly dilutes the analytes. Yet this has not proven to be infallible; in fact, regarding GDOES, scientists cannot fully explain the excitation and ionization by asymmetric charge transfer (ACT) reactions between argon ions and neutral analyte atoms (Me0), which is surprisingly strong in analytical glow discharges.
“There must be a reason for the discrepancy between theory and the experimental evidence about charge transfer reactions in emission spectra,” Weiss said in an email to Spectroscopy. “Either the assumption that the other plasmas are similar to the Grimm-type discharge does not hold, or there is something significant concerning the Grimm-type discharge. We don't know.”
Weiss formed experimental Boltzmann plots for glow discharge emission spectra and an inductively coupled plasma. He also modeled a Grimm-type discharge, which suggested that the charge transfer emissions mostly stem from the cathode sheath, because there are many collisions between the analyte atoms and argon ions that have been accelerated in the cathode fall.
However, this experiment did not explain the anomalously high rates of charge transfer reactions in this system compared to those of other plasmas. In fact, the amount of emission put the legitimacy of the glow discharge spectra Boltzmann plots into question and these plots “cannot be interpreted in the conventional way, Weiss said.
Weiss said that our understanding of what is happening in these plasmas is “far from satisfactory,” and that further research must be conducted to understand this phenomenon, specifically the observed features of glow discharge excitation.
“If the peculiar features described in the paper get clarified, there might be a chance to get rid of some matrix effects in chemical analyses by GDOES spectroscopy, [such as] those caused by the presence of hydrogen,” he said.
Reference
(1) Weiss, Z. Assessing the role of asymmetric charge transfer reactions in analytical glow discharges in argon. Spectrochim. Acta Part B At. Spectrosc. 2023, 207, 106756. DOI: https://doi.org/10.1016/j.sab.2023.106756
(2) Grimm, W. A new glow discharge lamp for optical emission spectral analysis. Spectrochim. Acta Part B At. Spectrosc. 1968, 23 (7), 443–454. DOI: https://doi.org/10.1016/0584-8547(68)80023-0
The Role of ICP-OES in Analyzing the Metal Content in Pet Food
June 19th 2025Because the United Arab Emirates is seeing an increase in pet ownership, the quality of both dry and wet pet food is undergoing greater scrutiny to ensure its safety and efficacy. Lucy Semerjian, who works as a Chair and Associate Professor in the Department of Environmental Health Science at the University of Sharjah in Sharjah, United Arab Emirates, recently explored this topic in a recent paper
Pet Food in the United Arab Emirates: An Interview with Lucy Semerjian
June 18th 2025A recent study conducted in the Journal of Food Composition and Analysis examined the concentrations of ten metals in 52 commercially available wet and dry cat food samples, assessing their compliance with U.S. and European pet food safety standards. The lead author of this study, Lucy Semerjian, recently sat down with Spectroscopy to discuss the findings of her study.
A Life Measured in Peaks: Honoring Alan George Marshall (1944–2025)
June 18th 2025A pioneer of FT-ICR Mass Spectrometry, Alan G. Marshall (1944–2025), is best known for co-inventing Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), a transformative technique that enabled ultrahigh-resolution analysis of complex mixtures. Over a career spanning more than five decades at institutions like the University of British Columbia, The Ohio State University, and Florida State University, he published over 650 peer-reviewed papers and mentored more than 150 scientists. Marshall’s work profoundly impacted fields ranging from astrobiology to petroleomics and earned him numerous prestigious awards and fellowships. Revered for his intellect, mentorship, and dedication to science, he leaves behind a legacy that continues to shape modern mass spectrometry.
New Study Finds Elevated Metal Levels in Some Cat Foods Sold in Sharjah
May 27th 2025A new study published in the Journal of Food Composition and Analysis by researchers at the University of Sharjah reveals that while most cat foods sold in Sharjah meet international safety standards, some contain elevated metal levels, prompting calls for stricter regulation and quality control to protect pet health.
