What Really Improves Nd Isotope Ratios?

At the Winter Conference on Plasma Spectrochemistry, which took place in Tucson, Arizona, Spectroscopy sat down with Ken Marcus, a Robert Adger Bowen Professor of Chemistry at Clemson University, to talk about his research (1–2). Part I of our conversation with Marcus focused on what makes the Winter Conference on Plasma Spectrochemistry unique and the instrumentation his research group uses to better separate isobars (3).

In Part II of our conversation with Marcus, he discusses the parameters that are most influential in enhancing Nd isotope ratio measurements, and the implications of monitoring oxide species rather than atomic ions for isotope ratio analysis, and the benefits and challenges of this approach.

Spectroscopy: Which parameters were found to be most influential in enhancing Nd isotope ratio measurements, and what mechanistic effects do those parameters have on ionization efficiency or spectral quality?

Ken Marcus: You asked sort of two questions. The first is making the ions, and the second is detecting the ions. It's a very low power plasma. It's only about 60 watts. And what we hope to do, because it's such low power, is to have the liquid and the particles become ions in the plasma as long as possible. We evolve them out through the plasma very slowly, making it a more efficient process. But the ions we make tend to be not just iron; they might be iron with some water molecules on them. Two of the important aspects in the Orbitrap (orbital ion trap) instrument are the ability to collisionally dissociate those ions. In the front end, we knock the waters off, and then there's a higher energy dissociation in the back end of the instrument that might break bonds for dimers and things like that.

That's how we clean up the spectra a lot to get all the signals from each element in one channel. They're all either atomic ions, mono-oxides, or dioxides, and we collapse them down into as few different species as possible. When we do the Orbitrap measurements, the key aspect is how long you can monitor the ion transient in the cell. The conventional Orbitrap that we have can measure ions for about 256milliseconds. That gives us a mass resolving power of 70,000 with the spectroscopist booster that we use, and we can take transients up to three and a half seconds. In that case, our instrument now can go up to a mass resolving power of 1,000,000. So, there’s a lot of games we can play along the way, but they're straightforward.

This video clip is the second part of our conversation with Marcus. To stay up to date on our coverage of the Winter Conference, click here.

References

1. IASA, Winter Conference on Plasma Spectrochemistry. IASA. Available at: https://iasa.world/winter-plasma-conference (accessed 2026-01-21).
2. Clemson University, R. Kenneth Marcus. Clemson.edu. Available at: https://www.clemson.edu/science/academics/departments/chemistry/about/profiles/marcusr (accessed 2026-01-21).
3. Wetzel, W. Improving High-Resolution Mass Spectrometry Platforms. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/improving-high-resolution-mass-spectrometry-platforms (accessed 2026-01-22).