Inside the Laboratory: The Stone Laboratory Group at the University of Iowa

Inside the Laboratory is a joint series with LCGC and Spectroscopy, profiling analytical scientists and their research groups at universities all over the world. This series will spotlight the current chromatographic and spectroscopic research their group is conducting, and the importance of their research in analytical chemistry and specific industries. In this edition of “Inside the Laboratory,” Betsy Stone, PhD, a professor of chemistry at the University of Iowa, discusses her group’s current research endeavors, including developing a new liquid chromatography–mass spectrometry (LC–MS) method to track secondary organic aerosol that forms in the atmosphere from D₅.

The Stone Research Group is in the University of Iowa’s Department Chemistry, and it is led by lead investigator Betsy Stone. The Stone Research Group investigates the chemistry of atmospheric aerosols and their impact on human health and the environment (1). Some of their research projects include characterizing bioaerosols under extreme weather conditions, developing instrumental methods for separating and quantifying molecular markers of aerosol sources, source apportionment of ambient particulate matter, and characterizing emissions from sea spray, biomass burning, and waste burning (1). To complete some of these projects, the research team uses liquid chromatography (LC) and gas chromatography (GC) coupled with mass spectrometry (MS).

Dr. Stone is a professor in the Department of Chemistry and the Department of Chemical and Biological Engineering at the University of Iowa in Iowa City, Iowa. Recently, LCGC International sat down with Dr. Stone to discuss her team’s current research endeavors, as well as the recent innovations that are helping to propel her team’s work forward.

Betsy Stone of the University of Iowa. Photo Credit: © Betsy Stone.

Can you briefly describe the mission of the Stone Laboratory Group?

My group conducts research on atmospheric chemistry with a focus on understanding the chemical composition and sources of airborne particulate matter. We utilize analytical measurements to characterize the chemical composition particulate matter, which enables us to identify the sources of atmospheric particles and evaluate their impacts. We develop new methods in gas and liquid chromatography (GC/LC) and mass spectrometry (MS) to measure molecular tracers of emerging aerosol sources. In this study, we advance develop a new LC–MS method to track secondary organic aerosol that forms in the atmosphere from D₅, a gas released by personal care products.

One of your recent studies introduced a new reversed-phase liquid chromatography (RP-LC) method combined with high-resolution mass spectrometry (HRMS) to detect D₅ oxidation products. Can you explain the challenges you faced in developing this method and how it improves upon previous techniques for characterizing oxidized D₅ in ambient aerosol?

Our recent article by Meepage and others (2) developed new LC separation of D₅ oxidation products that is coupled with HRMS. The LC method separates oxidation products of D₅. In many cases, the method can resolve individual isomers. When combined with high-resolution and tandem mass spectrometry, this separation provides new insight to the molecular structures of the prominent oxidation products.

An early challenge that we faced was in developing an efficient chromatographic separation for our analytes. We tried several columns and determined that the reversed-phase (RP) separation was the most promising. From there, we optimized the gradient and flow rate.A second challenge that we faced was the relatively low signal generated by silanols under negative electrospray ionization conditions. We addressed this issue by careful optimization of the mobile phase buffer regarding composition, pH, and concentration to maximize their signal.

Given that D₅ is a common ingredient in personal care products, how significant is its contribution to secondary organic aerosol (SOA) in urban environments like New York City? What implications might this have for public health and air quality regulations?

New York City has some of the highest D₅ concentrations in the world (3), making it a prime location to study the impact of D₅ on secondary organic aerosol. So far, we have detected D5 oxidation products in ambient fine particulate matter (PM_2.5­) in New York City, demonstrating that D₅-derived SOA is present in this urban area during the summertime. Our future work will examine the quantitative impact of D₅ on PM_2.5 mass.

The study found a series of oxidation products where one or more methyl groups in D₅ are replaced by hydroxyl groups. How does this oxidation process contribute to the formation of PM_2.5, and what does this tell us about the chemical behavior of D₅ in the atmosphere?

As D₅ is oxidized and methyl groups are replaced by hydroxyl groups, the volatility of the products decrease and their partitioning to the particle phase increases. Once in the particle phase, D₅ contributes to PM_2.5. Our observations indicate that D₅ can undergo multiple oxidation steps in the atmosphere, with more oxidized products expected to partition to a greater extent into the particle phase.

Several oxidation products of D₅ were proposed as molecular tracers for D₅-derived SOA. What criteria were used to select these molecular tracers, and how might they be utilized in future atmospheric studies to assess the impact of personal care products on air quality?

The criteria that we used to select molecular tracers of D₅-derived SOA in our recent article by Meepage and others (2) were: 1) confidence in their molecular structures, 2) their specificity to D₅, and 3) their detectability in ambient PM­_2.5 in New York City. The next criteria, which we are currently evaluating, is their gas-to-particle distributions. Molecular tracers can be used in source apportionment modeling to assess the impacts of sources on ambient PM_2.5.

How do the findings from this study on D₅-derived SOA contribute to the broader understanding of secondary organic aerosol formation and the role of anthropogenic sources in atmospheric chemistry? What future research directions do you anticipate based on these results?

Our study advances our ability to detect and quantify D₅ oxidation products in ambient air, which will support a better understanding of the impacts of D₅ on urban air quality. More broadly, we seek to gain a quantitative assessment of the contributions personal care products to SOA and PM_2.5, relative to other natural and anthropogenic sources.

How do you and your laboratory group stay updated with advancements in analytical chemistry techniques and technologies?

We stay up to date by reading scientific articles and attending atmospheric chemistry research symposia and conferences.

Can you discuss a recent innovation or development that you find particularly impactful or exciting?

Our research has been greatly and positively impacted by the improvements in HRMS. High resolution, accurate mass measurements advance our ability to identify SOA products and to accurately quantify these products.

References

1. University of Iowa, Stone Research Group. Iowa.edu. Available at: https://stone.lab.uiowa.edu/ (accessed 2024-09-10).
2. Meepage, J. N.; Welker, J. K.; Meyer, C. M.; et al. Advances in the Separation and Detection of Secondary Organic Aerosol Produced by Decamethylcyclopentasiloxane (D5) in Laboratory-Generated and Ambient Aerosol. ACS ES&T 2024, 1 (5), 365–375. DOI: 10.1021/acsestair.3c00073
3. Brunet, C. E.; Marek, R. F.; Stanier, C. O.; Hornbuckle, K. C. Concentrations of Volatile Methyl Siloxanes in New York City Reflect Emissions from Personal Care and Industrial Use. Environ. Sci. Technol. 2024, 58 (20), 8835–8845. DOI: 10.1021/acs.est.3c10752