Internal Standard Addition System for Online Breath Analysis.

Breath analysis with secondary electrospray ionization (SESI) coupled to mass spectrometry (MS) is a sensitive method for breath metabolomics. To enable quantitative assessments using SESI-MS, a system was developed to introduce controlled amounts of gases into breath samples and carry out standard addition experiments. The system combines gas standard generation through controlled evaporation, humidification, breath dilution, and standard injection with the help of mass-flow controllers. The system can also dilute breath, which affects the signal of the detected components. This response can be used to filter out contaminating compounds in an untargeted metabolomics workflow. The system's quantitative capabilities have been shown through standard addition of pyridine and butyric acid into breath in real time. This system can improve the quality and robustness of breath data.

A Comprehensive Nontarget Analysis for the Molecular Reconstruction of Organic Aerosol Composition from Glacier Ice Cores.

Ice cores are climate archives suitable for the reconstruction of past atmospheric composition changes. Ice core analysis provides valuable insight into the chemical nature of aerosols and enables constraining emission inventories of primary emissions and of gas-phase precursors. Changes in the emissions of volatile organic compounds (VOCs) can affect formation rates and mechanisms as well as chemical composition of aerosols during the preindustrial era, key information for understanding aerosol climate effects. Here, we present an analytical method for the reconstruction of organic aerosol composition preserved in glacier ice cores. A solid-phase-extraction method, optimized toward oxidation products of biogenic VOCs, provides an enrichment factor of ∼200 and quantitative recovery for compounds of interest. We applied the preconcentration method on ice core samples from the high-alpine Fiescherhorn glacier (Swiss Alps), and used high-performance liquid chromatography coupled to high-resolution mass spectrometry as a sensitive detection method. We describe a nontarget analysis that screens for organic molecules in the ice core samples. We evaluate the atmospheric origin of the detected compounds in the ice by molecular-resolved comparison with airborne particulate matter samples from the nearby high-alpine research station Jungfraujoch. The presented method is able to shed light upon the history of the evolution of organic aerosol composition in the anthropocene, a research field in paleoclimatology with considerable potential.

Probing Deuteration-Induced Phase Separation in Supported Lipid Monolayers using Hyperspectral TERS Imaging.

In this study, we investigate the impact of deuteration on the formation of phase-separated domains in supported lipid monolayers using hyperspectral Tip-Enhanced Raman Spectroscopy (TERS) imaging. The intricate organization of biological membranes plays a crucial role in cellular functions. Various factors that influence domain formation have been identified in previous studies such as lipid tail length and cholesterol concentration. Deuterium labeling of lipids has proven useful for probing cellular structures and dynamics, but its impact on lipid phase separation remains underexplored. By examining 1:1 mixed monolayers of dipalmitoylphosphatidylcholine (DPPC) and deuterated DPPC on Au(111) surfaces, we reveal partial segregation of domains rich in deuterated and nondeuterated lipids. This study addresses a gap in knowledge by examining the impact of deuteration on lipid tail behavior, offering new insights into how even subtle structural modifications can influence phase behavior. Furthermore, it demonstrates that TERS can be a powerful, nondestructive, and label-free nanoanalytical tool for analyzing lipid membranes and advance the field of membrane biophysics.

Visualizing On-Surface Decomposition Chemistry at the Nanoscale Using Tip-Enhanced Raman Spectroscopy.

Chemical imaging of molecular decomposition processes at solid-liquid interfaces is a long-standing problem in achieving mechanistic understanding. Conventional analytical tools fail to meet this challenge due to the lack of required chemical sensitivity and specificity at the nanometer scale. In this work, we demonstrate that high-resolution hyperspectral tip-enhanced Raman spectroscopy (TERS) imaging can be a powerful analytical tool for studying on-surface decomposition chemistry at the nanoscale. Specifically, we present a TERS-based hyperspectral approach to visualize the on-surface decomposition process of a pyridine-4-thiol self-assembled monolayer on atomically flat Au(111) surfaces under ambient conditions. Reactive intermediates involved in the degradation process are spectroscopically detected with 5 nm spatial resolution. With supporting density functional theory simulations, a key species could be assigned to the disulfide reaction intermediate. This work opens a new application area for studying on-surface decomposition chemistry and related dynamics quantitatively at solid-liquid interfaces with nanometer spatial resolution.