Ultrahigh-Resolution Mass Spectrometry Advances for Biogeochemical Analysis: From Seafloor Sediments to Petroleum and Marine Oil Spills

This Perspective explores the transformative impact of ultrahigh-resolution mass spectrometry (UHR-MS), particularly Fourier transform ion cyclotron resonance (FT-ICR-MS), in the characterization of complex environmental and petroleum samples. UHR-MS has significantly advanced our ability to identify molecular formulas in complex mixtures, revolutionizing the study of biogeochemical processes and organic matter evolution on wide time scales. We start by briefly reviewing the main technological advances of UHR-MS in the context of petroleum and environmental applications, highlighting some of the challenges of the technology such as quantitation and structural identification. We then showcase a selection of impactful applications published in the last 20+ years. In the field of environmental lipidomics, high-resolution analysis of lipids in sediments enables multiproxy studies and provides novel insights into past environmental conditions. UHR-MS has also facilitated the characterization of kerogen, a complex, poorly soluble mixture formed from sedimented organic matter over geological time scales, and the identification of polar compounds within its fractions. In petroleum (geo)chemistry, UHR-MS has enabled the identification of biomarkers such as petroporphyrins, asphaltenes, and high-molecular-weight naphthenic acids, shedding light on the molecular complexity of crude oil. The application of UHR-MS in oil spill science has revealed significant molecular transformations during weathering processes, such as photo-oxidation, which are crucial for assessing the environmental impact of past spills and improving the preparedness for future spills. These advancements underscore the role of this maturing analytical technology in deepening our understanding of geochemical processes and biogeochemical cycles, highlighting its potential for future research directions in organic geochemistry.

Twins in rotational spectroscopy: Does a rotational spectrum uniquely identify a molecule?

Rotational spectroscopy is the most accurate method for determining structures of molecules in the gas phase. It is often assumed that a rotational spectrum is a unique "fingerprint" of a molecule. The availability of large molecular databases and the development of artificial intelligence methods for spectroscopy make the testing of this assumption timely. In this paper, we pose the determination of molecular structures from rotational spectra as an inverse problem. Within this framework, we adopt a funnel-based approach to search for molecular twins, which are two or more molecules, which have similar rotational spectra but distinctly different molecular structures. We demonstrate that there are twins within standard levels of computational accuracy by generating rotational constants for many molecules from several large molecular databases, indicating that the inverse problem is ill-posed. However, some twins can be distinguished by increasing the accuracy of the theoretical methods or by performing additional experiments.

Solving Advanced Task-Specific Problems in Measurement Sciences with Generative AI

The Generative Pre-Trained Transformer known as ChatGPT-4 has undergone extensive pretraining on a diverse data set, enabling it to generate coherent and contextually relevant text based on the input it receives. This capability allows it to perform tasks from answering questions and has attracted significant interest in material sciences, synthetic chemistry, and drug discovery. In this work, we posed four advanced task-specific problems to ChatGPT, which were recently published in leading journals for topics in analytical chemistry, spectroscopy, bioimage super-resolution, and electrochemistry. ChatGPT-4 successfully implemented the four ideas after assigning the "persona" to the AI and posing targeted questions. We show two cases where "unguided" ChatGPT could complete the assignments with minimal human direction. The construction of a microwave spectrum from a free induction curve and super-resolution of bioimages was accomplished using this approach. Two other specific tasks, correcting a complex baseline with morphological operations of set theory and estimating the diffusion current, required additional input, e.g., equations and specific directions from the user. In each case, the MATLAB code was eventually generated by ChatGPT-4 even when the original authors did not provide any code themselves. We show that a validation test must be implemented to detect and correct mistakes made by ChatGPT-4, followed by feedback correction. These approaches will pave the way for open and transparent science and eliminate the black boxes in measurement science when it comes to advanced data processing.

Effect of position of deuterium atoms on gas chromatographic isotope effects

Deuterium substitution provides various benefits in drug molecules, including improvement in pharmacokinetic properties, reduction of toxicity, reduction of epimerization, etc. Also, it has been shown that the position of deuterium substitution affects the properties of drug molecules. Therefore, it is important to study low molecular weight deuterated isotopologues which constitute the deuterated pool and are building blocks of larger deuterated molecules. The effect of the position and number of deuterium atoms on the retention of 23 deuterated isotopologues on two gas chromatography stationary phases of different polarities was evaluated. It was observed that the ratio of calculated chromatographic isotope effects resulting from a deuterium atom connected to an sp² vs. an sp³ hybridized carbon was more on the polar IL-111i stationary phase compared to the nonpolar PDMS-5, for each group of isotopologues. Also, a compound with a deuterium atom connected to an sp² hybridized carbon always had greater retention than the analogous compound where deuterium was connected to an sp³ hybridized carbon. The van't Hoff plots for all analytes showed that the effect of entropy was almost negligible in the separation of deuterated vs. protiated isotopologues, thus these separations were mainly enthalpy driven.

High information spectroscopic detection techniques for gas chromatography

Gas chromatography has always been a simple and widely used technique for the separation of volatile compounds and their quantitation. However, the common detectors used with this technique are mostly universal and do not provide any specific qualitative information. There have been some attempts to combine the separation power of GC with the qualitative capabilities of "high-information" spectroscopic techniques including infrared spectroscopy, nuclear magnetic resonance spectroscopy, molecular rotational resonance spectroscopy, and vacuum ultraviolet spectroscopy. Some of these hyphenations have proven to be quite successful while others were less so. The history of such attempts, up to the most recent studies in this area, are discussed. Most recently, the hyphenation of GC with molecular rotational resonance spectroscopy which provides promising results and is a newly developed technique is reviewed and compared to previous high-information spectroscopic detection approaches. The history, description and features of each method along with their applications and challenges are discussed.