Collision-induced dissociation as "mass spectrometric filter" for rapid screening of tetrapyrrole derivatives and their chelated metal species in complex biological and environmental samples

Streamlined Arsenolipid Identification via Direct Arsenic Detection Using RPLC-ESI-QTOF-MS with Collision-Induced Dissociation

Arsenolipids are organoarsenicals with a long aliphatic chain that have been identified in a wide array of marine organisms. Precise analysis of arsenolipids is crucial for evaluating their toxicity, ensuring food safety, monitoring the environment, and gaining insights into the evolution of arsenic biogeochemistry. However, the discovery of new arsenolipids is often impeded by existing analytical challenges, notably the need for multiple instruments, such as the combination of liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS) and inductively coupled plasma mass spectrometry (LC-ICP-MS). This study introduces a high-throughput untargeted analytical method on the basis of an unsophisticated instrumental configuration, LC-ESI-MS with collision-induced dissociation (CID) at 200 eV. This approach provides efficient dissociation of arsenic atoms from their precursor lipids and direct detection of the organic-bound arsenic as monatomic cations, As+. Application of this method has shown promise in rapidly characterizing arsenolipids in diverse samples, which has led to the discovery of a wide range of novel arsenolipids, including seven previously unidentified thioxoarsenolipids in ancient marine sediments.

Tocopherols and associated derivatives track the phytoplanktonic response to evolving pelagic redox conditions spanning Oceanic Anoxic Event 2

Tocopherols serve a critical role as antioxidants inhibiting lipid peroxidation in photosynthetic organisms, yet are seldom used in geobiological investigations. The ubiquity of tocopherols in all photosynthetic lifeforms is often cited as an impediment to any diagnostic paleoenvironmental potential, while the inability to readily analyze these compounds via conventional methods, such as gas chromatography-mass spectrometry, further diminishes the capacity to serve as useful 'biomarkers'. Here, we analyzed an exceptionally preserved black shale sequence from the Demerara Rise that spans Oceanic Anoxic Event 2 (OAE-2) to reexamine the significance of tocopherols and associated derivatives (i.e. tocol derivatives) in ancient sediments. Tocol derivatives were analyzed via liquid chromatography-quadrupole time-of-flight-mass spectrometry and included tocopherols, a methyltrimethyltridecylchroman, and the first reported detection of tocopherol quinones and methylphytylbenzoquinones in the geologic record. Strong correlations between tocol derivatives were observed over the studied interval. Tocol derivative concentrations and ratios, which normalized tocopherols to potential derivatives, revealed absolute and relative increases in tocopherols as exclusive features of OAE-2 that can be explained by two possible mechanisms related to tocopherol production and preservation. The development of photic zone euxinia during OAE-2 likely forced an upward migration of oxygenic photoautotrophs, increasing oxidative stress that elicited heightened tocopherol biosynthesis. However, shoaling euxinic conditions may have simultaneously acted to enhance tocopherol preservation given the relatively high lability of tocopherols in the water column. Both scenarios could produce the observed stratigraphic distribution of tocol derivatives in this study, although the elevated tocopherol concentrations that define OAE-2 at the Demerara Rise are primarily attributed to enhanced tocopherol production by shoaling phytoplanktonic communities. Thus, the occurrence of tocopherols and associated derivatives in sediments and rocks of marine origin is likely indicative of shallow-water anoxia, tracking the phytoplanktonic response to the abiotic stresses associated with vertical fluctuations in pelagic redox.