Desorption electrospray ionization-high resolution mass spectrometry for the analysis of unknown materials: The phytosanitary product case

Critical assessment of the Kendrick mass defect analysis as an innovative approach to process high resolution mass spectrometry data for environmental applications

The growing application of high resolution mass spectrometry (HRMS) over the last decades has dramatically improved our knowledge about the occurrence of environmental contaminants. However, most of the compounds detected remain unknown and the large volume of data generated requires specific processing approaches. Therefore, this study presents the concepts of mass defect (MD), Kendrick mass (KM) and Kendrick mass defect (KMD) to the expert and non-expert reader along with relevant examples of applications in environmental HRMS data processing. A preliminary bibliometric overview indicates that the potential benefits of KMD analysis are rather overlooked in environmental science. In practice, a simple calculation allows transforming a mass from the IUPAC system (normalized so that the mass of ¹²C is exactly 12) to its corresponding KM normalized on a specific moiety such as CH₂ (the mass of CH₂ is exactly 14). Then, plotting the KMD according to the nominal KM allows revealing groups of compounds that differ only by their number of CH₂ moieties. For instance, data processing using KM and KMD was proven particularly useful to characterize natural organic matter in a sample, to reveal the occurrence of polymers as well as poly/perfluorinated alkylated substances (PFASs), and to search for transformation products (TPs) of a given chemical.

Trace analysis of polystyrene microplastics in natural waters

The development of quantitative and qualitative analytical methods to assess micro-plastics (MPLs) and nano-plastics (NPLs) content in the environment is a central issue for realistic risk assessment studies. However, the quantitative analysis continues being a critical issue, in particular for MPLs from 100 μm down to the nano-sized range in complex environmental samples. This paper evaluates the potential of mass spectrometry for the analysis of MPLs and NPLs. The performance of different techniques including matrix-assisted laser desorption ionisation (MALDI) coupled to time-of-flight mass spectrometry (TOF-MS), liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS), and the ambient ionisation approaches as desorption electrospray ionisation (DESI) and direct analysis real-time (DART), were assessed for the study of polystyrene (PS) MPLs and NPLs in natural waters. A method based on LC-HRMS, equipped with an atmospheric pressure photoionisation source (APPI), operated in negative conditions for the quantitative analysis of PS MPLs and NPLs in natural waters, was developed. The chromatographic separation was achieved using an advanced polymer chromatographic (APC) column using toluene isocratic as the mobile phase. The optimal analytical method showed an instrumental limit of detection (ILOD) of 20 pg and methods limits of detection and quantification around 30 pg L^-1 and 100 pg L^-1, respectively. And, recoveries of 60 and 70% in samples from rivers and the marine coast, respectively. The performance of the new method was proved by the analysis of fortified samples and natural seawater samples.