Advances in the development of analysis techniques for organophosphate diesters in water

Organophosphate triesters (tri-OPEs) are synthetic phosphate derivatives that are primarily used as flame retardants and plasticizers. Tri-OPEs have become significant aquatic contaminants owing to their large production volumes and wide range of applications. Organophosphate diesters (di-OPEs) are closely related to tri-OPEs. Aside from emissions resulting from the production and usage of di-OPEs themselves, tri-OPEs can become transformed into di-OPEs, which also provides a significant source of this environmental contaminant. The physicochemical properties of a di-OPE depend significantly on its structure, which provides challenges for their detection and analysis, including low extraction efficiencies, chromatographic separation difficulties, and a lack of highly sensitive quantitative methods for their analysis. An increasing number of studies have found that di-OPEs are present in industrial/domestic wastewater, surface water, and drinking water, with some concentrations in surface water and tap water close to or even higher than those of the corresponding tri-OPEs. Additionally, certain di-OPEs are somewhat more toxic than the corresponding tri-OPEs; hence, awareness that di-OPEs are present in aquatic environments has raised widespread concern. This review first systematically outlines the physicochemical properties of common di-OPEs and their potential sources based on previous research into di-OPEs in water matrices. In addition, the use of solid phase extraction (SPE) technology to extract, enrich, and purify di-OPEs from water matrices is summarized, while the advantages and limitations of SPE methodologies are critically evaluated. Furthermore, the use and distinctive features of reverse-phase chromatography, ion-pair reverse-phase chromatography, and hydrophilic interaction liquid chromatography (HILIC) for the chromatographic separation of di-OPEs are comprehensively summarized and compared. At the same time, advances in the quantitative analysis of di-OPEs using liquid chromatography-tandem triple quadrupole mass spectrometry (LC-MS/MS) and liquid chromatography-high-resolution mass spectrometry (LC-HRMS) are reviewed. Finally, in terms of efficient collection of water samples and high-throughput pretreatment of di-OPEs in water matrices, the prospect of developing novel sampling and on-site enrichment technologies for new pollutants in water matrices based on the principle of dispersed solid phase extraction is proposed. Additionally, the prospect of using liquid chromatography tandem high-resolution mass spectrometry for high-throughput screening and high-sensitivity detection of di-OPEs and unknown transformation products of tri-OPEs has been proposed.