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.