Solid-Phase Extraction for On-Site Sample Preparation and Preservation of Environmental Pollutants in Water: Shifting the Pretreatment Paradigm from the Laboratory to Field

Sample preservation is a prerequisite for the authenticity and reliability of analytical data on environmental organic/inorganic pollutants in water samples, as it directly determines the accuracy of subsequent qualitative and quantitative analysis. Despite its widespread use in routine environmental monitoring, the conventional protocol of “bottle sampling and cryopreservation” cannot eliminate the “spatiotemporal discontinuity” between sampling and laboratory pretreatment. Accordingly, this protocol suffers from inherent shortcomings, including analyte adsorption on container walls as well as biotic and abiotic transformations (e.g., microbial degradation and photodegradation) during transportation and storage, all of which introduce nonnegligible analytical biases. On-site solid-phase extraction (SPE) has emerged as a powerful alternative to tackle these challenges in sample pretreatment and preservation, integrating versatile performance, including selective enrichment, phase transfer, speciation stabilization, and matrix removal processes. On-site SPE, therefore, represents a shift from laboratory-based enrichment toward preservation-oriented field sampling and pretreatment of environmental contaminants. This review systematically elaborates the fundamental principles, technical approaches, and latest applications of on-site SPE for organic/inorganic pollutants in environmental water matrices, critically discusses its merits and limitations across diverse field scenarios, and highlights emerging perspectives for further advancing its capabilities in environmental monitoring.