Advancing antibiotic detection in environmental waters: Standardization of solid phase extraction procedures and development of certified reference materials

• Procedural steps of cartridge, on-line, and disk SPE methods are summarized. • pH adjustment to 3 experimentally improves antibiotic recovery across matrices. • The currently available CRMs for antibiotic analysis are queried and cataloged. • Highlights critical gaps in CRMs for reliable QA/QC of antibiotics using SPE-LC–MS/MS. Detecting antibiotics in environmental waters remains a challenge due to trace-level concentrations and matrix effects. Solid-phase extraction (SPE) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS) is the gold standard for trace analysis of multiclass antibiotics across various aquatic matrices. However, the efficacy of LC-MS/MS analysis is critically dependent on robust sample pretreatment to isolate target analytes and mitigate matrix effects. To this end, this review systematically collated and evaluated the prevalence along with the specific procedural protocols of cartridge-based, online, and disk-based SPE methods, focusing on their characteristics and typical applications in different water matrices. Critically, this review identified a significant inconsistency in sample pH adjustment protocols across the collated SPE methods. Consequently, it further evaluated the impact of pH adjustment on the recovery efficiencies of over 90 antibiotics in surface water, wastewater and groundwater, demonstrating that adjusting sample pH to approximately 3 improves recoveries for the majority of analytes. Moreover, certified reference materials (CRMs) for antibiotics were compiled from major suppliers and national metrology institutes, as CRMs are critical to ensure reliable Quality Assurance and Quality Control (QA/QC). This compilation revealed that existing gaps underscore the need for matrix-specific CRMs, isotope-labeled internal standards, and materials for transformation products. By summarizing existing methodologies and highlighting key conditions for improved antibiotic detection, this review provides practical insights to guide more standardized, accurate, and comparable antibiotic monitoring efforts in aquatic environments globally.