Analytical Strategies for Micro- and Nanoplastics in Aqueous Matrices: Progress and the Separation Bottleneck

Microplastics (MPs) and nanoplastics (NPs) are widespread contaminants, yet analytical workflows fail to generate consistent and comparable measurements, particularly at the nanoscale. Aggregation, together with interactions with dissolved and particulate matter, hinders MP and NP isolation and compromises analytical resolution. This review examines advances from 2019 to 2025 in sample preparation, separation and identification/quantification, with emphasis on aqueous matrices. Digestion methods have improved matrix removal while limiting polymer damage, although Quality Assurance/Quality Control (QA/QC) remains essential. Separation remains the main bottleneck, since conventional methods show low recovery for particles smaller than 100 nm and limited robustness in complex matrices. Emerging strategies improve size resolution but face challenges in scalability, reproducibility and consistency. Key gaps include lack of harmonised analytical protocols, limited certified reference materials and insufficient nanoscale sensitivity. By integrating recent methodological evidence, this review identifies key analytical developments required for reproducible and environmentally relevant monitoring of MPs and NPs. • Critical review of analytical workflows for micro- and nanoplastics (2019–2025). • Separation identified as the key analytical bottleneck. • Comparative assessment of physical, solvent-based, and hybrid separations. • Advances in green and hybrid separation media improve recovery and robustness. • AI-assisted imaging, harmonised protocols, and strong QA/QC are key for future progress.