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This study focuses on optimizing nanoparticle quantification in natural water samples. Colloids, nanoscale objects below 1000 nm, include diverse nanoparticles originating from various sources, posing ecological and human health risks. Metal-containing colloids, known for releasing toxic ions, have been extensively studied in surface waters. Advanced techniques like single particle-inductively coupled plasma-mass spectrometry (spICP-MS) and single particle inductively coupled plasma time-of-flight mass spectrometry (spICP-ToF-MS) are currently used for nanoparticle characterization and quantification. The lack of standardized protocols for surface water preparation led to the development of a methodology for fresh or aged samples. Different treatments (sonication, filtration, and centrifugation) were explored using spICP-ToF-MS for multi-element examination. Optimizing the methodology for river water samples systematically involved mechanical re-suspension, sonication, filtration at 1.2 m, and dilution ensuring reliable nanoparticle quantification. Multiple dilutions are recommended to recover the actual particle concentration and get a global view of the metal-containing colloids when using spICP-ToF-MS. Comparisons with previous studies revealed challenges but aligned with expectations considering instrumentation differences. The study recommends filtration at 1.2 m after sonication as a standard method, emphasizing caution in interpreting particle numbers. Future research may explore mono-elemental approaches for a comprehensive understanding. Overall, this work provides valuable insights into challenges and best practices for accurate NP quantification in complex natural water samples.
Wang et al. (Thu,) studied this question.