Characterizing the Stoichiometry of Individual Metal Sulfide and Phosphate Colloids in Soils, Sediments, and Industrial Processes by Inductively Coupled Plasma Time-of-Flight Mass Spectrometry
Jonas Wielinski et al.
Environmental Science & Technology, 2024
DOI: 10.1021/acs.est.3c10186
This recent publication in Environmental Science & Technology by researchers from the Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, USA utilized the icpTOF R to develop a new single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS) method that accurately identifies and characterizes metal phosphate and sulfide colloids, including their size and purity. This technique, enhanced by machine learning, allows for precise detection of different metal particle types and impurities in environmental samples, improving our understanding of their behavior in the environment and their potential impacts.
Metal phosphates and sulfides occur in natural systems, polluted areas, and engineered environments, playing crucial roles in biogeochemical processes and contaminant mobilization. Metal sulfides, like pyrite, can be released through human activities, posing environmental risks, while phosphates can help remediate contaminated soils by precipitating lead as pyromorphite. Furthermore, they can be found as part of airborne PM2.5 particles. Due to their small size, colloids are more reactive and potentially more toxic to both aquatic life and humans than larger particles.
Traditional methods like electron microscopy (EM) and X-ray absorption spectroscopy (XAS) provide valuable particle characterization but have limitations, such as slow analysis times and issues with sample concentration. Single particle ICP-TOFMS offers a rapid and efficient alternative for characterizing metal phosphates and sulfides. This technique can detect and measure thousands of particles across a broad range of elements and sizes, overcoming the limitations of XAS and EM.
This study demonstrated that sp-ICP-TOFMS can accurately characterize the elemental composition and stoichiometry of individual metal sulfide and phosphate colloids, including quantifying sulfur and phosphorus within each particle. The method successfully distinguished between different copper sulfide phases and confirmed the presence of pyrite in hydraulic fracturing wastewater, while revealing that metal sulfides in most environmental settings are impure. This has implications for understanding metal behavior in natural and impacted environments, highlighting the need to consider impurities in studies of reactivity and toxicity. Additionally, sp-ICP-TOFMS, combined with machine learning, could be used for environmental forensics, such as tracking mercury sources by identifying constant ratios of impurities in industrial samples.
Overall, this approach using our icpTOF R offers new opportunities for assessing the purity and potential toxicity of metal particles in various applications, including environmental monitoring and resource recovery.
