Characterization of Natural Nanomaterials in Soil With the icpTOF

Elemental Fingerprints in Natural Nanomaterials Determined Using SP-ICP-TOF-MS and Clustering Analysis 

Baalousha, M.; Wang, J.; Erfani, M.; Goharian, E.
Science of The Total Environment, 2021
DOI: 10.1016/j.scitotenv.2021.148426

Engineered nanomaterials are increasingly released into the environment. To understand their behavior and potential risks, analytical methods are required that can detect and quantify engineered nanomaterials (ENMs) while differentiating them from natural nanomaterials (NNMs). Therefore, detailed knowledge of the properties of NNMs (e.g., size distribution, elemental composition, elemental ratios) is needed to develop strategies for the detection and quantification of ENMs in environmental samples. 

Baalousha and co-workers from the University of South Carolina used single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-ICP-TOFMS) with a TOFWERK icpTOF R to characterize NNMs in different soil samples. Single particles were extracted from the soil samples by sieving and centrifugation, whereby ultra-pure water and tetrasodium pyrophosphate were tested as the extraction solutions. Ultra-pure water was found to yield higher total particle concentrations, but the elemental compositions were found to remain the same for both extraction solutions. 

Due to the fast, multi-elemental acquisition of the icpTOF, the authors were able to identify three different groups of NNMs in the soil samples occurring

1) as single-metal particles (e.g., Ti, Fe, Sn, Sb, Tm)
2) as multi-metal particles (e.g., V, Nb, Pr, Nd, Sm, Eu, Gd, Tb, Er, Dy, Yb, Lu, Hf, Ta, Pb, Th, U) 
3) as a mixture of single-metal and multi-metal particles (e.g., Al, Si, Cr, Mn, Ni, Cu, Zn, Ba, La, Ce, W, Bi). 

This has the important consequence that particle purity is a distinguishing feature for ENMs only for those metals that occur as impure metals in NNMs (i.e., Groups 2 and 3). For other elements (i.e., Group 1), other features are necessary to reliably differentiate ENMs from NNMs. 

These findings provide important baseline information for future studies aimed at the differentiation of ENMs from NNMs in environmental systems.