Detecting Polystyrene Nano-Particles in Environmental Samples: A Comprehensive Quantitative Approach Based on Td-Ptr-Ms and Multivariate Standard Addition

Sub-micrometer-sized plastic particles (nanoplastic; NP) have been detected in a large variety of different ecosystems. They occur in small quantities within complex mixtures, but robust quantification of their concentration requires the development of a comprehensive analytical workflow to handle potential interferents. Thermal Desorption-Proton Transfer Reaction-Mass Spectrometry (TD-PTR-MS) creates the necessary chemical selectivity to distinguish NP signals from remaining chemicals. Nevertheless, the recorded raw mass spectra are too complex to interpret and investigate directly, and further signal clustering/scoring is required for a more in-depth analysis. Here, we resolved this problem mathematically by combining Non-Negative Matrix Factorization (NMF) and multivariate standard addition (MSA) to isolate the NP's signature from the mixture as showcased for polystyrene. The method produces an unequivocal NP fingerprint that is used for identification and quantification. MSA and NMF enabled us to quantify polystyrene NP in different environmental samples in the lower nanogram range. The mass concentration of polystyrene NP in Waal River water was 4.7 ± 0.65 ng/mL, and 39 ± 0.70 ng/g in sand samples from the river's shore. A sand sample from a local playground in Nijmegen, Netherlands, exhibited a higher concentration of 129 ± 1.1 ng/g.