Preparation of a reference material for microplastics in water—evaluation of homogeneity

Validation of analytical methods for measurements of micro-plastics (MP) is severely hampered because of a general lack of reference materials RM. There is a great need to develop such reference materials although it is a challenging task. This study presents a concept of three-component kit that can be applied for the production of many types of MP reference materials. As proof of concept, an RM for Poly-Ethylene Terephthalate particles (PET) in water was prepared and evaluated for its homogeneity. The particles ranged from 30 µm (Feretmin) to about 200 µm adapted by wet sieving. A specific number of PET-particles were immobilized in about 0.29 g of solid NaCl by freeze-drying 1 ml of an NaCl-suspension. By using manual and automated counting, twenty reconstituted 1-L water samples were evaluated for homogeneity with respect to number of PET particles from 30 µm to >200 µm / L of water. The number of particles was 730 ± 120 (mean ± one standard deviation (SD); n = 10) and 865 ± 155 particles (n = 10) obtained by optical microscopy in two independent laboratories. This corresponded to relative SDs of 16.4 and 17.9 % and a mean of 797 ± 151 particles (18.9 % RSD, for n = 20). Homogeneity studies of the NaCl-carrier without reconstitution resulted in 794 ± 60 particles (7.5 % RSD). The homogeneity of PET in the salt-carrier was also evaluated directly with respect to mass of PET per vial using an ultra-micro balance. An average mass of 293 ± 41 µg of PET was obtained (14, % RSD for n = 14). Micrographs were recorded to demonstrate the absence of major sources of contamination of the RM components. Information about the particle size distribution and particle shapes was obtained by laser diffraction (LD) and dynamic image analysis (DIA). In addition, the identity of the PET polymer was confirmed by Raman and FT-IR spectroscopy. The reference material was developed for a large-scale inter-laboratory comparison of PET particles in water (ILC). Based on the homogeneity results, the material was found to be sufficiently homogeneous to be of meaningful use in the ILC. In a three-day process, more than 500 samples of PET particles in the NaCl-carrier were prepared with good potential for further up-scaling with respect to the number of vials or with other kinds of polymers. The stability of PET was not evaluated but it was deemed to be stable for the duration of the ILC.

SEGHERS John;  STEFANIAK Elzbieta;  LA SPINA Rita;  CELLA Claudia;  MĖHN Dóra;  GILLILAND Douglas;  HELD Andrea;  JAKOBSSON Ulf;  EMTEBORG Hakan; 

2022-01-26

SPRINGER HEIDELBERG

JRC123337

1618-2642 (online),   

https://publications.jrc.ec.europa.eu/repository/handle/JRC123337,   

10.1007/s00216-021-03198-7 (online),