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Novel microplastic reference particles could enable better data comparability

Researchers from the Collaborative Research Center (CRC) Microplastics at the University of Bayreuth have developed a new concept for the production of microplastic reference particles. These make it possible for the first time to introduce a precisely defined number of reference particles into experiments. In future, their use may enable better comparability of data from different microplastic studies.

The work is in the journal Microplastics and Nanoplastics.

Currently, different analysis methods are used in microplastics research, with different techniques being used for sample transfer, extraction, purification, sample division, measurement and evaluation, for example. This leads to data of varying quality and resolution, which makes it very difficult to compare studies and consequently also to carry out a reliable risk assessment.

A solution for comparing the data from different analysis techniques can only be achieved through a reliable quality assessment of the respective methods and harmonization of the results.

In order to enable such an evaluation, it must be known exactly how many microplastic particles are in the test samples for testing the analysis methods, e.g. to be able to determine the recovery rate. Therefore, reference microplastic particles are needed that can be added to the test samples in precisely known numbers as an internal standard.

Although this challenge was recognized early on in microplastics research, reference particles are currently only available in powder form or as a suspension. When these are added to test samples, there are therefore always more or less large deviations in the number of microplastics.

An exact evaluation of different analysis techniques is difficult with the reference materials currently available. The optimal solution would be particles that are embedded in an easy-to-use, soluble matrix in exact numbers and can be added to samples prior to analysis. Such particles have now been developed for the first time in the CRC 1357 Microplastics at the University of Bayreuth.

The process developed in Bayreuth is based on the production of very thin plastic columns, which are produced from a plastic block using CNC milling. The columns are embedded in gelatin and cut into identical gelatin disks using cryo-microtomy, a deep-freeze cutting process.

The gelatin disks each have the same, precisely defined number of microplastic particles. The shape, size and composition of the particles can be precisely determined using the plastic starting material and the CNC parameters.

For further use, the gelatin platelets with the microplastic as an internal standard can simply be added to a wide variety of samples, such as water, soil or tissue, and dissolved under mild heat.

"Our development in the CRC finally enables a simple and holistic validation of all processes involved in the various microplastic analysis methods, such as sample transfer, extraction, purification, sample division, measurement and evaluation, and is crucial for assessing the reliability and accuracy of analytical methods," says Dr. Martin Löder, head of the CRC-Keylab Microplastics Analysis.

Prof. Dr. Christian Laforsch, spokesperson of the CRC and co-developer, adds, "With our new reference particles, we have finally taken a major and significant step towards the harmonization and comparability of different analytical methods for microplastics."