Limits of quantification – a (hopefully) provocative discussion on our ability to quantify small microplastics in complex matrices

, Vollertsen Jes.

The group of small particles we tend to call ‘microplastics' covers a diverse group of manmade polymers. It also covers particles of natural polymers used by man, composite materials, particles of materials containing polymers, etc. Its chemical quantification hence becomes quite diverse. In addition we want to quantify polymer type, mass, particle numbers, sizes, shapes, and more. This further complicates its chemical quantification. At today's state-of-the-art, the scientific community is quite good at quantifying microplastics even in complex matrices, at least this statement holds true down to a certain size. The smaller the particles, the more difficult it is to sample them, extract them from the sampled material, and finally analyze them. But what is the size limit at which we are able to not just detect some particles in a matrix, but to arrive at a valid quantification? For sure this depends on the applied techniques for sampling, extraction, and analysis. For sure, an analytical technique like visual sorting is less able to quantify small particles than e.g. µRaman or µFTIR imaging. But how good is each method, and how honestly are these issues addressed when presenting scientific findings? Is it not so, that there is a strong tendency to state that the (size) limit of detection is the (size) limit of quantification? For example: I found a 20 µm microplastics in my matrix, hence I am able to quantify the amount of microplastics down to this size. And is it not true, that very few researchers do recovery tests, and those who do, typically use particles not necessarily representative of the ones in the analyzed matrix. This presentation discusses some issues about (size) limit of quantification and how these affect our measurements of microplastics in the environment.

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