Application of Quality by Design in the Optimization of Analytical Protocols for Microplastics Detection in Food

The increasing presence of microplastics (MPs) in the environment has raised significant concerns about human exposure to this contaminant through ingestion. To address this issue, several methodologies have been developed for the extraction and detection of MPs in food. However, complex matrices, especially lipid-rich food, often present challenges that require multiple pretreatment steps, and prevent analysis of polymers with most of the techniques recommended for MPs chemical characterization, such as micro-Fourier transform infrared (μFTIR) spectroscopy. This study applied, for the first time, the Analytical Quality by Design (AQbD) metod to develop and optimize an analytical protocol for the extraction and purification of MPs from food. AQbD has enabled the development of a systematic and efficient method minimizing solvent use and sample preparation time. Since fish is widely consumed by Mediterranean population, seafood was chosen as the most suitable matrix. Three species with different fat levels, i.e., salmon, tuna, and cod, were considered in this study. A preliminary literature search identified different digestion procedures, such as H2O2 oxidation, alkaline digestion with KOH, and the use of different type of enzymes as the most commonly used digestion solutions when dealing with complex matrices for MP detection. Method optimization was conducted according to QbD principles, selecting the type of solvent, digestion time, and temperature as the experimental domain. The efficacy of the digestion protocols in removing organic matter was further evaluated through the compatibility with μFTIR analysis, which allowed chemical characterization of the spiked polymeric standards. Additionally, spectroscopic analyses assessed the structural integrity of the polymers post-digestion. Recovery rates, variance and precision, expressed as relative standard deviations (RSD), were assessed using reference standard materials. Comprehensive quality assurance and quality control measures were implemented in all processes. Since current ecological risk assessment for MPs is based on the polymeric nature of the items, the importance of accurate and interference-free identification is paramount. The results obtained will provide an accurate protocol to better understand MP contamination levels in food. Moreover, the application of QbD principles can contribute not only to the optimization of accurate methods for the detection of MPs in complex food matrices, but also to the optimization of the number of experiments, thus leading to more sustainable approaches.