Enabling analytical precision in microplastic analysis: innovative solutions for precise method validation, evaluation and quality control

Abstract The growing concern over microplastic (MP) pollution has catalyzed extensive research efforts to comprehensively understand its environmental distribution and impact. Despite the growing number of studies documenting MP presence, the development of a standardized analytical protocol, particularly focusing on precise analytical method validation, remains a challenge. This gap arises from the complex nature of sample matrices and the diverse combinations of sample pretreatment and detection methodologies employed. Consequently, inconsistencies in detected quantities, attributed to overlooked recovery and blank measurements, persist, undermining data reliability and comparability. In this context, this study proposes an innovative solution to enhance the analytical precision for validation and evaluation of MP analysis. Leveraging Fourier Transform Infrared (FT-IR) and Quantum-cascade laser (QCL) imaging, we introduce a method that utilizes potassium bromide (KBr) pellets embedded with microplastics (MPs), facilitating exact particle number determination for method validation and quality control (QC) using FT-IR imaging of formed potassium bromide (KBr) pellets. KBr exhibits optimal properties as a matrix for MP-immobilization due to its excellent water solubility and infrared transparency. Through detailed validation, encompassing recovery, precision, and accuracy parameters, our approach represents a proof of concept that enables robust and reliable MP validation and quality control, addressing critical gaps in current methodologies. Achieved recovery rates for different polymer types and shapes, including LDPE and PVC fragments, as well as, spherical PS beads were all above the 95% mark, demonstrating high accuracy. This method serves to monitor and mitigate potential losses during sample preparation, ensuring greater accuracy and precision in microplastic analysis. By incorporating a custom synthesized polymer with a thione functionality as an internal standard alongside conventional MP polymers, we demonstrate the ability of this approach for comprehensive method validation, evaluation and quality control on a particle-based approach.