Low-Cost Separation of PET, PP, and PE Microplastics via Brine-Oil Density-Gradient Centrifugation

Microplastic contamination is an escalating global concern, yet existing isolation protocols remain slow, expensive, and reliant on hazardous chemicals. We present a $200 DIY centrifuge method that employs a three-tier brine–sample–oil column to separate microplastics quickly and safely. Twenty fragments each of polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE) with diameters of 100-400 μm were spiked into different matrices and spun at 412 ± 25 rpm for 20 minutes. The saturated NaCl layer functions as a density buffer, electrostatic screen, and viscous damper, while oleophilic adhesion traps particles at the oil–brine interface. Mean recoveries reached at most 93% for PET and 99% for PP, and 100% for PE. Because all reagents are food-grade and key parts are 3D printed, the protocol aligns with green-chemistry principles and is affordable for classrooms, laboratories, and field stations. Current limitations include imprecise fraction-collection tools, suboptimal centrifugal force, and limited validation in the variation of matrices. Planned upgrades such as narrow-bore collectors, low-cost imaging, tunable brines, and a faster centrifuge will enable rigorous mass-balance studies and extension to complex matrices such as urine, whole blood, and placenta. This work lays the groundwork for an accessible, non-toxic, and scalable platform for environmental and biomedical microplastic surveillance.