An Easy and Reliable Method for Calibrating Combustion-Based Total Organic Carbon Analyzers for Solid Samples...

Combustion-based total organic carbon (TOC) analyzers for solid samples are interesting tools for estimating the mass of microplastics in environmental samples. However, the low concentration of microplastics to be quantified may require TOC calibration below 100 μg of carbon (μgC), which could be laborious and tedious. This study proposes a fast, reliable, and easy-to-use calibration procedure that uses monomodal, compact polystyrene (PS) microspheres with nominal diameters of either 200 or 250 μm. Calibration curves obtained with the PS microspheres within the range of 8 to 50 μgC were linear and statistically equivalent to the reference calibration curve obtained with a diluted glucose solution. This demonstrates the effectiveness of this approach. This calibration procedure was successfully used to quantify the carbon content and accurately determine the size of unknown PS microspheres. The average size recovery was 98% ± 2% for 13 randomly selected particles ranging from 400 to 525 μm in diameter. Additionally, the study showed that the increase in carbon content following durable Nile Red staining of PS microspheres can be assessed using TOC analysis. This increase is likely due to organic solvent being trapped in the polymeric structure when PS particles are heated above their glass transition temperature. This alternative calibration procedure could improve the accuracy and ease of TOC analysis in various fields, including the monitoring of low microplastic content in environmental samples.