Total organic carbon (TOC): a simple tool for assessing micro(nano)plastics and nanocellulose recovery during size-based fractionation

Abstract

The assessment of analyte recovery during sample preparation is a critical quality control parameter in method development. While elemental mass spectrometry techniques, such as ICP-MS, are very effective for assessing the recovery of particulate materials containing metallic elements, there is no equivalent applicable to metal-free carbon or CHNO-based particulate polymer materials. Vibrational spectro-microscopy or thermo-analytical techniques can be used to quantify polymer-based micro- and nanoparticles, but are typically expensive and time-consuming techniques that require higher levels of expertise. This study investigated the potential of a liquid-based total organic carbon (TOC) analyzer as a simple, cost-effective, and universal method for determining the recovery of polymer-based particulate micro- and nanomaterials following filtration, centrifugation, and asymmetric flow field flow fractionation (AF4) processes. A good correlation between solid contents and TOC analysis was demonstrated for standard polystyrene (PS) particle suspensions of various sizes, ranging from 50 nm to 90 μm (79.2 to 113.6% recovery), and other types of synthetic and natural polymeric particle suspensions, including polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and cellulose (86.2 to 126.2% recovery). Liquid-based TOC was then successfully applied to estimate particle recovery after various preparatory and fractionation steps, including the determination of filtration recoveries for nanocellulose suspensions (99.0 to 101.4% recovery) and PS micro- and nanoparticles spiked into environmental lake and river freshwater samples (70 to 96% recovery). The combination of TOC and single particle extinction and scattering (SPES) measurements allowed the tracking and quantification of three different populations of PS particles in a mixture (200, 500, and 1000 nm) during successive centrifugation steps (113.8 ± 13.9% cumulative recovery). Finally, this study demonstrated the suitability of TOC for determining both the absolute and relative recoveries of polymer-based particulate materials after AF4 fractionation in line with ISO standards. Liquid-based TOC proved to be a valuable tool for directly tracking, quantifying, and evaluating the recovery of polymer-based micro- and nanoparticles in model and environmental water samples before and after routine size-based fractionation steps.