Nile Red Staining as a Subsidiary Method for Microplastic Quantifica-tion: A Comparison of Three Solvents and Factors Influencing Application Reliability

The quantification of microplastics is a challenging task to the scientific community, especially as the existing analytical methods limit sample numbers due to difficulties associated with high expenses and time consuming procedures. Quantifying microplastics by staining with Nile Red can be helpful in distinguishing these particles from other inorganic (e.g. sediment) or organic (e.g. plant material) matter. In the present study, the benefits of acetone, chloroform and nhexane as extraction solvents for Nile Red staining were investigated. For this study, various polymer types, namely highdensity and low-density polyethylene (HDPE, LDPE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyamide (PA), polyvinyl chloride (PVC) and cellulose acetate (CA), several post-consumer products (freezing bag, bottle cap, plastic bottle, styrofoam, fishing line, food container, pipe and cigarette butt) as well as biogenic material (algae, hard plant material, soft plant material) were used as test materials. Results indicated chloroform to be the most suitable solvent achieving recovery rates of 83.3% for the group of HDPE, LDPE, PP and PVC being the most demanded polymer types in Europe. However, the proposed method does not reach the reliable quantification capabilities of Raman-spectroscopy or Fourier transform infrared spectroscopy. Nevertheless, it can aid the assessment of microplastic abundances. In conclusion, staining with Nile Red does not require expensive equipment and allows the quick evaluation of a large number of samples for the assessment of microplastics.