Microplastic quantification of nylon and polyethylene terephthalate by chromic acid wet oxidation and ultraviolet spectrometry

Microplastics are ubiquitous and their quantification in an environmental sample is important. This study modified the Walkley–Black titration method to measure the organic content of a synthetic sample containing polyethylene terephthalate (PET) or/and Nylon66 (NY) dissolved in a concentrated sulfuric acid solution, which was further converted to mass by incorporating the factors of carbon mass ratios by their molecular structures. The PET mass in concentrated sulfuric acid was also measured using UV/VIS spectrophotometer. The experimental results from the chromic acid wet oxidation showed that almost-complete oxidation of PET and NY by dichromate was achieved at the elevated temperature of 135 ∼ 140 °C, and the organic carbon resulting from existing PET and NY can be determined accurately. This study is a pioneer investigation using wet oxidation for PET and NY quantification. A step-by-step protocol was proposed to delineate the operating procedure of the modified chromic acid wet oxidation. By incorporating the UV/VIS spectrometry with chromic acid wet oxidation, the PET and NY content in a synthetic sample can be quantified.