Visualization and (Semi-)quantification of submicrometer plastics through scanning electron microscopy and time-of-flight secondary ion mass spectrometry

• Published in: Environmental pollution (1987) 2022-05, Vol.300, p.118964-118964, Article 118964
• Main Authors: Chou, Shih-Hsuan, Chuang, Yung-Kun, Lee, Chi-Ming, Chang, Yu-Shan, Jhang, Ya-Jhu, Yeh, Ching-Wen, Wu, Tai-Sing, Chuang, Chun-Yu, Hsiao, I-Lun
• Format: Article
• Language: English
• Subjects: Coffee-ring effect; Microscopy, Electron, Scanning; Nanoparticle tracking analysis; Nanoplastics; Plastics - analysis; Polyethylene; Polystyrenes - analysis; Spectrometry, Mass, Secondary Ion; Tea bags; ToF-SIMS
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2022.118964

Increasing numbers of studies have demonstrated the existence of nanoplastics (1–999 nm) in the environment and commercial products, but the current technologies for detecting and quantifying nanoplastics are still developing. Herein, we present a combination of two techniques, e.g., scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), to analyze submicron-sized plastics. A drop-casting of a 20-nL particle suspension on a Piranha solution-cleaned silicon wafer with dry ice incubation and subsequent freeze-drying was used to suppress the coffee-ring effect. SEM images were used to quantify particles, and this technique is applicable for 0.195–1.04-μm polystyrene (PS), 0.311-μm polyethylene terephthalate (PET), and 0.344-μm polyethylene (PE) at a minimum concentration of 2.49 × 109 particles/mL. ToF-SIMS could not quantify the particle number, while it could semi-quantitatively estimate number ratios of submicron PE, PET, polyvinyl chloride (PVC), and PS particles in the mixture. Analysis of submicron plastics released from three hot water-steeped teabags (respectively made of PET/PE, polylactic acid (PLA), and PET) was revisited. The SEM-derived sizes and particle numbers were comparable to those measured by a nanoparticle tracking analysis (NTA) regardless of whether or not the hydro-soluble oligomers were removed. ToF-SIMS further confirmed the number ratios of different particles from a PET/PE composite teabag leachate. This method shows potential for application in analyzing more-complex plastic particles released from food contact materials. [Display omitted] •A freeze drying-based drop-casting is presented to suppress the coffee-ring effect.•SEM can observe and quantify different sizes and types of submicron particles.•ToF-SIMS can semi-quantitatively estimate the number ratios of four different plastics.•The SEM-derived data were similar to the NTA data when analyzing teabag leachates.•Oligomers in the teabag leachates did not affect the SEM-derived particle number.