Cloud-Point Extraction Combined with Thermal Degradation for Nanoplastic Analysis Using Pyrolysis Gas Chromatography–Mass Spectrometry

Abstract

The contamination of micro-and nanoplastics in marine systems and freshwater is a global issue. Determination of micro-and nanoplastics in the aqueous environment is of high priority to fully assess the risk that plastic particles will pose. Although microplastics have been detected in a variety of aquatic ecosystems, the analysis of nanoplastics remains an unsolved challenge. Herein, for the first time, a Triton X-45 (TX-45)-based cloud-point extraction (CPE) was proposed to preconcentrate trace nanoplastics in environmental waters. Under the optimum extraction conditions, an enrichment factor of 500 was obtained for two types of nanoplastics with different compositions, polystyrene (PS) and poly(methyl methacrylate) (PMMA), without disturbing their original morphology and sizes. Additionally, following thermal treatment at 190 °C for 3 h, the CPE-obtained extract could be submitted to pyrolysis gas chromatography−mass spectrometry (Py-GC/MS) analysis for mass quantification of nanoplastics. Taking 66.2 nm PS nanoplastics and 86.2 nm PMMA nanoplastics as examples, the proposed method showed excellent reproducibility, and high sensitivity with respective detection limits of 11.5 and 2.5 fM. Feasibility of the proposed approach was verified by application of the optimized procedure to four real water samples. Recoveries of 84.6−96.6% at a spiked level of 88.6 fM for PS nanoplastics and 76.5−96.6% at a spiked level of 50.4 fM for PMMA nanoplastics were obtained. Consequently, this work provides an efficient approach for nanoplastic analysis in environmental waters.

Microplastics Detection Using Pyrolysis-GC/MS-Based Methods

“…Temperature of pyrolysis is especially important for the study of PS. Indeed at temperatures lower than 600 C, styrene trimer is observed in a significant quantity (Fischer and Scholz-Böttcher 2017;Mintenig et al 2018;Zhou et al 2019;Gomiero et al 2019), whereas it is undetectable at a temperature of 700 C. Moreover, it should be noted that, at 700 C, styrene dimer areas are poorly repeatable and only present at a low quantity (Hermabessiere et al 2018). Except these molecules, α-methyl styrene, benzene, toluene, and other molecules described in Table 2 are also encountered.…”

“…4.1). Regarding the pyrolysis duration, 1 min is by far the most employed time parameters (Table 1), but for some works authors use shorter pyrolysis time, i.e., a few tens of seconds (Mintenig et al 2018;Hendrickson et al 2018;Zhou et al 2019).…”

“…Regarding the quantity of analytes steered into the column, different strategies exist in the literature (Table 1). Some authors prefer to inject the entirety of the pyrolyzates using a splitless mode (Dekiff et al 2014;Fries et al 2013;Nuelle et al 2014;Hendrickson et al 2018;Peters et al 2018), while others apply important split value, higher than 20:1 (Kusch 2017; Zhou et al 2019;Gomiero et al 2019). Finally, other authors decide to adapt the split values with regard to the samples sizes or weights to be analyzed (Ter Halle et al 2017;Hendrickson et al 2018;Doyen et al 2019).…”

“…In a way to perform a correct quantification, a calibration curve has to be established in order to relate the obtained signal to the mass of analyte. This methodology was employed by five authors on different polymers: PE, PP, PS, PET, PVC, PUR, PMMA, PA-66, PA-6, and PC Scholz-Böttcher 2017, 2019;Mintenig et al 2018;Dierkes et al 2019;Gomiero et al 2019;Zhou et al 2019). When a quantification is performed, samples have usually to be purified as much as possible to avoid the presence of organic matrix that can interfere with the detected signals.…”

“…This is a heavy process and preparative steps can be numerous and multiply the risks of losses. As performed by Fischer and Scholz-Böttcher (2017), Gomiero et al (2019), or Zhou et al (2019, the use of controls, like spiking, is essential here. Unfortunately, the risk of contamination of samples has been far less studied.…”