Applicable and cost‐efficient microplastic analysis by quantitative ¹H‐NMR spectroscopy using benchtop NMR and NoD methods

Abstract

In continuation of our work on the proof-of-concept that quantitative NMR spectroscopy may be a valuable tool in microplastic (MP) analysis and quantification, we present here investigations using low-field NMR spectrometers and nondeuterated solvents for the analysis of solutions of MP particles in suitable solvents. The use of low-field NMR spectrometers (benchtop NMR) that are considerably more cost-effective in terms of purchase and operating costs compared with high-field NMR spectrometers and the use of nondeuterated solvents (NoD method) leads to an applicable and cost-efficient method for mass-based MP analysis. For benchtop 80-MHz NMR, limits of detection for polyvinylchloride (PVC), polyethylene terephthalate (PET), and polystyrene (PS) are in the same range as if a high-field 500-MHz NMR spectrometer was used for quantification (500 MHz: PET 1 μg/ml, PVC 42 μg/ml, and PS 9 μg/ml; 80 MHz: PET 4 μg/ml, PVC 19 μg/ml, and PS 21 μg/ml) for polymers being dissolved in deuterated solvents. The same is true for the corresponding limits of quantification. Moreover, it is shown for the first time that quantitative determination of the mass concentration of PET, PVC, and PS is also possible using NoD methods by evaluating the integrals of polymer-specific signals relative to an internal or external standard. Detection limits for NoD methods are in a similar range as if deuterated solvents were used (PET 2 μg/ml, PVC 39 μg/ml, and PS 8 μg/ml) using a high-field 500-MHz spectrometer or the 80-MHz spectrometer (PET 5 μg/ml).

Simultaneous quantification of microplastic particles by non-deuterated (NoD) 1H-qNMR from samples comprising different polymer types

“…Peez et al ). 23–26 For the calibration between 2.5 and 0.5 mg mL −1 , precision values greater than 98% were achieved for all polymers, whereas for the lower concentration range of 0.5–0.1 mg mL −1 precision values greater than 89% were still possible. Fig.…”

“…Solvents for this study were selected according to several demands, listed in the next paragraph. These incorporate the necessary requirements for the selection of suitable solvents for simultaneous qNMR of multiple polymers and are based on considerations mentioned by Peez et al 23–26…”

“…23–26 Comprising all published papers, the technique already includes validated methods for low-density polyethylene (LDPE), polystyrene (PS), polyethylene terephthalate (PET), polyamide (PA), polyvinylchloride (PVC) and acrylonitrile–butadiene–styrene–copolymers (ABS). 23–26…”

Microplastics Derived from Food Packaging Waste—Their Origin and Health Risks

“…MPs are analyzed through several stages, such as separation, identification, visualization, and quantification. Techniques used to characterize MPs are mainly microscopic (optical microscopy, fluorescence microscopy, Scanning Electron Microscopy—SEM, Transmission Electron Microscopy—TEM, and Atomic Force Microscopy—AFM) and spectroscopic (Fourier Transform Infrared Spectroscopy—FT-IR, Raman Spectroscopy—RS, Nuclear Magnetic Resonance—NMR) methods [ 270 , 271 , 272 , 273 , 274 , 275 , 276 , 277 , 278 , 279 , 280 , 281 , 282 , 283 , 284 , 285 ] ( Figure 7 ). They are mostly used to identify the polymeric composition of MPs, analysis of the shape, color, and size of the particles, as well as their quantity in test samples.…”

Multi-Analytical Approach to Characterize the Degradation of Different Types of Microplastics: Identification and Quantification of Released Organic Compounds

“…Moreover, Peez et al [ 23 ] showed that in the case of PET microplastics derived from different environments and subjected to various external conditions, qNMR methodologies can achieve very high analytical standards when associated with appropriate calibration and sampling procedures. It is worth noticing that other NMR techniques, such as 2D 1 H NMR diffusion-ordered spectroscopy (DOSY) [ 24 ], low field 1 H NMR [ 25 ], and 13 C multi cross polarization (CP) [ 26 ], were recently used to investigate microplastics.…”