Feasibility of using quantitative 1H-NMR spectroscopy and ultra-microbalances for investigation of a PET microplastic reference material.

Here, we report on the feasibility of using quantitative NMR and ultra-microbalances for additional measurements of the mass of poly-ethylene terephthalate (PET) particles in a reference material (RM). The microplastic (MP) PET particles were immobilised in solid NaCl following freeze-drying of a 1-ml NaCl suspension. The particles ranged from 30 to about 200 µm (Feretmin). In a 3-day process, more than 500 such units of PET particles in the NaCl carrier were prepared and later used in a large-scale inter-laboratory comparison. The homogeneity of PET in the salt carrier over these 500 units had previously been evaluated with respect to the mass of PET using an ultra-microbalance. In addition to the original results obtained by weighing, two independent results of quantitative 1H-NMR have been obtained for further investigation of this reference material together with one additional set of weighing data. The NMR data were used for confirmation of the weighed amount of PET (as weighing is non-specific for PET). Average masses of 0.293 ± 0.04 mg and 0.286 ± 0.03 mg of PET were obtained using two different ultra-microbalances (14% RSD for n = 14 and 9% RSD for n = 4, respectively). The corresponding 1H-NMR data was 0.300 ± 0.02 mg of PET (6.7% RSD for n = 5) and 0.345 ± 0.04 mg of PET (12.5% RSD for n = 14), respectively. The average mass of PET obtained by 1H-NMR measurements was in agreement with the weighed amounts within their standard deviations. A mean value of 0.306 mg PET with an expanded uncertainty of 0.058 mg (± 19% relative) was calculated, and it is traceable to the SI system of measurements. Measurement of PET by quantitative 1H-NMR spectroscopy is also reported for a water sample. The PET contained in one RM sample was transferred to 1 L of water to mimic a drinking water sample for microplastics.

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

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).

Quantitative 1H-NMR spectroscopy as an efficient method for identification and quantification of PVC, ABS and PA microparticles.

As an extension of the new, size-independent, fast and easy quantitative 1H-NMR (qNMR) spectroscopy as an alternative method for microplastic (MP) analysis we herein present the possibility to analyze three environmentally highly relevant MP particles by qNMR spectroscopy. The investigations cover polyvinyl chloride (PVC) powder with a size <50 µm, acrylonitrile butadiene styrene (ABS) granules with a size distribution of 100-300 µm, and polyamide (PA) fibres with a length of approx. 500 µm and a diameter of approx. 20-30 µm. For quantification, the integration method or the peak-fitting method combined with the calibration curve method was used. Linearity above 0.99R2, precision of 99.1-99.9% and accuracy of 95.6-110% for all three polymer types demonstrate the high analytical potential of the method. Moreover, the limit of detection (40-84 µg mL-1) for all polymer types is in the lower environmentally relevant range.

Charged Tags for the Identification of Oxidative Drug Metabolites Based on Electrochemistry and Mass Spectrometry.

Most of the active pharmaceutical ingredients like Metoprolol are oxidatively metabolized by liver enzymes, such as Cytochrome P450 monooxygenases into oxygenates and therefore hydrophilic products. It is of utmost importance to identify the metabolites and to gain knowledge on their toxic impacts. By using electrochemistry, it is possible to mimic enzymatic transformations and to identify metabolic hot spots. By introducing charged-tags into the intermediate, it is possible to detect and isolate metabolic products. The identification and synthesis of initially oxidized metabolites are important to understand possible toxic activities. The gained knowledge about the metabolism will simplify interpretation and predictions of metabolitic pathways. The oxidized products were analyzed with high performance liquid chromatography-mass spectrometry using electrospray ionization (HPLC-ESI-MS) and nuclear magnetic resonance (NMR) spectroscopy. For proof-of-principle, we present a synthesis of one pyridinated main oxidation product of Metoprolol.

Correction to: Quantitative analysis of PET microplastics in environmental model samples using quantitative 1H-NMR spectroscopy: validation of an optimized and consistent sample clean-up method.

The original version of this article contained a mistake.

Quantitative analysis of PET microplastics in environmental model samples using quantitative 1H-NMR spectroscopy: validation of an optimized and consistent sample clean-up method.

Identification and quantification of microplastics (MP) in environmental samples is crucial for understanding the risk and distribution of MP in the environment. Currently, quantification of MP particles in environmental samples and the comparability of different matrices is a major research topic. Research also focusses on sample preparation, since environmental samples must be free of inorganic and organic matrix components for the MP analysis. Therefore, we would like to propose a new method that allows the comparison of the results of MP analysis from different environmental matrices and gives a MP concentration in mass of MP particles per gram of environmental sample. This is possible by developing and validating an optimized and consistent sample preparation scheme for quantitative analysis of MP particles in environmental model samples in conjunction with quantitative 1H-NMR spectroscopy (qNMR). We evaluated for the first time the effects of different environmental matrices on identification and quantification of polyethylene terephthalate (PET) fibers using the qNMR method. Furthermore, high recovery rates were obtained from spiked environmental model samples (without matrix ~ 90%, sediment ~ 97%, freshwater ~ 94%, aquatic biofilm ~ 95%, and invertebrate matrix ~ 72%), demonstrating the high analytical potential of the method. Graphical abstract.

The first application of quantitative 1H NMR spectroscopy as a simple and fast method of identification and quantification of microplastic particles (PE, PET, and PS).

Microplastic (0.001-5 mm) is a serious problem for the environment and is globally distributed. It has been detected in marine and limnic waters as well as in organisms. Until now, microplastic (MP) particles in environmental samples are mainly identified by Fourier transform infrared (FTIR) or Raman spectroscopy. Usually, for quantitative detection, time-consuming counting of MP particles in the sample is described. Therefore, a great need for research in the field of size-independent quantitative analysis of MP particles is evident. We present herein the application of quantitative 1H NMR spectroscopy (qNMR) as a new method for the qualitative and quantitative analysis of MP in solution. Polyethylene (PE) granules with a size distribution of < 300 µm, polyethylene terephthalate (PET) fibers with a length of approx. 500 µm, and polystyrene (PS) beads with a size distribution of 0.5-1 mm were qualitatively and quantitatively analyzed as prototypical MP particles in model samples using a calibration curve method. As internal standard, the residual proton signal of the deuterated solvent was used. For all polymer types, linearity of the method is > 0.994 R2, and the precision is in the range of 99.4-99.9%. The limit of detection (LOD) is in the range of 19-21 µg/mL and the limit of the quantification (LOQ) is in the range of 74-85 mg/mL, so the LOD and LOQ are observed in an environmentally relevant size. In this work, we therefore show that size-independent qualitative and quantitative determination of microplastic particles in model samples using qNMR is possible. Graphical abstract Working flow for the first application of qNMR as a simple and fast method of identification and quantification of microplastic (MP) particles (PE, PET, PS). 338 × 190 mm (96 × 96 DPI).