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

Abstract

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. Graphical abstract

Nutrición animal: Texto de formación universitaria

“…Ultramicrobalanza: se utilizan para pesar muestras más pequeñas, con una capacidad de hasta 6 g con una legibilidad de 7 decimales a la derecha del punto decimal (0.0000001 g) (Seghers et al, 2023). Es una de las balanzas más exactas del mercado.…”

Paving the way for new and challenging matrix reference materials—particle suspensions at the core of material processing providing RMs for method development and method validation

“…As with all such emerging measurement challenges, access to sufficiently homogeneous test materials to underpin such harmonisation and method validation efforts is crucial. During the last years, work has been undertaken at the JRC in order to pave the way for the production of such RMs [ 2 , 3 ]. To date, the two JRC publications cover the methodology and further characterisation of the polyethylene terephthalate PET in drinking water RM used in the JRC/BAM inter-laboratory comparison [ 14 ].…”

“…By using a balance for characterisation of the amount of microplastics, metrological traceability to the SI system was achieved as well as trueness check of the actual content in the samples. Subsequent efforts using quantitative 1 H-NMR that had shown promising features in the JRC/BAM inter-laboratory comparison provided more information about the homogeneity of the RM used [ 3 , 14 ]. Results obtained by 1 H-NMR are also traceable to the SI system with the additional advantage of being specific for PET [ 3 ].…”

“…This article will describe possible strategies for an RM producer to overcome such hurdles in an incremental fashion and highlight this inter-dependence for analytical method developers. Additionally, in a recent work on a microplastic (MP), RM demonstrates how improved analytical methods reveal better homogeneity of a reference material than initially established [ 2 , 3 ]. Under all circumstances, access to homogeneous testing materials is vital in the early steps of such an incremental development process.…”

“…Over the years, the European Commissions’ Joint Research Centre in Geel, Belgium, has prepared several new types of reference materials whereof one is a certified reference material for PM 2.5 -like atmospheric dust, which was described in two separate papers [ 5 , 6 ]. The other two examples discussed in this work encompass whole water reference materials for organic pollutants in environmental water samples [ 7 – 13 ] and two RMs for mass and/or particle number of microplastic in water [ 2 , 3 , 14 ]. These examples cover both the difficulty of access to sufficient amounts of a suitable starting material and inherent challenges associated with processing.…”