Analysis of polymer microparticles

Abstract

The invention relates to a method for determining the quantity and type of polymer microparticles present in a material to be examined, and to a method for validating a method for determining the quantity and type of polymer microparticles present in a material to be examined, comprising the step of providing a starting quantity of reference polymer microparticles on a die and adding an alkali metal halide, and the step of pressing the reference polymer microparticles with alkali metal halide to form a pressed article.

Description

[0001] ANALYSIS OF POLYMER MICROPARTICLES

[0002] The present invention relates to a method for determining the amount and type of polymer microparticles present in a material to be examined, wherein the method comprises the steps of •) taking at least one analysis sample from the material to be examined, •) carrying out sample preparation on the analysis sample and providing a measurement sample and •) carrying out a qualitative and quantitative analysis on the measurement sample to determine the type and amount of polymer microparticles in the measurement sample. The invention further relates to a method for validating a method for determining the amount and type of polymer microparticles present in a material to be examined. Furthermore, the invention relates to a polymer for the method and the invention relates to a method for producing the polymer.

[0003] BACKGROUND OF THE INVENTION

[0004] According to Regulation (EU) 2023 / 2055 of September 25, 2023, polymer microparticles (also called microplastics) are plastic particles with a diameter of no more than 5 mm, or no more than 15 mm if the length-to-diameter ratio is greater than 3. Polymer microparticles are often actively used in consumer goods such as cosmetics, toothpaste, cleaning products, etc., or they originate from the decomposition of larger plastic goods. Due to the increasing environmental pollution with polymer microparticles, there is a need for precise methods to determine the amount of polymer microparticles in a material in order to determine the degree of contamination.

[0005] There are various methods for the quantitative determination of polymer microparticles in a material sample, differing in their methodology and accuracy. Pyrolysis gas chromatography mass spectrometry is technically complex; in this method, samples are heated to break down the polymers contained into smaller molecules and then identified using gas chromatography and mass spectrometry. Microscopic methods, in which the polymer microparticles present are identified and counted, are also complex.

[0006] The most common methods for quantifying polymer microparticles in samples are Fourier transform infrared spectroscopy and Raman spectroscopy, with Raman spectroscopy being particularly useful for detecting smaller polymer microparticles. A major problem in the quantitative analysis of the total polymer microparticle content of a sample is inhomogeneities. These relate to the chemical nature of the plastics in a sample, the distribution of the polymer microparticles in the sample being analyzed, and possibly also the size distribution of the plastic particles themselves. Different measurement methods or instrument settings can produce different measurement results for the same samples.

[0007] The size and density distribution of the plastic particles in a sample proves to be particularly problematic. Different densities and particle sizes of the plastic particles can lead to an irregular distribution of the plastic particles in the sample being measured. This creates the risk that the measurement result will depend on the sample preparation or the sampling point, and that different results will occur for different samples of the same material.

[0008] To date, the validation of measurement methods for the determination of polymer microparticles in samples has presented a major challenge, as described, for example, in Schymanski et al. and Andrade et al. (Schymanski, D. et al. Analysis of microplastics in drinking water and other clean water samples with micro-Raman and micro-infrared spectroscopy: minimum requirements and best practice guidelines. Anal Bioanal. Chem. 413, 5969-5994 (2021) https: / / doi.org / 10.1007 / s00216-021-03498-y and Andrade JM et al. Standardization of the minimum information for publication of infrared-related data when microplastics are characterized, Marine Pollution Bulletin, 154, 111035 (2020) https: / / doi.Org / 10.1016 / j.marpolbul.2020.111035).

[0009] BRIEF DESCRIPTION OF THE INVENTION

[0010] In analytical procedures, it is generally customary to use a standard to make statements about the quality of an analysis and to enable comparisons between different laboratories, laboratory equipment, and operators. Key parameters for the validation of analytical methods include the reproducibility of results, the recovery rate, limit of detection (LOD) and limit of quantification (LOQ), linearity, and others. The Society for Toxicological and Forensic Chemistry (GTFCh) has published a guideline for quality assurance in forensic toxicological investigations, which describes the "Requirements for the Validation of Analytical Methods" in Appendix B (version dated June 1, 2009, valid from April 1, 2011, published in Toxichem Krimtech (2009) 76 (3): 185 - 208).

[0011] Currently, very complex methods are used for the quantitative determination of polymer microparticles, and suitable methods for validation and calibration are lacking. The lack of or inadequate validation also leads to inaccurate measurement results. The object of the present invention is therefore, on the one hand, to provide an exact method for determining the quantity and type of polymer microparticles present in a material under investigation. On the other hand, a method for validating a method for determining the quantity and type of polymer microparticles present in a material under investigation is to be provided in order to enable comparable results between different laboratories.

[0012] This task is solved by a method for determining the quantity and type of polymer microparticles present in a material to be examined, the method comprising the steps:

[0013] (a) taking at least one analytical sample from the material to be examined;

[0014] (b) providing an initial amount of reference polymer microparticles on a stamp and adding an alkali metal halide,

[0015] (c) Pressing the reference polymer microparticles with alkali metal halide to form a pellet,

[0016] (d) Carrying out a quantitative analysis on the pellet to determine the actual starting quantity of reference polymer microparticles,

[0017] (e) adding the pellet to the analysis sample, if necessary adding water and dissolving the alkali metal halide component of the pellet in the analysis sample,

[0018] (f) carrying out sample preparation on the analysis sample obtained from step (e) and providing a measurement sample,

[0019] (g) Conducting a quantitative analysis of the measurement sample to determine the residual amount of reference microparticles in the measurement sample and conducting a qualitative and quantitative analysis of the measurement sample to determine the type and amount of polymer microparticles in the measurement sample; (h) Determining a correction factor from the residual amount of reference polymer microparticles from step (g) and the actual initial amount of reference polymer microparticles from step (d);

[0020] (i) Applying the correction factor to the amount of polymer microparticles determined from step (g) and calculating the actual amount of polymer particles in the analysis sample.

[0021] The task is also solved by a method for validating a procedure for determining the quantity and type of polymer microparticles present in a material to be examined, whereby the procedure to be validated comprises the steps

[0022] • Taking an analysis sample from the material to be examined,

[0023] • Sample preparation to provide a measurement sample and

[0024] • the qualitative and quantitative analysis of the sample, characterized in that the method comprises the steps:

[0025] (i) Providing an initial amount of reference polymer microparticles on a stamp and adding an alkali metal halide,

[0026] (ii) pressing the reference polymer microparticles with alkali metal halide to form a pellet,

[0027] (iii) Carrying out a quantitative analysis on the pellet to determine the actual starting quantity of reference polymer microparticles,

[0028] (iv) adding the pellet to an aqueous medium and dissolving the alkali metal halide component of the pellet in the medium,

[0029] (v) Carrying out the sample preparation steps on the medium and preparing a calibration sample,

[0030] (vi) carrying out a quantitative analysis on the calibration sample and determining the residual amount of reference polymer microparticles;

[0031] (vii) determining a correction factor from the residual amount of reference polymer microparticles from step (vi) and the actual initial amount of reference polymer microparticles from step (iii);

[0032] (viii) Carrying out the procedure for determining the quantity and type of polymer microparticles present in a material to be tested; (ix) Applying the correction factor to the determined quantity of polymer microparticles from the test sample of the material to determine the actual quantity of polymer particles.

[0033] Within the scope of the invention, it was discovered that by providing an initial amount of reference polymer microparticles on a stamp, followed by the addition of alkali metal halide and the subsequent production of a compact, the quantification of the reference polymer microparticles in the compact can be carried out very precisely. This compact can then be placed in an analysis sample or an aqueous medium to dissolve the alkali metal halide, allowing the reference polymer microparticles—the quantity of which was previously precisely determined by quantitative analysis on the compact—to disperse in the analysis sample or aqueous medium. The detour via the use of reference polymer microparticles and the creation of the compact with the reference polymer microparticles has several advantages.In a quantitative spectroscopic analysis of the pellet, the amount of reference particles can be determined very precisely, since the alkali metal halide does not significantly influence spectroscopic analyses. Furthermore, the addition of the pellets to an analysis sample does not interfere with a subsequent qualitative and quantitative analysis of the polymer microparticles. Alkali metal halide dissolves and does not negatively affect subsequent measurements. The reference polymer microparticles in the analysis sample or in the aqueous medium are distributed inhomogeneously to the same extent as the polymer microparticles to be analyzed in the analysis sample and can therefore serve as a reference.

[0034] In the method according to the invention, the reference polymer microparticles can be used as an internal standard, which undergoes sample preparation to prepare the measurement sample. If losses of reference particles occur during sample preparation, these can be detected. The losses of reference particles are representative of the losses of the polymer microparticles, so that the determined correction factor can be used to compensate for the loss of polymer microparticles during sample preparation.

[0035] In the method according to the invention, the reference polymer microparticles are not used as an internal standard; instead, a validation of the method is performed by subjecting the reference polymer microparticles to the sample preparation steps. If any loss of reference particles occurs during the sample preparation steps, this loss can be determined. This loss of reference particles is representative of the loss of polymer microparticles, so that the determined correction factor can be used to compensate for the loss of polymer microparticles due to the actual sample preparation.

[0036] Typically, three different methods are distinguished using standards to calibrate measurements: methods with internal standards, external standards, and standard addition. The first method uses an internal standard to precisely determine the presence of polymer microparticles in a sample of a material under investigation. Losses that occur during sample preparation are determined by this method by determining a correction factor.

[0037] An internal standard is added to a sample in a known amount to make measurements more accurate. The internal standard should be chemically similar, but not identical, to the analyte and should not be present in the sample itself to avoid distorting measurement results. A polymer specifically designed and developed for the process and method according to the invention is described below.

[0038] Before sample preparation, the reference polymer particles are embedded in a precisely defined amount in a matrix formed by an alkali metal halide. The alkali metal halide is a salt of an alkali metal ion with a halide, with the alkali metal ion preferably being selected from the group Li + , N / a + or K + and the halide is preferably selected from the group consisting of F", Cl" or Br". The alkali metal halide potassium bromide (KBr) is particularly preferred.

[0039] A potassium bromide pellet is particularly suitable for spectroscopic techniques such as infrared spectroscopy or Raman spectroscopy. A pellet is a solid, essentially transparent disc produced by compressing potassium bromide (KBr) powder under high pressure. Potassium bromide exhibits a process known as cold flow under high pressure (0.7 to 1.0 GPa), making it glassy and transparent. The choice of the potassium bromide matrix was deliberate, as this salt forms a transparent medium under pressure. This makes it possible to clearly determine the type of polymer, particle size, and quantity. In addition, potassium bromide is characterized by its ideal property of being highly soluble in water, ensuring the addition of the entire quantity of particles.

[0040] First, an initial quantity of reference polymer microparticles is placed on the stamp. This is advantageously done from a suspension of reference polymer microparticles. The suspension medium can be, for example, aqueous or alcoholic (preferably ethanolic). The reference polymer microparticle suspension is applied to a stamp, and the suspension medium is evaporated. After evaporation, the reference polymer microparticles are in a plane on the stamp. Subsequently, (preferably dried) alkali metal halide (preferably KBr) is applied to the stamp with reference polymer microparticles. Applying high pressure (0.7 to 1.0 GPa; e.g., using a hydraulic press), the powder is pressed into a clear, solid disc.When performing the quantitative spectroscopic analysis on the pellet to determine the actual starting amount of reference polymer microparticles, the exact starting amount of reference polymer microparticles is determined.

[0041] When KBr is used, imaging infrared (IR) spectroscopy, preferably Fourier transform infrared (FTIR) imaging, is suitable for quantitative spectroscopic analysis. KBr is transparent in the infrared radiation range in which measurements are performed. This means that it does not absorb IR light, making it an ideal medium without disturbing the spectrum. When infrared light passes through the pellet, the sample absorbs certain frequencies corresponding to the molecular structure of the polymer microparticles. In imaging IR spectroscopy, in addition to the IR spectrometer, a microscope is used to examine areas of the surface of a sample in pixels. This is generally advantageous for heterogeneous samples or for the investigation of specific regions within a sample. The resulting spectra are analyzed to perform qualitative and quantitative analysis of polymer microparticles.The spectra obtained during imaging IR spectroscopy are compared for each recorded pixel with a polymer reference database to identify the polymer particles. This allows for qualitative and quantitative analysis of the polymer microparticles on a support such as a filter. The other alkali metal halides are also transparent in the IR range, but the preparation of the pellet requires higher pressure and lower water solubility. Raman spectroscopy can also be used. The internal standard method offers the advantage of a calibration technique that is independent of the qualitative and quantitative analysis. This is particularly useful when the matrix is ​​expected to interfere with the measurement. A typical example of this is unknown sample losses during sample preparation.The internal standard should not be identical to the analyte to be analyzed, but should have similar physicochemical properties.

[0042] For the reference polymer microparticles, a polymer with formula I, formula II or formula III has proven advantageous:

[0043] (Formula III) where n, m, and o are independently natural numbers > 1. The special feature of these new polymers is a specific marker that allows them to be distinguished from conventional polymer microparticles (found in typical materials). Unlike plastics typically used in consumer products or other products, the polymers according to the invention contain a thione group (C=S). Polymers with thione modification are used only in a few specific applications, so the polymer microparticle contamination from such polymers is negligible. Thione groups can be easily identified in the infrared because they exhibit specific absorption bands:

[0044] • SH at a wavenumber of about 2600 cm' 1

[0045] • N=C=S at a wavenumber of about 2100 cm' 1

[0046] • C=S at a wavenumber of about 1100 cm' 1

[0047] In principle, there is still no way to standardize polymer microparticle analysis, and this is precisely the problem criticized in the literature. Initial approaches have been developed by evaporating a salt-containing polymer microparticle suspension (Natalia P. Ivleva; Chemical Analysis of Microplastics and Nanoplastics: Challenges, Advanced Methods, and Perspectives, Chemical Reviews 2021 121 (19), 11886-11936, DOI:

[0048] 10.1021 / acs.chemrev.lc00178). Interlaboratory tests for these approaches show a quantitative deviation of 20%.

[0049] The invention also relates to a proprietary polymer with specific markers and its embedding in a transparent matrix for use as an internal standard for the analysis of polymer microparticles. This allows the standard to be clearly distinguished from conventional polymer microparticles, and embedding in a matrix enables defined addition. Furthermore, important criteria such as polymer type and particle size can be clearly determined.

[0050] Validation is best performed for polymer microparticle analyses using FTIR spectroscopy and / or Raman spectroscopy.

[0051] It is advantageous if the size and concentration of the polymer of formula I, II, or III are selected to be representative of the polymer microparticles expected in a sample. This adjustment can be made during the polymer preparation process and the corresponding dilution. For both processes, it is advantageous if the method for the qualitative and quantitative analysis of polymer microparticles includes a spectroscopic procedure, preferably FTIR spectroscopy and / or Raman spectroscopy.

[0052] In one aspect of the invention, therefore, a polymer of formula I, formula II or formula III is provided.

[0053] (Formula III) where n, m and o are independently natural numbers > 1. A process for preparing a polymer of formula I, II or III may comprise the steps:

[0054] (A) Providing a mixture of l-vinyl-4-imidazolidine-2-thione (VIT) and a divinylbenzene (DVB), and cellulose, wherein the DVB is selected from the group

[0055] 1, 2-DVB for the polymer of formula II, 1,3-DVB for the polymer of formula I or a mixture of 1,2-DVB and 1,3-DVB for the polymer of formula III

[0056] (B) Addition of azoisobutyronitrile (AIBN) as a radical initiator to the mixture,

[0057] (C) heating the mixture to a temperature suitable to initiate and maintain radical polymerization,

[0058] (D) maintaining the temperature for polymerization;

[0059] (E) Cooling and isolation of the polymer.

[0060] Preferably, the mass ratio of DVB (molecular mass: 130.18) to VIT (molecular mass: 126.18) is in the range of 1 : 0.5 to 1 : 1.5. This results in

[0061] The mass ratio of DVB to cellulose is advantageously 1:2 to 1:4.

[0062] The polymerization in step (D) can be carried out at a temperature in the range of 60°C to 120°C.

[0063] The proposed process utilizes the unique reactive properties of divinylbenzene and vinylimidazolidine-2-thione in combination with azoisobutyronitrile as the polymerization initiator. The selection of AIBN as the initiator is based on its ability to efficiently generate free radicals at elevated temperatures, which is necessary for initiating copolymerization. The ratio of DVB to VIT, as well as the reaction temperature and time, are crucial for controlling the molecular properties of the resulting polymer, such as the degree of crosslinking and associated particle size.

[0064] Preferably, the mass ratio of DVB to VIT is in the range of 1:0.5 to 1:1.5.

[0065] To optimally adjust the size of the desired polymer, it has proven advantageous if the mass ratio of DVB to cellulose is 1 : 2 to 1 : 4.

[0066] Preferably, the polymerization in step (iv) is carried out at a temperature in the range of 60°C to 120°C. Definitions:

[0067] Polymer microparticles within the meaning of the invention are plastic particles in accordance with Regulation (EU) 2023 / 2055 of September 25, 2023, with a diameter of not more than 5 mm or not more than 15 mm if the length-to-diameter ratio is greater than 3. The typical diameter can be between 0.1 pm and 5 mm, preferably between 1 pm and 5 mm.

[0068] DETAILED DESCRIPTION OF THE INVENTION

[0069] Fig. 1 shows an FT-IR spectrum of a pellet with reference polymer microparticles.

[0070] Fig. 2 shows an FT-IR spectrum of a qualitative and quantitative analysis of the sample.

[0071] Fig. 3 shows an exemplary representation of the particle size and number of a synthesis of the manufacturing process.

[0072] Fig. 4 shows an FT-IR spectrum of a polymer according to the invention.

[0073] Description of the method according to the invention:

[0074] The procedure for determining the amount and type of polymer microparticles present in a material under investigation is described in more detail below.

[0075] Step (a) Taking at least one analytical sample from the material to be analyzed: A sample is taken from the material to be analyzed. During sampling, care should be taken to ensure that all equipment (pipettes, containers) that come into contact with the sample are plastic-free. Sampling can be carried out, for example, according to ISO / TR 21960:2020.

[0076] Step (b) Providing an initial amount of reference polymer microparticles on a stamp and adding an alkali metal halide:

[0077] The reference polymer microparticles are applied to the designated stamps in a suitable amount of suspension medium (e.g., ethanol, as this improves wetting of the polymer particles and enables suspension with difficult-to-wetting polymers) at the appropriate concentration and in the smallest possible volume. Suitable volumes are, for example, 2 to 10 pL. After the suspension medium has completely evaporated and the surface is dry, the press device is assembled according to the operating instructions. Approximately 250 mg of potassium bromide is added.

[0078] Step (c) Pressing the reference polymer microparticles with alkali metal halide to form a pellet:

[0079] Subsequently, pressure is applied to the die, increasing it to approximately 98 kN (10 tons), and maintained constant for a period of 2 minutes. After this period, the pressure is gradually reduced over a period of 1 minute. The result is a KBr compact embedded with the reference polymer microparticles.

[0080] Step (d) Carrying out a quantitative spectroscopic analysis on the pellet to determine the actual starting amount of reference polymer microparticles:

[0081] The measurement can be carried out, for example, as described below: The IR measurement conditions are preferably in a wavenumber range of 4000-1000 cm' 1 Two scans are recorded per pixel. The spectral resolution can be, for example, 16 cm' 1The measurement range is the entire compact. A spectrum of polyethylene terephthalate (PET; formula shown below) is shown in Fig. 1, and a polymer according to the invention is shown in Fig. 4.

[0082] PET: where n is a natural number > 1. A polymer of formula I, II, or III has the advantage of being easily characterized compared to other polymers more commonly found in the environment. Therefore, a polymer should be used for the reference polymer particles that is unlikely to be present in the sample under investigation.

[0083] Step (e) Adding the pellet to the analysis sample, optionally adding water and dissolving the alkali metal halide component of the pellet in the analysis sample. Step (f) Performing sample preparation on the analysis sample obtained from step (e) and preparing a measurement sample:

[0084] Sample preparation depends on the type and amount of organic or inorganic components in the sample. This typically includes basic, acidic, or enzymatic digestion of organic compounds and density extraction to remove inorganic components.

[0085] An example of this would be an aqueous environmental sample: The organic components are dissolved by alkaline digestion (a mixture of KOH and H2O2), and the sample is then filtered onto a suitable filter (e.g., a metal-coated Kempore filter). The filter can then be used directly as a support for subsequent analysis.

[0086] Step (g) Carrying out a quantitative analysis on the test sample to determine the residual amount of reference microparticles in the test sample and carrying out a qualitative and quantitative analysis on the test sample to determine the type and amount of polymer microparticles in the test sample:

[0087] The spectroscopic measurement can be performed under the same measurement conditions as for the pellet. Subsequently, the data is evaluated (manually or automatically) by comparing the obtained spectra with a polymer database. This allows the identity, size, and number of polymer microparticles to be determined.

[0088] Step (h) Determination of a correction factor from the residual amount of reference polymer microparticles from step (g) and the actual initial amount of reference polymer microparticles from step (d):

[0089] The recovery rate (or recovery) and thus the correction factor can typically be determined using the formula: Recovery % = (number of particles found in the sample to be used in the pellet)* 100

[0090] Step (i) Apply the correction factor to the amount of polymer microparticles determined from step (g) and calculate the actual amount of polymer particles in the analysis sample: Divide the determined amount of polymer microparticles by the recovery rate. For example, if 80 out of 100 reference particles were recovered, the recovery rate is 80%. The correction factor is therefore 1 / 0.8.

[0091] Description of the method according to the invention:

[0092] The following describes in more detail the method for validating a procedure for determining the quantity and type of polymer microparticles present in a material under investigation. Reference is made to the procedure and, where possible, references are made to the procedure.

[0093] Step (i) Providing a mixture of an alkali metal halide and an initial amount of reference polymer microparticles on a stamp:

[0094] This step is carried out analogously to the process according to the invention (see step (b) of the process). Polymers of formulas I, II, or III, or other polymers such as PET, are suitable for the reference polymer particles.

[0095] Steps (ii) and (iii) Pressing the mixture into a pellet and performing a quantitative analysis on the pellet to determine the actual starting amount of reference polymer microparticles:

[0096] These steps are carried out analogously to the process according to the invention (see steps (c) and (d) of the process).

[0097] Step (iv) Adding the pellet to an aqueous medium and dissolving the alkali metal halide component of the pellet in the medium:

[0098] Instead of dissolving the pellet in the analysis sample as in step (e), the pellet is placed in an aqueous medium. The aqueous medium is preferably similar to the material under investigation, as the aqueous medium is intended to "simulate" the material.

[0099] Step (v) Carry out the sample preparation steps on the medium and prepare a calibration sample:

[0100] As in step (f), a sample preparation is carried out to determine the losses occurring during sample preparation. Step (vi) Carry out a quantitative analysis on the calibration sample and determine the

[0101] Remaining amount of reference polymer microparticles:

[0102] This step is carried out analogously to the process according to the invention (see step (g))

[0103] Step (vii) Determination of a correction factor from the residual amount of reference polymer microparticles from step (vi) and the actual initial amount of reference polymer microparticles from step (iii):

[0104] This step can be carried out analogously to step (h) of the procedure.

[0105] Step (viii) Carrying out the procedure for determining the quantity and type of polymer microparticles present in a material to be tested:

[0106] Any known method for determining the amount and type of polymer microparticles present in a material under investigation can be used here.

[0107] Step (ix) Applying the correction factor to the determined amount of polymer microparticles from the test sample of the material to determine the actual amount of polymer particles.

[0108] This step can be carried out analogously to step (i) of the procedure.

[0109] Validation process:

[0110] The KBr pellet is analyzed using imaging spectroscopic techniques, which allows the precise number of reference polymer microparticles to be determined. After this analysis, the pellet can serve as an internal standard for future measurements. This standard is added before processing a sample. Based on the known initial particle count and the number of particles detected after processing, the following validation criteria can be determined:

[0111] • LOD / LOQ (Limit of detection / Limit of quantification)

[0112] • Limit of detection / limit of quantification (LOD)

[0113] • Precision

[0114] • Linearity / working range

[0115] • Accuracy (bias)

[0116] • Recovery

[0117] • Inaccuracy Other important parameters that can be determined without the internal standard:

[0118] • Specificity / Selectivity

[0119] • Stability

[0120] The polymer according to the invention enables differentiation from conventional polymer microparticles and unambiguous identification in a sample.

[0121] Production of the polymer:

[0122] Polymers according to the invention can be prepared by copolymerization of 1,2-divinylbenzene (DVB) and / or 1,3-divinylbenzene, l-vinyl-4-imidazolidine-2-thione (VIT) and azoisobutyronitrile (AIBN), whereby the size of the polymer can be adjusted by the presence of cellulose in the polymerization mixture.

[0123] In one variant, the polymer can be produced as follows:

[0124] • Azoisobutyronitrile (AIBN) 30 mg

[0125] • Vinylimidazolidine-2-thione (VIT) 160 mg

[0126] • DVB 200 mg

[0127] • Organic solvent 600 pl

[0128] • Cellulose 700 mg

[0129] • Water 100 mL

[0130] DVB, VIT, AIBN, and an organic solvent are combined. This mixture is then gradually added to a 70°C solution of water and cellulose. The resulting reaction mixture is then mixed at a constant temperature of 70°C for 21 hours under controlled stirring. After this time, the resulting particles are isolated by centrifugation and resuspended in ethanol.

[0131] 200 mg DVB (divinylbenzene)

[0132] 160 mg VIT (vinylimidazolidine-2-thione)

[0133] 30 mg AIBN (Azo-bis-(isobutylonitrile))

[0134] 600 μl CHCl (chloroform)

[0135] 700 mg cellulose

[0136] 100 ml H2O Instructions:

[0137] 1 mL of DVB is shaken with four spatula tips of AI2O3 for 30 min (activation). From this, 200 mg of the supernatant is transferred to a flask along with 160 mg of VIT (monomer), 30 mg of AIBN (initiator), and 600 μL of chloroform (solvent). This mixture (Mixture 1) is dissolved in an ultrasonic bath for 10 min.

[0138] Simultaneously, 700 mg of cellulose (Methocel) is stirred in 100 mL of water at 1000 rpm for 30 min. Mixture 1 is then added to this solution, and the mixture is stirred using a precision glass stirrer at room temperature and 200 rpm for 30–60 min (t1). The synthesis then takes place at 70°C for 21 h at 200 rpm (t1). The polymer is purified by centrifugation and washing three times with water.

[0139] In general, the size distribution (Fig. 3) can be adjusted using several parameters. If tl is selected to be lower, more particles over 100 pm will be detected during the size distribution measurement. If tl is selected to be longer, more particles below 100 pm will be obtained. The stirring speed during synthesis also influences the particle size. If vl is selected to be lower (approx. 150 rpm), comparatively larger reference polymer microparticles (> 100 pm) will be obtained; if vl is set to be higher (> 300 rpm), significantly smaller reference polymer microparticles (< 100 pm) will be obtained. With the selected settings, the largest number of reference polymer microparticles close to 25 pm in diameter will be obtained. Separation according to particle size for specific applications can be achieved using suitable methods (e.g. field flow fractionation FFF).

Claims

CLAIMS 1. A method for determining the quantity and type of polymer microparticles present in a material to be examined, the method comprising the steps of: (a) taking at least one analytical sample from the material to be examined; (b) providing an initial amount of reference polymer microparticles on a stamp and adding an alkali metal halide, (c) Pressing the reference polymer microparticles with alkali metal halide to form a pellet, (d) carrying out a quantitative spectroscopic analysis on the pellet to determine the actual starting quantity of reference polymer microparticles, (e) adding the pellet to the analysis sample, if necessary adding water and dissolving the alkali metal halide component of the pellet in the analysis sample, (f) carrying out sample preparation on the analysis sample obtained from step (e) and providing a measurement sample, (g) carrying out a quantitative analysis on the test sample to determine the residual amount of reference microparticles in the test sample and carrying out a qualitative and quantitative analysis on the test sample to determine the type and amount of polymer microparticles in the test sample; (h) determining a correction factor from the residual amount of reference polymer microparticles from step (g) and the actual starting amount of reference polymer microparticles from step (d); (i) Applying the correction factor to the amount of polymer microparticles determined from step (g) and calculating the actual amount of polymer particles in the analysis sample.

2. Method for validating a procedure for determining the quantity and type of polymer microparticles present in a material to be tested, the method to be validated comprising the steps of • Taking an analysis sample from the material to be examined, • Sample preparation to provide a measurement sample and • the qualitative and quantitative analysis of the sample, characterized in that the method comprises the steps: (i) Providing an initial amount of reference polymer microparticles on a stamp and adding an alkali metal halide, (ii) pressing the reference polymer microparticles with alkali metal halide to form a pellet, (iii) Carrying out a quantitative analysis on the pellet to determine the actual starting quantity of reference polymer microparticles, (iv) adding the pellet to an aqueous medium and dissolving the alkali metal halide component of the pellet in the medium, (v) Carrying out the sample preparation steps on the medium and preparing a calibration sample, (vi) carrying out a quantitative analysis on the calibration sample and determining the residual amount of reference polymer microparticles; (vii) determining a correction factor from the residual amount of reference polymer microparticles from step (vi) and the actual initial amount of reference polymer microparticles from step (iii); (viii) carrying out the procedure for determining the quantity and type of polymer microparticles present in a material to be tested; (ix) Applying the correction factor to the determined amount of polymer microparticles from the test sample of the material to determine the actual amount of polymer particles.

3. The method according to claim 1 or claim 2, characterized in that the qualitative analysis comprises a spectroscopic method, preferably imaging FTIR spectroscopy and / or imaging Raman spectroscopy.

4. Method according to one of claims 1 to 3 or method according to claim 2 or claim 3, characterized in that the quantitative analysis comprises an imaging method, preferably an imaging spectroscopic method, preferably imaging FTIR spectroscopy and / or imaging Raman spectroscopy.

5. The method according to any one of claims 1 to 4 or the method according to any one of claims 2 to 4, characterized in that the size and concentration of the reference polymer microparticles is representative of the expected amount of polymer microparticles in the analysis sample.

6. Process according to one of claims 1 to 5 or method according to one of claims 2 to 5, characterized in that the alkali metal ion of the alkali metal halide is selected from the group Li + , N / a + or K + and that the halide of the alkali metal halide is selected from the group consisting of F", Cl" or Br".

7. Process according to one of claims 1 to 6 or method according to one of claims 2 to 6, characterized in that the alkali metal halide is potassium bromide (KBr).

8. Process according to one of claims 1 to 7 or method according to one of claims 2 to 7, characterized in that the reference polymer microparticles comprise a polymer of formula I, formula II or formula III: (Formula I), (Formula II), (Formula III) where n, m and o are independently natural numbers >

1.

9. Polymer of formula I, II or III (Formula III) where n, m and o are independently natural numbers >

1.

10. A process for preparing a polymer of formula I according to claim 9, comprising the steps (A) Providing a mixture of l-vinyl-4-imidazolidine-2-thione (VIT) and a divinylbenzene (DVB), and cellulose, wherein the DVB is selected from the group 1, 2-DVB for the polymer of formula II, 1,3-DVB for the polymer of formula I or a mixture of 1,2-DVB and 1,3-DVB for the polymer of formula III, (B) Addition of azoisobutyronitrile (AIBN) as a radical initiator to the mixture, (C) heating the mixture to a temperature suitable to initiate and maintain radical polymerization, (D) maintaining the temperature for polymerization; (E) Cooling and isolation of the polymer.

11. The method according to claim 10, wherein the mass ratio of DVB to VIT is in the range of 1:0.5 to 1:1.

5.

12. A process according to claim 10 or claim 11, characterized in that the mass ratio of DVB to cellulose is from 1:2 to 1:

4.

13. The process according to any one of claims 10 to 12, characterized in that the polymerization in step (D) is carried out at a temperature in the range from 60°C to 120°C.

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