Method for analysis of plastic particles

Abstract

The invention relates to the isolation and staining of plastic particles in food. Heating particles after analysis and repeating the analysis allows to determine non-plastic particles in the sample. The use of filters with a well-defined and homogeneous pore diameter results in a correct size determination of plastic particle fractions.

Description

[0001] METHOD FOR ANALYSIS OF PLASTIC PARTICLES

[0002] FIELD OF THE INVENTION

[0003] The invention relates to detection and analysis of plastic contamination in for example food and beverages.

[0004] BACKGROUND

[0005] Microplastics, defined in the art as plastic particles in the 5mm-l pm size range, and nanoplastics, defined in the art as plastic particles in the 1 nm -1000 nm size range, are described in literature as a significant environmental and health concern. Since 1950, more than 9 billion tons of plastics have been produced, among which more than 5 billion tons have been disposed as waste. It takes more than 300 years for plastics to degrade in the natural environment. During degradation, plastic waste fragments into smaller and smaller pieces and leaches out hazardous chemicals. Besides the unintentionally made microplastics, plastic microbeads are widely applied to personal care and house-hold products. Eventually, they enter the sewage system and then into the water system. These minuscule plastic fragments have infiltrated ecosystems and found their way into the food chain.

[0006] Microplastics can enter human gastrointestinal (GI) tract via ingestion. According to a recent report by WWF and the University of Newcastle, an average adult ingests 5 grams of microplastics weekly, equivalent to the weight of a credit card, or 250 grams in a year. So far, microplastics have been reported in food and water, and recently in human placenta. Although their impact on human health is not yet fully understood, microplastics are found to be associated with serious diseases such as cancer, immune system disruption, childbirth defects, diabetes, digestive system dysfunction, inflammation. The prevalence and persistence of microplastics have raised alarms about their long-term impact on human health.

[0007] As pointed out by the European Food Safety Authority (EFSA), there is not yet an effective analytical method for microplastics to assess their presence, identity, and to quantify their amount in food. Microplastic particles smaller than 150pm are the most concerning for food safety reasons, as they are small enough to be ingested unintentionally and are known to trigger inflammation and immune responses in the human GI tract. Microplastic particles smaller than 10pm can cross the biological barriers and can translocate into the edible parts of plants and animals for food consumption. The particles smaller than 300nm could enter the blood and organs of human body posing a health risk. In a recent interlaboratory comparison, labs across the globe applied a variety of analytical methods (MS-GC, FTIR, Raman, SEM, optical microscopy, fluorescence microscopy, NMR, HPLC, etc.) and reported a broad variation spanning 4 orders of magnitudes for the measured particle concentration of a standardized PET in water sample, ranging from 50 to 918,000 plastic particles per litre versus the indicative particle concentration 800±150 particles per litre. Lacking a robust analytical protocol for quantification of microplastics makes it impossible to directly compare the reported results of microplastics in literature and poses a significant challenge for understanding the environmental and health impact of microplastics.

[0008] Among the existing analytical approaches, micro-FTIR and micro-Raman have been widely applied to analyse microplastics down to 10 microns. Scanning electron microscopy could be applied to image particles down to the nanometre sizes, but with limited capability for chemical composition analysis. Identification of microplastics using SEM often relies on EDS to distinguish carbon-rich particles from particles made of other elements. The method, however, could not exclude any other carbonaceous micropollutants such as black-carbon or brown-carbon particles from the analysis. Although easy to implement, fluorescence microscopy has not been widely adopted for detecting microplastics due to the uncertain staining selectivity for plastic particles. Presence of other organic matters such as proteins, lipids could introduce artifacts and background signals that will interfere with those from stained particles.

[0009] Microplastic analysis in food is further complicated by the complicity of food itself. One will have to firstly remove the nutritious substances that may interfere with microplastics analysis using digestion treatments. Besides the potential artifacts introduced by the harsh chemical treatment at elevated temperatures, the different digestion protocols used for different types of food make the data not directly comparable.

[0010] Ashiq et al. (2023) Front. Environ. Sci. Eng 17, 124 disclose methods to measure microplastics in stormwater detention ponds. SUMMARY OF THE INVENTION

[0011] The present invention comprises of a method for separating and analysing plastic particles from food or beverage products. The method comprising the general steps of (1) an optional sample homogenization depending on the type of sample, (2) an optional filtration to remove coarse particles or food structures, (3) an optional digestion, (4) filtration to isolate particles with a desired size range for analysis, (5) staining, (6) imaging and analysis, (7) plastic content confirmation.

[0012] Herein in the digestion (3) step biological and chemical agents may be used. Biological agents such as enzymes or chemical agents (e.g. acids or bases) may be used to remove biological materials under these conditions, thereby avoiding any artifacts resulting from harsh treatments. After such digestion, the samples can go through one or several filtration steps to select particles of the targeted size ranges (>10pm, 10-lpm, 1-0. lpm).

[0013] Particles residing on the filters are stained with a one or more fluorescent dyes that have a high affinity to plastics. With the fluorescent staining, one can image and analyse the quantity and sizes of the isolated particles using fluorescence microscopy. In addition, by looking at the fluorescence emission spectra and lifetime, different types of plastics can be identified. In a further step, the sample on the filter undergoes a gradual thermal heating treatment. By monitoring the morphological evolution and heat decomposition of the particles, one can distinguish plastic particles from non-plastic particles in the previous fluorescence analysis and identify different plastic types based of their different melting points. The identification of different types of plastics can be carried out based on their melting points even without staining with a dye.

[0014] As the sample resides on the filter during the thermal heating, the filter being used is resistant to temperatures up to 400, 450 or 500 °C. Examples of suitable filter material are silicon based filters, aluminium or other metal based filters, and ceramic filters.

[0015] The invention relates particularly to the isolation and staining of plastic particles in food and food ingredients, and in beverages, including water, packaged in plastic bottles, as well as in glass bottles.

[0016] The methods of the present invention are also applicable for other types of samples such as plastic particle detection in environmental monitoring, wastewater treatment, biomedical research, detection in tissue samples or body samples such urine or blood. The same principle can be applied wherein the sample is processed such that isolate particles with a diameter below 100 pm are isolated, stained for the presence of plastic labels, and subsequently heated to detect the background signal by nonspecific staining of non-plastic particles.

[0017] Heating particles after analysis and repeating the analysis allows to determine nonplastic particles in the sample.

[0018] The use of filters with a defined and homogeneous pore diameter results in a correct size determination of plastic particle fractions.

[0019] Embodiments of the invention are further summarized in the following statements: 1. A method of determining plastic particles in a food or beverage sample comprising the steps of: a. Providing a food or beverage sample free from packaging material, b. Optionally homogenizing the food or beverage sample, c. Optionally performing a digestion on the food or beverage sample, d. Filtering the food or beverage sample to isolate particles with a diameter below 100 pm, e. Staining isolated particles of step d, f. Identifying particles stained in step e), g. Heating the stained particles of step e) thereby deforming or decomposing the plastic particles , h. Staining particles remaining after step g) i. Identifying stained particles of step h), j. Based on the identification in step f) and i) determining the number of plastic particles.

[0020] The method allows identifying the number of plastic particles in the method allowing to determine the concentration in the food or beverage sample.

[0021] Optionally the method allows to identify the type of plastic.

[0022] Depending on the sample the homogenizing step and digestion step can be omitted in case of for example bottled water and other liquids.

[0023] Sample can refer to a food or beverage ready for consumption, or can refer to an ingredient to be used in a food or beverage.

[0024] The method can be performed in a continuous setting whereby the steps or performed consecutively and in the same place. Alternatively, the homogenization and digestion, the coarse filtration of step d, optional further fractionation and the staining and analyses can be done at separate locations.

[0025] 2. The method according to statement 1, wherein particles with a diameter below 100 pm, are further fractioned by using one more of a filter with a pore diameter of 10 pm, 1 pm, and 100 nm.

[0026] 3. The method according to statement 2, wherein a filter is made of a thermally stable material ( i.e. silicone, ceramic, or of aluminium oxide).

[0027] Filters with a well-defined and homogeneous pore diameter and resistant against a temperature up to 400 or 500 °C can be used as well.

[0028] 4. The method according to any one of statements 1 to 3, wherein during step e to j the particles reside on the filter used to isolate them.

[0029] 5. The method according to any one of statements 1 to 4, wherein the filtered particles are stained using one or more fluorescent dyes.

[0030] 6. The method according to any one of statements 1 to 5, wherein analysis is performed using fluorescent microscopy.

[0031] 7. The method according to statement 6, wherein the fluorescent microscopy is used to analyse fluorescence intensity, fluorescence emission spectra or fluorescence lifetime of the particles.

[0032] 8. The method according to statement 6 or 7, wherein the particles are excited in the wavelength range of 405nm - 532nm during fluorescence microscopy.

[0033] 9. The method according to statement 6 or 7, wherein detection of plastic particles is done in the wavelength range of 450 nm to 700 nm.

[0034] 10. The method according to any one of statements 1 to 7, further comprising the step of using multiphoton excitation to determine white light emission from carbonaceous materials.

[0035] 11. The method according to any one of statements 1 to 9 wherein the digestion is an enzymatic or chemical digestion.

[0036] 13. The method according to statement 1, wherein the presence of plastic is confirmed by performing thermal heating.

[0037] 14. The method according to any one of statements 1 to 15 wherein the confirmed plastic content is further characterized into different types of plastics.

[0038] 15. A device for analysing plastic particles in a food or beverage sample comprising :

[0039] An optional unit for mechanically homogenizing a food or beverage sample,

[0040] An optional unit for chemical or enzymatic digestion of a food or beverage sample, A filtration unit for retaining particles with a diameter below 100 pm, 16. A unit for staining and detecting said particles on a support,

[0041] A unit for heating said particles on said support to a temperature modifying or decomposing plastic particles.

[0042] DETAILED DESCRIPTION OF THE INVENTION

[0043] Figure 1 : Flowchart of an embodiment of the present invention.

[0044] Figure 2: Fluorescence from NR-stained plastics can be used to distinguish different plastic types based on (a) emission spectra and (b) fluorescence lifetime.

[0045] Figure 1 gives a general overview of the methods of the invention. A food or beverages sample is homogenised, if necessary. A filtration step is performed to remove larger particles while allowing the passage of microplastics. Before or after the filtration an chemical or enzymatic treatment can be performed to e.g. further reduce the particle size of non-plastic material, reduce the viscosity of the sample or to degrade lipids or carbohydrates. The fraction with particle size below 100 pM is further fractionated by filtration over filters with decreasing pore size, where plastic particles and other small particles (organic and / or non-organic) remain on the filter.

[0046] Staining with a dye already allows to identify the plastic particles which reside on the filter.

[0047] The optical signal from a fluorescent dye can be used for determining fluorescence intensity, spectrum and lifetime.

[0048] Upon heating of the filters plastic particles will melt and degrade.

[0049] During the heating plastic particles can be identified and classified by their glass transition temperature, melting temperature, and differences in properties of the dye upon heating.

[0050] Non-plastic heat resistant particles which falls-positively stained with the dye will not degrade.

[0051] Upon a second staining this background will stain again, while there will be no signal from the degraded plastic.

[0052] "Plastic particles" in the context of the present invention relates to particles with a diameter less than 100 pm.

[0053] A specific embodiment hereof are particles with a diameter between 100 pm and 0.1 pm. Depending on the type of filters being used fractions can be isolated with a diameter below 100 pm, below 10 pm, below 1 pm; with a diameter between 100 pm and 10 pm, between 100 pm and 1 pm, between 100 pm and 100 nm; with a diameter between 10 pm and 1 pm, between 10 pm and 100 nm; and with a diameter between 1 pm and 100 nm.

[0054] Different embodiments of the methods of the invention are now disclosed in more detail.

[0055] (1) Homogenization steps: This breaks a food or beverage sample comprising solid parts into smaller pieces for analysis and comprises in a specific embodiment of the following steps: i. Collecting the food or beverage samples and remove any packaging materials or non-edible parts from the sample.

[0056] II. Weighing the food or beverage sample and dilute with water (eg mix 10 g of food with 10 mL water). ill. Blending the food or beverage sample until it reaches a consistent and uniform texture. iv. Filtering the food or beverage with a (eg. stainless steel wire) filter to remove larger particles. For liquid samples, typically a filter of with a pore diameter of at least 100 pm size is used and for samples comprising solid content, typically a filter with a pore diameter of at least 1mm is used v. The filtered liquid is further processed using enzymatic digestion.

[0057] (2) (Optional step) An additional and optional filtration to remove coarse particles or food structures may be carried out. In this step, stainless steel filters of varying pore diameter are used to remove the coarse particles and food structures. The filter pore diameter will be selected depending on the texture and nature of the food. If the sample for analysis is in a liquid form, this step could be skipped.

[0058] The purpose of this step is to remove the coarse particles that may enter the next digestion step. As larger particles are more difficult to be digested by enzymes or would require longer times for the enzymes to fully digest them. By removing the coarse particles, we expect to shorten the time duration and quantity of enzymes required in the digestion step. (3) digestion of organic matter in food or beverage samples may be done using biological and / or chemical agents. Biological agents such as enzymes may be used to perform enzymatic digestion of lipids and proteins may be done using lipase and proteinase-K. Enzymatic digestion take place under mild conditions and do not cause any artifacts on the plastic particles. The quantity and types of enzymes will depend on the organic (nutrition) content such as lipids, proteins, cellulose, carbohydrates, etc.

[0059] The purpose of this step is to remove the organic (nutrition) content that may interfere with the staining and fluorescence imaging steps, particularly to remove proteins and lipids that may be stained by fluorescent dyes.

[0060] In certain embodiments, chemical digestion may be performed using i.e. alkali (NaOH, KOH) or oxidizing agents (H2O2) to remove any remaining organic matter from the food or beverage samples.

[0061] An example of a digestion method comprises the following steps: i. OAdd lOOpL of digestion buffer (Triton X-100 2.5%) to the homogenized filtered food or beverage sample (1 mL) to create the desired enzymatic conditions.

[0062] II. Add 55 mg of lipase (Sigma Aldrich) to the sample. This will provide a final concentration of 5% lipase in the sample for efficient breakdown of lipids. ill. Add proteinase-K (ThermoFisher Scientific) to the sample with a final concentration of 100 pg / ml. iv. Vortex the samples for 30 seconds to mix it well. v. Sonicate the sample for 5 minutes at 40 kHz. vi. Incubate the sample with the enzymes for 16 hours at 50 degrees Celsius. Sufficient time and elevated temperature will allow digestion to occur.

[0063] Enzymatic digestion conditions may be optimized depending on the sample type. Additionally, samples may also be treated with 10 to 30 % H2O2 from room temperature to 70 ° C to oxidize organic matter.

[0064] In certain embodiments, extra steps are used. For example, in milk samples a calcium chelating agent such as EDTA.

[0065] (4) Filtration of food or beverage samples for analysis. In this step of filtration, vacuum filtration of samples is carried out to analyse the plastic particles detected on filter samples.

[0066] The use of micro-fabricated silicon filter allows to guarantee a robust analysis outcome. Silicon filters further have a flat surface, and good contract in transmission microscopy. In addition, these filters also do not get stained with fluorescent dye, resulting in lower background signal and provides better sensitivity.

[0067] Herein, micro-fabricated silicon filters that have well-defined and homogeneous pore diameter are used to collect plastic particles in the defined size ranges. The size ranges can be configured by using filters with corresponding pore diameter. For smaller pore diameters (below 1 micron), aluminium oxide filters may be used. Filters can be purchased from SmartMembranes GmbH. However, it is not necessary to utilize silicon or alumina filters. Filters made of other materials with flat surface and uniform pore size can be employed.

[0068] The samples after the filtration step and before the staining step can also be suitable for alternative analysis methods such as FTIR, Raman, and Scanning Electro Microscopy.

[0069] (5) Staining using fluorescent dye(s). Numerous dyes can be used for fluorescent tagging of custom-made plastic particles, enhancing the range of observable plastic shapes and polymer compositions. Among these dyes are Nile Red and its derivatives, 4-Dimethylamino-4'-nitrostilbene (DANS), oil red EGN, Rose Bengal, Neutral Red, Trypan Blue, and a selection of textile dyes available in the market. Although these dyes have demonstrated their effectiveness in staining plastic particles, their affinities for distinct polymers differ. Notably, Nile Red stands out as the most commonly employed dye for plastic staining.

[0070] (6) This staining step makes plastic particles visible for use in fluorescence microscopy.

[0071] In certain embodiments, a combination of a mixture of various fluorescent dyes may be used to ensure different types of plastics are labelled with a reasonable signal-to- background ratio;

[0072] In certain embodiments, analysis may be performed wherein multiple fluorescence signals are analysed such as intensity, emission spectra, and lifetime to distinguish different plastic types, this would work both in the single-dye settings and the multidye settings.

[0073] An example of a staining comprises the steps of: i. Prepare a solution of a one or more fluorescent dyes such as Nile Red (Sigma Aldrich) by dissolving the dye in an appropriate solvent DMSO / PBS (50 / 50). The concentration of the solution is 10 pg / mL

[0074] II. Keep the filter with the captured plastic particles (from the previous filtration step) inside the microanalysis filter holder. ill. Add 1 mL of the fluorescent dye such as Nile Red solution to cover the filter and plastic particles completely. Ensure that the plastic particles are immersed in the staining solution. iv. Remove the filter from the filter holder and incubate it on a heating plate at 70 °C for 1 hour to allow the fluorescent dye such as Nile Red dye to bind to the plastic particles. The elevated temperature helps the dye to get inside the plastic particles. v. Insert the filter again in the filter holder and rinse it with a 10 mL ultrapure to remove any dye residues on the filter. This helps to decrease the background during fluorescence microscopy imaging. vi. the steps may be repeated or carried out with a combination of fluorescent dye such as NR with other dyes i.e., DANS (4-Dimethylamino-4'-nitrostilbene). This helps in distinguishing different plastics efficiently.

[0075] (7) Fluorescence microscopy imaging and analysis. In certain embodiments, images of (i) fluorescence intensity, or (ii) fluorescence emission spectra, or (iii) fluorescence lifetime may be acquired for analysis.

[0076] Instrument used :

[0077] Optical microscope (Leica Sp8 X) with multiphoton and white light lasers, and hybrid detectors.

[0078] In the experimental setting, we used 488 nm excitation, and emission was detected in two different windows 520-570 nm, and 600-650 nm. a range of wavelengths to excite the plastic particles and detect their fluorescence emission is used. For example, other possible excitation wavelengths include 405 nm, 514 nm, and 532 nm. Whereas, detection can be performed in the wavelength range from 450 nm to 700 nm. This detection window can be divided into different channels for the quantification of their intensities.

[0079] In an example, Fluorescence imaging comprises the following steps: i. After placing the sample on the microscope stage focus on the samples using an objective lens ( i.e. 40x air objective (NA 0.60)).

[0080] II. After focusing using the binoculars using Brightfield, move to the fluorescence mode of the microscope for image acquisition. Adjust the focus to optimize the fluorescence signal from the plastic particles. ill. Once the plastic particles are in focus and the fluorescence settings are optimized, capture images of the stained plastic particles using LAS X software. The images are acquired using a pixel format of 512x512 pixels, 0.569x0.569 pm2pixel size, and 3.16 ps pixel dwell time. iv. Take multiple images at different areas of the sample to ensure a representative view of the plastic particles present on the filters. v. By focusing on single particles, also collect the emission spectra in the spectral range from 500 to 700 nm. vi. In addition, the temporal response of single particles is also recorded using fluorescence lifetime imaging (FLIM). vii. The acquisition of images is carried out for 50 frames per measurement. This system is integrated with a phasor analysis software, which allows the representation of decay lifetime components on a 2D vector plot.

[0081] In certain embodiments, an additional imaging may be performed to exclude possible contamination with carbonaceous particles:

[0082] In order to exclude the possibility of contamination due to the presence of carbonaceous materials (i.e., carbon black, black carbon), we use multiphoton excitation to look at the white light emission from carbonaceous materials.

[0083] An example hereof comprises steps of: i. Turn on the multiphoton laser and set the wavelength at 810 nm.

[0084] II. Use the appropriate filters to detect the WL emission in two different channels (Chi : 400-410 nm, and Ch2: 450-650 nm). ill. Acquire images similar to the image acquisition procedure for fluorescence imaging. WL emission from carbonaceous particles will generate a very strong signal in both channels.

[0085] (8) Confirmation of the presence of plastic particles content in a food or beverage product is by thermal heating . Thermal heating is used to eliminate the possibility of false positives from inorganic particles present in food or beverage samples. Most plastics have melting points below 400 Celsius degrees, whereas inorganic particles have much high melting temperatures. Therefore, heating the filter samples above 400 Celsius degrees will help to melt the plastic particles for their accurate quantification.

[0086] Also the dye that has been used for the staining will be decomposed at this temperature.

[0087] In this step, the entire food or beverage sample under analysis undergoes a thermal heating process, wherein the environmental temperature is increased from room temperature to temperatures up to 400 Celsius degrees. As different materials have different melting temperatures, the morphological changes of the particles while elevating the temperature can be monitored. The heating is done using a thermal stage for microscopes, detection can be performed by optical microscopes as well as electron microscopes. The upper temperature is selected to destroy certain types of plastics for analysis.

[0088] During the heating of particles the identity of the particle can be deduced from the melting point, as well as from the glass transition temperature (Tg). The structural change at Tg has an impact on the binding of a dye giving a different signal in fluorescence. This phenomenon is well described for solvatochromic dyes . This change in fluorescence in combination with the melting temperature can more accurately identify the type of plastic. Melting and glass transition temperatures of exemplary plastic are shown in the below table.

[0089] Table 1. Melting points and glass transition temperatures of common plastics

[0090] As an example thermal heating and staining comprising steps of: i. After microscopy analysis, keep the silicon membrane filters in the sample holder.

[0091] II. Heat the baking oven to above the melting point of interested type of plastic such as 400 Celsius degrees. ill. Place the sample holder (with three samples) inside the baking oven. iv. Heating, in the range of 1- 12hrs depending on the type of plastic particles. v. Remove the filters from the oven and let them cool to room temperature. vi. Stain the filters again by immersing them in a fluorescent dye such as Nile Red solution prepared earlier. vii. During heating in the oven, monitor the morphological change at least every 30 minutes. viii. By performing this procedure on different types of reference plastic particles, different types of plastics can be identified and further characterized.

[0092] (9) In certain embodiments, re-staining (optional) may be required, repeat step (5).

[0093] (10) Microscopy imaging. Follow the similar steps as microscope imaging 1 to discard the presence of fluorescently stained non-plastic particles after heating. So that the quantity of plastic particles can be determined by subtracting these from the imaging results of step (6).

[0094] (11) Steps (7) to (9) may be repeated multiple times with different heating upper temperatures to confirm different types of plastic particles.

Claims

CLAIMS1. A method of determining plastic particles in a food or beverage sample the method comprising the steps of: a. providing a food or beverage sample free from packaging material, b. optionally homogenizing the food or beverage sample, c. optionally performing, before or after the filtration of step d), a digestion on the food or beverage sample, d. filtering the food or beverage sample with a filter to isolate particles with a diameter below 100 pm, e. staining isolated particles of step d), f. identifying particles stained in step e), g. heating the stained particles of step e) thereby deforming or decomposing the plastic particles, h. staining particles remaining after step g), i. identifying stained particles of step e), and j. based on the identification in step f) and i) determining the number of plastic particles.

2. The method according to claim 1, wherein particles with a diameter below 100 pm, are further fractioned by using one or more of a filter with a pore diameter of 10 pm, 1 pm and 100 nm.

3. The method according to claim 2, wherein the filter has uniform pore sizes.

4. The method according to claim 2, wherein the filter is resistant to temperatures up to 500 °C.

5. The method according to claim 1, wherein the filter is a silicon, a ceramic or an aluminium oxide filter.

6. The method according to any one of claims 1 to 3, wherein during step e) to j) the particles reside on the filter used in step d) to isolate the particles.

7. The method according to any one of claims 1 to 4, wherein the filtered particles are stained using one or more fluorescent dyes.

8. The method according to any one of claims 1 to 5, wherein analysis is performed using fluorescence microscopy.

9. The method according to claim 6, wherein the fluorescence microscopy is used to analyse fluorescence intensity, fluorescence emission spectra, or fluorescence lifetime of the particles.

10. The method according to claim 6 or 7, wherein the particles are excited in the wavelength range of 405nm - 532 nm during fluorescence microscopy.

11. The method according to claim 6 or 7, wherein detection of plastic particles is done in the wavelength range of 450 nm to 700 nm.

12. The method according to any one of claims 1 to 7, further comprising the step of using multiphoton excitation to determine white light emission from carbonaceous materials.

13. The method according to any one of claims 1 to 9, wherein the digestion is an enzymatic digestion.

14. Use of a device for comprising :-An optional unit for mechanically homogenizing a food or beverage sample, -An optional unit for chemical or enzymatic digestion of a food or beverage sample,-A filtration unit for retaining particles with a diameter below 100 pM,-A unit for staining and detecting said stained particles on a support,-A unit for heating the retained particles on said support to a temperature modifying or decomposing plastic particles, for analysing plastic particles in a food or beverage sample.

15. The use according to claim 12, wherein the unit for heating can heat up to 500 °C.

16. The use according to claim 12, comprising a unit for mechanically homogenizing a food or beverage sample and / or a unit for chemical or enzymatic digestion of a food or beverage sample.

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