[0001] The present invention relates to a process for the quantification and analysis of microplastics contained in aqueous matrices, comprising the magnetic separation of microplastics by the interaction of said microplastics with magnetic iron material particles, forming microplastic/magnetic iron material aggregates, the selective oxidation of the particles of a non-plastic organic nature, and the quantification and/ of the separated microplastics.
1. A process for determining parameters for the quantification of microplastics in an aqueous matrix comprising microplastics and non-plastic organic particles, and optionally inorganic particles, the process comprising: a1) providing a first sample of the aqueous matrix comprising microplastics, non-plastic organic particles, and optionally inorganic particles, b1) adding magnetic iron material particles to the aqueous matrix provided in step a1) to form microplastic/magnetic iron material particle aggregates and to form non-plastic organic particle/magnetic iron material particle aggregates, c1) separating the formed aggregates and the free magnetic material particles from the mixture of step b1) by applying a magnetic field, d1) subjecting the aggregates and the free magnetic iron material particles separated in step c1) to a step of drying, e1) determining the weight of dry solids of step d1), obtaining parameter A, f1) preparing an aqueous suspension of the aggregates and the free magnetic iron material particles obtained in step d1), g1) subjecting the aqueous suspension prepared in step f1) to a microwave-assisted Fenton process, h1) separating the aggregates and the free magnetic material particles present in the aqueous suspension resulting from step g1), preferably by means of filtration, i1) subjecting the aggregates and the free magnetic iron material particles separated in step h1) to a step of drying, j1) determining the weight of dry solids in step i1), obtaining parameter AF, k1) subjecting the aggregates and the free magnetic material particles separated in step i1) to a step of combustion, and I1) determining the weight of solids obtained after step k1), obtaining parameter AFM. 2. A process for determining parameters for the quantification of microplastics in an aqueous matrix comprising microplastics and non-plastic organic particles, and optionally inorganic particles, the process comprising: a2) providing a first sample of the aqueous matrix comprising microplastics, non-plastic organic particles, and optionally inorganic particles, b2) separating the solids from the sample of step a2), preferably by means of filtration, c2) subjecting the solids separated in step b2) to a step of drying, d2) determining the weight of dry solids of step c2), obtaining parameter ST<M>, e2) subjecting the dry solids of step c2) to a step of combustion, and f2) determining the weight of solids obtained after step e2), obtaining parameter SI<M>, g2) providing a second sample of the aqueous matrix comprising microplastics, non-plastic organic particles, and optionally inorganic particles, h2) adding magnetic iron material particles to the aqueous matrix provided in step g2) to form microplastic/magnetic iron material particle aggregates and to form non-plastic organic particle/magnetic iron material particle aggregates, i2) separating the formed aggregates and the free magnetic material particles from the mixture of step h2) by applying a magnetic field, j2) preparing an aqueous suspension of the aggregates and the free magnetic iron material particles separated in step i2), k2) subjecting the aqueous suspension prepared in step j2) to a microwave-assisted Fenton process, l2) separating the aggregates and the free magnetic material particles present in the aqueous suspension resulting from step k2), preferably by means of filtration, m2) subjecting the aggregates and the free magnetic iron material particles separated in step 12) to a step of drying, n2) determining the weight of dry solids in step m2), obtaining parameter STNOX<A>, o2) subjecting the aggregates and the free magnetic material particles separated in step m2) to a step of combustion, p2) determining the weight of solids obtained after step o2), obtaining parameter SI<A>, q2) filtering the residual aqueous fraction obtained after the separation of step i2), r2) subjecting the solids separated in step q2) to a step of drying, s2) determining the weight of dry solids of step r2), obtaining parameter ST<SN>, and t2) subjecting the dry solids of step r2) to a step of combustion, u2) determining the weight of solids obtained after step t2), obtaining parameter SI<SN>. 3. The process according to claim 1 or 2, wherein the weight of the magnetic iron material particles which is added to the aqueous matrix in steps b1) or h2) is 0.1 to 20 times the weight of particles in suspension of the aqueous matrix provided in steps a1) or g2), respectively. 4. The process according to any of the preceding claims, wherein the magnetic iron material comprises an iron species selected from the group consisting of Fe(II), Fe(III), metallic Fe, and a mixture thereof, preferably the magnetic iron material is magnetite. 5. The process according to any of the preceding claims, wherein the average diameter of the magnetic iron mineral particles is comprised between 0.05 and 10 µm, preferably between 0.1 and 0.3 µm. 6. The process according to any of the preceding claims, wherein the microplastics are selected from the group consisting of polystyrenes (PS), polyethylene terephthalates (PET), polyethylenes (PE) including high-density polyethylenes (HDPE) and low-density polyethylenes (LDPE), polyvinyl chlorides (PVC), polypropylenes (PP), polycarbonates (PC) and polyurethanes (PU), and mixtures thereof. 7. The process according to any of the preceding claims, wherein the mixture obtained in steps b1) or/and h2) are subjected to stirring before performing steps c1) or/and i2), respectively, preferably wherein the stirring is mechanical or magnetic stirring, more preferably mechanical stirring. 8. The process according to any of the preceding embodiments, wherein the separation of steps c1) and/or i2) is performed using magnets or electromagnets. 9. The process according to any of the preceding claims, wherein in steps g1) or k2) hydrogen peroxide and an iron salt are added, preferably hydrogen peroxide and an iron salt selected from the group consisting of iron nitrate, iron chloride, iron sulfate, and mixtures thereof, more preferably hydrogen peroxide and iron nitrate. 10. The process according to claim 9, wherein the iron salt concentration in the aqueous suspension of steps g1) or k2) is in the range of 1 mg/L to 1000 mg/L and/or the hydrogen peroxide concentration in the aqueous suspension of steps g1) or k2), respectively, is in the range of 10 mg/L to 100 g/L. 11. The process according to any of the preceding claims, wherein step g1) or k2) is performed with a microwave power in the range of 50 to 1500 W and/or for a time in the range of 1 s to 2 h. 12. The process according to any of the preceding claims, wherein the pH of the aqueous suspension of steps g1) and/or k2) is adjusted in the range of 2 to 4. 13. The process according to any of the preceding claims, wherein the combustion of steps k1), e2), o2), and/or t2) is performed by subjecting the solids to a temperature of between 500°C and 600°C for 1 to 4 hours. 14. A process for the quantification of microplastics in an aqueous matrix comprising microplastics and non-plastic organic particles, and optionally inorganic particles, the process comprising: I-1) performing steps a1)-l1) of the process for determining parameters according to claims 1 and 3-13 for determining parameters A, AF, and AFM; II-1) calculating the weight of microplastics (MP<A>) by means of equation 1: MP A = A − AFM − MO NP , A <img class="EMIRef" id="0bd2fe61-1657-4a03-b242-4fdbe7d62022-ib0036" /> wherein A is the weight of solids determined in step e1) of the process according to claims 1 and 3-13, AFM is the weight of solids determined in step l1) of according to claims 1 and 3-13, MO<NP,A> is calculated by means of equation 2 MO NP , A = A − AF ∗ 1 a <img class="EMIRef" id="0bd2fe61-1657-4a03-b242-4fdbe7d62022-ib0037" /> wherein A is the weight of solids determined in step e1) of the process according to claims 1 and 3-13, AF is the weight of solids determined in step j1) of the process according to claims 1 and 3-13, and a is a number between 0.7 and 1, preferably between 0.8 and 0.9, most preferably 0.8. 15. A process for the quantification of microplastics in an aqueous matrix comprising microplastics and non-plastic organic particles, and optionally inorganic particles, the process comprising: I-2) performing steps a2)-u2) of the process for determining parameters according to claims 2-13 for determining parameters ST<M>, SI<M>, STNOX<A>, SI<A>, ST<SN>, and SI<SN>; II-2) calculating the weight of microplastics (MP<M>) by means of equation 3: MP M = % MP ⋅ SO A / 100 <img class="EMIRef" id="0bd2fe61-1657-4a03-b242-4fdbe7d62022-ib0038" /> wherein %MP is calculated by means of equation 4 % MP = 1 − 1 RMPSO + 1 ⋅ 100 <img class="EMIRef" id="0bd2fe61-1657-4a03-b242-4fdbe7d62022-ib0039" /> wherein RMPSO is calculated by means of equation 5 RMPSO = 1 − PPSO a ⋅ 100 / PPSO a ⋅ 100 <img class="EMIRef" id="0bd2fe61-1657-4a03-b242-4fdbe7d62022-ib0040" /> wherein a is a number between 0.7 and 1, preferably between 0.8 and 0.9, most preferably 0.8, and PPSO is calculated by means of equation 6 PPSO = SO A + SI A − STNOX A SO A ⋅ 100 <img class="EMIRef" id="0bd2fe61-1657-4a03-b242-4fdbe7d62022-ib0041" /> wherein STNOX<A> is the weight of solids determined in step n2) of the process according to claims 2-13, SI<A> is the weight of solids determined in step p2) of the process according to claims 2-13, and SO<A> is calculated by means of equation 7 SO A = SI SN + SI A − M ⋅ ST M − SI M SI M − ST SN − SI SN <img class="EMIRef" id="0bd2fe61-1657-4a03-b242-4fdbe7d62022-ib0042" /> wherein SI<A> is the weight of solids determined in step p2) of the process according to claims 2-13, SI<SN> is the weight of solids determined in step u2) of the process according to claims 2-13, ST<SN> is the weight of solids determined in step s2) of the process according to claims 2-13, M is the weight of magnetic material particles added in step h2) of the process according to claims 2-13, ST<M> is the weight of solids determined in step d2) of the process according to claims 2-13, and SI<M> is the weight of solids determined in step f2) of the process according to claims 2-13.