A spectroscopic method for quantitatively determining the content of microplastics and organic matter in a mixed system

Abstract

The present application relates to a kind of quantitative determination mixed system microplastic and the spectroscopy method of organic matter content, comprising: the establishment of initial NOM and PSMPs system or the establishment of NOM-F and PSMPs system after goethite adsorption, the initial NOM and PSMPs system includes HA or FA and PSMPs binary system and HA, FA and PSMPs ternary system;The NOM-F and PSMPs system after goethite adsorption includes HA-F or FA-F and PSMPs binary system and HA-F, FA-F and PSMPs ternary system.This method is according to the difference of different types of organic matter and microplastic ultraviolet-visible light absorption spectrum, using spectroscopy distinguishes and then quantifies respective content, this method is easy to operate, test cost is low, especially for the small particle size microplastic and organic matter system that is difficult to separate by centrifugation or filtration etc.It has good quantitative measurement effect.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering and relates to detection technology, particularly a spectroscopic method for quantitatively determining the content of microplastics and organic matter in a mixed system. Background Technology

[0002] Currently, plastic products are used in various industries. While bringing convenience to society, they have also caused a series of plastic pollution problems due to low recycling rates and management errors. Large amounts of plastic are continuously released into the environment, gradually decomposing and breaking down under the influence of weathering, ultraviolet radiation, and biodegradation, forming microplastics (<5 mm) and nanoplastics (1-100 nm). Early research on microplastics (nanoplastics) mainly focused on marine and freshwater environments. Statistical data shows that there are more than 5 trillion plastic fragments in the ocean (weighing approximately 250,000 tons); and more than 400,000 tons of microplastics may enter the terrestrial environment each year.

[0003] Microplastics are small in size and highly mobile, making them easily ingested by organisms at the bottom of the food chain, leading to bioaccumulation and biomagnification, which in turn causes changes in cell membrane structure and metabolic and circulatory disorders. In addition, microplastics are highly hydrophobic, making them potential adsorbents for organic pollutants and heavy metals, further aggravating their pollution capacity.

[0004] Organic matter and iron-containing minerals are abundant in soil. Natural organic matter (NOM) is generally divided into humic matter (large organic molecules with indefinite structures) and non-humic matter (with well-defined structures, such as proteins, carbohydrates, and small organic acids). Among them, humic acid (HA) is a type of humic matter with a medium molecular weight, insoluble in acids (pH < 2) and soluble only in alkalis, while fulvic acid (FA) is a type of humic matter with a small molecular weight, soluble in both acids and alkalis. Studies have shown that HA can interact with microplastics through hydrophobic interactions and π-π bonds, and that microplastics adsorb HA at a higher rate than FA. Goethite is a common iron oxide in soil, and due to its high stability and large specific surface area, it is an important adsorbent for pollutants and organic matter in soil. Studies have indicated that the hydroxyl functional groups on the surface of goethite are beneficial for its adsorption of microplastics. For NOM, it can be adsorbed onto the surface of goethite through electrostatic interactions, hydrophobic interactions, ligand exchange interactions, complexation interactions, and hydrogen bonding interactions. Due to the chemical heterogeneity and polydispersity of NOM, when the two interact, HA with an intermediate molecular weight and FA with a larger molecular weight will be preferentially and selectively adsorbed onto the surface of goethite.

[0005] Currently, for the detection of commercial micro / nanoplastics in indoor experimental studies, fluorescence spectrophotometry and traditional ultraviolet-visible spectrophotometry (UV-Vis) are commonly used. The first method requires that the micro / nanoplastics be fluorescent, but not all micro / nanoplastics in the real environment are fluorescent. Therefore, UV-Vis is the preferred method for detecting non-fluorescent micro / nanoplastics. Because commercial micro / nanoplastics and NOMs are similar in size and mass density, and also have overlapping UV-visible absorption wavelengths, the traditional UV-Vis method for detecting the concentration of micro / nanoplastics in a micro / nanoplastics-NOM mixture is often interfered with by NOMs, making it impossible to accurately determine the concentration of each. Since NOMs and micro / nanoplastics often coexist, a UV-Vis method capable of determining the concentrations of both in a micro / nanoplastics-NOM mixture is needed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a simple, low-cost spectroscopic method for quantitatively determining the content of microplastics and organic matter in a mixed system.

[0007] The technical problem solved by this invention is achieved through the following technical solution:

[0008] A spectroscopic method for quantitatively determining the content of microplastics and organic matter in a mixed system, the method comprising: establishing an initial NOM and PSMPs system or establishing a NOM-F and PSMPs system after goethite adsorption, wherein the initial NOM and PSMPs system includes a binary system of HA or FA and PSMPs and a ternary system of HA, FA and PSMPs; wherein the NOM-F and PSMPs system after goethite adsorption includes a binary system of HA-F or FA-F and PSMPs and a ternary system of HA-F, FA-F and PSMPs.

[0009] Furthermore, the method for establishing the binary system of HA or FA and PSMPs specifically includes:

[0010] Because of the hydrophobic interactions and π-π bonds between NOM and PSMPs, the spectra of NOM and PSMPs cannot be simply superimposed to obtain the spectrum of the mixture. Therefore, two parameters are introduced. β and γ The formula for correcting the effect of the interaction between the two on the mixture spectrum is as follows:

[0011] (1)

[0012] in, The specific UV-Vis absorbance (L mgC) of the mixture at wavelength i represents the specific UV-Vis absorbance of the mixture. -1 cm -1 ); and The specific UV-Vis absorbance values ​​(L mgC) of NOM and PSMPs at wavelength i represent the specific UV-Vis absorbance values. -1 cm -1 (i.e., absorbance / TOC concentration); Represents the mass fraction of organic carbon in NOM in the mixture. Represents the mass fraction of organic carbon in PSMPs in the mixture; β and γ These represent the interaction factors of NOM and PSMPs, respectively.

[0013] Formula (1) can be further simplified as follows:

[0014] (2)

[0015] in, , Assuming β and γ The value remains constant across the entire wavelength range, meaning the interaction between the two does not alter the shape of their respective spectra. A and B can achieve this by adjusting TS within a selected wavelength range. MIX(i) The sum of the squares of the measured and calculated values ​​is minimized (Σ(TS) MIX(i) -TS MIX(i) (model) ) 2 The proportion of NOM in the binary system is obtained through fitting. Therefore, the content of NOM and PSMPs (mg / L) -1 ) can be and the total organic carbon content of the mixture ( The calculations are shown in formulas (3) and (4):

[0016] (3)

[0017] (4). [1]

[0018] Furthermore, the method for establishing the ternary system of HA, FA, and PSMPs specifically includes:

[0019] Analogous to binary systems, the spectral relationships between ternary mixtures of HA, FA, and PSMPs and pure substances are as follows:

[0020] (5)

[0021] The values ​​of A, B, and C in the formula can be determined by making them within a selected wavelength range. The sum of the squares of the measured and calculated values ​​is minimized (Σ(TS) MIX(i) -TS MIX(i)(model) ) 2The proportions of HA, FA, and PSMPs were obtained through fitting. f HA , f FA and f PSMPs That is , )and Finally, the concentrations (mg / L) of HA, FA, and PSMPs are obtained using formulas (6)-(8). -1 ).

[0022] (6)

[0023] (7)

[0024] (8). [2]

[0025] Furthermore, the specific steps of the method for establishing the binary system of HA-F or FA-F and PSMPs include:

[0026] The UV-Vis method is based on the differences in specific UV-Vis absorption spectra between substances in the system. Therefore, theoretically, the UV-Vis method for quantitative determination of NOM-F and PSMPs in a mixed system can be established by using the specific UV-Vis absorption spectra of NOM-F and PSMPs. However, in a three-phase system composed of iron oxide, NOM and PSMPs, NOM-F cannot be separated from the solution to obtain its spectrum. Therefore, in a binary system of NOM-F and PSMPs, the concentrations of both are still calculated using formulas (2)-(4).

[0027] Furthermore, the specific steps of the method for establishing the HA-F, FA-F, and PSMPs ternary system include:

[0028] Similar to the binary system, the concentrations of NOM-F and PSMPs in the ternary system are obtained by formulas (5)-(8).

[0029] The advantages and positive effects of this invention are:

[0030] This invention application provides a spectroscopic method for quantitatively determining the content of microplastics and organic matter in a mixed system. Based on the differences in the ultraviolet-visible absorption spectra of different types of organic matter and microplastics, the method distinguishes and quantifies their respective contents using spectroscopy. This method is simple to operate and has low testing costs. It has a good quantitative measurement effect, especially for small-particle-size microplastics and organic matter systems that are difficult to separate by methods such as centrifugation or filtration. Attached Figure Description

[0031] Figure 1This is a specific UV-Vis absorption spectrum of the initial NOM and PSMPs in this invention;

[0032] Figure 2 The initial UV-Vis absorption spectra and first derivative spectra of HA after selective adsorption and the initial HA are shown in the present invention.

[0033] Figure 3 These are specific UV-Vis absorption spectra of three replicate samples from the same mixing system of this invention;

[0034] Figure 4 The comparison results of the calculated recovery concentration and its additive concentration of HA and PSMPs-200 in the wavelength range of 231-600 nm in the embodiments of the present invention are shown.

[0035] Figure 5 The comparison results of the calculated recovery concentration and its added concentration of HA and PSMPs-400 in the 231-600 nm wavelength range in the embodiments of the present invention are shown.

[0036] Figure 6 The comparison results of the calculated recovery concentration and its added concentration of HA and PSMPs-COOH-200 in the wavelength range of 231-600 nm in the embodiments of the present invention are shown.

[0037] Figure 7 The results show the comparison between the calculated recovery concentration and the added concentration of FA and PSMPs-200 in the 231-600 nm wavelength range in the embodiments of the present invention.

[0038] Figure 8 The comparison results of the calculated recovery concentration and its added concentration of FA and PSMPs-COOH-200 in the 231-600nm wavelength range in the embodiments of the present invention are shown.

[0039] Figure 9 The results show the comparison between the calculated recovery concentrations of the initial HA, FA, and PSMPs-200 in the wavelength range of 231-600 nm and their added concentrations in the embodiments of the present invention.

[0040] Figure 10 The results show the comparison between the calculated recovery concentrations of the initial HA, FA, and PSMPs-COOH-200 in the wavelength range of 231-600 nm and their added concentrations in the embodiments of the present invention.

[0041] Figure 11 The comparison results of the calculated recovery concentration and its additive concentration of HA-F350 and PSMPs-COOH-200 in the wavelength range of 231-600 nm in the embodiments of the present invention are shown.

[0042] Figure 12The comparison results of the calculated recovery concentration and its additive concentration of HA-F350 and PSMPs-200 in the wavelength range of 231-600nm in the embodiments of the present invention;

[0043] Figure 13 The comparison results of the calculated recovery concentration and its additive concentration of FA-F250 and PSMPs-COOH-200 in the wavelength range of 231-600 nm in the embodiments of the present invention are shown.

[0044] Figure 14 The comparison results of the calculated recovery concentration and its additive concentration of FA-F250 and PSMPs-200 in the wavelength range of 231-600 nm in the embodiments of the present invention are shown.

[0045] Figure 15 The comparison results of the calculated recovery concentration and its added concentration of HA-F350, FA-F250 and PSMPs-COOH-200 in the wavelength range of 231-600 nm in the embodiments of the present invention are shown. Detailed Implementation

[0046] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0047] 1. Creation of UV-Vis Spectroscopic Fingerprinting

[0048] Ultraviolet-visible spectroscopy is a traditional and simple analytical method that obtains information about a substance by calculating the absorption energy of the analyte in the ultraviolet-visible light wavelength range (200-800 nm). Currently, the most commonly used commercial micro / nanoplastics in indoor experimental research are polystyrene (PS). However, there are differences in the ultraviolet-visible absorption spectrum curves of different types of NOM and polystyrene microplastics (PSMPs). Figure 1 Therefore, a spectroscopic method for the quantitative determination of NOM and PSMPs can be established based on this.

[0049] 1.1 Initial NOM and PSMPs System

[0050] 1.1.1 Binary system of HA or FA and PSMPs

[0051] Because of the hydrophobic interactions and π-π bonds between NOM and PSMPs, the spectra of NOM and PSMPs cannot be simply superimposed to obtain the spectrum of the mixture. Therefore, two parameters are introduced. β and γ The formula for correcting the effect of the interaction between the two on the mixture spectrum is as follows:

[0052] (1)

[0053] in, The specific UV-Vis absorbance (L mgC) of the mixture at wavelength i represents the specific UV-Vis absorbance of the mixture. -1 cm -1 ); and The specific UV-Vis absorbance values ​​(L mgC) of NOM and PSMPs at wavelength i represent the specific UV-Vis absorbance values. -1 cm -1 (i.e., absorbance / TOC concentration); Represents the mass fraction of organic carbon in NOM in the mixture. Represents the mass fraction of organic carbon in PSMPs in the mixture; β and γ These represent the interaction factors of NOM and PSMPs, respectively.

[0054] Formula (1) can be further simplified as follows:

[0055] (2)

[0056] in, , Assuming β and γ The value remains constant across the entire wavelength range, meaning the interaction between the two does not alter the shape of their respective spectra. A and B can achieve this by adjusting TS within a selected wavelength range. MIX(i) The sum of the squares of the measured and calculated values ​​is minimized (Σ(TS) MIX(i) -TS MIX(i) (model) ) 2 The proportion of NOM in the binary system is obtained through fitting. Therefore, NOM and PSMP S Content (mg C L) -1 ) can be and the total organic carbon content of the mixture ( The calculations are shown in formulas (3) and (4):

[0057] (3)

[0058] (4)

[0059] 1.1.2 HA, FA and PSMPs ternary system

[0060] Analogous to binary systems, the spectral relationships between ternary mixtures of HA, FA, and PSMPs and pure substances are as follows:

[0061] (5)

[0062] The values ​​of A, B, and C in the formula can be determined by making them within a selected wavelength range. The sum of the squares of the measured and calculated values ​​is minimized (Σ(TS) MIX(i) -TS MIX(i)(model) ) 2 The proportions of HA, FA, and PSMPs were obtained through fitting. f HA , f FA and f PSMPs That is , )and Finally, HA, FA, and PSMP are obtained using formulas (6)-(8). S Concentration (mg C L) -1 ).

[0063] (6)

[0064] (7)

[0065] (8)

[0066] 1.2 NOM-F and PSMPs system after goethite adsorption

[0067] The specific UV absorption spectra of the initial NOM and the selectively adsorbed NOM (NOM-F) are different; compared with the initial NOM, the specific absorbance value of NOM-F is reduced, but the shapes of the two are similar. Figure 2 ).

[0068] 1.2.1 Binary system of HA-F or FA-F and PSMPs

[0069] The UV-Vis method is based on the differences in specific UV-Vis absorption spectra between substances in the system. Therefore, theoretically, the UV-Vis method for quantitative determination of NOM-F and PSMPs in a mixed system can be established by using the specific UV-Vis absorption spectra of NOM-F and PSMPs. However, in a three-phase system composed of iron oxide, NOM and PSMPs, NOM-F cannot be separated from the solution to obtain its spectrum. Therefore, in a binary system of NOM-F and PSMPs, the concentrations of both are still calculated using formulas (2)-(4).

[0070] 1.2.2 Ternary systems of HA-F, FA-F, and PSMPs

[0071] Similar to the binary system, the concentrations of NOM-F and PSMPs in the ternary system are obtained by formulas (5)-(8).

[0072] The experimental and measurement methods are as follows:

[0073] 1. Experimental Materials

[0074] Natural organic matter, represented by HA and FA, was extracted and purified from soil according to the methods recommended by the International Humic Substances Society. The preparation process for selectively adsorbed NOM was as follows: 3 g / L goethite was mixed with 350 mg / L HA and 250 mg / L FA, and the suspension was shaken for 2 days (180 rpm, 25℃) at pH=6 and IS=0.001 mol / L. Then, it was centrifuged at 10000 rpm for 30 min, and the supernatant was filtered through a 0.45 μm filter to remove goethite. The filtrate was the selectively adsorbed HA or FA (HA-F350 or FA-F250), and its TOC was determined. Each sample was tested in triplicate. The TOC contents of HA and FA were 46.25% and 40.04%, respectively.

[0075] The polystyrene microplastics (PSMPs) were purchased from Welab Biotechnology Co., Ltd. at an initial concentration of 5% (w / v). These included 200 nm and 400 nm polystyrene microplastics (PSMPs-200 and PSMPs-400) and a 200 nm carboxyl-modified polystyrene microplastic (PSMPs-COOH-200). The TOC contents of PSMPs-200, PSMPs-400, and PSMPs-COOH-200 were 65.29%, 65%, and 73.24%, respectively.

[0076] Goethite was prepared as follows: (1) 5 L of 0.5 mol / L Fe(NO3)3 solution was accurately prepared and titrated with 2.5 mol / L NaOH solution at a rate of 10 mL / min until the pH of the solution was 12; (2) After aging the above suspension at 60℃ for 4 days, the supernatant was discarded and the precipitate was placed in a dialysis bag for dialysis until the conductivity was <10 μS / cm and remained unchanged. Finally, it was freeze-dried to obtain goethite and stored in a refrigerator at 4℃ for later use.

[0077] 2. Determination of ultraviolet-visible spectra

[0078] The absorbance values ​​of the above samples were scanned in the wavelength range of 200-600 nm using a UV-2700 Shimadzu spectrophotometer with a resolution of 1 nm. Before scanning, the pH of each sample was adjusted to approximately 6.9 with 0.01 mol / L phosphate buffer to eliminate the influence of pH on absorbance measurement. Furthermore, samples with high absorbance were diluted to an absorbance <1 before measurement. The specific UV-Vis absorption spectrum of each sample was obtained by dividing the UV-Vis absorption spectrum by the TOC value.

[0079] Because the specific UV-Vis absorption values ​​of the initial NOM and PSMPs differ significantly in the 200-230 nm wavelength range, and the stability and repeatability of the mixture in this wavelength range are also poor, while the stability and repeatability are better in the 231-600 nm wavelength range (see...). Figure 3 Therefore, the initial NOM and PSMP in the mixed system are calculated using formulas (2)-(4) in three wavelength ranges: 200-600 nm, 200-230 nm, and 231-600 nm. S The content of NOM and PSMPs was analyzed, and the feasibility and accuracy of the method were compared with known theoretical values. Overall, taking a mixed system of NOM and PSMPs with a total concentration of 50 mg / L as an example, the recoveries of NOM and PSMPs in the 231-600 nm wavelength range were generally higher than those in the 200-600 nm and 200-230 nm wavelength ranges (Table 1). Therefore, the 231-600 nm wavelength range was selected for subsequent studies to calculate the concentrations of NOM and PSMPs in the mixed system.

[0080] Table 1. Concentration recoveries of NOM and PSMPs in the mixed system under different spectral ranges

[0081]

[0082]

[0083] a The mixed concentration of NOM and PSMPs in different systems was 50 mg / L; b The mass proportion of NOM in the mixed system

[0084] 3. Initial NOM and PSMPs System

[0085] 3.1 Binary system of HA or FA and PSMPs

[0086] Known concentrations of NOM (HA or FA) were mixed with microplastic (PSMPs-COOH-200, PSMPs-200, or PSMPs-400) solutions at mass ratios of 1:9, 1:3, 1:1, 3:1, and 9:1 to achieve total concentrations of 25, 50, 100, and 150 mg / L, respectively. The mixed solutions were then shaken for 7 days (180 rpm, 25°C) at pH 6 and IS 0.001 mol / L. The total organic carbon (TOC) of NOM, PSMPs, and the mixed solutions was determined using a MultiN / C 3100, AJ, Germany analyzer. Each sample was performed in triplicate, with samples containing only NOM or PSMPs serving as controls.

[0087] For the HA and PSMPs-200 system, if the relative error is ≤16% (i.e., the concentration recovery rate is 100±16%), the detection limit for HA is 20.8 mg C·L⁻¹. -1 The detection limit of PSMPs-200 is 1.7 mg / L. -1 At that time, the absolute error was 5.7 mgC·L. -1 However, when the HA concentration is less than 20.8 mg C·L... -1 However, when the mass ratio is greater than 0.25, the concentration recovery rate of HA can still reach 100±16%. Figure 4 For the HA and PSMPs-400 system, if a relative error of ≤16% is used as the standard, then the detection limit for HA in this system is 17.3 mg C·L⁻¹. -1 The detection limit of PSMPs-400 is 4.1 mg C·L⁻¹. -1 The absolute error is 3.7 mg C·L. -1 ( Figure 5 For the HA and PSMPs-COOH-200 system, if a relative error of ≤16% is used as the standard (i.e., a concentration recovery rate of 100±16%), then the detection limit for HA is 8.7 mg C·L⁻¹. -1 The detection limit of PSMPs-COOH-200 is 3.7 mg C·L⁻¹. -1 The absolute error is 2.9 mgC·L⁻¹. -1 ( Figure 6 For the FA and PSMPs-200 system, when the detection limits of FA and PSMPs-200 are 7.5 mg C·L⁻¹, respectively... -1 and 4.1 mg C·L -1 The recoveries of both were 100% ± 16%, with an absolute error of 3.2 mg C L. -1 ( Figure 7If a relative error of ≤16% is used as the standard, then the detection limits for both FA and PSMPs-COOH-200 in the binary system are 2.5 mg C·L⁻¹. -1 and 1.9 mg C·L -1 The absolute error is 2.6 mgC·L⁻¹. -1 ( Figure 8 ).

[0088] 3.2 Ternary System of HA, FA and PSMPs

[0089] Known concentrations of HA, FA, and microplastics (PSMPs-200 or PSMPs-COOH-200) were mixed at mass ratios (HA+FA:PSMPs) of 1:9, 1:3, 1:1, 3:1, and 9:1 to achieve total concentrations of 100 and 150 mg / L, respectively. The mass ratio of HA to FA was kept constant at 1.5:1 based on the properties of the sampled soil. The mixed solutions were shaken for 7 days (180 rpm, 25°C) at pH=6 and IS=0.001 mol / L. The total organic carbon (TOC) of HA, FA, PSMPs, and the mixed solutions was determined using a total organic carbon analyzer (MultiN / C 3100, AJ, Germany). Each sample was tested in triplicate, with samples containing only HA, FA, and PSMPs serving as controls.

[0090] In the ternary system of HA, FA, and PSMPs-200, if a relative error of ≤16% is used as the standard, the detection limit for HA, FA, and PSMPs-200 is 20.8 mg·L⁻¹. -1 12 mg C·L -1 and 6.9 mgC·L -1 ( Figure 9 In the ternary system of HA, FA, and PSMPs-COOH-200, if a relative error of ≤16% is used as the standard, the detection limits for HA, FA, and PSMPs-COOH-200 are 13.9 mg C·L⁻¹, respectively. -1 8 mg C·L -1 and 7.4 mgC·L -1 ( Figure 10 Under the same relative error (≤16%), the detection limits of HA, FA and PSMPs in the ternary system are higher than those in the binary system. This may be because there are more complex interactions among the three in the ternary system, or it may be because the specific UV-Vis absorption spectra of each component in the ternary system cannot be well resolved by the UV-Vis method, thus the concentration limits of each component are larger.

[0091] 4. NOM-F and PSMPs system after selective adsorption of goethite

[0092] 4.1 Binary system of HA-F or FA-F and PSMPs

[0093] HA-F350 was mixed with microplastics (PSMPs-COOH-200 or PSMPs-200) at a concentration of 100 mg / L. -1 The total concentration was mixed at mass ratios of 1:9, 1:3, 1:1, 3:1, and 9:1, with FA-F250 and PSMPs (PSMPs-COOH-200 or PSMPs-200) at 80 mg / L. -1 The total concentration was mixed at mass ratios of 1:9, 1:3, 1:1, 3:1, and 9:1. The mixed solutions were then shaken for 7 days (180 rpm, 25°C) at pH=6 and IS=0.001 mol / L. Each sample was tested in triplicate, with samples containing only selectively adsorbed NOM and PSMPs serving as controls.

[0094] In the binary system of HA-F350 and PSMPs-COOH-200, if a relative error of ≤16% is used as the standard, the detection limits for HA-F350 and PSMPs-COOH-200 are 23.1 mg C·L⁻¹, respectively. -1 and 7.4 mgC·L -1 The absolute error is 3.3 mg C·L. -1 ( Figure 11 However, this method performs poorly in the binary system of HA-F350 and PSMPs-200. Under the same relative error (≤16%), the detection limits for HA-F350 and PSMPs-200 are 34.7 mg C·L⁻¹, respectively. -1 and 49.0 mgC·L -1 The absolute error is 6.6 mgC·L⁻¹ -1 ( Figure 12Under the same relative error (≤16%), the detection limits and absolute errors of both the HA-F350 and PSMPs systems are higher than those of the initial binary system of HA and PSMPs. This may be because: 1) Goethite preferentially adsorbs HA, which has a higher density of carboxyl and hydroxyl groups, thus HA-F has a lower content of carboxyl and hydroxyl groups, stronger hydrophobicity, and is more likely to interact with PSMPs, thereby affecting the accuracy of this method. 2) The spectrum of the initial NOM is used as the reference spectrum in the calculation, so the difference between the specific UV-Vis absorption spectra of HA and HA-F may have a certain impact on this method. Similar to HA, there is also selective adsorption between goethite and FA. In the binary system of FA-F250 and PSMPs-COOH-200, if the relative error is ≤16%, the detection limits of FA-F250 and PSMPs-COOH-200 are 16.0 mgC·L⁻¹, respectively. -1 and 5.9 mg C·L -1 At that time, the absolute error was 3.54 mgC·L. -1 ( Figure 13 However, this method performs poorly in the binary system of FA-F250 and PSMPs-200. Under the same relative error (≤16%), the detection limits of FA-F250 and PSMPs-200 are 23.9 mg C·L⁻¹, respectively. -1 and 14.6 mg C·L -1 ( Figure 14 ).

[0095] 4.2 Ternary systems of HA-F, FA-F, and PSMPs

[0096] HA-F350, FA-F250, and PSMPs-COOH-200 were mixed at mass ratios (HA-F350+FA-F250 : PS-COOH-200) of 1:9, 1:3, 1:1, 3:1, and 9:1 to achieve a total concentration of 150 mg / L, with a mass ratio of HA-F350 to FA-F250 of 1.5:1. The mixed solution was shaken for 7 days (180 rpm, 25℃) at pH=6 and IS=0.001 mol / L, and its TOC was determined. Each sample was performed in triplicate, with a sample containing only HA-F350, FA-F250, and PSMPs-COOH-200 serving as a control.

[0097] When the relative error is ≤16%, the detection limits of the three components in the ternary system consisting of HA-F350, FA-F250, and PSMPs-COOH-200 are 31.2 mg·L⁻¹. -1 18 mg C·L -1 and 27.5 mg C·L -1The absolute errors were 4.87 mgC·L⁻¹. -1 6.31 mgC·L -1 and 7.77 mgC·L -1 ( Figure 15 The detection limits of the three components in the ternary system were higher than those in the binary system of HA-F350 and PSMPs-COOH-200, and also higher than those in the binary system of FA-F250 and PSMPs-COOH-200 (HA-F350 > 23.1 mg C·L). -1 FA-F250 > 16.0 mgC·L -1 PSMPs-COOH-200 > 7.4 mgC·L -1 ).

[0098] 5. Conclusion

[0099] Ultraviolet-visible absorption spectroscopy is well-suited for determining the concentration of NOM and PSMPs in coexisting systems. The accuracy of this method depends on the type of NOM and its selective adsorption on goethite, as well as the particle size and surface functional groups of the PSMPs. It is particularly suitable for determining the concentrations of both in binary systems. Under the experimental conditions set in this study, with a relative error ≤16% as the standard, the detection limit of PSMPs in a binary system initially composed of NOM and PSMPs is 1.7–4.1 mg C·L⁻¹. -1 The detection limit for HA is 8.7-20.8 mg C·L⁻¹. -1 The detection limit for FA is 7.5 mg C·L⁻¹. -1 The detection limit of PSMPs in the binary system composed of NOM-F and PSMPs after selective adsorption is 5.9-7.4 mg C·L. -1 The detection limit for HA-F is 23.1 mg C·L⁻¹. -1 The detection limit of FA-F is 16.0 mg C·L⁻¹. -1 .

[0100] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A spectroscopic method for quantitatively determining the content of microplastics and organic matter in a mixed system, characterized in that: The method includes: establishing an initial NOM and PSMPs system or establishing a NOM-F and PSMPs system after goethite adsorption, wherein the initial NOM and PSMPs system includes a binary system of HA or FA and PSMPs and a ternary system of HA, FA and PSMPs; the NOM-F and PSMPs system after goethite adsorption includes a binary system of HA-F or FA-F and PSMPs and a ternary system of HA-F, FA-F and PSMPs, wherein the method for establishing the binary system of HA or FA and PSMPs specifically includes: Because of the hydrophobic interactions and π-π bonds between NOM and PSMPs, the spectra of NOM and PSMPs cannot be simply superimposed to obtain the spectrum of the mixture. Therefore, two parameters are introduced. β and γ The formula for correcting the effect of the interaction between the two on the mixture spectrum is as follows: （1） in, The specific UV-Vis absorbance value (L mgC) of the mixture at wavelength i represents the specific UV-Vis absorbance value of the mixture. -1 cm -1 ; and The specific UV-Vis absorbance values ​​(L mgC) of NOM and PSMPs at wavelength i represent the specific UV-Vis absorbance values. -1 cm -1 That is, absorbance / TOC concentration; Represents the mass fraction of organic carbon in NOM in the mixture. Represents the mass fraction of organic carbon in PSMPs in the mixture; β and γ These represent the interaction factors between NOM and PSMPs, respectively. Formula (1) can be further simplified as follows: （2） in, , Assuming β and γ The value remains constant across the entire wavelength range, meaning the interaction between the two does not alter the shape of their respective spectra. A and B can achieve this by adjusting TS within a selected wavelength range. MIX(i) The minimum sum of squares of the measured and calculated values ​​Σ(TS) MIX(i) -TS MIX(i)(model) ) 2 The fitting yielded that the proportion of NOM in the binary system was... Therefore, NOM and PSMP S Content in mg C L -1 can be and the total organic carbon content of the mixture The calculations are shown in formulas (3) and (4): （3） （4）， The method for establishing the ternary system of HA, FA, and PSMPs specifically includes: Analogous to binary systems, the spectral relationships between ternary mixtures of HA, FA, and PSMPs and pure substances are as follows: （5） The values ​​of A, B, and C in the formula can be determined by making them within a selected wavelength range. The minimum sum of squares of the measured and calculated values ​​Σ(TS) MIX(i) -TS MIX(i)(model) ) 2 The fitting results showed the proportions of HA, FA, and PSMPs. f HA , f FA and f PSMPs That is , )and Finally, the concentrations of HA, FA, and PSMPs (mg / L) are obtained using formulas (6)-(8). -1 , （6） （7） （8）， The specific steps of the method for establishing the binary system of HA-F or FA-F and PSMPs include: The UV-Vis method is based on the differences in specific UV-Vis absorption spectra between substances in the system. Therefore, the UV-Vis method for quantitative determination of NOM-F and PSMPs in a mixed system can be established by using the specific UV-Vis absorption spectra of NOM-F and PSMPs. However, in a three-phase system composed of iron oxide, NOM and PSMPs, NOM-F cannot be separated from the solution and its spectrum cannot be obtained. Therefore, in the binary system of NOM-F and PSMPs, the concentrations of both are still calculated using formulas (2)-(4). The steps of the method for establishing the ternary system of HA-F, FA-F and PSMPs include: similar to the binary system, the concentrations of NOM-F and PSMPs in the ternary system are obtained by formulas (5)-(8).

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