Method for detecting rubber additives and oxidation products in surface water by liquid chromatography-tandem mass spectrometry

Abstract

The present invention belongs to the field of surface water detection technology, and specifically discloses a method for detecting rubber additives and oxidation products in surface water by liquid chromatography-tandem mass spectrometry. The detection method provided by the present invention has simple pre-treatment operation, and the recovery rate of the method can be improved by adding an appropriate amount of salt to the water sample combined with solid phase extraction technology. After that, HPLC-MS / MS analysis can be used to quantitatively detect 17 kinds of rubber additives and oxidation products in surface water. The detection time is short, and the method has high accuracy, sensitivity and stability, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of surface water detection, and in particular relates to a method for detecting rubber additives and oxidation products in surface water by using liquid chromatography-tandem mass spectrometry. Background Art

[0002] Surface water pollution is a common problem worldwide. With the urgent demand for water resources and the increasing attention paid to environmental issues, strengthening the monitoring and management of surface water quality has become the focus of current research. As an important part of surface water quality management, surface water environmental quality evaluation is the top priority of research. Early water quality evaluation work started with identifying simple indicators such as color, taste, and turbidity of water bodies. With the continuous deepening of evaluation research, the number of indicators for daily monitoring and participation in evaluation has gradually increased.

[0003] At present, the surface water quality evaluation indicators are mainly the basic items specified in the "Surface Water Environmental Quality Standard" (GB 3838-2002), including: water temperature, pH value, dissolved oxygen, permanganate index, chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), ammonia nitrogen (NH3-N), total phosphorus, total nitrogen, copper, zinc, fluoride, selenium, arsenic, mercury, cadmium, chromium (hexavalent), lead, cyanide, volatile phenol, petroleum, anionic surfactants, sulfide, fecal coliform bacteria, etc. The above evaluation indicators have corresponding national standard detection methods, but there is still a gap in the detection of rubber additives and oxidation products in surface water, and these substances contain a variety of components that have a negative impact on the environment, which require quantitative detection to assess risks.

[0004] "Determination of Rubber Antioxidants by Gas Chromatography-Mass Spectrometry" (GB / T 33078-2016) stipulates that the antioxidants in raw rubber, latex, unvulcanized rubber or vulcanized rubber products should be determined by gas chromatography-mass spectrometry. The antioxidants in the rubber should be treated by pyrolysis or solvent extraction, and then the qualitative and quantitative analysis should be performed by gas chromatography-mass spectrometry. The parameter conditions are shown in "4 Thermal Analysis Method" and "5 Solvent Extraction Method". In addition, Chinese patent application CN115469037A (Guangdong Power Grid) provides a method for detecting rubber antioxidants (N-isopropyl-N-phenyl-p-phenylenediamine, 7PPD, 8PPD) in transformer oil, including: adding the transformer oil sample to an activated MEGA-BE-SI solid phase extraction column, eluting with n-hexane and then draining, and then eluting with methanol and / or acetonitrile to obtain a test solution; taking the test solution for gas or liquid chromatography-tandem mass spectrometry analysis. However, this method can only detect three types of rubber antioxidants and does not provide specific chromatographic and mass spectrometric analysis conditions.

[0005] Therefore, it is urgent to develop a quantitative detection method for various rubber additives and oxidation products in surface water to achieve a comprehensive evaluation of surface water quality. Summary of the invention

[0006] The main technical problem solved by the present invention is to provide a quantitative detection method for rubber additives and oxidation products in surface water, and accurately determine 17 kinds of rubber additives and oxidation products in surface water by liquid chromatography-tandem mass spectrometry.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The method for detecting rubber additives and oxidation products in surface water by liquid chromatography-tandem mass spectrometry comprises the following steps:

[0009] (1) Add salt to the surface water sample, use solid phase extraction to enrich the rubber additives and oxidation products in the water sample, and then concentrate after elution to obtain a test solution;

[0010] (2) The test solution is subjected to liquid chromatography-tandem mass spectrometry analysis to calculate the concentration of rubber additives and oxidation products in the surface water.

[0011] As a preferred embodiment of the present invention, the rubber additive and the oxidation product are selected from N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (antioxidant 4020, 6PPD), N-(1,4-dimethylpentyl)-N'-phenylbenzene-1,4-diamine (7PPD), N-(1-methylheptyl)-N'-phenyl-1,4-phenylenediamine (8PPD), N-cyclohexyl-N'-phenyl-p-phenylenediamine (antioxidant 4010, CPPD), N,N-diphenyl-p-phenylenediamine (antioxidant H, DPPD), N-isopropyl-N'-phenyl-p-phenylenediamine (antioxidant 4010NA, IPPD), 6P One or more of PDquinone (6PPD-Q), IPPDquinone (IPPD-Q), 4,4'-di(phenylisopropyl)diphenylamine (antioxidant 445), p-aminodiphenylamine (2N), p-hydroxydiphenylamine (4OH), 4-nitrosodiphenylamine (4-NOH), 2-benzimidazoleethanol (MB), 1,2-dihydro-2,2,4-trimethylquinoline (TMQ), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (antioxidant RD, TMQ-3), 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine (HMMM), and N-nitrosodiphenylamine (NDPA).

[0012] As a preferred embodiment of the present invention, in step (1), the surface water sample is first refrigerated and protected from light after collection, then filtered to remove particulate impurities, and then salt is added and loaded onto a solid phase extraction column.

[0013] As a preferred embodiment of the present invention, in step (1), the salt is selected from one or both of sodium chloride and sodium thiosulfate, preferably sodium chloride (NaCl). Adding salt to the water sample can significantly improve the recovery rate of the target analyte.

[0014] Specifically, the amount of salt added is 1-10 g / L water sample.

[0015] As a preferred embodiment of the present invention, in step (1), the operation steps of the solid phase extraction method include: adding the treated water sample to an HLB solid phase extraction column, and controlling the flow rate to 1-2 mL / min, preferably 1.5 mL / min.

[0016] Specifically, the filler of the HLB solid phase extraction column is a macroporous copolymer formed by polymerizing two monomers, lipophilic divinylbenzene and hydrophilic N-vinyl pyrrolidone, in a certain ratio, and is a commercially available product.

[0017] Specifically, the HLB solid phase extraction column is activated by washing with methanol and water in sequence before loading, and the flow rate is controlled to be 1-2 mL / min, preferably 1.5 mL / min. During the activation process, the column should be prevented from drying up.

[0018] As a preferred embodiment of the present invention, in step (1), the elution is carried out with a methanol aqueous solution (cleaning solvent), and drying is performed after elution, and the drying time is at least 20 minutes, preferably more than 30 minutes.

[0019] Specifically, the concentration of the methanol aqueous solution is 40%-60% (v / v), preferably 50% (v / v).

[0020] Specifically, the drying can be carried out by vacuum filtration or nitrogen blowing. When high-purity nitrogen is used for drying, the longer the nitrogen blowing time is, the higher the recovery rate of the target analyte is, and it is also beneficial to shorten the concentration time and improve the detection efficiency.

[0021] As a preferred embodiment of the present invention, in step (1), the elution uses methanol and acetonitrile (elution solvents) in sequence, and the flow rate is controlled to be 0.1-1 mL / min, preferably 0.5 mL / min, and the eluate is collected after elution.

[0022] As a preferred embodiment of the present invention, in step (1), the concentration temperature is 35-45° C., preferably 40° C., to obtain a concentrated solution. An internal standard is added to the concentrated solution, and the volume is fixed to obtain a solution to be tested.

[0023] Specifically, the internal standard is benzophenone-d10 (BP-d10, CAS: 22583-75-1).

[0024] Specifically, the concentration of the internal standard is the same as the concentration of the internal standard in the series of standard curve solutions used to draw the standard curve, preferably 20.00 ng / mL.

[0025] As a preferred embodiment of the present invention, in step (2), the analysis conditions of the liquid chromatography are:

[0026] a) Chromatographic column: C 18 Column, 100 mm (length) × 2.1 mm (inner diameter), particle size 1.8 μm, column packing is octadecyl bonded silica gel C 18 ;

[0027] b) Mobile phase: A is methanol, B is 0.1% formic acid aqueous solution, and the gradient elution program is shown in Table 1;

[0028] c) flow rate: 0.2-0.5 mL / min, preferably 0.3 mL / min;

[0029] d) Column temperature: 40-50°C, preferably 45°C;

[0030] e) Drying gas: temperature 250-350°C, flow rate 1-5 L / min, preferably temperature 300°C, flow rate 3 L / min;

[0031] f) Atomizer pressure: 40-50 psi, preferably 45 psi;

[0032] g) Sheath gas: temperature 250-350°C, flow rate 5-15 L / min, preferably temperature 300°C, flow rate 11 L / min;

[0033] h) Capillary voltage: 3-4KV, preferably 3.5KV;

[0034] i) Nozzle voltage: 400-600V, preferably 500V;

[0035] j) Injection volume: 1.5-3 μL, preferably 2 μL.

[0036] Table 1 Mobile phase gradient elution program

[0037]

[0038] As a preferred embodiment of the present invention, in step (2), the mass spectrometry analysis conditions are:

[0039] a) Ionization method: electrospray ionization;

[0040] b) Scanning mode: positive ion scanning;

[0041] c) Detection method: Multiple reaction monitoring mode (MRM). The multiple reaction monitoring conditions are shown in Table 2.

[0042] Table 2 Multiple reaction monitoring conditions

[0043]

[0044]

[0045] As a preferred embodiment of the present invention, in step (2), the calculation formula is:

[0046]

[0047] In Formula I:

[0048] ω i : mass concentration of target analyte i in water sample, ng / L;

[0049] ρ i :The mass concentration of target analyte i is obtained from the standard curve, ng / mL;

[0050] V: volume of the solution to be tested after constant volume, mL;

[0051] V0: water sample volume, L.

[0052] Specifically, the method for drawing the standard curve is: prepare a mixed standard working solution with standard samples of rubber additives and oxidation products; take an appropriate amount of the mixed standard working solution, add the internal standard working solution, and dilute it with mobile phase A to obtain a series of standard curve solutions (the mass concentrations of rubber additives and oxidation products are 0.50 ng / mL, 1.00 ng / mL, 2.00 ng / mL, 5.00 ng / mL, 10.00 ng / mL, 20.00 ng / mL, 50.00 ng / mL, and 100.00 ng / mL, respectively, and the concentration of the internal standard is 20.00 ng / mL); take the series of standard curve solutions for liquid chromatography-tandem mass spectrometry analysis (inject the samples in sequence from low to high concentrations), use the ratio of the concentration of the target analyte to the concentration of the internal standard in the series of standard curve solutions as the horizontal coordinate, and use the ratio of the corresponding peak area to the peak area of ​​the internal standard as the vertical coordinate to establish a standard curve.

[0053] As a preferred embodiment of the present invention, in step (2), the information and quantitative limits of the rubber additives and oxidation products are shown in Table 3. The detection limits of the 300 mL water sample method (i.e., the minimum detection value of each substance) are shown in Table 3.

[0054] Table 3 Information and quantification limits of rubber additives and oxidation products

[0055]

[0056]

[0057] Beneficial effects of the present invention:

[0058] The detection method provided by the present invention has simple pretreatment operation. Adding an appropriate amount of salt to the water sample combined with solid phase extraction technology can improve the recovery rate of the method. Subsequently, HPLC-MS / MS analysis can be used to quantitatively detect 17 rubber additives and oxidation products in surface water. The detection time is short, the method has high accuracy, sensitivity and stability, and has good application prospects.

[0059] The method provided by the present invention can detect many types of target substances, with a detection limit of 0.36-1.13 ng / L and a relative standard deviation of 5.3-14.7%. It has the advantages of low reagent consumption, high sensitivity, fast analysis speed, less experimental waste liquid, simple and efficient operation, etc. It is particularly suitable for standardized analysis in surface water monitoring, and solves the problems of poor integration, high labor intensity and poor repeatability of current standard methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is the retention time of the qualitative ion and quantitative ion of 17 rubber additives and oxidation products in the example.

[0061] Figure 2 This is a graph showing the effect of different concentration temperatures on the recovery of the target analyte in the experimental example.

[0062] Figure 3 This is a graph showing the effect of different amounts of added salt on the recovery of the target analyte in the experimental example.

[0063] Figure 4 This is a graph showing the effect of different nitrogen purge times on the recovery of the target analyte in the experimental example.

[0064] Figure 5 This is a graph showing the effect of different eluents on the recovery of the target analyte in the experimental example.

[0065] Figure 6 This is a graph showing the effect of the mixed elution scheme on the recovery rate of the target analyte in the experimental example.

[0066] In order to more clearly illustrate the technical solution to be protected by the present invention, the drawings in the embodiments or experimental examples are briefly introduced above. It should be understood that the above drawings should not be regarded as any limitation on the protection scope of the present invention. For ordinary technicians in this field, other related drawings can also be obtained based on these drawings without paying creative work. DETAILED DESCRIPTION

[0067] The technical solution of the present invention will be clearly and completely explained below in conjunction with specific embodiments and experimental examples.

[0068] Those skilled in the art should understand that the following embodiments and experimental examples are only used to illustrate the technical solutions and technical effects of the present invention and should not be regarded as any limitation on the protection scope of the present invention. Based on the following embodiments, other technical solutions obtained by those skilled in the art without creative work, such as technical solutions obtained after modification, deformation or simple replacement, all belong to the protection scope of the present invention.

[0069] Unless otherwise specified, the standards, reagents, and equipment used in the examples or experimental examples are all commercially available products.

[0070] 1. Reagents

[0071] Methanol (CH3OH): chromatographically pure.

[0072] Acetonitrile (CH3CN): chromatographic grade.

[0073] Ultrapure water: distilled water that does not contain organic matter.

[0074] Sodium chloride (NaCl): high-grade pure, baked at 450℃ for 4h, stored in a ground glass bottle after cooling and sealed.

[0075] Glass fiber filter membrane: 0.7μm.

[0076] Solid phase extraction column: HLB, 500 mg / 6 mL, the filler is a macroporous copolymer (commercially available) formed by polymerizing lipophilic divinylbenzene and hydrophilic N-vinylpyrrolidone in a certain ratio, with an average particle size of 60 μm.

[0077] High purity nitrogen: purity not less than 99.999%.

[0078] 2. Standard products

[0079] The standard products of 17 rubber additives and oxidation products shown in Table 3 have a purity of ≥95% and are stored refrigerated below 4°C.

[0080] 3. Instruments

[0081] Liquid chromatography-mass spectrometry: equipped with electrospray ionization source (ESI).

[0082] Analytical balance: sensitivity 0.1 mg.

[0083] Water sample filtering device.

[0084] Solid phase extraction apparatus.

[0085] Rotary evaporator.

[0086] Ultrasonic cleaner.

[0087] Other commonly used laboratory instruments.

[0088] Example

[0089] This embodiment provides a method for detecting rubber additives and oxidation products in surface water by liquid chromatography-tandem mass spectrometry, comprising the following steps:

[0090] A. Drawing of standard curve

[0091] (1) 17 kinds of rubber additives and oxidation product standards were prepared with methanol to obtain a mixed standard working solution; methanol was used as a solvent to prepare an internal standard working solution with an internal standard.

[0092] (2) Take an appropriate amount of the mixed standard working solution, add the internal standard working solution, and dilute with methanol (i.e., mobile phase A) to obtain a series of standard curve solutions, wherein the mass concentrations of rubber additives and oxidation products are 0.50 ng / mL, 1.00 ng / mL, 2.00 ng / mL, 5.00 ng / mL, 10.00 ng / mL, 20.00 ng / mL, 50.00 ng / mL, and 100.00 ng / mL, respectively, and the concentration of the internal standard is 20.00 ng / mL.

[0093] (3) A series of standard curve solutions were taken for liquid chromatography-tandem mass spectrometry analysis, and the concentrations were injected in order from low to high, wherein the analysis conditions of the liquid chromatography were:

[0094] a) Chromatographic column: C 18 Column, 100 mm (length) × 2.1 mm (inner diameter), particle size 1.8 μm, column packing is octadecyl bonded silica gel C 18 ;

[0095] b) Mobile phase: A is methanol, B is 0.1% formic acid aqueous solution, and the gradient elution program is shown in Table 1;

[0096] c) Flow rate: 0.3 mL / min;

[0097] d) Column temperature: 45°C;

[0098] e) Drying gas: temperature 300°C, flow rate 3L / min;

[0099] f) Atomizer pressure: 45psi;

[0100] g) Sheath gas: temperature 300°C, flow rate 11 L / min;

[0101] h) Capillary voltage: 3.5KV;

[0102] i) Nozzle voltage: 500V;

[0103] j) Injection volume: 2 μL.

[0104] The analysis conditions of mass spectrometry were:

[0105] a) Ionization method: electrospray ionization;

[0106] b) Scanning mode: positive ion scanning;

[0107] c) Detection method: multiple reaction monitoring mode (MRM), the multiple reaction monitoring conditions are shown in Table 2;

[0108] The retention times of the qualitative and quantitative ions of 17 rubber additives and their oxidation products are as follows: Figure 1 shown.

[0109] The standard curve was established with the ratio of the concentration of the target analyte to the concentration of the internal standard in the series of standard curve solutions as the horizontal axis and the ratio of the corresponding peak area to the peak area of ​​the internal standard as the vertical axis. The quantitative limits of each substance are shown in Table 3.

[0110] B. Water Sample Analysis

[0111] (1) Water sample collection and storage

[0112] Collect surface water samples in accordance with the "Technical Specifications for Surface Water Environmental Quality Monitoring" (HJ 91.2-2022), place them in clean polyethylene containers, seal and label them, and store them in a refrigerated place below 4°C away from light.

[0113] (2) Water sample pretreatment

[0114] Place a 0.7 μm glass fiber filter membrane in a filtration device, draw a surface water sample and filter out particulate impurities through the filtration device, accurately measure 300.0 mL of the filtered water sample and place it in a brown glass bottle.

[0115] (3) Solid Phase Extraction

[0116] a) Column activation

[0117] Install the solid phase extraction HLB column on the solid phase extractor, and activate the HLB column with 10 mL of methanol and 10 mL of ultrapure water at a flow rate of 1.5 mL / min. Do not let the column run dry during the activation process.

[0118] b) Target analyte enrichment

[0119] Add 1.8 g of NaCl to 300 mL of filtered water sample (the volume of water sample used for enrichment can be appropriately increased or decreased according to water quality), mix well and flow through the activated HLB column at a flow rate of 1.5 mL / min.

[0120] When adding NaCl, 30 ng of recovery indicator 6PPD-Q-d5 can also be added to calculate the recovery rate.

[0121] c) Rinse and dry

[0122] After eluting the HLB column with 10 mL of a mixed solution of methanol and ultrapure water (50:50, v / v), vacuum filter for 10 min or blow the HLB column with high-purity nitrogen for 30 min to dry the column.

[0123] d) Elution

[0124] The HLB column was eluted with 10 mL of methanol at a flow rate of 0.5 mL / min, and the eluate was collected.

[0125] e) Concentration

[0126] The eluate was evaporated to 0.5 mL using a rotary evaporator at 40° C. and 110 psi, and 20 ng of the internal standard substance BP-d10 was added, followed by dilution with pure water to a final volume of 1 mL to obtain a test solution.

[0127] When analyzing water samples, a blank test group must also be set up, that is, ultrapure water is used instead of the water sample, and the same steps as the sample measurement are followed to check whether there is any contamination during the analysis and measurement process.

[0128] (4) Liquid chromatography-tandem mass spectrometry

[0129] The test solution was subjected to liquid chromatography-tandem mass spectrometry analysis. The liquid chromatography and mass spectrometry analysis conditions were the same as above. The concentrations of rubber additives and oxidation products in the surface water were calculated according to formula I. The results are shown in Table 6.

[0130] In other embodiments of the present invention, in order to ensure the quality of detection, the following quality control work should be carried out:

[0131] (1) Precision measurement

[0132] The absolute difference between two independent measurement results obtained under repeatability conditions shall not exceed 20% of their arithmetic mean.

[0133] (2) Blank analysis

[0134] At least one blank test should be performed for each analysis, and the concentration of each target analyte in the blank test must not be detected.

[0135] (3) Calibration

[0136] A standard curve should be drawn for each batch of water samples, and the correlation coefficient should be guaranteed to be ≥ 0.990, otherwise the standard curve should be redrawn.

[0137] For every 20 water samples or each batch of water samples (<20 samples / batch), a standard solution at the middle concentration point of the standard curve should be measured. The relative deviation between the measurement result and the concentration at that point should be ≤20%. Otherwise, the standard curve must be redrawn.

[0138] (4) Parallel sample measurement

[0139] One parallel duplicate sample should be made for every 20 water samples or each batch of water samples (<20 samples / batch), and the relative deviation of the parallel duplicate sample measurement results should be ≤20%.

[0140] (5) Determination of spike recovery

[0141] One spiked sample is required for every 20 water samples or each batch of water samples (<20 samples / batch). The spiked sample and the original water sample are analyzed under exactly the same test conditions, and the spiked recovery rate should be between 60% and 120%.

[0142] In other embodiments of the present invention, parameters such as solid phase extraction column activation, extraction, elution flow rate, and drying time, the amount of NaCl added to the water sample, the temperature for eluent concentration, and the injection volume of liquid chromatography analysis can all be arbitrarily set within a given range without substantially affecting the accuracy of the test results.

[0143] Experimental example

[0144] 1. Exploration of water sample pretreatment conditions

[0145] Using methanol as solvent, the solution was prepared with standard samples of rubber additives and oxidation products to explore the effect of concentration temperature on the recovery rate. The results are as follows: Figure 2 shown.

[0146] from Figure 2 It can be seen that the same compound was concentrated under 4 different temperature conditions, and the recovery rate decreased when concentrated at 30°C. Under other temperature conditions, the recovery rates of various rubber additives were not much different, but the RSD (%) was quite different. When concentrated at 35°C, 40°C, and 45°C, the RSDs were <43.37% (average 7.02%), <6.61% (average 1.21%), and <8.87% (average 5.56%), respectively. The results show that maintaining a temperature of about 40°C during the concentration process can minimize the loss of the target analyte and improve the recovery rate of the method.

[0147] Different natural water bodies have different physical and chemical properties (such as pH value, salt content, etc.). By adding sodium chloride or sodium thiosulfate to standard contaminated water samples, and adding different proportions of formic acid or ammonia to adjust the pH value of the water samples (in the range of 2.38-9.71), the effects of salt content and pH value in water samples on the recovery rate of target analytes were explored. The results are as follows: Figure 3 shown.

[0148] from Figure 3 It can be seen that increasing the salt content of the water sample can significantly improve the recovery rate of the target analyte, and the effect of sodium chloride is better than that of sodium thiosulfate. However, adjusting the pH value of the water sample has a limited effect on the recovery rate and can be ignored.

[0149] In order to study the effect of water content in the solid phase extraction column on the elution efficiency of the target analyte, different nitrogen blowing times (5, 10, 15, 20, 25, 30 min) were set and the recovery rate was calculated. The results are shown in Figure 2. Figure 4 shown.

[0150] from Figure 4 It can be seen that the longer the nitrogen blowing time, the higher the recovery rate of the target analyte, especially when the time was set to 30 min, the recovery rate was the highest.

[0151] In order to study the effect of sampling volume on the accuracy of test results, different sampling volumes (200-1000mL) were set for experiments. However, the results show that the effect of sampling volume on detection is not significant. For real environmental water samples, since the concentrations of rubber additives and oxidation products in the water environment are at trace levels, the ideal sampling volume is determined to be 1000mL. However, since controlling the flow rate of solid phase extraction column activation, extraction and elution can improve the extraction efficiency and thus reduce the sampling volume, a sampling volume of <500mL can be selected.

[0152] To ensure complete desorption of the target analytes on the HLB column, different eluents were designed, including methanol containing 0.1% formic acid, a mixed aqueous solution of methanol and formic acid (water: methanol: formic acid = 4:95:1), methanol, acetonitrile, and a mixed solution of methanol and dichloromethane (methanol: dichloromethane = 2:1). The results are shown in Figure 2. Figure 5 shown.

[0153] from Figure 5 It can be seen that the recoveries of the target analytes were higher when eluted with methanol or acetonitrile. When eluted with acetonitrile alone, the recoveries of NDPA, 7PPD, and CPPD were relatively good.

[0154] Based on the above experimental results, an elution scheme of methanol first and then acetonitrile was tried, that is, elution was performed 3 times with methanol first and then eluted 3 times with acetonitrile, and then the eluates were mixed and concentrated, or the eluates were concentrated separately to calculate the recovery rate. The results are as follows Figure 6 shown.

[0155] from Figure 6 It can be seen that the recovery rate obtained by mixing the two eluents and concentrating them in parallel is significantly different from the sum of the recovery rates obtained by concentrating the two eluents separately in parallel, which may be caused by the interaction of the solvents. Therefore, in subsequent experiments, the elution strategy of eluting with methanol 3 times and then eluting with acetonitrile 3 times was adopted to ensure that the substance was fully eluted and to improve the terminal stability of the entire pretreatment method.

[0156] 2. Methodological Validation

[0157] In order to verify the accuracy, feasibility and effectiveness of the water sample pretreatment method and HPLC-MS / MS analysis, three concentration levels (1, 10, and 100 ng) were set using standards of 12 rubber additives and oxidation products to analyze their stability in the aqueous phase. The pretreatment method and HPLC-MS / MS analysis conditions were the same as those of the real water samples, and solvent blank and matrix blank groups were set. The experimental results are shown in Table 4.

[0158] Table 4 Recovery of 12 target analytes in water samples with different concentrations (1, 10, 100 ng)

[0159]

[0160]

[0161] As can be seen from Table 4, the recoveries and RSDs of 12 rubber additives and oxidation products at three levels of aqueous phase (n=6) were 54.93%-136.03%, 5.3%-14.7% (1 ng), 52.73%-111.66%, 1.4%-12.6% (10 ng), 50.2%-100.3%, 1.7%-9.8% (100 ng), respectively, indicating that the method has good applicability.

[0162] Since endogenous matrix components can cause MS signal suppression or analyte ionization enhancement, the matrix effect (ME) of all 17 target analytes and the entire standard curve range was evaluated. When ME is higher than 100%, it means that the analytical response is enhanced, and when ME is lower than 100%, it means that the analytical response is suppressed. The evaluation results are shown in Table 5.

[0163] Table 5 Matrix effects of different rubber additives in river water matrix

[0164]

[0165]

[0166] As can be seen from Table 5, the accuracy of most matrix effects is between 85% and 115%, and the precision is within 15%, indicating that the river water matrix has no adverse effect on the determination of rubber additives and oxidation products.

[0167] 3. Real water sample analysis

[0168] In order to verify the practicability of the method of the present invention, river water, rainwater and surface runoff water samples were analyzed respectively. All environmental samples were from Kaifeng City, Henan Province to eliminate time and space differences. The results are shown in Table 6.

[0169] Table 6 Detection results of rubber additives and oxidation products in different environmental water samples (ng / L)

[0170]

[0171] As can be seen from Table 6, 11 rubber additives and oxidation products were detected in river water, with a concentration range of ND (not detected)-117.1ng / L; rainwater mainly contains TMQ, HMMM, 4OH, 445, and the content is relatively small, with a concentration range of 0.34-6.76ng / L; surface runoff water is a special environmental medium formed by rainwater scouring roads, and a total of 17 rubber additives and oxidation products were detected, with a concentration range of ND (not detected)-823.83ng / L. Compared with other water media, the content characteristics of rubber additives and oxidation products in surface runoff water are very prominent.

[0172] It can be seen that the types and content distribution characteristics of rubber additives and oxidation products in different environmental media vary greatly, and there is a correlation between them and the environmental media themselves. For example, on rainy days, rainwater washes away dust on the road, causing some dust particles to enter the river with surface runoff. Therefore, the detection of rubber additives and oxidation products in surface water can be used as an effective indicator of the degree of water pollution, reflecting the ecological risk of the water environment.

[0173] Although the technical solution of the present invention has been described in detail above with general descriptions, specific implementation methods and experimental examples, it should be noted that the embodiments and experimental examples are only used to illustrate the technical solution and technical effects of the present invention, and should not be regarded as any limitation on the protection scope of the present invention. Simple deformation, modification or improvement based on the technical concept of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for detecting rubber additives and oxidation products in surface water by liquid chromatography-tandem mass spectrometry, characterized in that: The method comprises the following steps: (1) Add salt to the surface water sample, use solid phase extraction to enrich the rubber additives and oxidation products in the water sample, and then concentrate after elution to obtain a test solution; (2) taking the test solution for liquid chromatography-tandem mass spectrometry analysis to calculate the concentration of rubber additives and oxidation products in the surface water; The rubber additives and oxidation products are N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-(1,4-dimethylpentyl)-N'-phenyl-1,4-phenylenediamine, N-(1-methylheptyl)-N'-phenyl-1,4-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, 6P PDquinone, IPPDquinone, 4,4'-di(phenylisopropyl)diphenylamine, p-aminodiphenylamine, p-hydroxydiphenylamine, 4-nitrosodiphenylamine, 2-mercaptobenzimidazole, 1,2-dihydro-2,2,4-trimethylquinoline, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine and N-nitrosodiphenylamine; In step (1), the salt is selected from one or both of sodium chloride and sodium thiosulfate; In step (1), the operation steps of the solid phase extraction method include: adding the treated water sample to the HLB solid phase extraction column, and controlling the flow rate to 1-2 mL / min; In step (1), the elution is carried out with a 40% to 60% methanol aqueous solution, and the elution is followed by drying for at least 20 minutes; In step (1), the elution is carried out using methanol and acetonitrile in sequence, and the flow rate is controlled to be 0.1-1 mL / min; In step (1), the concentration temperature is 35-45° C. to obtain a concentrated solution, and an internal standard is added to the concentrated solution to adjust the volume to obtain a solution to be tested; In step (2), the analysis conditions of the liquid chromatography are: Chromatographic column: C 18 Column, 100 mm × 2.1 mm, particle size 1.8 μm; Mobile phase: A is methanol, B is 0.1% formic acid aqueous solution, and the gradient elution program is shown in Table 1; Flow rate: 0.2-0.5mL / min; Column temperature: 40-50°C; Injection volume: 1.5-3 μL; Table 1 Mobile phase gradient elution program In step (2), the mass spectrometry analysis conditions are: Ionization method: electrospray ionization; Scanning mode: positive ion scanning; Detection method: multiple reaction monitoring mode, multiple reaction monitoring conditions are shown in Table 2; Drying gas: temperature 250-350°C, flow rate 1-5L / min; Atomizer pressure: 40-50psi; Sheath gas: temperature 250-350°C, flow rate 5-15L / min; Capillary voltage: 3-4KV; Nozzle voltage: 400-600V; Table 2 Multiple reaction monitoring conditions 2. The method according to claim 1, characterized in that: The treated water sample was added to the HLB solid phase extraction column and the flow rate was controlled at 1.5 mL / min.

3. The method according to claim 1, characterized in that: In step (2), the analysis conditions of the liquid chromatography are: Flow rate: 0.3 mL / min; Column temperature: 45°C; Injection volume: 2 μL; In step (2), the mass spectrometry analysis conditions are: Drying gas: temperature 300°C, flow rate 3L / min; Atomizer pressure: 45psi; Sheath gas: temperature 300°C, flow rate 11L / min; Capillary voltage: 3.5KV; Nozzle voltage: 500V.

4. The method according to claim 1, characterized in that: In step (2), the calculation formula is: In Formula I: ω i : mass concentration of target analyte i in water sample, ng / L; ρ i :The mass concentration of target analyte i is obtained from the standard curve, ng / mL; V: volume of the solution to be tested after constant volume, mL; V0: water sample volume, L.

5. The method according to claim 4, characterized in that: The method for drawing the standard curve is as follows: prepare a mixed standard working solution with standard products of rubber additives and oxidation products; take an appropriate amount of the mixed standard working solution, add an internal standard working solution, and dilute with mobile phase A to obtain a series of standard curve solutions; take the series of standard curve solutions for liquid chromatography-tandem mass spectrometry analysis to establish a standard curve.

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