A method for identifying precursors of disinfection by-products in natural waters based on fticr-ms

Abstract

The application discloses a method for identifying precursors of disinfection by-products in natural water based on Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) with high efficiency and rapidness, which comprises the following steps: S1, enriching water samples before and after disinfection by using solid-phase extraction columns respectively, and dissolving in methanol; S2, respectively determining FTICR-MS mass spectra of the samples before and after disinfection; S3, calculating chemical molecular formulas represented by each peak, and removing isotopic peaks; S4, extracting molecular formulas containing chlorine in the sample after disinfection, and respectively calculating precursors of addition and substitution reactions within 5 chlorines and 5 bromines; S5, matching the obtained molecular formulas with molecular formulas of the sample before disinfection, and making Van Krevelen VK diagrams according to matching results; and S6, calculating the number of compounds and peak intensity of each component in the VK diagram, and obtaining main categories of precursors of disinfection by-products.

Description

Technical Field

[0001] This invention belongs to the field of drinking water disinfection, and in particular relates to a method for identifying disinfection byproduct precursors in natural water based on Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Background Technology

[0002] To ensure drinking water safety and reduce biosafety risks, most water treatment plants in my country use chlorine disinfection. However, the reaction between disinfectants and organic matter in water produces a series of byproducts. The parent ions of disinfection byproducts (DBPs) are called DBP precursors.

[0003] The composition of organic matter in natural water is complex, with intricate structures and components, making it difficult to identify and study each component individually. Therefore, classifying dissolved organic matter (DOM) in water according to certain characteristics and studying the reaction properties of DOM with the same characteristics is currently a more preferable method for studying DBP precursors under analytical conditions. Chemical fractionation can separate DOM into hydrophobic, weakly hydrophobic, and hydrophilic components; physical fractionation can separate DOM into different components according to the pore size of ultrafiltration membranes. The separated components are evaluated for their DBP precursor status by measuring the disinfection byproduct formation potential (DBPFP).

[0004] There are many types of DBP precursors. Humic acid, fulvic acid, algae and their metabolites, proteins and other organic matter in natural water are all important disinfection byproduct precursors. Current research methods can only identify the hydrophilicity / hydrophobicity and molecular weight characteristics of the main DBP precursors, but cannot identify the chemical characteristics of the main disinfection byproduct precursors.

[0005] Another method for identifying DBP precursors is to utilize the fluorescence response relationships of organic compounds such as humic acid and fulvic acid.

[0006] The invention patent application with publication number CN105445243 A discloses a method for measuring chlorine disinfection byproduct precursors in water using three-dimensional fluorescence spectroscopy. This invention requires adjusting various parameters of the three-dimensional fluorescence spectrometer, then preparing chlorine disinfection byproducts of different concentrations in water, and then measuring the prepared chlorine disinfection byproducts in water using the three-dimensional fluorescence spectrometer. Finally, the content of chlorine disinfection byproduct precursors in water is determined by the measurement results, mainly including the content of humic acid and fulvic acid.

[0007] The invention in this application can only identify the content of disinfection byproduct precursors humic acid and fulvic acid through three-dimensional fluorescence semi-quantitative identification. Humic acid and fulvic acid are a very broad category of organic compounds, and their three-dimensional fluorescence peak positions overlap with many types of organic substances. Therefore, it is impossible to further subdivide the main categories of disinfection byproduct precursors. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for identifying disinfection byproduct precursors in natural water based on FTICR-MS to further classify the main disinfection byproduct precursor categories.

[0009] The technical solution of this invention: This invention provides a highly efficient and rapid method for identifying disinfection byproduct precursors in natural water based on FTICR-MS, comprising the following steps:

[0010] S1. Solid-phase extraction was used to enrich water samples before and after disinfection, and the samples were dissolved in methanol.

[0011] S2. Measure the FTICR-MS mass spectra of the samples before and after disinfection, respectively;

[0012] S3. Calculate the chemical formula represented by each peak and remove isotope peaks;

[0013] S4. Extract the molecular formula of chlorine-containing samples after disinfection, and calculate the precursors for addition and substitution reactions containing 5 chlorine molecules and 5 bromine molecules respectively;

[0014] S5. Match the obtained molecular formula with the molecular formula of the sample before disinfection, and plot the Van Cleeflan VK diagram based on the matching results;

[0015] S6. Calculate the number of compounds and peak intensities of each component in the VK graph to obtain the main disinfection byproduct precursor categories.

[0016] Furthermore, in step S4, the precursors for addition and substitution reactions containing up to 5 chlorine and 5 bromine molecules are calculated. The specific process is as follows: extract all chemical formulas containing 1-5 chlorine and 1-5 bromine molecules from the sterilized sample. If the molecular formula is C... a H b O c N d S e P f Cl g Br h The precursor for the addition reaction is C. a H b-g-h O c-g-h N d S e P f The precursor for the substitution reaction is C. a H b+g+h O c N d S e P f Where 1≤g≤5, 1≤h≤5.

[0017] Further, in said step S5, different regions of the VK diagram are divided according to the molecular formula of the precursor of the addition reaction and the ratio of C / O to C / H in the precursor of the substitution reaction.

[0018] Further, the different regions of said VK diagram comprise 8 regions, including

[0019] when 1.5<H / C≤2.0 and 0≤O / C≤0.3, it is a lipid region

[0020] when 1.5<H / C≤2.2 and 0.3<O / C≤0.67, it is an aliphatic / peptide compound region

[0021] when 1.5<H / C≤2.4 and 0.67<O / C≤1.2, it is a carbohydrate region

[0022] when 0.7<H / C≤1.5 and O / C<0.1, it is an unsaturated hydrocarbon compound region

[0023] when 0.7<H / C≤1.5 and 0.1≤O / C<0.67, it is a lignin compound region

[0024] when 0.6≤H / C≤1.5 and 0.67≤O / C<1.0, it is a tannic acid compound region

[0025] when 0.2<H / C≤0.7 and O / C≤0.67, it is a condensed aromatic structure organic matter region and other types of organic matter regions.

[0026] Further, in said step S3, data with a signal-to-noise ratio greater than 6 and a measurement error within 1 ppm is selected.

[0027] Further, said solid-phase extraction column enrichment method comprises activation, rinsing, enrichment, desalination, elution and constant volume.

[0028] Further, said solid-phase extraction column enrichment method comprises the following steps,

[0029] S11. Pass 400 mL of water sample through a 0.22 micron polyethersulfone aqueous filter membrane, and adjust the pH of the water sample to 2 with formic acid;

[0030] S12. Rinse the PPL solid-phase extraction column 3 times with 5 mL of chromatographic grade methanol to activate the column, with a flow rate of 5 mL / min;

[0031] S13. Rinse 3 times with 5 mL of ultrapure water with pH=2, at a flow rate of 5 mL / min;

[0032] S14. Pass the water sample in step S11 through the solid-phase extraction column at a flow rate of 5 mL / min to enrich organic matter;

[0033] S15. Rinse three times with 5 mL of pH=2 ultrapure water to remove residual salts in the solid phase extraction column at a flow rate of 5 mL / min, and then dry the solid phase extraction column with nitrogen.

[0034] S16. Elute the organic matter in the solid-phase extraction column three times with 10 mL of methanol at a flow rate of 5 mL / min, and collect the eluent; S17. Freeze-dry the eluent, and then make up to 2 mL with methanol.

[0035] Furthermore, the pH of the ultrapure water is adjusted using chromatographic formic acid.

[0036] Beneficial effects:

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention achieves accurate identification of the types of disinfection by-product precursors in natural water. Based on the matching results, a Van Cleeflan VK diagram can be generated, and the number of compounds and peak intensities of each component in the VK diagram can be calculated to obtain the main categories of disinfection by-product precursors. This is beneficial to deepen the understanding of disinfection by-product precursors in natural water and to infer their sources. Attached Figure Description

[0038] Figure 1 This is a mass spectrum of SRNOM before disinfection in a specific embodiment of the present invention;

[0039] Figure 2 This is a mass spectrum of SRNOM after disinfection in a specific embodiment of the present invention;

[0040] Figure 3 This is a VK diagram of the sterilization byproduct precursor of the SRNOM addition reaction in a specific embodiment of the present invention;

[0041] Figure 4 This is a VK diagram of the sterilization byproduct precursor of the SRNOM substitution reaction in a specific embodiment of the present invention;

[0042] Figure 5 The percentage of each component in the SRNOM addition and substitution disinfection byproduct precursors in specific embodiments of the present invention is shown. Detailed Implementation

[0043] To enhance understanding of the present invention, we will now describe it in further detail with reference to the embodiments. These embodiments are only for explaining the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0044] Example

[0045] Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is a technique proposed in this invention for identifying disinfection byproduct precursors in natural water. The method includes the following steps:

[0046] (1) Water sample pretreatment and solid phase extraction

[0047] Prepare 800 mL of SRNOM (a natural organic compound from the Sawani River) with a total organic carbon (TOC) of 5 mg / L using the Savanni River natural organic compound purchased from the International Humic Acid Association. Add 8 mL of phosphate buffer solution to 400 mL of the solution to maintain the pH at 6.8-7.2 during the disinfection process. Add 20 mg / L sodium hypochlorite solution and incubate at 25°C in the dark for 72 hours. After incubation, add 2 g of anhydrous sodium sulfite to quench the residual chlorine. This solution is the disinfected SRNOM solution.

[0048] The SRNOM solution before and after sterilization was filtered through a 0.22 μm polyethersulfone membrane, and the pH was adjusted to 2 with chromatographic formic acid. The PPL solid-phase extraction column (Anilent Bond Elut PPL, 1 g / 6 mL) was rinsed three times with 5 mL of chromatographic methanol at a flow rate of 5 mL / min. The column was then rinsed three times with 5 mL of pH 2 ultrapure water (pH adjusted with chromatographic formic acid) at a flow rate of 5 mL / min. The pre- and post-sterilization water samples (pH adjusted) were passed through the solid-phase extraction column at a flow rate of 5 mL / min to enrich organic matter. The column was rinsed three times with 5 mL of pH 2 ultrapure water (pH adjusted with chromatographic formic acid) at a flow rate of 5 mL / min, and the column was dried with nitrogen. The organic matter in the solid-phase extraction column was eluted three times with 10 mL of methanol at a flow rate of 5 mL / min, and the eluent was collected. The eluent was freeze-dried and then brought to a final volume of 2 mL with methanol.

[0049] (2) FTIR-MS determination of water samples

[0050] Data were acquired using a 9.4T FTICR-MS from Bruker Daltonics, Germany, under ESI(-) ionization. The sample obtained in step (1) was diluted with methanol in a proportional ratio before injection. The instrument's nebulizer gas pressure, drying gas pressure, and electrospray ionization heater temperature were 138 kPa, 103 kPa, and 200 °C, respectively. The data acquisition memory was 4 MB, and each mass spectrometry scan was performed 500 times. All mass spectrometry data were first externally calibrated using arginine clusters dissolved in methanol (0.57 μmol / L), with the m / z range set to 180-1000. Then, internal calibration was performed using a suitable reference mass table of common natural organic molecules. The calibration process ensured that the instrument accuracy was less than 500 ppb. The mass spectra before and after sterilization are shown below. Figure 1 and Figure 2 .

[0051] (3) Select data with a signal-to-noise ratio > 6 and a measurement error within 1 ppm; the range of theoretical chemical formulas identified is... 12 C1-50 , 1 H 1-80 , 16 O 1-50 , 14 N 0-5 , 32 S 0-5 , 31 P 0-2 , 35 Cl 0-5 , 79 Br 0-5 Isotope considerations 13 C 2 H, 16 O、 15 N、 34 S, 37 Cl and 81 Br was processed using Compass Data Analysis 4.1 software to calculate the chemical formula represented by each peak and remove isotope peaks. A total of 6696 chemical formulas were measured before disinfection, and 8064 chemical formulas were measured after disinfection, including 935 chlorinated chemical formulas, of which 346 were monochloro, 407 were dichloro, 69 were trichloro, 76 were tetrachloro, and 37 were pentachloro.

[0052] (4) Extract the molecular formula of chlorine-containing compounds from the sterilized sample, and calculate the precursors for addition and substitution reactions containing up to 5 chlorine and 5 bromine molecules, respectively. The specific process is as follows:

[0053] Extract all chemical molecules containing 1-5 chlorine atoms after disinfection. If the molecular formula is C... a H b O c N d S e P f Cl g Br h The precursor for the addition reaction is C. a H b-g-h O c-g-h N d S e P f The precursor for the substitution reaction is C. a H b+g+h O c N d S e P f .

[0054] For DBP precursors of substitution reactions, 316 monochloro DBP precursors, 369 dichloro DBP precursors, 48 ​​trichloro DBP precursors, 52 tetrachloro DBP precursors, and 0 pentachloro DBP precursors were calculated.

[0055] For addition reaction DBPs precursors, 317 monochloro DBPs precursors, 325 dichloro DBPs precursors, 19 trichloro DBPs precursors, 16 tetrachloro DBPs precursors, and 0 pentachloro DBPs precursors were calculated. The top 10 precursors with the highest peak intensity of addition and substitution sterilization byproducts are shown in Table 1.

[0056] Table 1 shows the top 10 precursors with the highest peak intensities of addition and substitution disinfection byproducts calculated.

[0057]

[0058] (5) Match the molecular formula obtained in step (4) with the molecular formula of the sample before sterilization, and plot a Van-Krevelen (VK) diagram based on the matching results. Divide the VK diagram into different regions according to the H / C and O / C ratios in the molecular formula. There are a total of 8 regions.

[0059] These are lipids (1.5) <H / C≤2.0,0≤O / C≤0.3);

[0060] Aliphatic / peptide compounds (1.5) <H / C≤2.2,0.3<O / C≤0.67);

[0061] Carbohydrates (1.5) <H / C≤2.4,0.67<O / C≤1.2);

[0062] Unsaturated hydrocarbons (0.7) <H / C≤1.5,O / C<0.1);

[0063] Lignin compounds (0.7) <H / C≤1.5,0.1≤O / C<0.67);

[0064] Tannic acid compounds (0.6≤H / C≤1.5, 0.67≤O / C<1.0);

[0065] Fused-ring aromatic organic compounds (0.2) <H / C≤0.7,O / C≤0.67);

[0066] Other types of organic matter.

[0067] SRNOM disinfection identifies precursors that generate DBPs through addition and substitution reactions, such as... Figure 3 and Figure 4 .

[0068] (6) Calculate the sum of the peak intensities of the chemical formulas of each component in the VK diagram, such as... Figure 5 As shown, the main disinfection byproduct precursors of SRNOM are lignin compounds.

[0069] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for identifying disinfection byproduct precursors in natural water based on FTICR-MS, characterized in that: comprising the following steps, S1. Enriching water samples before and after disinfection respectively with solid phase extraction cartridges, and dissolving the enriched substances in methanol; S2. Measuring FTICR-MS mass spectra of the samples before and after disinfection respectively; S3. Calculating the chemical molecular formula represented by each peak, and removing isotope peaks; S4. Extract the molecular formulas of chlorine-containing compounds from the sterilized sample, and calculate the precursors for addition and substitution reactions containing up to 5 chlorine and 5 bromine molecules respectively; In step S4, the specific process for calculating the precursors for addition and substitution reactions containing up to 5 chlorine and 5 bromine molecules is as follows: Extract all chemical formulas containing 1-5 chlorine and 1-5 bromine molecules from the sterilized sample. If the molecular formula is C... a H b O c N d S e P f Cl g Br h The precursor for the addition reaction is C. a H b-g-h O c-g-h N d S e P f The precursor for the substitution reaction is C. a H b+g+ h O c N d S e P f Where 1≤g≤5, 1≤h≤5; S5. Matching the obtained molecular formulas with the molecular formulas of the pre-disinfection sample, and drawing a Van Krevelen (VK) diagram according to the matching result; S6. Calculating the number of compounds and the sum of peak intensities of each component in the VK diagram, to obtain the main categories of disinfection byproduct precursors.

2. The method for identifying disinfection byproduct precursors in natural water based on FTICR-MS according to claim 1, characterized in that: In the step S5, different regions of the VK diagram are divided according to the molecular formula of precursors for addition reaction and the C / O and C / H ratios of precursors for substitution reaction.

3. The method for identifying disinfection byproduct precursors in natural water based on FTICR-MS according to claim 2, characterized in that: The different regions of the VK diagram include 8 regions, which comprise when 1.5<H / C≤2.0 and 0≤O / C≤0.3, it is a lipid region; when 1.5<H / C≤2.2 and 0.3<O / C≤0.67, it is an aliphatic / peptide compound region; when 1.5<H / C≤2.4 and 0.67<O / C≤1.2, it is a carbohydrate region; when 0.7<H / C≤1.5 and O / C<0.1, it is an unsaturated hydrocarbon region; when 0.7<H / C≤1.5 and 0.1 ≤O / C<0.67, it is a lignin compound region; when 0.6≤H / C≤1.5 and 0.67≤O / C<1.0, it is a tannic acid compound region; when 0.2<H / C≤0.7 and O / C≤0.67, it is a condensed ring aromatic organic matter region; and other types of organic matter regions.

4. The method for identifying disinfection byproduct precursors in natural water based on FTICR-MS according to claim 1, characterized in that: In the step S3, data with a signal-to-noise ratio > 6 and a measurement error within 1 ppm are selected.

5. The method for identifying disinfection byproduct precursors in natural water based on FTICR-MS according to claim 1, characterized in that: The enrichment method using solid phase extraction cartridges comprises activation, rinsing, enrichment, desalination, elution and constant volume preparation.

6. The method for identifying disinfection byproduct precursors in natural water based on FTICR-MS according to claim 5, characterized in that: The enrichment method using solid phase extraction cartridges comprises the following steps, S11. Passing 400 mL of water sample through a 0.22 μm polyethersulfone aqueous filter membrane, and adjusting the pH of the water sample to 2 with formic acid; S12. Rinsing a PPL solid phase extraction cartridge 3 times with 5 mL of chromatographic grade methanol to activate the cartridge, with a flow rate of 5 mL / min; S13. Rinsing 3 times with 5 mL of ultrapure water with pH=2, with a flow rate of 5 mL / min; S14. Passing the water sample obtained in step S11 through the solid phase extraction cartridge at a flow rate of 5 mL / min to enrich organic matters; S15. Rinsing 3 times with 5 mL of ultrapure water with pH=2 to remove salt residues in the solid phase extraction cartridge, with a flow rate of 5 mL / min, and drying the solid phase extraction cartridge with nitrogen; S16. Eluting the organic matters retained in the solid phase extraction cartridge with 10 mL of methanol in three portions, with a flow rate of 5 mL / min, and collecting the eluate; S17. Freeze-drying the eluate, and then adjusting the volume to 2 mL with methanol.

7. The method for identifying disinfection byproduct precursors in natural water based on FTICR-MS according to claim 6, characterized in that: The pH of the ultrapure water is adjusted with chromatographic grade formic acid.

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