A Gas Chromatography-Mass Spectrometry Analysis Method for Haloacetic Acids in Drinking Water

Abstract

The present invention relates to a gas chromatography-mass spectrometry analysis method for haloacetic acids in drinking water, belonging to the technical field of analytical chemistry. Compared with the prior art, the present invention uses GC-MS to establish a quantitative method for haloacetic acids in drinking water, overcomes the drawbacks of the standard method provided by the US Environmental Protection Agency (USEPA, 552.3), the supporting method of the "Drinking Water Quality Standard" in China (GB / T 5749-2006), and the diazomethane derivatization method, realizes one-step liquid-liquid extraction, can be directly analyzed quantitatively after simple derivatization, and obtains high sensitivity, high spiked recovery rate, low method detection limit, and low quantification limit. The method of the present invention can efficiently, rapidly and accurately determine haloacetic acids in drinking water.

Description

Technical Field

[0001] The present invention relates to the technical field of analytical chemistry, and particularly to a gas chromatography-mass spectrometry analysis method for haloacetic acids in drinking water. Background Art

[0002] Haloacetic acids are the most common disinfection by-products in drinking water. Their concentrations in drinking water usually range from dozens to hundreds of μg / L, making them the second most common carbon-containing disinfection by-products (C-DBPs) after trihalomethanes. However, haloacetic acids are more toxic than trihalomethanes and less volatile, so the threat they pose to drinking water safety and human health deserves more attention. In the "Sanitary Standard for Drinking Water" (GB / T 5749-2006) promulgated in China in 2006, the limits for dichloroacetic acid and trichloroacetic acid were specified, with maximum limits of 50 μg / L and 100 μg / L respectively. Establishing a sensitive, simple, and efficient analysis method for haloacetic acids is the basis for understanding the pollution status of these substances in drinking water and their potential human health risks.

[0003] Currently, there are many methods for the determination of haloacetic acids. The most mainstream methods are the standard method provided by the US Environmental Protection Agency (USEPA, 552.3) and the supporting method of the "Quality Standard for Drinking Water in China" (GB / T 5749-2006). Both of these methods use acidified methanol to derivatize haloacetic acids and then detect them using gas chromatography-electron capture detector (GC-ECD). This method has problems such as a complex process, low enrichment factor, high detection limit, and low recovery rate for monochloroacetic acid, and thus needs to be further improved. Diazomethane derivatization is also a commonly used method for the detection of haloacetic acids, which effectively overcomes the problems of low enrichment factor, high detection limit, and low recovery rate of monochloroacetic acid in USEPA 552.3 and GB / T 5749-2006. However, the preparation of diazomethane requires a complex process, and the generated diazomethane is prone to explosion and difficult to store, so it is not an ideal alternative method.

[0004] At present, many researchers at home and abroad have improved the standard method. For example, Ding Liping et al. disclosed "A gas chromatography method for the determination of nine trace haloacetic acids in barreled drinking water (Publication No.: CN 109212050 A)". This method uses hydroxymethylsulfonate-magnesium-aluminum type hydrotalcite to enrich haloacetic acids by dispersive solid-phase extraction, then uses acid to dissolve the adsorbent to elute haloacetic acids, then uses an organic solvent to extract haloacetic acids in the aqueous solution into the organic solvent, and then uses methanol and trimethylsilyldiazomethane n-hexane to derivatize haloacetic acids, and finally uses GC-ECD for detection. This method uses hydroxymethylsulfonate-magnesium-aluminum type hydrotalcite for extraction, and its materials are not easy to obtain and the price is not low, so it is not economical. Secondly, this method involves multiple extractions and elutions as well as relatively complex derivatization, and the process is cumbersome. In addition, for the determination of samples using GC-ECD, because there is no mass spectrometry, it is very easy to be interfered by the matrix and show false positives, and for most haloacetic acids, the detection limit and quantification limit of this method are too high and not sensitive enough. Especially for monochloroacetic acid, the quantification limit is as high as 3.1 μg / L, far higher than its actual concentration in drinking water.

[0005] Duan Jinming et al. published "A rapid detection method for disinfection by-product haloacetic acids in drinking water (Publication No.: CN102520083 A)". This method does not require pretreatment and directly uses liquid chromatography-mass spectrometry to detect haloacetic acids in drinking water and obtains a very low quantification limit (0.05 - 0.86 μg / L). However, according to the patent drawings and attempts, it can be seen that the method published by this author has obvious defects. First of all, because there is no enrichment, for such a low concentration, it is very difficult for the mass spectrometry to have a response. Moreover, the quantification limit of this method is basically the same as that reported in the literature for the same analysis using liquid chromatography-mass spectrometry, but the sample is enriched by several hundred times. In addition, we can see from the author's drawings that most of the haloacetic acids basically have no response, and the abundance of the noise peaks is basically the same as that of the target compounds. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a gas chromatography-mass spectrometry analysis method for haloacetic acids in drinking water. Compared with the existing analysis methods, the method of the present invention is simple and highly sensitive, and can be used for the accurate determination of haloacetic acids in drinking water.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] The present invention provides a gas chromatography-mass spectrometry analysis method for haloacetic acids in drinking water, comprising the following steps:

[0009] (1) Take a water sample of drinking water, quench it with a residual chlorine quenching agent, and extract haloacetic acids in the drinking water with an organic solvent to prepare a sample solution;

[0010] (2) Using haloacetic acid as the reference standard, and using an organic solvent as the solvent, a mixed standard solution is prepared by successive dilution.

[0011] (3) The mixed standard solution and the sample solution are respectively detected and analyzed by a gas chromatography-mass spectrometry (GC-MS) instrument.

[0012] (4) According to the detection and analysis results in step (3), a standard curve is plotted and sample analysis is performed.

[0013] In one embodiment of the present invention, in step (1), the haloacetic acid in the drinking water is a disinfection by-product obtained from the disinfection process of the drinking water.

[0014] In one embodiment of the present invention, in step (1), the organic solvent is selected from one or more of methyl tert-butyl ether, n-hexane, and ethyl acetate.

[0015] In one embodiment of the present invention, the specific steps of step (1) are: taking a water sample of the drinking water, measuring the residual chlorine in the water, quenching with a residual chlorine quenching agent, adjusting the pH to acidic, adding an injection internal standard and a derivatization reagent to obtain a sample solution.

[0016] In one embodiment of the present invention, the pH < 1.

[0017] In one embodiment of the present invention, the derivatization reagent is selected from silylation reagents.

[0018] In one embodiment of the present invention, the silylation reagent is selected from one or more of bis(trimethylsilyl)trifluoroacetamide, N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide, trimethylchlorosilane, hexamethyldisilazane, and N,N-dimethylformamide.

[0019] In one embodiment of the present invention, the residual chlorine quenching agent is ascorbic acid and / or ammonium chloride.

[0020] In one embodiment of the present invention, the derivatization conditions of the derivatization reagent are: heating temperature 25°C - 80°C, reaction time 10 min - 30 min.

[0021] In one embodiment of the present invention, in step (2), the haloacetic acid is selected from one or more of monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, dibromoacetic acid, monochloro monobromoacetic acid, and monoiodoacetic acid.

[0022] In one embodiment of the present invention, in step (3), the gas chromatography analysis conditions in the gas chromatography-mass spectrometry are as follows: the chromatographic column is an HP-5ms chromatographic column, the carrier gas is helium, and the carrier gas flow rate is 1 mL / min - 2 mL / min; the inlet temperature is 200°C - 280°C; splitless injection is used, and the injection volume is 1 μL - 2 μL; the temperature programming: the initial temperature is maintained at 35°C for 2 min, then heated to 100°C at a rate of 4°C / min and maintained for 2 min, then heated to 130°C at a rate of 9°C / min and maintained for 1 min, and finally heated to 280°C at a rate of 12°C / min, and the post-run time is 3 min.

[0023] The principle of the preparation method of the present invention is as follows:

[0024] The present invention targets 7 common haloacetic acids in drinking water, enriches them by liquid-liquid extraction, and then selects a silane reagent for derivatization. The reaction mechanism is shown in formula (1). By optimizing the capillary chromatographic column, inlet temperature, temperature programming, and characteristic ions of haloacetic acids, a selected ion (SIM) analysis method for 7 haloacetic acids is established. It provides an efficient, simple, and sensitive analysis method for the detection of haloacetic acids in drinking water.

[0025]

[0026] The technical solution of the present invention has the following advantages:

[0027] (1) The present invention uses a silane reagent to replace the active hydrogen in the haloacetic acid molecule, reduces the polarity of the haloacetic acid, increases the volatility of the haloacetic acid, and enables it to be analyzed by gas chromatography-mass spectrometry.

[0028] (2) The method of the present invention avoids the complex processes of diazomethane and acidified methanol derivatization methods, saving analysis time and chemical reagents.

[0029] (3) The method of the present invention has high sensitivity, low method detection limit and quantification limit, and can be used for the analysis of trace haloacetic acids with high toxicity in drinking water, such as monochloroacetic acid and monoiodoacetic acid.

[0030] (4) The method of the present invention uses mass spectrometry for quantification, avoiding the false positive problem of the GC-ECD method.

[0031] (5) The present invention provides a gas chromatography - mass spectrometry analysis method for haloacetic acids in drinking water, and a quantitative method for haloacetic acids in drinking water is established by using GC - MS. Compared with the prior art, the present invention overcomes the drawbacks of the standard method provided by the US Environmental Protection Agency (USEPA, 552.3), the supporting method of the "Drinking Water Quality Standard" in China (GB / T 5749 - 2006), and the diazomethane derivatization method. It realizes one - step liquid - liquid extraction, and can be directly quantified on the machine after simple derivatization, and obtains high sensitivity, high spike recovery rate, low method detection limit, and low quantification limit. Using the method of the present invention, haloacetic acids in drinking water can be determined efficiently, quickly, and accurately. Description of the Drawings

[0032] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in combination with the drawings, where

[0033] Figure 1 is the total ion chromatogram of haloacetic acids in drinking water in Example 1 of the present invention. Detailed Embodiments

[0034] The following further illustrates the present invention in combination with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the examples given are not intended to limit the present invention.

[0035] Example 1

[0036] (1) Sample collection

[0037] Collect 12 tap water samples from urban households in Suzhou. Before collection, let the water run for 3 minutes to ensure that the collected samples are tap water from the pipe network. Then wash the brown glass bottles three times with tap water, and then collect 500 mL of tap water at each sampling point. After the water samples are collected, immediately transport them to the laboratory for storage at low temperature (8 °C).

[0038] (2) Liquid - liquid extraction

[0039] After determining the residual chlorine in water using DPD reagent, quench with ascorbic acid at 110% (molar concentration) of the residual chlorine amount, then add 1 mL of concentrated sulfuric acid to make the pH of the solution < 1. Take 100 mL of the aqueous solution, transfer it to a 125 mL brown glass bottle, then add 15 g of anhydrous sodium sulfate and 8 mL of methyl tert-butyl ether. After shaking for 1 min, transfer it to a 15 mL glass test tube. Repeat this process twice and combine the organic phases. Add 5 g of anhydrous sodium sulfate to the organic phase to remove the water in the solution, then transfer the organic phase to a new glass test tube, concentrate it to 0.2 mL at room temperature using nitrogen blowing, then transfer it to a 2 mL injection vial with an inner insert tube, add 5 μL of injection internal standard (1,2-dibromopropane) and 10 μL of silanization reagent, and then react in an oven at 50 °C for 30 min. After the reaction is completed, cool it to room temperature and wait for instrumental analysis.

[0040] (3) Instrumental analysis

[0041] The analysis of the sample was performed using an Agilent 7890 gas chromatograph - 5977 mass spectrometer. The specific parameters are as follows: The chromatographic column was an HP-5ms chromatographic column (model 30 m x 0.25 mm x 0.25 μm). The carrier gas was ultra-high purity helium (purity greater than 99.999%), and the carrier gas flow rate was 1 mL / min; the inlet temperature was 250 °C; splitless injection was used, and the injection volume was 1 μL.

[0042] The temperature programming of the column oven was as follows: The initial temperature was maintained at 35 °C for 2 min, then it was heated at a rate of 4 °C / min to 100 °C and maintained for 2 min, then it was heated at a rate of 9 °C / min to 130 °C and maintained for 1 min, and finally it was heated at a rate of 12 °C / min to 280 °C, and the post-run time was 3 min. The mass spectrometry ion source temperature was 230 °C, the quadrupole temperature was 150 °C, and the electron energy was 70 eV. The sample analysis was carried out in selected ion (SIM) mode, and the quantitative and qualitative ion information of 7 haloacetic acids is shown in Table 1 and Figure 1 .. After the instrument settings were completed, the retention time was determined using the standard of haloacetic acid, and then the standard curve was plotted using the mixed standard. The specific content can be seen in the drawing of the working curve.

[0043] Table 1 Retention time, quantitative ion, qualitative ion, method detection limit and quantification limit (μg / L) of haloacetic acids in drinking water

[0044]

[0045] From Table 1 and Figure 1It can be seen that this method has good sensitivity. The method detection limits and quantification limits of the 7 haloacetic acids are mostly lower than 0.05 μg / L, far lower than the mainstream haloacetic acid analysis methods (the standard method provided by the US Environmental Protection Agency (USEPA, 552.3), the supporting method of the "Drinking Water Quality Standard" in China (GB / T 5749-2006), and the diazomethane derivatization method). However, the treatment process of this method is much simpler than the mainstream haloacetic acid analysis methods. In addition, for the 7 haloacetic acids on the HP-5 chromatographic column, they all have good peak shapes and responses( Figure 1 ), indicating that it is an ideal chromatographic column for haloacetic acid analysis.

[0046] (4) Working curve drawing

[0047] Purchase a mixed standard of haloacetic acids (1000 mg / L), and then dilute it with methyl tert-butyl ether to solutions of 20 mg / L, 2 mg / L, and 1 mg / L. Take 8 clean 125 mL brown glass bottles, add 100 mL of ultrapure water, and then use the above-diluted solutions to prepare haloacetic acid solutions with concentrations of 0.01 μL, 0.05 μL, 0.1 μL, 0.5 μL, 1 μL, 5 μL, 10 μL, and 20 μL. After acidification with concentrated sulfuric acid, add 15 g of anhydrous sodium sulfate and 8 mL of methyl tert-butyl ether. After shaking for 1 min, transfer it to a 15 mL glass test tube. This process is repeated twice, and the organic phases are combined. Add 5 g of anhydrous sodium sulfate to the organic phase to remove the water in the solution, then transfer the organic phase to a new glass test tube, concentrate it to 0.2 mL at room temperature with nitrogen blowing, then transfer it to a 2 mL injection vial with an inner insert tube, add 5 μL of injection internal standard (1,2-dibromopropane) and 10 μL of silanization reagent, and then react in an oven at 50 °C for 30 min. After the reaction is completed, cool it to room temperature and wait for instrumental analysis. After determination by gas chromatography-mass spectrometry, with the peak area of haloacetic acid as the abscissa and the concentration as the ordinate, perform linear fitting to obtain the working curve of haloacetic acid, as shown in Table 2 specifically.

[0048] Table 2 Fitting curves of haloacetic acids in drinking water

[0049]

[0050] As can be seen from Table 2, through silane derivatization, the working curves of all 7 haloacetic acids have very good linearity (>0.99), indicating that it can be used for the quantitative analysis of haloacetic acids in actual samples.

[0051] (5) Sample analysis

[0052] The 7 haloacetic acid contents in the tap water of 12 families were analyzed and measured using the above steps to obtain the peak areas, and then the concentrations in the drinking water were obtained by calibration with the working curve (internal standard method). The specific results are shown in (Table 3).

[0053] Table 3 Concentrations of haloacetic acids in tap water of urban families in Suzhou (μg / L).

[0054]

[0055] It can be concluded from Table 3 that all haloacetic acids exist in the drinking water of Suzhou families. Among them, the average concentrations of dichloroacetic acid, trichloroacetic acid, chlorobromoacetic acid and dibromoacetic acid are all >1 μg / L, showing relatively high concentration levels. The concentrations of monochloroacetic acid, bromoacetic acid and monoiodoacetic acid are all <1 μg / L, especially the concentration of monoiodoacetic acid is lower than 0.1 μg / L. Monoiodoacetic acid is currently the disinfection by-product with the strongest cytotoxicity, and animal experiments have proved its carcinogenicity. Therefore, developing a method that can detect low-concentration but highly toxic disinfection by-products is of great significance for protecting the safety of drinking water.

[0056] (6) Quality control and assurance

[0057] In order to investigate the reliability of the method, the present invention carried out recovery monitoring. Tap water samples from urban areas of Suzhou were selected for parallel sample experiments and matrix spike addition to determine the precision of the method. In addition, in order to obtain the detection limit of the method, we spiked ultrapure water with (0.1 μg / L) and then analyzed it in parallel seven times.

[0058] The method detection limit was determined by the following formula:

[0059] MDL = 3.14×S (1)

[0060]

[0061] In the formula, MDL is the method detection limit (μg / L), and S is the standard deviation. The specific results are shown in Table 1 and Table 4.

[0062] Table 4 Spike recovery rates and precisions of haloacetic acids in drinking water

[0063]

[0064] It can be seen from Table 4 that the spike recovery rates of this method are between 70 - 130%, and the precisions are all far <30%, all meeting the requirements of the analysis methods for pollutants in drinking water.

[0065] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A gas chromatography - mass spectrometry analysis method for haloacetic acids in drinking water, characterized in that, It includes the following steps: (1) Take a water sample of drinking water, quench it with a residual chlorine quenching agent, adjust the pH to acidic, extract haloacetic acids in the drinking water with an organic solvent, add an injection internal standard and a derivatization reagent to prepare a sample solution; (2) Use haloacetic acids as standards, use an organic solvent as a solvent, and prepare a mixed standard solution by stepwise dilution; (3) Detect and analyze the mixed standard solution and the sample solution respectively with a gas chromatography-mass spectrometry instrument; (4) Draw a standard curve and conduct sample analysis according to the detection and analysis results in step (3); The derivatization reagent is selected from silanization reagents; In step (1), the organic solvent is selected from one or more of methyl tert-butyl ether, n-hexane, and ethyl acetate; In step (2), the haloacetic acids are selected from chloroacetic acid, dichloroacetic acid, trichloroacetic acid, bromoacetic acid, dibromoacetic acid, bromochloroacetic acid, and iodoacetic acid; The silanization reagent is selected from one or more of bis(trimethylsilyl)trifluoroacetamide, N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide, trimethylchlorosilane, hexamethyldisilazane, and N,N-dimethylformamide; The derivatization conditions of the derivatization reagent are: heating temperature 25°C - 80°C, reaction time 10 min - 30 min.

2. The gas chromatography-mass spectrometry analysis method according to claim 1, wherein In step (1), the haloacetic acids in the drinking water are disinfection by-products obtained from the disinfection process of the drinking water.

3. The gas chromatography-mass spectrometry analysis method according to claim 1, wherein The pH < 1.

4. The gas chromatography-mass spectrometry analysis method according to claim 1, wherein The residual chlorine quenching agent is ascorbic acid and / or ammonium chloride.

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