Purge and trap-gas chromatography-mass spectrometry quantitative method for six haloacetonitrile in drinking water

Abstract

The invention discloses a purge and trap-gas chromatography-mass spectrometry quantitative method for six haloacetonitrile in drinking water, which comprises the following steps: controlling the content of water vapor entering a trap by using a water manager, enriching a target object in a sample by using a purge and trap device, and then performing thermal desorption to enter a gas chromatograph-mass spectrometer for sample analysis. According to the present invention, the synchronous quantification of the six main haloacetonitriles such as dichloroacetonitrile, chloroacetonitrile, bromoacetonitrile, bromochloroacetonitrile, dibromoacetonitrile and iodine acetonitrile in the drinking water is achieved, the operation is simple, the whole process is automatically determined after the sample collection, the pollution of the organic reagent is reduced, the environmental protection is achieved, and the green chemistry idea is met.

Description

Technical Field

[0001] The invention relates to the technical field of analytical chemistry, and in particular to a purge-trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water. Background Art

[0002] Disinfection byproducts (DBPs) have become important drinking water contaminants worldwide because of their widespread presence and high concentrations in tap water. Currently, more than 700 DBPs have been identified in drinking water, some of which are known to be cytotoxic, genotoxic, and carcinogenic. Haloacetonitriles (HANs) belong to nitrogen-containing disinfection byproducts (N-DBPs), which are much more toxic than carbon-containing disinfection byproducts (C-DBPs) and have attracted widespread attention. Therefore, the detection of haloacetonitriles in drinking water is of great significance to protecting drinking water safety.

[0003] Halogenated acetonitriles have been detected in many countries and regions. At present, many researchers at home and abroad have developed methods for the determination of halogenated acetonitriles. For example, in Chinese patent CN104713954B, Chen Jiping et al. published a method for detecting the content of halogenated acetonitriles in water samples by dispersed liquid-liquid microextraction programmed temperature gas chromatography / mass spectrometry, Chinese patent CN111307989B, Anton et al. published a method for simultaneously determining trihalomethanes and halogenated acetonitriles in water, Chinese patent CN111537636A, Wang Jingyu et al. published a headspace capillary gas chromatography method for determining four halogenated acetonitriles in water, and Chinese patent CN107192782A, Tao Hui et al. published a method for the simultaneous detection of eight disinfection by-products including four halogenated acetonitriles.

[0004] However, the above-mentioned prior art methods for detecting halogenated compounds have obvious disadvantages, including: 1) Traditional liquid-liquid extraction has problems such as cumbersome operation, serious organic reagent pollution, and susceptibility to interference of the detection structure; 2) The liquid-liquid microextraction method has cumbersome steps and is difficult to achieve automated connection and sampling; 3) The headspace method has low sensitivity; 4) Although the sample pretreatment technology of the solid phase microextraction method is highly automated and environmentally friendly, its sample preparation is slow and more expensive than the purge and trap method.

[0005] In addition, in Chinese patent CN103472167B, Jiang Jin et al. published an analytical method for detecting 10 highly toxic disinfection byproducts in drinking water, which uses a purge and trap instrument to pre-treat the sample and then enters the gas chromatography / mass spectrometry for analysis, and can simultaneously detect 10 disinfection byproducts including 2 halogenated acetonitriles. However, this method cannot be used to achieve the simultaneous determination of more toxic bromoacetonitrile and iodoacetonitrile.

[0006] Therefore, the methods in the prior art waste a large amount of reagents and pollute the environment on the one hand, and also have the problems of being cumbersome, inaccurate quantitative results, and limited simultaneous detection of target halogenated acetonitrile on the other hand. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for quantifying six halogenated acetonitriles in drinking water by purge and trap-gas chromatography-mass spectrometry.

[0008] The technical solution of the present invention is:

[0009] A purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water, characterized in that it comprises the following steps:

[0010] S1, sampling: take a number of drinking water samples and fill the headspace bottle as much as possible to obtain the sample solution;

[0011] S2, sample enrichment: using a purge-and-trap instrument to enrich the sample solution for target halogenated acetonitrile substances;

[0012] S3, determining the operating conditions of the gas chromatography-mass spectrometry instrument;

[0013] The operating conditions of the gas chromatography analysis include: capillary column; carrier gas is high-purity helium with a flow rate of 1 mL / min; injection port temperature is 200-220°C; split injection with a split ratio of 5:1; the chromatographic column box uses a programmed temperature increase from an initial temperature of 40°C to 200°C;

[0014] The mass spectrometry analysis conditions include: the ion source is an electrochemical ion source (EI) temperature of 280°C, the electron energy is 70eV, the transmission line temperature is 250°C, and the detection mode is selected ion detection;

[0015] S4, drawing of standard curves of 6 kinds of haloacetonitriles;

[0016] S5, sample analysis:

[0017] After the sample solution is enriched by the purge and trap instrument in step S2, it enters the gas chromatography-mass spectrometry for analysis to obtain an extracted ion flow chromatogram of the target halogenated acetonitrile substances; the contents of the six halogenated acetonitrile substances in the sample solution are determined based on the extracted ion flow chromatogram of the target halogenated acetonitrile substances and the standard curve.

[0018] Furthermore, the conditions for enriching the target halogenated acetonitrile substances by the purge-trap instrument include: carrier gas: high-purity helium, purge flow rate 40 mL / min; purge time 10 min-13 min, purge at room temperature, desorption temperature of the trap during desorption 160°C-180°C, desorption time 1 min-2 min, trap temperature during baking 180°C-200°C, baking time 15 min-20 min.

[0019] Preferably, the conditions for enriching the target halogenated acetonitrile substances by the purge-trap instrument are: purge time 13 min, purge temperature 25°C, trap desorption temperature 180°C, desorption time 1 min, trap temperature 200°C, baking time 15 min.

[0020] Furthermore, a water manager is provided at the purge trap, and the target halogenated acetonitrile substances enter the trap through the water manager, and the target halogenated acetonitrile substances are then desorbed and back-blown into the water manager through the trap and then enter the gas chromatography-mass spectrometry for sample analysis, which is used to control the water vapor content entering the trap; the temperature of the water manager is set as follows: the temperature during purge is 100°C-140°C, the reverse dry blowing of the water manager is 3min-4min, the temperature during desorption is 0°C-200°C, and the temperature during baking is 200°C-240°C.

[0021] Furthermore, the trap is a 7# trap (OV-1, Tenax).

[0022] Furthermore, the capillary column is a DB-624 chromatographic column with a specification of 60m×0.25mm×1.4μm.

[0023] Furthermore, the chromatographic column box uses programmed temperature increase, specifically including: an initial temperature of 40°C, maintaining the temperature for 2 minutes, then increasing the temperature to 120°C at a rate of 5°C / min, and then increasing the temperature to 200°C at a rate of 10°C / min.

[0024] Further, the drawing of the six haloacetonitriles standard curves includes:

[0025] The six halogenated acetonitrile standard mixtures were used as standards and gradiently diluted to preset concentrations of 10 μg / mL and 1 μg / mL using acetonitrile as a solvent. A certain amount of the mixed standard was then taken and diluted to 40 mL with ultrapure water to prepare aqueous solutions with target concentrations of 0.1, 0.2, 0.5, 1, 2, 5, 10 and 20 μg / L for preparing a standard curve.

[0026] Furthermore, the target halogenated acetonitrile substance is halogenated acetonitrile produced by a disinfection process of drinking water.

[0027] Furthermore, the target halogenated acetonitrile substances include: chloroacetonitrile, dichloroacetonitrile, bromoacetonitrile, bromochloroacetonitrile, dibromoacetonitrile and iodoacetonitrile.

[0028] Furthermore, when measuring six types of halogenated acetonitriles in drinking water, the detection limit was 0.00735μg / L-0.202μg / L, and the minimum detection mass concentration was 0.0245μg / L-0.675μg / L.

[0029] The beneficial technical effects of the present invention are:

[0030] Firstly, the method of the present invention adopts a purge and trap instrument to pretreat the sample, and uses a water manager to control the water vapor content in the trap, and then enters the gas chromatography-mass spectrometry instrument for sample analysis, thereby realizing the simultaneous quantification of six major halogenated acetonitriles, namely dichloroacetonitrile, chloroacetonitrile, bromoacetonitrile, bromochloroacetonitrile, dibromoacetonitrile, and iodoacetonitrile, in drinking water. In addition, the method of the present invention is simple to operate, and the sample is automatically measured throughout the process after collection, thereby reducing the pollution of organic reagents, being environmentally friendly, and conforming to the concept of green chemistry.

[0031] Secondly, the method of the present invention uses a more universal chromatographic column DB-624 column instead of a special Rtx-200 chromatographic column, thereby avoiding frequent replacement of chromatographic columns during sample analysis and greatly increasing analysis efficiency.

[0032] Thirdly, the method of the present invention has a very high sensitivity, and the detection limit of the target object is 0.00735 μg / L-0.202 μg / L, which is better than most of the published methods.

[0033] Fourthly, the method of the present invention overcomes the defects of the existing studies, such as poor sensitivity of detecting compounds and the need for complex derivatization, and provides a scientific and effective method for understanding and studying HANs in highly toxic drinking water. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a diagram showing the effect of the residual chlorine quencher of the present invention on the detection of 6 HANs;

[0035] Figure 2 It is a diagram showing the effect of water sample pH on the detection of 6 HANs in the present invention;

[0036] Figure 3 is a diagram showing the effect of the operating conditions of the water manager on the detection of six HANs in the present invention;

[0037] Figure 4 It is a standard curve diagram of chloroacetonitrile (CAN) in the present invention;

[0038] Figure 5 It is a standard curve diagram of dichloroacetonitrile (DCAN) in the present invention;

[0039] Figure 6 It is a standard curve diagram of bromoacetonitrile (BAN) in the present invention;

[0040] Figure 7 It is a standard curve diagram of dibromoacetonitrile (DBAN) in the present invention;

[0041] Figure 8 It is a standard curve diagram of bromochloroacetonitrile (BCAN) in the present invention;

[0042] Fig. 9 It is a standard curve diagram of iodoacetonitrile (IAN) in the present invention;

[0043] Fig.10 It is an extracted ion current chromatogram obtained after gas chromatography of the six halogen acetonitriles mixed standard in the present invention. DETAILED DESCRIPTION

[0044] In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples. The following examples are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0045] The present invention provides a method for quantifying six halogenated acetonitrile in drinking water by purge and trap-gas chromatography-mass spectrometry, which can realize the simultaneous determination of six halogenated acetonitrile substances produced in drinking water after disinfection process treatment, wherein the six halogenated acetonitrile substances include: chloroacetonitrile (CAN), dichloroacetonitrile (DCAN), bromoacetonitrile (BAN), dibromoacetonitrile (DBAN), bromochloroacetonitrile (BCAN) and iodoacetonitrile (IAN). The specific method includes sampling and sample pretreatment, instrument test condition selection optimization, working curve determination and sample determination.

[0046] S1, sample pretreatment:

[0047] 1) Sampling

[0048] In order to verify the feasibility and sensitivity of the method of the present invention, 16 household tap water samples were collected from the entire city of Kunshan, China for demonstration, and the presence, composition and toxicity of these HANs in household tap water were understood. In April 2024, 16 tap water samples were collected from the main urban areas of Kunshan City, each with 500 mL. The source water of the water plant in the area studied in this embodiment is mainly drinking water after chloramine disinfection process. Before sampling, the tap was drained for 3 minutes, and the brown glass bottle was rinsed with tap water 3 times. The effect of the bottle and the transportation process on the results was evaluated using MilliQ water (18.2MΩ). After the tap water was sampled, it was transported back to the laboratory with ice.

[0049] 2) Sample pretreatment

[0050] Sample pretreatment mainly includes the determination of water sample pH and residual chlorine quencher.

[0051] Effect of residual chlorine quencher on the detection of six HANs

[0052] Water samples with a free residual chlorine content of 1.0 mg / L were prepared and divided into 8 portions, each containing 1.0 L of water. 0 mg, 25 mg, 50 mg, 125 mg, 250 mg, 500 mg, 750 mg, and 1000 mg of ascorbic acid were added per liter of water. Spiking experiments were conducted on water samples with different ascorbic acid contents. The final spike concentration was 5.0 μg / L. The background of water samples with different ascorbic acid contents and the HANs content of spiked water samples were measured to evaluate the effect of ascorbic acid addition on the determination of 6 halogenated acetonitrile. The results are shown in Table 1. Figure 1 As shown in the figure, without adding residual chlorine quencher, the recovery rate of 6 HANs can reach more than 95%. With the increase of ascorbic acid added, the background content of BCAN and DBAN in the water sample gradually decreased, and the spiked recovery rate of BCAN and DBAN also gradually decreased to 30%-54%. It may be due to the reducing property of ascorbic acid that BCAN and DBAN in water will be destroyed. Therefore, in order to ensure the stability of HANs in water samples, the method provided by the present invention chooses not to add residual chlorine quencher.

[0053] Effect of water sample pH on the detection of seven HANs

[0054] The water sample was divided into two portions, each with a 1.0L spike concentration of 5μg / L. One portion was adjusted to a pH value less than 2 with hydrochloric acid, and the other portion was directly measured. The results of the spike recovery of HANs in water samples showed that adjusting the pH value of the water sample did not increase the recovery of the target, but instead reduced the recovery of BCAN, DBAN, and IAN from more than 95% to 20.6%-44.5%. The specific test results are as follows Figure 2 Therefore, the method provided by the present invention chooses to measure directly without adjusting the pH, that is, when the water sample is measured at a pH value of 6.5-8.5.

[0055] Therefore, 40 mL of each tap water sample was taken without adding residual chlorine quencher and adjusting its pH, and the headspace bottle was filled as much as possible to obtain a sample solution of each water sample, and each sample solution was analyzed within 24 hours.

[0056] S2, sample enrichment

[0057] Sample enrichment mainly depends on the selection of the trap in the purge-trap instrument, the selection of the purge time, and the setting and adjustment of the purge conditions.

[0058] Trap selection

[0059] The capture effect of the ion trap is one of the main factors affecting the detection of the target object. The present invention selects the 7# capture trap (OV-1, Tenax) based on the comprehensive capture effect on 6 kinds of HANs.

[0060] Selection of purge time

[0061] The purge time is one of the important factors affecting the sensitivity of compound detection. If the purge time is too short, the compound cannot be completely blown out of the sample. If the purge time is too long, a large amount of water will be blown out, which will affect the response intensity of the target and reduce the sensitivity. The purge time finally selected by the present invention is 13 minutes, at which time the response values ​​of the six HANs reach the highest.

[0062] Setting the purge conditions

[0063] Through experiments, it was found that the water manager conditions during the purge process have a great influence on the detection sensitivity and precision. The water manager temperature and the dry blowing time before purge are set in the purge, desorption, and baking stages to achieve the effect of water removal. In the purge stage, the organic matter blown out of the purge tube enters the trap through the water manager driven by the carrier gas, and then the water manager is dry-blown and back-blown for 2-3 minutes to remove the residual water in the water manager; entering the trap desorption stage, the target object is backblown from the trap back to the water manager. At this time, the water manager stops heating and sets 0℃. If the desorbed compound contains water vapor, the water vapor will cool and become droplets to be discharged, achieving the effect of water removal. The target object finally passes through the water manager and enters the capillary column through the six-way valve for separation and detection. In the above-mentioned backblowing target object from the trap back to the water manager step, if the water manager stops heating and sets 0℃, some compounds with strong polarity will obviously be discharged at the same time, which affects the sensitivity of its detection. This condition can be further optimized according to actual conditions.

[0064] In order to determine the optimal temperature of the water manager when the backflushing target returns to the water manager from the trap, the present invention divides the water sample into two portions of 1.0L each, with a spiked concentration of 5μg / L. Both water samples are blown out of organic matter from the purge tube, and the organic matter enters the trap through the water manager under the drive of the carrier gas, and then the water manager is dry-blown and backflushed. Then, the backflushing target returns from the trap to the water manager, and finally the target passes through the water manager and is controlled by a six-way valve to enter the capillary chromatographic column for separation and detection. One of the water samples does not perform dry backflushing on the water manager, and when the backflushing target returns to the water manager from the trap, the temperature of the water manager is 0°C. The other water sample performs dry backflushing on the water manager for 3 minutes, and when the backflushing target returns to the water manager from the trap, the temperature of the water manager is 120°C. In addition, the other separation test conditions of the two water samples are the same. Among them, the larger the peak area of ​​the separation detection of each target halogenated acetonitrile in the above water sample, the higher the sensitivity of its detection. Figure 3 The vertical axis is the peak area ratio of each target halogenated acetonitrile under different separation and detection conditions. Figure 3 It can be seen that the detection sensitivity of TCAN, BCAN, DBAN and IAN has been significantly improved, especially the detection sensitivity of IAN has increased by about 2 times.

[0065] In summary, the present invention adopts a purge-trap instrument (OI Analytic Eclipse 4760) to enrich the sample solution with the above 6 halogenated acetonitrile substances; the conditions for enriching the target halogenated acetonitrile substances with the purge-trap instrument include: carrier gas: high-purity helium (≥99.999%); purge time 13min, purge flow rate 40mL / min, purge tube quantitative loop 25mL during purge, trap temperature 25°C, desorption, trap desorption temperature 180°C, desorption time 1min, baking, trap temperature 200°C, baking time 15min, the trap is 7# trap (OV-1, Tenax); water manager condition settings: purge temperature 120°C; reverse dry blowing 3min; desorption temperature 120°C, that is, when the backblowing target returns to the water manager from the trap, the water manager temperature is 120°C, and the baking temperature is 240°C.

[0066] S3, determine the operating conditions of the gas chromatography-mass spectrometry instrument:

[0067] The specific operating parameters of the gas chromatograph (Thermo Fisher TRACE 1300) are as follows: the chromatographic column is a DB-624 chromatographic column with a specification of 60m×0.25mm×1.4μm; ultra-high purity helium with a purity greater than 99.999% is used as the carrier gas, and the flow rate is 1mL / min; the injection port temperature is set to 220°C; split injection, the split ratio is 5:1; the chromatographic column box uses a programmed temperature increase, specifically including: the initial temperature is 40°C, after maintaining for 2 minutes, the temperature is increased to 120°C at a rate of 5°C / min, and then the temperature is increased to 200°C at a rate of 10°C / min;

[0068] The specific operating parameters of the mass spectrometer (I SQ 7000) are as follows: the mass spectrometer ion source is an electrochemical ion source (EI), the transfer line temperature is 280 °C, the electron energy is 70 eV, and the sample analysis adopts the selected ion (SIM) mode;

[0069] After the above instrument operating parameters were set, a full scan with a range of m / z 35-200 was run, and the retention time, quantitative ion and qualitative ion information of HANs were determined using the NI ST library search, as shown in Table 1. The sample spike concentrations of chloroacetonitrile, dichloroacetonitrile, bromoacetonitrile, bromochloroacetonitrile, iodoacetonitrile and dibromoacetonitrile were 0.8 μg / L, 0.8 μg / L, 4 μg / L, 4 μg / L, 8 μg / L and 4 μg / L, respectively.

[0070] Table 1 Specific parameters of haloacetonitrile analyzed by this method

[0071]

[0072] As can be seen from Table 1, the method precision of the 6 HANs analyzed was less than 5%, indicating that this method has good reproducibility. For the sample spike recovery rate, the recovery rate of each HANs was between 87.5% and 110%, indicating that this method has excellent recovery. Seven parallel determinations were performed on samples with concentration values ​​of 0.1μg / L-2μg / L. The standard deviation S of the results of 7 parallel determinations was calculated, and 3 times the standard deviation was used as the method detection limit, and 10 times the standard deviation was used as the minimum detection mass concentration. The method detection limit and minimum detection mass concentration of HANs detected by this patent are 0.00735μg / L-0.202μg / L and 0.0245μg / L-0.675μg / L, respectively. The specific test results are shown in Table 2.

[0073] Table 2

[0074]

[0075] S4, drawing of standard curve:

[0076] Accurately pipette 4, 8, and 20 μL of 1 μg / mL 6 kinds of halogenated acetonitrile mixed standard products (Tianjin Alta 1ST82111-100A), dilute to 40 mL with ultrapure water, and prepare mixed standard solutions of 0.1, 0.2, and 0.5 μg / L; accurately pipette 4, 8, 20, 40, and 80 μL of 10 μg / mL 6 kinds of halogenated acetonitrile mixed standard products, dilute to 40 mL with ultrapure water, and prepare mixed standard solutions of 1, 2, 5, 10, and 20 μg / L; after gas chromatography determination, draw the standard curves of the 6 kinds of halogenated acetonitrile with concentration as the horizontal axis and HANs peak area as the vertical axis. The standard curves of the 6 kinds of halogenated acetonitrile are as follows: Figure 4-9 As shown in Table 3, the extracted ion chromatograms obtained after gas chromatography of the six halogenated acetonitrile mixtures are as follows: Fig.10 shown.

[0077] Table 3 Correlation coefficients and linearity of the standard curves of six halogenated acetonitrile

[0078] name Linear range (μg / L) <![CDATA[R 2 ]]> Chloroacetonitrile 0.2-2 0.9998 Dichloroacetonitrile 0.2-2 0.9995 Bromoacetonitrile 1-10 0.9994 Bromochloroacetonitrile 1-10 0.9984 Iodoacetonitrile 2-10 0.9998 Dibromoacetonitrile 1-10 0.9980

[0079] Table 3 shows that the standard curves of HANs have a good linear relationship, among which the R 2 It is 0.9980-0.9998.

[0080] S5, sample analysis

[0081] The above 16 sample solutions were enriched by the purge and trap instrument in step S2, and then entered into the gas chromatography-mass spectrometry for analysis and determination to obtain the peak area, and then calibrated using the working curve, and the concentration of the six halogenated acetonitriles in drinking water in each sample solution was obtained using the standard curve. The specific results are shown in Table 4.

[0082] Table 4 Concentration of halogenated acetonitrile in drinking water in Kunshan City (μg / L)

[0083]

[0084]

[0085] As can be seen from Table 4, the target halogenated acetonitrile analyzed was detected to a certain extent in the drinking water of Kunshan City. The total concentration of the six types of halogenated acetonitrile was 0.180-2.90 μg / L, and the average concentration was 1.32 μg / L. For the drinking water of Kunshan City, among the six types of halogenated acetonitrile in the measured samples, the one with the highest average concentration was bromochloroacetonitrile, 0.545 μg / L, and the highest concentration was 1.12 μg / L. For other types of halogenated acetonitrile, the highest concentration of chloroacetonitrile was 0.172 μg / L, the highest concentration of dichloroacetonitrile was 1.071 μg / L, and the highest concentration of dibromoacetonitrile was 0.749 μg / L. Bromoacetonitrile and iodoacetonitrile were not detected. Halogenated acetonitrile is a highly toxic nitrogen-DBPs (N-DBPs), and its cytotoxicity is 2-3 orders of magnitude higher than that of trihalomethanes. Therefore, its pollution status and its threat to drinking water safety cannot be ignored.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A purge and trap-gas chromatography-mass spectrometry method for quantifying six halogenated acetonitriles in drinking water, characterized in that: The following steps are involved: S1, sampling: take a number of drinking water samples and fill the headspace bottle as much as possible to obtain the sample solution; S2, sample enrichment: using a purge-and-trap instrument to enrich the sample solution for target halogenated acetonitrile substances; S3, determining the operating conditions of the gas chromatography-mass spectrometry instrument; The operating conditions of the gas chromatography analysis include: capillary column; carrier gas is high-purity helium with a flow rate of 1 mL / min; injection port temperature is 200-220°C; split injection with a split ratio of 5:1; the chromatographic column box uses a programmed temperature increase from an initial temperature of 40°C to 200°C; The mass spectrometry analysis conditions include: the ion source is an electrochemical ion source (EI) temperature of 280°C, the electron energy is 70eV, the transmission line temperature is 250°C, and the detection mode is selected ion detection; S4, drawing of standard curves of 6 kinds of haloacetonitriles; S5, sample analysis: After the sample solution is enriched by the purge and trap instrument in step S2, it enters the gas chromatography-mass spectrometry for analysis to obtain an extracted ion flow chromatogram of the target halogenated acetonitrile substances; the contents of the six halogenated acetonitrile substances in the sample solution are determined based on the extracted ion flow chromatogram of the target halogenated acetonitrile substances and the standard curve.

2. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 1, characterized in that: The conditions for enriching the target halogenated acetonitrile substances with the purge-trap instrument include: carrier gas: high-purity helium, purge flow rate 40 mL / min; purge time 10 min-13 min, purge at room temperature, trap desorption temperature 160° C.-180° C. during desorption, desorption time 1 min-2 min, trap temperature 180° C.-200° C. during baking, baking time 15 min-20 min.

3. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 2, characterized in that: The purge-trap instrument is provided with a water manager, and the target halogenated acetonitrile substances enter the trap through the water manager, and the target halogenated acetonitrile substances are then desorbed and back-blown into the water manager through the trap and then enter the gas chromatography-mass spectrometry for sample analysis, which is used to control the water vapor content entering the trap; the temperature of the water manager is set as follows: the temperature during purge is 100°C-140°C, the reverse dry-blowing water manager is 3min-4min, the temperature during desorption is 0°C-200°C, and the temperature during baking is 200°C-240°C.

4. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 2, characterized in that: The trap is a 7# trap (OV-1, Tenax).

5. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 1, characterized in that: The capillary column is a DB-624 chromatographic column with a specification of 60m×0.25mm×1.4μm.

6. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 1, characterized in that: The chromatographic column box uses a programmed temperature increase, specifically including: an initial temperature of 40°C, the temperature is maintained for 2 minutes, the temperature is increased to 120°C at a rate of 5°C / min, and then the temperature is increased to 200°C at a rate of 10°C / min.

7. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 1, characterized in that: The drawing of the six haloacetonitriles standard curves includes: The six halogenated acetonitrile standard mixtures were used as standards and gradiently diluted to preset concentrations of 10 μg / mL and 1 μg / mL using acetonitrile as a solvent. A certain amount of the mixed standard was then taken and diluted to 40 mL with ultrapure water to prepare aqueous solutions with target concentrations of 0.1, 0.2, 0.5, 1, 2, 5, 10 and 20 μg / L for preparing a standard curve.

8. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 1, characterized in that: The target halogenated acetonitrile substances are halogenated acetonitrile produced by a disinfection process of drinking water.

9. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 1, characterized in that: The target halogenated acetonitrile substances include: chloroacetonitrile, dichloroacetonitrile, bromoacetonitrile, bromochloroacetonitrile, dibromoacetonitrile and iodoacetonitrile.

10. The purge and trap-gas chromatography-mass spectrometry quantitative method for six halogenated acetonitriles in drinking water according to claim 1, characterized in that: When measuring 6 types of halogenated acetonitriles in drinking water, the detection limit was 0.00735μg / L-0.202μg / L, and the minimum detection mass concentration was 0.0245μg / L-0.675μg / L.

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