Method for detecting contents of trichloromethane and carbon tetrachloride in water body

Abstract

The invention provides a method for detecting the content of trichloromethane and carbon tetrachloride in a water body, which comprises the following steps: S1, pretreatment: collecting a to-be-detected water sample, placing the collected to-be-detected water sample in a headspace bottle, enabling the headspace bottle to enter a headspace automatic sampler, and heating at 60-70 DEG C for 15-25 minutes; s2, detecting and analyzing the water sample to be detected by using a gas chromatography-mass spectrometry analyzer; s3, substituting the obtained detection result into the standard curve to determine the content of trichloromethane and carbon tetrachloride in the water sample to be detected; a standard curve is drawn as follows: step 1, N, N-dimethylformamide and water are taken as diluents, trichloromethane and a carbon tetrachloride standard mother solution are diluted, and a standard use solution is obtained; respectively preparing standard working solutions with different concentrations by using the standard use solutions; and 2, detecting and analyzing the standard working solutions with different concentrations according to the sequence of S1 and S2, and drawing a standard curve according to obtained detection results. The method can realize accurate determination of trichloromethane and carbon tetrachloride in a water sample, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental detection, and in particular relates to a method for detecting the contents of chloroform and carbon tetrachloride in water. Background Art

[0002] Chloroform and carbon tetrachloride are two of the most common laboratory parameters for daily testing in water. They belong to a category of highly toxic chemicals (halogenated hydrocarbons), and their sources are products of water disinfection or environmental pollution. Human production and life are inseparable from water, and they can easily migrate from the environment to the human body. In particular, long-term drinking of water contaminated by chloroform and carbon tetrachloride will increase the risk of cancer in humans. Therefore, it is of great significance to accurately determine the content of such halogenated hydrocarbons in water.

[0003] At present, the more popular method for determining chloroform and carbon tetrachloride in water is headspace capillary gas chromatography, ECD detector determination, and the implementation standard is GB / T 5750.8-2023 Standard Test Method for Drinking Water (Part 8 Organic Matter Index). However, the chloroform and carbon tetrachloride standards currently on the market all use methanol as the matrix liquid, and the HP-5 column recommended by the national standard can indeed separate chloroform and carbon tetrachloride, but studies have shown that methanol used in the laboratory can also produce peaks, and the elution time of its main target peak is basically the same as the elution time of chloroform. The same situation is inferred from the commonly used organic reagents such as acetone and acetonitrile in the laboratory. In other words, the HP-5 column GC-ECD method cannot effectively distinguish organic reagents from chloroform, because there is no way to prove that the target peak is chloroform, or an interference peak, or a coexistence of chloroform and organic reagents. Therefore, if methanol is continued to be used to dilute the standard stock solution, the actual content of methanol entering the headspace bottle will further increase, and the distortion of the obtained chloroform standard curve will also be greater; if pure water is used to dilute the standard stock solution, although the distortion of the chloroform standard curve is reduced, due to the characteristics of chloroform that it is not easily miscible with water, theoretically, the effect of uniform distribution of chloroform in water mainly depends on the uniform diffusion of methanol in water to maintain the good linearity of the chloroform standard curve. Studies have shown that DB-1 column, DB-1701 column, DB-FFAP column, DB-WAX column, DB-624ultrainert (30m×0.25mm×1.4μm) column can also not effectively distinguish organic reagents such as methanol from chloroform.

[0004] The current national standard GB / T 5750.8-2023 (4.2) also stipulates the purge and trap gas chromatography-mass spectrometry method, which brings hope for effectively distinguishing organic reagents such as methanol from chloroform, but its disadvantages are obvious: first, a dedicated purge and trap device is required, which is also a low-usage device in specialized testing institutions and is difficult to popularize; second, the mass spectrometer uses full scan mode (scan mode) to obtain target information, which undoubtedly greatly reduces the detection sensitivity. At the same time, the characteristic ions of the target recommended by this standard are close to or the same as the characteristic ions of other halogenated hydrocarbons. Therefore, the target is easily interfered by other organic substances in the water sample during data analysis. Summary of the invention

[0005] In order to solve the problems and shortcomings in the prior art, the present invention provides a method for detecting the content of chloroform and carbon tetrachloride in water. The method develops a headspace + gas chromatography-mass spectrometry (GC-MS / MS) detection technology, and uses a multiple reaction ion monitoring mode (dMRM mode) to efficiently and accurately determine chloroform and carbon tetrachloride in water. Under existing instrument conditions, only one headspace automatic sampler is needed to accurately determine chloroform and carbon tetrachloride in a water sample, which has a good application prospect.

[0006] The invention provides a method for detecting the contents of chloroform and carbon tetrachloride in water, comprising the following steps: S1. pretreatment: collecting a water sample to be tested and placing it in a headspace bottle, allowing the headspace bottle to enter a headspace automatic sampler, and heating it at 60-70 DEG C for 15-25 minutes; S2. using a gas chromatograph-mass spectrometer to detect and analyze the water sample to be tested; S3. substituting the obtained detection results into a standard curve to determine the contents of chloroform and carbon tetrachloride in the water sample to be tested; the standard curve is drawn as follows: step 1, using N, N-dimethylformamide and water as diluents to dilute chloroform and carbon tetrachloride standard mother solutions to obtain standard use solutions; using the standard use solutions to prepare standard working solutions of different concentrations; step 2, detecting and analyzing the standard working solutions of different concentrations in the order of S1 and S2, and drawing the standard curve with the obtained detection results.

[0007] In the method for detecting the content of chloroform and carbon tetrachloride in water provided by the present invention, the detection and analysis means adopted is headspace + gas chromatography-mass spectrometry, and the relative abundance of the characteristic ions of the sample chromatographic peak and the characteristic ions of the standard chromatographic peak are compared for qualitative judgment; based on the quantitative ion response value of the sample as the quantitative reference, quantitative judgment is performed by standard curve regression according to the external standard method.

[0008] The standard curve has a vital impact on the accuracy of the test results in water testing. The standard curve is a numerical curve of properties obtained by measuring a certain physical and chemical property of a series of standard substances with known components. It is a functional relationship between the physical / chemical properties of the standard substance and the instrument response, and is mainly used to derive the physical and chemical properties of the substance to be tested. In the process of drawing and using the standard curve, it is necessary to pay attention to many aspects to ensure the accuracy of the test results. Among the many influencing factors, the selection of appropriate standards is crucial for the drawing of standard curves, especially the solutes and solvents of the standard substances, which have a certain influence on the drawing of the standard curve and affect the accuracy of the test results.

[0009] The invention uses N,N-dimethylformamide and water as diluents for the standard mother liquors of chloroform and carbon tetrachloride, thereby effectively improving the accuracy of the drawn standard curve, thereby greatly improving the accuracy and sensitivity of detecting the contents of chloroform and carbon tetrachloride in water.

[0010] The current relevant standards do not mention the dilution of chloroform and carbon tetrachloride standard products at all, and all pre-treatment operations are carried out according to the personal will of the experimenter, so the data detected will vary from person to person. As described in the background technology, the commonly used reagents such as methanol, acetone and acetonitrile in the laboratory that are easily miscible with water contain chloroform. Since the measured target product has abnormal interference, some experimenters will definitely give up using these reagents and directly use pure water to dilute the standard products to save trouble. But the prerequisite is that the standard products must be prepared and used now, because the standard use solution obtained by diluting it like this is not suitable for preservation. Studies have shown that only 24 hours intervals, the peak area of ​​the standard products at the same concentration point can be reduced by 50%. If the experimenter continues to retain the use of the remaining standard products, it will cause the inaccuracy of the next test result, and the preparation and use of the standard products each time will increase the detection cost. The diluent used in the present invention contains N, N-dimethylformamide and water. N, N-dimethylformamide, as a strong polar reagent, can be mixed with chloroform and carbon tetrachloride of weak polarity and evenly distributed in the water layer of strong polarity. Since the target is locked by N, N-dimethylformamide, the shelf life will be significantly extended. When the headspace bottle is heated, the target is freed from the bondage of N, N-dimethylformamide and is effectively detected after reaching a stable state of gas-liquid separation, so the detection accuracy and sensitivity of chloroform and carbon tetrachloride can be effectively improved.

[0011] In addition, in the detection method provided by the present invention, the water sample to be tested is first heat-treated at a specific temperature for a period of time. This is because the water sample to be tested is sealed in the headspace bottle. As the temperature cools, a part of the target will return to the liquid, so the content of the target in the upper air layer of the liquid surface will decrease. If the sample is directly injected at this moment, the content of the target in the gas layer of the headspace bottle will decrease, and even a false negative situation may occur. The relative deviation between parallel samples will also increase at the same time. On the contrary, heating is performed before injection, and the target reaches the best gas-liquid equilibrium state between the liquid and the air layer, the response value increases, and the parallelism becomes better. The heating temperature and heating time of different detection targets will have certain differences. Under the heating temperature and heating time of the above-mentioned S1, it is conducive to chloroform and carbon tetrachloride to reach the best gas-liquid equilibrium state between the liquid and the air layer, increase the response value, and optimize parallelism.

[0012] Preferably, in S1, the headspace conditions are: oven temperature: 63-67°C; equilibrium time: 18-22 min; transfer line temperature: 113-117°C; injection needle temperature: 83-87°C; injection interval time: not less than the time from the gas chromatography to the temperature stabilization.

[0013] Preferably, in S1, the headspace conditions are: oven temperature: 65°C; equilibration time: 20 min; transfer line temperature: 115°C; injection needle temperature: 85°C; injection interval time: 22 min.

[0014] Preferably, in S2, in the gas chromatography-mass spectrometer, the gas chromatography-mass spectrometry analysis conditions are: capillary column: DB-5MS capillary column; injection port temperature: 278-282°C; carrier gas: He; flow rate 1.1-1.3 mL / min, constant flow mode; split injection, split ratio 10:1; column box temperature: initial 39-41°C maintained for 4.5-5.5 min, program temperature rise 18-22°C / min to 98-102°C, maintained for 3 min; continue program temperature rise 23-27°C / min n to 148-152℃, maintain for 1.8-2.2min; EI ion source temperature: 278-282℃; ionization voltage: 68-72ev; quadrupole temperature: 148-152℃; auxiliary channel temperature: 278-282℃; emission voltage: 1495-1505ev; collision cell quenching gas, helium, 2.20-2.30mL / min; collision gas, nitrogen, 1.45-1.55mL / min; scanning mode: multiple reaction ion monitoring mode; solvent delay: 2.5-3.5min.

[0015] Preferably, in S2, the gas chromatography-mass spectrometry analysis conditions are as follows: capillary column: DB-5MS capillary column, injection port temperature: 280°C; carrier gas: He; flow rate 1.2 mL / min, constant flow mode; split injection, split ratio 10:1; column box temperature: initially 40°C for 5 min, program temperature rise 20°C / min to 100°C, maintain for 3 min; continue program temperature rise 25°C / min to 150°C, maintain for 2 min; EI ion source temperature: 280°C; ionization voltage: 70 ev; quadrupole temperature: 150°C; auxiliary channel temperature: 280°C; emission voltage: 1500 ev; collision cell quenching gas, helium, 2.25 mL / min; collision gas, nitrogen, 1.5 mL / min; scanning mode: multiple reaction ion monitoring mode (dMRM); solvent delay: 3 min.

[0016] Preferably, the DB-5MS capillary tube chromatographic column is an ultra-high inert capillary tube chromatographic column with a column length of 60 m, an inner diameter of 0.320 mm, and a film thickness of 1.00 μm.

[0017] Preferably, in S2, in the gas chromatography-mass spectrometer, the retention time, detection limit, monitoring ions and collision energy of chloroform and carbon tetrachloride in the multiple reaction ion monitoring mode are as follows:

[0018]

[0019]

[0020] Among them, * is the quantitative ion.

[0021] The detection method provided by the present invention adopts headspace + gas chromatography-mass spectrometry (triple quadrupole) dMRM mode sample injection detection, which has obvious advantages over the gas chromatography ECD detection method or gas chromatography-mass spectrometry Scan scanning method of the existing detection standard mentioned in the background technology. In particular, the establishment of the respective quantitative ion pairs and qualitative ion pairs (each totaling 4 groups) of chloroform and carbon tetrachloride can accurately determine whether there is a target object for any sample. According to the condition setting of the instrument, chloroform and carbon tetrachloride can be seen to have separate peak times on the same total ion map, which are independent of each other. Of course, since the instrument we use is a gas chromatography-mass spectrometry dMRM detection mode, even if the peak times of chloroform and carbon tetrachloride are consistent, that is, there is only one peak on the total ion map, it does not affect the content calculation of the two, because they have different characteristic ions and fragment ions after bombardment, according to the abundance of the respective fragment ions, the instrument can automatically and accurately calculate the content of chloroform and carbon tetrachloride and accurately determine it.

[0022] Preferably, in the method for detecting the content of chloroform and carbon tetrachloride in water provided by the present invention, the detection limit and quantification limit of chloroform and carbon tetrachloride are calculated by the signal-to-noise ratio method, and the signal-to-noise ratio multiples used are 3 times and 10 times.

[0023] Preferably, in S2, during the detection and analysis of the water sample to be tested, the samples are injected alternately in the form of one injection of the water sample to be tested and one injection of anhydrous ethanol sample; one injection of the calibration standard sample and one injection of anhydrous ethanol sample; and the first and last injections of the injection sequence are both set to anhydrous ethanol sample.

[0024] Due to the design and construction of the instrument, if the pipeline is not flushed after the previous sample contains chloroform, a small amount of chloroform remaining in the detection path will continue to be detected and superimposed with the chloroform in the next sample, resulting in inaccurate test data. Flushing the detection pipeline with anhydrous ethanol can effectively remove the chloroform in the detection path of the previous sample, improve the detection accuracy, and reduce the distortion of the test results. In addition, practice shows that the residual degree of carbon tetrachloride is much smaller than that of chloroform, so the injection effect of different substances is still quite different. Therefore, for the detection of water containing chloroform, the injection of the above steps is important for improving the detection accuracy and sensitivity.

[0025] Preferably, in S3, in step 1, the volume ratio of N,N-dimethylformamide to water is 1: 1. At this volume ratio, the standard mother liquor of chloroform and carbon tetrachloride can be well diluted, so that chloroform and carbon tetrachloride can be fully and evenly dissolved. As an ideal solvent, it can promote the target to reach the best gas-liquid equilibrium state between the liquid and the air layer after being added to the headspace bottle and preheated, optimize the response value and parallelism, improve the accuracy of the drawn standard curve, and thus improve the accuracy of the detection result.

[0026] Preferably, in S3, in step 1, N,N-dimethylformamide and water are boiled for 15 to 25 minutes. Chloroform has a boiling point of 61°C and carbon tetrachloride has a boiling point of 77°C. As an organic reagent, N,N-dimethylformamide also contains the target chloroform. Boiling (up to 100°C) can remove the target chloroform and carbon tetrachloride as much as possible, which is convenient for accurate preparation of standard products, thereby improving the accuracy of experimental data.

[0027] Preferably, in S3, in step 1, N,N-dimethylformamide and water are boiled for 20 minutes.

[0028] Preferably, in S3, in step 1, the chloroform and carbon tetrachloride standard mother solutions are diluted to 1000 ng / mL.

[0029] Preferably, in S3, in step 1, ultrapure water is used to prepare standard working solutions of different concentrations. Preferably, the ultrapure water is boiled for 15 to 25 minutes.

[0030] Preferably, in S3, in step 2, the standard working solutions of different concentrations are 1 ppb, 2 ppb, 5 ppb, 10 ppb, 20 ppb, 50 ppb, and 100 ppb, respectively.

[0031] Preferably, in S3, in fitting the standard curve, the correlation coefficient R 2 Not less than 0.990; in the process of drawing the standard curve, the response peak of the standard substance is used as the ordinate Y, and the corresponding standard working solution concentration is used as the abscissa X. It should be noted here that in the process of drawing the standard curve in the present invention, a blank sample should be added, and the peak value of each concentration point should be corrected with its background peak value as the deduction value to formulate the standard curve. In the present invention, the quadratic fitting equation is preferably used for drawing the standard curve, and the calculation through the origin is forced.

[0032] Preferably, the contents of chloroform and carbon tetrachloride in the water sample to be tested are calculated according to the following formula: ρ = (A s－ A 0 ) / 1000; where ρ is the content of chloroform and carbon tetrachloride in the water sample to be tested, in mg / L; A s —The concentration of the target substance in the headspace bottle of the water sample to be tested is calculated by the standard curve, in ng / mL; A 0 —The background concentration of the blank sample in the headspace vial, in ng / mL. s With A 0 The value is calculated from the standard curve, and the instrument analysis software will automatically calculate the data.

[0033] In addition, in the detection method provided by the present invention, because the injection method is to inject one needle of the water sample to be tested and one needle of the anhydrous ethanol sample; one needle of the calibration standard sample and one needle of the anhydrous ethanol sample in an alternating manner, there must be a blank sample in each batch of samples, so the background concentration value must be deducted to correct the target content of the water sample to be tested and the standard curve. At the same time, it should be noted that in the present invention, the injection sequence includes the calibration standard sample and the water sample to be tested, so that they are injected under the same instrument conditions, and it does not matter who injects the sample first or later. The key point is to flush the pipeline with anhydrous ethanol after each sample is injected to ensure that the peak area of ​​each sample is not interfered by the previous sample, so as to ensure the accurate drawing of the standard curve and the accuracy of the detection results of the water sample to be tested.

[0034] The background concentration value of the blank sample refers to the reagent blank sample carried when the headspace sampling and capping operation is performed in the water sample chamber. In order to avoid the risk of chloroform contamination in the water sample chamber, which may increase the detection value and cause data distortion, the experimental water is taken to maintain the same environmental conditions as the actual water sample for measurement, and the instrument's measurement value is used as the blank value of the batch of samples. The blank value is also a weather vane reflecting the degree of contamination of the target object in the experimental environment. All other sample measurement values ​​must be subtracted from the blank value to be the accurate actual value, so the blank sample background concentration value is used here to describe it. Similarly, a blank sample must be carried when preparing a standard curve. This blank value is used to subtract the corresponding values ​​of each concentration point to establish an accurate standard curve. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the total ion diagram of chloroform and carbon tetrachloride standards at a concentration of 25 ppb.

[0036] Figure 2 This is the standard mass spectrum of chloroform at a concentration of 25 ppb.

[0037] Figure 3 This is the standard mass spectrum of carbon tetrachloride at a concentration of 25 ppb.

[0038] Figure 4 This is the standard curve of chloroform in Example 1.

[0039] Figure 5 This is the carbon tetrachloride standard curve diagram in Example 1. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only embodiments of a part of the present invention, rather than all embodiments.

[0041] Example 1: Establishment of detection method

[0042] Follow the steps below to determine the content of chloroform and carbon tetrachloride in the water sample:

[0043] S1. Pretreatment: Collect the water sample to be tested, place 5 mL of the water sample to be tested in a headspace bottle, immediately seal the bottle mouth, place the headspace bottle in the headspace autosampler, and heat at 65°C for 20 minutes; the headspace conditions are: oven temperature: 65°C; equilibrium time: 20 minutes; transmission line temperature: 115°C; injection needle temperature: 85°C; injection interval time: 22 minutes;

[0044] S2. Use gas chromatography-mass spectrometry to detect and analyze the water sample to be tested; during the detection and analysis process, one needle of the water sample to be tested, one needle of anhydrous ethanol sample; one needle of the calibration standard sample, and one needle of anhydrous ethanol sample are injected alternately; and the first and last needles of the injection sequence are set to anhydrous ethanol sample; the gas chromatography-mass spectrometry analysis conditions are as follows: capillary column: DB-5MS capillary column (ultra-high inertness, column length 60m, inner diameter 0.320mm, film thickness 1.00μm), injection port temperature: 280℃; carrier gas: He; flow rate 1.2mL / min, constant flow mode; split injection , split ratio 10:1; column box temperature: initially 40℃ for 5min, program temperature rise 20℃ / min to 100℃, maintain for 3min; continue program temperature rise 25℃ / min to 150℃, maintain for 2min; EI ion source temperature: 280℃; ionization voltage: 70ev; quadrupole temperature: 150℃; auxiliary channel temperature: 280℃; emission voltage: 1500ev; collision cell quenching gas, helium, 2.25mL / min; collision gas, nitrogen, 1.5mL / min; scanning mode: multiple reaction ion monitoring mode (dMRM); solvent delay: 3min;

[0045] Among them, the retention time, detection limit, monitoring ion and collision energy of chloroform and carbon tetrachloride are shown in Table 1:

[0046] Table 1 Retention time, detection limit, monitoring ions and collision energy of the target

[0047]

[0048] Among them, * is the quantitative ion;

[0049] The allowable deviation range of the relative abundance of ions in the sample mass spectrum is shown in Table 2:

[0050] Table 2 Permissible deviation range of ion relative abundance in sample mass spectra

[0051]

[0052]

[0053] S3. Substituting the obtained test results into the standard curve to determine the content of chloroform and carbon tetrachloride in the water sample to be tested;

[0054] The standard curve is drawn as follows:

[0055] Step 1, dilute the chloroform and carbon tetrachloride standard mother solutions with N, N-dimethylformamide + ultrapure water (volume ratio of 1:1, pre-boiled for 20 minutes) to prepare a secondary standard solution of 10 μg / mL; take 500 μL of the standard solution into a 5 mL volumetric flask, and dilute to the mark with ultrapure water (boiled for 20 minutes) to obtain a standard working solution concentration of 1000 ng / mL; pre-add ultrapure water (boiled for 20 minutes) 5000 μL, 4995 μL, 4990 μL, and 10 μL, respectively, into a group of 20 mL headspace bottles. 4975μL, 4950μL, 4900μL, 4750μL, 4500μL, add 0μL, 5μL, 10μL, 25μL, 50μL, 100μL, 250μL, 500μL of chloroform and carbon tetrachloride standard working solution respectively, cover the stopper immediately, and obtain the concentration points of each standard working solution: 0ppb, 1ppb, 2ppb, 5ppb, 10ppb, 20ppb, 50ppb, 100ppb, among which 0ppb point is the reagent blank sample;

[0056] Step 2, testing the standard working solutions of different concentrations in the order of S1 and S2; performing standard curve regression after deducting the blank background value from the chromatographic peak area corresponding to each concentration point to obtain a standard curve.

[0057] Figure 1 to Figure 3 The total ion map and mass spectrum of chloroform and carbon tetrachloride standards at 25 ppb concentration point obtained by gas chromatography-mass spectrometry peak analysis. Figure 4 , Figure 5 They are respectively the standard curves of chloroform and carbon tetrachloride. In addition, in the process of drawing the standard curve, the 0ppb here refers to the use of pure water for the experiment as the background value, which is used to deduct the peak area of ​​the other 7 concentration points to obtain an accurate standard curve. Because practice has proved that any blank sample will have the detection of chloroform in the triple quadrupole gas chromatography-mass spectrometry detection, the difference is that the peak area is different. So the purpose of 0ppb is to use its peak area to subtract the peak area of ​​the peak area of ​​each concentration, and then draw the standard curve, so 0ppb is not used to draw the standard curve together. In the scheme of the present embodiment, the drawing method of the standard curve is quadratic fitting, which is forced to pass through the origin, and this forced passing through the origin is to express that the drawing of the standard curve also includes 0ppb, that is, 0ppb is also involved in the drawing of the standard curve, and the peak area of ​​0ppb is zero.

[0058] It should be noted that the method for detecting the content of chloroform and carbon tetrachloride in water provided by the present invention (the present embodiment) is related to the preparation of standard products. Since the solvent of the commercially available chloroform and carbon tetrachloride mixed standard products is methanol, it is more suitable to dilute the standard mother liquor with methanol in principle. However, the test results show that the conventional chromatographic pure organic reagents (such as methanol, acetonitrile, acetone) used in the laboratory contain chloroform to varying degrees and cannot be used directly. The premise is to remove the chloroform therein. The boiling method is a common method, but the boiling points of methanol, acetonitrile, acetone, etc. are all lower than 100°C, which is unfriendly to the environment, so these reagents are not considered for application. Instead, the target is locked on N, N-dimethylformamide, which has a boiling point of 153°C. In addition, N, N-dimethylformamide is easily mixed with water. After boiling, chloroform evaporates, but N, N-dimethylformamide does not lose the slightest amount. It can help the target substance and water to mix more evenly when preparing chloroform and carbon tetrachloride standard solutions. Studies have shown that after 20 minutes of boiling, the background value of chloroform is low, which is suitable for use as a diluent for the standard mother solution. Therefore, this study uses N, N-dimethylformamide + water (volume ratio of 1:1) as a diluent.

[0059] Further, according to the standard curve obtained above, the contents of chloroform and carbon tetrachloride in the water sample to be tested can be calculated according to the following formula:

[0060] ρ=(A s－ A 0 ) / 1000;

[0061] Where, ρ is the content of chloroform and carbon tetrachloride in the water sample to be tested, in mg / L;

[0062] A s —The concentration of the target substance in the headspace bottle of the water sample to be tested is calculated by the standard curve, in ng / mL;

[0063] A 0 —The background concentration value of the blank sample in the headspace vial, in ng / mL.

[0064] The present invention adopts external standard method for quantification, and the series of standard working solutions show good linear relationship (R 2>0.990); put the sample on the machine, and obtain the detection limit and quantitative limit of the method calculated by 3 times and 10 times the signal-to-noise ratio. The detection limit and quantitative limit of the method are: 0.00005mg / L and 0.0001mg / L for chloroform; 0.00002mg / L and 0.00006mg / L for carbon tetrachloride. It can be seen from this that the detection limit and quantitative limit of the detection method provided in the present invention are very low, which greatly improves the detection sensitivity. Not only that, under such low detection limit and quantitative limit, the detection accuracy is also high. In actual situations, such low concentrations are difficult to be detected in conventional samples. The reasons are: (1) As mentioned above, due to the reasons of the instrument itself and the characteristics of chloroform, it is impossible to make the detection pipeline absolutely clean and free of residues. Even the reagent blank sample can exceed this value. This is also the reason why the actual value of the sample must be the detection value minus the background value. Therefore, the description of the detection of actual samples in this scheme as quantitative limit is more in line with practical conditions. (2) Setting a detection limit that is too small has no practical significance. As a routine constant detection in a laboratory, being able to detect a target content of 1 ppb is already a high sensitivity characteristic. According to the determination requirements (in the national standard GB17323-1998), the contents of chloroform and carbon tetrachloride in drinking pure water shall not exceed 0.02 mg / L and 0.001 mg / L, respectively. Therefore, the present invention is fully capable of performing routine detection work.

[0065] Example 2: Testing of samples submitted for inspection

[0066] The detection method established in Example 1 was used to determine the content of chloroform and carbon tetrachloride in 16 water samples (water for production and processing). It was found that the target component of chloroform was detected in multiple samples, while carbon tetrachloride was not detected. The specific implementation process is as follows: First, the sample is placed in a room away from the laboratory, and a 5mL pipette is used to directly transfer the water sample to a 20mL headspace bottle on site and cover it. As a sample for injection. As a sample for adding a mark, the water sample is taken and transferred to a room with better environmental conditions for adding a mark and then covered for standby use. At the same time, the preparation of the standard curve is completed under the same conditions.

[0067] According to the test results, chloroform was not detected in 4 of the 16 water samples, chloroform was detected in all of the remaining 12 water samples, and carbon tetrachloride was not detected in all of the 16 water samples. The chloroform detection value range of the 12 water samples was: 0.0043 mg / L to 0.027 mg / L, and the spike recovery rate was 91.1 to 116.7%, as shown in Table 3, indicating that the detection method provided by the present invention has a high detection accuracy.

[0068] The data also show that the detection rate of chloroform in the samples submitted for inspection is relatively high, indicating that the detection method provided by the present invention has a low detection limit and quantification limit, and can more accurately detect chloroform and carbon tetrachloride with low content, which can greatly meet the needs of daily inspection and can further realize the important guarantee for water quality safety monitoring.

[0069] Table 3 Detection results and spiked recoveries of chloroform in processing water of 16 manufacturers

[0070]

[0071]

[0072] In addition, the present invention further studies the use of methanol, a commonly used organic solvent in laboratories, to dilute the standard solution of chloroform and carbon tetrachloride and then inject the solution. Finally, the gas chromatograph ECD detector shows a flat peak phenomenon at the chloroform peak time point, indicating that the concentration of the substance has exceeded the limit of accurate measurement of the instrument; and the samples treated in the same way and the reagent blank samples were measured by gas chromatography-mass spectrometry, and chloroform was detected, so it was confirmed that the interference substance of the gas chromatograph was chloroform, and the results obtained by the gas chromatography-mass spectrometry showed that not only the peak time was consistent, but also the quantitative ions and qualitative ions all met the requirements. This shows that the chloroform in the environment does interfere with the detection of normal samples. This shows that the huge interference peak mentioned in the background technology when measured by the gas chromatography ECD detector is definitely chloroform. In addition, 200 μL of chromatographically pure reagents commonly used in laboratories, such as acetonitrile, acetone, and n-hexane, were taken and diluted to 5 mL with pure water. After plugging, chloroform was detected in different levels. For example, the concentration of chloroform in acetone was as high as 13.5 mg / L; the concentration of chloroform in acetonitrile could reach 6.08 mg / L, which shows that the organic reagents we use daily contain chloroform. The research results also show that carbon tetrachloride was not detected in the above organic reagents.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention is described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the technical solutions of the present invention can be modified or equivalently replaced, but these modifications or replacements are all within the protection scope of the present invention.

Claims

1. A method for detecting the content of chloroform and carbon tetrachloride in water, characterized in that: The steps include: S1. Pretreatment: Collect the water sample to be tested and place it in a headspace bottle, place the headspace bottle into a headspace autosampler, and heat it at 60-70°C for 15-25min; S2. Detect and analyze the water sample to be tested using a gas chromatography-mass spectrometer; S3. Substituting the obtained test results into the standard curve to determine the content of chloroform and carbon tetrachloride in the water sample to be tested; The standard curve is drawn as follows: Step 1, using N,N-dimethylformamide and water as diluents to dilute chloroform and carbon tetrachloride standard mother solutions to obtain standard working solutions; using the standard working solutions to prepare standard working solutions of different concentrations; Step 2: Detect and analyze the standard working solutions of different concentrations in the order of S1 and S2, and draw the standard curve based on the obtained detection results.

2. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 1, characterized in that: In S2, in the gas chromatography-mass spectrometer, the gas chromatography-mass spectrometry analysis conditions are as follows: capillary column: DB-5MS capillary column; injection port temperature: 278-282°C; carrier gas: He; flow rate 1.1-1.3 mL / min, constant flow mode; split injection, split ratio 10:1; column box temperature: initial 39-41°C maintained for 4.5-5.5 min, program temperature rise 18-22°C / min to 98-102°C, maintained for 3 min; continue program temperature rise 23-27°C / min n to 148-152℃, maintain for 1.8-2.2min; EI ion source temperature: 278-282℃; ionization voltage: 68-72ev; quadrupole temperature: 148-152℃; auxiliary channel temperature: 278-282℃; emission voltage: 1495-1505ev; collision cell quenching gas, helium, 2.20-2.30mL / min; collision gas, nitrogen, 1.45-1.55mL / min; scanning mode: multiple reaction ion monitoring mode; solvent delay: 2.5-3.5min.

3. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 1, characterized in that: In S2, in the gas chromatograph-mass spectrometer, the retention time, detection limit, monitoring ions and collision energy of chloroform and carbon tetrachloride in the multiple reaction ion monitoring mode are as follows: Among them, * is the quantitative ion.

4. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 1, characterized in that: In S2, during the detection and analysis of the water sample to be tested, the samples are injected alternately in the form of one injection of the water sample to be tested and one injection of anhydrous ethanol sample; one injection of a calibration standard sample and one injection of anhydrous ethanol sample; and the first injection and the last injection of the injection sequence are both set to anhydrous ethanol sample.

5. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 1, characterized in that: In S3, in step 1, the volume ratio of the N,N-dimethylformamide to the water is 1:

1.

6. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 1, characterized in that: In S3, in step 1, the N,N-dimethylformamide and the water are boiled for 15 to 25 minutes.

7. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 1, characterized in that: In said S3, in said step 1, the chloroform and carbon tetrachloride standard mother solution are diluted to 1000 ng / mL.

8. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 1, characterized in that: In S3, in step 2, the standard working solutions of different concentrations are 1 ppb, 2 ppb, 5 ppb, 10 ppb, 20 ppb, 50 ppb, and 100 ppb, respectively.

9. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 8, characterized in that: In S3, in fitting the standard curve, the correlation coefficient R 2 Not less than 0.990; In the process of drawing the standard curve, the response peak value of the standard substance is used as the ordinate Y and the corresponding standard working solution concentration is used as the abscissa X.

10. The method for detecting the content of chloroform and carbon tetrachloride in water as claimed in claim 9, characterized in that: The contents of chloroform and carbon tetrachloride in the water sample to be tested are calculated according to the following formula: ρ=(A s－ A0) / 1000; Wherein, ρ is the content of chloroform and carbon tetrachloride in the water sample to be tested, in mg / L; A s —The concentration of the target substance in the headspace bottle of the water sample to be tested is calculated by the standard curve, in ng / mL; A0—Background concentration value of blank sample in headspace vial, in ng / mL.

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