Method for detecting indole compounds in ambient air

Abstract

The invention belongs to the technical field of environment detection, and particularly relates to a method for detecting indole compounds in ambient air. According to the method, the GDX-502 sampling tube is adopted to adsorb and sample the indole compounds in the ambient air, and meanwhile, acetone / n-hexane is used as an elution solvent to elute the sampling tube, so that the sampling effect of the sampling tube on the indole compounds in the ambient air is remarkably improved, and further, the sampling efficiency of the indole compounds in the ambient air is improved. According to the method disclosed by the invention, the indole compounds are quantified by adopting a gas chromatography-mass spectrometry method, the detection limit is lower due to pressurized sample injection during sample injection, and a result shows that the standard addition recovery rate of the method for indole and 3-methylindole with low, medium and high concentrations is 98.7%-112%, and the relative standard deviation is less than 10%. The invention establishes a rapid, sensitive and accurate analysis method for indole and 3-methylindole in ambient air, and provides a theoretical basis for formulation and quality control of indole substance detection standards.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental detection, and in particular relates to a method for detecting indole compounds in ambient air. Background Art

[0002] Indole compounds such as indole, 3-methylindole, 1-nitroindole, etc. are a class of nitrogen-containing heterocyclic organic substances with foul odor and biological toxicity. The volatilization of nitrogen-containing organic fertilizers or pesticides in farmland, motor vehicle exhaust and coal combustion, as well as industrial production such as leather processing, pharmaceuticals, printing and dyeing, petrochemicals and other processes will release indole substances, causing the content of indole compounds in the air environment to increase.

[0003] Indoles can inhibit plant photosynthesis and aggravate the formation of haze. In addition, low concentrations of indole vapor can irritate the respiratory mucosa, causing symptoms such as coughing and chest tightness, while high concentrations of indole can cause hemolysis, hemoglobinuria, temporary skin irritation, and even tumors in animals. Therefore, rapid detection of indoles in ambient air is crucial in industrial production.

[0004] At present, commonly used detection methods for indole substances include liquid chromatography, gas chromatography, liquid chromatography-tandem mass spectrometry, gas chromatography-mass spectrometry and other methods. For example, patent CN113358798A uses thermal desorption-gas chromatography-mass spectrometry to detect indole and 3-methylindole in ambient air, with a detection limit of 0.26-0.29; patent CN117723688A uses high performance liquid chromatography-tandem mass spectrometry to detect indole and 3-methylindole in aquatic products, but the pretreatment method is complicated and the detection limit is high; patent CN104034823A uses high performance liquid chromatography to detect indole substances in toads.

[0005] However, the above detection methods generally have problems such as complicated pre-treatment operations and high detection limits of the detection methods. For 3-methylindole with a low olfactory threshold, it is even difficult to accurately detect it.

[0006] Therefore, there is an urgent need to develop a trace detection technology for indole compounds with high sensitivity and good accuracy to cope with practical challenges such as industrial emissions and urban pollution, and to provide data support for global atmospheric environmental governance. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for detecting indole compounds in ambient air.

[0008] The present invention provides a method for detecting indole compounds in ambient air, comprising the following steps: Preparation of S1 standard solution: Accurately weigh the indole compound standard and dissolve it in methanol to prepare a methanol stock solution of 100 mg / L indole compound standard. Then, dilute the methanol stock solution of indole compound standard with an organic solvent to prepare indole compound standard solutions with certain concentration gradients in the range of 0.5 μg / L - 20 μg / L; The organic solvent selected is at least one of acetone, n-hexane, and carbon disulfide; S2 Drawing of standard curve: Inject and detect the indole compound standard solution prepared in S1 by gas chromatography-mass spectrometry to draw the standard curve of indole compound; Among them, the detection conditions of gas chromatography are: Injection port temperature: 220 - 260 °C, injection mode: splitless injection, injection volume 1 - 2 μL, injection port pressure injection for 0.5 - 2 min, pressure 180 - 220 kPa; TG-5MS chromatographic column: 30 m × 0.25 μm × 0.25 mm, column flow rate: 1 - 1.5 mL / min; The temperature programming is: initial temperature 35 °C for 1 min, first increase the temperature at a rate of 20 °C / min to 168 °C, then increase the temperature at a rate of 2 °C / min to 178 °C, and finally increase the temperature at a rate of 30 °C / min to 300 °C and hold for 1 min; The detection conditions of mass spectrometry are: transfer line temperature: 280 °C; ion source temperature: 280 °C; quantitative analysis: select ion scanning mode and full scan mode for simultaneous scanning; S3 Sampling and detection of ambient air samples: Add an indole compound standard solution with a concentration of 0.1 - 1 mg / L to the sampling tube to sample the ambient air, elute the sampling tube with an elution reagent, and then inject the sample in sequence according to the chromatographic conditions and mass spectrometry conditions described in S2. Substitute the obtained quantitative ion peak area into the standard curve drawn in S2 to obtain the specific content of indole compounds contained in the ambient air sample.

[0009] In the above method, preferably, the indole compounds include indole and 3-methylindole.

[0010] Preferably, in S1, accurately weigh the indole compound standard and dissolve it in methanol to prepare a methanol stock solution of 100 mg / L indole compound standard. Then, dilute the methanol stock solution of indole compound standard with an organic solvent to prepare indole compound standard solutions with concentrations of 0.5 μg / L, 1 μg / L, 2 μg / L, 5 μg / L, 8 μg / L, 10 μg / L, and 20 μg / L respectively.

[0011] Preferably, the organic solvent described in S1 is a mixed solution of acetone and n-hexane, and the volume ratio of acetone to n-hexane is 1:1.

[0012] Preferably, when detecting indole and 3-methylindole, the mass spectrometry conditions described in S2 are as follows: the quantitative ion of indole is 117, the qualitative ions are 89 and 90, the quantitative ion of 3-methylindole is 130, and the qualitative ions are 77, 103, and 131.

[0013] Preferably, the sampling tube described in S3 is a GDX-502 sampling tube.

[0014] For the GDX-502 sampling tube used in the present invention, the filler material inside is polystyrene divinylbenzene porous bead filler.

[0015] Preferably, before sampling, the GXD-502 sampling tube is activated, and the activation steps are as follows: Add 4 mL of mass spectrometry grade methanol to clean and activate the GXD-502 sampling tube (0.2 g). After drying the GDX-502 sampling tube rinsed with methanol with high-purity nitrogen for 30 min, seal both ends of the sampling tube with rubber caps for later use.

[0016] The purpose of activating the sampling tube in the present invention is to remove the adsorbed impurities in the sampling tube and activate the filler, so that the miscellaneous peaks of the measured sample become fewer and the baseline becomes flatter, so that the blank level of the blank tube is lower than the detection limit, and the detection limit of indole compounds can also reach a lower level.

[0017] Preferably, for the sampling described in S3, the sampling flow rate is 0.2 - 1.0 L / min, and the sampling time is 15 - 30 min.

[0018] More preferably, for the sampling described in S3, the sampling flow rate is 0.3 - 0.6 L / min, and the sampling time is 18 - 25 min.

[0019] Preferably, the elution reagent described in S3 is selected from at least one of acetone, n-hexane, and carbon disulfide.

[0020] Preferably, the elution reagent described in S3 is a mixed solution of acetone and n-hexane, and the volume ratio of acetone to n-hexane is 1:1.

[0021] The beneficial effects of the present invention are as follows: (1) Using a GDX-502 sampling tube to adsorb indole compounds in ambient air, and at the same time using acetone / n-hexane as the elution solvent for elution, this operation significantly improves the adsorption effect of the sampling tube on indole compounds in ambient air; (2)The indole compounds were quantified by gas chromatography - mass spectrometry. When injecting the sample, pressure injection was used, and the detection limit was lower. The detection methods in the existing literature include gas chromatography, liquid chromatography, and liquid chromatography - mass spectrometry, all of which are not as accurate in qualitative and quantitative analysis and have a lower detection limit as the gas chromatography - mass spectrometry method in the present invention. (3)The method of the present invention not only has a low detection limit, but also has good repeatability, a high recovery rate, and is simple and convenient to operate. It is suitable for the detection of indole and 3 - methyl indole in a large number of environmental air samples. The results show that for indole and 3 - methyl indole with low, medium, and high concentrations, the recovery rates of the method of the present invention are between 98.7% - 112%, and the relative standard deviations are all less than 10%. Description of the Drawings

[0022] Figure 1 This shows the influence of whether to use pressure injection at the injection port on the detection response of 3 - methyl indole in Example 1 of the present invention. Figure 2 This shows the response results of 0.1 μg / L of 3 - methyl indole at different injection volumes in Example 1 of the present invention, where (A) is the injection volume of 1 μL and (B) is the injection volume of 2 μL. Figure 3 This shows the response results of 5 μg / L of 3 - methyl indole at different injection volumes in Example 1 of the present invention, where (A) is the injection volume of 1 μL and (B) is the injection volume of 2 μL. Figure 4 This shows the detection response of indole and 3 - methyl indole after elution with different elution solvents in Example 3 of the present invention. Detailed Embodiments

[0023] In order to enable those skilled in the art to better understand the present invention, the present invention will be further elaborated below in conjunction with specific embodiments.

[0024] Example 1 The indole compound 3 - methyl indole in environmental air was detected by gas chromatography - mass spectrometry. Among them, the detection conditions of gas chromatography are as follows: Injection port temperature: 250 °C, injection mode: splitless injection, injection volume is 1 μL, sample concentration is 0.1 μg / L, pressure injection at the injection port for 1 min, pressure 200 kPa. TG-5MS chromatographic column: 30 m × 0.25 μm × 0.25 mm, column flow rate: 1.2 mL / min; the temperature programming is as follows: the initial temperature is maintained at 35°C for 1 min, first heated at a rate of 20°C / min to 168°C, then heated at a rate of 2°C / min to 178°C, and finally heated at a rate of 30°C / min to 300°C and maintained for 1 min; the detection conditions of the mass spectrometry are: transfer line temperature: 280°C; ion source temperature: 280°C; quantitative analysis: select ion scanning mode and full scanning mode for simultaneous scanning, the quantitative ion of indole is 117, the qualitative ions are 89 and 90, the quantitative ion of 3-methylindole is 130, and the qualitative ions are 77, 103, and 131.

[0025] Under exactly the same conditions, the peak shapes of 3-methylindole were compared when injecting 1 μL without pressurizing the injection port and when injecting 2 μL with the same conditions.

[0026] When the injection volume is 1 μL, the response results of 0.1 μg / L of 3-methylindole measured without pressurizing the injection port and with pressurizing the injection port at 200 kPa are shown in the appendix Figure 1 As shown, in the figure, (A) is the response result without pressurizing the injection port, and (B) is the response result with pressurizing the injection port at 200 kPa.

[0027] As can be seen from the figure, the response result of 3-methylindole detected after pressurizing the injection port at 200 kPa is significantly higher than that without pressurizing the injection port, and the peak shape becomes better.

[0028] In addition, when injecting 3-methylindole at a concentration of 0.1 μg / L with pressurizing the injection port at 200 kPa, when the injection volume is increased from 1 μL to 2 μL, the response results of 3-methylindole are shown in the appendix Figure 2 As shown, in the appendix Figure 2 Among them, (A) is the injection volume of 1 μL, and (B) is the injection volume of 2 μL; as can be seen from the results in the appendix Figure 2 after the injection volume is increased, the peak area of 3-methylindole becomes larger and the peak shape becomes wider.

[0029] When measuring the concentration of 3-methylindole in the injection to be 5 μg / L, the response conditions of 3-methylindole at different injection volumes are shown in the appendix Figure 3 As shown, in the appendix Figure 3 Among them, (A) is the response result with an injection concentration of 5 μg / L and an injection volume of 1 μL; (B) is the response result with an injection concentration of 5 μg / L and an injection volume of 2 μL.

[0030] Figure 3 As can be seen, the originally symmetric and sharp peak shape of 3-methylindole also becomes wider and fatter with the increase of the injection concentration and injection volume. Therefore, the injection volume is set to 1 μL in the present invention.

[0031] In addition, it should be noted that among the indole compounds to be detected in the present invention, such as indole and 3-methylindole, due to the very low olfactory threshold of 3-methylindole, which is 0.0000056 ppm, in order to detect 3-methylindole at such a low concentration in the air, the gas chromatograph-mass spectrometer must achieve a sufficiently low instrument detection limit.

[0032] In the present invention, when the sampling flow rate is 0.5 L / min, the sampling time is 20 min, and a total of 10 L of ambient air gas is collected, it is calculated that the concentration of 3-methylindole with a concentration of 0.0000056 ppm adsorbed by the GDX-502 sampling tube and eluted with 2 mL of acetone / n-hexane (v / v, 1 / 1) into a vial is 0.16 μg / L. Therefore, it is very important to accurately measure 0.1 μg / L of 3-methylindole. In this way, there is no need to rely on extending the sampling time and increasing the sampling volume to reduce the method detection limit, and the actual detection requirements can be met. This can save a large amount of time in emergency monitoring.

[0033] Moreover, since the olfactory threshold of indole is much higher than that of 3-methylindole, only the conditions need to be optimized to achieve an extremely low detection limit for 3-methylindole.

[0034] Example 2 Using a GDX-502 sampling tube, adding 5 μL of standard solution (the concentration of indole and 3-methylindole standard solution is 10 mg / L), sampling ambient air, setting the sampling rate to 0.2 L / min or 0.5 L / min, sampling for 20 min, eluting with 2 mL of acetone / n-hexane (v / v, 1 / 1), and injecting samples in sequence according to the above chromatographic and mass spectrometric conditions to determine the recovery rates of indole and 3-methylindole.

[0035] In addition, according to the following detection conditions, only the filler composition in the sampling tube is adjusted to determine the influence of the sampling tube filler composition on the recovery rates of indole and 3-methylindole.

[0036] The detection conditions are as follows: The detection conditions of gas chromatography are: inlet temperature: 250 °C, injection mode: splitless injection, injection volume: 1 μL, sample concentration: 0.1 μg / L, inlet pressure injection for 1 min, pressure: 200 kPa; TG-5MS chromatographic column: 30 m × 0.25 μm × 0.25 mm, column flow rate: 1.2 mL / min; temperature programming is: initial temperature 35 °C for 1 min, first rising at a heating rate of 20 °C / min to 168 °C, then rising at a heating rate of 2 °C / min to 178 °C, and finally rising at a heating rate of 30 °C / min to 300 °C and holding for 1 min; The detection conditions of the mass spectrometry are as follows: transfer line temperature: 280 °C; ion source temperature: 280 °C; for quantitative analysis, selective ion scanning mode and full-scan mode are used simultaneously. The quantitative ion of indole is 117, and the qualitative ions are 89 and 90. The quantitative ion of 3-methylindole is 130, and the qualitative ions are 77, 103, and 131. The components of the packing materials in the sampling tubes are respectively set as: alkaline silica gel tube, neutral silica gel tube, acidic silica gel tube, activated carbon tube, coconut shell activated carbon tube, MOF packing, silica gel tube coated with isopropanol, silica gel tube coated with glycerol and isopropanol.

[0037] The recovery rates of indole and 3-methylindole after sampling with sampling tubes filled with different packing materials are shown in Table 1 below.

[0038] Table 1 Recovery rates of indole and 3-methylindole in sampling tubes with different packing materials at different sampling flow rates (%)

[0039] As can be seen from Table 1, when using the GDX-502 sampling tube, the recovery rates of indole and 3-methylindole are both between 95.0% and 120%. When the sampling flow rate is 0.2 L / min, the recovery rates of indole and 3-methylindole for other various packing materials are all less than 70%. When the sampling flow rate is 0.5 L / min, the recovery rates of indole and 3-methylindole are both less than 20%.

[0040] Example 3 Prepare a mixed standard solution of indole and 3-methylindole at 2 mg / L, add 5 μL of the standard to the GDX-502 sampling tube respectively. Select methanol, ethanol, acetone, carbon disulfide, n-hexane, acetone / carbon disulfide (v / v, 1 / 1), acetone / n-hexane (v / v, 1 / 1) as the elution solvents. After taking 2 mL to elute 3 identical GDX-502 spiked sampling tubes respectively and then making up the volume to 2 mL, detect using the above-mentioned chromatographic detection conditions.

[0041] The response comparison of indole and 3-methylindole measured with different elution solvents is shown in Figure 4 .

[0042] It can be Figure 4 seen that the responses of indole and 3-methylindole eluted with acetone are the highest, followed by acetone / n-hexane (v / v, 1 / 1). Considering comprehensively, since the most commonly used 5 ms chromatographic column in the gas chromatography-mass spectrometry is a non-polar chromatographic column, and acetone is a solvent with relatively strong polarity, regular injection with acetone will damage the non-polar chromatographic column. Therefore, acetone / n-hexane (v / v, 1 / 1) is selected as the elution solvent, which can not only ensure relatively high responses of indole and 3-methylindole, but also protect the chromatographic column.

[0043] Example 4 Adsorbed with a GDX-502 sampling tube, set the sampling flow rates at 0.2, 0.5, 0.8, and 1.0 L / min, each sample for 20 min, elute with 2 mL of acetone / n-hexane (v / v, 1 / 1) and then make up the volume to 2 mL. After determination, it is found that when sampling at 0.2 - 1.0 L / min, the recovery rates of indole and 3-methylindole are shown in Table 2 below. As can be seen from Table 2, the recovery rates of indole and 3-methylindole are both between 95.0% and 115%.

[0044] Table 2 Recovery Rates of Indole and 3-Methylindole (%) Sampling flow rate (L / min) 0.2 0.5 0.8 1.0 Indole 109-112 107-111 101-103 107-111 3-Methylindole 100-105 101-104 95.8-96.8 104-105

[0045] Therefore, any sampling flow rate between 0.2 - 1.0 L / min can be selected. Considering that the method detection limits of indole and 3-methylindole need to be reduced, it is not advisable to use a relatively low sampling flow rate. Finally, a medium sampling flow rate of 0.5 L / min is selected.

[0046] Example 5 A method for detecting indole compounds in ambient air, the specific steps are as follows: S1 Preparation of standard solution: The standard methanol solutions of indole and 3-methylindole are 100 mg / L, dilute the standard curve in 1 mL of acetone / n-hexane (v / v, 1 / 1) to prepare a series of standard solutions with concentrations of 0.5, 1, 2, 5, 8, 10, and 20 μg / L; S2 Plotting of standard curve: Use gas chromatography - mass spectrometry to inject and detect the indole compound standard solutions prepared in S1, and plot the standard curve of indole compounds. The results are shown in Table 3 below.

[0047] Among them, the detection conditions of gas chromatography are: TG-5MS chromatographic column: 30 m × 0.25 μm × 0.25 mm, column flow rate: 1.2 mL / min; temperature programming: initial temperature 35°C, hold for 1 min, first increase the temperature at a rate of 20°C / min to 168°C, then increase the temperature at a rate of 2°C / min to 178°C, and finally increase the temperature at a rate of 30°C / min to 300°C and hold for 1 min; Injection port temperature: 250°C, injection mode: splitless injection, injection volume 1 μL, injection port pressurized injection for 1 min, pressure 200 kPa; The detection conditions of mass spectrometry are: transfer line temperature: 280°C; ion source temperature: 280°C; quantitative analysis: select ion scanning mode and full scan mode for simultaneous scanning.

[0048] Table 3 Retention Times, Standard Curves, and Correlation Coefficients of Indole and 3-Methylindole Name Retention time / min Standard curve Correlation coefficient r Indole 8.11 Y = 115504 * X 0.998 3-Methylindole 8.93 Y = 136197 * X 0.998

[0049] Detection method for indole and 3-methylindole in ambient air of S3, the specific steps are as follows: 3-methylindole: A mixed standard of indole and 3-methylindole with a concentration of 0.1 mg / L, 2 μL was added to a GDX-502 sampling tube, the sampling rate was set at 0.5 L / min, sampling was carried out for 20 min, and elution was performed with 2 mL of acetone / n-hexane (v / v, 1 / 1), repeated 7 times.

[0050] Indole: A mixed standard of indole and 3-methylindole with a concentration of 1.0 mg / L, 2 μL was added to a GDX-502 sampling tube, the sampling rate was set at 0.5 L / min, sampling was carried out for 20 min, and elution was performed with 2 mL of acetone / n-hexane (v / v, 1 / 1), repeated 7 times.

[0051] The method detection limit is calculated according to the specified detection limit (MDL)=t(n - 1, 0.99)×s. When the number of repeated samples n = 7, t(n - 1, 0.99) is 3.143. Calculated according to the sampling volume of 10 L, the method detection limit of indole is 0.04 μg / m 3 , and the method detection limit of 3-methylindole is 0.004 μg / m 3 , and the determination lower limits are 0.16 μg / m for indole 3 , and 0.016 μg / m for 3-methylindole 3 .

[0052] In addition, mixed standards of indole and 3-methylindole with concentrations of 1 mg / L, 5 mg / L, and 20 mg / L were respectively added with 2 μL to a GDX-502 sampling tube, the sampling rate was set at 0.5 L / min, sampling was carried out for 20 min, and elution was performed with 2 mL of acetone / n-hexane (v / v, 1 / 1), repeated 6 times. The precision and recovery rates of low, medium, and high concentration spike additions are shown in Table 4.

[0053] Table 4 Precision and recovery rates of indole and 3-methylindole spike additions

[0054] As can be seen from Table 4, the spike addition recovery rates of indole and 3-methylindole at low, medium, and high concentrations are between 98.7% and 112%, and the relative standard deviations are all less than 10%.

[0055] Example 6 The ambient air near a pigsty and a chicken coop in a certain village was sampled for 20 min using a GDX-502 sampling tube at a flow rate of 0.5 L / min, and elution was performed with 2 mL of acetone / n-hexane (v / v, 1 / 1). The concentrations of indole and 3-methylindole are shown in Table 5 below.

[0056] Table 5 Concentrations of indole and 3-methylindole near pigsties and chicken coops <![CDATA[Indole / (μg / m 3 )]]> <![CDATA[3-Methylindole / (μg / m 3 )]]> Pigsty 1.33 0.21 Chicken coop 0.19 0.08

[0057] Comparative Example 1 Indole and 3-methylindole were determined by thermal desorption-gas chromatography-mass spectrometry: After injecting 1 μL of a 10 mg / L indole and 3-methylindole standard solution into a Tenax thermal desorption tube, the methanol solvent brought in by the standard solution was blown off with high-purity nitrogen for 2 min, and then it was placed in a thermal desorption instrument and measured by a gas chromatograph and a gas chromatography-mass spectrometer respectively. No obvious indole and 3-methylindole peaks were found in the measured chromatogram and the SCAN and SIM chromatograms of the gas chromatography-mass spectrometer.

[0058] Comparative Example 2 A 5 μg / L indole and 3-methylindole standard solution was determined by liquid chromatography and liquid chromatography-mass spectrometry, and no peaks were detected.

[0059] In the present invention, a GDX-502 sampling tube is used to adsorb and sample indole compounds in ambient air, especially indole and 3-methylindole. At the same time, a mixed solution of acetone / n-hexane is used as an elution solvent to elute the sampling tube, which significantly improves the adsorption effect of the sampling tube on indole compounds in ambient air. Moreover, the detection limit and recovery rate of the samples detected by gas chromatography-mass spectrometry are significantly improved compared with traditional methods such as thermal desorption gas chromatography-mass spectrometry, liquid chromatography, and liquid chromatography-mass spectrometry. A rapid, sensitive, and accurate analytical method for indole and 3-methylindole in ambient air is established in the present invention, providing a basis for the formulation of detection standards and quality control of indole substances.

Claims

1. A detection method for indole compounds in ambient air, characterized in that, It includes the following steps: Preparation of the standard solution: Accurately weigh the indole compound standard and dissolve it in methanol to prepare a methanol stock solution of 100 mg / L indole compound standard. Then, dilute the methanol stock solution of the indole compound standard with an organic solvent to prepare indole compound standard solutions with certain concentration gradients in the range of 0.5 μg / L - 20 μg / L; The organic solvent is selected from at least one of acetone, n-hexane, and carbon disulfide; S2 Plotting of the standard curve: Inject and detect the indole compound standard solution prepared in S1 by gas chromatography - mass spectrometry to plot the standard curve of the indole compound; Among them, the detection conditions of gas chromatography are: Injection port temperature: 220 - 260 °C, injection mode: splitless injection, injection volume 1 - 2 μL, injection port pressure injection for 0.5 - 2 min, pressure 180 - 220 kPa; TG - 5MS chromatographic column: 30 m × 0.25 μm × 0.25 mm, column flow rate: 1 - 1.5 mL / min; The temperature programming is: initial temperature 35 °C for 1 min, first increase the temperature at a rate of 20 °C / min to 168 °C, then increase the temperature at a rate of 2 °C / min to 178 °C, and finally increase the temperature at a rate of 30 °C / min to 300 °C and hold for 1 min; The detection conditions of mass spectrometry are: transfer line temperature: 280 °C; ion source temperature: 280 °C; quantitative analysis: select ion scanning mode and full scan mode for simultaneous scanning; S3 Sampling and detection of environmental air samples: Add an indole compound standard solution with a concentration of 0.1 - 10 mg / L to the sampling tube to sample the environmental air. Elute the sampling tube with an elution reagent. Then, inject the sample successively according to the chromatographic conditions and mass spectrometry conditions described in S2. Substitute the obtained quantitative ion peak area into the standard curve plotted in S2 to obtain the specific content of the indole compound contained in the environmental air sample.

2. The detection method according to claim 1, wherein The indole compounds include indole and 3 - methylindole.

3. The detection method according to claim 1, characterized in that, In S1, accurately weigh the indole compound standard and dissolve it in methanol to prepare a methanol stock solution of 100 mg / L indole compound standard. Then, dilute the methanol stock solution of the indole compound standard with an organic solvent to prepare indole compound standard solutions with concentrations of 0.5 μg / L, 1 μg / L, 2 μg / L, 5 μg / L, 8 μg / L, 10 μg / L, and 20 μg / L respectively; The organic solvent is a mixed solution of acetone and n - hexane, and the volume ratio of acetone to n - hexane is 1:

1.

4. The detection method according to claim 1, wherein The sampling tube described in S3 is a GDX - 502 sampling tube.

5. The detection method according to claim 1, wherein For the sampling described in S3, the sampling flow rate is 0.2 - 1.0 L / min, and the sampling time is 15 - 30 min.

6. The detection method according to claim 1, characterized in that, The elution reagent described in S3 is selected from at least one of acetone, n - hexane, and carbon disulfide.

7. The detection method according to claim 6, wherein The elution reagent described in S3 is a mixed solution of acetone and n - hexane, and the volume ratio of acetone to n - hexane is 1:1.

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