A detection method for specific gas concentration in an explosion-hazardous area

Abstract

This application relates to the technical field of gas detection, and particularly to a method for detecting the concentration of specific gases in explosion - hazardous areas. This method uses solid - phase microextraction sampling on - site. The collected samples are detected offline using a surface acoustic wave gas chromatograph, and the gas concentration of the target component in the explosion - hazardous area is calculated and analyzed based on the detection results, ultimately achieving rapid detection of the concentration of specific gases in explosion - hazardous areas. The method for analyzing the concentration of specific gases in explosion - hazardous areas by coupling SPME with GC - SAW proposed in this application does not require pretreatment of the samples collected by SPME and can be directly injected for detection. The sampling and detection methods are safe, and the entire detection time cycle is greatly shortened.

Description

Technical Field

[0001] This application relates to the technical field of gas detection, and particularly to a method for detecting the concentration of specific gases in explosion - hazardous areas. Step 1) Utilize surface acoustic wave gas phase Background Art

[0002] The "explosion - hazardous area" frequently mentioned in this application refers to a place where flammable and explosive substances are produced, used, or stored, and can form an explosive mixture, and there is an explosion hazard. Detecting the concentration of specific gases (such as explosive gases like nitroglycerin, TNT, and RDX) in explosion - hazardous areas helps to timely analyze whether there are explosion safety hazards in the area.

[0003] Existing methods for detecting explosive gas, such as detecting the concentration of nitroglycerin gas, generally use adsorption tube sampling method or absorption liquid sampling method to collect on - site gas, and then use a gas chromatograph - electron capture detector (GC - ECD) and a spectrophotometer (naphthylethylenediamine hydrochloride colorimetric method) respectively in the laboratory for detection; for detecting RDX, it generally uses ultra - fine glass fiber filter paper for collection, elutes with acetone and then transfers it into methanol for injection, and uses high - performance liquid chromatography (HPLC) for detection. However, these methods all require the use of a sampling pump during on - site sampling, and the safety requirements for explosion - hazardous areas are getting higher and higher, strictly restricting the use of equipment such as charged, impact - prone, and pumps. Therefore, the existing sampling and detection methods are difficult to meet the above - mentioned detection requirements. In addition, even using the existing methods, there are also problems such as cumbersome pretreatment processes and long detection times (>30 min), which cannot timely reflect the on - site concentration situation. Therefore, there is an urgent need for a safe and rapid detection method to meet the detection of specific gas concentrations in explosion - hazardous areas. Summary of the Invention

[0004] To solve the above problems, this application proposes a solution of using solid - phase microextraction (SPME) for sampling on - site, and using a surface acoustic wave gas chromatograph for off - line detection of the collected samples to achieve rapid detection of specific gas concentrations in explosion - hazardous areas.

[0005] To achieve the above - mentioned invention purpose, this application provides a method for detecting the concentration of specific gases in explosion - hazardous areas. This method uses solid - phase microextraction for sampling on - site, and uses a surface acoustic wave gas chromatograph for off - line detection of the collected samples, and calculates and analyzes based on the detection results to obtain the concentration of the target component gas in the explosion - hazardous area, ultimately achieving rapid detection of specific gas concentrations in explosion - hazardous areas;

[0006] Specifically, it includes:

[0007] Pretreatment step:

[0008] Step 1) Use a surface acoustic wave gas chromatograph to test standard solutions of target components with different concentrations, obtain the response A of the injected standard solution of the target component, and establish a relationship curve L1 between the mass m of the injected target component and the response A;

[0009] Step 2) Enrich target component gases with different concentrations by solid-phase microextraction, and then use a surface acoustic wave gas chromatograph to test the enriched samples to obtain the mass m of the target component enriched by solid-phase microextraction, and establish a relationship curve L2 between the gas concentration C of the target component and the mass m of the target component enriched by solid-phase microextraction;

[0010] Steps for on-site collection and off-line detection:

[0011] Step 3) Use solid-phase microextraction to enrich and sample in an explosion-hazardous area for 5 - 60 s; perform off-line detection with a surface acoustic wave gas chromatograph to obtain the response A of the target component collected by solid-phase microextraction;

[0012] Step 4) According to the relationship curve L1 between the mass m of the injected target component and the response A, obtain the mass m of the target component collected on-site by solid-phase microextraction;

[0013] Step 5) Then, according to the relationship curve L2 between the gas concentration C of the target component and the mass m of the target component enriched by solid-phase microextraction, obtain the gas concentration of the target component in the explosion-hazardous area.

[0014] The target components include explosive components or / and combustible organic components; among them, the explosive components are: nitroglycerin, 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, or cyclotrimethylenetrinitramine; the combustible organic components are benzene series or acetate substances.

[0015] The benzene series is benzene or toluene; the acetate substances are ethyl acetate or butyl acetate.

[0016] As an improvement of the above technical solution, the target component is nitroglycerin, and the target component standard solution is a 100 μg / mL nitroglycerin standard solution;

[0017] Step 1) includes: using methanol as a solvent and a 100 μg / mL nitroglycerin standard solution as a stock solution, diluting to obtain a series of nitroglycerin-methanol solutions with a concentration range of 1 - 20 μg / mL, using a surface acoustic wave gas chromatograph to test standard solutions of target components with different concentrations, and establishing a relationship curve L1 between the mass m of injected nitroglycerin and the response A.

[0018] In Step 2), nitroglycerin gases with different concentrations are prepared by the gas bag method, and the preparation process is as follows:

[0019] Step 2-1) Use a microsyringe to pipette a certain volume of nitroglycerin solution with a known concentration and inject it into a certain volume of a polytetrafluoroethylene gas bag. By adjusting the volume of the nitroglycerin solution added to the gas bag, multiple nitroglycerin gases with different concentrations are obtained;

[0020] Step 2-2) Subsequently, use a flow controller to control the gas flow and fill the gas bag with an appropriate amount of high-purity nitrogen as a balance gas;

[0021] Step 2-3) After equilibration at room temperature, the nitroglycerin gas prepared in the gas bag is detected by a surface acoustic wave gas chromatograph to obtain the gas concentration C of the nitroglycerin prepared in the gas bag.

[0022] Further, the said Step 2-3) includes: when directly sampling and testing by a surface acoustic wave gas chromatograph, the sampling flow rate is fixed, and the volume V of the target component gas in the sampling gas bag is obtained by controlling the sampling time; meanwhile, according to the relationship curve L1 between the mass m and the response A of the target component injection, the mass m of the target component injected is obtained; then the gas concentration of the nitroglycerin gas prepared in the gas bag is:

[0023] C = m / V;

[0024] wherein, C is the gas concentration of the nitroglycerin prepared in the gas bag; m is the mass of the target component injected; V is the volume of the target component gas in the sampling gas bag during testing.

[0025] As another improvement of the above technical solution, the said Step 4) includes:

[0026] Step 4-1) Fix the solid-phase microextraction enrichment time at 10 s and use a 65 μm PDMS / DVB extraction head to enrich nitroglycerin gases with multiple concentrations respectively;

[0027] Step 4-2) The enriched sample is directly injected and detected by a surface acoustic wave gas chromatograph to obtain the nitroglycerin test response, and according to the relationship L1 between the mass and the response of the target component established in Step 1), the mass m of the nitroglycerin enriched in situ by solid-phase microextraction is obtained.

[0028] In actual use, the surface acoustic wave gas chromatograph uses a capillary column; the temperature of the injection port is 160°C to 200°C, the temperature of the valve box is 140°C to 180°C, the initial temperature of the chromatographic column is 30°C to 60°C, and then it is programmed to rise to 180°C at a rate of 6°C / s to 16°C / s, the detector temperature is 40°C to 100°C, the sampling time is 10 to 60 s; the desorption temperature of the preconcentration tube is 200°C to 250°C, the sampling flow rate is 15 to 40 mL / min; the carrier gas uses nitrogen or helium.

[0029] As another improvement of the above technical solution, step (3) further includes: retracting the solid-phase microextraction fiber head that has completed aging into the extraction needle, and then storing it in a clean headspace vial. Compared with the prior art, the advantages of this application are as follows, and its advantages are specifically reflected in:

[0030] (1) The solid-phase microextraction (SPME) enrichment sampling adopted in this solution is a passive sampling method, which will not introduce stimulating factors and can meet the safety requirements for collecting specific gases in places with explosion safety hazards;

[0031] (2) The surface acoustic wave gas chromatography detection technology (GC-SAW) adopted in this solution has the characteristics of high detection sensitivity. When using SPME enrichment sampling, the required sampling time is short, such as only 10 s (5 - 60 s), and the concentration of specific gases in explosion-hazardous areas can be quickly detected;

[0032] In summary, this application proposes a method for analyzing the concentration of specific gases in explosion-hazardous areas by coupling SPME with GC-SAW. The samples collected by SPME do not require pretreatment and can be directly injected for detection. Moreover, the sampling and detection methods are safe, and the entire detection time cycle is greatly shortened (GC-SAW chromatographic separation time < 20 s, single-sample analysis time < 2.5 min).

[0033] Table 1 Comparison between the prior art and the technical solution of this application

[0034]

[0035] As can be seen from the above table, the technical solution of this application has obvious advantages and can safely and quickly detect the concentration of specific gases in explosion-hazardous areas. Brief Description of the Drawings

[0036] Figure 1 is a schematic flow chart of the method for detecting the concentration of specific gases in explosion-hazardous areas of this application;

[0037] Figure 2a is the chromatogram for the qualitative analysis test of nitroglycerin in this application, where the abscissa is shown in retention index;

[0038] Figure 2b is the chromatogram for the qualitative analysis test of nitroglycerin in this application, where the abscissa is shown in retention time;

[0039] Figure 3 is the relationship curve L1 between the mass m of the target component liquid injection and the response A in this application;

[0040] Figure 4 is the relationship curve L2 between the concentration of the target component gas and the SPME enrichment mass in this application;

[0041] Figure 5 shows the interference peak conditions of the SPME extraction fiber head in this application when stored for different times;

[0042] Figure 6 is the GC-SAW test chromatogram after SPME enrichment in a certain explosion-hazardous area in this application;

[0043] Figure 7 is the qualitative analysis test chromatogram of 2,4,6-trinitrotoluene in this application;

[0044] Figure 8 is the qualitative analysis test chromatogram of toluene in this application. Detailed implementation manners

[0045] The technical solutions of this application will be described in detail below in conjunction with the accompanying drawings and embodiments. In these drawings, the same or similar components are denoted by the same or similar reference numerals.

[0046] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principle of the present invention and do not limit the protection scope of the present invention.

[0047] It should be noted that in the description of the present invention, the terms indicating directions or positional relationships such as "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings. This is only for convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0048] As Figure 1 shown, the present invention provides a method for rapid analysis of specific gas concentrations in an explosion-hazardous area. The detection process of specific gas concentrations in an explosion-hazardous area is as follows:

[0049] 1) Use GC-SAW to test standard solutions of target components at different concentrations, and establish a relationship curve L1 between the injection mass m and the response A;

[0050] 2) Use SPME to enrich target component gases at different concentrations, and use GC-SAW to test the enriched samples, and establish a relationship curve L2 between the target component gas concentration C and the SPME enrichment mass m;

[0051] 3) Use SPME to enrich and sample in an explosion-hazardous area, and perform off-line detection with GC-SAW to obtain the response A of the SPME collected samples;

[0052] 4) According to the relationship curve L1 between the injection mass m and the response A, obtain the mass of the target components collected by SPME on-site;

[0053] 5) According to the relationship curve L2 between the concentration C of the target component gas and the enrichment mass m of SPME, the concentration of the target component gas in the explosion-hazardous area is obtained.

[0054] The solid-phase microextraction (SPME) sampling technique and the detection technique of the surface acoustic wave gas chromatograph involved in this application are both publicly available in the existing literature. However, in the process of applying them to specific occasions to achieve various detections, various problems still need to be solved. For example:

[0055] (1) Can the surface acoustic wave gas chromatograph (GC-SAW) be used to detect nitroglycerin (NG)?

[0056] Through literature research, it is found that when using traditional gas chromatography methods (such as GC-ECD, GC-TCD, etc.) or gas chromatography-mass spectrometry to detect NG, there is a problem that NG is easily decomposed. It is necessary to study the influence of the temperature of different components on the detection of NG, such as the injection port, valve box, chromatographic column, etc., and provide corresponding solutions.

[0057] (2) When simply using solid-phase microextraction (SPME) to collect samples, the specific gas concentration cannot be directly obtained by using GC-SAW for detection.

[0058] Using solid-phase microextraction (SPME) as a sampling method in the explosion-hazardous area, when using GC-SAW for detection after sampling, it is also necessary to develop corresponding detection methods for specific gases.

[0059] When using solid-phase microextraction (SPME) to collect samples, the target components in the air are adsorbed by the extraction fiber head. When using GC-SAW for detection, only the qualitative analysis results of the components adsorbed by SPME and the enrichment mass can be obtained, and the concentration of the target components in the on-site air cannot be directly obtained.

[0060] (3) There are no standard concentration gases available for some target components, such as nitroglycerin, 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, and cyclotrimethylenetrinitramine existing in the explosion-hazardous area.

[0061] Therefore, this application also designs to prepare the target component gas by the gas bag method, directly collect the gas in the gas bag by GC-SAW for detection, and according to the relationship between the mass and the response, as well as the flow parameters during the detection by GC-SAW, the concentration of the prepared target gas can be calculated. According to the above method for preparation and detection, by adjusting the addition amount of the sample when preparing the gas bag, the preparation methods of several concentration target component gases are determined, that is, the problem of obtaining target component gases with different concentrations is solved.

[0062] Then, through SPME enrichment sampling and using GC-SAW for detection, the relationship between the gas concentration of this kind of substance and the enrichment mass is established.

[0063] (4) Selection and Use of SPME Extraction Head

[0064] a Literature Research

[0065] For small molecular weight or volatile compounds, an extraction head with a 100 µm PDMS coating is usually selected. For polar volatile substances such as alcohols, amines or nitroaromatic compounds, an extraction head with a 65 µm PDMS / DVB coating is selected, which has more efficient adsorption and faster desorption.

[0066] b Appropriate Aging Method and Aging Equipment

[0067] Aging of various different models of SPME extraction heads was carried out. It was found that the extraction head with a 65 µm PDMS / DVB coating can be aged at 200 °C in a shorter time, and there is no interference in the extraction head blank background. Moreover, the aging time of the 65 µm PDMS / DVB extraction head can be controlled within 10 min, which can achieve the goal of rapid detection; for the 100 μm PDMS / DVB and other extraction heads, the aging time at 200 °C is up to 30 min.

[0068] In addition, combined with the characteristics of the GC-SAW instrument, the injection port temperature can reach 200 °C, which can meet the aging of the 65 µm PDMS / DVB extraction head without using an additional aging device.

[0069] SPME Extraction Head Aging Method:

[0070] ① Push out the extraction fiber head of the SPME extraction device and extend it into the injection port of the GC-SAW instrument, and set the injection port temperature to 200 °C;

[0071] ② The GC-SAW switches the valve to the injection state, turns on the sampling pump. While the SPME extraction fiber head is heated, the air flow draws away the impurities or pollutants desorbed by the extraction head due to heat, realizing the aging of the extraction head.

[0072] c Experimental Verification

[0073] Using a 65 µm PDMS / DVB SPME extraction head to enrich nitroglycerin gas, nitroglycerin can be detected using GC-SAW.

[0074] Protection of SPME Extraction Head

[0075] SPME can adsorb the target components and also the pollutants in the air.

[0076] The following problems exist in practical applications: SPME needs to be aged before use. After aging, it is carried to the sampling site. If the extraction head is directly exposed to the air during the carrying process, SPME will adsorb pollutants in the air, which will affect the sampling effect on site on the one hand, and on the other hand, the adsorbed interfering substances will affect the quantitative analysis of the target components. Therefore, it is necessary to solve the problem of introducing interfering substances due to the adsorption of the extraction head during transportation.

[0077] The solution we adopted is: after SPME is aged, the SPME extraction fiber head is retracted into the extraction needle, and then it is placed in a clean headspace vial for storage. Through experimental verification, when using this method for storage, the time can be up to 28 h. Especially, there is no interference in the detection of NG. As Figure 5 shown, it presents the comparison of the blank interference and the test chromatogram of the nitroglycerin standard solution at different storage times of the SPME extraction head in the headspace vial. It can be found that there is no obvious large interference peak after storing for 8 h; after storing for 28 h, although interference peaks appear, the distance from the chromatographic peaks of nitroglycerin is far, which does not affect the qualitative and quantitative analysis of nitroglycerin, indicating that the method of sealing and storing the extraction head with a headspace vial in this application has a good effect.

[0078] Example 1

[0079] Instruments and reagents used:

[0080] Surface acoustic wave gas chromatograph, MXT-5 capillary column (1m×0.25mm×0.25μm), C6-C18 mixed standard solution, 100 μg / mL nitroglycerin standard solution.

[0081] (1) Qualitative analysis of nitroglycerin

[0082] The temperature conditions for testing with the surface acoustic wave gas chromatograph are as follows: injection port 180°C, valve box 165°C, MXT-5 chromatographic column (1m×0.25mm×0.25μm), initial temperature of the chromatographic column 45°C, programmed temperature rise to 180°C at 12°C / s, detector temperature 40°C, sampling (pump suction) time 10 s; desorption temperature of the preconcentration tube 250°C, sampling flow rate 30 mL / min; carrier gas nitrogen, carrier gas flow rate 3.0 mL / min.

[0083] When performing qualitative analysis of nitroglycerin, first test the normal alkanes to calibrate the retention index; then use a micro syringe to take liquid standard samples for testing. The measured retention index of nitroglycerin is 1371. The test chromatogram of the nitroglycerin standard sample is as Figure 2a and Figure 2b shown. Among them, Figure 2a the abscissa of the chromatogram shows the retention index. GC-SAW qualitatively analyzes the measured components by the size of the retention index. The measured retention index of nitroglycerin is 1371; Figure 2bThe abscissa of the chromatogram is shown in retention time, with the unit of seconds (s). The entire chromatographic separation time is only 20 s, which reflects the advantage of fast chromatographic separation speed of GC-SAW for testing samples.

[0084] (2)Relationship curve between the injection mass and response of nitroglycerin liquid

[0085] Using methanol as the solvent and a 100 μg / mL nitroglycerin standard solution as the stock solution, a series of nitroglycerin-methanol solutions with a concentration range of 1 - 20 μg / mL were diluted. During GC-SAW detection, a microsyringe was used to sample 0.1 - 0.3 μL, and the relationship curve L1 between the injection mass and response of nitroglycerin was established, as Figure 3 shown.

[0086] (3)Preparation and testing of nitroglycerin gas

[0087] The gas bag method was used to prepare nitroglycerin gas, and the preparation process was as follows:

[0088] 1) Use a microsyringe to transfer a certain volume (Vl) of a nitroglycerin solution with a known concentration and inject it into a polytetrafluoroethylene gas bag with a certain volume (such as 1 L);

[0089] 2) Subsequently, use a flow controller to control the gas flow and fill the gas bag with an appropriate volume of high-purity nitrogen as the balance gas;

[0090] 3) Equilibrate at room temperature for about 60 min to obtain nitroglycerin gas with an undetermined concentration;

[0091] 4) The concentration of the prepared gas was obtained through direct detection and analysis by GC-SAW.

[0092] 5) By adjusting the volume of the nitroglycerin solution added to the gas bag, nitroglycerin gas with multiple concentrations was achieved.

[0093] Testing of the nitroglycerin gas bag and determination of the concentration:

[0094] During direct sampling and testing by GC-SAW, the sampling flow rate was fixed, and the volume V (mL) of the collected gas could be adjusted by controlling the sampling time. If the response of the prepared gas bag was measured as A, then according to the established relationship between the injection mass and response of nitroglycerin, the mass m of nitroglycerin collected during detection could be calculated. Then, the concentration of nitroglycerin in the gas bag could be calculated according to the following formula:

[0095] C = m / V;

[0096] where C is the concentration of the prepared nitroglycerin gas bag, mg / m 3 ; m is the mass collected during gas bag testing, ng; V is the volume of the gas collected during gas bag testing, mL.

[0097] Since ① nitroglycerin is a liquid at room temperature, it has a certain volatility, but its boiling point is relatively high, and it cannot all volatilize into a gaseous state at room temperature; ② the volatilized nitroglycerin will also re-adsorb onto the surface of the airbag, eventually forming a relatively balanced state, making it impossible to directly obtain the gas concentration in the airbag through calculation. However, if the gas being tested here is replaced with other substances with better volatility, such as benzene, toluene, n-hexane, etc., it can be obtained through direct calculation.

[0098] (4)Enrichment and detection of nitroglycerin gas, establishing the relationship between nitroglycerin gas concentration and enrichment mass

[0099] 1) Fix the SPME enrichment time at 10 s, and use a 65 μm PDMS / DVB extraction head to enrich nitroglycerin gas at multiple concentrations respectively;

[0100] 2) The enriched sample is directly injected for detection to obtain the test response of nitroglycerin. Combining the established relationship between injection mass and response, the mass of nitroglycerin enriched by SPME can be obtained. Therefore, the relationship curve L2 between nitroglycerin gas concentration and enrichment mass can be established, as Figure 4 shown.

[0101] (5)Detection of nitroglycerin gas concentration in the air of explosion-hazardous areas

[0102] 1) Use a solid-phase microextraction device to collect gas at a certain point in an explosives production site for 10 s;

[0103] 2) After the collection, the SPME extraction fiber head is immediately retracted and stored in a headspace vial.

[0104] 3) Transfer the sample collected by SPME to the storage place of GC-SAW, and directly inject the SPME for detection. The test chromatogram is as Figure 6 shown. The test results show that NG is detected in the sample enriched on-site. The NG chromatographic peak has a symmetric shape and no interference, indicating that the method can achieve the enrichment and detection of NG in on-site gas. There are also other volatile components in the on-site air and are detected by GC-SAW and shown in the chromatogram. However, since no other standard substances are used for calibration testing, their specific components cannot be identified.

[0105] 4) Calculate the mass enriched by SPME according to the response obtained from the test, and then combine the relationship between nitroglycerin gas concentration and enrichment mass to calculate the nitroglycerin gas concentration.

[0106] Regarding the C6 - C18 mixed standard solution, it contains thirteen n-alkanes from C6 (n-hexane) to C18 (n-octadecane).

[0107] As we know, traditional gas chromatographs usually use the retention time (t) of substances for qualitative analysis, while the gas chromatograph with surface acoustic wave (GC-SAW) uses the retention index (RI) for qualitative analysis. However, in essence, it is still the retention time.

[0108] The following briefly introduces the process of retention index calibration and qualitative analysis of target components:

[0109] 1) First, test the C6 - C18 mixed standard solution to calibrate the retention index of the instrument. In the chromatogram obtained from the test, the abscissa is the retention index and the ordinate is the peak intensity. After calibrating the test chromatogram, the retention index of the chromatographic peak of C6 is forced to be calibrated to 600, the retention index of C7 is calibrated to 700, and so on.

[0110] 2) After the retention index calibration is completed, test the target component, such as nitroglycerin. Its peak emergence position will be between C13 and C14. Then the retention index of nitroglycerin will be in the range of 1300 - 1400. According to the retention index formula and the retention times (peak emergence times) of C13, C14, and nitroglycerin, the specific retention index value of nitroglycerin can be calculated, which serves as the basis for the qualitative analysis of nitroglycerin.

[0111] Under the same chromatographic conditions, the retention index of the same substance does not change with the changes of external conditions such as equipment and testers. Therefore, it has relatively good stability and reliability for the qualitative analysis of unknown substances. (There is comparability and reference between different instruments; and there is an authoritative NIST database to query the retention indices of different substances. If the retention time is used for qualitative analysis, since GC-SAW has a fast detection speed and the peak emergence times of various substances on the instrument are within 20 s, while traditional gas chromatographs are generally in the minute order of magnitude, there is no comparability between them).

[0112] Example 2

[0113] The content of this part of the example is basically similar to the content and principle of nitroglycerin. Replace the tested component with 2,4,6-trinitrotoluene. The specific process is as follows:

[0114] The instruments and reagents used are:

[0115] Gas chromatograph with surface acoustic wave, MXT-5 capillary column (1 m × 0.25 mm × 0.25 μm), C6 - C18 mixed standard solution, 1.0 mg / mL 2,4,6-trinitrotoluene standard solution.

[0116] (1) Qualitative analysis of 2,4,6-trinitrotoluene

[0117] Conditions for testing the surface acoustic wave gas chromatograph: injection port at 200 °C, valve box at 180 °C, MXT-5 chromatographic column (1 m × 0.25 mm × 0.25 μm), initial column temperature at 60 °C, programmed temperature increase to 180 °C at 16 °C / s, detector temperature at 100 °C, sampling (pump suction) time at 30 s; desorption temperature of the preconcentration tube at 250 °C, sampling flow rate at 40 mL / min; carrier gas is helium, carrier gas flow rate at 3.0 mL / min.

[0118] For the qualitative analysis of 2,4,6-trinitrotoluene, first test the n-alkanes to calibrate the retention index; then use a microinjector to take liquid standard samples for testing. The chromatogram of the 2,4,6-trinitrotoluene standard sample test is as Figure 7 shown. The retention index of TNT is measured to be 1734, and this retention index is used as the qualitative reference basis for TNT.

[0119] (2)Relationship curve between the injection mass and response of 2,4,6-trinitrotoluene liquid

[0120] Using methanol as the solvent and a 1.0 mg / mL 2,4,6-trinitrotoluene standard solution as the mother liquor, a series of 2,4,6-trinitrotoluene-methanol solutions with a concentration range of 1 - 20 μg / mL are diluted. During GC-SAW detection, a microinjector is used to take 0.1 - 0.3 μL of samples to establish the relationship curve between the injection mass and response of 2,4,6-trinitrotoluene.

[0121] (3)Preparation and testing of 2,4,6-trinitrotoluene gas

[0122] The gas bag method is used to prepare 2,4,6-trinitrotoluene gas, and the preparation process is as follows:

[0123] 1) Use a micro syringe to transfer a certain volume (Vl) of a 2,4,6-trinitrotoluene solution with a known concentration and inject it into a polytetrafluoroethylene gas bag with a certain volume (such as 1 L);

[0124] 2) Subsequently, use a flow controller to control the gas flow rate and fill the gas bag with an appropriate volume of high-purity nitrogen as the balance gas;

[0125] 3) Equilibrate at room temperature for about 60 min to obtain 2,4,6-trinitrotoluene gas with an undetermined concentration;

[0126] 4) The concentration of the prepared gas is directly detected and analyzed by GC-SAW.

[0127] 5) By adjusting the volume of the 2,4,6-trinitrotoluene solution added to the gas bag, 2,4,6-trinitrotoluene gas with multiple concentrations is achieved.

[0128] Testing of 2,4,6-trinitrotoluene gas bag and determination of concentration:

[0129] During the GC-SAW direct sampling test, the sampling flow rate is fixed, and the volume V (mL) of the collected gas can be adjusted by controlling the sampling time. If the response of the prepared gas bag is measured as A, then according to the established relationship between the injection mass of nitroglycerin and the response, the mass m of 2,4,6-trinitrotoluene collected during the test can be calculated. Then, the concentration of 2,4,6-trinitrotoluene in the gas bag can be calculated according to the following formula:

[0130] C = m / V;

[0131] where C is the concentration of the prepared 2,4,6-trinitrotoluene gas bag, μg / m 3 ; m is the mass collected during the gas bag test, ng; V is the volume of the gas collected during the gas bag test, mL.

[0132] (4) Enrichment and detection of 2,4,6-trinitrotoluene gas, and establishment of the relationship between 2,4,6-trinitrotoluene gas concentration and enrichment mass

[0133] 1) Fix the SPME enrichment time at 10 s, and use a 65 μm PDMS / DVB extraction head to enrich 2,4,6-trinitrotoluene gas at multiple concentrations;

[0134] 2) The enriched sample is directly injected for detection to obtain the test response of 2,4,6-trinitrotoluene. Combining the established relationship between the injection mass and the response, the mass of 2,4,6-trinitrotoluene enriched by SPME can be obtained. Therefore, the relationship curve between 2,4,6-trinitrotoluene gas concentration and enrichment mass can be established.

[0135] (5) Detection of 2,4,6-trinitrotoluene gas concentration in the air of explosion hazardous areas

[0136] 1) Use a solid-phase microextraction device to collect gas at a certain point at an explosives production site for 10 s;

[0137] 2) After the collection, the SPME extraction fiber head is immediately retracted and stored in a headspace vial.

[0138] 3) Transfer the sample collected by SPME to the storage location of GC-SAW, and directly inject the SPME for detection;

[0139] 4) Calculate the mass enriched by SPME according to the response obtained from the test, and then combine the relationship between 2,4,6-trinitrotoluene gas concentration and enrichment mass to calculate the 2,4,6-trinitrotoluene gas concentration.

[0140] Example 3

[0141] In this Example 3, the detection is carried out for non-explosive gases, and there are relevant standard gases available for direct use. Therefore, the whole detection process is different from the above two examples.

[0142] Instruments and reagents used:

[0143] Surface acoustic wave gas chromatograph, MXT-5 capillary column (1m×0.25mm×0.25μm), C6-C18 mixed standard solution, 1.0 mg / mL toluene standard solution, 10 ppm toluene standard gas.

[0144] (1) Qualitative analysis of toluene

[0145] Test conditions of the surface acoustic wave gas chromatograph: injection port 140°C, valve box 140°C, MXT-5 chromatographic column (1m×0.25mm×0.25μm), initial temperature of the chromatographic column 30°C, programmed temperature rise to 180°C at 6°C / s, detector temperature 60°C, sampling (pump suction) time 60 s; desorption temperature of the preconcentration tube 250°C, sampling flow rate 15 mL / min; carrier gas is nitrogen, carrier gas flow rate 3.0 mL / min.

[0146] During the qualitative analysis of toluene, first, n-alkanes are tested to calibrate the retention index; then, a liquid standard sample is taken using a microsyringe for testing. The chromatogram of the toluene standard sample test is as shown in Figure 8 , and the measured retention index of toluene is 758, which is used as the qualitative reference basis for TNT.

[0147] (2) A series of toluene gas concentrations are obtained by dilution using the static gas blending method;

[0148] (3) Enrichment and detection of toluene gas, establishing the relationship between toluene gas concentration and enrichment response:

[0149] 1) Fix the SPME enrichment time at 10 - 60 s, and use a 65 μm PDMS / DVB extraction head to enrich toluene gas at multiple concentrations respectively;

[0150] 2) The enriched sample is directly injected for detection, and the relationship between toluene gas concentration and enrichment mass can be established by obtaining the toluene test response.

[0151] (4) Detection of toluene gas concentration in the air of explosive hazardous areas

[0152] 1) Use a solid-phase microextraction device to collect gas at a certain point in an explosive production site, with the collection time being 10 - 60 s;

[0153] 2) After the collection, the SPME extraction fiber head is immediately retracted and stored in a headspace vial.

[0154] 3) Transfer the sample collected by SPME to the storage location of GC-SAW, and directly inject the sample from SPME for detection;

[0155] 4) Calculate the mass enriched by SPME based on the response obtained from the test. Then, combined with the relationship between the toluene gas concentration and the response after enrichment, the toluene gas concentration can be calculated.

[0156] For volatile organic compound gases such as benzene series, they are different from explosive gases such as nitroglycerin. For the former, standard gases are available for direct use.

[0157] Therefore, when testing benzene series, the process of preparing benzene series gas with liquid standard substances and determining the concentration can be omitted. Instead, directly use SPME to enrich benzene series standard gases with different concentrations and establish the relationship between the enrichment response and the gas concentration. The detection process for explosive gases is relatively simpler.

[0158] Based on the special requirements of the detection scenario, this application proposes a targeted detection scheme / method, which solves some problems that may exist in implementing this scheme.

[0159] The advantages of the scheme proposed in this application are as follows: (1) The SPME sampling method adopted uses sampling instruments that are non-magnetic, non-electric, and do not introduce other stimulating factors, so there is no safety hazard when used in explosive hazardous areas; (2) The samples collected by SPME on-site can be directly connected to the instrument for detection without additional pretreatment; (3) Based on the high sensitivity characteristics of the surface acoustic wave gas chromatograph, the time required for SPME to collect samples on-site is short (as low as 10 s); (4) When GC-SAW detects samples, the chromatographic separation time of the samples < 20 s, which can more timely reflect the on-site concentration. In summary, this scheme has advantages such as a safe sampling method, short sampling time, and short detection time, and can meet the rapid quantitative detection of specific gases in explosive hazardous areas.

[0160] Other advantages of this scheme:

[0161] By regulating the temperature of the SAW detector, it can meet the detection of specific gases in a wider concentration range in explosive hazardous areas. The characteristics of the SAW detector are as follows: the lower the detector temperature, the easier it is for the component to be detected to condense on the detector surface. Therefore, it has higher detection sensitivity; when the detector temperature is increased, the component to be detected is not easily condensed and the detection sensitivity decreases. Therefore, by regulating the detector temperature, the detection of specific gas concentrations in a wider concentration range can be achieved.

[0162] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application rather than to limit them. The data in the upper right table in the chromatogram in the embodiments are actually data automatically generated by the instrument software, including information such as retention indices, response values, and substance names. In fact, they are the direct evidence that a certain chromatographic peak corresponds to a certain component, and what the corresponding response value is. Although the present application has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present application does not depart from the spirit and scope of the technical solutions of the present application, and they should all be covered within the scope of the claims of the present application.

Claims

1. A method for detecting the concentration of a specific gas in an explosion-hazardous place, wherein the method uses solid phase microextraction sampling on site, and the collected samples are detected offline using a surface acoustic wave gas chromatograph, and the concentration of the target component gas in the explosion-hazardous place is calculated and analyzed based on the detection results, thereby finally realizing the rapid detection of the concentration of a specific gas in the explosion-hazardous place; Specifically include: Step 1) using a surface acoustic wave gas chromatograph to test target component standard solutions of different concentrations, obtaining a response A of the injected target component standard solution, and establishing a relationship curve L1 between the mass m of the injected target component and the response A; the target component is nitroglycerin; Step 2) using solid phase microextraction to enrich target component gases of different concentrations, and then testing the enriched samples by surface acoustic wave gas chromatography to obtain the mass m of the target component enriched by solid phase microextraction, and establishing a relationship curve L2 between the gas concentration C of the target component and the mass m of the target component enriched by solid phase microextraction; Step 3) using solid phase microextraction to enrich samples in explosion-hazardous areas, with a sampling time of 5 to 60 seconds; using surface acoustic wave gas chromatography for offline detection, obtaining the response A of the target component collected by solid phase microextraction; Step 4) according to the relationship curve L1 between the mass m of the injected target component and the response A, the mass m of the target component collected on-site by the solid phase microextraction is obtained; Step 5) The target component gas concentration in the explosion hazardous area is obtained based on the relationship curve L2 between the target component gas concentration C and the mass m of the target component enriched by solid phase microextraction; In step 2), target component gases of different concentrations are prepared by the air bag method, and the preparation process is as follows: Step 2-1) using a microsyringe to pipette a certain volume of a nitroglycerin solution of known concentration, injecting it into a polytetrafluoroethylene gas bag of a certain volume, and obtaining a plurality of nitroglycerin gases of different concentrations by adjusting the volume of the nitroglycerin solution added to the gas bag; Step 2-2) Then, the gas flow rate is controlled by a flow controller to fill the gas bag with an appropriate amount of high-purity nitrogen as a balance gas; Step 2-3) After equilibration at room temperature, the nitroglycerin gas prepared in the air bag is detected by a surface acoustic wave gas chromatograph to obtain the gas concentration C of the nitroglycerin prepared in the air bag.

2. The method for detecting the concentration of a specific gas in an explosion-hazardous area according to claim 1, characterized in that: The step 1) comprises: using methanol as a solvent and a 100 μg / mL nitroglycerin standard solution as a mother solution, diluting to obtain a series of nitroglycerin-methanol solutions with a concentration range of 1 to 20 μg / mL, using a surface acoustic wave gas chromatograph to test target component standard solutions of different concentrations, and establishing a relationship curve L1 between the mass m of the nitroglycerin injection and the response A.

3. The method for detecting the concentration of a specific gas in an explosion-hazardous area according to claim 1, characterized in that: The step 2-3) includes: when using the surface acoustic wave gas chromatograph for direct sampling test, the sampling flow rate is fixed, and the volume V of the target component gas in the sampling bag is obtained by controlling the sampling time; at the same time, according to the relationship curve L1 between the mass m of the sampled target component and the response A, the mass m of the sampled target component is obtained; then the concentration of the nitroglycerin gas prepared in the air bag is: C = m / V; Wherein, C is the gas concentration of nitroglycerin prepared in the air bag; m is the mass of the injected target component; and V is the volume of the target component gas collected in the air bag during the test.

4. The method for detecting the concentration of a specific gas in an explosion-hazardous area according to claim 1, characterized in that: The step 4) comprises: Step 4-1) The fixed solid phase microextraction enrichment time was 10 s, and a 65 μm PDMS / DVB extraction head was used to enrich nitroglycerin gas at multiple concentrations; Step 4-2) The enriched sample is directly sampled and tested by surface acoustic wave gas chromatography to obtain a nitroglycerin test response, and the mass m of nitroglycerin enriched on-site by solid phase microextraction is obtained based on the relationship L1 between the mass of the target component and the response established in step 1).

5. The method for detecting the concentration of a specific gas in an explosion-hazardous area according to claim 1, characterized in that: The surface acoustic wave gas chromatograph adopts a capillary column; the temperature of the injection port is 160°C to 200°C, the temperature of the valve box is 140°C to 180°C, the initial temperature of the chromatographic column is 30°C to 60°C, and then the temperature is raised to 180°C at a rate of 6°C / s to 16°C / s, the detector temperature is 40°C to 100°C, and the sampling time is 10 to 60s; The desorption temperature of the pre-concentrator is 200℃~250℃, the sampling flow rate is 15~40mL / min; the carrier gas is nitrogen or helium.

6. The method for detecting the concentration of a specific gas in an explosion-hazardous area according to claim 1, characterized in that: The step 3) further comprises: retracting the solid phase microextraction extraction fiber head that has completed aging into the extraction needle, and then storing it in a clean headspace bottle.

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