Method for detecting peroxynitrate species in the atmosphere

Abstract

The present application relates to the detection method of peroxynitrate in the atmosphere, comprising: the six-way valve is adjusted to the sampling mode, the carrier gas and air inlet are opened, the carrier gas is swept to the chromatographic column and the electron capture detector in turn after passing through the first passage of the six-way valve, and the negative pressure device on the downstream side of the electron capture detector is opened at the same time; the air enters the sampling ring through the second passage of the six-way valve, and the excess air is discharged by using the air pump; the six-way valve is adjusted to the detection mode, the carrier gas enters the sampling ring through the third passage, the air sample in the sampling ring is taken out and brought into the chromatographic column; the PANs in the air sample are separated in the chromatographic column, and then enter the electron capture detector for detection, at the same time, the internal pressure of the electron capture detector is regulated and controlled by the negative pressure device to be stable negative pressure, the peak of the compound to be detected is accelerated, and the sensitivity of the electron capture detector to the detection is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of detection of trace components in the atmosphere, and particularly relates to a detection method of peroxyacyl nitrates in the atmosphere. BACKGROUND

[0002] The atmosphere includes nitrogen, oxygen, argon, carbon dioxide, carbon monoxide, sulfur dioxide, ozone, water vapor, dust and the like, and the components are relatively complex. The atmosphere contains trace peroxyacyl nitrates (PANs), which are a marker of secondary pollutants in photochemical smog. PANs have strong oxidizing properties, can stimulate the conjunctiva and respiratory tract of the human body, and cause toxicity to plants. The main components of PANs include peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN) and peroxy-methyl-propenoyl nitrate (MPAN). PPN is a product of photochemical reaction of VOCs produced by human activities and nitrogen oxides, and MPAN is a product of photochemical reaction of biogenic VOCs and nitrogen oxides. Therefore, the two can be used as tracers of anthropogenic sources and natural sources of regional photochemical pollution, respectively. The synchronous detection of the two can quantify the contribution of anthropogenic sources and natural sources to regional photochemical pollutants, and has great research value. Therefore, it is necessary to detect PANs in the atmosphere. At present, gas chromatography with an electron capture detector is mainly used to detect PANs in the atmosphere, and the detection limit is generally 30-50 ppt (volume ratio, 10 -12 SUMMARY

[0003] In view of the above problems, the application provides a detection method of peroxyacyl nitrates in the atmosphere, which comprises

[0004] S1: adjusting the six-way valve to the sampling mode, opening the carrier gas inlet and the air inlet, and sequentially purging the chromatographic column and the electron capture detector with the carrier gas passing through the first passage of the six-way valve, while opening the negative pressure device on the downstream side of the electron capture detector to promote the carrier gas to pass through the electron capture detector;

[0005] The air enters the sampling ring through the second passage of the six-way valve, and the excess air is discharged from the gas chromatograph by using a gas suction pump;

[0006] S2: adjusting the six-way valve to the detection mode, and bringing the air sample in the sampling ring out of the sampling ring and into the chromatographic column by the carrier gas passing through the third passage of the six-way valve;

[0007] ​S3: the PANs in the air sample are separated into components in the chromatographic column, and then enter the electron capture detector for detection, and at the same time, the negative pressure device controls the internal pressure of the electron capture detector to be stable negative pressure, accelerates the out-of-peak of the to-be-detected compound, and improves the sensitivity of the electron capture detector to the to-be-detected compound;

[0008] In step S3, the internal pressure of the electron capture detector is -19~-11kPa.

[0009] Optionally, the gas chromatograph device comprises a sampling ring, a chromatographic column, a six-way valve, a gas suction pump, an electron capture detector and a negative pressure device, the six-way valve is provided with a first interface, a second interface, a third interface, a fourth interface, a fifth interface and a sixth interface in counterclockwise order, and pipelines are connected between the interfaces;

[0010] The inlet end of the sampling ring is connected to the second interface, and the outlet end is connected to the fifth interface; the inlet end of the chromatographic column is connected to the sixth interface, and the outlet end is connected to the electron capture detector and the negative pressure device in sequence; the carrier gas inlet pipe is connected to the first interface, the air inlet pipe is connected to the third interface, and the inlet of the gas suction pump is connected to the fourth interface.

[0011] Optionally, the negative pressure device comprises a differential pressure controller and a diaphragm pump, and the downstream side of the electron capture detector is connected to the differential pressure controller and the diaphragm pump in sequence through a pipeline, the diaphragm pump can suck air for the electron capture detector, so that the electron capture detector is in a negative pressure environment, and the differential pressure controller is used to adjust the negative pressure in the electron capture detector.

[0012] The negative pressure device can provide an adjustable and stable negative pressure environment for the electron capture detector, so that the chromatographic column and the electron capture detector can stably output. Moreover, the negative pressure environment is conducive to the rapid and efficient elution of each component in the chromatographic column, and is also conducive to the rapid flow of each component in the electron capture detector, so as to shorten the sample flow time and improve the overall detection efficiency. The present inventors unexpectedly found that the electron capture detector can exhibit higher detection efficiency in a negative pressure environment, and the detection sensitivity of PANs is also improved, so that the peak is detected faster. Due to the increase in the height of the spectrum peak and the shortening of the peak time, the spectrum peak is more obvious, which is convenient for calculating the content of each component.

[0013] Optionally, the pipeline between the first interface and the second interface is a first pipeline, the pipeline between the second interface and the third interface is a second pipeline, the pipeline between the third interface and the fourth interface is a third pipeline, the pipeline between the fourth interface and the fifth interface is a fourth pipeline, the pipeline between the fifth interface and the sixth interface is a fifth pipeline, and the pipeline between the sixth interface and the first interface is a sixth pipeline, and the six-way valve can control the opening or closing of each pipeline.

[0014] Further, the first passage is a sixth pipeline, the second passage is a second pipeline and a fourth pipeline, and the third passage is a first pipeline and a fifth pipeline.

[0015] Further, in step S1, in the sampling mode, the second pipeline, the fourth pipeline and the sixth pipeline of the six-way valve are opened, and other pipelines of the six-way valve are closed.

[0016] Specifically, the carrier gas enters the first interface, flows to the sixth interface through the sixth pipeline (the first passage), and then enters the chromatographic column; the air enters the third interface, enters the sampling ring through the second pipeline, flows out of the sampling ring, enters the fifth interface, flows to the fourth interface through the fourth pipeline, and then enters the air pump.

[0017] Further, in step S2, in the detection mode, the first pipeline, the third pipeline and the fifth pipeline of the six-way valve are opened, and other pipelines of the six-way valve are closed.

[0018] Specifically, the carrier gas enters the first interface, flows to the second interface through the second pipeline, enters the sampling ring, mixes with the air sample in the sampling ring and flows out of the sampling ring, then enters the fifth interface, flows to the sixth interface through the fifth pipeline, and then enters the chromatographic column; the air enters the third interface, flows to the fourth interface through the third pipeline (the fourth passage), and then enters the air pump.

[0019] Optionally, in step S1, the temperature of the air inlet is controlled at 25-30℃; in steps S1 and S2, the air sample is in the sampling ring, the temperature of the outer side of the sampling ring is controlled at 25-30℃, and the temperature of the carrier gas inlet is controlled at 25-30℃ in the sampling mode and the detection mode.

[0020] Optionally, in step S3, the temperature of the gas pipeline between the chromatographic column and the electron capture detector is controlled at 0-5℃.

[0021] The present application optimizes the detection process of the gas chromatography of PANs and the electron capture detector according to the properties of PANs and the characteristics of the electron capture detector. Specifically, the temperature of the air inlet, the sampling ring and the carrier gas inlet on the upstream side of the chromatographic column is controlled at 25-30℃, and the temperature of the gas pipeline between the chromatographic column and the electron capture detector is controlled at 0-5℃. The temperature of the air inlet on the upstream side of the chromatographic column is higher than the normal room temperature, so that the air inlet can maintain good activity, and the activity of the molecules of each component in the air is good. Since PANs are prone to decomposition at a higher temperature, the temperature of the air inlet on the upstream side of the chromatographic column cannot be too high, and when the temperature is 25-30℃, the decomposition time of PANs is much longer than the required detection time.

[0022] The gas temperature on the upstream side of the electron capture detector is lower than the gas temperature on the upstream side of the chromatographic column. When the gas temperature is low, the gas pressure is also low. The low gas pressure on the upstream side of the electron capture detector can match the negative pressure environment in the electron capture detector, and accelerate the flow rate of the gas output from the chromatographic column. The temperature difference between the upstream side and the downstream side of the chromatographic column also causes a difference in gas pressure between the upstream side and the downstream side, which increases the speed of the gas passing through the chromatographic column, thereby shortening the chromatographic time. At the same time, the present inventors unexpectedly found that when there is a temperature difference between the upstream side and the downstream side of the chromatographic column, the separation efficiency of the chromatographic column for each component in the air sample is improved, which may be due to the effect of gas pressure on the microscopic process of adsorption and elution of the chromatographic column material, and further exploration by those skilled in the art is needed.

[0023] Preferably, the temperature difference between the upstream side and the downstream side of the chromatographic column is 23-28°C.

[0024] Further preferably, in step S3, the peak order of the PANs is PAN, PPN and MPAN in sequence; the internal pressure of the electron capture detector is kept constant at -17.3 kPa from the start of the detection cycle to the complete peak of PPN; after the peak of PPN ends, the pressure at the downstream end of the electron capture detector is uniformly increased to -19 kPa at a rate of 0.2 kPa / s; if the pressure reaches -19 kPa and MPAN has not yet peaked, the pressure is kept at -19 kPa until the end of the detection; if the pressure has not reached -19 kPa and MPAN has peaked, the pressure is kept at the pressure at which MPAN peaked until the end of the detection. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A schematic diagram of the piping connection of the gas chromatograph;

[0026] Figure 2 A gas chromatogram of the PANs of Example 1, Comparative Example 1 and Example 15 (the red spectrum in the figure corresponds to Comparative Example 1, the black spectrum corresponds to Example 1, and the blue spectrum corresponds to Example 15);

[0027] Figure 3 A gas chromatogram of the PANs of Example 1, Examples 11-14.

[0028] In the drawings, 1 is a sampling ring, 2 is a chromatographic column, 3 is a six-way valve, 4 is a vacuum pump, 5 is an electron capture detector, 6 is a differential pressure controller, 7 is a diaphragm pump, 8 is a pressure controller, ① is a first interface, ② is a second interface, ③ is a third interface, ④ is a fourth interface, ⑤ is a fifth interface, and ⑥ is a sixth interface. DETAILED DESCRIPTION

[0029] Example 1

[0030] The present embodiment provides a detection method for peroxycarbonyl nitrate substances in the atmosphere, which comprises the following steps:Figure 1 As shown, comprising

[0031] S1: adjust the six-way valve 3 to the sample mode, open the carrier gas inlet and air inlet, the carrier gas through the first passage of the six-way valve 3, and then sequentially purge the chromatographic column 2 and the electron capture detector 5, while opening the negative pressure device on the downstream side of the electron capture detector 5 to promote the carrier gas through the electron capture detector 5;

[0032] The air enters the sampling ring 1 through the second passage of the six-way valve 3, and the excess air is discharged from the gas chromatograph using the air pump 4;

[0033] S2: adjust the six-way valve 3 to the detection mode, the carrier gas enters the sampling ring 1 through the third passage of the six-way valve 3, and the air sample in the sampling ring 1 is taken out and brought into the chromatographic column 2;

[0034] S3: the PANs in the air sample are separated in the chromatographic column 2, and then enter the electron capture detector 5 for detection, while the negative pressure device controls the internal pressure of the electron capture detector 5 to be a stable negative pressure, which accelerates the out-of-peak of the detected compounds and improves the sensitivity of the electron capture detector 5 to the detected compounds;

[0035] S4: after the detection is completed, the six-way valve 3 remains in the detection mode, and the carrier gas purges the sampling ring 1, the chromatographic column 2 and the electron capture detector 5.

[0036] The gas chromatograph comprises a sampling ring 1, a chromatographic column 2, a six-way valve 3, an air pump 4, an electron capture detector 5 and a negative pressure device, the six-way valve 3 is provided with a first interface ①, a second interface ②, a third interface ③, a fourth interface ④, a fifth interface ⑤ and a sixth interface ⑥ in counterclockwise order, and the interfaces are connected by pipelines;

[0037] The inlet end of the sampling ring 1 is connected to the second interface ②, and the outlet end is connected to the fifth interface ⑤; the inlet end of the chromatographic column 2 is connected to the sixth interface ⑥, and the outlet end is connected to the electron capture detector 5 and the negative pressure device in turn; the carrier gas inlet pipe is connected to the first interface ①, the air inlet pipe is connected to the third interface ③, and the inlet of the air pump 4 is connected to the fourth interface ④.

[0038] The upstream side of the electron capture detector 5 is also connected to a make-up gas inlet pipe, which can input make-up gas to the electron capture detector 5 to supplement the insufficient purging effect of the carrier gas on the electron capture detector 5; the make-up gas and the carrier gas are of the same type, both being nitrogen.

[0039] The negative pressure device comprises a differential pressure controller 6 and a diaphragm pump 7, and the downstream side of the electron capture detector 5 is connected to the valve of the differential pressure controller 6 and the diaphragm pump 7 in sequence through pipelines, the diaphragm pump 7 can pump air for the electron capture detector 5, so that the electron capture detector 5 is in a negative pressure environment, and the differential pressure controller 6 is used for adjusting the negative pressure in the electron capture detector 5.

[0040] A control terminal (such as a computer) is connected to and controls the differential pressure controller, so as to control the pressure of the electron capture detector. The pipeline on the downstream side of the electron capture detector is connected to a differential pressure sensor, which is used for detecting the difference (△P) between the internal pressure of the electron capture detector and the pressure of the external environment.

[0041] The pressure change of the external environment will slightly affect the pressure difference between the inside and outside of the chromatograph, and then affect the stability of the material precipitation time and the performance of the electron capture detector. By adding the differential pressure sensor, the pressure difference between the internal pressure of the electron capture detector and the pressure of the external environment is kept constant at all times, which can improve the stability of the electron capture detector. The negative pressure environment in the electron capture detector can also improve the detection performance of the electron capture detector. By adding the differential pressure controller, the chromatographic column (material precipitation) can be controlled more finely.

[0042] In step S1, the carrier gas is introduced at the same time, and the auxiliary gas on the upstream side of the electron capture detector 5 is turned on, so that the auxiliary gas can be swept together with the carrier gas. When the carrier gas flow is too small, the detection signal (chromatographic baseline) is usually unstable, and the auxiliary gas cooperates with the carrier gas to stabilize the baseline.

[0043] In step S2, the air is kept introduced, the air is pumped out by the air pump 4 through the fourth passage of the six-way valve 3, and is discharged from the gas chromatograph, which is conducive to keeping the air flow unobstructed. If the air introduction is normal and unobstructed, the air pump can also be turned off in time.

[0044] The pipeline between the first interface ① and the second interface ② is the first pipeline, the pipeline between the second interface ② and the third interface ③ is the second pipeline, the pipeline between the third interface ③ and the fourth interface ④ is the third pipeline, the pipeline between the fourth interface ④ and the fifth interface ⑤ is the fourth pipeline, the pipeline between the fifth interface ⑤ and the sixth interface ⑥ is the fifth pipeline, and the pipeline between the sixth interface ⑥ and the first interface ① is the sixth pipeline. The six-way valve 3 can control the opening or closing of each pipeline.

[0045] The first passage is the sixth pipeline, the second passage is the second pipeline and the fourth pipeline, the third passage is the first pipeline and the fifth pipeline, and the fourth passage is the third pipeline.

[0046] In step S1, the six-way valve 3 is in the sampling mode, the second pipeline, the fourth pipeline and the sixth pipeline are opened, and the other pipelines of the six-way valve 3 are closed, Figure 1The red line of the six-way valve is opened, and the black line is closed.

[0047] The specific flow of the carrier gas and air is as follows: the carrier gas enters the first interface ①, flows to the sixth interface ⑥ through the sixth line (the first passage), and then enters the chromatographic column 2; the air enters the third interface ③, enters the sampling ring 1 through the second line, and then enters the fifth interface ⑤ after flowing out of the sampling ring 1, flows to the fourth interface ④ through the fourth line, and then enters the air pump 4.

[0048] In step S2, the first line, the third line and the fifth line of the six-way valve 3 are opened in the detection mode, and the other lines of the six-way valve 3 are closed, Figure 1 The red line of the six-way valve is closed, and the black line is opened.

[0049] The specific flow of the carrier gas and air is as follows: the carrier gas enters the first interface ①, flows to the sixth interface ⑥ through the sixth line (the first passage), and then enters the chromatographic column 2; the air enters the third interface ③, flows to the fourth interface ④ through the third line (the fourth passage), and then enters the air pump 4.

[0050] In steps S1 and S2, the air inlet line is connected to the pressure controller 8, and then connected to the six-way valve 3, and the pressure controller 8 is used to control and stabilize the pressure of the air inlet.

[0051] The pressure controller is used to control the pressure on the upstream side of the chromatographic column to be constant at 2 kPa, and the negative pressure device is used to adjust the pressure on the downstream end of the electron capture detector to be-17.3 kPa. The temperature of the chromatographic column is set to 8 ℃, the temperature of the electron capture detector is set to 50 ℃, the current of the electron capture detector is set to 1.3 nA, 50 mL / min of N2 (99.999%) is used as the auxiliary gas of the electron capture detector, and the response chromatographic peak height and peak time of PANs are measured.

[0052] Comparative Example 1

[0053] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the comparative example is the same as that of example 1, except that the pressure on the upstream side of the chromatographic column is constant at 15 kPa (since the flow in the chromatographic column is too small at 2 kPa, and the observed substance cannot be eluted, therefore, the pre-column pressure is 15 kPa in this example), no negative pressure device is set, the downstream side of the electron capture detector is connected to the fume hood through the line, and the electron capture detector is not pumped on the downstream side in steps S1-S3, and the internal environment of the electron capture detector is positive pressure.

[0054] As Figure 2As shown, the electron capture detector of the comparative example 1 is at normal pressure, and the detection sensitivity of the electron capture detector is low, and only the out-of-peak of PAN is obvious, and the out-of-peak of PPN and MPAN is almost invisible. The out-of-peak of PAN and PPN of the example 1 is obvious, and the out-of-peak of MPAN can be seen, which indicates that the detection sensitivity of the electron capture detector is high at this time, and the three substances can be detected.

[0055] In addition, the spectrum peak of oxygen before the out-of-peak of PAN in the spectrum is due to the fact that the electron capture detector is extremely sensitive to oxygen, and the signal of the electron capture detector reaches the range limit in an instant. After the oxygen is completely eluted, the signal is restored to the baseline level. Figure 2 The time of the abscissa axis contains the sampling stage (1 min), so the retention time is the difference between the out-of-peak time and the sampling time.

[0056] Example 2

[0057] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the example is the same as that of the example 1, and the difference lies in that in the step S1, the air is first subjected to a dehumidification treatment to remove most of the water, and then the dry air is input into the six-way valve to avoid the water vapor in the air sample from blocking the pipeline due to icing in the subsequent pipeline.

[0058] The step S1 further comprises the following steps: the air sample is in the sampling ring, the temperature of the outer side of the sampling ring is controlled to be 25℃, and the temperature of the air sample in the sampling ring is stabilized;

[0059] The temperature of the carrier gas inlet is controlled to be 25℃, so that the temperature of the air sample and the carrier gas entering the chromatographic column in the step S2 is the same, and the temperature and pressure of the gas path are more stable.

[0060] In the step S3, the gas pipeline between the chromatographic column and the electron capture detector is temperature-controlled, and the temperature of the gas pipeline is controlled to be 0℃.

[0061] The difference between the gas temperatures of the upstream and downstream of the chromatographic column is 25℃.

[0062] Example 3

[0063] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the example is the same as that of the example 2, and the difference lies in that the temperature of the air sample in the sampling ring and the temperature of the carrier gas are both 30℃, and the temperature of the gas in the pipeline on the downstream side of the chromatographic column is 0℃. The difference between the gas temperatures of the upstream and downstream of the chromatographic column is 30℃.

[0064] Example 4

[0065] The detection method of peroxycarbonyl nitrate substances in the atmosphere of this example is the same as that of Example 2, except that the temperature of the air sample in the sampling loop and the carrier gas is 24°C, and the temperature of the gas in the downstream side of the column is 0°C. The difference in the gas temperature between the upstream and downstream of the column is 24°C.

[0066] Example 5

[0067] The detection method of peroxycarbonyl nitrate substances in the atmosphere of this example is the same as that of Example 2, except that the temperature of the air sample in the sampling loop and the carrier gas is 25°C, and the temperature of the gas in the downstream side of the column is 5°C. The difference in the gas temperature between the upstream and downstream of the column is 20°C.

[0068] Example 6

[0069] The detection method of peroxycarbonyl nitrate substances in the atmosphere of this example is the same as that of Example 2, except that the temperature of the air sample in the sampling loop and the carrier gas is 25°C, and the temperature of the gas in the downstream side of the column is -1°C. The difference in the gas temperature between the upstream and downstream of the column is 26°C.

[0070] Example 7

[0071] The detection method of peroxycarbonyl nitrate substances in the atmosphere of this example is the same as that of Example 2, except that the temperature of the air sample in the sampling loop and the carrier gas is 25°C, and the temperature of the gas in the downstream side of the column is 2°C. The difference in the gas temperature between the upstream and downstream of the column is 23°C.

[0072] Example 8

[0073] The detection method of peroxycarbonyl nitrate substances in the atmosphere of this example is the same as that of Example 2, except that the temperature of the air sample in the sampling loop and the carrier gas is 28°C, and the temperature of the gas in the downstream side of the column is 0°C. The difference in the gas temperature between the upstream and downstream of the column is 28°C.

[0074] Example 9

[0075] The detection method of peroxycarbonyl nitrate substances in the atmosphere of this example is the same as that of Example 2, except that the temperature of the air sample in the sampling loop and the carrier gas is 25°C, and the temperature of the gas in the downstream side of the column is 3°C. The difference in the gas temperature between the upstream and downstream of the column is 22°C.

[0076] Example 10

[0077] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the embodiment is the same as that of embodiment 2, except that the temperature of the air sample in the sampling ring and the carrier gas is 30℃, and the temperature of the gas in the pipeline downstream of the chromatographic column is 1℃. The difference between the gas temperatures upstream and downstream of the chromatographic column is 29℃.

[0078] Table 1: Comparison of PAN retention time in embodiments 2-10

[0079] .

[0080] As shown in Table 1, in the detection method of the present application, appropriate control of the gas temperature on both sides of the chromatographic column is beneficial to shorten the retention time and improve the peak efficiency.

[0081] Embodiment 11

[0082] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the embodiment is the same as that of embodiment 1, except that the negative pressure device is used to adjust the pressure at the downstream end of the electron capture detector to-15kPa.

[0083] Embodiment 12

[0084] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the embodiment is the same as that of embodiment 1, except that the negative pressure device is used to adjust the pressure at the downstream end of the electron capture detector to-13kPa.

[0085] Embodiment 13

[0086] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the embodiment is the same as that of embodiment 1, except that the negative pressure device is used to adjust the pressure at the downstream end of the electron capture detector to-11kPa.

[0087] Embodiment 14

[0088] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the embodiment is the same as that of embodiment 1, except that the negative pressure device is used to adjust the pressure at the downstream end of the electron capture detector to-9kPa.

[0089] As shown in Figure 3 , the black line, red line, blue line, brown line and green line correspond to the pressure at the downstream end of the electron capture detector of-17.3kPa, -15kPa, -13kPa, -11kPa and -9kPa, respectively. The greater the pressure at the downstream end of the electron capture detector (ECD), the earlier the peak time of PAN. The peak time of PAN with a pressure of-17.3kPa and-9kPa differs by about 4min, and the peak time of PAN with a pressure of-17.3kPa and-11kPa differs by about 1.5min, and the detection efficiency is higher.

[0090] Embodiment 15

[0091] The detection method of the peroxycarbonyl nitrate substance in the atmosphere of the present embodiment is the same as that of Embodiment 1, except that, as shown by the blue spectrum line in the middle, the pressure at the downstream end of the electron capture detector is constant at -17.3 kPa from the start of the detection cycle to the complete elution of PPN; after the elution of PPN is complete (at about 4.3 min), the pressure at the downstream end of the electron capture detector is increased at a rate of 0.2 kPa / s until the pressure at the downstream end of the electron capture detector reaches -19 kPa, at which point the increase in pressure is stopped, and the pressure is maintained at -19 kPa until the end of the detection. Figure 2

[0092] As can be seen, the black spectrum line of Embodiment 1 and the blue spectrum line of Embodiment 15 have basically the same signal intensity of PAN and PPN, and the response of MPAN is significantly improved after the pressure is increased in Embodiment 15. The peak height of the MPAN signal of the black spectrum line that does not increase in pressure is 247.9 pA, and the peak height of the MPAN signal of the blue spectrum line that increases in pressure is 397.1 pA. Figure 2 As can be seen, the black spectrum line of Embodiment 1 and the blue spectrum line of Embodiment 15 have basically the same signal intensity of PAN and PPN, and the response of MPAN is significantly improved after the pressure is increased in Embodiment 15. The peak height of the MPAN signal of the black spectrum line that does not increase in pressure is 247.9 pA, and the peak height of the MPAN signal of the blue spectrum line that increases in pressure is 397.1 pA.​

Claims

1. A method for detecting peroxycarbonyl nitrates in the atmosphere, characterized in that, The application relates to a gas chromatograph device. S1: adjusting a six-way valve to a sample injection mode, opening carrier gas and air inlets, the carrier gas sequentially blowing the chromatographic column and the electron capture detector after passing through the first passage of the six-way valve, and simultaneously opening a negative pressure device on the downstream side of the electron capture detector to accelerate the carrier gas through the electron capture detector; The air enters the sampling ring through the second passage of the six-way valve, and the excess air is discharged from the gas chromatograph device by using a gas suction pump; S2: adjusting the six-way valve to a detection mode, the carrier gas entering the sampling ring through the third passage of the six-way valve to take out the air sample in the sampling ring and bring it into the chromatographic column; S3: the PANs in the air sample are separated in the chromatographic column and then enter the electron capture detector for detection, meanwhile, the internal pressure of the electron capture detector is controlled by the negative pressure device to be stable negative pressure, which accelerates the outburst of the to-be-detected compound and improves the sensitivity of the electron capture detector to the to-be-detected compound; In step S3, the internal pressure of the electron capture detector is-19~-11kPa.

2. The detection method according to claim 1, characterized in that, The gas chromatograph device comprises a sampling ring, a chromatographic column, a six-way valve, a gas suction pump, an electron capture detector and a negative pressure device, the six-way valve is provided with a first interface, a second interface, a third interface, a fourth interface, a fifth interface and a sixth interface in counterclockwise order; the interfaces are connected by pipelines; The inlet end of the sampling ring is connected with the second interface, and the outlet end is connected with the fifth interface; the inlet end of the chromatographic column is connected with the sixth interface, and the outlet end is connected with the electron capture detector and the negative pressure device in sequence; a carrier gas inlet pipe is connected with the first interface, an air inlet pipe is connected with the third interface, and the inlet of the gas suction pump is connected with the fourth interface.

3. The detection method according to claim 2, characterized in that, The negative pressure device comprises a differential pressure controller and a diaphragm pump, the downstream side of the electron capture detector is sequentially connected with the differential pressure controller and the diaphragm pump through pipelines, the diaphragm pump can suck air for the electron capture detector, so that the electron capture detector is in a negative pressure environment, and the differential pressure controller is used for adjusting the negative pressure in the electron capture detector.

4. The detection method according to claim 2, characterized in that, The pipeline between the first interface and the second interface is a first pipeline, the pipeline between the second interface and the third interface is a second pipeline, the pipeline between the third interface and the fourth interface is a third pipeline, the pipeline between the fourth interface and the fifth interface is a fourth pipeline, the pipeline between the fifth interface and the sixth interface is a fifth pipeline, and the pipeline between the sixth interface and the first interface is a sixth pipeline; the six-way valve can control the opening or closing of each pipeline.

5. The detection method according to claim 4, characterized in that, The first passage is the sixth pipeline, the second passage is the second pipeline and the fourth pipeline, and the third passage is the first pipeline and the fifth pipeline.

6. The detection method according to claim 5, characterized in that, In step S1, in the sample injection mode of the six-way valve, the second pipeline, the fourth pipeline and the sixth pipeline are opened, and the other pipelines of the six-way valve are closed. The specific flow of the carrier gas and the air is as follows: the carrier gas enters the first interface, flows to the sixth interface through the sixth pipeline, and then enters the chromatographic column; the air enters the third interface, enters the sampling ring through the second pipeline, flows out of the sampling ring, enters the fifth interface, flows to the fourth interface through the fourth pipeline, and then enters the gas suction pump.

7. The detection method according to claim 5, characterized in that, In step S2, in the detection mode of the six-way valve, the first pipeline, the third pipeline and the fifth pipeline are opened, and the other pipelines of the six-way valve are closed. The specific flow of the carrier gas and the air is as follows: the carrier gas enters the first interface, flows to the second interface through the second pipeline, enters the sampling ring, mixes with the air sample in the sampling ring and flows out from the sampling ring, then enters the fifth interface, flows to the sixth interface through the fifth pipeline, and enters the chromatographic column; the air enters the third interface, flows to the fourth interface through the third pipeline, and enters the air pump.

8. The method of claim 1, wherein, In step S1, the temperature of the air inlet is controlled at 25-30℃; in steps S1 and S2, the air sample is in the sampling ring, the temperature of the outer side of the sampling ring is controlled at 25-30℃, and the temperature of the carrier gas inlet is controlled at 25-30℃ in the sampling mode and the detection mode.

9. The detection method according to claim 8, characterized in that, In step S3, the gas pipeline between the chromatographic column and the electron capture detector is temperature-controlled, and the temperature of the gas pipeline is controlled at 0-5℃.

10. The method of claim 1, wherein, In step S3, the peak order of the PANs is PAN, PPN and MPAN in sequence; from the start of the detection cycle to the complete peak of PPN, the internal pressure of the electron capture detector is constant at-17.3 kPa; after the peak of PPN ends, the pressure at the downstream end of the electron capture detector is uniformly increased at a speed of 0.2 kPa / s to-19 kPa; if the pressure reaches-19 kPa and MPAN has not yet peaked, the pressure is kept at-19 kPa until the end of the detection; if the pressure has not reached-19 kPa and MPAN has peaked, the pressure is kept at the pressure when MPAN peaks until the end of the detection.

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