Method for determining epichlorohydrin in drinking water

Abstract

The application discloses an epoxy chloropropane determination field and a method for determining epoxy chloropropane in drinking water, which comprises the following steps: step one: sample collection; taking drinking water to a sample bottle and storing in the dark; step two: purging and trapping; when determining, an automatic sampler is used to suck the sample into a purging pipe of a purging and trapping instrument, then one of high-purity helium or nitrogen is used to purge the sample, the epoxy chloropropane in the sample is adsorbed in a trapping pipe of the purging and trapping instrument after purging, the trapping pipe is heated and back-purged with pure helium; when the trapping pipe is heated, a higher temperature can accelerate evaporation of the water sample, more water vapor is retained in the trapping pipe, and the internal pressure of the trapping pipe is too high; the trapping pipe is connected with a collection box in advance to slow down the internal pressure of the trapping pipe when the trapping pipe is heated; step three: gas chromatography-mass spectrometry analysis; the gas chromatograph is connected with the collection box, the components desorbed by heating are separated by the gas chromatograph, and then are detected by a mass spectrometer.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of epichlorohydrin determination, and particularly relates to a method for determining epichlorohydrin in drinking water. BACKGROUND

[0002] Epichlorohydrin is a volatile organic compound, has a solubility of 6.48% in water, is a colorless oily liquid, and has a pungent odor. Epichlorohydrin belongs to a highly toxic epoxide compound, can cause neurasthenic syndrome and peripheral neuropathy, even inhibit the central nervous system and can be fatal. Epichlorohydrin mainly comes from: firstly, when industrial wastewater containing epichlorohydrin enters a drinking water source, water source pollution is caused; secondly, epichlorohydrin residues are contained in water flocculants; and thirdly, epichlorohydrin is released from epoxy resin materials in water pipes. Therefore, epichlorohydrin is an environmental pollutant that cannot be ignored, and China lists epichlorohydrin in toxicological indexes, and stipulates that the allowable limit value of epichlorohydrin is not more than 0.0004 mg / L, and strict control is implemented on epichlorohydrin in drinking water.

[0003] For example, Chinese patent publication No. CN102998396A discloses a method for determining epichlorohydrin in water. The method adopts salting-out-liquid-liquid extraction to pretreat water samples, uses magnesium chloride as a salting-out agent, uses dichloromethane as an extractant to extract epichlorohydrin in water, and adopts capillary gas chromatography and external standard curve method for quantitative analysis. The method has high extraction efficiency, is simple, fast, accurate, highly sensitive, and has good reproducibility, and can meet the requirements of environmental monitoring and water quality analysis.

[0004] The above scheme uses dichloromethane as an extractant to extract epichlorohydrin in water, but dichloromethane is also a toxic and harmful substance, is not conducive to the health of detection personnel, and can also pollute the experimental environment; therefore, it is necessary to propose a method for determining epichlorohydrin in drinking water, which adopts a purge and trap method, and combines gas chromatography-mass spectrometry to determine epichlorohydrin in a certain degree of rapidity, accuracy, greenness and energy saving. SUMMARY

[0005] The purpose of the present application is to propose a method for determining epichlorohydrin in drinking water, which adopts a purge and trap method, and combines gas chromatography-mass spectrometry to determine epichlorohydrin in a certain degree of rapidity, accuracy, greenness and energy saving.

[0006] In order to achieve the above purpose, the technical scheme of the present application is as follows: a method for determining epichlorohydrin in drinking water, comprising the following steps:

[0007] Step 1: sample collection; take drinking water to a sample bottle, and store in the dark;

[0008] Step two: Purge and trap; when determining, the automatic sampler is used to suck the sample into the purge tube of the purge and trap instrument, and then one of the high-purity helium or nitrogen is used to purge the sample, and the epichlorohydrin in the sample is adsorbed in the capture tube of the purge and trap instrument after purging, and the capture tube is heated and back-flushed with pure helium;

[0009] When the capture tube is heated, the temperature is high, which can accelerate the evaporation of the water sample, so that more water vapor is retained in the capture tube, and the internal pressure of the capture tube is too high. By connecting the capture tube with the collection tank in advance, the internal pressure of the capture tube during heating is reduced.

[0010] Step three: Gas chromatography-mass spectrometry analysis; the gas chromatograph is connected with the collection tank, and the components desorbed by heating are separated by the gas chromatograph and detected by the mass spectrometer.

[0011] Further, in step one, before sampling, the sample bottle is cleaned with methanol.

[0012] Further, when sampling, the sampling amount is determined according to whether the sample can overflow in the sample bottle without air bubbles.

[0013] Further, the carrier gas is nitrogen, the purging temperature is 20-30℃, the purging flow rate is 40-50mL / min, the purging time is 30-40min, the dry purging time is 4-6min, the analysis temperature is 250-300℃, the analysis time is 6-9min, the baking temperature is 280-300℃, and the baking time is 5-7min.

[0014] Further, the chromatographic column is a DB-624 capillary column, and the parameters of the capillary column are 30m x 0.25mm, 1.4μm; the carrier gas is helium, the flow rate is 0.5-1mL / min, the injection port temperature is 250-300℃, the injection mode is split injection, and the split ratio is 10:1; the initial temperature of the programmed temperature is 35℃, maintained for 1min, increased to 83-100℃ at 2℃ / min, then increased to 180-200℃ at 20℃ / min, and maintained for 5min.

[0015] Further, the ionization mode of the mass spectrometer is EI, the ion source temperature is 230℃, and the quadrupole rod temperature is 150-200℃; the GC-MS interface temperature is 200-300℃, the solvent delay time is 2min, and the scanning mode is ion scanning.

[0016] Further, the side wall of the collection tank is sequentially connected with an outlet pipe and an inlet pipe from top to bottom, the inlet pipe is connected with the capture tube of the purge and trap instrument, and the outlet pipe is connected with the injection port of the gas chromatograph;

[0017] The collecting box is communicated with a pressure reduction pipe and a gas return pipe from top to bottom at the side far from the gas outlet pipe, and the pressure reduction pipe is in a ladder type; the bottom of the pressure reduction pipe is communicated with a separation pipe and an oil inlet pipe from left to right; the end of the separation pipe far from the pressure reduction pipe is provided with an oil-gas separator, the separation pipe is communicated with the oil-gas inlet of the oil-gas separator, and the gas outlet of the oil-gas separator is communicated with the gas return pipe; the oil outlet of the oil-gas separator is communicated with an oil outlet pipe, and the end of the oil outlet pipe far from the oil-gas separator is communicated with an oil tank;

[0018] A gravity sensor is installed at the communication position of the oil inlet pipe and the pressure reduction pipe; the end of the oil inlet pipe far from the pressure reduction pipe is provided with an oil pump, the output end of the oil pump is communicated with the oil inlet pipe, and the input end of the oil pump is communicated with the oil tank;

[0019] The communication positions of the gas outlet pipe, the gas inlet pipe and the gas return pipe with the collecting box are all communicated with a one-way valve; the communication positions of the separation pipe and the oil inlet pipe with the pressure reduction pipe are also all communicated with a one-way valve; the communication position of the pressure reduction pipe with the collecting box is communicated with a valve.

[0020] The above scheme realizes the following principles and beneficial effects:

[0021] (1) The concentration efficiency of the extracted epichlorohydrin is high, no organic solvents such as methanol and dichloromethane are used, no secondary pollution to the environment is caused, the detection efficiency is high, and the labor cost can be saved; the purge and trap method is combined with gas chromatography-mass spectrometry for detection, the gas chromatography-mass spectrometry has the technical advantages of high sensitivity, high accuracy and high selectivity, and is widely used in the analysis and determination of organic pollutants in water and environment; the present application can realize the detection of trace epichlorohydrin in water by using the purge and trap and gas chromatography-mass spectrometry technology, and create a new method for detecting trace epichlorohydrin; the method is fast, accurate and green and energy-saving, no organic reagent is needed, the cost is greatly saved, the social benefits in energy saving and environmental protection are remarkable, and it will play an important role in ensuring the safe water supply in cities.

[0022] (2) When the trap pipe is heated, the temperature is high, which can accelerate the evaporation of the water sample, so that more water vapor is retained in the trap pipe, so that the pressure in the trap pipe is too high, so the trap pipe can be connected with the gas inlet pipe in advance, and the one-way valve at the communication position of the gas inlet pipe and the collecting box is opened, the setting of the collecting box can reduce the pressure in the trap pipe to a certain extent, and can reduce the damage to the trap pipe caused by the too high pressure to a certain extent.

[0023] (3) due to the over-high pressure in the collecting tank, water vapor will flow into the pressure-reducing pipe to balance the air pressure in the collecting tank; at the same time, the oil pump continuously pumps oil into the pressure-reducing pipe through the oil inlet pipe, and the oil will be sequentially separated from the water vapor in the pressure-reducing pipe to form an oil-water vapor-oil-water vapor... structure; since the communication part of the oil inlet pipe and the pressure-reducing pipe is provided with a one-way valve, the oil-water vapor-oil cannot flow back into the oil inlet pipe, and since the pressure in the collecting tank is relatively high, the oil-water vapor-oil can only move to the inside of the pressure-reducing pipe, thereby balancing the air pressure in the collecting tank.

[0024] (4) the gravity sensor is used to sense the gravity of the oil at the communication part of the pressure-reducing pipe and the oil inlet pipe; when the gravity sensor does not sense the gravity of the oil or the gravity of the oil is very small, it indicates that the oil pump is malfunctioning or the oil pump is pumping insufficient oil, and the operator needs to adjust the oil pump in time.

[0025] (5) the oil-gas separator separates the oil-water vapor-oil, and if recycling is needed, the one-way valve at the communication part of the gas return pipe and the collecting tank can be opened, the separated water vapor is transported into the collecting tank through the gas return pipe, and the separated oil is transported into the oil tank through the oil outlet pipe, thereby avoiding the waste of resources to a certain extent. BRIEF DESCRIPTION OF DRAWINGS

[0026] Fig. 1 The flowchart of the embodiment of the application is shown.

[0027] Fig. 2 The isometric view of the collecting tank of the embodiment of the application is shown. DETAILED DESCRIPTION

[0028] The following will be further described in detail through specific embodiments:

[0029] The reference signs in the drawings of the specification include: collecting tank 1, air inlet pipe 2, air outlet pipe 3, pressure-reducing pipe 4, separation pipe 5, oil-gas separator 6, gas return pipe 7, oil outlet pipe 8, oil inlet pipe 9, and oil tank 10.

[0030] The embodiment is basically as shown in the accompanying drawings: Figs. 1-2

[0031] A method for determining epichlorohydrin in drinking water, comprising the following steps:

[0032] Step one: sample collection

[0033] Take the sample of drinking water into a sample bottle and store it in the dark; before sampling, clean the sample bottle with methanol; when sampling, the sampling amount should be such that the sample can overflow in the sample bottle without leaving air bubbles.

[0034] Step two: purging and trapping

[0035] ​During the determination, the automatic sampler is used to suck the sample into the purge tube of the purge and trap instrument, and then one of high-purity helium or nitrogen is used to purge the sample, and the epichlorohydrin in the sample is adsorbed in the trap tube of the purge and trap instrument after purging, and the trap tube is heated and back-purged with pure helium; when the trap tube is heated, the temperature is high, which can accelerate the evaporation of the water sample, so that more water vapor is retained in the trap tube, and the internal pressure of the trap tube is too high; by connecting the trap tube with the collection box 1 in advance, the internal pressure of the trap tube during heating is reduced.

[0036] The carrier gas is nitrogen, the purging temperature is 20℃, the purging flow rate is 40mL / min, the purging time is 30min, the dry purging time is 4min, the analysis temperature is 250℃, the analysis time is 6min, the baking temperature is 280℃, and the baking time is 5min.

[0037] Step three: gas chromatography-mass spectrometry analysis

[0038] The gas chromatograph is connected with the collection box 1, and the components desorbed by heating are separated by the gas chromatograph and detected by the mass spectrometer; wherein the chromatographic column is a DB-624 capillary column, and the parameters of the capillary column are 30m*0.25mm*1.4um; the carrier gas is helium, the flow rate is 0.5mL / min, the injection port temperature is 250℃, the injection mode is split injection, and the split ratio is 10:1; the program temperature is started at 35℃ and kept for 1min, then increased to 83℃ at a rate of 2℃ / min, and then increased to 180℃ at a rate of 20℃ / min and kept for 5min; the ionization mode of the mass spectrometer is EI, the ion source temperature is 230℃, and the quadrupole rod temperature is 150℃; the gas mass interface temperature is 200℃, the solvent delay time is 2min, and the scanning mode is ion scanning.

[0039] The side wall of the collection box 1 is sequentially connected from top to bottom with the gas outlet pipe 3 and the gas inlet pipe 2, the gas inlet pipe 2 is connected with the trap tube of the purge and trap instrument, and the gas outlet pipe 3 is connected with the injection port of the gas chromatograph.

[0040] The side of the collection box 1 away from the gas outlet pipe 3 is sequentially connected from top to bottom with the pressure reduction pipe 4 and the gas return pipe 7, and the pressure reduction pipe 4 is in a stepped shape; the bottom of the pressure reduction pipe 4 is sequentially connected from left to right with the separation pipe 5 and the oil inlet pipe 9; the separation pipe 5 is provided with the oil-gas separator 6 at the end away from the pressure reduction pipe 4, the separation pipe 5 is connected with the oil-gas inlet of the oil-gas separator 6, and the gas outlet of the oil-gas separator 6 is connected with the gas return pipe 7; the oil outlet of the oil-gas separator 6 is connected with the oil outlet pipe 8, and the end of the oil outlet pipe 8 away from the oil-gas separator 6 is connected with the oil tank 10.

[0041] The oil inlet pipe 9 is provided with a gravity sensor (not shown in the figure) at the connection position with the pressure reduction pipe 4; the end of the oil inlet pipe 9 away from the pressure reduction pipe 4 is provided with an oil pump (not shown in the figure), the output end of the oil pump is connected with the oil inlet pipe 9, and the input end of the oil pump is connected with the oil tank 10.

[0042] The communication between the outlet pipe 3, the inlet pipe 2 and the gas collection tank 1 is communicated with a one-way valve; the communication between the separation pipe 5 and the oil inlet pipe 9 and the decompression pipe 4 is also communicated with a one-way valve; the communication between the decompression pipe 4 and the gas collection tank 1 is communicated with a valve.

[0043] The specific implementation process is as follows:

[0044] The first step is sample collection

[0045] The sample of drinking water is taken into the sample bottle, and it is stored in the dark; before sampling, the sample bottle is cleaned with methanol; when sampling, the sampling amount is determined according to whether the sample can overflow in the sample bottle without leaving bubbles.

[0046] The second step is purging and trapping

[0047] When measuring, the automatic sampler is used to suck the sample into the purging pipe of the purging and trapping instrument, and then the sample is purged with nitrogen. The epichlorohydrin in the sample is adsorbed in the trapping pipe of the purging and trapping instrument after purging, and the trapping pipe is heated and back-flushed with pure helium.

[0048] When the trapping pipe is heated, the temperature is high, which can accelerate the evaporation of the water sample, so that more water vapor is retained in the trapping pipe, causing the pressure in the trapping pipe to be too high. Therefore, the trapping pipe can be connected with the inlet pipe 2 in advance, and the one-way valve at the communication between the inlet pipe 2 and the gas collection tank 1 is opened. The gas collection tank 1 can reduce the pressure in the trapping pipe to a certain extent, and can reduce the damage to the trapping pipe caused by the excessive pressure to a certain extent.

[0049] When the trapping pipe is heated, the sample quickly evaporates into water vapor, which continuously flows into the gas collection tank 1, causing the internal pressure of the gas collection tank 1 to gradually increase. At this time, the valve at the communication between the decompression pipe 4 and the gas collection tank 1 is opened, and the water vapor will flow into the decompression pipe 4 to balance the air pressure in the gas collection tank 1. Then, the oil pump can be opened, and the oil pump continuously pumps oil into the decompression pipe 4 through the oil inlet pipe 9. At the same time, the water vapor still flows into the decompression pipe 4. When the water vapor contacts the oil, the oil will successively cut off the water vapor in the decompression pipe 4, forming an oil-water vapor-oil-water vapor... structure. Since the one-way valve is arranged at the communication between the oil inlet pipe 9 and the decompression pipe 4, the oil-water vapor-oil cannot flow back to the oil inlet pipe 9, and since the pressure in the gas collection tank 1 is relatively high, the oil-water vapor-oil can only move to the inside of the decompression pipe 4, thereby balancing the air pressure in the gas collection tank 1.

[0050] The gravity sensor is used to sense the gravity of the oil at the communication between the decompression pipe 4 and the oil inlet pipe 9. When the gravity sensor does not sense the gravity of the oil or the gravity of the oil is very small, it indicates that the oil pump is malfunctioning or the oil pump is not pumping enough oil, and the operator needs to adjust the oil pump in time.

[0051] When the trapping tube stops heating, the pressure inside the collection box 1 gradually tends to balance, at this time, because the water vapor between the oil-water vapor-oil is a high-pressure gas after heating, the high-pressure water vapor will push the oil to move to the direction of the collection box 1, and due to the structural characteristics of the pressure reduction pipe 4, the oil-water vapor-oil will also flow to the collection box 1 under the action of its own gravity.

[0052] At this time, the valve at the communication between the pressure reduction pipe 4 and the collection box 1 is closed, and the one-way valve at the communication between the pressure reduction pipe 4 and the separation pipe 5 is opened, and the oil-water vapor-oil is transported to the oil-gas separator 6 through the separation pipe 5, and the oil-gas separator 6 separates the oil-water vapor-oil; if recycling is required, the one-way valve at the communication between the gas return pipe 7 and the collection box 1 can be opened, and the separated water vapor is transported to the collection box 1 through the gas return pipe 7, and the separated oil is transported to the oil tank 10 through the oil outlet pipe 8, thereby to some extent avoiding the waste of resources.

[0053] Among them, the carrier gas is nitrogen, the purging temperature is 20℃, the purging flow rate is 40mL / min, the purging time is 30min, the dry purging time is 4min, the analysis temperature is 250℃, the analysis time is 6min, the baking temperature is 280℃, and the baking time is 5min.

[0054] Third step, gas chromatography-mass spectrometry analysis

[0055] The gas outlet pipe 3 is communicated with the sample inlet of the gas chromatograph, the one-way valve at the communication between the gas outlet pipe 3 and the collection box 1 is opened, and the components thermally desorbed are transported to the gas chromatograph through the gas outlet pipe 3, separated by the gas chromatograph, and detected by the mass spectrometer.

[0056] Among them, the chromatographic column is a DB-624 capillary column, the parameters of the capillary column are 30m*0.25mm, 1.4μm; the carrier gas is helium, the flow rate is 0.5mL / min, the sample inlet temperature is 250℃, the sample inlet mode is split injection, and the split ratio is 10:1; the initial temperature of the programmed temperature is 35℃, maintained for 1min, increased to 83℃ at a rate of 2℃ / min, and then increased to 180℃ at a rate of 20℃ / min, maintained for 5min; the ionization mode of the mass spectrometer is EI, the ion source temperature is 230℃, and the quadrupole rod temperature is 150℃; the gas mass interface temperature is 200℃, and the solvent delay time is 2min; the scanning mode is ion scanning; the type of the gas chromatography-mass spectrometry instrument in this embodiment is preferably 7890B-5977A, Agilent Technologies; the type of the purging and trapping instrument in this embodiment is preferably AQUATek100, TEKMAR company, USA.

[0057] The above-mentioned are only embodiments of the present application, and the common knowledge of specific structures and characteristics in the scheme is not described too much herein. The ordinary skilled person in the art knows all the ordinary technical knowledge in the field of the present application before the application date or the priority date, can know all the prior art in the field, and has the ability to apply conventional experimental means before that date. The ordinary skilled person in the art can perfect and implement the present scheme under the guidance of the present application, combined with their own ability. Some typical known structures or known methods should not be an obstacle for the ordinary skilled person in the art to implement the present application. It should be noted that, for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application. These will not affect the effect and practicality of the patent. The protection scope of the present application should be subject to the content of its claims, and the specific implementation mode and the like in the specification can be used to explain the content of the claims.

Claims

1. A method for determining epichlorohydrin in drinking water, characterized in that: Includes the following steps: Step 1: Sample collection; collect samples of drinking water into a sample bottle and store them away from light; Step 2: Purge and trap; During the determination, the sample is drawn into the purge tube of the purge and trap instrument using an autosampler, and then the sample is purged with either high-purity helium or nitrogen. After the epichlorohydrin in the sample is purged, it is adsorbed into the trap tube of the purge and trap instrument. The trap tube is heated and backflushed with pure helium. When the collection tube is heated, the temperature is high, which will accelerate the evaporation of the water sample, causing more water vapor to remain in the collection tube and making the pressure inside the collection tube too high. By connecting the collection tube to the collection box in advance, the internal pressure of the collection tube when it is heated can be reduced. The side wall of the collection box is connected to an outlet pipe and an inlet pipe from top to bottom. The inlet pipe is connected to the collection pipe of the purge and trap instrument, and the outlet pipe is connected to the sample inlet of the gas chromatograph. The side of the collection box away from the outlet pipe is connected to a pressure reducing pipe and a return pipe from top to bottom, with the pressure reducing pipe being stepped. The bottom of the pressure reducing pipe is connected to a separation pipe and an oil inlet pipe from left to right. An oil-gas separator is installed at the end of the separation pipe away from the pressure reducing pipe, and the separation pipe is connected to the oil-gas inlet of the oil-gas separator. The outlet of the oil-gas separator is connected to the return pipe. The oil outlet of the oil-gas separator is connected to an oil outlet pipe, and the end of the oil outlet pipe away from the oil-gas separator is connected to an oil tank. A gravity sensor is installed at the connection between the oil inlet pipe and the pressure reducing pipe; an oil pump is installed at the end of the oil inlet pipe away from the pressure reducing pipe, the output end of the oil pump is connected to the oil inlet pipe, and the input end of the oil pump is connected to the oil tank. Step 3: Gas chromatography-mass spectrometry analysis; connect the gas chromatograph to the collection box, and after the components desorbed by heat are separated by the gas chromatograph, they are detected by the mass spectrometer; One-way valves are connected to the outlet pipe, inlet pipe, and return pipe at the connection points with the collection box; one-way valves are also connected to the connection points with the separator pipe and oil inlet pipe and the pressure reducing pipe; a valve is connected to the connection point between the pressure reducing pipe and the collection box.

2. The method for determining epichlorohydrin in drinking water according to claim 1, characterized in that: In step one, the sample bottle is cleaned with methanol before sampling.

3. The method for determining epichlorohydrin in drinking water according to claim 2, characterized in that: In step one, the sampling volume should be such that the sample overflows into the sample bottle without leaving air bubbles.

4. The method for determining epichlorohydrin in drinking water according to claim 3, characterized in that: In step two, the carrier gas is nitrogen, the purging temperature is 20-30℃, the purging flow rate is 40-50 mL / min, the purging time is 30-40 min, the dry purging time is 4-6 min, the desorption temperature is 250-300℃, the desorption time is 6-9 min, the baking temperature is 280-300℃, and the baking time is 5-7 min.

5. The method for determining epichlorohydrin in drinking water according to claim 4, characterized in that: In step three, the chromatographic column is a DB-624 capillary column with parameters of 30m × 0.25mm and 1.4μm; the carrier gas is helium with a flow rate of 0.5–1mL / min; the injection port temperature is 250–300℃; the injection method is split injection with a split ratio of 10:1; the temperature program starts at 35℃, holds for 1 min, increases to 83–100℃ at 2℃ / min, and then increases to 180–200℃ at 20℃ / min, holding for 5 min.

6. The method for determining epichlorohydrin in drinking water according to claim 5, characterized in that: In step three, the ionization mode of the mass spectrometer is EI, the ion source temperature is 230℃, the quadrupole temperature is 150~200℃, the gas chromatography-mass spectrometry interface temperature is 200~300℃, the solvent delay time is 2min, and the scanning mode is ion scanning.

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