Disclosure of Invention
The invention aims to provide a sample pretreatment method, a halogen content detection method and application.
The invention is realized in the following way:
in a first aspect, an embodiment of the present invention provides a sample pretreatment method, including:
Reacting the sample to be detected with a first iodide aqueous solution to enable fluorine, chlorine and bromide ions in insoluble inorganic halide to be dissociated to obtain an intermediate sample;
and (3) reacting the intermediate sample with a calcium hydroxide aqueous solution, and filtering to obtain a defluorination sample.
In an alternative embodiment, the sample to be tested is filtered to remove the precipitate after reaction with the first aqueous iodide solution is completed;
In an alternative embodiment, the filtration means is microfiltration membrane filtration.
In an alternative embodiment, the first aqueous iodide solution is selected from at least one of a sodium iodide solution and a potassium iodide solution.
In a second aspect, an embodiment of the present invention provides a method for detecting halogen content, including:
the sample pretreatment method provided by the embodiment of the invention is adopted to carry out pretreatment on the sample to be tested;
respectively detecting the ion content in the intermediate sample and the defluorination sample by adopting an ion chromatography method;
Subtracting the measured ion content of the peak between 2 and 4 minutes from the measured ion content of the peak between 2 and 4 minutes in the defluorination sample to obtain the free fluorine content in the sample to be detected.
In an alternative embodiment, the method further comprises:
Converting halogen-containing organic compounds in a sample to be detected into inorganic halides through combustion by adopting an oxygen bomb method to obtain a partial conversion sample, reacting the partial conversion sample with a second iodide aqueous solution, filtering and removing precipitates to obtain a conversion sample;
Detecting the ion content in the converted sample by adopting an ion chromatography method;
subtracting the corresponding halogen ion content in the intermediate sample from the measured halogen ion content in the conversion sample to obtain the combined halogen content in the sample to be detected.
In an alternative embodiment, the second aqueous iodide solution is selected from at least one of a sodium iodide solution and a potassium iodide solution.
In an alternative embodiment, the oxygen bomb method is used to convert the halogen-containing organic compound in the sample to be tested into inorganic halide by burning, which is:
placing a sample to be tested in a crucible of an oxygen bomb device, and installing an ignition wire;
adding absorption liquid into the oxygen bomb cup in a mode of leaching the inner wall of the oxygen bomb cup so as to completely wet the inner wall of the oxygen bomb cup;
Oxygen is filled into the oxygen bomb cup;
Closing a circuit of the ignition wire to burn the sample to be tested;
And after the combustion is finished, cooling the oxygen bomb device, and fully absorbing combustion products by the absorption liquid to obtain a partial conversion sample.
In an alternative embodiment, ethanol is used as a combustion improver when the sample to be tested is combusted by an oxygen bomb method.
In an alternative embodiment, at least one of deionized water, sodium carbonate solution and sodium bicarbonate solution is used as absorption liquid when the sample to be tested is burnt by adopting an oxygen bomb method;
in an alternative embodiment, the concentration of the sodium carbonate solution is 50-200 mg/l;
In an alternative embodiment, the concentration of sodium bicarbonate solution is 40 to 200mg/l.
In an alternative embodiment, the oxygen is filled into the oxygen bomb cup by:
oxygen is filled into the oxygen bomb cup, so that the air pressure in the oxygen bomb cup is 2.8-3.2 MPa, the oxygen bomb cup is kept for 15-20 s, then air in the oxygen bomb cup is discharged, the oxygen pressure gauge is displayed as 2.8-3.2 MPa after repeating for three times, and the oxygen is stopped for 15-20 s to enable the oxygen to be used as combustion-supporting gas.
The method for detecting the halogen content provided by the embodiment of the invention is applied to detecting the halogen content in wastewater.
The invention has the following beneficial effects:
The sample pretreatment method enables insoluble fluoride, chloride and bromide in the sample to react with iodide to generate iodide precipitate, so that fluorine, chlorine and bromide ions in the original insoluble inorganic halide are dissociated, the recovery rate of free halogen is greatly improved, the subsequent ion chromatograph is convenient for testing, and the accuracy of detecting the content of free halogen in the halide is improved; the intermediate sample is then reacted with calcium hydroxide to precipitate fluoride ions in the sample. And the inaccurate fluorine ion detection data caused by the fact that the peak time and the peak shape of hypophosphite ions are close to each other when the ion content is detected by adopting an ion chromatography method are avoided.
The detection method comprises the sample pretreatment method provided by the invention, so that the detection method can more accurately detect the fluorine, chlorine and bromine ion content in the sample compared with the existing detection method. The detection method provided by the invention can be applied to the detection of halogen content in wastewater.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The inventors have made a lot of creative efforts and found that in the ion chromatography test, the peak-out time and peak shape of the hypophosphite and the fluoride ion are very close, when the sample contains the fluoride ion and the hypophosphite, the software cannot distinguish, and the sum of the contents of the two ions is quantified. If the test sample contains hypophosphite, serious interference is easily caused to the qualitative and quantitative analysis of fluoride ions. Therefore, aiming at a test sample of wastewater possibly containing hypophosphite, the inventor proposes the technical scheme of the application to improve the accuracy of halogen test in the wastewater.
The embodiment of the invention provides a sample pretreatment method, which comprises the following steps:
Reacting the sample to be detected with a first iodide aqueous solution to enable fluorine, chlorine and bromide ions in insoluble inorganic halide to be dissociated to obtain an intermediate sample;
and (3) reacting the intermediate sample with a calcium hydroxide aqueous solution, and filtering to obtain a defluorination sample.
Insoluble fluoride, chloride and bromide in the sample react with iodide to generate iodide precipitate, so that fluorine, chlorine and bromide ions in the original insoluble inorganic halide are dissociated, the recovery rate of free halogen is greatly improved, the subsequent ion chromatograph is convenient for testing, and the accuracy of detecting the content of free halogen in the halide is improved; the intermediate sample is then reacted with calcium hydroxide to precipitate fluoride ions in the sample. As the peak time and the peak shape of the hypophosphite ion and the fluoride ion are very close, the fluoride ion is precipitated first, and the ion content is detected by adopting an ion chromatography method subsequently, the confusion of the hypophosphite ion and the fluoride ion can be avoided. Testing the sum of the content of fluoride ions and hypophosphite ions in the intermediate sample to be C1 by adopting an ion chromatography method, and testing the content of hypophosphite ions in the defluorination sample to be C2 by adopting the ion chromatography method; then C1-C2 is the true fluoride ion content of the sample.
Therefore, the sample pretreatment method provided by the invention is adopted to treat the sample to be tested, and then the ion chromatography is adopted to test the fluorine ion content in the sample, so that the test result can be ensured to be more accurate.
Preferably, the sample to be tested is filtered to remove the precipitate after reaction with the first aqueous iodide solution is completed.
Preferably, the filtration mode is microporous membrane filtration.
Preferably, the first aqueous iodide solution is selected from at least one of a sodium iodide solution and a potassium iodide solution.
The embodiment of the invention provides a method for detecting halogen content, which comprises the following steps:
the sample pretreatment method provided by the embodiment of the invention is adopted to carry out pretreatment on the sample;
respectively detecting the ion content in the intermediate sample and the defluorination sample by adopting an ion chromatography method;
subtracting the ion content of the peak between 2 and 4 minutes from the measured defluorination sample to obtain the fluorine content in the sample to be measured.
The peak time of the hypophosphite ions and the fluoride ions is about 3min, and the peak shapes of the hypophosphite ions and the fluoride ions are very similar, so that the total amount of the hypophosphite ions and the fluoride ions is detected by adopting an ion chromatography method for an intermediate sample. The detection method comprises the sample pretreatment method provided by the embodiment of the invention, so that the detection method provided by the invention can be used for accurately testing the content of halogen ions, particularly fluorine ions, in the sample.
Preferably, in order to be able to test the resulting combined state (e.g. halogen-containing organic compound) halogen ion content of the sample. The method for detecting the halogen content provided by the embodiment of the invention further comprises the following steps:
Converting halogen-containing organic compounds in a sample to be detected into inorganic halides through combustion by adopting an oxygen bomb method to obtain a partial conversion sample, reacting the partial conversion sample with a second iodide aqueous solution, filtering and removing precipitates to obtain a conversion sample;
Detecting the ion content in the converted sample by adopting an ion chromatography method;
Subtracting the corresponding halogen ion content in the intermediate sample from the halogen ion content in the conversion sample to obtain the combined halogen content in the sample to be detected.
The halogen contained in the sample is completely dissociated into the converted sample as far as possible by the mode, and the chloride ion is taken as an example, the chloride ion content in the converted sample is detected to be C3 by adopting an ion chromatography, the chloride ion content in the intermediate sample is detected to be C4 by adopting an ion chromatography, and the C3-C4 is the combined chloride ion content.
Preferably, the second aqueous iodide solution is selected from at least one of a sodium iodide solution and a potassium iodide solution.
The detection method specifically comprises the following steps:
S1, sample pretreatment:
Taking 0.1-1 g (accurate to 0.0001 g) of the sample into a 50ml volumetric flask, and then adding 10-20 ml of iodide aqueous solution with the concentration of 10-50 mmol/l of soluble iodide into the volumetric flask. And (3) fully and uniformly mixing the sample with the iodide aqueous solution, standing for reaction for 5-10min, filtering by a microporous filter membrane, transferring to a 50ml volumetric flask, and fixing the volume to 50ml by using a proper amount of deionized water to obtain an intermediate sample.
10G of the intermediate sample is taken into a 50ml volumetric flask, 10ml of calcium hydroxide aqueous solution (the concentration is 20 mmol/L) is added, and the mixture is sufficiently vibrated to enable fluorine ions in the sample to react with calcium ions to generate insoluble calcium fluoride precipitate, and the insoluble calcium fluoride precipitate is filtered, so that hypophosphite is reserved. And (5) the volume is fixed to 50ml by a proper amount of deionized water, and a defluorination sample is obtained.
S2, converting halogen-containing organic compounds in a sample to be detected into inorganic halides by adopting an oxygen bomb method through combustion, wherein the method specifically comprises the following steps:
1. The sample was weighed 0.5g (accurate to 0.0001 g) into an oxygen bomb nickel crucible, and about 1.5ml of ethanol was added as a combustion improver to some samples which were not easily burnt.
2. Installing an ignition wire and a sample, opening an oxygen bomb upper cover, fixing a nickel crucible containing the sample, fixing two ends of the ignition wire on an electrode column, selecting cotton threads with proper length to bind on the ignition wire, and enabling the cotton threads to be in contact with the sample.
3. Adding an absorption liquid:
(1) Preparing an absorption liquid: pure water can be added as an absorption liquid to a sample with low halogen content, and a sample with high halogen content can be added into an eluting liquid used by an instrument. Na2CO3 concentration is 50-200 mg/l and NaHCO3 concentration is 40-200 mg/l in leaching, and the materials are fully and uniformly mixed to prepare the absorption liquid.
(2) Adding an absorption liquid: about 20ml of absorption liquid is added into the oxygen bomb cup in a mode of leaching the inner wall of the oxygen bomb, so that the inner wall of the oxygen bomb cup is completely wetted, and the oxygen bomb cup is covered and screwed up;
4. Oxygenation: connecting an oxygen conduit to an oxygen bomb cup cover, slowly filling oxygen, increasing the pressure from zero to about 3MPa at intervals, stopping for 15-20 s, slowly discharging air in the oxygen bomb, and stopping for about 15s when an oxygen pressure gauge shows 3.0MPa after repeating for three times to serve as combustion-supporting gas during combustion; the oxygen bomb device is placed in cold water for ignition: and connecting an ignition wire, and igniting the sample by a closed circuit until the sample in the oxygen bomb burns and releases heat.
5. Cooling and oscillating: the oxygen bomb was placed in a cold water bath to fully submerge the oxygen bomb device to the water level. About 40min, the oxygen bomb device can be properly shaken in the cooling process, so that the measured ions are completely absorbed by the absorption liquid.
6. Deflating: taking out the oxygen bomb to wipe the water on the surface of the oxygen bomb clean, slowly discharging the oxygen in the oxygen bomb by using a gas discharge valve, and absorbing the discharged waste gas into the leaching liquid when necessary.
7. Filtering and fixing volume: and leaching the oxygen bomb cylinder, the sample cup and the oxygen bomb cover with a proper amount of deionized water for more than 3 times, mixing the leached tail liquid with the absorption liquid to obtain a partial conversion sample, then standing the partial conversion sample and 10-20 mL of iodide aqueous solution (the concentration of soluble iodide is 10-50 mmol/l) for reaction for 5-10min, filtering and transferring the reaction product to a 100mL volumetric flask after the reaction is finished, and then fixing the volume by using deionized water to obtain the conversion sample.
S3, detecting the ion content in the intermediate sample, the defluorination sample and the conversion sample by adopting an ion chromatography method. Sample testing:
1. And (3) standard curve preparation: 100mg/l standard solution, diluting and configuring standard element solutions with different gradients of the measured element, and respectively configuring 1mg/l,2mg/l,4mg/l and 8mg/l standard solutions to prepare a calibration curve. And measuring the absorption intensity peak area reading of the target element, and establishing a calibration curve of the relation between the absorption intensity and the concentration of the target element by using a calibration curve method.
2. Test sample: and under the condition of establishing a corresponding sequence of a standard curve, testing the ion content in a reagent blank, an intermediate sample, a defluorination sample and a conversion sample respectively, and adopting an integration mode which is the same as that of the standard curve. If the concentration of the sample solution exceeds the concentration range of the calibration curve, the sample solution is diluted to be within the concentration range of the corresponding calibration curve and then retested.
The method for detecting the halogen content provided by the embodiment of the invention can be applied to the detection of the halogen content in the wastewater.
The features and capabilities of the present invention are described in further detail below in connection with the examples.
Example 1
1. Sample weighing: the initial sample to be measured is weighed into a volumetric flask of 0.5000g to 50ml, and then 15ml of aqueous potassium iodide solution with a concentration of 30mmol/l is added into the volumetric flask. And (3) fully and uniformly mixing the sample with the potassium iodide aqueous solution, standing for reaction for 10min, filtering by a microporous filter membrane, transferring to a 50ml volumetric flask, and fixing the volume to 50ml by using a proper amount of deionized water to obtain an intermediate sample. 10g of the intermediate sample is taken into a 50ml volumetric flask, 10ml of calcium hydroxide aqueous solution (the concentration is 20 mmol/L) is added, and the mixture is sufficiently vibrated to enable fluorine ions in the sample to react with calcium ions to generate insoluble calcium fluoride precipitate, and the insoluble calcium fluoride precipitate is filtered, so that hypophosphite is reserved. And (5) the volume is fixed to 50ml by a proper amount of deionized water, and a defluorination sample is obtained.
2. 0.5000G (accurate to 0.0001 g) of an initial sample to be measured is weighed into an oxygen bomb nickel crucible, and 1.5ml of ethanol is added as a combustion improver.
3. Mounting ignition wires and samples: opening an oxygen bomb upper cover, fixing a nickel crucible containing a sample, fixing two ends of an ignition wire on an electrode column, selecting cotton threads with proper length to bind on the ignition wire, and enabling the cotton threads to be in contact with the sample;
4. Adding an absorption liquid:
(1) Preparing an absorption liquid: the leaching absorption liquid used by the instrument is prepared, wherein the concentration of Na2CO3 is 100mg/l, the concentration of NaHCO3 is 100mg/l, and the absorption liquid is prepared by fully and uniformly mixing.
(2) Adding an absorption liquid: adding 20ml of absorption liquid into the oxygen bomb cup in a mode of leaching the inner wall of the oxygen bomb, so that the inner wall of the oxygen bomb cup is completely wetted, and covering and screwing the oxygen bomb cup;
5. Oxygenation and ignition: connecting an oxygen conduit to an oxygen bomb cup cover, slowly filling oxygen, increasing the pressure from zero to about 3MPa at intervals, stopping 20s, slowly discharging air in an oxygen bomb, stopping 15s when an oxygen pressure gauge shows 3.0MPa after repeating for three times, and filling the oxygen bomb cup cover with combustion-supporting gas used for combustion; the oxygen bomb device is placed in cold water for ignition: connecting an ignition wire, and igniting the sample by a closed circuit until the sample in the oxygen bomb burns and releases heat;
6. cooling and oscillating: the oxygen bomb was placed in a cold water bath to fully submerge the oxygen bomb device to the water level. And cooling for about 40min, and properly shaking the oxygen bomb device in the cooling process to ensure that the halogen ions are completely absorbed by the absorption liquid.
7. Deflating: taking out the oxygen bomb to wipe the water on the surface of the oxygen bomb clean, slowly discharging oxygen in the oxygen bomb by using a gas discharge valve, and absorbing discharged waste gas in the leaching liquid if necessary;
8. Filtering and fixing volume: and (3) leaching the oxygen bomb cylinder, the sample cup and the oxygen bomb cover with a proper amount of deionized water for more than 3 times, mixing the leaching tail liquid with the absorption liquid to obtain a partial conversion sample, standing the partial conversion sample and 15mL (the potassium iodide concentration is 30 mmol/l) of iodide aqueous solution for reaction for 10min, filtering and transferring the reaction product to a 100mL volumetric flask after the reaction is finished, and then fixing the volume by using deionized water to obtain the conversion sample.
And (3) respectively detecting the ion content in the intermediate sample, the defluorination sample and the conversion sample by adopting an ion chromatography method.
Comparative example 1:
1. The sample was weighed 0.5000g (to the nearest 0.0001 g) into an oxygen bomb nickel crucible.
2. Mounting ignition wires and samples: opening an oxygen bomb upper cover, fixing a nickel crucible containing a sample, fixing two ends of an ignition wire on an electrode column, selecting cotton threads with proper length to bind on the ignition wire, and enabling the cotton threads to be in contact with the sample;
3. Adding an absorption liquid: adding the absorption liquid prepared in the example 1, adding 20ml of the absorption liquid into an oxygen bomb cup in a mode of leaching the inner wall of the oxygen bomb, completely wetting the inner wall of the oxygen bomb cup, covering the oxygen bomb cup and screwing the oxygen bomb cup;
4. Oxygenation and ignition: connecting an oxygen conduit to an oxygen bomb cup cover, slowly filling oxygen, increasing the pressure from zero to about 3MPa at intervals, stopping 20s, slowly discharging air in an oxygen bomb, stopping 15s when an oxygen pressure gauge shows 3.0MPa after repeating for three times, and filling the oxygen bomb cup cover with combustion-supporting gas used for combustion; the oxygen bomb device is placed in cold water for ignition: connecting an ignition wire, and igniting the sample by a closed circuit until the sample in the oxygen bomb burns and releases heat;
5. cooling and oscillating: the oxygen bomb was placed in a cold water bath to fully submerge the oxygen bomb device to the water level. Cooling for about 40min, and properly shaking the oxygen bomb device in the cooling process to ensure that the halogen ions are completely absorbed by the absorption liquid;
6. deflating: taking out the oxygen bomb to wipe the water on the surface of the oxygen bomb clean, slowly discharging oxygen in the oxygen bomb by using a gas discharge valve, and absorbing discharged waste gas in the leaching liquid if necessary;
7. filtering and fixing volume: and filtering and transferring the absorption liquid into a volumetric flask of 100mL, leaching the oxygen bomb cylinder, the sample cup and the oxygen bomb cover with a proper amount of deionized water for more than 3 times, transferring into the volumetric flask, and then fixing the volume with deionized water to obtain a comparison sample.
Experimental example 1
According to the detection method provided by the embodiment and the comparative example of the invention, the content of chloride ions in each sample is detected by taking waste water as an object, and the recovery rate of free halogen and combined halogen in the waste water is calculated by taking chloride ions as an example. Analysis was performed using a standard solution of chlorinated paraffin containing 1.0mg/L of free chlorine and 1.0mg/L of bound chlorine. The data are recorded in tables 1 and 2.
TABLE 1 results of chloride ion content test
TABLE 2 results of chlorine ion recovery measurements
The results in tables 1 and 2 show that the contents of free chlorine and bound chlorine can be obtained by measuring the contents of free chlorine and total chlorine in two steps after the samples to be measured are treated with the aqueous solution of soluble iodide, respectively. The recovery rate of the scheme of the invention is obviously higher than that of the conventional oxygen bomb method, the deviation of parallel samples is smaller, and the loss of halogen in the sample in the pretreatment process is smaller, so that the sample pretreatment method of the scheme has high accuracy and feasibility.
Experimental example 2
Analysis was performed according to the procedure provided in the examples and comparative examples, using 1.0mg/L sodium fluoride containing fluoride and 1.0mg/L sodium hypophosphite standard solution containing hypophosphite.
TABLE 3 fluorine content test results
The results in Table 3 demonstrate that when the sample contains both fluoride and hypophosphite, the peak times of the two ions are consistent, see FIGS. 1 and 2. Because the software cannot distinguish, the sum of the contents of the two ions is quantified, and hypophosphite is easily classified as fluoride. After calcium hydroxide solution is introduced to separate calcium fluoride from calcium hypophosphite by filtration, the content of hypophosphite and fluoride ions can be distinguished and measured, namely, the content of fluoride ions and hypophosphite measured by an intermediate sample is C1, the content of hypophosphite measured by a defluorination sample is C2, and the content of fluoride ions corresponds to C1-C2.
In summary, according to the sample pretreatment method provided by the invention, insoluble fluoride, chloride and bromide in the sample react with iodide to generate iodide precipitate, so that fluorine, chlorine and bromine ions in the original insoluble inorganic halide are dissociated, the recovery rate of free halogen is greatly improved, the subsequent ion chromatograph is convenient for testing, and the accuracy of detecting the content of free halogen in the halide is increased; the intermediate sample is then reacted with calcium hydroxide to precipitate fluoride ions in the sample. And the inaccurate fluorine ion detection data caused by the fact that the peak time and the peak shape of hypophosphite ions are close to each other when the ion content is detected by adopting an ion chromatography method are avoided.
The detection method of halogen content provided by the invention can more accurately detect the content of fluorine, chlorine and bromine ions in the sample compared with the existing detection method because the detection method comprises the sample pretreatment method provided by the invention. The detection method provided by the invention can be applied to the detection of halogen content in wastewater.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.