Method for analyzing total nitrogen in water

Abstract

The invention belongs to the technical field of environment detection, and particularly relates to a method for analyzing total nitrogen in water. The method includes: preparing a nitrogen standard solution; injecting a nitrogen standard solution into the quartz tube by using an injector, and vaporizing the nitrogen standard solution in the quartz tube; introducing the vaporized nitrogen standard solution into a reaction chamber by using argon, carrying out combustion cracking reaction on the vaporized nitrogen standard solution in the reaction chamber to convert into NO, reacting NO with O3 gas to convert into excited state NO2 *, and emitting photons when the excited state NO2 * jumps to a ground state; and the photomultiplier is used for detecting the photon intensity according to a specific wavelength. The method is wide in linear range, the water sample does not need to be diluted during detection, and errors caused in the dilution process are avoided. The method is good in detection repeatability and high in accuracy, the analysis time is shortened by 50 min compared with an existing method, and the analysis time and the labor intensity are effectively reduced. The sample can be directly injected, the environmental pollution is avoided, and the pollution or element loss possibly caused in the pretreatment process of the sample is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental detection, and particularly relates to an analysis method for total nitrogen in water. Background Art

[0002] Regarding the analysis or measurement method of total nitrogen in water, laboratories generally use the "HJ636-2012 Determination of total nitrogen in water quality - alkaline potassium persulfate digestion ultraviolet spectrophotometry" for determination. The principle of the method is: at 120-124°C, alkaline potassium persulfate solution converts the nitrogen of nitrogen-containing compounds in the sample into nitrate, and ultraviolet spectrophotometry is used to determine the absorbance at 220nm and 275nm in proportion to the content to obtain the total nitrogen content of the sample.

[0003] However, this method has high requirements for the purity of chemical reagents. The digestion temperature, pressure and time of water samples and the water used in the laboratory will affect the analysis results. It also has high requirements for the cleanliness of the glassware used, which is related to the conversion rate of nitrogen-containing compounds in the water sample under the action of alkaline potassium persulfate solution. For water samples containing many interferences, it is sometimes necessary to repeat the analysis many times to obtain accurate results. Especially for samples with high total nitrogen content, because the water samples need to be diluted, errors will be introduced due to different dilution ratios. Therefore, it is necessary to design an analytical method for total nitrogen in water to solve the above problems. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for analyzing total nitrogen in water to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for analyzing total nitrogen in water, comprising the following steps:

[0006] Step S1 includes preparing a nitrogen standard solution;

[0007] Step S2 includes injecting a nitrogen standard solution into a quartz tube using a syringe, and vaporizing the nitrogen standard solution in the quartz tube;

[0008] Step S3 includes using argon gas to bring the vaporized nitrogen standard solution into the reaction chamber, where the vaporized nitrogen standard solution undergoes combustion and cracking reactions in the reaction chamber to convert into NO, NO and O 3 The gas reacts and converts into excited NO 2 *, excited state of NO 2 *Emits a photon when transitioning to the ground state;

[0009] Step S4 includes detecting the intensity of photons at a specific wavelength using a photomultiplier tube.

[0010] Furthermore, the step S1 includes:

[0011] Step S11, weigh 7.2180 g of potassium nitrate, dissolve it in 500 ml of ammonia-free water, transfer it to a 1000 ml volumetric flask, dilute it to the mark with ammonia-free water, and prepare a nitrogen standard solution with a nitrogen concentration of 1000 mg / L;

[0012] Step S12, measure 500.00 ml of potassium nitrate solution with a nitrogen concentration of 1000 mg / L into a 1000 ml volumetric flask, dilute it to 1000 ml to the mark with ammonia-free water, and prepare a nitrogen standard solution with a nitrogen concentration of 500.0 mg / L.

[0013] Furthermore, the step S1 further includes:

[0014] Step S13, respectively measure 0.00, 1.00, 2.00, 5.00, 10.00, 20.00, 50.00, and 100.00 of a potassium nitrate solution with a nitrogen concentration of 500.0 mg / L into a 500 ml volumetric flask, dilute to the mark with ammonia-free water, and prepare nitrogen standard solutions with nitrogen concentrations of 0.00, 1.00, 2.00, 5.00, 10.00, 20.00, 50.00, and 100.00 mg / L respectively.

[0015] Furthermore, the step S2 comprises:

[0016] Step S21, using a 25ul syringe to extract 10ul nitrogen standard solution;

[0017] Step S22, injecting 10 μl of nitrogen standard solution into a quartz tube at 1050° C. through an automatic sample injector.

[0018] Furthermore, the step S3 includes:

[0019] Step S31, the nitrogen standard solution undergoes the following chemical reaction in the quartz tube:

[0020] R-N+O 2 → NO+CO 2 +H 2 O+MO x NO+O 3 →NO 2 * +O 2 NO 2 +hv,

[0021] The reaction products include CO 2 , H 2 O, NO and other oxides.

[0022] Furthermore, the step S3 further includes:

[0023] Step S32: The reaction product is carried by argon gas, passes through a membrane dryer to remove moisture, and enters a reaction chamber, where NO and O from an ozone generator react. 3 The gas reacts and converts into excited NO 2 *.

[0024] Furthermore, the step S11 includes:

[0025] Step S111, adding old potassium nitrate into water, heating and stirring until boiling, to obtain a potassium nitrate solution;

[0026] Step S112, after filtering, cooling until a large amount of crystals are precipitated;

[0027] Step S113, washing the crystals, drying them at 105-110° C. for 2 hours, and cooling them to room temperature to obtain purified potassium nitrate.

[0028] Furthermore, the step S31 includes: the nitrogen standard solution is vaporized by an automatic sampler, argon gas is introduced from a carrier gas inlet and brings the vaporized nitrogen standard solution into the quartz tube, and an auxiliary gas enters the inner tube from an auxiliary gas inlet, mixes with the vaporized nitrogen standard solution and burns.

[0029] Further, the step S3 also includes:

[0030] Step S33, by removing the redundant O 3 The gas is thermally decomposed in the reaction chamber to convert O 3 The gas is decomposed into oxygen and then discharged directly.

[0031] Technical effects and advantages of the present invention:

[0032] 1. This method has a wide linear range and does not require dilution of water samples during detection, thus avoiding errors caused by the dilution process.

[0033] 2. The detection has good repeatability and high accuracy. The analysis time is shortened by 50 minutes compared with the existing method, which effectively reduces the analysis time and labor intensity.

[0034] 3. After the sample is collected, it can be directly analyzed without pre-treatment, that is, there is no need to use chemical reagents such as alkaline potassium persulfate, sodium hydroxide, sulfuric acid, hydrochloric acid, etc. The sample can be directly injected without causing environmental pollution, thus avoiding the contamination or element loss that may be caused by the sample during the pre-treatment process.

[0035] 4. The sample is burned at high temperature, which can convert nitrogen in nitrogen-containing organic and inorganic substances into NO. The conversion rate is high and the total nitrogen content in the water sample can be detected well.

[0036] 5. Through the spike recovery test, the recovery rate is between 98.3-105, which is relatively high.

[0037] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 A flow chart of a method for analyzing total nitrogen in water according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] like Figure 1 As shown, a method for analyzing total nitrogen in water according to an embodiment of the present invention comprises the following steps:

[0042] Step S1 includes preparing a nitrogen standard solution;

[0043] Step S2 includes injecting a nitrogen standard solution into a quartz tube using a syringe, and vaporizing the nitrogen standard solution in the quartz tube;

[0044] Step S3 includes using argon gas to bring the vaporized nitrogen standard solution into the reaction chamber, where the vaporized nitrogen standard solution undergoes combustion and cracking reactions in the reaction chamber to convert into NO, NO and O 3 The gas reacts and converts into excited NO 2 *, excited state of NO 2 *Emits a photon when transitioning to the ground state;

[0045] Step S4 includes detecting the intensity of photons at a specific wavelength using a photomultiplier tube.

[0046] Optionally, the step S1 includes:

[0047] Step S11, weigh 7.2180 g of potassium nitrate, dissolve it in 500 ml of ammonia-free water, transfer it to a 1000 ml volumetric flask, dilute it to the mark with ammonia-free water, and prepare a nitrogen standard solution with a nitrogen concentration of 1000 mg / L;

[0048] Step S12, measure 500.00 ml of potassium nitrate solution with a nitrogen concentration of 1000 mg / L into a 1000 ml volumetric flask, dilute it to 1000 ml to the mark with ammonia-free water, and prepare a nitrogen standard solution with a nitrogen concentration of 500.0 mg / L.

[0049] Optionally, the step S1 further includes:

[0050] Step S13, respectively measure 0.00, 1.00, 2.00, 5.00, 10.00, 20.00, 50.00, and 100.00 of a potassium nitrate solution with a nitrogen concentration of 500.0 mg / L into a 500 ml volumetric flask, dilute to the mark with ammonia-free water, and prepare nitrogen standard solutions with nitrogen concentrations of 0.00, 1.00, 2.00, 5.00, 10.00, 20.00, 50.00, and 100.00 mg / L respectively.

[0051] Optionally, step S2 includes:

[0052] Step S21, using a 25ul syringe to extract 10ul of nitrogen standard solution;

[0053] Step S22, injecting 10ul of nitrogen standard solution into a quartz tube at 1050°C through an automatic sample injector.

[0054] Optionally, step S3 includes:

[0055] Step S31, the nitrogen standard solution undergoes the following chemical reaction in the quartz tube:

[0056] R-N+O 2 → NO + CO 2 +H 2 O+MO x NO+O 3 →NO 2 * +O 2 NO 2 +hv;

[0057] The reaction products include CO 2 , H 2 O, NO and other oxides.

[0058] Optionally, step S3 further includes:

[0059] Step S32: The reaction product is carried by argon gas, passes through a membrane dryer to remove moisture, and enters a reaction chamber, where NO and O from an ozone generator react. 3 The gas reacts and converts into excited NO 2 *.

[0060] In this embodiment, a standard curve is drawn according to the above method, and the R of the standard curve should be ≥ 0.999.

[0061] Standard curve related data summary

[0062]

[0063]

[0064] The instrument can draw more than 2 standard curves at the same time. If the total nitrogen content of the water sample is high, a standard solution with high total nitrogen content can be prepared according to actual needs. Curves of different ranges can be selected according to the actual water sample concentration.

[0065] Before each analysis, the standard curve within the linear range is called to analyze the total nitrogen content of the sample.

[0066] Summary of test sample data:

[0067] Water Sample Instrument Count Analytical data, mg / L Call Curve 1 861 1.38 0-10 curve 2 13061 31.13 10-100 Curve 3 119390 287.85 100-1000 curve 4 22832 54.05 10-100 Curve

[0068] Spike recovery experiment

[0069]

[0070]

[0071] Optionally, the step S11 includes:

[0072] Step S111, adding old potassium nitrate into water, heating and stirring until boiling, to obtain a potassium nitrate solution;

[0073] Step S112, after filtering, cooling until a large amount of crystals are precipitated;

[0074] Step S113, washing the crystals, drying them at 105-110° C. for 2 hours, and cooling them to room temperature to obtain purified potassium nitrate.

[0075] In this embodiment, impurities and moisture in the potassium nitrate can be removed by washing, filtering, drying and cooling the potassium nitrate just taken out, which is beneficial to improving the measurement accuracy.

[0076] Optionally, the step S31 includes: the nitrogen standard solution is vaporized by an automatic sampler, argon gas is introduced from a carrier gas inlet to bring the vaporized nitrogen standard solution into the quartz tube, and an auxiliary gas enters the inner tube from an auxiliary gas inlet to mix with the vaporized nitrogen standard solution and burn.

[0077] Optionally, step S3 further includes:

[0078] Step S33, by removing the redundant O 3 The gas is thermally decomposed in the reaction chamber to convert O 3 The gas is decomposed into oxygen and then discharged directly.

[0079] In this embodiment, since O 3 Direct discharge of gas can easily cause harm to the human body. 3 The gas is decomposed into oxygen in the reaction chamber and then discharged directly, which can eliminate the harm.

[0080] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for analyzing total nitrogen in water, characterized in that: The following steps are involved: Step S1, preparing a nitrogen standard solution; Step S2, injecting a nitrogen standard solution into the quartz tube using a syringe, and vaporizing the nitrogen standard solution in the quartz tube; Step S3, using argon gas to bring the vaporized nitrogen standard solution into the reaction chamber, the vaporized nitrogen standard solution undergoes combustion and cracking reaction in the reaction chamber to be converted into NO, NO reacts with O3 gas to be converted into excited state NO2*, and the excited state NO2* emits photons when it transitions to the ground state; Step S4, using a photomultiplier tube to detect the intensity of photons at a specific wavelength.

2. The method for analyzing total nitrogen in water according to claim 1, characterized in that: The step S1 comprises: Step S11, weigh 7.2180 g of potassium nitrate, dissolve it in 500 ml of ammonia-free water, transfer it to a 1000 ml volumetric flask, dilute it to the mark with ammonia-free water, and prepare a nitrogen standard solution with a nitrogen concentration of 1000 mg / L; Step S12, measure 500.00 ml of potassium nitrate solution with a nitrogen concentration of 1000 mg / L into a 1000 ml volumetric flask, dilute it to 1000 ml to the mark with ammonia-free water, and prepare a nitrogen standard solution with a nitrogen concentration of 500.0 mg / L.

3. The method for analyzing total nitrogen in water according to claim 2, characterized in that: The step S1 further comprises: Step S13, respectively measure 0.00, 1.00, 2.00, 5.00, 10.00, 20.00, 50.00, and 100.00 of a potassium nitrate solution with a nitrogen concentration of 500.0 mg / L into a 500 ml volumetric flask, dilute to the mark with ammonia-free water, and prepare nitrogen standard solutions with nitrogen concentrations of 0.00, 1.00, 2.00, 5.00, 10.00, 20.00, 50.00, and 100.00 mg / L respectively.

4. The method for analyzing total nitrogen in water according to claim 3, characterized in that: The step S2 comprises: Step S21, using a 25ul syringe to extract 10ul nitrogen standard solution; Step S22, injecting 10ul of nitrogen standard solution into a quartz tube at 1050°C through an automatic sample injector.

5. The method for analyzing total nitrogen in water according to claim 4, characterized in that: The step S3 comprises: Step S31, the nitrogen standard solution undergoes the following chemical reaction in the quartz tube: R-N+O2→·NO+CO2+H2O+MO x ·NO+O3→NO2 * +O2NO2+hv, The reaction products include CO2, H2O, NO and other oxides.

6. The method for analyzing total nitrogen in water according to claim 5, characterized in that: The step S3 further comprises: Step S32, the reaction product is carried by argon gas, passes through a membrane dryer to remove moisture therein, and enters a reaction chamber, where NO reacts with O3 gas from an ozone generator to be converted into excited NO2*.

7. The method for analyzing total nitrogen in water according to claim 2, characterized in that: The step S11 comprises: Step S111, adding old potassium nitrate into water, heating and stirring until boiling, to obtain a potassium nitrate solution; Step S112, after filtering, cooling until a large amount of crystals are precipitated; Step S113, washing the crystals, drying them at 105-110° C. for 2 hours, and cooling them to room temperature to obtain purified potassium nitrate.

8. The method for analyzing total nitrogen in water according to claim 5, characterized in that: The step S31 includes: the nitrogen standard solution is gasified by the automatic sample injector, argon gas is brought into the quartz tube from the carrier gas inlet, and the supporting gas enters the inner tube from the supporting gas inlet, mixes with the gasified nitrogen standard solution and burns.

9. The method for analyzing total nitrogen in water according to claim 1, characterized in that: The step S3 also includes: Step S33, decomposing the excess O3 gas by heat in the reaction chamber, decomposing the O3 gas into oxygen and then directly discharging it.

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