Total nitrogen analysis method

Abstract

The invention belongs to the field of photoelectric analysis, and particularly relates to a total nitrogen analysis method which comprises the following steps: (A1) obtaining the turbidity of an unknown water sample, and judging whether the turbidity exceeds a threshold value or not; if the result is yes, entering the step (A2); (A2) establishing a first mapping relation; (A3) the first water sample enters a detection chamber after being digested, first wavelength absorbance A11, second wavelength absorbance A21 and third wavelength absorbance A31 are obtained, and the total nitrogen C1 of the first water sample is obtained through a second mapping relation; (A4) diluting the first water sample, digesting the first water sample, and feeding the first water sample into the detection chamber to obtain total nitrogen C2 of the diluted water sample; (A5) determining a second mapping relation by utilizing the first mapping relation, the total nitrogen C1 and the total nitrogen C2; (A6) the unknown water sample enters the detection chamber after being digested, and the total nitrogen of the unknown water sample is obtained according to the second mapping relation. The method has the advantages of accurate detection and the like, and can be applied to water quality analysis.

Description

Technical Field

[0001] This invention relates to water quality analysis, and particularly to a method for total nitrogen analysis. Background Technology

[0002] In the automatic monitoring of surface water, drinking water, and source water, total nitrogen is an important indicator and is often detected using the alkaline potassium persulfate method.

[0003] The main content of the total nitrogen detection standard "HJ 636-2012" is as follows: Nitrite nitrogen, nitrate nitrogen, inorganic ammonium salts, dissolved ammonia, and nitrogen in most nitrogen-containing organic matter in water samples are converted into nitrates by alkaline persulfate solution at 120℃~124℃. The absorbance A is measured at wavelengths of 220nm and 275nm using ultraviolet spectrophotometry. 220 and A 275 However, in the current national standard method and actual instrument measurement process, when the turbidity content in the water sample is high (>100 NTU), the turbid substances are absorbed in the full spectrum of 190 nm-1100 nm, which can lead to comparison deviations or anomalies in the measurement results. In addition, the national standard method is cumbersome and not conducive to online monitoring. Summary of the Invention

[0004] To address the shortcomings of the existing technical solutions, the present invention provides a total nitrogen analyzer.

[0005] The objective of this invention is achieved through the following technical solution: A method for total nitrogen analysis includes the following steps: (A1) Obtain the turbidity of an unknown water sample and determine whether the turbidity exceeds the threshold; If the result is yes, proceed to step (A2); if the result is no, proceed to normal analysis. (A2) Establish a first mapping relationship between total nitrogen and absorbance, wherein the first mapping relationship is the correspondence between total nitrogen and absorbance at a first wavelength and absorbance at a second wavelength; (A3) After digestion, the first water sample enters the detection chamber to obtain the absorbance A at the first wavelength. 11 Absorbance A at the second wavelength 21 and the absorbance at the third wavelength A 31 The total nitrogen C1 of the first water sample is obtained using the second mapping relationship; the second mapping relationship is the correspondence between total nitrogen and absorbance at the first wavelength, the second wavelength, and the third wavelength. (A4) The first water sample is diluted, digested, and then introduced into the detection chamber to obtain the absorbance A at the first wavelength. 12 Absorbance A at the second wavelength 22 and the absorbance at the third wavelength A 32And the total nitrogen C2 of the water sample was obtained using the second mapping relationship; (A5) Determine the second mapping relationship using the first mapping relationship, total nitrogen C1, and total nitrogen C2; (A6) After digestion, the unknown water sample enters the detection chamber, and the total nitrogen of the unknown water sample is obtained by using the second mapping relationship, the first wavelength absorbance, the second wavelength absorbance and the third wavelength absorbance.

[0006] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. High detection efficiency; The water sample test takes no more than one hour, and even with the calibration time of g(A3), it will not exceed three hours. Compared with the national standard method, which requires four hours for a single water sample test, the efficiency is significantly improved. Whether to proceed with g(A3) calibration is determined based on the turbidity of the unknown water sample, thus saving on related reagents, standard solutions, and related costs when the turbidity of the water sample is low. 2. The test results are accurate; For unknown water samples with high turbidity, the quantitative results are accurate in the detection after g(A3) calibration, and g(A3) is dynamically calibrated and updated, making it suitable for long-term measurements. Attached Figure Description

[0007] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are merely illustrative of the technical solutions of this invention and are not intended to limit the scope of protection of this invention. In the drawings: Figure 1 This is a schematic flowchart of the total nitrogen analysis method of the present invention; Figure 2 This is a schematic diagram of the water sample flow path of the present invention.

[0008] In the attached diagram, 11-first pump, 12-second pump, 21-multi-channel directional valve, 31-digestion tank, 32-detection chamber, 41-upstream valve, 42-downstream valve, 43-on / off valve, 51-tee, 61-light source, 62-detector, 71-reagent container. Detailed Implementation

[0009] Figure 1-Figure 2 The following description illustrates optional embodiments of the invention to teach those skilled in the art how to implement and reproduce the invention. Some conventional aspects have been simplified or omitted to teach the technical solutions of the invention. Those skilled in the art should understand that variations or substitutions derived from these embodiments will be within the scope of the invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the invention. Therefore, the invention is not limited to the optional embodiments described below, but is defined only by the claims and their equivalents.

[0010] Example 1.

[0011] An embodiment of the present invention provides a method for total nitrogen analysis, such as... Figure 1 As shown, it includes the following steps: (A1) Obtain the turbidity of an unknown water sample and determine whether the turbidity exceeds the threshold; If the result is yes, proceed to step (A2); if the result is no, proceed to normal analysis. (A2) Establish a first mapping relationship between total nitrogen and absorbance, wherein the first mapping relationship is the correspondence between total nitrogen and absorbance at a first wavelength and absorbance at a second wavelength; (A3) After digestion, the first water sample enters the detection chamber 32 to obtain the absorbance A at the first wavelength. 11 Absorbance A at the second wavelength 21 and the absorbance at the third wavelength A 31 The total nitrogen C1 of the first water sample is obtained using the second mapping relationship; the second mapping relationship is the correspondence between total nitrogen and absorbance at the first wavelength, the second wavelength, and the third wavelength. (A4) The first water sample is diluted, digested, and then introduced into the detection chamber 32 to obtain the absorbance A at the first wavelength. 12 Absorbance A at the second wavelength 22 and the absorbance at the third wavelength A 32 And the total nitrogen C2 of the water sample was obtained using the second mapping relationship; (A5) Determine the second mapping relationship using the first mapping relationship, total nitrogen C1, and total nitrogen C2; (A6) After digestion, the unknown water sample enters the detection chamber 32. The total nitrogen of the unknown water sample is obtained by using the second mapping relationship, the first wavelength absorbance, the second wavelength absorbance and the third wavelength absorbance.

[0012] To improve the accuracy of total nitrogen detection, the first mapping relationship is further defined as C = f(A1, A2), where C is total nitrogen, A1 is the absorbance at the first wavelength, and A2 is the absorbance at the second wavelength. The second mapping relationship is C=f(A1,A2)+g(A3), where A3 is the absorbance at the third wavelength, and f and g are functional relationships.

[0013] To reduce the complexity of the second mapping relationship while ensuring the accuracy of total nitrogen detection, g(A3) = kA3, where k is a constant.

[0014] To obtain an accurate g(A3), further, in step (A4), , a and b are constants, and n is the dilution factor of the first water sample in step (A3). Given this ratio, it is not necessary to obtain the specific values ​​of C1 and C2 in the above steps.

[0015] To efficiently obtain an accurate first mapping relationship, the method for obtaining the first mapping relationship is further as follows: Standard solutions with total nitrogen of zero and CO were respectively introduced into the detection chamber 32, where CO≠0. The absorbance at the first wavelength and the absorbance at the second wavelength were obtained respectively, and the first mapping relationship was obtained using the total nitrogen value.

[0016] To verify whether the second mapping relationship meets the requirements, further verification is performed between steps (A5) and (A6): The first water sample mixed standard solution, after digestion, enters the detection chamber 32, and the total nitrogen C4 of the mixed solution is obtained by using the second mapping relationship; Determine whether (C4-C1) / (C3-C1) is greater than the second threshold, where C3 is the theoretical total nitrogen value of the mixture; If the result is yes, proceed to step (A6); If the result is negative, return to step (A2).

[0017] To achieve the digestion and detection of water samples, further, such as Figure 2 As shown, the water sample enters the digestion tank 31 in the following manner: The first pump 11 draws water samples, which then enter the digestion tank 31 through the multi-channel directional valve 21. The upstream valve 41 and the downstream valve 42 are closed, and the water samples in the digestion tank 31 are digested. The method by which the water sample enters the testing chamber 32 after digestion is as follows: When valve 41 is opened upstream of digestion tank 31, the water sample in digestion tank 31 enters the detection chamber directly through the second pump 12 downstream of detection chamber 32 without passing through multiple channel directional valves 21, that is, through upstream valve 41 and switch valve 43.

[0018] Furthermore, the turbidity is obtained as follows: Under the suction of the second pump 12, the unknown water sample enters the detection chamber 32 in reverse through the second pump 12.

[0019] In order to avoid the multi-channel directional valve 21 when sharing pipelines and transferring water samples (transferring digested water samples to the testing chamber 32), the port of the multi-channel directional valve, the inlet of the digestion tank 31 and the inlet of the testing chamber 32 are respectively connected to the tee 51.

[0020] Example 2.

[0021] An application example of the total nitrogen analysis method in Example 1 of the present invention.

[0022] In this application example, such as Figure 1 As shown, the total nitrogen analysis method includes the following steps: (A1) such as Figure 2 As shown, under the suction of the second pump 12 (a peristaltic pump is used in this embodiment), the unknown water sample enters the detection chamber 32 in reverse through the second pump 12.

[0023] Light emitted from light source 61 (using a xenon lamp with emission wavelengths including 220nm, 275nm, and 660nm) enters detection chamber 32. Detector 62 outputs the received light intensity, analyzes it to obtain the turbidity of the unknown water sample, and determines whether the turbidity exceeds a first threshold (turbidity 100 NTU, absorbance at 660nm 0.438; others such as 0 NTU, absorbance 0.001; 20 NTU, absorbance 0.079; 40 NTU, absorbance 0.169; 60 NTU, absorbance 0.261; 90 NTU, absorbance 0.391; 100 NTU, absorbance 0.438; 110 NTU, absorbance 0.480). The method of obtaining turbidity is existing technology in this field.

[0024] If the result is yes, proceed to step (A2); if the result is no, proceed to normal analysis, i.e., the total nitrogen analysis method in the prior art. (A2) Establish a first mapping relationship between total nitrogen and absorbance using standard solution. The first mapping relationship is the correspondence between total nitrogen and absorbance at a first wavelength and absorbance at a second wavelength. Under the action of the first pump 11 (a plunger pump is used in this embodiment) and the multi-channel directional valve 21, the standard solution of total nitrogen C0 (C0≠0) enters the digestion tank through the multi-channel directional valve 21, the three-way valve 51 and the upstream valve 41 respectively. The reagent in the reagent tank 71 enters the digestion tank through the multi-channel directional valve 21, the three-way valve 51 and the upstream valve 41 respectively. Then the upstream valve 41 and the downstream valve 42 are closed, and the standard solution is digested.

[0025] With both upstream valve 41 and downstream valve 42 open, the digested standard solution, under the suction of the second pump 12, sequentially passes through upstream valve 41, tee 51 and valve 43, and enters the detection chamber 32 in the forward direction.

[0026] The light emitted by the light source 61 enters the detection chamber 32, and the detector 62 outputs the received light intensity to obtain the absorbance at the first wavelength of 220nm and the absorbance at the second wavelength of 275nm.

[0027] Similarly, a standard solution with zero total nitrogen enters the detection chamber 32 to obtain absorbance at a first wavelength of 220 nm and a second wavelength of 275 nm.

[0028] The first mapping relationship is obtained based on the above absorbance values ​​and total nitrogen values: a and b are both constants, and f is a function.

[0029] (A3) Under the action of the first pump 11 (a plunger pump is used in this embodiment) and the multi-channel directional valve 21, the first water sample enters the digestion tank 31 through the multi-channel directional valve 21, the three-way valve 51 and the upstream valve 41 respectively. The reagent in the reagent tank 71 enters the digestion tank 31 through the multi-channel directional valve 21, the three-way valve 51 and the upstream valve 41 respectively. Then the upstream valve 41 and the downstream valve 42 are closed, and the first water sample is digested.

[0030] With both upstream valve 41 and downstream valve 42 open, the first water sample after digestion is drawn in sequence through upstream valve 41, tee 51 and valve 43, i.e., without passing through multiple channel directional valve 21, and enters the detection chamber 32 in the forward direction.

[0031] Light emitted from light source 61 enters detection chamber 32, and detector 62 outputs the received light intensity to obtain the absorbance A at the first wavelength of 220nm. 11 Absorbance A at the second wavelength of 275nm 21 and the absorbance A at the third wavelength of 660nm 31 And using the second mapping relationship C=f(A1,A2)+g (A3), the total nitrogen C1 of the first water sample is obtained, where g is a functional relationship.

[0032] C1=f(A 11 A 21 )+g (A 31 )= f(A 11 A 21 )+ kA 31 It is neither possible nor necessary to give a specific value for C1.

[0033] The second mapping relationship is the correspondence between total nitrogen and absorbance at the first wavelength, the second wavelength, and the third wavelength. (A4) Dilute the first water sample according to the dilution factor n, and send it to the digestion tank 31 for digestion in the manner of step (A3). Then, send the diluted water sample after digestion forward into the detection chamber 32 to obtain the absorbance A at the first wavelength. 12 Absorbance A at the second wavelength 22 and the absorbance at the third wavelength A 32 And the total nitrogen C2 of the water sample was obtained using the second mapping relationship; C2 = C1 / n = f(A) 12 A 22 )+ kA 32 It is neither possible nor necessary to provide a specific value for C2. (A5) Determine the second mapping relationship using the first mapping relationship, total nitrogen C1 and total nitrogen C2.

[0034] .

[0035] The first water sample mixed standard solution is digested in the manner described above, and then enters the detection chamber 32 to obtain the total nitrogen C4 using the second mapping relationship.

[0036] Determine whether (C4-C1) / (C3-C1) is greater than 0.8, where C3 is the theoretical total nitrogen value of the mixture.

[0037] If the result is yes, proceed to step (A6); if the result is no, return to step (A2).

[0038] (A6) The water sample is digested and then enters the detection chamber 32 in accordance with the above method. The total nitrogen of the unknown water sample is obtained by using the second mapping relationship, the first wavelength absorbance, the second wavelength absorbance and the third wavelength absorbance.

[0039] Actual water sample 1: 1. The instrument was used for testing at a total nitrogen value of 0-2 mg / L (range 1). The absorbance of the standard solution with a total nitrogen value of 0 was 0.0888 at 220 nm and 0.0199 at 275 nm. The absorbance of the standard solution with a total nitrogen value of 2 mg / L was 1.0076 at 220 nm and 0.0278 at 275 nm. The first mapping relationship obtained is: C = 2.2148 * (A1 - 2A2) - 0.1085, that is, a = 2.2148, b = -0.1085.

[0040] 2. In the test results, A 11 A is 1.01. 21 A is 0.47. 31 The value is 0.40, and n=2.

[0041] A 12 A is 0.588. 22 A is 0.213. 32 It is 0.130.

[0042] 3. The second mapping relationship is obtained: C=2.2148*(A1-2A2) +1.344 A3-0.1085.

[0043] 4. In verifying the second mapping relationship, 0.07 mL of mother liquor (total nitrogen value 1000 mg / L) was added to 99.93 mL of the first water sample to obtain a mixed solution. Using the above method and the second mapping relationship, the total nitrogen C4 of the mixed solution was obtained as 1.988 mg / L.

[0044] The total nitrogen C1 of the first water sample was measured to be 1.344 mg / L using the above method. Based on the total nitrogen C1 and volume of the first water sample, and the total nitrogen and volume of the mother liquor, the theoretical total nitrogen value C3 of the mixed liquor was calculated to be 2.043 mg / L, with a concentration value of [missing value].

[0045] (C4-C1) / (C3-C1)=0.92>0.8, indicating that the above method and the second mapping relationship both meet the requirements.

[0046] Actual water sample 2: 1. The instrument was used for testing at a range of 0-10 mg / L (range 3). The absorbance of the standard solution with a total nitrogen value of 0 was 0.0882 at 220 nm and 0.0176 at 275 nm. The absorbance of the standard solution with a total nitrogen value of 2 mg / L was 1.003 at 220 nm and 0.025 at 275 nm. The first mapping relationship was obtained. C = 11.111 * (A1 - 2A2) - 0.5889, that is, a = 11.111, b = -0.5889.

[0047] 2. In the test results, A 11 A is 0.683. 21 A is 0.400. 31 The value is 0.440, and n=2.

[0048] A 12 A is 0.350. 22 A is 0.200. 32 It is 0.230.

[0049] 3. The second mapping relationship is obtained: C=11.111*(A1-2A2) +1.800A3-0.5889.

[0050] 4. In verifying the second mapping relationship, 0.35 mL of mother liquor (total nitrogen value 1000 mg / L) was added to 99.65 mL of the first water sample to obtain a mixed solution. Using the above method and the second mapping relationship, the total nitrogen C4 of the mixed solution was obtained as 9.989 mg / L.

[0051] The total nitrogen C1 of the first water sample was measured to be 6.911 mg / L using the above method. Based on the total nitrogen C1 and volume of the first water sample, and the total nitrogen and volume of the mother liquor, the theoretical total nitrogen value C3 of the mixed liquor was calculated to be 10.387 mg / L, with a concentration value of [missing value].

[0052] (C4-C1) / (C3-C1)=0.89>0.8, indicating that the above method and the second mapping relationship both meet the requirements.

[0053] Actual water sample 3: 1. The instrument was used for testing at 0-10 mg / L (range 3). The absorbance of the standard solution with a total nitrogen value of 0 was: 0.0882 at 220 nm and 0.0176 at 275 nm. The absorbance of the standard solution with a total nitrogen value of 2 mg / L was: 1.003 at 220 nm and 0.025 at 275 nm. The first mapping relationship was obtained. C = 11.111 * (A1 - 2A2) - 0.5889, that is, a = 11.111, b = -0.5889.

[0054] 2. In the test results, A 11 A is 0.755. 21 A is 0.510. 31 The value is 0.470, and n=2.

[0055] A 12 A is 0.394. 22 A is 0.290. 32 It is 0.280.

[0056] 3. The second mapping relationship is obtained: C=11.111*(A1-2A2) +1.778A3-0.5889.

[0057] 4. In verifying the second mapping relationship, 0.3 mL of mother liquor (total nitrogen value 1000 mg / L) was added to 99.7 mL of the first water sample to obtain a mixed solution. Using the above method and the second mapping relationship, the total nitrogen C4 of the mixed solution was obtained as 8.675 mg / L.

[0058] The total nitrogen C1 of the first water sample was measured to be 5.752 mg / L using the above method. Based on the total nitrogen C1 and volume of the first water sample, and the total nitrogen and volume of the mother liquor, the theoretical total nitrogen value C3 of the mixed liquor was calculated to be 8.738 mg / L, with a concentration value of [missing value].

[0059] (C4-C1) / (C3-C1)=0.98>0.8, indicating that the above method and the second mapping relationship both meet the requirements.

Claims

1. A total nitrogen analysis method comprising the following steps: (A1) Obtain the turbidity of an unknown water sample and determine whether the turbidity exceeds a threshold; If the result is yes, go to step (A2); if the result is no, go to normal analysis; (A2) establishing a first mapping relationship between total nitrogen and absorbance, wherein the first mapping relationship is a corresponding relationship between total nitrogen and absorbance at a first wavelength and absorbance at a second wavelength; (A3) After digestion, the first water sample enters the detection chamber and obtains the absorbance of the first wavelength A 11 , Absorbance at the second wavelength A 21 and the third wavelength absorbance A 31 , and using the second mapping relationship to obtain the total nitrogen C1 of the first water sample; the second mapping relationship is the correspondence between the total nitrogen and the absorbance at the first wavelength, the absorbance at the second wavelength, and the absorbance at the third wavelength; (A4) diluting the first water sample, and after digestion, entering the detection chamber to obtain the absorbance A at the first wavelength 12 , Absorbance at the second wavelength A 22 and the third wavelength absorbance A 32 , and use the second mapping relationship to obtain the total nitrogen C2 of the water sample; (A5) determining a second mapping relationship using the first mapping relationship, total nitrogen C1, and total nitrogen C2; (A6) After digestion, the unknown water sample enters the detection chamber, and the total nitrogen of the unknown water sample is obtained using the second mapping relationship, the absorbance at the first wavelength, the absorbance at the second wavelength, and the absorbance at the third wavelength.

2. The total nitrogen analysis method according to claim 1, characterized in that The first mapping relationship is, C=f(A1,A2), C is total nitrogen, A1 is the absorbance at the first wavelength, and A2 is the absorbance at the second wavelength; The second mapping relationship is C=f(A1, A2)+g (A3), A3 is the absorbance at the third wavelength, and f and g are functional relationships.

3. The total nitrogen analysis method according to claim 2, characterized in that g(A3)=kA3, k is a constant.

4. The total nitrogen analysis method according to claim 2, characterized in that In step (A4), , , a and b are constants, and n is the dilution multiple of the first water sample in step (A4).

5. The total nitrogen analysis method according to claim 1, characterized in that The first mapping relationship is obtained as follows: The standard solutions of total nitrogen being zero and C0 enter the detection chamber respectively, C0≠0, and the absorbance of the first wavelength and the absorbance of the second wavelength are obtained respectively, and the first mapping relationship is obtained using the total nitrogen value.

6. The total nitrogen analysis method according to claim 1, characterized in that: Verify between step (A5) and step (A6): The first water sample is mixed with a standard solution, and the mixed solution enters the detection chamber after being digested, and the total nitrogen C4 of the mixed solution is obtained by using a second mapping relationship; Determine whether (C4- C1) / (C3- C1) is greater than a second threshold, where C3 is a theoretical value of total nitrogen in the mixed liquid; If the answer is yes, go to step (A6); If the answer is no, return to step (A2).

7. The total nitrogen analysis method according to claim 1, characterized in that: The water sample enters the digestion tank in the following ways: The first pump draws water samples, which then enter the digestion tank through the multi-channel directional valve. The valves upstream and downstream of the digestion tank are closed, and the water samples in the digestion tank are digested. The way the water sample enters the detection chamber after digestion is: The valve upstream of the digestion tank is opened, and under the suction of the second pump downstream of the detection chamber, the water sample in the digestion tank enters the detection chamber in a positive direction without passing through the multi-channel selection valve.

8. The total nitrogen analysis method according to claim 7, characterized in that: The turbidity is obtained as follows: Under the suction of the second pump, the unknown water sample enters the detection chamber in the reverse direction through the second pump.

9. The total nitrogen analysis method according to claim 7, characterized in that: The port of the multi-channel directional selector valve, the inlet of the digestion tank and the inlet of the detection chamber are respectively connected with three-ways.

10. The total nitrogen analysis method according to claim 1, characterized in that: The first wavelength is 220 nm, the second wavelength is 275 nm, and the third wavelength is 660 nm.

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