CN109827922B - Correction method for copper ion interference during determination of nitrate nitrogen in water polluted by copper ions - Google Patents
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Abstract
A method for correcting interference of copper ions during determination of nitrate nitrogen in water polluted by copper ions comprises the steps of repeatedly adding standard curves of nitrate nitrogen in samples of the water polluted by copper ions for multiple times according to an ultraviolet spectrophotometry, calculating the concentration of the nitrate nitrogen in each sample through designing an experimental scheme table, performing nonlinear surface fitting and polynomial fitting correction on the concentration of the nitrate nitrogen in the samples, calculating the concentration of the nitrate nitrogen in the water polluted by copper, and deducting the concentration of the nitrate nitrogen in the water polluted by copper from a test apparent result to obtain the real concentration of the nitrate nitrogen, so that the interference of copper ions during determination of the nitrate nitrogen in the water polluted by copper ions is corrected. The invention has the characteristics of strong reliability and simple operation.
Description
[ technical field ] A method for producing a semiconductor device
The invention relates to a method for measuring nitrate nitrogen in water polluted by copper, in particular to a correction method for copper ion interference during measuring nitrate nitrogen in water polluted by copper ions by an ultraviolet spectrophotometry, which has strong reliability and simple and convenient operation.
[ background of the invention ]
Nitrate (measured as nitrogen) is widely present in natural water bodies, and the content of nitrate in deep groundwater is also high. After the nitrate is taken into a human body, the nitrate can be converted into nitrite through the absorption of microorganisms in intestinal tracts and generates toxic reaction, and nitrate nitrogen or total nitrogen is one of necessary items for environmental monitoring. The standard limits for nitrate nitrogen in existing water are as follows: ground Water quality Standard (GB/T14848-2017) specifies class III Water NO-3N is less than or equal to 20mg/L and is the reference value of human health. Table 2 of the standard of surface water environment quality (GB3838-2002) the limit of nitrate nitrogen in the standard of the surface water source of centralized drinking water is 10 mg/L. The sanitary Standard for Drinking Water (GB 5749 and 2006) stipulates that the nitrogen limit value of nitrate in the conventional index of water quality in the table 1 is 10mg/L, and when the nitrogen limit value is limited by an underground water source, the nitrogen limit value is 20 mg/L. Electroplating pollutant discharge standardStandard "(GB 21900-2008) shows that the total nitrogen of the water pollutant emission limit of the existing enterprises is 30mg/L, and the total nitrogen of the water pollutant emission limit of the newly-built enterprises is 20mg/L in Table 2. At present, the total nitrogen determination method related to nitrate nitrogen or convertible to nitrate mainly comprises ultraviolet spectrophotometry, thymol spectrophotometry, disulfonic acid phenol spectrophotometry, ion chromatography, cadmium column reduction method, gas phase molecular absorption spectrometry and the like, wherein the ultraviolet spectrophotometry and the ion chromatography are most commonly adopted. The ion chromatography can be used for simultaneously measuring the contents of a plurality of anions, is convenient and quick, but can be used for measuring when the content of ions to be measured in a water sample is very high, so that a plurality of ions cannot be measured at one time, a sample needs to be diluted to a proper multiple for improvement, the process cannot be completed at one time, and a large amount of time is consumed. And because the sample injection amount is very small, the pollution of pure water, vessels and a water sample pretreatment process is strictly prevented. In addition, ion chromatographs are expensive and lack operability in terms of their popularity. The ultraviolet spectrophotometry method is simple to operate, high in reliability, wide in measuring range, strong in anti-interference capacity, small in pollution of used chemical reagents, short in analysis period and suitable for measuring mass samples. In the ultraviolet spectrophotometry, dissolved organic substances, surfactants, nitrite nitrogen, hexavalent chromium, bromides, carbonates and bicarbonates influence the determination, and appropriate pretreatment is required. If two times the absorbance at 275nm wavelength is greater than 10% of the absorbance at 220nm wavelength, the method will not work. At present, the domestic standards related to the detection of nitrate nitrogen by an ultraviolet photometry mainly comprise: GB/T6912.1-2006 boiler water and cooling water analysis method. Determination of nitrate and nitrite part 1: nitrate ultraviolet photometry; GB/T8538.42.3-1995A method for testing natural mineral water for drinking by ultraviolet spectrophotometry; GB/T5750.5-2006 drinking water standard test method inorganic nonmetal index ultraviolet spectrophotometry; HJ/T346-2007 water quality nitrate nitrogen determination ultraviolet spectrophotometry (trial); DB 22/T175-1998 ultraviolet spectrophotometry is used for measuring nitrate nitrogen in the drinking water; SL 84-1994 nitrate nitrogen determination (ultraviolet spectrophotometry); DZ/T0064.59-1993 underground water quality testing method. Nitrate was measured by uv spectrophotometry.
When the ultraviolet photometry is adopted to analyze nitrate nitrogen in copper-polluted wastewater, the copper has stronger absorption interference at the 220nm ultraviolet absorption wavelength of nitrate nitrogen, when the concentration of copper ions reaches 0.3mg/L, the copper ions generate 0.01 absorbance at the 220nm wavelength, and when the concentration of the copper ions reaches 10mg/L, the copper ions generate the absorbance as high as about 0.16. The standard HJ/T346-2007 determination of total nitrogen in water by alkaline potassium persulfate digestion UV spectrophotometry only mentions the following aspects in interference and elimination: when the content of iodide ions is more than 2.2 times of the total nitrogen content and the content of bromide ions is more than 3.4 times of the total nitrogen content, interference is generated on the measurement; hexavalent chromium ions and ferric ions in the water sample interfere with the determination, and 1-2 ml of 5% hydroxylamine hydrochloride solution can be added for elimination. Through comparison with a large number of standard analysis methods and on the basis of looking up relevant literature data for analyzing nitrate nitrogen by using an ultraviolet photometry, the evidence that a technical means for eliminating copper ion interference is applied to the nitrate nitrogen ultraviolet photometry is found to be unavailable at present.
[ summary of the invention ]
The invention aims to solve the problems and provides a correction method for copper ion interference during the determination of nitrate nitrogen in water polluted by copper ions by an ultraviolet spectrophotometry, which has strong reliability and simple and convenient operation.
In order to realize the aim of the invention, the invention provides a method for correcting the interference of copper ions during the determination of nitrate nitrogen in copper ion polluted water, which comprises the following steps:
a. preparing a copper standard stock solution, and then respectively diluting the stock solution into copper standard use solutions with various concentrations of 10-1000 mug/mL;
b. respectively preparing nitrate nitrogen standard series solutions with various concentrations of 0.00-2.00 mu g/mL;
c. carrying out multiple standard adding on a nitrate nitrogen standard curve in a water sample polluted by copper ions according to an ultraviolet spectrophotometry, designing an experimental scheme table formed by a plurality of samples of a plurality of groups of experiments, wherein the experimental scheme table comprises a nitrate nitrogen preparation concentration, a copper standard adding volume, an absorbance A220nm and an absorbance A275nm value which correspond to each sample, and calculating to obtain corrected absorbance, actually measured apparent concentration X data and correction factor K data;
d. and c, carrying out nonlinear surface fitting and polynomial fitting correction on the nitrate nitrogen concentration in the sample according to the data in the experimental scheme table in the step c, calculating the nitrate nitrogen concentration in the copper-polluted water, and deducting the concentration from the actually measured apparent concentration X to obtain the real nitrate nitrogen concentration.
In the step a, the concentration of the copper standard stock solution is 10000 mug/mL, and the preparation method comprises the following steps: weighing 1.0023g of 98% pure copper sulfate pentahydrate into a 100mL beaker, adding 3mL of concentrated sulfuric acid, heating on an electric heating plate until smoke is emitted to drive nitrate radical contained as much as possible, cooling, and transferring to a 25mL volumetric flask or a colorimetric tube; and respectively diluting the copper standard stock solution into copper standard use solutions with various concentrations which are gradually decreased according to an equal ratio.
In the step b, nitrate nitrogen standard series solutions with various concentrations and the concentration of 0.00-2.00 mu g/mL are respectively prepared and are increased according to equal ratio.
In the step c, the method for adding the standard curve of the nitrate nitrogen for multiple times comprises the following steps: b, calculating the preparation concentration of the nitrate nitrogen of all the subsequent samples according to the concentration x of the nitrate nitrogen series prepared in the step b and the consumption Vs after each absorbance test; calculating the subsequent Cu standard series concentration y according to the Cu standard concentration, the Cu standard adding volume and the final constant volume, and the consumption Vs after each absorbance test; and fitting a nitrate nitrogen series concentration X-to-correction absorbance curve through the data to calculate the measured apparent concentration X-column data and the correction factor K-column data of the nitrate nitrogen.
In the multi-group experiment, each group of 6 samples reduces Vs in each sample tube after one group of test from each nitrate nitrogen standard series solution, then copper ion concentration is added into each colorimetric tube of each group to reach corresponding concentration, the mixture is shaken up after the volume is fixed back to scale by ultrapure water, and then the labeling step is carried out after the previous group of test is finished.
In step c, the corrected absorbance is: a220nm-2 xa 275nm, and the correction factor K ═ X-X, where X is the measured apparent concentration of nitrate nitrogen and X is the nitrate nitrogen series concentration.
In the step d, the nonlinear surface fitting takes the concentration of the prepared nitrate nitrogen as an X axis, the concentration of a Cu standard series as a y axis, a correction factor K is X-X as a z axis, and after the copper concentration overrun data is eliminated, a function model in originPro software is utilized: poly2D, Levenberg-Marquardt optimization algorithm fitted a surface plot.
The nonlinear surface graph corresponds to the surface equation: k-0.00836-0.07999 x +0.04807y +0.02588x2+4.75835×10-6y2-0.00114xy。
In the step d, the polynomial fitting curve takes Cu standard series concentration as an x axis, and 6 groups of correction factors are (i) - (sixth): and K-X is a plurality of groups of y-axes, and all data are selected to be fitted by utilizing a polynomial fitting function in originPro software to obtain an optimized polynomial fitting parameter table and an optimized polynomial fitting curve chart.
Further, the linear range of the copper ion interference curve is obtained: 1-100 mu g/mL, and the linear fitting curve equation is as follows: k-0.0478417 y-0.03034, and gave an absorbance of 0.16 when referenced at 220nm with pure water as a reference when the copper ion concentration was 10 mg/L.
The contribution of the invention is that the problem of copper ion interference when the nitrate nitrogen in the copper-polluted water is measured by the existing ultraviolet spectrophotometry is effectively solved. According to the method, the standard curve of the nitrate nitrogen in the water sample polluted by the copper ions is repeatedly subjected to multiple-time standard addition according to an ultraviolet spectrophotometry, the nitrate nitrogen concentration in each sample is calculated through designing an experimental scheme table, and nonlinear surface fitting and polynomial fitting correction are performed on the nitrate nitrogen concentration in the sample to obtain the real nitrate nitrogen concentration, so that the copper ion interference during the nitrate nitrogen measurement in the water polluted by the copper ions is corrected. The invention has the characteristics of strong reliability and simple operation.
[ description of the drawings ]
Fig. 1 is a plot of a non-linear Poly2D surface in accordance with the present invention.
FIG. 2 is a graph of the optimized polynomial fit of the present invention.
[ detailed description ] embodiments
The following examples are further illustrative and supplementary to the present invention and do not limit the present invention in any way.
The method for correcting the interference of the copper ions during the determination of the nitrate nitrogen in the water polluted by the copper ions comprises the following steps:
1. copper standard stock solution with the concentration of 10000 mug/mL is prepared
1.0023g of 98% pure copper sulfate pentahydrate are accurately weighed into a 100mL beaker, 3mL of concentrated sulfuric acid is added, the beaker is heated on an electric heating plate until sulfuric acid smoke is emitted to drive nitrate radical contained as far as possible, and the beaker is cooled and transferred into a 25mL volumetric flask or a colorimetric tube. Simultaneously, a full program blank test is carried out, and the other steps are completely consistent except that copper sulfate is not added. And (5) checking whether ultraviolet absorption at 220nm and 275nm exists in the blank of the whole program on a computer.
Wherein, the copper sulfate weighing calculation example:
CuSO4·5H2O→Cu
249.68→63.55
98.0％×m→10000μg/mL×25mL/1000000
m＝((10000*25/1000000)*249.68)/(63.55*98％)＝1.0023g
2. copper standard use solutions with concentrations of 1000. mu.g/mL, 100. mu.g/mL and 10. mu.g/mL were prepared by dilution in sequence
And (3) transferring 2.5mL of the previous-stage copper standard solution to a 25mL colorimetric tube by using a 5mL liquid weighing gun, and fixing the volume to a scale with deionized water to obtain copper standard use solutions with the concentrations of 1000 mu g/mL, 100 mu g/mL and 10 mu g/mL after dilution by 10 times.
3. Preparing nitrate nitrogen standard series solution
0.00mL, 0.25mL, 0.50mL, 1.00mL, 1.50mL, and 2.00mL of the nitrate nitrogen standard solution use solution with the concentration of 25. mu.g/mL (calculated as nitrogen) are respectively transferred to a 25mL colorimetric tube by using a liquid transfer gun, and ultrapure water is added to the colorimetric tube to obtain the nitrate nitrogen standard series solutions with the concentrations of 0.00. mu.g/mL, 0.25. mu.g/mL, 0.50. mu.g/mL, 1.00. mu.g/mL, 1.50. mu.g/mL, and 2.00. mu.g/mL respectively.
4. Absorbance measurement and design Experimental protocol Table
A special glass suction pipe is prepared, a mark is marked on a certain position, the weight of the pure water sucked to the marked mark is weighed in advance, the volume is converted, and the volume is fixed to the volume Vs, wherein the volume Vs is 0.8 mL. Using paired 1cm quartz cuvettes, using ultrapure water to adjust zero at wavelengths of 220nm and 275nm, taking out the sample cuvettes, completely sucking the liquid in the sample cuvettes by using a suction tube, sucking the test liquid to the marked lines of the suction tube, repeatedly using the test liquid to rinse the inner wall of the sample cuvettes, completely sucking the test liquid, then using a glass suction tube to suck the test liquid to the height of 2/3 of the sample cuvettes, and reading the absorbance. And taking out the sample vessel, and transferring the test solution to the original sample tube. And sucking ultrapure water by using a suction tube to repeatedly flush the sample vessel for 2-3 times, sucking residual liquid in the vessel as far as possible, sucking next test solution to the mark scribing position, repeatedly using the test solution to rinse the inner wall of the sample vessel, sucking the test solution to the greatest extent and discarding the test solution, and completing the test of all subsequent samples according to the measurement operation steps.
An experimental scheme table formed by a plurality of sets of experiments is designed, the experiments in the embodiment are divided into nine sets of A, B, C, D, E, F, H, I, J, each set comprises 6 test solutions, each set comprises nitrate nitrogen standard series solutions with the concentrations of 0.00 mu g/mL, 0.25 mu g/mL, 0.50 mu g/mL, 1.00 mu g/mL, 1.50 mu g/mL and 2.00 mu g/mL, each sample tube reduces Vs to 0.8mL after one set of tests are finished, then, the copper ion concentration is respectively added into each colorimetric tube according to each group until the copper ion concentration is 0.020 mug/mL, 0.099 mug/mL, 0.296 mug/mL, 1.087 mug/mL, 3.052 mug/mL, 10.954 mug/mL, 30.604 mug/mL, 109.624 mug/mL and 306.116 mug/mL are back scaled by ultrapure water constant volume and then shaken up, and then the labeling step is carried out after the previous group of tests are finished. The specific test protocol is shown in table 1.
Table 1 experimental design scheme table
5. Fitting of curves
In the 4 th step of grouping experiments, the corresponding Cu standard concentration, Cu standard adding volume, absorbance A220nm and absorbance A275nm of each sample are recorded or read. From the absorbance a220nm and the absorbance a275nm, the corrected absorbance was calculated as a220nm to 2 × a275 nm. Then according to the initial configuration of nitrate nitrogen series concentrations: 0.00. mu.g/mL, 0.25. mu.g/mL, 0.50. mu.g/mL, 1.00. mu.g/mL, 1.50. mu.g/mL, 2.00. mu.g/mL, and the consumption Vs after each absorbance test was 0.8mL, after which the nitrate nitrogen preparation concentration x of the whole sample was calculated. And calculating the subsequent Cu standard series concentration y according to the Cu standard concentration, the Cu standard adding volume and the final constant volume of 25mL, wherein the consumption Vs after each absorbance test is 0.8mL, and the calculation result is shown in Table 1.
In this example, the corrected absorbance was linearly fitted with the nitrate nitrogen concentration x of the data of a 1-a 6 to obtain a curve slope of 0.2561, intercept 0.004793, and correlation coefficient r of 0.99997, and a curve equation was fitted: corrected absorbance is 0.2561 × x + 0.004793. And calculating the measured apparent concentration X column data according to the obtained fitting equation. Let K be X-X, the correction factor K column data is calculated, and the calculation results are shown in table 1.
6. Nonlinear surface correction
Taking the prepared concentration of nitrate nitrogen as an X axis, the standard series concentration of Cu as a y axis, and a correction factor K which is X-X as a z axis, and after removing the over-limit data of copper concentration of lines J1-J6, utilizing a function model in originPro software: poly2D, Levenberg-Marquardt optimization algorithm fitted a surface plot, as shown in FIG. 1.
The obtained nonlinear surface graph corresponds to a surface equation:
K＝z0+a*x+b*y+c*x^2+d*y^2+f*x*y (1)
in the formula:
z0＝0.00836
a＝-0.07999
b＝0.04807
c＝0.02588
d＝4.75835E-6
f＝-0.00114
correlation coefficient R ═ 0.9997
Substituting the above z0, a, b, c, d, f values into the equation to obtain:
K＝0.00836-0.07999x+0.04807y+0.02588x2+4.75835×10-6y2-0.00114xy (2)
7. using non-linear surface correction
In this example, using sample No. H5 as an example, assuming that the exact nitrate nitrogen concentration is unknown, for a sample which is not contaminated by copper, the copper ion concentration y is 30.604 obtained by other known analysis methods, and then the measured apparent concentration X is 2.510 obtained by ultraviolet spectrophotometry, and based on K being X-X, X-K being 2.510-K, the formula (2) is substituted to obtain:
0＝-K+0.00836-0.07999*(2.510-K)+0.04807*30.604+0.02588*(2.510-K)2+4.75835×10-6*30.6042-0.00114*(2.510-K)*30.604 (3)
solving the load term by using excel programming to solve the equation (3) unitary high-order equation, wherein the specific method comprises the following steps: variable cell B3, target cell B4, constraint cell B5 are set. The formula is entered in variable cell B3:
-B3+0.00836-0.07999 (2.51-B3) +0.04807 30.604+0.02588 (2.51-B3) ^2+4.75835 ^ 10 (-6) ^ 30.604^2-0.00114 (2.51-B3) × 30.604, and 0 is input in B5 in the constraint condition cell. Entering a planning solution parameter window, clicking a solution button, obtaining a variable cell K of 1.388 and a target cell of 1.89 multiplied by 10 according to a planning solution result-07And calculating the regression nitrate nitrogen concentration: X-K-2.510-1.388-1.122 μ g/mL. The actual nitrate nitrogen formulation concentration was 1.19, with a relative deviation of (1.122-1.19)/(1.122+1.19) — 2.9%.
In another embodiment, the difference between the apparent nitrate nitrogen concentration and the nitrate nitrogen concentration contributed by the copper ion interference is determined by using a double-fit curve.
8. Polynomial fitting curve
Sequencing rows in the experimental design scheme table of table 1 according to A1-J1, A2-J2, A3-J3, A4-J4, A5-J5 and A6-J6, and marking the concentration y of Cu series, and a correction factor: the K ═ X-X are summarized in the data in table 2.
TABLE 2 Multi-y tabulated data
In the embodiment, the Cu standard series concentration is taken as an x axis, and 6 groups of correction factors (i) to (sixth): and K-X is a plurality of groups of y-axes, and a polynomial fitting function in originPro software is utilized to select all data to be fitted to obtain a full data polynomial fitting parameter table in the table 3.
TABLE 3 full data polynomial fitting parameter table
The row in Table 2 where the Cu standard series concentration is 306.11643 μ g/mL is shielded and then re-fitted to obtain the polynomial fitting parameter table after optimization in Table 4 and the polynomial fitting curve chart after optimization shown in FIG. 2.
TABLE 4 optimized polynomial fitting parameter Table
As shown by comparing Table 4 with Table 3, the correlation coefficient is generally increased from the original two "9" to more than 3 "9", which indicates that the absorbance at the point where the concentration of Cu is 306.11643 μ g/mL has sag. And substituting the fitting parameter average slope and the Intercept average value into an equation K-Intercept + B1 y ^1 to obtain K-0.0478417 y-0.03034, wherein the equation has the significance that if the concentration of copper ions in the water polluted by copper is known to be y, the equivalent nitrate nitrogen concentration can be calculated, and the equivalent nitrate nitrogen concentration can be subtracted from the apparent nitrate nitrogen concentration measured by the ultraviolet photometry as a subtraction term to obtain the real nitrate nitrogen concentration in the sample.
9. Fitting curves using polynomials
In this example, taking sample No. H5 as an example, it is known that the concentration of copper in the sample is 30.604 μ g/mL, and substituting it into y in K0.0478417 y-0.03034, so as to obtain the concentration of nitrate nitrogen generated by copper ion interference, K0.0478417 y-0.03034 0.0478417 30.604-0.03034 μ g/m, measured apparent concentration of nitrate nitrogen is X2.510, and actual concentration of nitrate nitrogen in sample No. H5 is X-K2.510-1.4338 1.076. The formulated concentration of nitrate nitrogen was 1.19, and the relative deviation between them was-5.0% (1.076-1.19)/(1.076+ 1.19).
Therefore, the method repeatedly and repeatedly adds the standard curve of the nitrate nitrogen in the water sample polluted by the copper ions for multiple times according to the ultraviolet spectrophotometry, calculates the nitrate nitrogen concentration in each sample by designing an experimental scheme table, and performs nonlinear surface fitting and polynomial fitting correction on the nitrate nitrogen concentration in the sample to obtain the real nitrate nitrogen concentration, thereby correcting the interference of the copper ions when the nitrate nitrogen in the water polluted by the copper ions is measured. The invention has the characteristics of strong reliability and simple operation.
Although the present invention has been described with reference to the above embodiments, the scope of the present invention is not limited thereto, and the equivalent structures or equivalent processes of the above embodiments, or directly or indirectly applied to other related technical fields, will fall within the scope of the claims of the present invention without departing from the concept of the present invention.
Claims (8)
1. A method for correcting interference of copper ions during measurement of nitrate nitrogen in water polluted by copper ions is characterized by comprising the following steps:
a. preparing a copper standard stock solution, and then respectively diluting the stock solution into copper standard use solutions with various concentrations of 10-1000 mug/mL;
b. respectively preparing nitrate nitrogen standard series solutions with various concentrations of 0.00-2.00 mu g/mL;
c. the method comprises the following steps of performing multiple labeling on a nitrate nitrogen standard curve in a water sample polluted by copper ions according to an ultraviolet spectrophotometry, designing an experimental scheme table formed by a plurality of samples of a plurality of groups of experiments, wherein the experimental scheme table comprises a nitrate nitrogen preparation concentration, a copper standard addition volume, an absorbance A220nm and an absorbance A275nm value corresponding to each sample, and calculating to obtain corrected absorbance, actually measured apparent concentration X data and correction factor K data, wherein the method for performing multiple labeling on the nitrate nitrogen standard curve comprises the following steps: b, calculating the preparation concentration of the nitrate nitrogen of all the subsequent samples according to the concentration x of the nitrate nitrogen series prepared in the step b and the consumption Vs after each absorbance test; calculating the subsequent Cu standard series concentration y according to the Cu standard concentration, the Cu standard adding volume and the final constant volume, and the consumption Vs after each absorbance test; fitting a nitrate nitrogen series concentration X-to-correction absorbance curve through the data, and calculating the actually measured apparent concentration X column data and the correction factor K column data of the nitrate nitrogen, wherein the correction absorbance is as follows: a220nm-2 xa 275nm, wherein the correction factor K is X-X, where X is the measured apparent concentration of nitrate nitrogen and X is the nitrate nitrogen series concentration;
d. and c, carrying out nonlinear surface fitting and polynomial fitting correction on the nitrate nitrogen concentration in the sample according to the data in the experimental scheme table in the step c, calculating the nitrate nitrogen concentration in the copper-polluted water, and deducting the concentration from the actually measured apparent concentration X to obtain the real nitrate nitrogen concentration.
2. The method for correcting interference of copper ions in the determination of nitrate nitrogen in copper ion polluted water as claimed in claim 1, wherein in the step a, the concentration of the copper standard stock solution is 10000 μ g/mL, and the preparation method comprises: weighing 1.0023g of 98% pure copper sulfate pentahydrate into a 100mL beaker, adding 3mL of concentrated sulfuric acid, heating on an electric heating plate until smoke is emitted to drive nitrate radical contained as much as possible, cooling, and transferring to a 25mL volumetric flask or a colorimetric tube; and respectively diluting the copper standard stock solution into copper standard use solutions with various concentrations which are gradually decreased according to an equal ratio.
3. The method for correcting the interference of the copper ions during the measurement of the nitrate nitrogen in the water polluted by the copper ions according to claim 1, wherein in the step b, nitrate nitrogen standard series solutions with various concentrations which are increased according to an equal ratio and have the concentration of 0.00-2.00 mu g/mL are respectively prepared.
4. The method according to claim 1, wherein in the plurality of experiments, each 6 samples in each group are subjected to Vs reduction in each sample tube from each nitrate nitrogen standard series solution after one group of tests, then the copper ion concentration is added to each colorimetric tube of each group to reach the corresponding concentration, the volume is adjusted back to scale by ultrapure water and then shaken up, and then the labeling step is performed after the previous group of tests are completed.
5. The method for correcting interference of copper ions during measurement of nitrate nitrogen in water polluted by copper ions according to claim 1, wherein in the step d, the nonlinear surface fitting is performed by taking the prepared concentration of nitrate nitrogen as an X axis, the standard series concentration of Cu as a y axis, a correction factor K-X-X as a z axis, and after the copper concentration overrun data is eliminated, a function model in originPro software is utilized: poly2D, Levenberg-Marquardt optimization algorithm fitted a surface plot.
6. The method for correcting interference of copper ions in the determination of nitrate nitrogen in water polluted by copper ions according to claim 5, wherein the nonlinear surface graph corresponds to a surface equation: k-0.00836-0.07999 x +0.04807y +0.02588x2+4.75835×10-6y2-0.00114xy。
7. The method for correcting interference of copper ions in the measurement of nitrate nitrogen in water polluted by copper ions according to claim 1, wherein in the step d, the polynomial fitting curve takes the concentration of a Cu standard series as an x-axis, and 6 groups of correction factors are (i) - (phi): and K-X is a plurality of groups of y-axes, and all data are selected to be fitted by utilizing a polynomial fitting function in originPro software to obtain an optimized polynomial fitting parameter table and an optimized polynomial fitting curve chart.
8. The method for correcting the interference of the copper ions during the determination of the nitrate nitrogen in the water polluted by the copper ions according to claim 7, wherein the linear range of the interference curve of the copper ions is obtained by: 1-100 mu g/mL, and the linear fitting curve equation is as follows: k-0.0478417 y-0.03034, and gave an absorbance of 0.16 when referenced at 220nm with pure water as a reference when the copper ion concentration was 10 mg/L.
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