CN109799203B - Wide-range high-precision spectrum detection method for COD concentration in water body - Google Patents
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Abstract
The invention provides a wide-range high-precision spectrum detection method for COD concentration in a water body, which comprises the following steps: measuring N standard COD solution samples with concentration gradients by using an ultraviolet spectrophotometer or a spectrum measuring device with corresponding functions, and calculating absorbance values of N groups of full spectrum data at each wavelength; calculating the functional relation between the absorbance and the COD concentration at each wavelength by least square fitting; selecting proper n wavelengths as modeling wavelengths; respectively calculating the linear relation between absorbance and concentration in the optimal measurement concentration range corresponding to each wavelength at the n wavelengths; measuring and calculating the absorbance of the COD solution with unknown concentration at n wavelengths; selecting the optimal measurement wavelength corresponding to the concentration of the COD solution; calculating the COD concentration value of the unknown solution. The invention applies the full spectrum data processing and analyzing technology, can ensure high precision and obviously enlarge the concentration measuring range of the COD solution.
Description
Technical Field
The invention relates to the field of water quality detection and analysis, in particular to the technical field of a COD concentration detection method and environmental optical detection, and specifically relates to a wide-range high-precision spectrum detection method for COD concentration in a water body.
Background
Chemical Oxygen Demand (COD) refers to the amount of oxidant consumed when reducing substances in a water body are oxidized by a strong oxidant under a certain condition, and is a comprehensive index for representing the reducing substances in the water, wherein the amount of oxidant is converted into the concentration of oxygen in mg/L. In recent years, the national economy of China is rapidly developed, but the environmental pollution problem is increasingly serious, especially the water body pollution problem. The COD concentration index can be used for judging the relative content of organic matters in the water body, and is one of the most important organic pollution comprehensive indexes in environmental monitoring. At present, most of domestic water quality COD detection is based on a chemical method of national standard or an improvement method thereof. The measurement process needs heating digestion and titration, and the required chemical reagents have various types, and have the problems of secondary pollution, complex operation, long time consumption, slow analysis speed and poor stability.
The ultraviolet-visible absorption spectrometry is a method based on Lambert-beer's law for quantitative analysis of the degree of absorption of characteristic electromagnetic radiation by molecules or ions of a substance to be detected, and is a purely physical optical detection method without chemical reagents and secondary pollution. In recent years, a great deal of research on ultraviolet absorption water quality detection technology is carried out at home and abroad. At present, the COD concentration is measured by mostly utilizing the absorbance at 254nm, the method is simple and easy to implement, but due to the influences of factors such as low resolution of an instrument, nonlinearity generated by the application of Lambert-beer law in the measurement of a high concentration section and the like, the COD concentration is calculated by only using the absorbance value of single wavelength or specific multiple wavelengths, the measurement range is small, and the precision is low.
If the COD content of low concentration or high concentration needs to be measured, firstly, the COD content is measured by adjusting the optical path, and a sample cell with a specific optical path can be selected according to the requirements of users. If an instrument using a 10mm optical path sample cell is used, the measurement range is small and is 10-200mg/L, the precision is high, and the accuracy is 1 mg/L; the instrument using the 1mm optical path sample cell has a large measurement range of 100-2000mg/L, but has lower precision and 10mg/L accuracy. The detection precision of the instrument can be reduced while the measuring range is expanded by changing the optical path; and if the water quality with a large concentration span range needs to be measured, a plurality of instruments need to be used, and the measurement cost is increased. Secondly, the measurement range is expanded by adjusting the power of the light source or the number of times of the light source flickering, but the method cannot calculate the accurate COD concentration value through the spectral absorption data obtained by one-time measurement for the sample with unknown COD concentration.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a COD concentration full-spectrum analysis detection method which has high detection speed, does not need chemical reagents, does not need to replace a sample cell for adjusting the optical path or adjust a light source and is based on an ultraviolet-visible absorption method, and can ensure the precision and simultaneously expand the measurement range.
The invention provides a wide-range high-precision spectrum detection method for COD concentration in a water body, which comprises the following steps:
modeling process:
preparing N groups of COD standard solutions with certain concentration gradient as modeling samples, and measuring the absorbance of each modeling sample in a certain spectral range (such as 200nm-600nm) by using an ultraviolet-visible spectrophotometer or a spectral measurement device, wherein the absorbance is called full-spectrum data;
fitting and calculating the functional relation between the absorbance at each wavelength of the modeling sample and the concentration of the COD standard solution by a fitting method such as a least square method;
then selecting n wavelengths as modeling wavelengths (n) according to the linearity of the absorbance and concentration at each wavelength>2) (ii) a The modeling wavelength selects a COD concentration range with a linear correlation coefficient larger than 0.99 (can be other values according to the precision requirement) as a measurable linear concentration range, and the selected modeling wavelength is numbered as lambda according to the measurable linear concentration range corresponding to the modeling wavelength from small to large in sequence1，λ2，……，λnIn which λ is to be ensured1The highest concentration measured at the wavelength is equal to λ2The lowest concentration measured at the wavelength, and so on, enables the measurement range to be spread from small to large;
the concentration range corresponding to the optimal linear section of the relation between the absorbance and the COD concentration at each wavelength is the optimal measurable linear concentration range corresponding to the wavelength;
the threshold value of the optimal measurable linear concentration range corresponding to each wavelength is the lowest concentration and the highest concentration of the concentration section, the highest concentration absorbance and the lowest concentration absorbance of the measurable linear concentration range of the modeling wavelength are calculated, and the linear relation between the absorbance and the concentration of the modeling wavelength in the measurable linear concentration range is calculated through a least square method;
calculating the highest concentration absorbance and the lowest concentration absorbance of the measurable linear concentration range of the modeling wavelength, and fitting and calculating the linear relation between the absorbance and the concentration of the modeling wavelength in the measurable linear concentration range by a fitting method;
a COD solution of unknown concentration was measured comprising: measuring full spectrum data of the COD solution with the unknown concentration, and calculating the absorbance of the COD solution with the unknown concentration at n wavelengths according to n modeling wavelengths selected from the modeling sample; selecting the optimal measurement wavelength corresponding to the concentration of the COD solution with the unknown concentration; and calculating the COD concentration value of the unknown solution according to the fitting function relationship between the concentration at the modeling wavelength and the absorbance.
The measurement process comprises the following steps:
the method for measuring the COD solution with unknown concentration comprises the following steps:
the measured instrument parameter setting is the same as the modeling process, the full spectrum data of the COD solution with unknown concentration is measured, and the absorbance A of the COD solution with unknown concentration at n wavelengths is calculated according to n modeling wavelengths selected from the modeling sample1,A2，……，An；
Selecting the optimal measurement wavelength corresponding to the concentration of the COD solution with the unknown concentration; the absorbance A of the COD solution with unknown concentration is measured1,A2，……，AnSequentially comparing the model wavelength lambda in the model sample with the model wavelength lambda1，λ2，……，λnThe absorbance A of the COD solution with unknown concentration is compared when the absorbance A of the COD solution with unknown concentration is obtainedmLess than the maximum concentration absorbance at the wavelength of the modeling wavelength λ m (1. ltoreq. m. ltoreq.n), the λ mmThe wavelength is the optimal measuring wavelength of the solution;
and calculating the COD concentration value of the unknown solution according to the fitting function relationship between the concentration at the modeling wavelength and the absorbance.
Preferably, an ultraviolet-visible spectrophotometry system is adopted to measure the absorption spectrum of the template sample, the wavelength range is 200-600nm, the spectral bandwidth is less than 10nm, and the optical path is 10 mm.
Preferably, a spectrum measuring device system is adopted to measure the absorbance full spectrum data of the modeling sample, and the spectrum measuring device comprises a light source, a collimation system, a sample pool, a convergence system and a spectrometer, wherein light emitted by the light source enters the sample pool through the collimation system, is absorbed by the modeling sample and then exits the sample pool, and is subjected to light splitting detection by the spectrometer after passing through the convergence system.
Preferably, configuring N groups of different COD concentration gradient solutions as modeling samples comprises: preparing N standard solutions with a certain COD concentration gradient as modeling samples, repeatedly measuring each modeling sample for M times to obtain N groups of full spectrum data with different COD concentrations, and calculating the average value of the M full spectrum data at each wavelength in each group to obtain N groups of full spectrum data with different COD concentrations.
Preferably, according to a formula, the light intensity values of N groups of different concentrations of the modeling samples at each wavelength are calculated to be I,
wherein A is the absorbance value, I0The intensity of light when the COD concentration is zero;
calculating absorbance values of the N groups of different concentrations of the modeling samples at each wavelength according to Lambert-beer law,
A＝KCL
where K is the absorption constant, C is the COD concentration value, and L is the optical path length.
Preferably, the modeling wavelength is a wavelength with small change of absorbance under the same concentration gradient in a high concentration range of COD, and a wavelength with large change of absorbance under the same concentration gradient in a low concentration range of COD.
Preferably, the method is performed according to the following steps:
s1, selecting potassium hydrogen phthalate to configure N groups of COD standard solutions with certain concentration gradient as modeling samples, measuring the absorption spectrum of each modeling sample, wherein the wavelength range is 200-600nm, the spectral bandwidth is less than 10nm, and repeatedly measuring the modeling samples for M times to obtain N groups of full-spectrum data with different COD concentrations;
s2, calculating the average value of M full spectrum data at each wavelength in each group as the spectrum data of the group COD concentration;
s3, calculating absorbance values of the N groups of modeling samples with different concentrations at each wavelength;
the method specifically comprises the following steps:
according to a formula, calculating to obtain the light intensity value I of N groups of samples with different concentrations at each wavelength,
wherein A is the absorbance value, I0The intensity of light when the COD concentration is zero;
calculating the absorbance values of N groups of samples with different concentrations at each wavelength according to the Lambert-beer law;
A＝KCL
where K is the absorption constant, C is the COD concentration value, and L is the optical path length.
As shown in FIG. 2, it can be seen that the COD solution has absorption not only at 254nm, but also in the wavelength range of 220nm to 300nm, and the wavelengths are different, and the corresponding K values are different, resulting in different absorbances of the wavelengths at the same concentration.
S4, calculating the functional relation between the absorbance and the COD concentration at each wavelength by least square fitting according to the full-wave-band absorbance values of the COD standard solutions with different concentrations;
s5, selecting n wavelengths as modeling wavelengths, wherein the COD concentration range corresponding to the optimal linear section of the relation between the absorbance and the COD concentration at each modeling wavelength is the optimal measurable linear COD concentration range corresponding to the modeling wavelength, and each modeling wavelength is numbered as lambda according to the number of the corresponding optimal measurable linear COD concentration range from small to large1，λ2…λn(ii) a Therefore, the measurement range is expanded, and the measurement precision is ensured.
The optimal measurable linear COD concentration range of the modeling wavelength refers to that the COD concentration range with the linear correlation coefficient larger than 0.99 is selected as a measurable concentration range of the modeling wavelength;
s6, the threshold value of the optimal measurable linear concentration range corresponding to each modeling wavelength is the lowest concentration and the highest concentration of the optimal measurable linear concentration range, the highest concentration absorbance and the lowest concentration absorbance value of the measurable concentration range of the selected n modeling wavelengths are calculated, and the linear relation between the absorbance and the concentration of the n modeling wavelengths in the measurable concentration range is calculated through a least square method;
wherein the highest concentration absorbance (A) of n of said modeled wavelengths corresponding to a measurable linear concentration rangeh1，Ah2，……，Ahn) And minimum concentration absorbance (A)l1，Al2，……，Aln) As the basis for selecting the range when detecting unknown COD concentration.
S7, taking the COD solution with unknown concentration as a test sample, measuring the full spectrum data of the test sample, and calculating the absorbance (A) of the COD solution with unknown concentration at n wavelengths according to the selected n modeling wavelengths by using the absorbance calculation formula in S31,A2，……，An)；
S8, selecting the optimal measurement wavelength corresponding to the concentration of the COD solution of the test sample, namely, the absorbance A of the test sample1,A2，……，AnSequentially comparing the model wavelength lambda in the model sample with the model wavelength lambda1，λ2，……，λnWhen the absorbance of the test sample is AmLess than said modeling wavelength λmThe modeled sample λ at the highest concentration absorbance at wavelengthmThe wavelength is the optimal measurement wavelength for the solution.
And S9, calculating the COD concentration value of the test sample according to the linear fitting function of the absorbance and the concentration in the S6.
Preferably, the n modeling wavelengths selected in S5 mean that the absorbance change rates are different under the equal concentration gradient, so that the linear relationship between absorbance and concentration of each wavelength is good only in a certain concentration range; and in the COD high concentration range, the wavelength with small change of the absorbance under the same concentration gradient is used as the modeling wavelength, and in the COD low concentration range, the wavelength with large change of the absorbance under the same concentration gradient is used as the modeling wavelength.
More preferably, the S8: selecting the wavelength of the test sample according to n modeling wavelengths selected in S5, and enabling the wavelength of the test sample to be lambda1To lambdanArranged from λ1Initially, the test samples are compared at λ1Absorbance A at wavelength1Whether or not it is greater than lambda1Absorbance A at the highest concentration at wavelengthh1If less than, the COD solution concentration range of the test sample is lambda1Within the wavelength range, if the wavelength is greater than or equal to Ah1Comparing said test sample at λ2Absorbance A at wavelength2Whether or not greater than said lambda2Absorbance A at the highest concentration at wavelengthh2And so on until a selected wavelength λ is foundm(m is more than or equal to 1 and less than or equal to n), and the absorbance A of the test sample at the wavelengthmLess than λ in the modeled wavelengthmAbsorbance A at the highest concentration at wavelengthhmI.e. λmThe wavelength is the optimal measurement wavelength for the solution.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, by analyzing and processing the spectrum full-spectrum data of the COD sample solution, the unknown sample is measured only once, and the sample pool does not need to be replaced for multiple times or the power and the flicker frequency of the light source do not need to be adjusted, so that the test time and the cost are saved.
The linear correlation coefficient between the COD concentration and the absorbance in the measurable concentration range at each optimal wavelength is not lower than 0.9964, and the measurement error is about 0.29 percent. The result can show the feasibility of the full spectrum measurement and analysis method, and the method can remarkably enlarge the measurement range of the COD concentration while ensuring high precision.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a flow chart of a method in a preferred embodiment of the invention;
FIG. 2 is a full spectrum of absorbance of COD solution with various concentrations in a preferred embodiment of the present invention;
FIG. 3 is a graph of COD concentration at a wavelength as a function of absorbance in a preferred embodiment of the invention;
FIG. 4 is a graph of the COD concentration versus absorbance for the wavelength modeled in a preferred embodiment of the present invention over its optimal measured concentration range.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Referring to fig. 1, a flow chart of the wide-range high-precision full spectrum detection method for COD concentration in water according to the present invention is provided, and a description of a specific preferred embodiment of the present invention is provided in conjunction with the flow chart.
In the following examples, the tested samples were prepared standard solutions of potassium hydrogen phthalate in COD, 20 standard solutions with a certain COD concentration gradient were prepared as model samples, the COD concentration range was 0.1mg/L to 900mg/L, and the prepared 20 model samples were numbered as 1, 2, …, i, …, and 20, respectively.
In the following examples, the absorption spectrum of each modeled sample was measured using a spectral measurement device comprising a light source, a collimating system, a sample cell, a converging system and a spectrometer. Light emitted by the light source passes through a quartz sample cell with an incident optical path of 10mm of the collimation system, is absorbed by a water sample and then is emitted, and is subjected to light splitting detection by a spectrometer after passing through the convergence system.
In the following embodiments, the light source can be a wide-band light source (the band includes 200nm to 600nm) such as a xenon lamp, a pulsed xenon lamp, a deuterium lamp, etc.; the collimation system can adopt a concave reflector or a collimation lens plated with an ultraviolet enhanced reflection film; the convergence system can adopt a concave reflector or a convergence mirror plated with an ultraviolet enhanced reflecting film; the spectrometer can adopt a light splitting detection module which can obtain full spectrum data, such as a fiber spectrometer. In other embodiments, the selection of the light source, the collimating system, the converging system, and the spectrometer is not limited to the above, and other selections may be made according to application requirements.
Based on the above, referring to fig. 1, the specific steps of the embodiment are as follows:
step 1: using an experimental device, 20 modeling samples are measured, and each modeling sample is repeatedly measured for 5 times to obtain 20 groups of original spectrum full spectrum data with different COD concentrations, and each group of 5 original spectrum full spectrum data.
Step 2: obtaining the average value of 5 original spectrum data in each group at each wavelength as the full spectrum data of the group of COD concentration;
and step 3: according to the formula, the light intensity value of 20 groups of full spectrum data at each wavelength is calculated to be I.
Wherein A is the absorbance value, I0The intensity of light when the COD concentration was zero.
And calculating the absorbance values of the 20 groups of full spectrum data at all wavelengths according to the Lambert-beer law.
A＝KCL
Where K is the absorption constant, C is the COD concentration value, and L is the optical path length.
As shown in FIG. 2, it can be seen that the COD solution has absorption not only at 254nm, but also in the wavelength range of 220nm to 300nm, and the wavelengths are different, and the corresponding K values are different, resulting in different absorbances of the same concentration at each wavelength.
And 4, step 4: according to the full-wave-band absorbance values of 20 groups of COD standard solutions with different concentrations, the functional relationship between the absorbance and the COD concentration at each wavelength is calculated by least square fitting, as shown in FIG. 3.
And 5: and 3 wavelengths, namely 224.3nm, 258.0nm and 297.3nm are selected as modeling wavelengths, wherein only a concentration section with a linear correlation coefficient larger than 0.99 in each modeling wavelength is selected as a measurable linear concentration range. The linear correlation coefficient in the concentration range of 0.1-10mg/L at the wavelength of 224.3nm is 0.9964; the linear correlation coefficient of the concentration range of 10-200mg/L at the wavelength of 258.0nm is 0.9993; the linear correlation coefficient of the 200-and 900-mg/L concentration band at the wavelength of 297.3nm is 0.9964.
The selected 3 modeling wavelengths are numbered as lambda from small to large according to the corresponding measurable linear concentration range1，λ2，λ3In which λ is to be ensured1The highest concentration measured at the wavelength is equal to λ2The lowest concentration measured at the wavelength, and so on. 224.3nm is lambda1The maximum concentration measured at a wavelength of 224.3nm was 10mg/L, which is equal to the minimum concentration measured at a wavelength of 258.0nm, and the maximum concentration measured at a wavelength of 258.0nm was 200mg/L, which is equal to the minimum concentration measured at a wavelength of 297.3 nm. So that the measurement range can be spread from small to large. Therefore, the measurement range is expanded, and the measurement precision is ensured.
Step 6, calculating the highest concentration absorbance of the corresponding measurable linear concentration ranges of the selected 3 modeling wavelengths as Ah1Is 0.134, Ah2Is 0.700, Ah3The absorbance at the lowest concentration was A at 0.297l1Is 0.009, Al2Is 0.050, Al3Is 0.089, which is used as the basis for selecting the range when detecting the COD concentration. As shown in fig. 4, the linear relationship between the absorbance and the concentration of 3 wavelengths in each measurable linear concentration range was calculated by the least square method as a fitting function to the concentration range.
And 7, preparing a standard solution with the COD concentration of 46mg/L as a test sample. Detecting the test sample by using the device in the step 1, measuring the full spectrum data of the test sample, calculating the absorbance of the test sample at the 3 modeling wavelengths according to the 3 modeling wavelengths selected in the step 5 by using the formula in the step 3, wherein the absorbance at the 3 modeling wavelengths is A1Is 0.344, A2Is 0.170, A3Is 0.021.
Step 8, according to the modeling wavelengths 224.3nm, 258.0nm and 297.3nm selected in the step 5, the wavelengths are set to be lambda1To lambda3Arranged from λ1Initially, the COD solutions of the test samples were compared at lambda1Absorbance A at wavelength1And modeling lambda in the sample1Absorbance A at the highest concentration at wavelengthh1When a is large or small, when A is1Greater than Ah1When the temperature of the water is higher than the set temperature,continue to compare it at λ2Absorbance A at wavelength2Whether greater than λ in the modeled sample2Absorbance A at the highest concentration at wavelengthh2When A is2Is less than Ah2. I.e. lambda2The wavelength is the optimal measurement wavelength for the solution.
Step 9, according to the lambda obtained in the modeling of step 62The linear fitting function y of the absorbance and the concentration at the wavelength is 293.41x-4.0127, and the COD solution of the test sample at lambda is obtained by measurement2Absorbance value A at wavelength2Then, the COD concentration value was calculated to be 45.867 mg/L.
By adopting the embodiment of the invention, the modeling linear correlation can reach 0.9964, and the measurement error is 0.29%.
The experimental results fully prove that compared with the traditional methods of changing the optical path length, the light source power, the flicker frequency and the like, the method provided by the invention only needs to measure an unknown sample once, and after the obtained absorption spectrum full-spectrum information is processed by the data method, the COD concentration can be measured with high precision, the measuring range is remarkably expanded, and the testing time and the testing cost are saved.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.
Claims (7)
1. A wide-range high-precision spectrum detection method for COD concentration in a water body is characterized in that: the method comprises the following steps:
n groups of solutions with different COD concentration gradients are configured to serve as modeling samples, and an ultraviolet spectrophotometer or a spectrum measuring device is used for measuring the absorbance of each modeling sample in a certain spectrum range;
fitting and calculating the functional relation between the absorbance of the modeling sample at each wavelength and the concentration of the COD standard solution by a fitting method;
then selecting n wavelengths as modeling wavelengths according to the linearity of the absorbance and the concentration at each wavelength, wherein n is greater than 2; the modeling wavelength selects a COD concentration range of a corresponding linear correlation coefficient as a measurable linear concentration range according to the precision requirement;
calculating the highest concentration absorbance and the lowest concentration absorbance of the measurable linear concentration range of the modeling wavelength, and fitting and calculating the linear relation between the absorbance and the concentration of the modeling wavelength in the measurable linear concentration range by a fitting method;
a COD solution of unknown concentration was measured comprising: measuring full spectrum data of the COD solution with the unknown concentration, and calculating the absorbance of the COD solution with the unknown concentration at n wavelengths according to n modeling wavelengths selected from the modeling sample; selecting the optimal measurement wavelength corresponding to the concentration of the COD solution with the unknown concentration; calculating the COD concentration value of the unknown solution according to the fitting function relationship between the concentration at the modeling wavelength and the absorbance;
the optimal measurable linear COD concentration range of the modeling wavelength refers to the following steps: selecting a COD concentration range with a linear correlation coefficient larger than 0.99 for the modeling wavelength;
numbering each modeling wavelength from small to large according to the corresponding optimal measurable linear COD concentration range as lambda1，λ2…λnIn which λ is to be ensured1The highest concentration measured at the wavelength is equal to λ2The lowest concentration measured at the wavelength, and so on, enables the measurement range to be spread from small to large;
the selecting of the optimal measurement wavelength corresponding to the concentration of the COD solution with the unknown concentration comprises the following steps: sequentially comparing the absorbance of the COD solution with unknown concentration with the modeling wavelength lambda in the modeling sample1，λ2，……，λnThe absorbance of the COD solution with unknown concentration is sequentially compared, and when the absorbance of the COD solution with unknown concentration is less than the absorbance of the highest concentration at the modeling wavelength, the modeling wavelength is the optimal measurement wavelength of the solution;
the modeling wavelength refers to: in the COD high concentration range, the wavelength with small change of absorbance under the same concentration gradient is adopted, and in the COD low concentration range, the wavelength with large change of absorbance under the same concentration gradient is adopted.
2. The wide-range high-precision spectrum detection method for COD concentration in water body according to claim 1, characterized in that: has one or more of the following characteristics:
-measuring the absorption spectrum of the modeled sample using an ultraviolet-visible spectrophotometric system;
measuring absorbance full spectrum data of the modeling sample by using a spectrum measuring device, wherein the device comprises a light source, a collimation system, a sample cell, a convergence system and a spectrometer, wherein light emitted by the light source enters the sample cell through the collimation system, is absorbed by the modeling sample, then exits from the sample cell, and is received by the spectrometer through the convergence system.
3. The wide-range high-precision spectrum detection method for COD concentration in water body according to claim 1, characterized in that: the method for preparing N groups of solutions with different COD concentration gradients as modeling samples comprises the following steps: preparing N standard solutions with a certain COD concentration gradient as modeling samples, repeatedly measuring each modeling sample for M times to obtain N groups of full spectrum data with different COD concentrations, and calculating the average value of the M full spectrum data at each wavelength in each group to obtain N groups of full spectrum data with different COD concentrations.
4. The wide-range high-precision spectrum detection method for COD concentration in water body according to claim 3, characterized in that: and calculating to obtain the light intensity value I of the N groups of different COD concentrations of the modeling sample at each wavelength, and calculating the absorbance values of the N groups of different COD concentrations of the modeling sample at each wavelength according to the Lambert-beer law.
5. The wide-range high-precision spectrum detection method for the concentration of COD in the water body according to any one of claims 1 to 4, characterized in that: the method comprises the following steps:
s1, selecting potassium hydrogen phthalate to prepare N groups of solutions with different COD concentration gradients as modeling samples, measuring the absorption spectrum of each modeling sample, and repeatedly measuring the modeling samples for M times to obtain N groups of full spectrum data with different COD concentrations;
s2, calculating the average value of M full spectrum data at each wavelength in each group as the spectrum data of the group COD concentration;
s3, calculating absorbance values of the N groups of modeling samples with different concentrations at each wavelength;
s4, calculating the functional relation between the absorbance and the COD concentration at each wavelength by least square fitting according to the full-wave-band absorbance values of the COD standard solutions with different concentrations;
s5, selecting n wavelengths as modeling wavelengths, wherein the COD concentration range corresponding to the optimal linear section of the relation between the absorbance and the COD concentration at each modeling wavelength is the optimal measurable linear COD concentration range corresponding to the modeling wavelength, and each modeling wavelength is numbered as lambda according to the number of the corresponding optimal measurable linear COD concentration range from small to large1，λ2…λn；
The optimal measurable linear COD concentration range of the modeling wavelength refers to the COD concentration range with the linear correlation coefficient larger than 0.99 selected by the modeling wavelength;
s6, the threshold value of the optimal measurable linear concentration range corresponding to each modeling wavelength is the lowest concentration and the highest concentration of the optimal measurable linear concentration range, the highest concentration absorbance and the lowest concentration absorbance value of the measurable concentration range of the selected n modeling wavelengths are calculated, and the linear relation between the absorbance and the concentration of the n modeling wavelengths in the respective optimal measurable concentration range is calculated through a least square method;
s7, taking the COD solution with unknown concentration as a test sample, measuring the full spectrum data of the test sample, and calculating the absorbance of the test sample at n modeling wavelengths to be A according to n modeling wavelengths selected by the modeling sample1,A2，……An；
S8, selecting the optimal measurement wavelength corresponding to the concentration of the COD solution of the test sample, namely, the absorbance A of the test sample1,A2，……，AnSequentially comparing the model wavelength lambda in the model sample with the model wavelength lambda1，λ2，……，λnWhen the absorbance of the test sample is AmLess than said modeling wavelength λmThe modeled sample λ at the highest concentration absorbance at wavelengthmThe wavelength is the optimal measurement wavelength of the solution;
and S9, calculating the COD concentration value of the test sample according to the linear fitting function of the absorbance and the concentration in the S6.
6. The wide-range high-precision spectrum detection method for COD concentration in water body according to claim 5, characterized in that: in the step S5, selecting n modeling wavelengths means that the absorbance change rates are different under the equal concentration gradient, so that the linear relationship between absorbance and concentration of each wavelength is good only in a certain concentration range; and in the COD high concentration range, the wavelength with small change of the absorbance under the same concentration gradient is used as the modeling wavelength, and in the COD low concentration range, the wavelength with large change of the absorbance under the same concentration gradient is used as the modeling wavelength.
7. The wide-range high-precision spectrum detection method for COD concentration in water body according to claim 5, characterized in that: the S8, including: selecting the wavelength of the test sample according to the n modeling wavelengths selected in the S5, and enabling the wavelength of the test sample to be lambda1To lambdanArranged from λ1Initially, the test samples are compared at λ1Absorbance A at wavelength1Whether or not it is greater than lambda1Absorbance A at the highest concentration at wavelengthh1If less than, the COD solution concentration range of the test sample is lambda1Within the wavelength range, if the wavelength is greater than or equal to Ah1Comparing said test sample at λ2Absorbance A at wavelength2Whether or not greater than said lambda2Absorbance A at the highest concentration at wavelengthh2And so on until a selected wavelength λ is foundmAbsorbance A of the test sample at this wavelengthmIs less thanλ in the modeling wavelengthmAbsorbance A at the highest concentration at wavelengthhmI.e. λmThe wavelength is the optimal measurement wavelength for the solution.
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| CN110779889A (en) * | 2019-11-12 | 2020-02-11 | 华润三九（雅安）药业有限公司 | Mathematical model establishing method and device, and total saponin content measuring method and device |
| CN112945876B (en) * | 2021-01-29 | 2023-12-08 | 聚光科技(杭州)股份有限公司 | Method for generating gas vector to be measured |
| CN113740281A (en) * | 2021-08-11 | 2021-12-03 | 同济大学 | Real-time original-state nondestructive monitoring method for pollutants in high-concentration solution |
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| CN116297280B (en) * | 2023-05-22 | 2023-08-01 | 成都博瑞科传科技有限公司 | UCOD coefficient detection method and sensor for organic matters in water based on array spectrum |
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