Dual-beam three-wavelength multi-parameter water quality detection device and detection method

Abstract

A kind of dual-beam three-wavelength multi-parameter water quality detection device, including optical path detection part and computing module;The optical path detection part includes: fixed wavelength LED array light source generates optical path, in turn through collimating lens and beam splitter along optical path direction, and is divided into reference light path and detection light path by the beam splitter;The reference light path includes first focusing lens and reference detector;The detection light path includes diaphragm, digestion colorimetric sample cell, plane mirror, second focusing lens and detection detector;Three-wavelength inversion detection algorithm is loaded in the computing module.The present application can effectively reduce the absorbance fluctuation and the precision of detection result caused by light source fluctuation.Single-beam because light source influence, light intensity is easy to fluctuate, therefore absorbance value will also change, if it is the environment of bad on-site environment, it will affect the precision of detection result.The present application uses dual-beam, and the fluctuation of light source is eliminated because of the existence of reference light path.

Description

Technical Field

[0001] This invention discloses a dual-beam, three-wavelength, multi-parameter water quality detection device and method, belonging to the technical field of water quality detection. Background Technology

[0002] Current optical detection technologies are basically single-beam, single-source, single-parameter detection. Firstly, during online detection, they are easily affected by external environmental vibrations, leading to unstable light sources and poor detection accuracy. Secondly, the light sources are mostly broadband, requiring filter devices when measuring single parameters. Thirdly, the sample may contain other ions that interfere with the measurement; currently, the problem of cross-interference cannot be solved, affecting detection accuracy. Therefore, this technical field needs a water quality testing device that balances price and instrument stability while reducing ion cross-interference, offering a high overall cost-performance ratio. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention discloses a dual-beam, three-wavelength, multi-parameter water quality detection device.

[0004] The present invention also discloses a method for water quality testing using the above-described device. Invention Overview:

[0006] This invention uses a reference wavelength determination method to link array light source, three-wavelength inversion, and multi-parameter detection, so that the logical relationship of the entire device is progressively advanced. It proposes a novel method that balances the cost-effectiveness and performance of instrument detection, while overcoming technical problems such as unstable light source and ion cross-interference.

[0007] The detailed technical solution of this invention is as follows:

[0008] A dual-beam, three-wavelength, multi-parameter water quality detection device, characterized in that it includes an optical path detection unit and a calculation module; the optical path detection unit includes: a fixed-wavelength LED array light source generating an optical path, which passes sequentially along the optical path direction, a collimating lens and a beam splitter, which divide the optical path into a reference optical path and a detection optical path;

[0009] The reference optical path includes a first focusing lens and a reference detector; the detection optical path includes an aperture stop, a digestion colorimetric sample cell, a plane mirror, a second focusing lens, and a detection detector.

[0010] The calculation module is loaded with a three-wavelength inversion detection algorithm.

[0011] According to a preferred embodiment of the present invention, the three-wavelength inversion detection algorithm includes: on the wavelength-absorbance curve, measuring wavelength λ2 to form a second intersection point on the curve, and forming a perpendicular line segment A2; then obtaining two reference wavelengths λ1 and λ3 using a method for obtaining reference wavelengths, forming a first intersection point and a third intersection point on the curve, and forming perpendicular line segments A1 and A3 respectively; connecting the first intersection point and the third intersection point, intersecting with the perpendicular line segment A2 to form a fourth intersection point M; and connecting the intersection point of reference wavelength λ3 with the abscissa and the first intersection point, intersecting with the perpendicular line segment A2 to form a fifth intersection point N.

[0012] According to the principle of similar triangles, we have:

[0013] ΔA = A² - (|N| + |MN|)

[0014] =A2-(mA1+nA3) / (m+n)

[0015] =A2-[(λ2-λ3)A1+(λ1-λ2)A3] / (λ1-λ3)

[0016] ={ε(λ2)-[(λ2-λ3)ε(λ1)+(λ1-λ2)ε(λ3)] / (λ1-λ3)}bc(III)

[0017] In formula (III), ε(λ) is the molar absorptivity of the analyte at each wavelength; b is the optical path length; c is the concentration of the analyte; the value of ε(λ) is obtained by measuring the standard solution with light sources of different wavelengths, and is generally assumed to be a constant value; thus, the concentration c of the analyte is obtained. This invention utilizes a similar triangle formed by one measurement wavelength and two reference wavelengths to perform three-wavelength concentration inversion calculation, which can effectively solve the problem of cross-interference of interfering components.

[0018] exist Figure 2 The wavelength-absorbance curve shown is used, where the horizontal axis represents wavelength and the vertical axis represents absorbance. The curve is obtained by selecting different wavelengths from the array light source and detecting different standard solutions. The array light source has wavelength ranges of 220nm, 280nm, 400nm, 420nm, 460nm, 540nm, 620nm, 710nm, and 900nm. The wavelength-absorbance curve is used to better understand the three-wavelength inversion detection algorithm. In practice, as long as three corresponding points are obtained and can form a similar triangle, the three-wavelength inversion detection algorithm can be used.

[0019] The transmitted light intensity I at the measurement wavelength λ2 is obtained by the detection detector. t The principle behind this is Beer-Lambert's principle, according to...

[0020] The energy changes of the incident and transmitted light yield the relationship between the transmittance T, absorbance A, and transmitted light intensity:

[0021] A = -lg(T) = εbc(I)

[0022] In formula (I), b is the optical path length and c is the concentration of the analyte.

[0023] Because this scheme uses a dual-beam design, the formula for calculating the absorbance difference between the two beams is ΔA = A1 - A2. In practical applications, the absorbance calculation formula needs to consider the influence of dark current. During system detection, dark current correction is required. Dark current is the conversion of light energy sensed by the photoelectric sensor into an electrical signal under conditions of no light intensity. This part is called dark current. Therefore, the influence of this factor needs to be deducted when calculating the photometer's output. o Subtract dark current I d The bright current is obtained, and the transmitted light intensity of the test solution is detected as I. t Subtract dark current I d By obtaining the bright current, the absorbance of the sample solution can be obtained:

[0024]

[0025] In formula (II), A is the absorbance of the sample solution to be tested; T is the transmittance; It is the transmitted light intensity of the main optical path of the sample solution, i.e., the value obtained by the detector; Io is the transmitted light intensity of the reference optical path of the sample solution; Id is the dark current; K is the ratio of the transmitted light intensity of the main optical path of the reference solution to the transmitted light intensity of the reference optical path of the reference solution.

[0026] The concentration c of the analyte can be obtained by further calculating A = ε(λ)cb.

[0027] The fixed-wavelength LED array light source consists of nine different fixed-wavelength LED light source arrays. When performing detection by selecting parameters, an automatic wavelength selection algorithm selects the measurement wavelength and reference wavelength, automatically selects different wavelength light sources, and sequentially detects the absorbance of the test liquid. This scheme can be applied to multiple fixed-wavelength light source schemes; it is not necessary to have exactly nine. Currently, nine wavelength light sources are selected, among which the 220nm and 900nm wavelength light sources are commonly used reference light sources. However, this instrument mainly measures ammonia nitrogen (420nm), COD (620nm), and phosphate (710nm). When the measurement wavelengths are similar or the identification colors are similar, there will be cross-interference in identification. Therefore, total nitrogen (280nm), chromium (540nm), chloride ion (460nm), and sulfide (400nm) are set as interference parameter reference wavelengths. The wavelength selection algorithm mainly selects suitable measurement wavelengths and two reference wavelengths from the commonly used reference wavelengths and interference parameter reference wavelengths as the three-wavelength inversion measurement wavelengths. The light source is selected to allow the light beam to enter the optical path. Only one light source is allowed to be selected during measurement, and the light source is selected according to the sequence of the detection process.

[0028] According to a preferred embodiment of the present invention, the method for determining the reference wavelength is characterized by comprising:

[0029] The measurement parameters of the device are: ammonia nitrogen (420nm), COD (620nm), and phosphate (710nm); the interference parameters are: total nitrogen (280nm), chromium (540nm), chloride ion (460nm), and sulfide (400nm). The interference parameters are mostly due to similar wavelengths or colors. The interference wavelengths for ammonia nitrogen are generally chloride ion and sulfide; the interference wavelengths for COD are generally chromium ion.

[0030] Step 1: Determine the absorbance value of the standard solution: Use formula (II) to obtain the absorbance value of the standard solution at the corresponding wavelength, and obtain the corresponding [x,y], where x is the center wavelength of the light source, and y is the absorbance value of the corresponding solution at this wavelength. According to formula (II), given b, c, and A, ε(λ) can be obtained. Purchase ammonia nitrogen, COD, and phosphate standard solutions from the market, and measure them sequentially from 220nm to 900nm using nine wavelength light sources. The optical path of the above detection device is b = 1cm. Using formula (II), a total of 27 absorbance values ​​of the three solutions at nine wavelengths can be obtained, and obtain the corresponding [x,y], where x is the center wavelength of the light source, and y is the absorbance value of the corresponding solution at this wavelength. According to formula (II), given b, c, and A, ε(λ) can be obtained.

[0031] Step 2: Select measurement parameters;

[0032] 2-1) When the measurement parameter is a single parameter: first determine whether there is interference from interfering parameters, then select a reference wavelength, and finally calculate the concentration of the parameter to be detected using the three-wavelength inversion detection algorithm.

[0033] Start the light source and sequentially analyze the sample solution:

[0034] The absorption peak wavelength of the measured parameter and the absorption peak wavelength of the interference parameter;

[0035] Two absorbance values ​​were obtained, and the ratio F of the absorbance of the measured parameter to the absorbance of the interfering parameter was calculated.

[0036] If the value is greater than or equal to a preset threshold, such as 1.8, and the threshold can be changed, then it is determined that the parameter has no cross-interference with other parameters.

[0037] If the wavelength is less than the preset threshold, then the reference wavelength is selected based on the interference parameters.

[0038] 2-2) When there are two or more parameters to be measured: first determine the order of the measured parameters, then determine whether there are interfering parameters. The determination of whether there are interfering parameters is a conventional method in this field and is not the content to be protected by this invention. Then select a reference wavelength, and finally use the three-wavelength inversion detection algorithm to calculate the concentration of the parameter to be detected.

[0039] According to a preferred embodiment of the present invention, the specific methods in steps 2-1) and 2-2) are as follows:

[0040] A. When the ratio F is greater than or equal to the preset threshold, there are 0 interference parameters. Taking phosphate ion detection (710nm) as an example, the [x,y] phosphate under 9 light sources is queried. The query method is: by judging that x = 710nm, the corresponding array is queried; x1 is the measurement wavelength (λ2 = 710nm), and then the reference wavelength 1 and reference wavelength 2 are obtained for the measurement wavelength. Since there are no interference parameters, the reference wavelength selection algorithm is: first, in the [x,y] phosphate, when x < 710nm, find the array corresponding to the minimum absorbance y. The x value of the array is the reference wavelength 1. At the same time, based on the idea of ​​similar triangles and the setting of the light source band, it can be known that the other reference wavelength 2 is 900nm.

[0041] The light source is activated to begin detection in the following sequence: measurement wavelength, reference wavelength 1, reference wavelength 2. Sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Absorbance is then measured to obtain the corresponding absorbance value of the sample solution. The absorbance value of the reference wavelength is then compared to the reference wavelength. The reference wavelength with the higher absorbance between reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and vice versa. Substituting these values ​​into formula (III), the concentration is calculated. There is one measurement parameter, F>=1.8, and zero interference parameters. Taking phosphate ion detection (710nm) as an example, the [x,y] phosphate values ​​under nine light sources are queried. The query method is: by determining x==710nm, the corresponding array is queried; x1 is the measurement wavelength (λ2=710nm), and then the corresponding... The measurement wavelength is used to determine the corresponding reference wavelength 1 and reference wavelength 2. Since there are no interference parameters, the algorithm for selecting the reference wavelength is as follows: First, determine the array of phosphate groups in the range [x,y]. When x < 710nm, find the array corresponding to the minimum absorbance y. The x value of the array is the reference wavelength 1. At the same time, based on the idea of ​​similar triangles and the setting of the light source band, it can be known that the other reference wavelength 2 is 900nm. Start the light source to start detection. The sequence is: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, the absorbance is measured to obtain the absorbance value corresponding to the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with a large absorbance corresponds to λ3 in formula (III), and the other is λ1. Substitute it into formula (III) to perform concentration inversion.

[0042] B. When the ratio F is less than the preset threshold, one interference parameter is detected. The light source is activated to start detection in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with higher absorbance in reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and vice versa. The absorbance is substituted into formula (III) to perform concentration inversion calculation. Taking COD measurement (620nm) as an example, the interference parameter is generally chromium ions (540nm). The method involves querying the COD [x,y] under nine light sources corresponding to the COD. The query method is as follows: by determining that x = 620nm, the corresponding array is queried; x1 is the measurement wavelength (λ2 = 620nm); then the reference wavelength 1 and reference wavelength 2 corresponding to the measurement wavelength are obtained. Because there is an interference parameter, the absorption peak wavelength of the interference parameter is the first reference wavelength 1 (540nm). Based on the idea of ​​similar triangles and the setting of the light source band, it can be known that the other reference wavelength is greater than 620nm. In the [x,y] COD, when x > 710nm, the array corresponding to the minimum absorbance y is found. The x value of the array is the reference wavelength 2.

[0043] C. When the ratio F is less than the preset threshold, two interference parameters are detected by starting the light source in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is then compared with that of the reference wavelength 1 and reference wavelength 2. The reference wavelength with the higher absorbance corresponds to λ3 in formula (III), and vice versa. These values ​​are then substituted into formula (III) to perform concentration inversion calculation. Taking ammonia nitrogen (420nm) as an example, the interference parameters are generally chloride ions (460nm) and sulfides (400nm). By querying the [x,y] ammonia nitrogen under 9 light sources, the query method is as follows: by determining that x = 420nm, query the corresponding array; x1 is the measurement wavelength (λ2 = 420nm); then, the corresponding reference wavelength 1 and reference wavelength 2 are obtained for the measurement wavelength. Since there are 2 interference parameters, the absorption peak wavelengths of the interference parameters are used as reference wavelength 1 (400nm) and reference wavelength 2 (460nm) respectively.

[0044] A method for water quality testing using the above-mentioned apparatus, characterized in that it includes:

[0045] (a) Determining the reference wavelength:

[0046] Step 1: Determine the absorbance value of the standard solution: Use the formula (II) to obtain the absorbance value of the standard solution at the corresponding wavelength, and obtain the corresponding [x,y], where x is the center wavelength value of the light source, y is the absorbance value of the corresponding solution at this wavelength, and according to the formula (II), given b, c and A, ε(λ) can be obtained.

[0047] Step 2: Select measurement parameters;

[0048] 2-1) When the measurement parameter is a single parameter: first determine whether there is interference from interfering parameters, then select a reference wavelength, and finally calculate the concentration of the parameter to be detected using the three-wavelength inversion detection algorithm.

[0049] Start the light source and sequentially analyze the sample solution:

[0050] The absorption peak wavelength of the measured parameter and the absorption peak wavelength of the interference parameter;

[0051] Two absorbance values ​​were obtained, and the ratio F of the absorbance of the measured parameter to the absorbance of the interfering parameter was calculated.

[0052] If the value is greater than or equal to the preset threshold, it is determined that the parameter has no cross-interference with other parameters;

[0053] If the wavelength is less than the preset threshold, then the reference wavelength is selected based on the interference parameters.

[0054] 2-2) When there are two or more parameters to be measured: first determine the order of the measured parameters, then determine whether there are interfering parameters, then select the reference wavelength, and finally use the three-wavelength inversion detection algorithm to calculate the concentration of the parameter to be detected.

[0055] The specific methods in steps 2-1) and 2-2) are as follows:

[0056] A. When the ratio F is greater than or equal to the preset threshold, there are 0 interference parameters. The light source is started to detect in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other is λ1. The absorbance is substituted into formula (III) to perform concentration inversion calculation.

[0057] B. When the ratio F is less than the preset threshold, one interference parameter is detected. The light source is started to detect the following sequence: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other corresponds to λ1. The absorbance is substituted into formula (III) to perform concentration inversion calculation.

[0058] C. When the ratio F is less than the preset threshold, two interference parameters are detected by starting the light source in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other corresponds to λ1. The absorbance is substituted into formula (III) to perform concentration inversion calculation.

[0059] (ii) Determine the concentration c of the analyte:

[0060] On the wavelength-absorbance curve, the second intersection point is formed by measuring wavelength λ2, and a perpendicular line segment A2 is formed. Then, two reference wavelengths λ1 and λ3 are obtained by using the method for determining the reference wavelength, forming the first and third intersection points on the curve, and forming perpendicular line segments A1 and A3, respectively. The line connecting the first and third intersection points intersects with the perpendicular line segment A2 to form the fourth intersection point M. The line connecting the intersection point of the reference wavelength λ3 with the abscissa and the first intersection point intersects with the perpendicular line segment A2 to form the fifth intersection point N.

[0061] According to the principle of similar triangles, we have:

[0062] ΔA = A² - (|N| + |MN|)

[0063] =A2-(mA1+nA3) / (m+n)

[0064] =A2-[(λ2-λ3)A1+(λ1-λ2)A3] / (λ1-λ3)

[0065] ={ε(λ2)-[(λ2-λ3)ε(λ1)+(λ1-λ2)ε(λ3)] / (λ1-λ3)}bc(III) In formula (III), ε(λ) is the molar absorptivity of the analyte at each wavelength; b is the optical path length; c is the concentration of the analyte; the value of ε(λ) is obtained by measuring the standard solution with light sources of different wavelengths, thereby obtaining the concentration c of the analyte.

[0066] Technical advantages of the present invention:

[0067] 1. This invention can effectively reduce absorbance fluctuations and improve the accuracy of detection results caused by light source fluctuations. Single-beam light intensity is easily affected by light source fluctuations, thus changing the absorbance value. In poor environmental conditions, this can affect the accuracy of detection results. This invention, however, uses a dual-beam system, eliminating light source fluctuations due to the presence of a reference optical path.

[0068] 2. This invention can effectively reduce cross-interference from other components in multi-parameter analysis and improve the detection accuracy of specific ions in the sample. This invention mainly solves the problem of cross-interference caused by similar absorption peak wavelengths and colors in current water quality detection. The principle is a three-parameter wavelength inversion algorithm. By using the measurement wavelength and the reference wavelength of the interference parameter to form a similar triangle, and calculating ΔA, the technical bottleneck of ion cross-interference can be solved. Furthermore, to support the three-parameter wavelength inversion algorithm, an innovative reference wavelength selection algorithm and the concept of the interference factor F are proposed. Through the design of the array light source, the detection of multiple parameters can be expanded. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the optical path detection unit within the device described in this invention;

[0070] Figure 2 This is a schematic diagram illustrating the principle of determining the concentration of the sample solution to be tested according to the present invention. Detailed Implementation

[0071] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0072] Example 1

[0073] like Figure 1 As shown:

[0074] A dual-beam, three-wavelength, multi-parameter water quality detection device includes an optical path detection unit and a calculation module; the optical path detection unit includes: a fixed-wavelength LED array light source generating an optical path, which passes sequentially along the optical path direction, a collimating lens and a beam splitter, which divide the optical path into a reference optical path and a detection optical path;

[0075] The reference optical path includes a first focusing lens and a reference detector; the detection optical path includes an aperture stop, a digestion colorimetric sample cell, a plane mirror, a second focusing lens, and a detection detector.

[0076] The calculation module is loaded with a three-wavelength inversion detection algorithm.

[0077] The LED array light source is controlled by a constant current drive circuit. The beam is collimated by a collimating plano-convex lens (collimating lens), at which point the beam divergence angle is less than 2° and the beam diameter is 5mm. The beam is then split at 45° by a beam splitter, resulting in two paths: a reference path and a detection path. The reference path passes directly through air into the reference detector. The detection path is constrained by an aperture, then passes through a digestion colorimetric sample cell for digestion and colorimetric analysis. After reflection by a plane mirror, the light is focused by a second focusing lens before finally entering the detection detector.

[0078] Example 2

[0079] As described in the embodiment, the three-wavelength inversion detection algorithm of the water quality detection device includes: on the wavelength-absorbance curve, by measuring wavelength λ2, a second intersection point is formed on the curve, and a vertical line segment A2 is formed; then, two reference wavelengths λ1 and λ3 are obtained by the method of obtaining reference wavelengths, forming a first intersection point and a third intersection point on the curve, and forming vertical line segments A1 and A3 respectively; the line connecting the first intersection point and the third intersection point intersects with the vertical line segment A2 to form a fourth intersection point M; the line connecting the intersection point of reference wavelength λ3 and the horizontal axis with the first intersection point intersects with the vertical line segment A2 to form a fifth intersection point N;

[0080] According to the principle of similar triangles, we have:

[0081] ΔA = A² - (|N| + |MN|)

[0082] =A2-(mA1+nA3) / (m+n)

[0083] =A2-[(λ2-λ3)A1+(λ1-λ2)A3] / (λ1-λ3)

[0084] ={ε(λ2)-[(λ2-λ3)ε(λ1)+(λ1-λ2)ε(λ3)] / (λ1-λ3)}bc(III)

[0085] In formula (III), ε(λ) is the molar absorptivity of the analyte at each wavelength; b is the optical path length; c is the concentration of the analyte; the value of ε(λ) is obtained by measuring the standard solution with light sources of different wavelengths, and is generally assumed to be a constant value; thus, the concentration c of the analyte is obtained. This invention utilizes a similar triangle formed by one measurement wavelength and two reference wavelengths to perform three-wavelength concentration inversion calculation, which can effectively solve the problem of cross-interference of interfering components.

[0086] exist Figure 2The wavelength-absorbance curve shown is used, where the horizontal axis represents wavelength and the vertical axis represents absorbance. The curve is obtained by selecting different wavelengths from the array light source and detecting different standard solutions. The array light source has wavelength ranges of 220nm, 280nm, 400nm, 420nm, 460nm, 540nm, 620nm, 710nm, and 900nm. The wavelength-absorbance curve is used to better understand the three-wavelength inversion detection algorithm. In practice, as long as three corresponding points are obtained and can form a similar triangle, the three-wavelength inversion detection algorithm can be used.

[0087] The transmitted light intensity I at the measurement wavelength λ2 is obtained by the detection detector. t Based on the Beer-Lambert principle, the relationship between transmittance T, absorbance A, and transmitted light intensity is derived from the energy change between transmitted and incident light.

[0088] A = -lg(T) = εbc(I)

[0089] In formula (I), b is the optical path length and c is the concentration of the analyte.

[0090] Because this scheme uses a dual-beam design, the formula for calculating the absorbance difference between the two beams is ΔA = A1 - A2. In practical applications, the absorbance calculation formula needs to consider the influence of dark current. During system detection, dark current correction is required. Dark current is the conversion of light energy sensed by the photoelectric sensor into an electrical signal under conditions of no light intensity. This part is called dark current. Therefore, the influence of this factor needs to be deducted when calculating the photometer's output. o Subtract dark current I d The bright current is obtained, and the transmitted light intensity of the test solution is detected as I. t Subtract dark current I d By obtaining the bright current, the absorbance of the sample solution can be obtained:

[0091]

[0092] In formula (II), A is the absorbance of the sample solution to be tested; T is the transmittance; It is the transmitted light intensity of the main optical path of the sample solution, i.e., the value obtained by the detector; Io is the transmitted light intensity of the reference optical path of the sample solution; Id is the dark current; K is the ratio of the transmitted light intensity of the main optical path of the reference solution to the transmitted light intensity of the reference optical path of the reference solution.

[0093] The concentration c of the analyte can be obtained by further calculating A = ε(λ)cb.

[0094] The fixed-wavelength LED array light source consists of nine different fixed-wavelength LED light source arrays. When performing detection by selecting parameters, an automatic wavelength selection algorithm selects the measurement wavelength and reference wavelength, automatically selects different wavelength light sources, and sequentially detects the absorbance of the test liquid. This scheme can be applied to multiple fixed-wavelength light source schemes; it is not necessary to have exactly nine. Currently, nine wavelength light sources are selected, among which the 220nm and 900nm wavelength light sources are commonly used reference light sources. However, this instrument mainly measures ammonia nitrogen (420nm), COD (620nm), and phosphate (710nm). When the measurement wavelengths are similar or the identification colors are similar, there will be cross-interference in identification. Therefore, total nitrogen (280nm), chromium (540nm), chloride ion (460nm), and sulfide (400nm) are set as interference parameter reference wavelengths. The wavelength selection algorithm mainly selects suitable measurement wavelengths and two reference wavelengths from the commonly used reference wavelengths and interference parameter reference wavelengths as the three-wavelength inversion measurement wavelengths. The light source is selected to allow the light beam to enter the optical path. Only one light source is allowed to be selected during measurement, and the light source is selected according to the sequence of the detection process.

[0095] The method for determining the reference wavelength is characterized by comprising:

[0096] The measurement parameters of the device are: ammonia nitrogen (420nm), COD (620nm), and phosphate (710nm); the interference parameters are: total nitrogen (280nm), chromium (540nm), chloride ion (460nm), and sulfide (400nm). The interference parameters are mostly due to similar wavelengths or colors. The interference wavelengths for ammonia nitrogen are generally chloride ion and sulfide; the interference wavelengths for COD are generally chromium ion.

[0097] Step 1: Determine the absorbance value of the standard solution: Use formula (II) to obtain the absorbance value of the standard solution at the corresponding wavelength, and obtain the corresponding [x,y], where x is the center wavelength of the light source, and y is the absorbance value of the corresponding solution at this wavelength. According to formula (II), given b, c, and A, ε(λ) can be obtained. Purchase ammonia nitrogen, COD, and phosphate standard solutions from the market, and measure them sequentially from 220nm to 900nm using nine wavelength light sources. The optical path of the above detection device is b = 1cm. Using formula (II), a total of 27 absorbance values ​​of the three solutions at nine wavelengths can be obtained, and obtain the corresponding [x,y], where x is the center wavelength of the light source, and y is the absorbance value of the corresponding solution at this wavelength. According to formula (II), given b, c, and A, ε(λ) can be obtained.

[0098] Step 2: Select measurement parameters;

[0099] 2-1) When the measurement parameter is a single parameter: first determine whether there is interference from interfering parameters, then select a reference wavelength, and finally calculate the concentration of the parameter to be detected using the three-wavelength inversion detection algorithm.

[0100] Start the light source and sequentially analyze the sample solution:

[0101] The absorption peak wavelength of the measured parameter and the absorption peak wavelength of the interference parameter;

[0102] Two absorbance values ​​were obtained, and the ratio F of the absorbance of the measured parameter to the absorbance of the interfering parameter was calculated.

[0103] If the value is greater than or equal to a preset threshold, such as 1.8, and the threshold can be changed, then it is determined that the parameter has no cross-interference with other parameters.

[0104] If the wavelength is less than the preset threshold, then the reference wavelength is selected based on the interference parameters.

[0105] 2-2) When there are two or more parameters to be measured: first determine the order of the measured parameters, then determine whether there are interfering parameters. The determination of whether there are interfering parameters is a conventional method in this field and is not the content to be protected by this invention. Then select a reference wavelength, and finally use the three-wavelength inversion detection algorithm to calculate the concentration of the parameter to be detected.

[0106] The specific methods in steps 2-1) and 2-2) are as follows:

[0107] A. When the ratio F is greater than or equal to the preset threshold, there are 0 interference parameters. Taking phosphate ion detection (710nm) as an example, the [x,y] phosphate under 9 light sources is queried. The query method is: by judging that x = 710nm, the corresponding array is queried; x1 is the measurement wavelength (λ2 = 710nm), and then the reference wavelength 1 and reference wavelength 2 are obtained for the measurement wavelength. Since there are no interference parameters, the reference wavelength selection algorithm is: first, in the [x,y] phosphate, when x < 710nm, find the array corresponding to the minimum absorbance y. The x value of the array is the reference wavelength 1. At the same time, based on the idea of ​​similar triangles and the setting of the light source band, it can be known that the other reference wavelength 2 is 900nm.

[0108] The light source is activated to begin detection in the following sequence: measurement wavelength, reference wavelength 1, reference wavelength 2. Sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Absorbance is then measured to obtain the corresponding absorbance value of the sample solution. The absorbance value of the reference wavelength is then compared to the reference wavelength. The reference wavelength with the higher absorbance between reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and vice versa. Substituting these values ​​into formula (III), the concentration is calculated. There is one measurement parameter, F>=1.8, and zero interference parameters. Taking phosphate ion detection (710nm) as an example, the [x,y] phosphate values ​​under nine light sources are queried. The query method is: by determining x==710nm, the corresponding array is queried; x1 is the measurement wavelength (λ2=710nm), and then the corresponding... The measurement wavelength is used to determine the corresponding reference wavelength 1 and reference wavelength 2. Since there are no interference parameters, the algorithm for selecting the reference wavelength is as follows: First, determine the array of phosphate groups in the range [x,y]. When x < 710nm, find the array corresponding to the minimum absorbance y. The x value of the array is the reference wavelength 1. At the same time, based on the idea of ​​similar triangles and the setting of the light source band, it can be known that the other reference wavelength 2 is 900nm. Start the light source to start detection. The sequence is: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, the absorbance is measured to obtain the absorbance value corresponding to the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with a large absorbance corresponds to λ3 in formula (III), and the other is λ1. Substitute it into formula (III) to perform concentration inversion.

[0109] B. When the ratio F is less than the preset threshold, one interference parameter is detected. The light source is activated to start detection in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with higher absorbance in reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and vice versa. The absorbance is substituted into formula (III) to perform concentration inversion calculation. Taking COD measurement (620nm) as an example, the interference parameter is generally chromium ions (540nm). The method involves querying the COD [x,y] under nine light sources corresponding to the COD. The query method is as follows: by determining that x = 620nm, the corresponding array is queried; x1 is the measurement wavelength (λ2 = 620nm); then the reference wavelength 1 and reference wavelength 2 corresponding to the measurement wavelength are obtained. Because there is an interference parameter, the absorption peak wavelength of the interference parameter is the first reference wavelength 1 (540nm). Based on the idea of ​​similar triangles and the setting of the light source band, it can be known that the other reference wavelength is greater than 620nm. In the [x,y] COD, when x > 710nm, the array corresponding to the minimum absorbance y is found. The x value of the array is the reference wavelength 2.

[0110] C. When the ratio F is less than the preset threshold, two interference parameters are detected by starting the light source in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is then compared with that of the reference wavelength 1 and reference wavelength 2. The reference wavelength with the higher absorbance corresponds to λ3 in formula (III), and vice versa. These values ​​are then substituted into formula (III) to perform concentration inversion calculation. Taking ammonia nitrogen (420nm) as an example, the interference parameters are generally chloride ions (460nm) and sulfides (400nm). By querying the [x,y] ammonia nitrogen under 9 light sources, the query method is as follows: by determining that x = 420nm, query the corresponding array; x1 is the measurement wavelength (λ2 = 420nm); then, the corresponding reference wavelength 1 and reference wavelength 2 are obtained for the measurement wavelength. Since there are 2 interference parameters, the absorption peak wavelengths of the interference parameters are used as reference wavelength 1 (400nm) and reference wavelength 2 (460nm) respectively.

[0111] Example 3

[0112] A method for water quality testing using the apparatus described in Examples 1 and 2 includes:

[0113] (a) Determining the reference wavelength:

[0114] Step 1: Determine the absorbance value of the standard solution: Use the formula (II) to obtain the absorbance value of the standard solution at the corresponding wavelength, and obtain the corresponding [x,y], where x is the center wavelength value of the light source, y is the absorbance value of the corresponding solution at this wavelength, and according to the formula (II), given b, c and A, ε(λ) can be obtained.

[0115] Step 2: Select measurement parameters;

[0116] 2-1) When the measurement parameter is a single parameter: first determine whether there is interference from interfering parameters, then select a reference wavelength, and finally calculate the concentration of the parameter to be detected using the three-wavelength inversion detection algorithm.

[0117] Start the light source and sequentially analyze the sample solution:

[0118] The absorption peak wavelength of the measured parameter and the absorption peak wavelength of the interference parameter;

[0119] Two absorbance values ​​were obtained, and the ratio F of the absorbance of the measured parameter to the absorbance of the interfering parameter was calculated.

[0120] If the value is greater than or equal to the preset threshold, it is determined that the parameter has no cross-interference with other parameters;

[0121] If the wavelength is less than the preset threshold, then the reference wavelength is selected based on the interference parameters.

[0122] 2-2) When there are two or more parameters to be measured: first determine the order of the measured parameters, then determine whether there are interfering parameters, then select the reference wavelength, and finally use the three-wavelength inversion detection algorithm to calculate the concentration of the parameter to be detected.

[0123] The specific methods in steps 2-1) and 2-2) are as follows:

[0124] A. When the ratio F is greater than or equal to the preset threshold, there are 0 interference parameters. The light source is started to detect in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other is λ1. The absorbance is substituted into formula (III) to perform concentration inversion calculation.

[0125] B. When the ratio F is less than the preset threshold, one interference parameter is detected. The light source is started to detect the following sequence: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other corresponds to λ1. The absorbance is substituted into formula (III) to perform concentration inversion calculation.

[0126] C. When the ratio F is less than the preset threshold, two interference parameters are detected by starting the light source in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other corresponds to λ1. The absorbance is substituted into formula (III) to perform concentration inversion calculation.

[0127] (ii) Determine the concentration c of the analyte:

[0128] On the wavelength-absorbance curve, the second intersection point is formed by measuring wavelength λ2, and a perpendicular line segment A2 is formed. Then, two reference wavelengths λ1 and λ3 are obtained by using the method for determining the reference wavelength, forming the first and third intersection points on the curve, and forming perpendicular line segments A1 and A3, respectively. The line connecting the first and third intersection points intersects with the perpendicular line segment A2 to form the fourth intersection point M. The line connecting the intersection point of the reference wavelength λ3 with the abscissa and the first intersection point intersects with the perpendicular line segment A2 to form the fifth intersection point N.

[0129] According to the principle of similar triangles, we have:

[0130] ΔA = A² - (|N| + |MN|)

[0131] =A2-(mA1+nA3) / (m+n)

[0132] =A2-[(λ2-λ3)A1+(λ1-λ2)A3] / (λ1-λ3)

[0133] ={ε(λ2)-[(λ2-λ3)ε(λ1)+(λ1-λ2)ε(λ3)] / (λ1-λ3)}bc(III) In formula (III), ε(λ) is the molar absorptivity of the analyte at each wavelength; b is the optical path length; c is the concentration of the analyte; the value of ε(λ) is obtained by measuring the standard solution with light sources of different wavelengths, thereby obtaining the concentration c of the analyte.

[0134] Taking COD testing in water quality as an example, there will be interference from sulfite ions and free chlorine. The absorption peak wavelength of COD is 600nm. Through the automatic wavelength selection algorithm, the reference wavelengths are selected as 515nm and 620nm, which can be known from similar triangles.

[0135] Accordingly, the present invention can also detect multiple parameters such as ammonia nitrogen, COD, silicate ions, and phosphate ions.

Claims

1. A dual-beam, three-wavelength, multi-parameter water quality detection device, characterized in that, It includes an optical path detection unit and a computing module; the optical path detection unit includes: a fixed wavelength LED array light source generating an optical path, which passes sequentially along the optical path direction, a collimating lens and a beam splitter, which divide the optical path into a reference optical path and a detection optical path by the beam splitter; The reference optical path includes a first focusing lens and a reference detector; the detection optical path includes an aperture stop, a digestion colorimetric sample cell, a plane mirror, a second focusing lens, and a detection detector. The calculation module is loaded with a three-wavelength inversion detection algorithm; The three-wavelength inversion detection algorithm includes: on the wavelength-absorbance curve, measuring wavelength λ2 to form a second intersection point on the curve, and forming a perpendicular line segment A2; then obtaining two reference wavelengths λ1 and λ3 using the reference wavelength determination method, forming a first intersection point and a third intersection point on the curve, and forming perpendicular line segments A1 and A3 respectively; connecting the first intersection point and the third intersection point, intersecting with the perpendicular line segment A2 to form a fourth intersection point M; and connecting the intersection point of reference wavelength λ3 with the horizontal axis and the first intersection point, intersecting with the perpendicular line segment A2 to form a fifth intersection point N. According to the principle of similar triangles, we have: ΔA = A² - (|N| + |MN|) =A2-(mA1+nA3) / (m+n) =A2-[(λ2-λ3)A1+(λ1-λ2)A3] / (λ1-λ3) ={ε(λ2)-[(λ2-λ3)ε(λ1)+(λ1-λ2)ε(λ3)] / (λ1-λ3)}bc(III) In formula (III), ε(λ) is the molar absorptivity of the analyte at each wavelength; b is the optical path length; c is the concentration of the analyte; the value of ε(λ) is obtained by measuring the standard solution with light sources of different wavelengths, thereby obtaining the concentration c of the analyte. The method for determining the reference wavelength includes: Step 1: Determine the absorbance value of the standard solution: Use the formula (II) to obtain the absorbance value of the standard solution at the corresponding wavelength, and obtain the corresponding [x,y], where x is the center wavelength value of the light source, y is the absorbance value of the corresponding solution at this wavelength, and according to the formula (I), given b, c and A, ε(λ) can be obtained; A= lg(T)=εbc (I); In equation (I), A is absorbance, T is transmittance, b is optical path length, and c is the concentration of the analyte. (II) In equation (II), It is the transmitted light intensity of the main optical path of the sample solution, Id is the dark current, K is the ratio of the transmitted light intensity of the main optical path of the reference solution to the transmitted light intensity of the reference optical path of the reference solution, and Io is the transmitted light intensity of the reference optical path of the sample solution. Step 2: Select measurement parameters; 2-1) When the measurement parameter is a single parameter: first determine whether there is interference from interfering parameters, then select the reference wavelength, and finally calculate the concentration of the component to be detected using the three-wavelength inversion detection algorithm. Start the light source and sequentially analyze the sample solution: The absorption peak wavelength of the measured parameter and the absorption peak wavelength of the interference parameter; Two absorbance values ​​were obtained, and the ratio F of the absorbance of the measured parameter to the absorbance of the interfering parameter was calculated. If F is greater than or equal to the preset threshold, it is determined that the measurement parameter has no cross-interference with other parameters; If F is less than the preset threshold, then the reference wavelength is selected based on the interference parameters. 2-2) When the number of measurement parameters is greater than or equal to 2: first determine the order of measurement parameters, then determine whether there are interfering parameters, then select the reference wavelength, and finally use the three-wavelength inversion detection algorithm to calculate the concentration of the component to be detected. The specific methods in steps 2-1) and 2-2) are as follows: A. When the ratio F is greater than or equal to the preset threshold, there are 0 interference parameters; The light source is started to begin detection, in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance of the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other corresponds to λ1. The absorbance is substituted into formula (III) to perform concentration inversion calculation. B. When the ratio F is less than the preset threshold, one interference parameter is activated, and the light source is started to detect the sample solution in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other corresponds to λ1. The absorbance is substituted into formula (III) to perform the concentration inversion calculation. C. When the ratio F is less than the preset threshold, the two interference parameters are activated and the light source is started to detect them in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other is λ1. The absorbance is substituted into formula (III) to perform the concentration inversion calculation. The methods for determining reference wavelength 1 and reference wavelength 2 are as follows: To retrieve the [x,y] values ​​of the measurement parameters for all light sources of the fixed-wavelength LED array, where x is the wavelength and y is the absorbance value at that wavelength: A. When the ratio F is greater than or equal to the preset threshold, there are 0 interference parameters: First, determine the array of [x,y] of the measurement parameters. Among the arrays where x is less than the measurement wavelength, find the array corresponding to the minimum absorbance y. The x value of the array is the reference wavelength 1, and the reference wavelength 2 is 900nm. B. When the ratio F is less than the preset threshold, one interference parameter is used: The wavelength of the absorption peak of the interference parameter is the reference wavelength 1. If the reference wavelength 1 is less than the measurement wavelength, then find the array with the minimum absorbance y from the array where x is greater than the measurement wavelength. The x value of this array is the reference wavelength 2. If the reference wavelength 1 is greater than the measurement wavelength, then find the array with the minimum absorbance y from the array where x is less than the measurement wavelength. The x value of this array is the reference wavelength 2. C. When the ratio F is less than the preset threshold, there are two interference parameters: The wavelengths of the absorption peaks of the interference parameters are used as reference wavelength 1 and reference wavelength 2, respectively.

2. A method for water quality testing using the apparatus as described in claim 1, characterized in that, include: (a) Determining the reference wavelength: Step 1: Determine the absorbance value of the standard solution: Use the formula (II) to obtain the absorbance value of the standard solution at the corresponding wavelength, and obtain the corresponding [x,y], where x is the center wavelength value of the light source, y is the absorbance value of the corresponding solution at this wavelength, and according to the formula (I), given b, c and A, ε(λ) can be obtained; Step 2: Select measurement parameters; 2-1) When the measurement parameter is a single parameter: first determine whether there is interference from interfering parameters, then select the reference wavelength, and finally calculate the concentration of the component to be detected using the three-wavelength inversion detection algorithm. Start the light source and sequentially analyze the sample solution: The absorption peak wavelength of the measured parameter and the absorption peak wavelength of the interference parameter; Two absorbance values ​​were obtained, and the ratio F of the absorbance of the measured parameter to the absorbance of the interfering parameter was calculated. If F is greater than or equal to the preset threshold, it is determined that the measurement parameter has no cross-interference with other parameters; If F is less than the preset threshold, then the reference wavelength is selected based on the interference parameters. 2-2) When the number of measurement parameters is greater than or equal to 2: first determine the order of measurement parameters, then determine whether there are interfering parameters, then select the reference wavelength, and finally use the three-wavelength inversion detection algorithm to calculate the concentration of the component to be detected. The specific methods in steps 2-1) and 2-2) are as follows: A. When the ratio F is greater than or equal to the preset threshold, there are 0 interference parameters. The light source is started to detect in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other is λ1. The absorbance is substituted into formula (III) to perform the concentration inversion calculation. B. When the ratio F is less than the preset threshold, one interference parameter is activated, and the light source is started to detect the sample solution in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then, the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other corresponds to λ1. The absorbance is substituted into formula (III) to perform the concentration inversion calculation. C. When the ratio F is less than the preset threshold, the two interference parameters are activated and the light source is started to detect them in the following order: measurement wavelength, reference wavelength 1, reference wavelength 2. The sample solution is extracted, pretreatment solution is injected, and reaction solution is injected according to national standards. Then the absorbance is measured to obtain the absorbance value of the sample solution at this time. The absorbance value of the reference wavelength is judged. The reference wavelength with the larger absorbance in the reference wavelength 1 and reference wavelength 2 corresponds to λ3 in formula (III), and the other is λ1. The absorbance is substituted into formula (III) to perform the concentration inversion calculation. (ii) Determine the concentration c of the analyte: On the wavelength-absorbance curve, the second intersection point is formed by measuring wavelength λ2, and a perpendicular line segment A2 is formed. Then, two reference wavelengths λ1 and λ3 are obtained by using the method for determining the reference wavelength, forming the first and third intersection points on the curve, and forming perpendicular line segments A1 and A3, respectively. The line connecting the first and third intersection points intersects with the perpendicular line segment A2 to form the fourth intersection point M. The line connecting the intersection of the reference wavelength λ3 and the abscissa with the first intersection point intersects the vertical line segment A2 to form the fifth intersection point N; According to the principle of similar triangles, we have: ΔA = A² - (|N| + |MN|) =A2-(mA1+nA3) / (m+n) =A2-[(λ2-λ3)A1+(λ1-λ2)A3] / (λ1-λ3) ={ε(λ2)-[(λ2-λ3)ε(λ1)+(λ1-λ2)ε(λ3)] / (λ1-λ3)}bc(III) In formula (III), ε(λ) is the molar absorptivity of the analyte at each wavelength; b is the optical path length; c is the concentration of the analyte; the value of ε(λ) is obtained by measuring the standard solution with light sources of different wavelengths, thereby obtaining the concentration c of the analyte.

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