RU2234693C2 - Method for measuring concentration of optically active substances in solutions (variants) - Google Patents

Abstract

FIELD: measuring equipment engineering.

SUBSTANCE: method includes collection of radiation on three polarizer-analyzers, while second and first polarizer-analyzers are rotated symmetrically relatively to plane of plane-polarized radiation coming into solution, and third polarizer-analyzer is directed in same plane of plane-polarized radiation coming into solution. Signals from three photoelectric receptors are amplified in these three channels, synchronously detected, transformed into digital form and handled. Measurement of polarization plane rotation angle is performed in two stages on basis of relations, which exclude influence of non-identity of channels and allow to measure polarization plane rotation angle at large range.

EFFECT: higher precision.

2 dwg

Description

The invention relates to photoelectric polarimeters and can be used to measure the concentration of optically active substances in medicine, chemistry, biology, food industry.

For solutions containing optically active substances, there is a relationship between the rotation angle φ of the plane of polarization of the solution and the concentration C of the optically active substance: φ = α · l · C, where l is the thickness of the solution layer, α is the specific rotational ability of the substance, depending on the length waves of light in which the measurement is taken. Based on this law, to measure the concentration of a solution, it is sufficient to calculate the angle of rotation of the plane of polarization.

A known polarimeter (patent RU No. 2007694 C1, class G 01 J 4/04, 02.15.94) containing a source of modulated plane-polarized radiation, three analyzer polaroids, with the first and second polaroids analyzers being deployed symmetrically with respect to the polaroid of a plane-polarized radiation source, and the third polaroid analyzer is oriented in the same way as the polaroid of a plane-polarized radiation source, three photodetectors, three amplifiers, three synchronous detectors, a reference voltage generator, a subtraction unit, two addition blocks, two multiplied blocks selectable constants, a division unit, while the output of the first addition unit through the first unit of multiplication by a selectable constant is connected to the first input of the second addition unit, the second input of which is connected to the output of the second unit of multiplication by a selectable constant, the input of which is connected to the output of the third synchronous detector the second input of which is connected to one of the outputs of the reference voltage generator, and the output of the subtraction unit and the output of the second addition unit are connected to the corresponding inputs of the division unit.

A further increase in the accuracy of measurements is hindered by the non-identity of the channels and the inaccuracy of the exhibition of polaroid analyzers.

A known method of measuring the concentration of optically active substances in solutions according to the angle of rotation of the plane of polarization (patent RU No. 2180733 C2, class G 01 J 4/04, 05.15.00), including transmitting modulated plane-polarized radiation through the test solution, collecting the transmitted radiation into three polaroids analyzer with photodetectors, while the first and second polaroid analyzers are rotated symmetrically relative to the plane of plane-polarized radiation entering the solution, and the third polaroid analyzer is oriented in the same plane the plane polarized radiation entering the solution, the signals from three photodetectors are amplified in these three channels, synchronously detected, digitized and processed, the angle of rotation of the plane of polarization φ is measured in one of the variants according to the following relation:

,

,

Where

W ₁ , W ₂ , W ₃ - signal values at the output of the first, second and third synchronous detectors, respectively, when there is no cuvette with the test solution and polaroids analyzers are installed on the receiving part; R ₁ , R ₂ , R ₃ - signal values at the output of the first, second and third synchronous detectors, respectively, when a cell with the test solution is installed and polaroids analyzers are installed on the receiving part; P ₁ , P ₂ , P ₃ - signal values at the output of the first, second and third synchronous detectors, respectively, when a cuvette with the test solution is installed and there are no polaroid analyzers on the receiving part; V ₁ , V ₂ , V ₃ are the values of the signals at the output of the first, second and third synchronous detectors, respectively, when there is no cuvette with the test solution and there are no analyzer polaroids on the receiving part, the parameters k ₁ , k ₂ are uniquely determined by the angles of rotation of the polaroids analyzers.

The disadvantage of this method of measuring concentration is a decrease in accuracy when measuring large concentrations (angles of rotation of the plane of polarization).

The objective of the invention is to accurately measure large concentrations of optically active substances in solution (or angles of rotation of the plane of polarization in a wide range).

The solution of the problem in the first embodiment is achieved by the fact that in the method for measuring the concentration of optically active substances in solutions by the angle of rotation of the plane of polarization, including transmitting modulated plane-polarized radiation through the test solution, collecting the transmitted radiation into three polaroid analyzers with photodetectors, the first and second analyzer polaroids are deployed symmetrically relative to the plane of plane-polarized radiation entering the solution, and the third polaroid analyzer is oriented in the same way as a polaroid of a plane-polarized radiation source, amplification of signals from three photodetectors, synchronous detection, digitization and processing, obtaining signal values R ₁ , R ₂ , R ₃ - at the output of the first, second and third synchronous detectors, respectively, when a cuvette with the test solution is installed and polaroids analyzers are installed on the receiving part, receiving the values of the signals W ₁ , W ₂ , W ₃ - at the output of the first, second and third synchronous detectors, respectively, when there is no cuve the ones with the test solution and the receiving part are equipped with polaroids analyzers; obtaining the values of the signals P ₁ , P ₂ , P ₃ - at the output of the first, second and third synchronous detectors, respectively, when a cuvette with the test solution is installed and there are no polaroid analyzers at the receiving part; receiving the values of the signals V ₁ , V ₂ , V ₃ - at the output of the first, second and third synchronous detectors, respectively, when there is no cuvette with the test solution and there are no analyzer polaroids on the receiving part, and the angle of rotation of the plane of polarization φ is measured in two steps: first by ratio

calculate the angle θ, the numerical value of which is close to the numerical value of the measured angle φ,

k ₁ , k ₂ , k ₃ , k ₄ , k ₅ - the parameters are uniquely determined by the rotation angles of the polaroids-analyzers, divide the entire range of measured angles into N intersecting numerical intervals, and the total part of two adjacent intervals is much larger than the error in measuring the angle θ, determine to which numerical interval the numerical value of the angle θ belongs, then by the relation

the exact value of the measured angle φ, q _1i , q _2i , q _3i , q _4i , q _5i is calculated - the parameters are uniquely determined by the rotation angles of the polaroids analyzers for the i-th numerical range of the numerical values of the measured angle φ.

In the second embodiment, the solution of the problem is achieved by the fact that in the method of measuring the concentration of optically active substances in solutions by the angle of rotation of the plane of polarization, including transmitting modulated plane-polarized radiation through the test solution, collecting the transmitted radiation into two polaroid analyzers with photodetectors, while polaroids analyzers amplified symmetrically relative to the plane of plane-polarized radiation entering the solution, amplification of signals from two photodetectors, syn ronnoe detection, digitization and processing, deriving R ₁ signal values, R ₂ - at the output of the first, second synchronous detectors, respectively, when installed cuvette with the test solution, and the receiving parts are mounted polaroids analyzers, obtaining values of the signals W _1, W ₂ - at the output of the first and second synchronous detectors, respectively, when there is no cuvette with the test solution and polaroids analyzers are installed on the receiving part; obtaining the values of the signals P ₁ , P ₂ - at the output of the first and second synchronous detectors, respectively, when a cell with the test solution is installed and there are no polaroid analyzers at the receiving part; receiving the values of signals V ₁ , V ₂ - at the output of the first and second synchronous detectors, respectively, when there is no cuvette with the test solution and there are no analyzer polaroids at the receiving part, and the angle of rotation of the plane of polarization φ is measured in two steps: first, by the ratio

calculate the angle θ, the numerical value of which is close to the numerical value of the measured angle φ,

вычисляется точное численное значение измеряемого угла, q_1i, q_2i, q_3i - параметры однозначно определяются по углам разворота поляроидов-анализаторов для i-го числового интервала численных значений измеряемого угла φ .k ₁ , k ₂ , k ₃ - the parameters are uniquely determined by the rotation angles of the polaroids analyzers, dividing the entire range of measured angles into N intersecting numerical intervals, and the total part of two adjacent intervals numerically far exceeds the error in measuring the angle θ, determine to which numerical interval the numerical value of the angle θ belongs, then, by the relation

the exact numerical value of the measured angle is calculated, q _1i , q _2i , q _3i - the parameters are uniquely determined by the rotation angles of the analyzer polaroids for the ith numerical interval of the numerical values of the measured angle φ.

Figure 1 presents the implementation diagram of the first variant of the proposed method for measuring the concentration of optically active substances in solutions.

A diagram of an implementation of a method for measuring the concentration of optically active substances in solutions (Fig. 1) contains a source of modular plane-polarized radiation 1, polaroids-analyzers 3.1, 3.2, 3.3, in front of which there is a cell with optically active analyte 2, photodetectors 4.1, 4.2, 4.3, amplifiers 5.1, 5.2, 5.3, reference voltage generator 6, synchronous detectors 7.1, 7.2, 7.3, calculation unit 8, display unit 9.

Figure 2 presents the implementation diagram of the second variant of the proposed method for measuring the concentration of optically active substances in solutions.

The implementation diagram of a method for measuring the concentration of optically active substances in solutions (Fig. 2) contains a source of modular plane-polarized radiation 1, polaroids-analyzers 3.1, 3.2, in front of which there is a cuvette with optically active analyte 2, photodetectors 4.1, 4.2, amplifiers 5.1, 5.2, reference voltage generator 6, synchronous detectors 7.1, 7.2, calculation unit 8, display unit 9.

In the proposed method for measuring the concentration of optically active substances in solutions, the radiation flux from the source of modulated plane-polarized radiation 1 in the absence of a cuvette enters the inputs of polaroids analyzers 3.1, 3.2, 3.3 and then passes through photodetectors 4.1, 4.2, 4.3, amplifiers 5.1, 5.2, 5.3, synchronous detectors 7.1, 7.2, 7.3.

The signals at the outputs of synchronous detectors 7.1, 7.2, 7.3 are described by the relations:

where V ₁ , V ₂ , V ₃ are the values of the signals at the outputs of synchronous detectors 7.1, 7.2, 7.3, when there is no cuvette with the test solution and there are no polaroid analyzers on the receiving part, α ₁ is the angle of the turn of the polaroid analyzer of the 1st channel relative to the polaroid of the radiating part, α ₁ ≈ -45 °, α ₂ is the angle of rotation of the polaroid analyzer of the 2nd channel relative to the polaroid of the radiating part, α ₂ ≈ 45 °, α ₃ is the angle of rotation of the polaroid analyzer of the 3rd channel, α ₃ ≈ 0 °, T _0i - energy transmittance of ordinary wave polarizer-analyzer i-th anal, ε _i = T _oi / T _ei, T _ei - energy transmittance of extraordinary wave polarizer-analyzer i-th channel.

When linearly polarized radiation is transmitted through a cuvette with a solution containing an optically active substance, to three polaroid analyzers with photodetectors, we obtain the signals described by the relations at the output of the photo-receivers:

where P _i is the signal value from the i-th channel in the absence of a polaroid analyzer, φ is the angle by which the plane of polarization rotates when passing through the solution.

In the first embodiment, the determination of the angle of rotation of the plane of polarization in the test solution φ is carried out by the ratio:

Where

the parameters k ₁ , k ₂ , k ₃ , k ₄ , k _{5 are} uniquely determined by the rotation angles of the polaroids analyzers. The implementation of this option is possible due to the following equality:

Where

which happens if in the formula

substitute the values of the previously described signals. The above equality holds very precisely, for example, at α ₁ = -45.5 °, α ₂ = 46.0 °, α ₃ = 0.0 °, ε ₁ = 0.0003, ε ₂ = 0.0004, ε ₃ = 0.0004 in the range of measuring the angle φ from 0 to 15 °, k ₁ = 0.477811; k ₂ = 0.522188; k ₃ = 0.629531; k ₄ = 0.367876; k ₅ = 2.025456; deviation from equality does not exceed 0.0000005 radians. When measuring large angles, deviation from equality can take large values. For example, when measuring an angle in the range from 0 to π / 2, the radian deviates from equality for the same values of α ₁ , α ₂ , α ₃ , ε ₁ , ε ₂ , ε ₃ and optimal parameters k ₁ = -0.533983; k ₂ = 1.529613; k ₃ = 0.785223; k ₄ = 0.198574; k ₅ = 0.038871; reaches a value of 0.0043 radians or ≈ 0.246 °. Therefore, it is proposed to measure the angle in two steps. First, by the ratio

where θ is a numerical value close to the numerical value of the measured angle φ. For the range from 0 to π / 2 radians at k ₁ = -0.533983; k ₂ = 1.529613; k ₃ = 0.785223; k ₄ = 0.198574; k ₅ = 0.038871 θ is calculated with an error of ≈ 0.246 °. The range from 0 to 90 ° is divided into 5 intersecting intervals: (0 °, 17 °), (15 °, 32 °), (30 °, 52 °), (50 °, 72 °), (70 °, 90 ° ) Each interval has its own parameter values: for the interval (0 °, 17 °) - q ₁₁ = 0.430238, q ₂₁ = 0.569760, q ₃₁ = 0.630668, q ₄₁ = 0.345084, q ₅₁ = 1 , 948745, for the interval (15 °, 32 °) - q ₁₂ = -0.091711, q ₂₂ = 1.089950, g ₃₂ = 0.688517, q ₄₂ = 0.184822, q ₅₂ = 0.993514, for interval (30 °, 52 °) - q ₁₃ = -0.488712, q ₂₃ = 1.465473, q ₃₃ = 0.765861, q ₄₃ = 0.219123, q ₅₃ = 0.199223, for the interval (50 ° , 72 °) - q ₁₄ = -0.929894, q ₂₄ = 1.783103, q ₃₄ = 0.836253, q ₄₄ = 0.401093, q ₅₄ = -0.490758, for the interval (70 °, 90 ° ) - q ₁₅ = -1.505484, q ₂₅ = 1.951184, q ₃₅ = 0.902783, q ₄₅ = 0.701295, q ₅₅ = -1.002961. Suppose, for example, after calculating by the relation

received θ = 0.8 radians or 45.8366 °. It belongs to the third interval (from 30 to 52 °). Then by the ratio

the numerical value of the angle φ is calculated with an accuracy of 0.000001 radians or ≈ 0.0000573 °. After calculating θ, it may turn out that this numerical value is at the intersection of two adjacent intervals. When choosing an interval, one must choose the interval for which the number θ is further from the boundary of the interval. The implementation of the calculation of the angle of rotation of the plane of polarization in two steps has significantly increased the accuracy of measuring concentration.

The implementation of the measurement in two steps allows accurate measurements of the concentration of optically active substances in solutions with two-channel execution. When linearly polarized radiation is transmitted through a cuvette with a solution containing an optically active substance, into two polaroid analyzers with photodetectors, we obtain the signals described by the relations at the output of the photo-receivers:

where P _i is the signal value from the ith channel in the absence of a polaroid analyzer, φ is the angle by which the plane of polarization rotates when passing through the solution.

In the second embodiment, the determination of the angle of rotation of the plane of polarization in the test solution φ is carried out by the ratio:

Where

the parameters k ₁ , k ₂ , k _{3 are} uniquely determined by the rotation angles of the polaroids analyzers. The implementation of this option is possible due to the following equality:

,

,

Where

which happens if in the formula

substitute the values of the previously described signals.

The above equality is fulfilled very precisely, for example, at α ₁ = -30.5 °, α ₂ = 31.0 °, ε ₁ = 0.0003, ε ₂ = 0.0004, in the measurement range of the angle φ from 0 to 10 ° , k ₁ = 0.9999838; k ₂ = 1,1892767; k ₃ = 1,1904993; deviation from equality does not exceed 0.000004 radians. When measuring large angles, deviation from equality can take large values. For example, when measuring an angle in the range from 0 to π / 6 radians, deviation from equality for the same values of α ₁ , α ₂ , ε ₁ , ε ₂ and optimal parameters k ₁ = 0.99883493; k ₂ = 1.16504930; k ₃ = 1.23837467 reaches 0.0005 radians or ≈ 0.03 °. Therefore, it is proposed to measure the angle in two steps. First, by the ratio

where θ is a numerical value close to the numerical value of the measured angle φ. For the range from 0 to π / 6 radians, the optimal parameters are: k ₁ = 0.99883493; k ₂ = 1.16504930; k ₃ = 1.23837467. The range from 0 to π / 6 radians is divided into 4 intersecting intervals: (0 °, 11 °), (10 °, 19 °), (18 °, 25 °), (24 °, 30 °). Each interval has its own parameter values: for the interval (0 °, 11 °) - q ₁₁ = 0.99997755, q ₂₁ = 1.18856876, q ₃₁ = 1.19148684, for the interval (10 °, 19 °) - q ₁₂ = 0.99769378, q ₂₂ = 1.17233575, q ₃₂ = 1.22900843, for the interval (18 °, 25 °) - q ₁₃ = 0.9846406, q ₂₃ = 1.15209097, q ₃₃ = 1.31469975 , for the interval (24 °, 30 °) - q ₁₄ = 0.94876981, q ₂₄ = 1.13150574, q ₃₄ = 1.46123698. Suppose, for example, after calculating by the relation

received θ = 0.3 radians or ≈ 17.189 °. It belongs to the second interval (from 10 ° to 19 °). Then by the ratio

the numerical value of the angle φ is calculated with an accuracy of 0.000008 radians or ≈ 0.00046 °. The implementation of the calculation of the angle of rotation of the plane of polarization in two steps has significantly increased the accuracy of measuring concentration.

The collection of information and calculations are performed in the block of calculations 8.

In the display unit 9, the number corresponding to the concentration of the optically active substance in the solution is displayed.

Thus, it is possible to increase the accuracy of measuring the concentration of optically active substance in a solution with a large concentration of the solution.

Claims (2)

1. A method for measuring the concentration of optically active substances in solutions according to the angle of rotation of the plane of polarization, including transmitting modulated plane-polarized radiation through the test solution, collecting the transmitted radiation into three polaroid analyzers with photodetectors, the first and second polaroids analyzers being deployed symmetrically relative to the plane of plane-polarized radiation entering the solution, and the third polaroid analyzer is oriented in the same way as the polaroid source of plane-polarized radiation, amplification of signals from three photodetectors, synchronous detection, digitization and processing, obtaining signal values R ₁ , R ₂ , R ₃ at the output of the first, second and third synchronous detectors, respectively, when a cuvette with the test solution and the receiving part are installed polaroids-analyzers are installed, obtaining the values of the signals W ₁ , W ₂ , W ₃ at the output of the first, second and third synchronous detectors, respectively, when there is no cuvette with the test solution and polaroids are installed at the receiving part analyzers; obtaining the values of the signals P ₁ , P ₂ , P ₃ at the output of the first, second, and third synchronous detectors, respectively, when a cuvette with the test solution is installed and there are no polaroid analyzers at the receiving part; obtaining the values of the signals V ₁ , V ₂ , V ₃ at the output of the first, second and third synchronous detectors, respectively, when there is no cuvette with the test solution and there are no polaroid analyzers at the receiving part, characterized in that the angle of rotation of the plane of polarization φ is measured in two admission: first in the ratio

calculate the angle θ, the numerical value of which is close to the numerical value of the measured angle φ,

k ₁ , k ₂ , k ₃ , k ₄ , k ₅ - the parameters are uniquely determined by the rotation angles of the polaroids-analyzers, divide the entire range of measured angles into N intersecting numerical intervals, and the total part of two adjacent intervals is much larger than the error in measuring the angle θ, determine to which numerical interval the numerical value of the angle θ belongs, then by the relation

calculate the exact numerical value of the measured angle φ, q _1i, q _2i , q _3i , q _4i , q _5i - the parameters are uniquely determined by the rotation angles of the polaroids analyzers for the i-th numerical range of the numerical values of the measured angle φ. 2. A method for measuring the concentration of optically active substances in solutions by the angle of rotation of the plane of polarization, including transmitting modulated plane-polarized radiation through the test solution, collecting the transmitted radiation into two polaroid analyzers with photodetectors, while the polaroids analyzers are deployed symmetrically with respect to the plane of plane-polarized radiation entering solution, amplification of signals from two photodetectors, synchronous detection, digitization and processing, obtained e signal values R _1, R ₂ at the output of the first, second synchronous detectors, respectively, when installed cuvette with the test solution, and the receiving parts are mounted polaroids analyzers, obtaining signal values W _1, W ₂ at the output of the first and second synchronous detectors, respectively, when there is no cuvette with the test solution and polaroids analyzers are installed on the receiving part; obtaining the values of the signals P ₁ , P _{2 the} output of the first and second synchronous detectors, respectively, when a cuvette with the test solution is installed and there are no analyzer polaroids on the receiving part; obtaining the values of the signals V ₁ , V ₂ at the output of the first and second synchronous detectors, respectively, when there is no cuvette with the test solution and there are no polaroids analyzers at the receiving part, characterized in that the angle of rotation of the plane of polarization φ is measured in two steps: first, by the ratio

calculate the angle θ - the numerical value of which is close to the numerical value of the measured angle φ,

k ₁ , k ₂ , k ₃ - the parameters are uniquely determined by the rotation angles of the polaroids analyzers, dividing the entire range of measured angles into N intersecting numerical intervals, and the total part of two adjacent intervals numerically far exceeds the error in measuring the angle θ, determine to which numerical interval the numerical value of the angle θ belongs, then, by the relation

calculate the exact numerical value of the measured angle φ, q _1i , q _2i , q _3i - the parameters are uniquely determined by the rotation angles of the polaroids analyzers for the i-th numerical range of the numerical values of the measured angle φ.

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