An automatic titration device based on differential spectroscopy and a method for measuring titration volume

Abstract

The present invention provides an automatic titration device based on differential spectroscopy and a method for measuring titration volume. The automatic titration device includes a reaction vessel, an injection pump connected to a plurality of reagent conduits through a multi-channel switching valve for sucking liquid into the reaction vessel; a light source and a multi-channel spectral sensor symmetrically arranged on both sides of the reaction vessel, and their installation positions are not higher than the height of the sample to be measured in the reaction vessel; a control module communicatively connected to the multi-channel spectral sensor for collecting the transmitted light intensity I at multiple measurement wavelengths, and also for calculating the titration volume V of the indicator and calculating the differential absorbance A after adding the titration volume V of the indicator into the sample to be measured. By adopting the method of on-site fitting calibration lines, factors such as the temperature and volume of the liquid in the reaction vessel at the end of titration that affect absorbance are fully considered, significantly improving the resolution and measurement accuracy of the on-line automatic analysis instrument.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic analysis instruments, and particularly relates to an automatic titration device based on differential spectroscopy and a method for measuring titration volume. Background Art

[0002] Online automatic analysis instruments are increasingly widely used in the field of water quality monitoring. They are not only easy to operate, but also consume extremely small amounts of samples and reagents during each measurement process, significantly reducing secondary pollution to the environment. The automatic titration device is an important component of the online instrument. It can not only sequentially drop a standard reagent of a fixed volume, but also automatically determine whether the titration end point is reached after each drop of the reagent is dropped. After reaching the titration end point, the titration stops, and the total volume of the standard reagent consumed in the titration can be calculated by the total number of droplets and the volume of each drop of the reagent, and thus the monitoring index of the water sample can be obtained.

[0003] Since the total volume of the standard reagent consumed in the titration is equal to the product of the total number of droplets and the volume of each drop of the reagent, the volume of each drop of the reagent is directly related to the resolution of the instrument. Considering the effect of liquid surface tension, droplets with too small a volume will only hang on the burette and will not immediately drip. Even if a high-precision injection pump is used to precisely control the dosage of each drop of the standard reagent, it is impossible to significantly reduce the volume of each drop of the standard reagent during the automatic titration process. Whether it is manual or automatic titration, the volume of each drop of the standard reagent is several tens of microliters. In online automatic analysis instruments, the usage amounts of the water sample and the reagent are only about one-twentieth of those in manual experiments. Therefore, the influence of each drop of the standard reagent on the measurement result in the automatic titration is also enlarged by about twenty times.

[0004] The above reasons result in the resolution of the automatic analysis instrument being enlarged to several hundred micrograms per liter, far exceeding the resolution of the manual method, seriously affecting the measurement accuracy of the instrument. In addition, during the titration process, methods such as filling with bubbles are often used for mixing, and the bubbles in the liquid will interfere with the photoelectric detection system, causing problems in the determination of the titration end point.

[0005] In summary, there is a need to design an automatic titration device based on differential spectroscopy and a method for measuring titration volume to solve the problem of low measurement accuracy of the existing automatic titration device. Summary of the Invention

[0006] The present invention provides an automatic titration device based on differential spectroscopy and a method for measuring titration volume, which solves the interference of mixing bubbles on the photoelectric system during the titration process, as well as the technical problems of relatively low resolution and measurement accuracy of the automatic titration instrument.

[0007] To achieve the purpose of solving the above technical problems, the present invention adopts the following technical solutions:

[0008] An automatic titration device based on differential spectroscopy, comprising:

[0009] A reaction vessel for placing a sample to be tested and an indicator.

[0010] An injection pump, connected to a plurality of reagent conduits by a multi-channel switching valve, for sucking liquid into the reaction vessel.

[0011] A light source and a multi-channel spectral sensor, symmetrically arranged on both sides of the reaction vessel, and their installation positions are not higher than the height of the sample to be tested in the reaction vessel.

[0012] A control module, communicatively connected to the multi-channel spectral sensor, for collecting the transmitted light intensity I at a plurality of measurement wavelengths, and also for calculating the titration volume V of the indicator and calculating the differential absorbance A after adding the titration volume V of the indicator to the sample to be tested.

[0013] In some embodiments of the present invention, the sample to be tested is a colorless liquid; the indicator is a colored liquid; the light source is a white light source, and the multi-channel spectral sensor selects the measurement wavelength according to the absorption spectrum of the indicator.

[0014] In some embodiments of the present invention, an air conduit is connected to the bottom of the reaction vessel, and the air conduit is connected to a peristaltic pump, and the peristaltic pump is used to pump air into the reaction vessel to generate mixing bubbles.

[0015] In some embodiments of the present invention, the method for measuring the titration volume of the automatic titration device includes the following steps:

[0016] S1. After the sample to be tested is made colorless, it is injected into the reaction vessel by an injection pump.

[0017] S2. Start the peristaltic pump to inject mixing bubbles into the reaction vessel.

[0018] S3. Turn on the light source and start the multi-channel spectral sensor to collect the initial light intensity I at the measurement wavelength. α 0 and I β 0 ;

[0019] S4. After injecting a drop of the indicator into the reaction vessel, start the multi-channel spectral sensor to collect the light intensity I at the measurement wavelength. α 1 and I β 1 , and the control module calculates and records the total volume V of the indicator dropped into the reaction vessel. 1 and calculates the differential absorbance A. 1 ;

[0020] S5. Repeat step S4 for N times. After each end, the control module records the total volume V of the indicator dropped into the reaction vessel and the differential absorbance A in sequence as V 2 , V 3 ,,, V N and A 2 , A 3 ,,, A N , and establish a linear relationship between the total volume V and the differential absorbance A: V = k·A + b;

[0021] S6. Substitute the differential absorbance A at the titration end point T into the linear relationship, and the titration volume V of the indicator solution can be calculated T :

[0022] V T = k·A T + b.

[0023] In some embodiments of the present invention, step S4 specifically includes the following steps:

[0024] S41. Control the injection pump to suck the indicator and then switch the multi-channel switching valve to the reaction vessel. Control the injection pump to move upward at a fixed step size, and inject a drop of the indicator into the reaction vessel. The control module calculates and records the total volume V of the indicator dropped into the reaction vessel;

[0025] S42. Start the multi-channel spectral sensor to collect the light intensity I α 1 and I β 1 ;

[0026] S43. The control module calculates the differential absorbance A using formula one,

[0027] S44. Determine whether the differential absorbance A reaches the threshold. If not, repeat steps S41 - S43 until the differential absorbance A reaches the threshold, and record the differential absorbance A that reaches the threshold as A 1 and the total volume V of the indicator dropped into the reaction vessel at this time as V 1 .

[0028] In some embodiments of the present invention, formula one in step S43 is as follows:

[0029] A = log(I α 0 / I α 1 ) - log(I β 0 / Iβ 1 )。

[0030] In some embodiments of the present invention, in step S5, the recorded data V 1 -V N and A 1 -A N average value and calculate the slope k and intercept b in the linear relationship; the calculation formula for the slope k is:

[0031] ;

[0032] The calculation formula for the intercept b is: 。

[0033] In some embodiments of the present invention, in step S1, after the sample to be measured is injected into the reaction vessel, the liquid level in the reaction vessel is higher than the fixed position of the light source.

[0034] In some embodiments of the present invention, both the air duct and the reagent duct are made of polytetrafluoroethylene ducts.

[0035] In some embodiments of the present invention, after the titration volume is calculated, the multi-channel switching valve is controlled to switch to the waste discharge duct, then the peristaltic pump is started, and the rotation direction of the peristaltic pump is controlled to drain the waste liquid in the reaction vessel along the waste discharge duct, and the detection is ended.

[0036] The technical solution of the present invention has the following technical effects compared with the prior art:

[0037] The technical solution of the present invention adopts the differential spectroscopy method, uses the differential absorbance at multiple wavelengths to determine the titration end point, and eliminates the interference factor of the mixed bubbles on the optical signal; at the same time, after each titration reaches the differential absorbance threshold, the method of on-site fitting the calibration line is adopted, and the linear regression method is used to calculate the total volume of the indicator consumed when the titration end point is reached, fully considering the factors such as the temperature and volume of the liquid in the reaction vessel at the end of the titration on the absorbance, and significantly improving the resolution and measurement accuracy of the on-line automatic analyzer. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0039] Figure 1It is a schematic structural diagram of the automatic titration device.

[0040] Figure 2 It is a schematic diagram of the linear relationship and fitting scale line between the differential absorbance and the titration volume of the indicator.

[0041] Reference numerals: 1 - multi-channel switching valve; 2 - first control line; 3 - first reagent conduit; 4 - control module; 5 - second control line; 6 - light source; 7 - reaction vessel; 8 - first air conduit; 9 - peristaltic pump; 10 - electromagnetic switching valve; 11 - second air conduit; 12 - waste liquid recovery part; 13 - syringe pump; 14 - first liquid; 15 - second liquid; 16 - third liquid; 17 - second reagent conduit; 18 - first waste discharge conduit; 19 - second waste discharge conduit; 20 - third control line; 21 - fourth control line; 22 - fifth control line; 23 - multi-channel spectral sensor. Detailed implementation manners

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0043] Embodiment 1

[0044] Referring to Figure 1 As shown, an automatic titration device based on differential spectroscopy involved in this embodiment includes:

[0045] A reaction vessel 7 for placing a sample to be measured and an indicator.

[0046] A syringe pump 13, connected to a plurality of reagent conduits by a multi-channel switching valve 1, for sucking liquid into the reaction vessel 7.

[0047] A light source 6 and a multi-channel spectral sensor 23, symmetrically arranged on both sides of the reaction vessel 7, and their installation positions are not higher than the height of the sample to be measured in the reaction vessel 7.

[0048] A control module 4, communicatively connected to the multi-channel spectral sensor 23, for collecting the transmitted light intensity I at a plurality of measurement wavelengths, and also for calculating the titration volume V of the indicator and calculating the differential absorbance A after adding the titration volume V of the indicator to the sample to be measured.

[0049] In some embodiments of the present invention, the sample to be measured is a colorless liquid; the indicator is a colored liquid; the light source 6 is a white light LED light source, and the multi-channel spectral sensor 23 selects the measurement wavelength according to the absorption spectrum of the indicator. For example, if potassium permanganate is used as the indicator, the measurement wavelengths are selected as 550 nm and 680 nm.

[0050] In some embodiments of the present invention, the reaction vessel 7 is made of a quartz tube, and an air duct is connected to its bottom. The air duct is connected to a peristaltic pump 9, and the peristaltic pump 9 is used to pump air into the reaction vessel 7 to generate mixing bubbles.

[0051] In some embodiments of the present invention, the multi-channel switching valve 1 is a multi-channel electrically controlled rotary switching valve, which is communicatively connected to the control module through the first control line 2 and is used to receive control instructions. The multi-channel switching valve 1 is connected to the reaction vessel 7 through the first reagent conduit 3 and is used to inject reagents into the reaction vessel 7; the multi-channel switching valve 1 is also connected to each reagent-containing container through a plurality of second reagent conduits 17 respectively. In this embodiment, the first liquid 14 is pure water, the second liquid 15 is a potassium permanganate reagent, and the third solution 16 is the sample to be measured; the multi-channel switching valve 1 is also connected to an injection pump 13 to realize the injection of each liquid into the reaction vessel 7.

[0052] In some embodiments of the present invention, the peristaltic pump 9 is connected to the reaction vessel 7 through the first air duct 8. Additionally, an electromagnetic switching valve 10 is included, which is connected to a second air duct 11 and cooperates with the peristaltic pump 9 to inject air into the reaction vessel 7 to generate mixing bubbles; furthermore, the electromagnetic switching valve 10 and the multi-channel switching valve 1 are respectively connected to a waste liquid recovery member 12 through a first waste discharge conduit 18 and a second waste discharge conduit 19 to discharge the waste liquid in the reaction vessel 7 after the detection is completed.

[0053] In some embodiments of the present invention, both the first reagent conduit 3 and the first air duct 8 connected to the reaction vessel 7 are made of polytetrafluoroethylene conduits.

[0054] In some embodiments of the present invention, the control module 4 is also communicatively connected to the light source 6 through a second control line, to the electromagnetic switching valve 10 through a third control line 20, to the peristaltic pump 9 through a fourth control line 21, and to the multi-channel spectral sensor 23 through a fifth control line 22; that is, the control module 4 transmits control instructions to other devices through each control line.

[0055] In some embodiments of the present invention, the permanganate index is an important indicator for evaluating the water quality of surface water, drinking water, and domestic sewage. The amount of potassium permanganate consumed in the reaction can be measured by titration to obtain the permanganate index. Next, the description of the measurement method will specifically take potassium permanganate as an example of the indicator.

[0056] The method for measuring the titration volume of the automatic titration device includes the following steps:

[0057] S1. After the sample to be measured is made colorless, it is injected into the reaction vessel 7 by the injection pump 13;

[0058] Regarding the process of making colorless: Add 100 ml of water sample, 10 ml of potassium permanganate solution with a concentration of 0.01 mol / L, and 5 ml of 1:3 dilute sulfuric acid to a conical flask, place it in a boiling water bath, and heat for 30 minutes;

[0059] Add 10 ml of sodium oxalate solution with a concentration of 0.01 mol / L to the heated mixed reagent until the solution becomes colorless, and use it as the sample to be measured;

[0060] Then the control module 4 controls the multi-channel switching valve 1 and the injection pump 13 to aspirate a volume of V0, specifically 7.8125 ml of the sample to be measured, and inject it into the reaction vessel 7 to make the liquid level in the reaction vessel 7 higher than the light source 6;

[0061] S2. Control the electromagnetic switching valve 10 to switch to the air duct channel; turn on the peristaltic pump 9, control the rotation direction of the peristaltic pump 9, and pump air into the bottom of the reaction vessel 7 along the air duct to generate mixing bubbles for mixing the titration reagent;

[0062] S3. Turn on the light source 6. In this embodiment, a high-directivity LED warm white light source with a color temperature of 2900K and a light-emitting angle of 20 degrees is used; start the multi-channel spectral sensor 23 to measure the initial light intensities I 550 0 and I 680 0 ;

[0063] S41. First, control the multi-channel switching valve 1 to the second liquid 15, control the injection pump 13 to move down, and aspirate 1 ml of potassium permanganate reagent;

[0064] Then control the multi-channel switching valve 1 to switch to the reaction vessel 7, control the injection pump 13 to move up at a fixed step, and inject a drop of potassium permanganate into the reaction vessel 7. The control module 4 calculates and records the total volume V of the potassium permanganate dropped into the reaction vessel 7.

[0065] S42. Start the multi-channel spectral sensor 23 to measure the light intensities I 550 1 and I 680 1 ;

[0066] S43. The control module 4 calculates the differential absorbance A using Equation 1. 550-680 Equation 1 is as follows:

[0067] A 550-680 = log(I α 0 / I α 1 ) - log(I β 0 / I β 1 );

[0068] S44. Determine whether the differential absorbance A 550-680 reaches the threshold value, which can be 0.01; if so, continue with the detection step; if not, repeat steps S41 - S43 until the differential absorbance A 550-680 reaches the threshold value of 0.01, and record the differential absorbance A that reaches the threshold value of 0.01 as A 1 and the total volume V of the potassium permanganate dropped into the reaction vessel 7 at this time as V 1 ;

[0069] S5. Repeat step S4 N times. After each completion, the control module 4 records the total volume V of the potassium permanganate dropped into the reaction vessel 7 and the differential absorbance A as V 2 , V 3 ,..., V N and A 2 , A 3 ,..., A N . Control the volume of each drop of potassium permanganate to 0.0208 ml using the syringe pump 13; refer to the following table.

[0070]

[0071] The control module 4 establishes a linear relationship between the total volume V and the differential absorbance A: V = k·A + b;

[0072] Use the recorded data V 1 - V N and A 1 - A N average values and to calculate the slope k and intercept b in the linear relationship; the calculation formula for the slope k is:

[0073] ;

[0074] The calculation formula for the intercept b is: ;

[0075] Refer to Figure 2 As shown, the calculated slope k is 1.4281, the intercept b is 0.1184, and R 2 is 0.9994.

[0076] S6. Substitute the differential absorbance A T at the titration end point into the linear relationship formula, and the titration volume V T of potassium permanganate can be calculated as follows:

[0077] V T = 1.4281·A T + 0.1184;

[0078] In this embodiment, the differential absorbance A T at the titration end point takes the value of 0.025. Substituting it into the above formula, the accurate titration volume at the titration end point can be obtained as 0.1541 ml.

[0079] However, usually when the volume of the indicator is less than one drop, the titration end point can be reached. Therefore, the calculation result of the titration volume in this embodiment is not related to the fixed volume V0 (0.0208 ml) of one drop injected by the injection pump 13.

[0080] The traditional titration method in the prior art can only provide the resolution ability of multiples of the fixed volume V0 (0.0208 ml) of each drop of reagent, that is, the titration volume obtained by the traditional method is 7 times of V0 (0.1458 ml) or 8 times of V0 (0.1667 ml). Compared with the resolution ability of the fixed volume V0 of each drop of reagent during titration, the present invention can accurately calculate the accurate volume of the potassium permanganate solution consumed when the titration end point is reached by using linear regression to fit the calibration curve on site, and can effectively improve the resolution and measurement accuracy.

[0081] In some embodiments of the present invention, after the titration volume is calculated, control the multi-channel switching valve 1 and the electromagnetic switching valve 10 to switch to the first waste discharge conduit 18 and the second waste discharge conduit 19, then turn on the peristaltic pump 9, control the rotation direction of the peristaltic pump 9, and drain the waste liquid in the reaction vessel 7 along the waste discharge conduit direction to end the detection.

[0082] The technical solution of the present invention has the following technical effects compared with the prior art:

[0083] The technical solution of the present invention adopts the differential spectroscopy method, determines the titration end point by using the differential absorbance at multiple wavelengths, and eliminates the interference factors of the mixed bubbles on the optical signal; at the same time, after each titration reaches the differential absorbance threshold, the method of on-site fitting calibration lines is adopted, and the linear regression method is used to calculate the total volume of the indicator consumed when the titration end point is reached, fully considering the influence of factors such as the temperature and volume of the liquid in the reaction vessel at the end of the titration on the absorbance, and significantly improving the resolution and measurement accuracy of the on-line automatic analyzer.

[0084] The above are only the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for measuring the titration volume of an automatic titration device based on differential spectroscopy, characterized in that, It includes the following steps: S1. After the sample to be tested is made colorless, it is injected into the reaction vessel by an injection pump; S2. Start the peristaltic pump and inject mixed bubbles into the reaction vessel; S3. Turn on the light source and start the multi-channel spectral sensor to collect the initial light intensity I of the measurement wavelength α 0 and I β 0 ; S4. After injecting a drop of indicator into the reaction vessel, start the multi-channel spectral sensor to collect the light intensity I at the measurement wavelength α 1 and I β 1 , the control module calculates and records the total volume V of the indicator dropped into the reaction vessel 1 and calculates the differential absorbance A 1 ; S5. Repeat step S4 for N times. After each repetition, the control module successively records the total volume V of the indicator dropped into the reaction vessel and the differential absorbance A as V 2 , V 3 , …, V N and A 2 , A 3 , …, A N , and establish a linear relationship between the total volume V and the differential absorbance A: V = k·A + b; S6. Substitute the differential absorbance A at the titration end point T into the linear relationship formula to calculate the titration volume V of the indicator T : V T = k·A T + b; The specific steps of step S4 include the following steps: S41. Control the injection pump to suck the indicator, then switch the multi-channel switching valve to the reaction vessel, control the injection pump to move up at a fixed step, inject a drop of the indicator into the reaction vessel, and the control module calculates and records the total volume V of the indicator dropped into the reaction vessel; S42. Start the multi-channel spectral sensor to collect the light intensity I at the measurement wavelength α 1 and I β 1 ; S43. The control module calculates the differential absorbance A using formula 1, and formula 1 is as follows: A = log(I α 0 / I α 1 ) - log(I β 0 / I β 1 ); S44. Determine whether the differential absorbance A reaches the threshold. If not, repeat steps S41 - S43 until the differential absorbance A reaches the threshold, and record the differential absorbance A that reaches the threshold as A 1 and record the total volume V of the indicator dropped into the reaction vessel at this time as V 1 ; In the step S5, the recorded data V 1 -V N and the average value of A 1 -A N are used to calculate the slope k and the intercept b in the linear relationship; the calculation formula for the slope k is as follows: and ​ ； The calculation formula for the intercept b is as follows: ; The measurement method is implemented by an automatic titration device, and the automatic titration device includes: A reaction vessel for placing the sample to be tested and the indicator; An injection pump connected to multiple reagent conduits through a multi-channel switching valve, for sucking liquid into the reaction vessel; A light source and a multi-channel spectral sensor, symmetrically arranged on both sides of the reaction vessel, and their installation positions are not higher than the height of the sample to be tested in the reaction vessel; A control module, which is communicatively connected to the multi-channel spectral sensor, for collecting the transmitted light intensity I at multiple measurement wavelengths, and also for calculating the titration volume V of the indicator and calculating the differential absorbance A after adding the titration volume V of the indicator to the sample to be tested.

2. The measurement method according to claim 1, characterized in that, The sample to be tested is a colorless liquid; the indicator is a colored liquid; the light source is a white light source, and the multi-channel spectral sensor selects the measurement wavelength according to the absorption spectrum of the indicator.

3. The measuring method according to claim 1, characterized in that An air conduit is connected to the bottom of the reaction vessel, and the air conduit is connected to the peristaltic pump. The peristaltic pump is used to pump air into the reaction vessel to generate mixed bubbles.

4. The measurement method according to claim 1, wherein In step S1, after the sample to be tested is injected into the reaction vessel, the liquid level in the reaction vessel is higher than the fixed position of the light source.

5. The measuring method according to claim 3, characterized in that Both the air conduit and the reagent conduit are made of polytetrafluoroethylene conduits.

6. The measuring method according to claim 1, characterized in that, After the titration volume is calculated, control the multi-channel switching valve to switch to the waste discharge conduit, then start the peristaltic pump, control the rotation direction of the peristaltic pump, and drain the waste liquid in the reaction vessel along the waste discharge conduit to end the detection.

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