A device and method for measuring water sample alkalinity based on ORP electrode

Abstract

The invention relates to a device and method for measuring the alkalinity of a water sample based on an ORP electrode. The device comprises a controller, a measuring component and a sample adding component. The measuring component comprises a water sample container and an ORP electrode. The water sample container is used to place a water sample to be measured. The ORP electrode is electrically connected to the controller and is arranged in the water sample container. The sample adding component comprises a metering pump. The metering pump is connected to a standard hydrochloric acid solution container and the water sample container through a pipeline and is electrically connected to the controller. By adopting the ORP electrode, a change in the ORP redox potential is utilized during the titration process to identify the endpoint of the titration, replacing manual judgment of the color change endpoint in the titration. The device has good measurement accuracy and consistency, and can accurately measure the phenolphthalein alkalinity and total alkalinity in water quality. Compared with the limitation that an optical titration method is only applicable to colorless and low-turbidity water samples, the ORP electrode can measure not only colorless and low-turbidity water samples, but also colored water samples and water samples with a certain turbidity. It has a wide range of applications and can realize online and real-time measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion content detection, and in particular relates to a water sample alkalinity measurement device and method based on an ORP electrode. Background Art

[0002] Water alkalinity refers to the amount of substances in the water that can accept hydrogen ions. Examples include hydroxide, carbonate, bicarbonate, phosphate, hydrogen phosphate, silicate, hydrogen silicate, sulfite, humate, and ammonia. These are all common alkaline substances in water and react with acids. Alkalinity is a crucial indicator for industrial boilers and industrial circulating cooling equipment. The amount of sodium carbonate and other substances added must be controlled based on the alkalinity to maintain the proper alkalinity in the boiler water. This optimizes the ratio of calcium, magnesium, carbonate, phosphate, and hydroxide ions, allowing the calcium and magnesium to form a dispersed slag precipitate that doesn't adhere to the boiler's heating surfaces and is discharged with the boiler's blowdown to prevent scaling and corrosion. According to national standards such as GB / T 1576 "Industrial Boiler Water Quality", the alkalinity of water quality is divided into total alkalinity and phenolphthalein alkalinity. Phenolphthalein alkalinity is the amount of substances that can accept hydrogen ions measured when phenolphthalein is used as an indicator, while total alkalinity is the amount of substances that can accept hydrogen ions measured when methyl orange or methyl red-methylene blue are used as indicators.

[0003] Currently, the determination of phenolphthalein alkalinity and / or total alkalinity in water quality uses phenolphthalein and methyl orange as indicators, titrating with a standard acid solution of known concentration. The titration endpoint is determined based on the color change of the mixed solution, and the phenolphthalein alkalinity and / or total alkalinity is calculated based on the volume of the standard acid solution consumed. However, since the pH range of phenolphthalein's color change is 8.2-10.0, and the pH range of methyl orange's color change is 3.1-4.4, different people may judge the endpoint differently within the color change range of the indicator, which can easily lead to errors in the amount of standard acid solution used, resulting in errors in the calculated content of phenolphthalein alkalinity and / or total alkalinity. Summary of the Invention

[0004] In view of the defects in the prior art, the object of the present invention is to provide a device and method for measuring the alkalinity in water samples such as boiler water and surface water.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a water sample alkalinity measuring device based on an ORP electrode, comprising:

[0006] Controller;

[0007] The measuring component includes a water sample container and an ORP electrode. The water sample container is used to place the water sample to be measured. The ORP electrode is electrically connected to the controller and is arranged in the water sample container.

[0008] The sample adding component comprises a quantitative pump, which is connected to a standard hydrochloric acid solution container and a water sample container through a pipeline, and is electrically connected to a controller.

[0009] Furthermore, the controller includes a main board, an output control board, a signal board, a display screen and a power supply. The output control board, the signal board, the display screen and the power supply are all electrically connected to the main board; the output control board is electrically connected to the metering pump for controlling the action of the metering pump; the signal board is electrically connected to the ORP electrode for receiving the potential signal of the ORP electrode.

[0010] Furthermore, the measuring component also includes a stirrer, which is installed at the bottom of the water sample container.

[0011] Furthermore, the stirrer is electrically connected to the main board via the output control board.

[0012] Furthermore, the measuring component also includes a sampling solenoid valve and a constant volume solenoid valve. The sampling solenoid valve is connected to the water sample pool to be tested and the water sample container through a pipeline, and the constant volume solenoid valve is connected to the sewage pool and the water sample container through a pipeline.

[0013] Furthermore, a constant volume solenoid valve is installed at the 100 mL liquid level of the water sample container.

[0014] Furthermore, the signal board includes an amplifying circuit, a measuring circuit and a single-chip microcomputer connected in sequence. The measuring circuit can measure the electrical signal of the ORP electrode. The measuring circuit is connected to the main board through an internal CAN bus. The main board has a resistive touch screen interface and a CAN_bus communication interface.

[0015] Furthermore, the mainboard is an EPC-287I-LT industrial control mainboard.

[0016] A method for measuring the alkalinity of a water sample based on an ORP electrode is performed using the above-mentioned device for measuring the alkalinity of a water sample based on an ORP electrode, comprising the following steps:

[0017] Step (1), taking a water sample to be tested and placing it in a water sample container, and recording the volume of the water sample to be tested as V;

[0018] Step (2), adding hydrochloric acid solution to the water sample to be tested at a uniform rate, recording the concentration c(HCl) of the hydrochloric acid solution, and recording the ORP value change curve of the water sample to be tested that changes with the amount of hydrochloric acid solution added;

[0019] Step (3), determining whether the ORP value change curve of the water sample solution to be tested has two peaks, if yes, recording the two peaks as the first characteristic point and the second characteristic point, recording the volume V1 of the hydrochloric acid solution added from the beginning to the first characteristic point and the volume V2 of the hydrochloric acid solution from the first characteristic point to the second characteristic point, otherwise proceeding to step (4);

[0020] Step (4): record the peak value of the ORP value change curve of the water sample solution to be tested as the third characteristic point, and record the volume V3 of the hydrochloric acid solution added from the beginning to the third characteristic point.

[0021] Furthermore, the ORP values ​​of the water sample solutions to be tested are all less than 440 mV.

[0022] Furthermore, the ORP value of the first characteristic point is within the range of 180 to 300 mV, the ORP value of the second characteristic point is within the range of 320 to 440 mV, and the ORP value of the third characteristic point is within the range of 320 to 440 mV.

[0023] Furthermore, in step (3), the calculation method of phenolphthalein alkalinity and total alkalinity in the water sample to be tested is:

[0024] JD P =V1×c(HCl)×1000 / V;

[0025] JD T =(V1+V2)×c(HCl)×1000 / V;

[0026] JD P is the phenolphthalein alkalinity, in millimoles per liter (mmol / L);

[0027] JD T is the total alkalinity, in millimoles per liter (mmol / L);

[0028] V1 is the volume of the hydrochloric acid solution from the beginning of addition to the first characteristic point, in milliliters (mL);

[0029] V2 is the volume of the hydrochloric acid solution from the first characteristic point to the second characteristic point, in milliliters (mL);

[0030] c(HCl) is the concentration of the hydrochloric acid solution in moles per liter (mol / L);

[0031] V is the volume of the water sample to be tested, in mL.

[0032] Furthermore, in step (4), the calculation method of phenolphthalein alkalinity and total alkalinity in the water sample to be tested is:

[0033] JD P =0;

[0034] JD T =(0+V3)×c(HCl)×1000 / V;

[0035] JD P is the phenolphthalein alkalinity, in millimoles per liter (mmol / L);

[0036] JDT is the total alkalinity, in millimoles per liter (mmol / L);

[0037] V3 is the volume of the hydrochloric acid solution added from the beginning to the third characteristic point, in milliliters (mL);

[0038] c(HCl) is the concentration of the hydrochloric acid solution in moles per liter (mol / L);

[0039] V is the volume of the water sample to be tested, in mL.

[0040] The present invention has the following effects: the system and method of the present invention adopt an ORP electrode, and during the titration process, the endpoint of the titration is identified by utilizing the change of the ORP redox potential, thereby replacing manual judgment of the color change endpoint in the titration and replacing judgment of the endpoint by a pH titration method in which the pH reaches a preset value; the measurement accuracy and consistency are good, and the phenolphthalein alkalinity and total alkalinity in water quality can be measured in real time and accurately; compared with the limitation that the optical titration method is only applicable to colorless and low-turbidity water samples, the ORP electrode can measure not only colorless and low-turbidity water samples, but also colored water samples and water samples with a certain turbidity; the application range is wide, and online and real-time measurement can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of the water sample alkalinity measuring device based on the ORP electrode of the present invention;

[0042] Figure 2 is a flow chart of the method for measuring alkalinity of a water sample based on an ORP electrode of the present invention;

[0043] Figure 3 This is the hydrochloric acid volume-OPR value change curve in Example 1 of the present invention;

[0044] Figure 4 This is the hydrochloric acid volume-OPR value change curve in Example 2 of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0046] Example 1

[0047] like Figure 1As shown, this embodiment discloses a device for measuring the alkalinity of a water sample based on an ORP electrode, which includes a controller 1, a measuring component 2, and a sample adding component 3. The measuring component 2 includes a water sample container 21 and an ORP electrode 22. The water sample container 21 is used to place the water sample to be tested. The ORP electrode 22 is electrically connected to the controller 1 and is disposed inside the water sample container 21. Under the control of the controller 1, the ORP electrode 22 can stably collect the potential of the redox reaction in the water sample to be tested.

[0048] Furthermore, the sample adding component 3 of this embodiment includes a metering pump, which is electrically connected to the controller 1 ; the metering pump is connected to the standard hydrochloric acid solution container and the water sample container 21 through a pipeline, and can automatically add hydrochloric acid to the water sample container 21 under the control of the controller 1 .

[0049] Furthermore, the controller 1 of this embodiment includes a mainboard 11, an output control board 12, a signal board 13, a display screen 14, and a power supply 15. The mainboard 11 is an EPC-287I-LT industrial control mainboard, but can be replaced with other mainboards capable of communication, measurement, and control functions depending on the reagent requirements. The output control board 12, signal board 13, display screen 14, and power supply 15 are all electrically connected to the mainboard 11; the output control board 12 is electrically connected to the metering pump for controlling its operation; and the signal board 13 is electrically connected to the ORP electrode 22 for receiving the potential signal from the ORP electrode 22.

[0050] Furthermore, the measuring component 2 of this embodiment also includes a stirrer 23, which is installed at the bottom of the water sample container 21, and the stirrer 23 is electrically connected to the main board 11 through the output control board 12. Under the electrical control of the output control board 12, the stirrer 23 can mix the water sample to be tested and the added reagent evenly.

[0051] Furthermore, the measuring component 2 also includes a sampling solenoid valve 24 and a constant volume solenoid valve 25. The sampling solenoid valve 24 is connected to the water sample pool to be measured and the water sample container 21 through a pipeline, and the constant volume solenoid valve 25 is connected to the sewage tank and the water sample container 21 through a pipeline. The constant volume solenoid valve 25 is installed at the 100 mL liquid level of the water sample container.

[0052] Furthermore, signal board 13 includes an amplifier circuit, a measurement circuit, and a single-chip microcomputer connected in sequence. The measurement circuit is capable of measuring the potential signal of the ORP electrode 22. The measurement circuit is connected to main board 11 via an internal CAN bus. Main board 11 has a resistive touch screen interface and a CAN-bus communication interface. Signal board 13 amplifies the potential signal of the ORP electrode 22, facilitating data capture and observation.

[0053] Example 2

[0054] This embodiment discloses a method for measuring the alkalinity of a water sample based on an ORP electrode, which is performed using the device for measuring the alkalinity of a water sample based on an ORP electrode in Example 1, and includes the following steps:

[0055] Step (1), taking the water sample to be tested and placing it in the water sample container, recording the volume of the water sample to be tested as V; specifically, first passing the water sample to be tested to rinse the water sample container, the flow rate of the water sample to be tested is 100-200mL / min, the rinsing time is 3 minutes, then taking 100mL of the water sample to be tested and placing it in the water sample container, that is, V=100mL. The water sample to be tested can be introduced through the sampling solenoid valve and discharged through the constant volume solenoid valve. After closing the sampling solenoid valve to stop the introduction of the water sample to be tested, the constant volume solenoid valve can control the volume of the water sample to be tested in the water sample container to be 100mL.

[0056] Step (2), add hydrochloric acid solution to the water sample to be tested at a uniform speed, record the concentration c (HCl) of the hydrochloric acid solution, and record the ORP value change curve of the water sample to be tested as the amount of hydrochloric acid solution added changes. The hydrochloric acid solution of this embodiment is added at a uniform and stable speed of 100 μL / s by a metering pump, and the concentration of the hydrochloric acid solution is 0.1 mol / L. In this embodiment, the titration experiment is repeated using the same water sample to be tested, and the data of the two titration experiments are collected and the ORP value change curve of the water sample to be tested is recorded as shown in FIG. Figure 3 shown.

[0057] Step (3) determines whether the ORP value change curve of the water sample solution to be tested has two peaks. If so, record the two peaks as the first characteristic point and the second characteristic point, and record the volume V1 of the hydrochloric acid solution added from the beginning to the first characteristic point and the volume V2 of the hydrochloric acid solution from the first characteristic point to the second characteristic point. In this embodiment, the ORP value change curve has two peaks, and the two peaks are the first characteristic point and the second characteristic point. The ORP value of the first characteristic point should be within the range of 180 to 300 mV, and the ORP value of the second characteristic point should be within the range of 320 to 440 mV. This embodiment meets the requirements, and the ORP values ​​of the water sample solution to be tested are all less than 440 mV. This embodiment also meets the requirements. Therefore, it can be determined that the first characteristic point is the titration end point of phenolphthalein alkalinity, and the second characteristic point is the titration end point of full alkalinity. Then, record the volume V1 of the hydrochloric acid solution added from the beginning to the first characteristic point as 0.5 mL; record the volume V2 of the hydrochloric acid solution from the first characteristic point to the second characteristic point as 0.15 mL.

[0058] Then, in step (3), the calculation method of phenolphthalein alkalinity and total alkalinity in the water sample to be tested is:

[0059] JD P=V1×c(HCl)×1000 / V=0.5mL×0.1mol / L×1000 / 100mL=0.5mmol / L;

[0060] JD T =(V1+V2)×c(HCl)×1000 / V=(0.5+0.15)mL×0.1mol / L×1000 / 100mL=0.65mmol / L;

[0061] JD P is the phenolphthalein alkalinity, in millimoles per liter (mmol / L);

[0062] JD T is the total alkalinity, in millimoles per liter (mmol / L);

[0063] V1 is the volume of the hydrochloric acid solution from the beginning of addition to the first characteristic point, in milliliters (mL);

[0064] V2 is the volume of the hydrochloric acid solution from the first characteristic point to the second characteristic point, in milliliters (mL);

[0065] c(HCl) is the concentration of the hydrochloric acid solution in moles per liter (mol / L);

[0066] V is the volume of the water sample to be tested, in mL.

[0067] Example 3

[0068] As another embodiment of the present invention, this embodiment also discloses a method for measuring the alkalinity of a water sample based on an ORP electrode, which is performed using the water sample alkalinity measuring device based on an ORP electrode in Example 1, comprising the following steps:

[0069] Step (1), taking the water sample to be tested and placing it in the water sample container, recording the volume of the water sample to be tested as V; specifically, first passing the water sample to be tested to rinse the water sample container, the flow rate of the water sample to be tested is 100-200mL / min, the rinsing time is 3 minutes, then taking 100mL of the water sample to be tested and placing it in the water sample container, that is, V=100mL. The water sample to be tested can be introduced through the sampling solenoid valve and discharged through the constant volume solenoid valve. After closing the sampling solenoid valve to stop the introduction of the water sample to be tested, the constant volume solenoid valve can control the volume of the water sample to be tested in the water sample container to be 100mL.

[0070] Step (2) adds hydrochloric acid solution to the water sample to be tested at a uniform speed, records the concentration c(HCl) of the hydrochloric acid solution, and records the ORP value change curve of the water sample to be tested as the amount of hydrochloric acid solution added changes. The hydrochloric acid solution of this embodiment is added at a uniform and stable speed of 100 μL / s by a quantitative pump, and the concentration of the hydrochloric acid solution is 0.1 mol / L. And the ORP value change curve of the water sample to be tested is recorded as follows: Figure 4 shown.

[0071] Step (3) determines whether the ORP value change curve of the water sample solution to be tested has two peaks. Otherwise, it means that the ORP value change curve of the water sample solution to be tested has only one peak. Record the peak as the third characteristic point, and record the volume V3 of the hydrochloric acid solution added from the beginning to the third characteristic point. In this embodiment, the ORP value change curve has only one obvious peak, and the ORP value of the third characteristic point is within the range of 320 to 440 mV. This embodiment meets the requirements, and the ORP values ​​of the water sample solution to be tested are all less than 440 mV. This embodiment also meets the requirements. Therefore, it can be determined that the water sample to be tested in this embodiment does not contain phenolphthalein alkalinity, and the third characteristic point is the titration end point of full alkalinity. Then, record the volume V3 of the hydrochloric acid solution added from the beginning to the third characteristic point as 0.995 mL.

[0072] Then, in step (3) of this embodiment, the calculation method of phenolphthalein alkalinity and total alkalinity in the water sample to be tested is:

[0073] JD P =0mmol / L;

[0074] JD=(0+V3)×c(HCl)×1000 / V=(0+0.995)mL×0.1mol / L×1000 / 100mL=0.995mmol / L;

[0075] JD P is the phenolphthalein alkalinity, in millimoles per liter (mmol / L);

[0076] JD is the total alkalinity, in millimoles per liter (mmol / L);

[0077] V1 is the volume of the hydrochloric acid solution added first, in milliliters (mL);

[0078] V2 is the volume of hydrochloric acid solution added again, in milliliters (mL);

[0079] c1(HCl) is the concentration of hydrochloric acid solution, in moles per liter (mol / L);

[0080] V is the volume of the water sample to be tested, in mL.

[0081] Those skilled in the art should understand that the methods and systems of the present invention are not limited to the embodiments described in the specific embodiments. The above detailed description is only for the purpose of explaining the present invention and is not intended to limit the present invention. Those skilled in the art may derive other embodiments based on the technical solution of the present invention, which also fall within the scope of the technical innovation of the present invention. The scope of protection of the present invention is defined by the claims and their equivalents.

Claims

1. A method for measuring the alkalinity of a water sample based on an ORP electrode, characterized in that: The method is based on a water sample alkalinity measurement device, which includes: Controller; The measuring component includes a water sample container and an ORP electrode, wherein the water sample container is used to place the water sample to be measured, the ORP electrode is electrically connected to the controller, and the ORP electrode is arranged in the water sample container; A sample adding component, comprising a metering pump, the metering pump being connected to the standard hydrochloric acid solution container and the water sample container via a pipeline, and the metering pump being electrically connected to the controller; The method comprises the following steps: Step (1), taking 100 mL of the water sample to be tested and placing it in a water sample container, the ORP value of the water sample solution to be tested is less than 440 mV, and the volume of the water sample to be tested is recorded as V; Step (2), adding hydrochloric acid solution to the water sample to be tested at a uniform rate, recording the concentration c(HCl) of the hydrochloric acid solution, and recording the ORP value change curve of the water sample to be tested that changes with the amount of hydrochloric acid solution added; Step (3), determining whether the ORP value change curve of the water sample solution to be tested has two peaks, if so, recording the two peaks as a first characteristic point and a second characteristic point, the ORP value of the first characteristic point being within the range of 180 to 300 mV, and the ORP value of the second characteristic point being within the range of 320 to 440 mV, recording the volume V1 of the hydrochloric acid solution added from the beginning to the first characteristic point and the volume V2 of the hydrochloric acid solution from the first characteristic point to the second characteristic point, otherwise proceeding to step (4); Step (4), recording the peak value of the ORP value change curve of the water sample solution to be tested as the third characteristic point, the ORP value of the third characteristic point is in the range of 320 to 440 mV, and recording the volume V3 of the hydrochloric acid solution added from the beginning to the third characteristic point; In step (3), the calculation method of phenolphthalein alkalinity and total alkalinity in the water sample to be tested is: JD P =V1×c(HCl)×1000 / V; JD T =(V1+V2)×c(HCl)×1000 / V; The JD P is the phenolphthalein alkalinity, in millimoles per liter (mmol / L); The JD T is the total alkalinity, in millimoles per liter (mmol / L); V1 is the volume of the hydrochloric acid solution added from the beginning to the first characteristic point, in milliliters (mL); V2 is the volume of the hydrochloric acid solution from the first characteristic point to the second characteristic point, in milliliters (mL); c(HCl) is the concentration of the hydrochloric acid solution, in moles per liter (mol / L); V is the volume of the water sample to be tested, in mL; In step (4), the calculation method of phenolphthalein alkalinity and total alkalinity in the water sample to be tested is: JD P =0; JD T =(0+V3)×c(HCl)×1000 / V; The JD P is the phenolphthalein alkalinity, in millimoles per liter (mmol / L); The JD T is the total alkalinity, in millimoles per liter (mmol / L); V3 is the volume of the hydrochloric acid solution added from the beginning to the third characteristic point, in milliliters (mL); c(HCl) is the concentration of the hydrochloric acid solution, in moles per liter (mol / L); V is the volume of the water sample to be tested, in mL.

2. The method for measuring alkalinity of a water sample based on an ORP electrode according to claim 1, wherein: The controller includes a main board, an output control board, a signal board, a display screen and a power supply. The output control board, the signal board, the display screen and the power supply are all electrically connected to the main board; the output control board is electrically connected to the metering pump for controlling the action of the metering pump; the signal board is electrically connected to the ORP electrode for receiving the potential signal of the ORP electrode.

3. The method for measuring alkalinity of a water sample based on an ORP electrode according to claim 2, wherein: The measuring component further includes a stirrer, which is installed at the bottom of the water sample container and is electrically connected to the main board via the output control board.

4. The method for measuring alkalinity of a water sample based on an ORP electrode according to claim 3, wherein: The measuring component also includes a sampling solenoid valve and a constant volume solenoid valve. The sampling solenoid valve is connected to the water sample pool to be measured and the water sample container through a pipeline, and the constant volume solenoid valve is connected to the sewage pool and the water sample container through a pipeline.

5. The method for measuring alkalinity of a water sample based on an ORP electrode according to claim 4, wherein: The constant volume solenoid valve is installed at the 100 mL liquid level of the water sample container.

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