Device and method for measuring purity of ammonium chloride by weighing potentiometric titration method

Abstract

The invention relates to a device and a method for determining the purity of high-purity ammonium chloride by a weighing potentiometric titration method, and belongs to the field of chemical standard substance purity constant value testing. The device comprises a sample introduction system, a reaction system and a detection system, a sample introduction pipe and a sample discharge pipe in the sample introduction system are respectively introduced into a weighing bottle and a reaction tank, and a flow type intelligent metering pump assembly can accurately control the sample introduction pipe to convey liquid at high speed, medium speed and low speed or stop conveying liquid; the reaction system comprises a reaction tank and a stirring device, the reaction tank contains a tested solution, and the stirring device can be an electromagnetic stirrer or a magnetic rotor; and the detection system comprises an electrode and an automatic titrator. The device is used for titrating the purity of ammonium chloride and evaluating the uncertainty of the purity value of ammonium chloride. The device is convenient to operate, easy to control and high in automation degree, the precision meets the national standard requirement, and the method can be used for purity titration experiments of high-purity substances.

Description

Technical Field

[0001] The invention belongs to the field of purity determination test of chemical standard substances, and in particular relates to a device and a method for determining the purity of high-purity ammonium chloride by weighing potentiometric titration. Background Art

[0002] At present, volumetric titration is widely used in laboratory titration analysis, especially the newly developed automatic titrator. The equipment used in this method is simple, easy to operate and rapid, and it is widely used for the determination of constant components. However, due to the thermal expansion and contraction of the burette material and the volume of the solution with temperature, the measurement accuracy is limited. The repeatability of the volumetric titration test can only reach 0.1%, and it is difficult to achieve a higher titration accuracy. The gravimetric titration method uses a balance to weigh instead of volumetric measurement. The quality of the solution is not affected by temperature changes, and a higher titration accuracy can be achieved.

[0003] In the two national standards GB 10737-2007 "General Rules for Determination of Working Standard Reagent Content - Weighing Potentiometric Titration" and GB 10738-2007 "General Rules for Determination of Working Standard Reagent Content - Weighing Titration", the relative standard deviation can reach 0.02% when the standard reagent is determined using a special glass weighing titration device. In addition, there are also literature reports on weighing titration using a plastic dropper bottle, or microtitration using a syringe and a homemade plastic capillary dropper. In short, the current weighing titration method is inconvenient to operate, difficult to control, and difficult to use in daily analysis. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention has designed and developed a complete set of weighing potentiometric titration devices and testing methods which are easy to operate, easy to control, highly automated and have met the precision requirements. In the experiment, the purity of high-purity ammonium chloride was measured by using the device and method, the purity of high-purity substances was determined, and the uncertainty of the titration process was analyzed and evaluated.

[0005] The invention designs and assembles a complete set of weighing potentiometric titration device, and uses the device to titrate and measure the purity of ammonium chloride.

[0006] A device for determining the purity of ammonium chloride by weighing potentiometric titration comprises three parts: a sample injection system, a reaction system and a detection system; the sample injection system mainly comprises a flow-type intelligent metering pump assembly, a sample injection tube, a sample outlet tube, a weighing bottle, a balance and a wind shield, etc., the flow-type intelligent metering pump assembly is connected to the weighing bottle and the reaction system (reaction pool) through the sample injection tube and the sample outlet tube respectively, the weighing bottle is placed on the balance, and the wind shield is installed on the periphery of the balance; the reaction system comprises a reaction pool, a stirring device and an iron frame assembly, etc., the reaction pool is fixedly mounted on a stirrer through the iron frame assembly; the detection system comprises an electrode and an automatic titrator, etc., the electrode is suspended and fixed in the reaction pool by the iron frame assembly, and is connected to the automatic titrator.

[0007] Furthermore, the sampling system also includes a sampling forearm, a sampling forearm fixing column, a sampling rear arm and a sampling rear arm fixing column, etc. The sampling tube is fixed on the sampling forearm, the sampling forearm is fixed on the sampling forearm fixing column, the sampling tube is connected to the sampling port of the flow-type intelligent metering pump assembly, the sampling outlet tube is fixed on the sampling rear arm, the sampling rear arm is fixed on the sampling rear arm fixing column, and the sampling outlet tube is connected to the sampling outlet of the flow-type intelligent metering pump assembly.

[0008] Furthermore, the flow-type intelligent metering pump assembly can accurately control the injection tube to deliver liquid at high speed, medium speed, low speed or stop. The high-speed injection flow range of the flow-type intelligent metering pump assembly is: 5mL / min~10mL / min, the medium speed range is: 0.5mL / min~1mL / min, and the low speed range is: 0.001mL / min~0.005mL / min; the swing angle α of the injection front arm is 0°~180°, and the lifting height is 10cm~40cm; the swing angle β of the injection rear arm is 0°~180°, and the lifting height is 10cm~30cm.

[0009] Furthermore, the weighing bottle is a wide-mouth brown corrosion-resistant high-density polyethylene bottle with a perforated bottle cap, the aperture of which is just large enough to insert the sample injection tube, in order to reduce the volatilization of the titrant. The balance is a 100,000th Class I precision balance.

[0010] Furthermore, the sampling system also includes a sampling tube cleaning position, which is composed of a cleaning liquid and a container for containing the cleaning liquid.

[0011] Furthermore, in the reaction system, the stirring device may be an electromagnetic stirrer or a magnetic rotor, and the reaction tank is used to contain the solution to be tested.

[0012] Furthermore, the reaction pool is a flat-bottomed three-hole glass flask, the first hole is equipped with a sealing plug with micropores, the sample outlet tube is inserted into the reaction pool through the sealing plug with micropores, the second hole is equipped with a composite Ag electrode, the third hole is equipped with a double-bulb tube, and a cotton ball is placed in the double-bulb tube.

[0013] Furthermore, the reaction pool is fixedly mounted on the stirring device through an iron frame assembly, and the rotation speed of the stirring device can be controlled at 20 rpm to 2000 rpm to ensure that the chemical reaction in the titration process proceeds evenly.

[0014] Furthermore, the reaction system also includes a sample tube cleaning position, which is composed of a cleaning liquid and a container for containing the cleaning liquid.

[0015] Furthermore, in the detection system, the electrode is a composite Ag electrode, and a composite silver ring analog electrode or a digital combined silver ring electrode can be selected. The measurable range of the potential of the automatic titrator is 0 to 2000mV, and the control accuracy of the potential is ±0.1mV. The automatic titrator has a complete data processing system, which can display the complete titration curve on the display screen, monitor the mutation point of the titration potential curve, and alarm to remind the titration end point.

[0016] A method for determining the purity of ammonium chloride by weighing potentiometric titration comprises the following steps:

[0017] (1) Titration method: Prepare AgNO3 titration solution and add it to the weighing bottle. Control the injection forearm to reset to 0°, lower the injection tube to a position below the liquid level of the weighing bottle, and run the flow-type intelligent metering pump in high-speed flow mode to rinse the titrant and fill the entire pipeline. The titrant in this process is discharged into the waste liquid beaker and does not enter the reaction tank; lift the injection forearm 10cm to 20cm to separate the injection tube from the liquid surface and record the displayed quality of the balance at this time; lower the injection forearm and allow the injection tube to be below the liquid level of the weighing bottle. Reset the sample-discharging arm to the top of the reaction tank and discharge the sample tube to the reaction tank filled with the solution to be tested. In the reaction pool, the sample tube is always above the liquid level of the reaction pool during the titration process; insert the electrode into the reaction pool, connect the automatic titrator, start the agitator, automatic titrator, and flow-type intelligent metering pump assembly in sequence for titration, and observe the potential change during the titration process; when the titration end point is reached, the automatic titrator alarms and the flow-type intelligent metering pump assembly is turned off; lift the sample tube above the liquid level and record the mass of the balance at this time; the mass difference between the two weighings is the mass of the consumed titrant after air buoyancy correction. After each titration experiment, the device needs to be cleaned; this step can obtain m2 and m 2k ,m4,m 4k The value of

[0018] (2) Ammonium chloride purity titration scheme: In each experiment, the AgNO3 titration solution is first calibrated with the primary standard substance sodium chloride, and the ammonium chloride sample is immediately titrated after the calibration is completed. During the experiment, the weighing and titration of sodium chloride and ammonium chloride are performed alternately. The raw data of the adjacent AgNO3 titration solution calibration and ammonium chloride sample titration are compiled into a group for calculation as the result of a single determination of the purity of ammonium chloride; the titration operation is performed by two operators A and B, and each operator performs 6 groups of titration analysis experiments in parallel to obtain the ammonium chloride purity titration data;

[0019] (3) Data processing of ammonium chloride purity titration experiment: The relative value of the range of the 12 parallel experimental results of two people can be calculated, which can be used to determine whether the requirements of the relative value of the critical range of repeatability are met, whether the titration operation meets the analysis requirements, and whether the ammonium chloride purity measurement results are accurate and reliable; the Grubbs method is used to perform an outlier test on the above ammonium chloride purity titration data to determine whether there are outliers in the titration data; an F test is performed on the titration data of A and B to test whether the measurement results of A and B are of equal accuracy; if there are no outliers, the average value of the total 12 analysis results of the two people is taken as the purity value of the ammonium chloride sample measured by the weighing potentiometric titration method.

[0020] In step (1), the flow mode of the flow-type intelligent metering pump assembly is set according to the consumption mass of the titrant. When the consumption of the titrant is less than 30 g, the high-speed flow mode is selected; when the consumption is between 30 g and 33 g, the medium-speed mode is selected; and when the consumption is above 33 g, the low-speed mode is selected.

[0021] In step (1), about 100 g of AgNO3 titration solution is added to the weighing bottle, and the concentration of the AgNO3 titration solution is 0.1 mol / L.

[0022] The solution to be tested is a sodium chloride solution or an ammonium chloride solution, and the mass of the sodium chloride in the reaction tank is 0.2±0.01g or the mass of the ammonium chloride is 0.18±0.01g.

[0023] In step (1), the device cleaning method is as follows: after the titration experiment is completed, the sample injection tube, the sample outlet tube and the circulation pipeline are cleaned, the sample injection front arm is controlled to swing at an angle of 0° to 180° to the sample injection tube cleaning position, and the sample outlet rear arm is controlled to swing at an angle of 0° to 180° to the sample outlet tube cleaning position, and can be rinsed with deionized water; the sample injection tube is lowered to the cleaning beaker in the sample injection tube cleaning position, and the sample outlet tube is raised to a height of 20cm to 30cm to the waste liquid cup on the sample outlet tube cleaning position, and the flow type intelligent metering pump assembly is started to rinse the instrument in high-speed flow mode for 10-20min; the sample injection tube is raised to a position above the liquid surface, and the outer walls of the sample injection tube and the sample outlet tube are rinsed with a washing bottle; after cleaning, the sample injection tube, the sample outlet tube, the sample injection front arm and the sample outlet rear arm are reset.

[0024] In step (2), the measurement formula for determining the purity value of ammonium chloride by weighing potentiometric titration is as follows:

[0025]

[0026] Among them, m1 is the weighed mass of sodium chloride, m2 is the mass of the silver nitrate titration solution used to titrate the sodium chloride, and m 2k is the mass of the silver nitrate titration solution used to titrate the blank solution in the sodium chloride process, w B is the purity of the primary standard substance sodium chloride, M B is the molar mass of sodium chloride, m3 is the weighed mass of ammonium chloride, m4 is the mass of the silver nitrate titration solution used to titrate ammonium chloride, and m 4k is the mass of the silver nitrate titration solution used to titrate the blank solution in the ammonium chloride process, M G is the molar mass of ammonium chloride, w G is the purity of ammonium chloride (wt.%).

[0027] The method for determining the purity of ammonium chloride by weighing potentiometric titration of the present invention also includes the following uncertainty evaluation steps of the purity value of ammonium chloride:

[0028] According to the measurement model, the uncertainty sources of the purity value of ammonium chloride determined by weighing potentiometric titration are as follows:

[0029] ① Class A relative standard uncertainty u of ammonium chloride purity titration result A ;

[0030] ② Type B relative standard uncertainty u of ammonium chloride purity titration result B ,include:

[0031] a) Relative standard uncertainty introduced by the weighing mass of sodium chloride;

[0032] b) The relative standard uncertainty introduced by the mass of AgNO3 solution consumed in the AgNO3 calibration process after deducting the blank;

[0033] c) Relative standard uncertainty introduced by the weighing mass of ammonium chloride;

[0034] d) The relative standard uncertainty introduced by the mass of the AgNO3 solution used to titrate ammonium chloride after deducting the blank;

[0035] e) Relative standard uncertainty introduced by the purity of sodium chloride;

[0036] f) Relative standard uncertainty introduced by the molar mass value of sodium chloride;

[0037] g) Relative standard uncertainty introduced by the value of the molar mass of ammonium chloride;

[0038] h) Relative standard uncertainty introduced by rounding off the value of ammonium chloride purity result;

[0039] i) Relative standard uncertainty introduced at the titration endpoint during the calibration process of AgNO3 solution;

[0040] j) Relative standard uncertainty introduced into the titration endpoint of ammonium chloride titration with AgNO3 solution.

[0041] Type B relative standard uncertainty u in the ammonium chloride purity titration process B It is the synthesis of the above components.

[0042] Synthetic relative standard uncertainty u for determination of ammonium chloride purity by gravimetric potentiometric titration C for:

[0043] Under the condition of inclusion probability of 95% and inclusion factor k = 2, the relative expanded uncertainty of the result of ammonium chloride purity determination is: U = ku C .

[0044] The invention discloses a set of weighing potentiometric titration device, and uses the device to test the purity value of high-purity ammonium chloride. Other high-purity salts that meet the weighing titration requirements can also be tested by referring to the method.

[0045] Beneficial effects:

[0046] The invention designs and assembles a set of weighing potentiometric titration device, including a sample injection system, a reaction system and a detection system. The device is complete, easy to operate, easy to control, has a high degree of automation and meets the accuracy requirements, and can be used for purity titration experiments of high-purity substances.

[0047] In the weighing potentiometric titration device of the present invention, the sample feeding system: the sample feeding tube and the sample outlet tube are respectively introduced into the weighing bottle and the reaction tank, and the flow-type intelligent metering pump component can accurately control the sample feeding tube to deliver liquid at high speed, medium speed, low speed or stop. The reaction system: includes a reaction tank and a stirring device, the reaction tank contains the solution to be tested, and the stirring device can use an electromagnetic stirrer or a magnetic rotor. The detection system: includes electrodes and an automatic titrator. The device is used to titrate the purity of ammonium chloride, and the uncertainty of the purity value of ammonium chloride is evaluated. The device is easy to operate, easy to control, has a high degree of automation, and the accuracy meets the requirements of national standards. The method can be used for purity titration experiments of high-purity substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The invention discloses a structural schematic diagram of a device for determining the purity of ammonium chloride by weighing potentiometric titration.

[0049] Description of main reference numerals:

[0050] 1-injection tube; 2-output tube; 3-weighing bottle; 4-reaction pool; 5-flow type intelligent metering pump assembly; 6-stirring device; 7-electrode; 8-automatic titrator; 9-injection front arm; 10-injection front arm fixing column; 11-output rear arm; 12-output rear arm fixing column; 13-balance; 14-wind shield; 15-double ball tube; 16-iron stand assembly; 17-injection tube cleaning position; 18-output tube cleaning position. DETAILED DESCRIPTION

[0051] The following is used to explain the present invention in conjunction with the accompanying drawings and embodiments of the present invention. The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0052] The invention discloses a device for determining the purity of ammonium chloride by weighing potentiometric titration method, which comprises three parts: a sample injection system, a reaction system and a detection system. The device can be used for titration measurement of the purity of ammonium chloride.

[0053] The sampling system mainly includes a sampling tube 1, a sampling outlet tube 2, a weighing bottle 3, a flow-type intelligent metering pump assembly 5, a sampling forearm 9, a sampling forearm fixing column 10, a sampling rear arm 11, a sampling rear arm fixing column 12, a balance 13, a wind shield 14, and a sampling tube cleaning position 17. The flow-type intelligent metering pump assembly 5 is connected to the weighing bottle 3 and the reaction pool 4 of the reaction system through the sampling tube 1 and the sampling outlet tube 2, respectively. The weighing bottle 3 is placed on the balance 13, and the wind shield 14 is installed on the periphery of the balance 13. The sampling tube 1 is fixed on the sampling forearm 9, the sampling forearm 9 is fixed on the sampling forearm fixing column 10, the sampling tube 1 is connected to the sampling port of the flow-type intelligent metering pump assembly 5, the sampling outlet tube 2 is fixed on the sampling rear arm 11, the sampling rear arm 11 is fixed on the sampling rear arm fixing column 12, and the sampling outlet tube 2 is connected to the sampling outlet of the flow-type intelligent metering pump assembly 5. The sample injection tube cleaning position 17 is composed of a cleaning liquid (water) and a container for containing the cleaning liquid.

[0054] In the sampling system, the sampling tube 1 and the sampling tube 2 are respectively introduced into the weighing bottle 3 and the reaction pool 4, and the flow-type intelligent metering pump component 5 can accurately control the sampling tube to deliver liquid at high speed, medium speed, low speed or stop. The injection tube 1 is fixed on the injection forearm 9, and its position is controlled by the injection forearm 9. The injection forearm fixing column 10 is used to support the injection forearm 9. The sample outlet tube 2 is fixed on the sample outlet rear arm 11, and its position is controlled by the sample outlet rear arm 11. The sample outlet rear arm fixing column 12 is used to support the sample outlet rear arm 11; the flow type intelligent metering pump 5 can be set to a high-speed injection flow range of: 5mL / min~10mL / min, a medium speed range of: 0.5mL / min~1mL / min, and a low speed range of: 0.001mL / min~0.005mL / min; the swing angle α of the injection forearm 9 is 0°~180°, and the lifting height is 10cm~40cm; the swing angle β of the injection rear arm 11 is 0°~180°, and the lifting height is 10cm~30cm. The weighing bottle 3 is a wide-mouth brown corrosion-resistant high-density polyethylene bottle with a perforated bottle cap, and the aperture is preferably such that the injection tube 1 can be inserted, in order to reduce the volatilization of the titration solution. The weighing bottle 3 is placed on a balance 13, which is a 1 / 100,000 Class I precision balance, and is equipped with a wind shield 14 to prevent airflow and vibration factors from affecting the reading of the balance 13.

[0055] The reaction system includes a reaction tank 4, a stirring device 6, a double ball tube 15, an iron stand assembly 16 and a sample tube cleaning position 18. The reaction tank 4 is fixedly mounted on the stirring device 6 through the iron stand assembly 16; the stirring device 6 can be an electromagnetic stirrer or a magnetic rotor, and the reaction tank 4 is used to hold the solution to be tested. The reaction tank 4 is fixedly mounted on the stirring device 6 through the iron stand assembly 16. The rotation speed of the stirring device 6 can be controlled at 20rpm to 2000rpm to ensure that the chemical reaction of the titration process is carried out evenly. The sample tube cleaning position 18 is composed of a cleaning liquid (water) and a container for holding the cleaning liquid.

[0056] The reaction pool 4 is a flat-bottomed three-hole glass flask. The first hole is equipped with a sealing plug with micropores. The sample outlet tube 2 is inserted into the reaction pool 4 through the sealing plug with micropores. The second hole is equipped with a composite Ag electrode 7. The third hole is equipped with a double-bulb tube 15. A cotton ball is placed in the double-bulb tube 15.

[0057] The detection system includes an electrode 7 and an automatic titrator 8. The electrode 7 is suspended and fixed by an iron frame assembly 16. When in use, it extends into the reaction liquid in the reaction tank 4 and is connected to the automatic titrator 8. The electrode 7 is a composite Ag electrode, and a composite silver ring analog electrode or a digital combined silver ring electrode can be selected. The measurable range of the potential of the automatic titrator 8 is 0 to 2000mV, and the control accuracy of the potential is ±0.1mV. The automatic titrator 8 has a complete data processing system, which can display the complete titration curve on the display screen, monitor the mutation point of the titration potential curve, and alarm to remind the titration end point.

[0058] The titration method of the device is as follows: prepare the titration solution in advance, add about 100g to the weighing bottle, control the injection forearm 9 to reset to 0°, lower the injection tube 1 to a position below the liquid level of the weighing bottle, run the high-speed flow mode of the flow-type intelligent metering pump component 5, so that the titration solution rinses and fills the entire pipeline. The titration solution in this process is discharged into the waste liquid beaker and does not enter the reaction tank 4; lift the injection forearm 9 10cm~20cm, make the sample tube 1 separate from the liquid surface, and record the displayed mass of the balance 13 at this time; the sample front arm 9 descends, the sample tube 1 is below the liquid surface of the weighing bottle 3, the sample rear arm 11 is reset to the top of the reaction tank 4, and the sample tube 2 is in the reaction tank 4 filled with the measured solution. The sample tube 2 is always above the liquid surface of the reaction tank 4 during the titration process; insert the electrode 7 in the reaction tank 4, connect the automatic titrator 8, start the stirring device 6, the automatic titrator 8, and the flow type intelligent metering pump assembly 5 in sequence for titration, and observe the potential change during the titration process; according to the consumption mass of the titration solution, set the flow mode of the flow type intelligent metering pump assembly 5, and select the high-speed flow mode for the process of consuming less than 30g of the titration solution, select the medium-speed mode for 30g~33g, and select the low-speed mode for more than 33g. When the titration end point is reached, the automatic titrator alarms and turns off the flow type intelligent metering pump assembly 5. Lift the sample tube 1 above the liquid surface and record the mass of the balance 13 at this time. The difference in mass between the two weighings is the mass of the consumed titrant after correction for air buoyancy.

[0059] Cleaning method of this device: After the titration experiment is completed, it is necessary to clean the sample injection tube 1, the sample outlet tube 2 and the circulation pipeline. Control the sample injection front arm 9 to swing at an angle of 0°~180° to the sample injection tube cleaning position 17, and the sample outlet rear arm 11 to swing at an angle of 0°~180° to the sample outlet cleaning position 18. This experiment can be rinsed with deionized water. Lower the sample injection tube 1 to the cleaning beaker in the sample injection tube cleaning position 17, lift the sample outlet tube 2 20cm~30cm to the waste liquid cup on the sample outlet cleaning position 18, start the flow type intelligent metering pump component 5 high-speed flow mode to rinse the instrument for 10 minutes; lift the sample injection tube 1 to a position above the liquid surface, and use a washing bottle to rinse the outer wall of the sample injection tube 1 and the sample outlet tube 2; after cleaning, the sample injection tube 1, the sample outlet tube 2, the sample injection front arm 9, and the sample outlet rear arm 11 are reset.

[0060] Ammonium chloride purity titration experiment plan: Each group of experiments first calibrates the AgNO3 titration solution, and then immediately titrates the ammonium chloride sample. During the experiment, the weighing and titration of sodium chloride and ammonium chloride are performed alternately. The raw data of the adjacent AgNO3 titration solution calibration and ammonium chloride sample titration are compiled into a group for calculation as the result of a single measurement. The titration operation is performed by two operators, A and B, and each person performs 6 groups of titration analysis experiments in parallel. The experiment can obtain the ammonium chloride purity titration data.

[0061] Data processing of ammonium chloride purity titration experiment: The relative value of the range of the results of 12 parallel experiments by two people can be calculated, which can be used to determine whether the requirements of the relative value of the critical range of repeatability are met, whether the titration operation meets the analysis requirements, and whether the results of the ammonium chloride purity determination are accurate and reliable. The Grubbs method is used to perform an outlier test on the above ammonium chloride purity titration data to determine whether there are outliers in the titration data; an F test is performed on the titration data of A and B to test whether the measurement results of A and B are of equal accuracy. If there are no outliers, the average value of the total 12 analysis results of the two people is taken as the purity value of the ammonium chloride sample measured by the weighing potentiometric titration method.

[0062] Uncertainty evaluation of ammonium chloride purity value:

[0063] The measurement model for determining the purity value of ammonium chloride by weighing potentiometric titration is as follows:

[0064]

[0065] According to the measurement model, the uncertainty sources of the purity value of ammonium chloride determined by weighing potentiometric titration are as follows:

[0066] ① Class A relative standard uncertainty u of ammonium chloride purity titration result A ;

[0067] ② Type B relative standard uncertainty u of ammonium chloride purity titration result B ,include:

[0068] a) Relative standard uncertainty introduced by the weighing mass of sodium chloride;

[0069] b) The relative standard uncertainty introduced by the mass of AgNO3 solution consumed in the AgNO3 calibration process after deducting the blank;

[0070] c) Relative standard uncertainty introduced by the weighing mass of ammonium chloride;

[0071] d) The relative standard uncertainty introduced by the mass of the AgNO3 solution used to titrate ammonium chloride after deducting the blank;

[0072] e) Relative standard uncertainty introduced by the purity of sodium chloride;

[0073] f) Relative standard uncertainty introduced by the molar mass value of sodium chloride;

[0074] g) Relative standard uncertainty introduced by the value of the molar mass of ammonium chloride;

[0075] h) Relative standard uncertainty introduced by rounding off the value of ammonium chloride purity result;

[0076] i) Relative standard uncertainty introduced at the titration endpoint during the calibration process of AgNO3 solution;

[0077] j) Relative standard uncertainty introduced into the titration endpoint of ammonium chloride titration with AgNO3 solution.

[0078] Type B relative standard uncertainty u in the ammonium chloride purity titration process B It is the synthesis of the above components.

[0079] Synthetic relative standard uncertainty u for determination of ammonium chloride purity by gravimetric potentiometric titration C for:

[0080] Under the condition of inclusion probability of 95% and inclusion factor k = 2, the relative expanded uncertainty of the result of ammonium chloride purity determination is: U = ku C .

[0081] In the following examples, a weighing potentiometric titration device was designed and assembled, and the purity of high-purity ammonium chloride was tested.

[0082] 1) The weighing potentiometric titration device includes three parts: a sample injection system, a reaction system, and a detection system. Sample injection system: the sample injection tube 1 and the sample outlet tube 2 are respectively introduced into the weighing bottle 3 and the reaction tank 4, and the flow-type intelligent metering pump assembly 5 can accurately control the sample injection tube to deliver liquid at high speed, medium speed, low speed, or stop. Reaction system: includes a reaction tank 4 and a stirring device 6. The reaction tank 4 contains the solution to be tested, and the stirring device 6 uses an electromagnetic stirrer. Detection system: includes electrodes 7 and an automatic titrator 8.

[0083] 2) The above-mentioned weighing potentiometric titration device, wherein the sampling system includes a sampling tube 1, a sampling forearm 9, a sampling forearm fixing column 10, a flow-type intelligent metering pump assembly 5, a sampling tube 2, a sampling rear arm 11, and a sampling rear arm fixing column 12. The sampling tube 1 is fixed on the sampling forearm 9, and its position is controlled by the sampling forearm 9. The sampling forearm fixing column 10 is used to support the sampling forearm 9. The sampling tube 2 is fixed on the sampling rear arm 11, and its position is controlled by the sampling rear arm 11. The sampling rear arm fixing column 12 is used to support the sampling rear arm 1 1; The flow-type intelligent metering pump assembly 5 can be set to a high-speed injection flow range of 5mL / min to 10mL / min, a medium-speed range of 0.5mL / min to 1mL / min, and a low-speed range of 0.001mL / min to 0.005mL / min; the swing angle α of the injection front arm 9 is 0° to 180°, and the lifting height is 10cm to 40cm; the swing angle β of the injection rear arm 11 is 0° to 180°, and the lifting height is 10cm to 30cm. The weighing bottle 3 is a wide-mouth brown corrosion-resistant high-density polyethylene bottle with a perforated bottle cap. The aperture is suitable for just inserting the injection tube 1, in order to reduce the volatilization of the titration solution. The weighing bottle 3 is placed on the balance 13, which uses a one-hundred-thousandth Class I precision balance and is equipped with a wind shield 14 to prevent the influence of airflow and vibration factors on the reading of the balance 13. The reaction pool 4 is a flat-bottomed 500mL three-hole glass flask. A sealing plug with micropores is installed in hole 1. The titration solution can enter the reaction pool 4 through the sample outlet tube 2. The composite Ag electrode 7 is installed in hole 2. The double bulb tube 15 is installed in hole 3. The absorbent cotton ball is placed in the double bulb tube 15. The reaction pool 4 is fixedly installed on the stirrer through the iron stand assembly 16. The stirrer speed can be controlled at 20rpm~2000rpm to ensure that the chemical reaction in the titration process is carried out uniformly. The composite Ag electrode 7 uses a composite silver ring simulation electrode. The composite electrode is suspended and fixed by the iron stand assembly 16 and connected to the automatic titrator 8. The measurable range of the potential of the automatic titrator 8 is 0~2000mV, and the control accuracy of the potential is ±0.1mV. The automatic titrator 8 has a complete data processing system, which can display the complete titration curve on the display screen, monitor the mutation point of the titration potential curve, and alarm to remind the titration end point.

[0084] 3) Titration method of the device: prepare the titration solution in advance, add about 100g to the weighing bottle 3, control the injection forearm 9 to reset to 0°, lower the injection tube 1 to a position below the liquid level of the weighing bottle 3, run the flow type intelligent metering pump component 5 high-speed flow mode, so that the titration solution rinses and fills the entire pipeline. The titration solution in this process is discharged into the waste liquid beaker and does not enter the reaction tank 4; raise the injection forearm 9 to a height of 15cm, so that the injection tube 1 is separated from the liquid surface, and record the display quality of the balance 13 at this time; the injection forearm 9 is lowered, the injection tube 1 is below the liquid level of the weighing bottle 3, and the sample-discharging arm 11 is reset To the top of the reaction pool 4, the sample tube 2 is put into the reaction pool 4 filled with the solution to be tested, and the sample tube 2 is always above the liquid level of the reaction pool 4 during the titration process; insert the electrode 7 into the reaction pool 4, connect the automatic titrator 8, start the agitator 6, the automatic titrator 8, and the flow-type intelligent metering pump assembly 5 in sequence for titration, and observe the potential change during the titration process; according to the consumption mass of the titration solution, set the flow mode of the injector, and select the high-speed flow mode for the process of consuming less than 30g of titration solution, select the medium-speed mode between 30g and 33g, and select the low-speed mode for more than 33g. When the titration end point is reached, the automatic titrator 8 alarms and turns off the injector. Lift the injection tube 1 above the liquid level and record the mass of the balance 13 at this time. The mass difference between the two weighings is the mass of the consumed titration solution after air buoyancy correction.

[0085] 4) Cleaning method of this device: After the titration experiment is completed, the sample injection tube 1, the sample outlet tube 2 and the circulation pipeline need to be cleaned. The sample injection front arm 9 is controlled to swing at an angle of 0°~180° to the sample injection tube cleaning position 17, and the sample outlet rear arm 11 is controlled to swing at an angle of 0°~180° to the sample outlet cleaning position 18. Deionized water can be used for flushing in this experiment. Lower the sample injection tube 1 to the cleaning beaker in the sample injection tube cleaning position 17, raise the sample outlet tube 2 25cm to the waste liquid cup on the sample outlet cleaning position 18, start the high-speed flow mode of the sampler to flush the instrument for 10 minutes; lift the sample injection tube 1 to a position above the liquid surface, and use a washing bottle to flush the outer walls of the sample injection tube 1 and the sample outlet tube 2; after cleaning, the sample injection tube 1, the sample outlet tube 2, the sample injection front arm 9, and the sample outlet rear arm 11 are reset.

[0086] 5) Ammonium chloride purity titration experimental plan: Each group of experiments first calibrates the AgNO3 titration solution, and then immediately titrates the ammonium chloride sample. During the experiment, the weighing and titration of sodium chloride and ammonium chloride are performed alternately. The raw data of the adjacent AgNO3 titration solution calibration and ammonium chloride sample titration are compiled into a group for calculation as the result of a single measurement. The titration operation is performed by two operators, A and B, and each person performs 6 groups of titration analysis experiments in parallel. The experiment can obtain the ammonium chloride purity titration data, see Table 1.

[0087] Table 1 Results of determination of ammonium chloride purity by weighing potentiometric titration

[0088]

[0089] Note: m1, m2, m3, and m4 in the table are all values ​​after buoyancy correction. G is the purity of ammonium chloride (wt.%), is the average purity of ammonium chloride (wt.%).

[0090] 6) Data processing of ammonium chloride purity titration experiment:

[0091] Calculate the relative value of the range of the parallel experimental results:

[0092] The relative value of the extreme difference of the six parallel determination results in group A is:

[0093]

[0094] The relative values ​​of the extreme values ​​of the six parallel determination results of group B are:

[0095]

[0096] The relative value of the extreme difference of the twelve parallel determination results of groups A and B is:

[0097]

[0098] The calculated relative values ​​of the range of the two parallel experimental results were all less than the relative value of the critical range of repeatability, indicating that the titration operation met the analysis requirements and the ammonium chloride purity determination results were accurate and reliable.

[0099] The Grubbs method was used to test the above ammonium chloride purity titration data for outliers:

[0100] In a set of measured values, such as a measured value x i , with residual When |v i |>λ(α, n)S, it should be eliminated. λ(α, n) is a value related to the number of measurements and the given significance level. The value of λ(0.05, 6) is 1.887.

[0101] The test data of groups A and B were inspected and no abnormal values ​​were found.

[0102] Use the F test to test whether the measurement results of A and B are of equal accuracy:

[0103] The F test was performed on the measured data using the variance analysis method. 0.05 (ν1,ν2), there is no significant difference between the data within and between groups, and the uniformity test is qualified. 0.05 (1, 10) value is 4.96, F<F 0.05(1, 10), indicating that the measurement results of A and B have equal accuracy.

[0104] Therefore, the average value of the 12 analysis results of the two people was taken as the purity value of the ammonium chloride sample measured by the gravimetric potentiometric titration method, which was 99.974%.

[0105] 7) Uncertainty assessment of ammonium chloride purity value:

[0106] The measurement model for determining the purity value of ammonium chloride by weighing potentiometric titration is as follows:

[0107]

[0108] According to the measurement model, the uncertainty sources of the purity value of ammonium chloride determined by weighing potentiometric titration are as follows:

[0109] ① Class A relative standard uncertainty u of ammonium chloride purity titration result A ;

[0110]

[0111] ② Type B relative standard uncertainty u of chlorination purity titration result B ,include:

[0112] a) Relative standard uncertainty introduced by the weighing mass of sodium chloride;

[0113] The mass of sodium chloride in the calculation process is the value after buoyancy correction. The uncertainty of this part is composed of the maximum allowable error of the balance weighing and the repeatability of the weighing. According to the calibration certificate of the balance, when the weighing mass is within the range of (0-5)g, the maximum allowable error of the balance is ±0.05mg. Assuming uniform distribution, the net weight is obtained by two weighing operations. The uncertainty introduced by the accuracy of the balance is:

[0114]

[0115] Select a weight close to the mass of sodium chloride and repeat the weighing 11 times. The standard deviation of the 11 weighing results is 0.02 mg. According to the uniform distribution, the standard uncertainty introduced by the repeatability of the electronic balance is:

[0116]

[0117] Therefore, the relative standard uncertainty introduced by the weighing mass of sodium chloride is:

[0118]

[0119] b) The relative standard uncertainty of the mass of silver nitrate solution used to titrate sodium chloride after deducting the blank;

[0120] When the weighing mass is within the range of (20-120) g, the maximum allowable error of the balance weighing result is ±0.15 mg. After deducting the blank, the average mass of the silver nitrate solution consumed in the titration of sodium chloride is 34.2484 g. The relative standard uncertainty introduced by the balance weighing accuracy is:

[0121]

[0122] Select a weight close to the weighing mass and repeat the weighing 11 times. The standard deviation of the 11 weighing results is 0.06

[0123] mg, the relative standard uncertainty introduced by the balance repeatability is:

[0124]

[0125] Therefore, the relative standard uncertainty of the mass of silver nitrate solution used to titrate sodium chloride after deducting the blank is:

[0126]

[0127] c) Relative standard uncertainty introduced by the weighing mass of ammonium chloride;

[0128] The uncertainty introduced by the balance accuracy is:

[0129]

[0130] Select a weight close to the mass of sodium chloride and repeat the weighing 11 times. The standard deviation of the 11 weighing results is 0.02 mg. According to the uniform distribution, the standard uncertainty introduced by the repeatability of the electronic balance is:

[0131]

[0132] Therefore, the relative standard uncertainty introduced by the weighing mass of ammonium chloride is:

[0133]

[0134] d) The relative standard uncertainty introduced by the mass of silver nitrate solution used to titrate ammonium chloride after deducting the blank;

[0135] After deducting the blank, the average mass of silver nitrate solution consumed in the titration of ammonium chloride is 33.6423g. The relative standard uncertainty introduced by the balance weighing accuracy is:

[0136]

[0137] The relative standard uncertainty introduced by the balance repeatability is:

[0138]

[0139] Therefore, the relative standard uncertainty of the mass of silver nitrate solution used to titrate ammonium chloride after deducting the blank is:

[0140]

[0141] e) Relative standard uncertainty introduced by the purity of sodium chloride;

[0142] According to the purity value of 99.992% (U=0.008%, k=2) on the sodium chloride purity standard material certificate, the relative standard uncertainty introduced by the sodium chloride purity is:

[0143]

[0144] f) Relative standard uncertainty introduced by the molar mass value of sodium chloride;

[0145] According to the IUPAC International Atomic Weight Table, the relative atomic masses and uncertainties of the two atoms in sodium chloride are:

[0146] Na: 22.98976928±0.00000002; Cl: 35.453±0.002. The relative molecular mass of sodium chloride is 58.44276928.

[0147] The standard uncertainty component introduced by the standard uncertainty of the relative atomic mass values ​​of each element in the NaCl molecule is:

[0148]

[0149] The standard uncertainty component introduced by the rounding error of the numerical value of the molar mass of NaCl is:

[0150]

[0151] Therefore, the relative standard uncertainty introduced by the molar mass value of sodium chloride is:

[0152]

[0153] g) Relative standard uncertainty introduced by the value of the molar mass of ammonium chloride;

[0154] The relative atomic masses and uncertainties of the three atoms in ammonium chloride are:

[0155] N: 14.0067±0.0002; H: 1.00794±0.00007; Cl: 35.453±0.002. The relative molecular mass of ammonium chloride is 53.49146.

[0156] The standard uncertainty components introduced by the standard uncertainty of the relative atomic mass values ​​of each element in the NH4Cl molecule are:

[0157]

[0158] The standard uncertainty component introduced by the rounding error of the numerical value of NH4Cl molar mass is:

[0159]

[0160] Therefore, the relative standard uncertainty introduced by the molar mass value of ammonium chloride is:

[0161]

[0162] h) Relative standard uncertainty introduced by rounding off the value of ammonium chloride purity result;

[0163] The titration purity of ammonium chloride is 99.974%, and the half-width of the numerical rounding error interval is 0.0005%. According to the uniform distribution, the relative standard uncertainty introduced by the numerical rounding of the titration purity of ammonium chloride is:

[0164]

[0165] i) Relative standard uncertainty introduced at the titration endpoint during the calibration process of AgNO3 solution;

[0166] Before and after the chemical measurement point, the addition rate was 0.001mL / min to 0.005mL / min, the mass change interval of the excess titrant was 5mg, and the average mass of AgNO3 titrant consumed in the calibration process was 34.2484g. According to the uniform distribution, the relative standard uncertainty introduced by the endpoint error of the titration reaction is:

[0167]

[0168] According to the potentiometric titrator calibration certificate, the relative expanded uncertainty of the composite electrode indication error measurement result is U r =0.01%, k=2, then the relative standard uncertainty introduced by the titration endpoint potential error is:

[0169]

[0170] Therefore, the relative standard uncertainty component introduced by the titration endpoint of the AgNO3 solution calibration process is:

[0171]

[0172] j) Relative standard uncertainty introduced into the titration endpoint of ammonium chloride titration with AgNO3 solution;

[0173] The average mass of AgNO3 titrant consumed in the calibration process is 33.6423 g. According to the uniform distribution, the relative standard uncertainty introduced by the endpoint error of the titration reaction is:

[0174]

[0175] According to the potentiometric titrator calibration certificate, the relative expanded uncertainty of the composite electrode indication error measurement result is U r =0.01%, k=2, then the relative standard uncertainty introduced by the titration endpoint potential error is:

[0176]

[0177] Therefore, the relative standard uncertainty component introduced by the titration endpoint of the titration of ammonium chloride with AgNO3 solution is:

[0178]

[0179] Type B relative standard uncertainty u in the ammonium chloride purity titration process B That is the synthesis of the above components:

[0180]

[0181] Synthetic relative standard uncertainty u for determination of ammonium chloride purity by gravimetric potentiometric titration C for:

[0182]

[0183] Under the condition of inclusion probability of 95% and inclusion factor k = 2, the relative expanded uncertainty of the result of ammonium chloride purity determination is: U = ku C .

[0184] U=ku C =2×0.035%=0.07%

[0185] The solution of the embodiment of the present invention is that the weighing potentiometric titration device includes a sample introduction system with a high degree of automation, a reaction system that is easy to operate and control, a detection system with accuracy that meets the requirements, and a complete device; the titration process is carried out under closed-loop sealing conditions, which reduces the volatilization loss of the titration solution and the impact of the environment. The uncertainty introduced in the experimental process is controllable and easy to obtain. It has been verified that the experimental data of the purity of high-purity ammonium chloride tested by the weighing potentiometric titration method is accurate and reliable.

[0186] The present invention provides a complete set of weighing potentiometric titration devices, including a sample injection system, a reaction system and a detection system. The sample injection system: the sample injection tube and the sample outlet tube are respectively introduced into a weighing bottle and a reaction tank, and the flow-type intelligent metering pump component can accurately control the sample injection tube to deliver liquid at high speed, medium speed, low speed or stop. The reaction system: includes a reaction tank and a stirring device. The reaction tank contains the solution to be tested. The stirring device can use an electromagnetic stirrer or a magnetic rotor. The detection system: includes electrodes and an automatic titrator. The device is used to titrate the purity of ammonium chloride, and the uncertainty of the purity value of ammonium chloride is evaluated. The device is easy to operate, easy to control, has a high degree of automation, and the accuracy meets the requirements of national standards. The method can be used for purity titration experiments of high-purity substances.

Claims

1. A device for measuring the purity of ammonium chloride by weighing potentiometric titration, characterized in that: It includes a sampling system, a reaction system and a detection system; the sampling system mainly includes a flow-type intelligent metering pump component, a sampling tube, a sampling tube, a weighing bottle, a balance and a wind shield, the flow-type intelligent metering pump component is connected to the weighing bottle and the reaction system through the sampling tube and the sampling tube respectively, the weighing bottle is placed on the balance, and the wind shield is installed on the periphery of the balance; the reaction system includes a reaction pool, a stirring device and an iron frame assembly, the reaction pool is fixedly installed on the stirrer through the iron frame assembly; the detection system includes an electrode and an automatic titrator, the electrode is suspended and fixed in the reaction pool by the iron frame assembly, and is connected to the automatic titrator.

2. The device for measuring the purity of ammonium chloride by weighing potentiometric titration according to claim 1, characterized in that: The sampling system also includes a sampling forearm, a sampling forearm fixing column, a sampling rear arm and a sampling rear arm fixing column. The sampling tube is fixed on the sampling forearm, the sampling forearm is fixed on the sampling forearm fixing column, the sampling tube is connected to the sampling port of the flow type intelligent metering pump assembly, the sampling outlet tube is fixed on the sampling rear arm, the sampling rear arm is fixed on the sampling rear arm fixing column, and the sampling outlet tube is connected to the sampling outlet of the flow type intelligent metering pump assembly.

3. The device for measuring the purity of ammonium chloride by weighing potentiometric titration according to claim 1, characterized in that: The flow-type intelligent metering pump assembly can accurately control the injection tube to deliver liquid at high speed, medium speed, low speed or stop; the high-speed injection flow range of the flow-type intelligent metering pump assembly is: 5mL / min~10mL / min, the medium speed range is: 0.5mL / min~1mL / min, and the low speed range is: 0.001mL / min~0.005mL / min; the swing angle α of the injection front arm is 0°~180°, and the lifting height is 10cm~40cm; the swing angle β of the injection rear arm is 0°~180°, and the lifting height is 10cm~30cm; the weighing bottle is a wide-mouth brown corrosion-resistant high-density polyethylene bottle with an open-hole bottle cap, and the aperture is just enough to insert the injection tube.

4. The device for measuring the purity of ammonium chloride by weighing potentiometric titration according to claim 1, characterized in that: The stirring device is an electromagnetic stirrer or a magnetic rotor; the reaction pool is a flat-bottomed three-hole glass flask, the first hole is equipped with a sealing plug with micropores, the sample outlet tube is inserted into the reaction pool through the sealing plug with micropores, the second hole is equipped with an electrode, the third hole is equipped with a double-bulb tube, and absorbent cotton balls are placed in the double-bulb tube; the reaction pool is fixedly installed on the stirring device through an iron frame assembly, and the rotation speed of the stirring device is controlled at 20rpm to 2000rpm to ensure that the chemical reaction in the titration process is carried out evenly.

5. The device for measuring the purity of ammonium chloride by weighing potentiometric titration according to claim 1, characterized in that: The electrode is a composite Ag electrode, which is a composite silver ring analog electrode or a digital combined silver ring electrode; the measurement range of the potential of the automatic titrator is 0-2000mV, and the control accuracy of the potential is ±0.1mV. The automatic titrator is equipped with a complete data processing system, which can display the complete titration curve on the display screen, monitor the mutation point of the titration potential curve, and alarm to remind the titration end point.

6. The device for measuring the purity of ammonium chloride by weighing potentiometric titration according to claim 1, characterized in that: The sample injection system also includes a sample injection tube cleaning position and a sample output tube cleaning position.

7. A method for measuring the purity of ammonium chloride by weighing potentiometric titration, comprising the following steps: (1) Titration method: Prepare AgNO3 titration solution and add it to the weighing bottle. Control the injection forearm to reset to 0°, lower the injection tube to a position below the liquid level of the weighing bottle, and run the flow-type intelligent metering pump in high-speed flow mode to rinse the titrant and fill the entire pipeline. The titrant in this process is discharged into the waste liquid beaker and does not enter the reaction tank; lift the injection forearm 10cm to 20cm to separate the injection tube from the liquid surface, and record the displayed mass of the balance at this time; lower the injection forearm to allow the injection tube to be below the liquid level of the weighing bottle, reset the sample-discharging arm to the top of the reaction tank, and discharge the sample tube to the liquid level of the weighing bottle. In the reaction pool of the measuring solution, the sample outlet tube is always located above the liquid level of the reaction pool during the titration process; insert the electrode into the reaction pool, connect the automatic titrator, start the agitator, automatic titrator, and flow-type intelligent metering pump assembly in sequence for titration, and observe the potential change during the titration process; when the titration end point is reached, the automatic titrator alarms and the flow-type intelligent metering pump assembly is turned off; lift the sample inlet tube above the liquid level and record the mass of the balance at this time; the mass difference between the two weighings is the mass of the consumed titrant after air buoyancy correction; the device needs to be cleaned after each titration experiment; (2) Ammonium chloride purity titration scheme: In each experiment, the AgNO3 titration solution was calibrated with the primary standard substance sodium chloride, and the ammonium chloride sample was titrated immediately after the calibration. During the experiment, the weighing and titration of sodium chloride and ammonium chloride were performed alternately. The raw data of the adjacent AgNO3 titration solution calibration and ammonium chloride sample titration were compiled into a group for calculation as the result of a single determination of the purity of ammonium chloride; the titration operation was performed by two operators, A and B, and each of them performed 6 groups of titration analysis experiments in parallel to obtain the ammonium chloride purity titration data; (3) Data processing of ammonium chloride purity titration experiment: The relative values ​​of the range of the results of 12 parallel experiments by two people can be calculated, which can be used to determine whether the requirements of the relative value of the critical range of repeatability are met, whether the titration operation meets the analysis requirements, and whether the results of ammonium chloride purity determination are accurate and reliable; The Grubbs method was used to test the above ammonium chloride purity titration data for outliers to determine whether the titration data had outliers. Perform an F test on the titration data of A and B to check whether the measurement results of A and B are of equal accuracy; if there are no abnormal values, take the average value of the total 12 analysis results of the two people as the purity value of the ammonium chloride sample measured by gravimetric potentiometric titration.

8. The method for measuring the purity of ammonium chloride by weighing potentiometric titration according to claim 7, characterized in that: According to the consumption mass of the titrant, the flow mode of the flow-type intelligent metering pump component is set. When the consumption of titrant is less than 30g, the high-speed flow mode is selected. Between 30g and 33g, the medium-speed mode is selected. When the consumption is above 33g, the low-speed mode is selected.

9. The method for measuring the purity of ammonium chloride by weighing potentiometric titration according to claim 7, wherein: It also includes the uncertainty assessment steps for the purity value of ammonium chloride: According to the measurement model, the uncertainty sources of the purity value of ammonium chloride determined by weighing potentiometric titration are as follows: ① Class A relative standard uncertainty u of ammonium chloride purity titration result A ; ② Type B relative standard uncertainty u of ammonium chloride purity titration result B ,include: a) Relative standard uncertainty introduced by the weighing mass of sodium chloride; b) The relative standard uncertainty introduced by the mass of AgNO3 solution consumed in the AgNO3 calibration process after deducting the blank; c) Relative standard uncertainty introduced by the weighing mass of ammonium chloride; d) The relative standard uncertainty introduced by the mass of the AgNO3 solution used to titrate ammonium chloride after deducting the blank; e) Relative standard uncertainty introduced by the purity of sodium chloride; f) Relative standard uncertainty introduced by the molar mass value of sodium chloride; g) Relative standard uncertainty introduced by the value of the molar mass of ammonium chloride; h) Relative standard uncertainty introduced by rounding off the value of ammonium chloride purity result; i) Relative standard uncertainty introduced at the titration endpoint during the calibration process of AgNO3 solution; j) Relative standard uncertainty introduced into the titration endpoint of ammonium chloride titration with AgNO3 solution; Type B relative standard uncertainty u in the ammonium chloride purity titration process B It is the synthesis of the above components; Synthetic relative standard uncertainty u for determination of ammonium chloride purity by gravimetric potentiometric titration C for: Under the condition of inclusion probability of 95% and inclusion factor k = 2, the relative expanded uncertainty of the result of ammonium chloride purity determination is: U = ku C .

10. The method for measuring the purity of ammonium chloride by weighing potentiometric titration according to claim 7, characterized in that: The method for determining the purity of ammonium chloride by weighing potentiometric titration also includes a cleaning method: after the titration experiment is completed, the sample injection tube, the sample outlet tube and the circulation pipeline are cleaned, the sample injection front arm swing angle is controlled to be 0° to 180° to the sample injection tube cleaning position, and the sample outlet rear arm swing angle is 0° to 180° to the sample outlet tube cleaning position, and can be rinsed with deionized water; the sample injection tube is lowered to the cleaning beaker in the sample injection tube cleaning position, the sample outlet tube is raised to a height of 20cm to 30cm to the waste liquid cup on the sample outlet tube cleaning position, and the flow-type intelligent metering pump assembly is started to rinse the instrument in high-speed flow mode for 10-20min; Lift the sample inlet tube to a position above the liquid surface, and use a wash bottle to rinse the outer walls of the sample inlet tube and the sample outlet tube; After cleaning is completed, the sample inlet tube, sample outlet tube, sample inlet front arm and sample outlet rear arm are reset.

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