A burette volume calibration device and method suitable for automatic potentiometric titrator

Abstract

The present invention discloses a burette volume calibration device and method suitable for an automatic potentiometric titrator, comprising a mainframe with a truncated cone base at the bottom, a closable barrel cover on the truncated cone base, an electronic weighing platform covered in the barrel cover at the center of the truncated cone base, a receiving container placed on the electronic weighing platform, and a cannula sealing positioning mechanism and a vacuum interface at the top of the receiving container. The burette connected to the lower end of the burette of the automatic potentiometric titrator is inserted into the receiving container through the cannula sealing positioning mechanism, and the end of the burette is suspended in the receiving container. A swing mechanism connected to the mainframe is fixed in the barrel cover. After the burette of the automatic potentiometric titrator drips a certain volume of distilled water, the swing mechanism responds to the control instruction, outputs a swing action, and touches the end tube body of the burette, so that the water droplets retained at the end of the burette fall into the receiving container. The present invention can perform high-precision calibration on the burette of the automatic potentiometric titrator.

Description

Technical Field

[0001] The invention relates to the technical field of instrument calibration for precision chemical experiments, and in particular to a burette volume calibration device and method suitable for an automatic potentiometric titrator. Background Art

[0002] The national metrology verification regulations JJG 196-2006 "Common Glass Measuring Apparatus" limits the nominal capacity of stopperless and stoppered burettes. The most commonly used capacity of laboratory burettes (Class A) is 50mL. The regulations also clearly stipulate the capacity tolerance of Class A burettes (the capacity tolerance is the nominal capacity of the burette and the maximum error from zero to any component, as well as between any two verification points): no more than ±0.05mL. Since glass has the characteristics of thermal expansion and contraction, the volume of volumetric vessels is different at different temperatures. Therefore, when calibrating glass volumetric vessels, a common temperature value must be specified. This specified temperature value is the standard temperature. The international standard temperature of glass volumetric vessels is 20℃, that is, when calibrating, the volume of glass volumetric vessels is calibrated to the actual volume at 20℃. The regulations also stipulate the selection of calibration points for the burette. A 50mL burette needs to be tested at five points: (0-10)mL, (0-20)mL, (0-30)mL, (0-40)mL, and (0-50)mL.

[0003] The operating steps for burette calibration can be found in A.1.1 weighing method in Appendix A of JJG 196-2006. The principle of this method is the water density formula, that is, ρ = m / V. The air temperature is kept constant at 20°C, and the water density value at 20°C is found through a water density table. Then a certain amount of distilled water is released and accurately weighed on a balance. The theoretical volume of the released distilled water can be calculated by V = m / ρ, and then the laboratory technician reads the scale value on the burette. The difference between the two volumes is the calibration value of the burette at this scale. The reading of a traditional burette can be accurate to the percentile, and the percentile is usually estimated by the laboratory technician. There may be some differences in the reading results for laboratory technicians with different qualifications and levels.

[0004] However, the burette in the automatic potentiometric titrator is a special burette, which is fixedly installed in the instrument and is not convenient to be disassembled for verification and correction during use. The automatic potentiometric titrator is superior to the traditional burette in that it has higher precision and sensitivity. The minimum graduation value of the traditional burette can only be 0.01mL, but the minimum reading of the automatic potentiometric titrator can be accurate to 0.0001mL. Since the instrument is less disturbed, each reading can maintain good parallelism. Therefore, in the prior art, it is usually assumed that the volume of the solution output by the burette titration of the automatic potentiometric titrator is the titration liquid addition amount of the automatic potentiometric titrator. In some conventional chemical analysis experiments, this operation has little effect on the deviation of the experimental data and has no significant effect on the accuracy of the experimental results. However, for some chemical analysis experiments that require precision, such as the experiment of calibrating the concentration of potassium permanganate standard solution with sodium oxalate, the experiment of calibrating the concentration of sodium hydroxide standard solution with potassium hydrogen phthalate, etc., the slight error of the burette will have a great impact on the calibration result, and it will be difficult to ensure the accuracy of the calibration result by using an uncalibrated burette. Therefore, when conducting such precise chemical analysis experiments, the burette in the automatic potentiometric titrator must be volume-calibrated and corrected. Based on this, the present invention proposes a burette volume calibration device and method suitable for an automatic potentiometric titrator. Summary of the invention

[0005] In order to realize volume correction of a burette in an automatic potentiometric titrator to further improve the accuracy of experimental results, the present invention provides a burette volume calibration device and method suitable for an automatic potentiometric titrator, wherein the calibration process is simple and fast, interference factors are few, and calibration accuracy is high.

[0006] The technical solution adopted by the present invention to achieve the above technical effects is:

[0007] A burette volume calibration device suitable for an automatic potentiometric titrator comprises a main machine with a truncated cone base at the bottom, a closable barrel cover on the truncated cone base, an electronic weighing platform covered in the barrel cover at the center of the truncated cone base, a vacuum receiving container placed on the electronic weighing platform, a cannula sealing positioning mechanism and a vacuum interface on the top of the receiving container, a burette connected to the lower end of the burette of the automatic potentiometric titrator penetrates into the barrel cover and extends into the cannula through the cannula sealing positioning mechanism. In the receiving container, the end of the burette is suspended in the receiving container, the vacuum interface is connected to an external vacuum pump via a hose that penetrates the barrel cover, and a rocker mechanism connected to the host is fixed in the barrel cover. After the burette of the automatic potentiometric titrator drips a certain volume of distilled water, the rocker mechanism responds to the control instruction and outputs a swing action to touch the tube body of the burette at the outer end of the receiving container, so that the water droplets retained at the end of the burette fall into the receiving container.

[0008] Preferably, in the above-mentioned burette volume calibration device suitable for an automatic potentiometric titrator, the tube cover includes a transparent cylindrical glass cover with openings at both ends, a metal fixing frame connected to the transparent cylindrical glass cover, and an openable tube cover for closing the upper end opening of the transparent cylindrical glass cover, the lower end opening of the transparent cylindrical glass cover is sealed and connected to the surface of the frustum base, and the tube cover is provided with an adapting through-hole through which the burette tube and the hose pass.

[0009] Preferably, in the above-mentioned burette volume calibration device suitable for an automatic potentiometric titrator, the metal fixing frame includes a lower hoop sleeved on the lower edge of the transparent cylindrical glass cover, an upper hoop sleeved on the upper edge of the transparent cylindrical glass cover, and an arc-shaped portion connecting the lower hoop and the upper hoop, and the curvature of the arc-shaped portion is adapted to the curvature of the outer wall of the transparent cylindrical glass cover.

[0010] Preferably, in the above-mentioned burette volume calibration device suitable for an automatic potentiometric titrator, the arc portion is located on one side of the mainframe, and the arc length is one third of the outer circumference of the transparent cylindrical glass cover.

[0011] Preferably, in the above-mentioned burette volume calibration device suitable for automatic potentiometric titrator, the tube sealing and positioning mechanism includes a positioning tube connected to the sealing cover of the receiving container and a sealing plunger slidably sleeved on the burette tube, the upper and lower ends of the positioning tube are open, the upper end tube mouth is flush with the upper surface of the tube cover, a trumpet-shaped inlet is formed at the connection, and the lower end tube mouth is located in the receiving container, the sealing plunger is pluggable and sealed at the upper end tube mouth of the positioning tube, the end of the burette tube passes through the sealing cover through the positioning tube, and is suspended in the upper position of the receiving container.

[0012] Preferably, in the above-mentioned burette volume calibration device suitable for an automatic potentiometric titrator, the rocker mechanism includes a micro-servo motor, a rocker seat connected to the micro-servo motor by a reduction transmission, and a rocker fixed on the rocker seat, and a "U"-shaped constraint arm is provided at the end of the rocker. The end of the burette passes through the middle of the "U"-shaped constraint arm.

[0013] Preferably, in the above-mentioned burette volume calibration device suitable for an automatic potentiometric titrator, a control console is connected to the top of the main machine, and a calibration data display screen and volume addition and subtraction buttons and switches are provided on the control console.

[0014] A method for calibrating the volume of a burette of an automatic potentiometric titrator using the above device, the method comprising the steps of:

[0015] S1. Place a clean and dry receiving container in a barrel cover, pass the burette through the barrel cover, and then insert it into the receiving container through the cannula sealing and positioning mechanism, and let the end of the burette hang in the upper part of the receiving container;

[0016] S2, connect the receiving container to an external vacuum pump, cover the cylinder cover, and evacuate the inside of the receiving container. After the vacuum is completed, peel the current electronic weighing table to set the current mass reading to zero;

[0017] S3. Perform the liquid addition operation on the automatic potentiometric titrator and input the liquid addition volume v of this liquid addition operation into the host. i ;

[0018] S4, starting the titration of the added amount, until the titration of the added amount is displayed on the automatic potentiometric titrator as finished, controlling the swing rod mechanism to output a swing action, touching the end of the burette tube, so that the water droplets retained at the end of the burette tube fall into the receiving container;

[0019] S5, the host synchronizes the mass reading of the current electronic weighing platform m i , and combined with the current experimental environment temperature, retrieve the distilled water density value ρ at the corresponding temperature preset in the host i , according to the formula V i =m i / ρ i Calculate the actual volume value V at this time i ;

[0020] S6, the host outputs the correction value ΔV of the burette of the automatic potentiometric titrator i =V i -v i , and output the calibration value of the burette of the automatic potentiometric titrator

[0021] Preferably, in the above method, according to steps S3 to S6, five liquid adding operations are performed sequentially on the automatic potentiometric titrator, and the liquid adding amount of the five liquid adding operations is 10 mL. Each time the liquid adding operation is performed, a correction value is calculated once, and the correction values ​​corresponding to the five liquid adding operations are ΔV1, ΔV2, ΔV3, ΔV4, and ΔV5, respectively.

[0022] Preferably, in the above method, at least three parallel calibration experiments are carried out on the burette of the same automatic potentiometric titrator, and the corrected average values ​​of the liquid addition amounts of 10 mL, 20 mL, 30 mL, 40 mL, and 50 mL are calculated respectively, and the calibration value corresponding to the liquid addition amount is the corrected average value at the liquid addition amount and the set value of the automatic potentiometric titrator at the liquid addition amount.

[0023] The beneficial effects of the present invention are as follows: the device and method of the present invention evacuates the receiving container and then measures the mass of the receiving container after the titration is completed, and combines the rocker mechanism to trigger the end tube body of the burette, so that the water droplets retained at the end of the burette fall into the receiving container, and the mass data obtained by final weighing has high accuracy, the accuracy of the burette of the calibrated automatic potentiometric titrator is further improved, and the data is accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a state diagram of the device of the present invention during titration operation;

[0025] Figure 2 A perspective view of the device of the present invention;

[0026] Figure 3 It is a structural diagram of the barrel cover of the device described in the present invention;

[0027] Figure 4 It is a structural schematic diagram of the cannula sealing and positioning mechanism of the present invention;

[0028] Figure 5 It is a three-dimensional diagram of the rocker mechanism of the present invention. DETAILED DESCRIPTION

[0029] In order to further understand the present invention, the present invention is further described below with reference to the accompanying drawings and specific embodiments:

[0030] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0031] See also Figure 1 , Figure 2 The embodiment of the present invention provides a burette volume calibration device suitable for an automatic potentiometric titrator, the device comprising a main unit 1 with a truncated cone base 11 at the bottom, specifically, the truncated cone base 11 is integrally connected with the bottom of the main unit 1 and formed on one side of the main unit 1. The top of the main unit 1 is connected to a console 12, which is provided with a calibration data display screen 121 and volume addition and subtraction buttons and switches. Figure 2As shown, the truncated cone base 11 is provided with a closable barrel cover 2, and the central part of the truncated cone base 11 is provided with an electronic weighing platform 111 covered in the barrel cover 2, and a receiving container 3 is placed on the electronic weighing platform 111. Specifically, the receiving container 3 is used to receive the quantitative volume of distilled water titrated by the burette of the automatic potentiometric titrator (the known volume of liquid added set on the automatic potentiometric titrator), and then the mass of the titrated quantitative volume of distilled water is weighed by the electronic weighing platform 111. Combined with the temperature in the current experimental environment, the density value of the distilled water at the corresponding temperature is queried, and the actual volume of the distilled water of the quantitative volume titrated (the set liquid addition amount of the automatic potentiometric titrator) is calculated by dividing the mass by the density value. At this time, the correction value of the burette is the difference between the set liquid addition amount of the automatic potentiometric titrator and the calculated actual volume. Under laboratory conditions, there is a certain amount of airflow (such as the airflow from the air conditioner inlet of the laboratory), and the electronic weighing platform 111 has a high precision. Therefore, if the weighing is disturbed by the airflow, the weighed mass number will be biased, generally too large. Therefore, the present invention can provide a closed weighing space through the closable cylinder cover 2, which can prevent the airflow in the laboratory from interfering with the mass weighing result. Specifically, if Figure 1 As shown, the top of the receiving container 3 is provided with an insert tube sealing positioning mechanism 4 and a vacuum interface, wherein the burette 100 connected to the lower end of the burette of the automatic potentiometric titrator penetrates the barrel cover 2 and extends into the receiving container 3 through the insert tube sealing positioning mechanism 4. Specifically, the end of the burette 100 is suspended in the receiving container 3, specifically, the horizontal plane where the end of the burette 100 is located is kept higher than the maximum scale of the receiving container 3 to prevent the end of the burette 100 from being immersed below the water surface of the distilled water received in the receiving container 3. The insert tube sealing positioning mechanism 4 can seal the insert interface between the burette 100 and the receiving container 3 on the one hand, and can also position the posture of the burette 100 on the other hand. Since the burette 100 is made of a hose material, there may be a tail section bend when it is not constrained, so the burette 100 can maintain a vertical downward posture of the tube section extending into the receiving container 3 through the insert tube sealing positioning mechanism 4. When the end of the burette 100 is inserted into the receiving container 3, the end of the burette 100 is suspended in the upper position of the receiving container 3, that is, the end of the burette 100 is kept in the receiving container 3, but does not contact the inner wall or bottom of the receiving container 3. Since the diameter of the burette 100 is small, when the amount of liquid added set by the automatic potentiometric titrator in the burette is titrated to the end, the last drop of distilled water will be retained at the end of the burette 100 due to the tension operation instead of dripping, and therefore, the final weighing mass reading will have an error value (due to the high precision requirements, the mass of the drop cannot be ignored). In order to eliminate the influence of this error factor, such as Figure 1 , Figure 2and Figure 3 As shown, a swing mechanism 5 is fixed in the barrel cover 2, and the swing mechanism 5 is used to trigger the tube body of the burette 100 at the outer end of the receiving container 3, and the liquid droplets retained at the end of the burette 100 fall into the receiving container 3 by triggering. Specifically, the swing mechanism 5 is connected to the host 1. After the burette of the automatic potentiometric titrator drips a certain volume of distilled water, the swing mechanism 5 responds to the control instruction, outputs a swing action, and triggers the burette 100. Under the triggering of the swing mechanism 5, the liquid droplets retained at the end of the burette 100 will fall into the receiving container 3. Specifically, the swing mechanism 5 is arranged on the side wall of the barrel cover 2 close to the host 1, and a lead hole is provided on the side wall of the barrel cover 2, and a sealing ring is provided around the lead hole. The power supply line of the swing mechanism 5 is led out through the lead hole and connected to the control circuit board and the power module in the host 1. Under the sealing of the sealing ring arranged around the hole, the lead hole and the power supply line of the rocker mechanism 5 are sealed, which can ensure the sealing of the barrel cover 2. In order to eliminate the influence of the air in the receiving container 3 on the mass weighing of the distilled water dripping into the receiving container 3, the vacuum interface on the top of the receiving container 3 is connected to the external vacuum pump through the hose 6 penetrating the barrel cover 2. Before starting the titration, the inside of the receiving container 3 is evacuated by connecting the external vacuum pump to the vacuum interface.

[0032] Further, in a preferred embodiment of the present invention, Figure 3 As shown, the cylinder cover 2 includes a transparent cylindrical glass cover 21, a metal fixing frame 23 connected to the transparent cylindrical glass cover 21, and a cylinder cover 22 for sealing the transparent cylindrical glass cover 21. The upper and lower ends of the transparent cylindrical glass cover 21 are provided with openings, and the cylinder cover 22 is openably connected to the upper opening of the transparent cylindrical glass cover 21, and the lower opening of the transparent cylindrical glass cover 21 is sealed and connected through the surface of the truncated cone base 11. Figure 3 As shown, the cylinder cover 22 is provided with a matching hole through which the burette 100 and the hose 6 pass. When in use, the cylinder cover 22 is used to seal the transparent cylindrical glass cover 21, so as to construct a "static" precision weighing space without air disturbance inside, so that the weighing mass number of the distilled water titrated into the receiving container 3 is more accurate. After the titration is completed and the correction value is calculated, the cylinder cover 22 is opened and the receiving container 3 containing the distilled water can be taken out. Figure 3As shown, the metal fixing frame 23 includes a lower hoop 231 that is hooped around the lower edge of the transparent cylindrical glass cover 21, an upper hoop 232 that is hooped around the upper edge of the transparent cylindrical glass cover 21, and an arcuate portion 233 connecting the lower hoop 231 and the upper hoop 232. The arcuate portion 233 is adapted to the arcuate portion of the outer wall of the transparent cylindrical glass cover 21. The metal fixing frame 23 supports and surrounds the transparent cylindrical glass cover 21. As a preferred embodiment of the present invention, the lower hoop 231 of the metal fixing frame 23 is integrally connected with the surface of the truncated cone base 11, that is, in the preferred embodiment, the entire barrel cover 2 is fixed on the truncated cone base 11. In order to ensure the sealing of the barrel cover 2, a sealing ring is provided between the lower hoop 231 and the lower edge of the transparent cylindrical glass cover 21, and a sealing ring is provided between the upper hoop 232 and the upper edge of the transparent cylindrical glass cover 21.

[0033] In some embodiments, the barrel cover 2 and the truncated cone base 11 may also be a separate structure, that is, the entire barrel cover 2 is detachably mounted on the truncated cone base 11. In this embodiment, a circular sealing groove is provided on the truncated cone base 11, wherein the lower edge of the transparent cylindrical glass cover 21 is embedded and assembled in the sealing groove. Figure 1 and Figure 3 As shown, the lower hoop 231 is also provided with a bent handle 234, through which the entire barrel cover 2 can be removed.

[0034] Further, in a preferred embodiment of the present invention, Figure 3 As shown, the arc portion 233 on the metal fixing frame 23 is located on one side of the main unit 1, and its arc length is one-third of the outer circumference of the transparent cylindrical glass cover 21. The arc portion 233 provides structural strength support, and the rest of the transparent cylindrical glass cover 21 is in an unobstructed transparent visible state, which is convenient for the experimenter to observe the titration situation inside the cylinder cover 2.

[0035] Further, in a preferred embodiment of the present invention, Figure 4As shown, the cannula sealing and positioning mechanism 4 comprises a positioning tube 41 connected to the sealing cover 31 of the receiving container 3 and a sealing plunger 42 slidably sleeved on the burette 100. The upper and lower ends of the positioning tube 41 are open, the upper end of the tube mouth edge is flush with the upper surface of the sealing cover 31, and a trumpet-shaped introduction port 411 is formed at the joint, and the lower end of the tube mouth is located in the receiving container 3. The sealing plunger 42 is pluggable and sealed at the upper end of the positioning tube 41, and the end of the burette 100 passes through the sealing cover 31 through the positioning tube 41 and is suspended in the upper position of the receiving container 3. When in use, the position of the sealing plunger 42 on the burette 100 is first adjusted so that the length of the tube section extending into the receiving container 3 is kept at a controlled extension amount, that is, the end of the burette 100 is suspended in the receiving container 3, and the bottom is located above the maximum scale value of the receiving container 3 and below the edge of the receiving container 3. After adjusting the position of the sealing plunger 42 on the burette 100, the end tube section of the burette 100 is extended from the upper end of the positioning tube 41 into the receiving container 3, and finally the sealing plunger 42 is inserted from the trumpet-shaped introduction port 411 to the upper end of the positioning tube 41 to seal the connection. The trumpet-shaped introduction port 411 can facilitate the rapid and accurate insertion of the sealing plunger 42.

[0036] Exemplarily, the end of the burette 100 is suspended in the receiving container 3, and the height difference between the end and the edge of the receiving container 3 is controlled to be about 2 to 3 cm, so as to ensure that when the titration is completed, when the retained droplets touch the end of the burette 100, the touched droplets will not fall into the outside of the receiving container 3. At the same time, it also ensures that the end of the burette 100 does not extend too far into the receiving container 3, so as to avoid the liquid surface of the distilled water in the receiving container 3 from contacting the end of the burette 100, which would affect the accuracy of the mass reading of the distilled water in the receiving container 3.

[0037] Further, in a preferred embodiment of the present invention, Figure 5As shown, the swing mechanism 5 includes a micro servo motor 51, a swing seat 52 connected to the micro servo motor 51 by a reduction transmission, and a swing rod 53 fixed on the swing seat 52. Among them, a "U"-shaped constraint arm 531 is provided at the end of the swing rod 53, and the end of the burette 100 passes through the middle of the "U"-shaped constraint arm 531. After the burette of the automatic potentiometric titrator drips a certain volume of distilled water, the experimenter operates the console 12 on the host 1 and controls the swing mechanism 5 to start through the trigger switch on the console 12. After the swing mechanism 5 responds to the control instruction, it outputs a swing action, and the swing angle of the swing action is controlled within a small range, so that the "U"-shaped constraint arm 531 can touch the end tube body of the burette 100. The "U"-shaped constraint arm 531 resets after swinging an angle, and at the same time, the "U"-shaped constraint arm 531 also controls the end tube body of the burette 100 between the two arms of the "U"-shaped constraint arm 531.

[0038] On the other hand, the present invention also proposes a method for calibrating the volume of a burette of an automatic potentiometric titrator using the above device, the method comprising the steps of:

[0039] S1, take a clean and dry receiving container 3 and place it in the barrel cover 2, pass the burette 100 through the barrel cover 2, and then penetrate into the receiving container 3 through the cannula sealing and positioning mechanism 4, and make the end of the burette 100 hang in the upper position of the receiving container 3;

[0040] S2, connecting the receiving container 3 to an external vacuum pump, covering the cylinder cover 22, and evacuating the interior of the receiving container 3. After the vacuuming is completed, the current electronic weighing platform 111 is peeled to set the current mass reading to zero;

[0041] S3, perform the liquid addition operation on the automatic potentiometric titrator, and input the liquid addition volume v of this liquid addition operation in the host 1 at the same time. i ;

[0042] S4, start titration of the added amount, until the titration of the added amount is displayed on the automatic potentiometric titrator, control the swing mechanism 5 to output a swing action, touch the end of the burette 100, and make the water droplets retained at the end of the burette 100 fall into the receiving container 3;

[0043] S5, the host 1 synchronizes the mass reading m of the current electronic weighing platform 111 i , and combined with the current experimental environment temperature, retrieve the distilled water density value ρ at the corresponding temperature preset in host 1 i , according to the formula V i =m i / ρ i Calculate the actual volume value V at this time i ;

[0044] S6, host 1 outputs the correction value ΔV of the burette of the automatic potentiometric titrator i =V i -v i , and output the calibration value of the burette of the automatic potentiometric titrator

[0045] Specifically, as a preferred embodiment of the present invention, according to steps S3 to S6, five liquid adding operations are performed in sequence on the automatic potentiometric titrator, and the liquid adding amount of the five liquid adding operations is 10 mL. Each time the liquid adding operation is performed, a correction value is calculated once, and the correction values ​​corresponding to the five liquid adding operations are ΔV1, ΔV2, ΔV3, ΔV4, and ΔV5, respectively.

[0046] Specifically, as a preferred embodiment of the present invention, at least three parallel calibration experiments are carried out on the burette of the same automatic potentiometric titrator, and the corrected average values ​​of the liquid addition amounts of 10mL, 20mL, 30mL, 40mL, and 50mL are calculated respectively, wherein the calibration value corresponding to the liquid addition amount is the corrected average value at the liquid addition amount and the set value of the automatic potentiometric titrator at the liquid addition amount.

[0047] The embodiments of the present invention are described below with three sets of parallel experiments:

[0048] Under the same laboratory conditions, the burette of the same automatic potentiometric titrator was calibrated three times. The three calibration results are shown in Table 1, Table 2, and Table 3, respectively.

[0049] Table 1 Results of the first calibration burette experiment

[0050]

[0051] Table 2 Results of the second calibration burette experiment

[0052]

[0053] Table 3 Results of the third calibration burette experiment

[0054]

[0055] Analysis of the results in Table 1, Table 2, and Table 3 shows that the correction value of the burette is slightly larger at the two end points (i.e., 10mL and 50mL), and the correction value is smaller at the other three selected points, but all correction values ​​are less than ±0.01mL, which fully meets the capacity tolerance requirements of Class A burettes and is significantly higher than the manual identification standard of ordinary burettes. The correction values ​​of the three calibration results are averaged as the final burette correction value of the burette. Among them, Table 4 lists the corresponding correction values ​​in the scale value range of 0mL to 50mL. After rounding off the titration results of the laboratory technician, find the correction value under the titration value according to the corresponding reading value in Table 4, and then get the final calibration value.

[0056] Table 4 Burette correction table

[0057]

[0058] It can be seen that the burette of the automatic potentiometric titrator can be accurately calibrated by the method of the present invention in combination with the device, and the accuracy of the burette of the automatic potentiometric titrator after calibration is further improved, and the data is accurate and reliable.

[0059] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions only describe the principles of the present invention. The present invention may have various changes and improvements without departing from the spirit and scope of the present invention, and these changes and improvements fall within the scope of the present invention to be protected, and the scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A burette volume calibration device suitable for an automatic potentiometric titrator, characterized in that: The invention comprises a main machine (1) with a truncated cone base (11) at the bottom, a closable barrel cover (2) on the truncated cone base (11), an electronic weighing platform (111) covered in the barrel cover (2) at the center of the truncated cone base (11), a vacuum receiving container (3) placed on the electronic weighing platform (111), a tube sealing positioning mechanism (4) and a vacuum interface provided on the top of the receiving container (3), a burette (100) connected to the lower end of the burette of the automatic potentiometric titrator penetrates the barrel cover (2) and extends into the receiving container (3) through the tube sealing positioning mechanism (4). The end of the burette (100) is suspended in the receiving container (3), the vacuum interface is connected to an external vacuum pump via a hose (6) that penetrates the barrel cover (2), and a swing mechanism (5) connected to the host (1) is fixed in the barrel cover (2). After the burette of the automatic potentiometric titrator drips a certain volume of distilled water, the swing mechanism (5) responds to the control instruction and outputs a swing action to touch the tube body of the burette (100) at the outer end of the receiving container (3), so that the water droplets retained at the end of the burette (100) fall into the receiving container (3); The barrel cover (2) comprises a transparent cylindrical glass cover (21) with openings at both ends, a metal fixing frame (23) connected to the transparent cylindrical glass cover (21), and an openable barrel cover (22) for closing the upper opening of the transparent cylindrical glass cover (21); the lower opening of the transparent cylindrical glass cover (21) is sealed and connected to the surface of the truncated cone base (11); and the barrel cover (22) is provided with an adapting through hole through which the burette (100) and the hose (6) pass; The metal fixing frame (23) comprises a lower hoop (231) which is hooped around the lower edge of the transparent cylindrical glass cover (21), an upper hoop (232) which is hooped around the upper edge of the transparent cylindrical glass cover (21), and an arc-shaped portion (233) which connects the lower hoop (231) and the upper hoop (232), wherein the curvature of the arc-shaped portion (233) matches the curvature of the outer wall of the transparent cylindrical glass cover (21); The insert tube sealing and positioning mechanism (4) comprises a positioning tube (41) connected to the sealing cover (31) of the receiving container (3) and a sealing plunger (42) slidably sleeved on the burette (100); the upper and lower ends of the positioning tube (41) are open, the upper end of the tube mouth is flush with the upper surface of the sealing cover (31), a trumpet-shaped introduction port (411) is formed at the connection, and the lower end of the tube mouth is located in the receiving container (3); the sealing plunger (42) is pluggable and sealed at the upper end of the positioning tube (41); the end of the burette (100) passes through the sealing cover (31) through the positioning tube (41) and is suspended in the upper position of the receiving container (3); The rocker mechanism (5) comprises a micro servo motor (51), a rocker seat (52) connected to the micro servo motor (51) by a reduction transmission, and a rocker (53) fixed to the rocker seat (52), wherein a "U"-shaped restraining arm (531) is provided at the end of the rocker (53), and the end of the burette (100) passes through the middle of the "U"-shaped restraining arm (531).

2. The burette volume calibration device suitable for an automatic potentiometric titrator according to claim 1, characterized in that: The arc-shaped portion (233) is located on one side of the main unit (1), and the arc length is one third of the outer circumference of the transparent cylindrical glass cover (21).

3. The burette volume calibration device suitable for an automatic potentiometric titrator according to claim 1, characterized in that: The top of the host (1) is connected to a control console (12), and the control console (12) is provided with a calibration data display screen (121) and volume addition and subtraction buttons and switches.

4. A method for calibrating the volume of a burette of an automatic potentiometric titrator using the device according to any one of claims 1 to 3, characterized in that: The method comprises the steps of: S1. Place a clean and dry receiving container (3) in the barrel cover (2), pass the burette (100) through the barrel cover (2), and then insert it into the receiving container (3) through the cannula sealing and positioning mechanism (4), and let its end hang in the air above the receiving container (3); S2, connecting the receiving container (3) to an external vacuum pump, covering the cylinder cover (22), and evacuating the interior of the receiving container (3). After the evacuation is completed, the current electronic weighing platform (111) is peeled to set the current mass reading to zero; S3. Perform the liquid addition operation on the automatic potentiometric titrator and input the liquid addition amount v of the liquid addition operation into the host (1). i ; S4, starting the titration of the added amount of liquid, until the titration of the added amount of liquid is displayed on the automatic potentiometric titrator as completed, controlling the swing rod mechanism (5) to output a swing action, touching the end tube body of the burette (100), so that the water droplets retained at the end of the burette (100) fall into the receiving container (3); S5. The host (1) synchronizes the mass reading m of the current electronic weighing platform (111) i , and combined with the current experimental environment temperature, retrieve the distilled water density value ρ at the corresponding temperature preset in the host (1) i , according to the formula V i =m i / ρ i Calculate the actual volume value V at this time i ; S6. The host (1) outputs the correction value ΔV of the burette of the automatic potentiometric titrator. i =V i -v i , and output the calibration value of the burette of the automatic potentiometric titrator ▽V i =v i +ΔV i .

5. The method according to claim 4, characterized in that According to steps S3 to S6, five liquid adding operations are performed in sequence on the automatic potentiometric titrator. The liquid adding amount of each of the five liquid adding operations is 10 mL. Each time a liquid adding operation is performed, a correction value is calculated. The correction values ​​corresponding to the five liquid adding operations are ΔV1, ΔV2, ΔV3, ΔV4, and ΔV5, respectively.

6. The method according to claim 5, characterized in that Carry out at least three parallel calibration experiments on the burette of the same automatic potentiometric titrator, and calculate the corrected average values ​​of the added liquid amounts of 10mL, 20mL, 30mL, 40mL, and 50mL respectively. The calibration value at the corresponding added liquid amount is the corrected average value at the added liquid amount and the set value of the automatic potentiometric titrator at the added liquid amount.

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