Calibration method of sulfuric acid standard solution

Abstract

The invention relates to the field of analytical chemistry, in particular to a calibration method of a sulfuric acid standard solution. The potential calibration method is adopted, in the titration process, the second potential jump point serves as the titration end point recognition standard, the titration volume of the sulfuric acid standard solution corresponding to the second potential jump point serves as the final consumption volume, the calibration result precision is improved, the error problem of end point color judgment through manual calibration is effectively avoided, and the accuracy is high.

Description

Technical Field

[0001] The present application relates to the field of analytical chemistry, and in particular to a method for calibrating a sulfuric acid standard solution. Background Art

[0002] The traditional method for the calibration of sulfuric acid in GB / T 601-2016 "Preparation of Standard Titration Solutions for Chemical Reagents" is to use bromocresol green-methyl red as an indicator, use an acid burette to manually titrate the prepared sulfuric acid standard solution with the reference anhydrous sodium carbonate, determine the titration end point by color change, and calculate the concentration of the target solution by the consumption of the sulfuric acid standard solution. This method consumes a lot of reagents, has long detection time, low accuracy, and there are problems such as differences in human judgment in the determination of the calibration end point. Based on this, it is necessary to provide an efficient, high-precision calibration method for sulfuric acid standard solution that can avoid subjective judgment errors. Summary of the invention

[0003] One or more embodiments of the present application provide a method for calibrating a sulfuric acid standard solution, including the following technical solutions:

[0004] One or more embodiments of the present application provide a method for calibrating a sulfuric acid standard solution, the method comprising the following steps:

[0005] The potentiometric calibration method is used to titrate the sodium carbonate solution and the blank reagent with the sulfuric acid standard solution to be calibrated.

[0006] During the titration of the sodium carbonate solution, the titration volume corresponding to the potential value at the second potential jump point is determined according to the relationship curve 1 between the titration volume and the potential value, which is recorded as V1.

[0007] In the process of titrating the blank reagent, the titration volume corresponding to the potential value at the potential jump point is determined according to the relationship curve 2 between the titration volume and the potential value, which is recorded as V2.

[0008] The concentration of the sulfuric acid standard solution to be calibrated is calculated according to the following formula:

[0009]

[0010] Where:

[0011] m——the mass of sodium carbonate in the sodium carbonate solution, in grams (g);

[0012] V1——unit is milliliter (mL);

[0013] V2——unit is milliliter (mL);

[0014] M is the molar mass of sodium carbonate in the sodium carbonate solution, in grams per mole (g / mol).

[0015] In some embodiments of the present application, during the titration of the sodium carbonate solution, the potentiometric calibration method satisfies one or more of the following conditions (1) to (2):

[0016] (1) a threshold value of 0.5 pH / mL to 1.0 pH / mL; and,

[0017] (2) The upper limit-lower limit potential is 4.0pH-3.0pH.

[0018] In some embodiments of the present application, during the titration of the sodium carbonate solution, the potentiometric calibration method further satisfies one or more of the following conditions (3) to (11):

[0019] (3) stirring speed is 20%-60%;

[0020] (4) The waiting time is 3s-12s;

[0021] (5) The control mode is normal mode;

[0022] (6) The addition mode is DT addition;

[0023] (7) dV(min)-dV(max) is 0.001mL-2.0mL;

[0024] (8) The trend is negative;

[0025] (9) EQP standard is the steepest jump;

[0026] (10) The number of EQP points is 2-3; and,

[0027] (11) The termination condition is that the titration volume is 50 mL-60 mL.

[0028] In some embodiments of the present application, during the titration of the sodium carbonate solution, the potentiometric calibration method further satisfies the following condition (12):

[0029] (12) The pre-feed solution is 0 mL or 1 / 3-2 / 3 of the estimated titration volume.

[0030] In some embodiments of the present application, the blank reagent includes water, optionally grade tertiary water.

[0031] In some embodiments of the present application, during the titration of the blank reagent, the potentiometric calibration method satisfies the following condition (A):

[0032] (A) The threshold value is 0.01-0.02 pH / mL.

[0033] In some embodiments of the present application, during the titration of the blank reagent, the potentiometric calibration method further satisfies one or more of the following conditions (B) to (F):

[0034] (B) stirring speed is 20%-60%;

[0035] (C) Waiting time is 3s-12s;

[0036] (D) The control mode is slow mode;

[0037] (E) dV(min)-dV(max) is 0.001 mL-0.50 mL; and,

[0038] (F) The termination condition is that the titration volume is 1.8 mL-2.2 mL.

[0039] In some embodiments of the present application, the titration method includes: automatic titration.

[0040] In some implementations of the present application, the relationship curve 1 and the relationship curve 2 are both drawn using the second-order derivative method.

[0041] In some embodiments of the present application, the solvent of the sodium carbonate solution includes tertiary water.

[0042] The details of one or more embodiments of the present application are set forth in the description which follows, and other features, objects, and advantages of the present application will be apparent from the description and its claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application and to more completely understand the present application and its beneficial effects, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0044] Figure 1 This is a flow chart of the calibration method of an embodiment of the present application;

[0045] Figure 2 is the titration curve of the sodium carbonate solution in the embodiment of the present application;

[0046] Figure 3 This is the titration curve of the blank reagent in the examples of this application. DETAILED DESCRIPTION

[0047] The present application will be further described in detail below in conjunction with the accompanying drawings, embodiments and examples. It should be understood that these embodiments and examples are only used to illustrate the present application and are not used to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the understanding of the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms, is not limited to the embodiments and examples described herein, and those skilled in the art can make various changes or modifications without violating the connotation of the present application, and the equivalent form obtained also falls within the protection scope of the present application. In addition, in the description below, a large number of specific details are given in order to provide a more comprehensive understanding of the present application, and it should be understood that the present application can be implemented without one or more of these details.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing implementation modes and embodiments and are not intended to limit this application.

[0049] the term

[0050] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0051] The terms "and / or", "or / and", and "and / or" used in this article include any one of two or more related listed items, and also include any and all combinations of related listed items, and the arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected by at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that in this application, the technical solution undoubtedly includes technical solutions that are all connected by "logical and", and undoubtedly includes technical solutions that are all connected by "logical or". For example, "A and / or B" includes three parallel solutions of A, B and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, the technical solution that is all connected by "logical OR"), and also includes any and all combinations of A, B, C, and D, that is, the combination of any two or any three of A, B, C, and D, and also includes the combination of four of A, B, C, and D (that is, the technical solution that is all connected by "logical AND").

[0052] In the present application, "plurality", "multiple", "multiple times", "multiples", etc., unless otherwise specified, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0053] As used herein, "combination thereof", "any combination thereof", "any combination thereof" etc. include all suitable combinations of any two or more of the listed items.

[0054] Herein, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc., shall be based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0055] Herein, “preferred”, “better”, “more preferred” and “suitable” are merely used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute limitations on the scope of protection of this application.

[0056] In the present application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present application.

[0057] In this application, "optionally", "optional", and "optional" mean optional or dispensable, that is, any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0058] In the present application, the terms "first", "second", "third", "fourth", etc. in "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0059] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0060] In the present application, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges included therein.

[0061] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0062] In the present application, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass volume percentage.

[0063] All documents mentioned in this application are cited as references in this application, just as each document is cited as reference separately. Unless they conflict with the application purpose and / or technical solution of this application, the cited documents involved in this application are cited with all contents and all purposes. When the cited documents are involved in this application, the definitions of relevant technical features, terms, nouns, phrases, etc. in the cited documents are also cited. When the cited documents are involved in this application, the examples and preferred methods of the cited relevant technical features can also be incorporated into this application as references, but are limited to the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, the present application shall prevail or be modified adaptively according to the description of this application.

[0064] One or more embodiments of the present application provide a method for calibrating a sulfuric acid standard solution, the method comprising the following steps:

[0065] The potentiometric calibration method is used to titrate the sodium carbonate solution and the blank reagent with the sulfuric acid standard solution to be calibrated.

[0066] During the titration of the sodium carbonate solution, the titration volume corresponding to the potential value at the second potential jump point is determined according to the relationship curve 1 between the titration volume and the potential value, which is recorded as V1.

[0067] In the process of titrating the blank reagent, the titration volume corresponding to the potential value at the potential jump point is determined according to the relationship curve 2 between the titration volume and the potential value, which is recorded as V2.

[0068] The concentration of the sulfuric acid standard solution to be calibrated is calculated according to the following formula:

[0069]

[0070] Where:

[0071] m——the mass of sodium carbonate in the sodium carbonate solution, in grams (g);

[0072] V1——unit is milliliter (mL);

[0073] V2——unit is milliliter (mL);

[0074] M is the molar mass of sodium carbonate in the sodium carbonate solution, in grams per mole (g / mol).

[0075] This application adopts the potentiometric calibration method. During the titration process, the second potential jump point is used as the titration endpoint identification standard, and the titration volume of the corresponding sulfuric acid standard solution is used as the final consumption volume, which improves the accuracy of the calibration result (accuracy reaches 0.001mL) and effectively avoids errors such as manual calibration of the endpoint color judgment, with high accuracy. In addition, the potentiometric method has the functions of automatic stirring and automatic pre-feeding liquid, which greatly improves the efficiency of the titration process.

[0076] In some of the examples, during the titration of the sodium carbonate solution, the potentiometric calibration method satisfies one or more of the following conditions (1) to (2):

[0077] (1) a threshold value of 0.5 pH / mL to 1.0 pH / mL (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, 1 pH / mL); and,

[0078] (2) The upper limit-lower limit potential is 4.0 pH to 3.0 pH (e.g., 4, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3 pH).

[0079] In some of the examples, during the titration of the sodium carbonate solution, the potentiometric calibration method also satisfies one or more of the following conditions (3) to (11):

[0080] (3) the stirring speed is 20%-60% (e.g., 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%);

[0081] (4) The waiting time is 3s-12s (for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12s);

[0082] (5) The control mode is normal mode;

[0083] (6) The addition mode is DT addition;

[0084] (7) dV(min)-dV(max) is 0.001 mL-2.0 mL (e.g., 0.001, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 mL);

[0085] (8) The trend is negative;

[0086] (9) EQP standard is the steepest jump;

[0087] (10) The number of EQP points is 2-3; and,

[0088] (11) The termination condition is that the titration volume is 50 mL-60 mL (for example, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60 mL).

[0089] In some of the examples, during the titration of the sodium carbonate solution, the potentiometric calibration method also satisfies the following condition (12):

[0090] (12) The pre-feed solution is 0 mL or 1 / 3-2 / 3 of the estimated titration volume (e.g., 35%, 40%, 45%, 50%, 55%, 60%).

[0091] In some examples, the blank reagent includes water, optionally grade tertiary water.

[0092] In some of these examples, during the titration of the blank reagent, the potentiometric calibration method satisfies the following condition (A):

[0093] (A) The threshold value is 0.01-0.02 pH / mL (for example, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02 pH / mL).

[0094] In some examples, during the titration of the blank reagent, the potentiometric calibration method also satisfies one or more of the following conditions (B) to (F):

[0095] (B) a stirring speed of 20%-60% (e.g., 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%);

[0096] (C) the waiting time is 3s-12s (for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12s);

[0097] (D) The control mode is slow mode;

[0098] (E) dV(min)-dV(max) is 0.001 mL-0.50 mL (e.g., 0.001, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 mL); and,

[0099] (F) The termination condition is that the titration volume is 1.8 mL-2.2 mL (e.g., 1.8, 1.9, 2.0, 2.1, 2.2 mL).

[0100] In some of these examples, the titration method includes: automatic titration.

[0101] In some of the examples, the relationship curve 1 and the relationship curve 2 are both drawn using the second-order derivative method.

[0102] In some examples, the solvent of the sodium carbonate solution includes tertiary water.

[0103] The embodiments of the present application will be described in detail below in conjunction with examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are preferably referred to the guidance provided in the present application, and can also be based on the experimental manual or normal conditions in this area, can also be based on the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0104] In the following specific embodiments, the measured parameters of raw material components may have slight deviations within the range of weighing accuracy unless otherwise specified. For temperature and time parameters, acceptable deviations caused by instrument test accuracy or operation accuracy are allowed.

[0105] Combination Figure 1 , the technical solution of this application is described as follows:

[0106] 1. Method implementation steps

[0107] Step 1: Preparation Sulfuric acid standard titration solution, refer to GB / T 601

[0108] Slowly inject the amount of sulfuric acid standard titration solution of other concentrations into 1000mL of grade 3 water according to the amount specified in the table below, mix well after cooling, and put into a reagent bottle, seal and set aside.

[0109] Table 1

[0110]

[0111]

[0112] Step 2: Prepare the calibration reference substance solution according to GB / T 601

[0113] Weigh about 0.1g (accurate to 0.0001) of standard anhydrous sodium carbonate that has been burned to constant weight in a Maffei furnace at 270-300℃ into a 150mL beaker, and add 50-80mL of grade 3 water to completely dissolve it. The standard reagent needs to be burned and weighed in advance to prevent the introduction of moisture.

[0114] For solutions of calibration reference substances with other concentrations, weigh the mass of the calibration reference substances as specified in the table below.

[0115] Table 2

[0116]

[0117] Step 3: Potentiometric Calibration Solution

[0118] Place the calibration reference substance solution prepared in step 2 on the automatic titrator platform, connect the instrument, call out the pre-set detection program for the calibration sulfuric acid standard titration solution, input the reference reagent sample weight, press the instrument "start" button, and the instrument will automatically add the sulfuric acid standard titration solution prepared in step 1 to start automatic titration detection.

[0119] Taking the calibration of 0.05 mol / L sulfuric acid standard solution by the automatic titrator currently on the market as an example, the sample detection parameter settings and process titration curve are as follows:

[0120] Table 3

[0121]

[0122]

[0123] Note that during the titration process, the instrument threshold and the upper and lower potential limits are the key parameters. The threshold is generally the titration potential. Figure 1The value of the upper and lower pH control limits is 40-80% of the main peak of the derivative. If the value is set too large, the instrument cannot find the jump point. If the value is set too small, the jump point cannot be identified and the titration end point cannot be found. Improper settings of the upper and lower pH control limits will result in the inability to find the end point. For other concentrations such as 0.1mol / L, 0.5mol / L and other concentration calibration parameters, please refer to Table 3.

[0124] The following table shows the orthogonal test results of sulfuric acid standard solution under different threshold values ​​and upper and lower potential limit combinations. The actual concentration of the reagent is 0.04902 mol / L:

[0125] Table 4

[0126]

[0127] As can be seen from the above table, the threshold of the potentiometric titrator in this method is preferably set to 0.5-1.0 pH / mL, and the upper and lower control limits are set to 4-3 pH, so that the correct potential jump point, i.e., the titration end point, can be found.

[0128] The titrator pre-feeds liquid for titration (i.e., a portion of solution is pre-added before the titration reaches the endpoint to react in advance, so as to improve the solution calibration efficiency). At the beginning of the titration, the volume of standard solution is added at one time. The pre-added volume cannot be too much at one time. For unknown blind sample solutions, the pre-feed liquid volume parameter is set to 0mL to prevent the pre-feed liquid from exceeding the endpoint titration number after it is added. The titration process cannot find the jump point, resulting in the inability to find the endpoint titration number. When the approximate calibration titration volume of a certain concentration of sulfuric acid solution can be estimated, the pre-feed liquid value is generally set to 1 / 3-2 / 3 of the estimated titration volume. This can not only speed up the titration speed of the instrument, but also make it easier to find the titration endpoint and speed up the analysis. In this application, the pre-feed liquid parameter of the 0.05mol / L concentration sulfuric acid standard solution is set to 25-30mL, and other concentration solutions are set in combination with the actual titration data.

[0129] Note that the weighed working standard reagent anhydrous sodium carbonate should be placed on the titration platform for titration in time after adding 50-80mL of grade 3 water. If it cannot be tested on the machine in time, sealing measures should be taken to reduce the reaction of the standard anhydrous sodium carbonate solution with carbon dioxide in the air before titration, which will affect the calibration results. The specific reaction formula is as follows:

[0130] Na2CO3+CO2+H2O=2NaHCO3↓

[0131] A small amount of sodium bicarbonate will be produced during the reaction. The solubility of sodium bicarbonate is lower than that of sodium carbonate, so a precipitate will be formed, causing the calibration result to be higher.

[0132] Step 4: Blank test

[0133] Place the third-grade water on the automatic titrator platform, use the pre-set calibration test program, and press the instrument "start"

[0134] Press the (Start) key, the instrument automatically adds the sulfuric acid standard titration solution prepared in step 1, and starts automatic titration detection. The endpoint consumption volume number is the blank result.

[0135] Taking the automatic titrator currently on the market as an example, its potential blank detection parameter settings and process titration curve are as follows:

[0136] Table 5

[0137]

[0138] The following table shows the titration results of the three-level water potential blank test at different thresholds. The concentration data of the detected standard solution are obtained by setting different threshold parameters:

[0139] Table 6

[0140] Threshold Potential blank (mL) 0.05pH / mL Can't find the end 0.03pH / mL Can't find the end 0.02pH / mL 0.022mL 0.01pH / mL 0.020mL 0.005pH / mL Can't find the end 0.001pH / mL Can't find the end

[0141] Note that it is necessary to set reasonable reagent potential blank detection threshold parameters. If the parameters are not set reasonably, the instrument cannot find the blank jump point. In this method, the potential blank detection threshold parameters of the potentiometric titrator are preferably set to 0.01-0.02pH / mL.

[0142] Step 5: Calculate the results

[0143] Sulfuric acid standard solution The reference reagent anhydrous sodium carbonate solution was titrated dynamically, and the electrode titration volume V and potential value E were recorded. In the dynamic titration, when the potential value showed a second mutation, the titration volume V and the corresponding potential value E were recorded. The potential jump point was calculated by the second-order differential method, and the titration volume was determined to obtain the endpoint consumption volume number. The formula is as follows:

[0144]

[0145] Where:

[0146] V——titration volume, in milliliters (mL);

[0147] E——The electrode potential corresponding to the above titration volume, in millivolts (mV);

[0148] when When , it is the titration endpoint, calculate the titration volume V in milliliters.

[0149] Concentration of sulfuric acid standard solution The value is expressed in moles per liter (mol / L), referring to the national standard (GB / T 601-2016) formula as follows:

[0150]

[0151] Where:

[0152] m——mass of anhydrous sodium carbonate, in grams (g);

[0153] V1——Use the second-order derivative method to draw the relationship curve between the titration volume V and the potential value E, and find the volume of the titrated sulfuric acid standard solution at the potential jump point, in milliliters (mL);

[0154] V2——The titration volume at the blank potential jump point determined by the above method for the blank sample, in milliliters (mL);

[0155] M——molar mass of anhydrous sodium carbonate, in grams per mole (g / mol)

[0156] 2. Implementation Cases

[0157] Example 1: Calibration of 0.05 mol / L sulfuric acid standard solution

[0158] 1. Weigh about 0.1g (accurate to 0.0001) of standard anhydrous sodium carbonate that has been burned to constant weight in a Maffei furnace at 270-300℃ into a 150mL beaker, and add 50-80mL of grade 3 water to completely dissolve it. The standard reagent needs to be burned and weighed in advance to prevent the introduction of moisture.

[0159] 2. Place the standard anhydrous sodium carbonate solution on the automatic titrator platform, connect the instrument, call out the pre-set test program for calibrating the sulfuric acid standard titration solution, input the sample weight of the standard reagent, press the "start" button of the instrument, and the instrument will automatically add the sulfuric acid standard titration solution prepared in step 1 to start automatic titration detection; measure the pH value change of the solution during the titration process through the pH composite electrode on the instrument. Two titration jumps will occur during the titration process, and the second titration jump is the titration end point. The reaction formula includes:

[0160] First jump: H + +CO3 2- →HCO3; Second jump: H + +HCO3 - →CO2↑+H2O.

[0161] 3. Two people tested 8 times in parallel and the results are as follows:

[0162] Table 7

[0163]

[0164] According to the national standard GB / T 601, when calibrating the concentration of the standard solution, two people must conduct the experiment, each doing four parallels, and the relative value of the range of the four parallel determination results of each person shall not be greater than the relative value of the critical range of repeatability by 0.15%. The average value of the eight parallel determination results of the two people shall not be greater than the relative value of the critical range of repeatability by 0.18%. The average value of the average determination results of the two people shall be taken as the determination result.

[0165] The relative values ​​of the extreme values ​​of the results of four parallel determinations of sulfuric acid standard solution by two persons using this method were 0.08% and 0.04% respectively, and the relative value of the extreme value of the results of eight parallel determinations by two persons was 0.08%, which met the national standard requirements.

[0166] Example 2: Calibration of 0.1 mol / L sulfuric acid standard solution

[0167] 1. Weigh about 0.2g (accurate to 0.0001) of standard anhydrous sodium carbonate that has been burned to constant weight in a Maffei furnace at 270-300℃ into a 150mL beaker, and add 50-80mL of grade 3 water to completely dissolve it. The standard reagent needs to be burned and weighed in advance to prevent the introduction of water.

[0168] 2. Place the reference anhydrous sodium carbonate solution on the automatic titrator platform, connect the instrument, call out the pre-set detection program for the standard sulfuric acid titration solution, input the reference reagent sample weight, press the "start" button on the instrument, and the instrument will automatically add the step 1 solution to start automatic titration detection; use the pH composite electrode on the instrument to measure the pH change of the solution during the titration process. Two titration jumps will occur during the titration process, and the second titration jump is the titration endpoint.

[0169] The reaction formula includes:

[0170] First jump: H + +CO3 2- →HCO3; Second jump: H + +HCO3 - →CO2↑+H2O

[0171] 3. Two people tested 8 times in parallel and the results are as follows:

[0172] Table 8

[0173]

[0174] According to the national standard GB / T 601, when calibrating the concentration of the standard solution, two people must conduct the experiment, each doing four parallels, and the relative value of the range of the four parallel determination results of each person shall not be greater than the relative value of the critical range of repeatability by 0.15%. The average value of the eight parallel determination results of the two people shall not be greater than the relative value of the critical range of repeatability by 0.18%. The average value of the average determination results of the two people shall be taken as the determination result.

[0175] The relative values ​​of the extreme differences of the results of four parallel determinations of sulfuric acid standard solution by two persons using this method were 0.07% and 0.12% respectively, and the relative value of the extreme differences of the results of eight parallel determinations by two persons was 0.15%, which met the national standard requirements.

[0176] Example 3: Calibration of 0.5 mol / L sulfuric acid standard solution

[0177] 1. Weigh about 0.95g (accurate to 0.0001) of standard anhydrous sodium carbonate that has been burned to constant weight in a Maffei furnace at 270-300℃ into a 150mL beaker, and add 50-80mL of grade 3 water to completely dissolve it. The standard reagent needs to be burned and weighed in advance to prevent the introduction of moisture.

[0178] 2. Place the standard anhydrous sodium carbonate solution on the automatic titrator platform, connect the instrument, call out the pre-set test program for the standard sulfuric acid titration solution, input the sample weight of the standard reagent, press the "start" button of the instrument, and the instrument will automatically add the solution of step 1 to start the automatic titration test; the pH value change of the solution during the titration process is measured by the pH composite electrode on the instrument. Two titration jumps will occur during the titration process, and the second titration jump is the titration end point. The reaction formula includes:

[0179] First jump: H + +CO3 2- →HCO3; Second jump: H + +HCO3 - →CO2↑+H2O

[0180] 3. Two people tested 8 times in parallel and the results are as follows:

[0181] Table 9

[0182]

[0183] According to the national standard GB / T 601, when calibrating the concentration of the standard solution, two people must conduct the experiment, each doing four parallels, and the relative value of the range of the four parallel determination results of each person shall not be greater than the relative value of the critical range of repeatability by 0.15%. The average value of the eight parallel determination results of the two people shall not be greater than the relative value of the critical range of repeatability by 0.18%. The average value of the average determination results of the two people shall be taken as the determination result.

[0184] The relative values ​​of the extreme differences of the results of four parallel determinations of sulfuric acid standard solution by two persons using this method were 0.07% and 0.10% respectively, and the relative value of the extreme differences of the results of eight parallel determinations by two persons was 0.13%, which met the national standard requirements.

[0185] Overall, the embodiment of the present application provides a potentiometric calibration method for a sulfuric acid standard solution, which titrates the sulfuric acid standard solution using an automatic potentiometric titrator electrode, thereby improving the accuracy of the existing sulfuric acid standard solution calibration results and the error problems such as the endpoint color determination in manual calibration.

[0186] The technical features of the above-mentioned implementation modes and examples can be combined in any appropriate manner. To make the description concise, not all possible combinations of the technical features in the above-mentioned implementation modes and examples are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0187] The above-described embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solution of the present application in detail, but it cannot be understood as a limitation on the scope of protection of the patent application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several deformations and improvements can be made, which all belong to the protection scope of the present application. In addition, it should be understood that after reading the above-mentioned teaching content of the present application, the technicians in this field can make various changes or modifications to the present application, and the equivalent forms obtained also fall within the protection scope of the present application. It should also be understood that the technical solutions obtained by the technicians in this field through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the protection scope of the claims attached to the present application. Therefore, the protection scope of the patent of the present application shall be based on the content of the attached claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A method for calibrating a sulfuric acid standard solution, characterized in that: The calibration method comprises the following steps: The potentiometric calibration method is used to titrate the sodium carbonate solution and the blank reagent with the sulfuric acid standard solution to be calibrated. During the titration of the sodium carbonate solution, the titration volume corresponding to the potential value at the second potential jump point is determined according to the relationship curve 1 between the titration volume and the potential value, which is recorded as V1. In the process of titrating the blank reagent, the titration volume corresponding to the potential value at the potential jump point is determined according to the relationship curve 2 between the titration volume and the potential value, which is recorded as V2. The concentration of the sulfuric acid standard solution to be calibrated is calculated according to the following formula: Where: m——the mass of sodium carbonate in the sodium carbonate solution, in grams (g); V1——unit is milliliter (mL); V2——unit is milliliter (mL); M is the molar mass of sodium carbonate in the sodium carbonate solution, in grams per mole (g / mol).

2. The method for demarcating a sulfuric acid standard solution according to claim 1, wherein: During the titration of the sodium carbonate solution, the potentiometric calibration method satisfies one or more of the following conditions (1) to (2): (1) a threshold value of 0.5 pH / mL to 1.0 pH / mL; and, (2) The upper limit-lower limit potential is 4.0pH-3.0pH.

3. The calibration method of sulfuric acid standard solution according to claim 2, characterized in that: During the titration of the sodium carbonate solution, the potentiometric calibration method further satisfies one or more of the following conditions (3) to (11): (3) stirring speed is 20%-60%; (4) The waiting time is 3s-12s; (5) The control mode is normal mode; (6) The addition mode is DT addition; (7) dV(min)-dV(max) is 0.001mL-2.0mL; (8) The trend is negative; (9) EQP standard is the steepest jump; (10) The number of EQP points is 2-3; and, (11) The termination condition is that the titration volume is 50 mL-60 mL.

4. The method for demarcating a sulfuric acid standard solution according to claim 3, wherein: During the titration of the sodium carbonate solution, the potentiometric calibration method also satisfies the following condition (12): (12) The pre-feed solution is 0 mL or 1 / 3-2 / 3 of the estimated titration volume.

5. The method for calibrating a sulfuric acid standard solution according to any one of claims 1 to 4, characterized in that: The blank reagent includes water, optionally grade tertiary water.

6. The method for calibrating a sulfuric acid standard solution according to claim 5, characterized in that: During the titration of the blank reagent, the potentiometric calibration method satisfies the following conditions (A): (A) The threshold value is 0.01-0.02 pH / mL.

7. The method for calibrating a sulfuric acid standard solution according to claim 6, characterized in that: During the titration of the blank reagent, the potentiometric calibration method further satisfies one or more of the following conditions (B) to (F): (B) stirring speed is 20%-60%; (C) Waiting time is 3s-12s; (D) The control mode is slow mode; (E) dV(min)-dV(max) is 0.001 mL-0.50 mL; and, (F) The termination condition is that the titration volume is 1.8 mL-2.2 mL.

8. The method for calibrating a sulfuric acid standard solution according to any one of claims 1 to 4 and 6 to 7, characterized in that: Titration methods include: automatic titration.

9. The method for calibrating a sulfuric acid standard solution according to any one of claims 1 to 4 and 6 to 7, characterized in that: The relationship curve 1 and the relationship curve 2 are both drawn using the second-order derivative method.

10. The method for calibrating a sulfuric acid standard solution according to any one of claims 1 to 4 and 6 to 7, characterized in that: The solvent of the sodium carbonate solution includes grade tertiary water.

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