JPS6331735B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a potentiometric titration device that automatically determines the end point of titration. [Prior Art] A conventional potentiometric titration apparatus employs a method of determining the titration end point by detecting an inflection point of a potentiometric titration curve or a preset equivalence point potential. However, with these methods, the potential change is large, and the potential change near the equivalence point must be accurately measured, which takes time for the electrode to equilibrate. The titration required at least 5 to 10 minutes. [Problems to be solved by the invention] In order to solve the above-mentioned problems, the present applicant filed a patent application for a high-speed potentiometric titration device using a linear titration plot method (Japanese Patent Application Laid-Open No. 1983-1993).
26427). This titrator has a titration rate of 50 before the equivalence point.
This is an excellent device that can complete the titration in a short time by measuring the titration point in the ~90% range several times and then calculating the equivalence point. However, this titrator uses a glass electrode to detect
It is essential to accurately measure the PH value, and it is not suitable for titration of organic solvents, etc., which have poor reproducibility of PH values. The present invention improves these points, and aims to provide an automatic titration device that can determine the titration end point in a short time and with extremely high accuracy even when the sample solution is an organic solvent. [Means for Solving the Problems] The present invention provides a titration unit that stores a sample solution and drops a titrant into the sample solution, a billet that measures the titrant to be dropped into the titration unit, and a titration unit that stores a sample solution and drops a titrant into the sample solution. In an automatic titration apparatus, the automatic titration apparatus is equipped with a potential detection section for detecting the potential E of the sample solution, and a burette control means for controlling the titration amount of the burette to be dropped based on the detection output of the potential detection section. The control means is configured to calculate the amount of titrant liquid to be dropped next, ΔV _{o +1, when the amount of titrant liquid dropped into the titration unit from the burette is ΔV o:} A/S _o +ΔS _o +B=ΔV _o+1 ( However, S _o is the absolute value of the change in the potential E (E _o −E _o-1 ) that occurs when the above ΔV _o is dropped,
ΔS _o is the change in S _o when the above ΔV _o is dropped (S _o -S _o-1 ), A and B are constants, and n is the number of drops of the titrant. ), and the titrant volume ΔV _o+1 is ΔV _nio ≦ΔV _o+1 ≦ΔV _nax (where ΔV _nio and ΔV _nax are the predetermined minimum and maximum titrant drop amounts, respectively). .)
A means for setting ΔV _o+1 = ΔV _o when this titration liquid volume ΔV _o+1 is 0 < ΔV _o+1 < ΔV _nio , a means for setting ΔV _o+1 = ΔV _nio , and this titration. When the liquid volume ΔV _o+1 is ΔV _o+1 > ΔV _nax or ΔV _o+1 < 0, there is a means for setting ΔV _o+1 = ΔV _nax , and further, when the above-mentioned ΔS _o becomes negative, dropping is stopped. It is characterized by including means for stopping. Incidentally, it is preferable that the first two drops of the titrant solution ΔV ₁ and ΔV ₂ from the titration unit are predetermined. Further, it is preferable to control the brewet so as to stop dropping when ΔS becomes negative twice. [Function] In controlling the titration amount, the present invention uses the amount of potential change S and the increment ΔS of the amount of change from the start of titration as parameters, and the titer amount is large in the flat portion of the potential change curve, and at the inflection point. By decreasing the titration amount in the vicinity of , titration is performed with high accuracy. In other words, in the titration curve shown in Figure 2, the potential change is almost constant in the flat curve part from the start of titration, so S _o and S _o-1 are almost equal, ΔS _o ≒ 0, and this When, the above ΔV _o+1
Since ΔS _o is not included as a denominator in the calculation formula, the titer volume ΔV _o+1 is constant as ΔV _o+1 =A/(S _o +B). However, as shown in Figure 2, as the slope of this curve gets closer to the inflection point P, the slope of this curve increases, so ΔS _o becomes larger, and this increased ΔS _o enters the denominator of the calculation formula, so ΔV _o+1 becomes smaller. . In this way, by controlling ΔV _o+1 to a small value where the change is large, titration accuracy can be increased. When the inflection point is exceeded, ΔS _o <0, and the titration is stopped at this point. [Example] A detailed explanation will be given below with reference to the drawings of the example. FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.
In FIG. 1, 1 is a sample feeding device, and 2 is an automatic brewet. A flask 5, which is a titration container, is placed on the rotary table 3 of the sample feeding device 1. A certain amount of sample solution is stored in the flask 5, and this solution is stirred by a magnetic stirrer in the flask 5. Also flask 5
includes an electrode 6 for detecting the potential of this sample solution and a pipe 7 for conveying the titrant from the automatic brewet 2.
is installed. These electrodes 6 and pipes 7 can be moved up and down by the drive mechanism of the sample feeding device 1 so that they can be taken in and out of the flask 5. The automatic brewer 2 is also connected via a pipe 9 to a titrant tank 10 in which a titrant is stored. Further, the control output of the microcomputer 11 is connected to the automatic brewet 2, and the automatic brewet 2 automatically transfers the titrant to the titrant tank 10 in a range of 0.06 ml to 1 ml at a time under the control of the microcomputer 11. It is sucked up from the sample solution and dripped into the sample solution in the flask 5 through the pipe 7. The total amount of titration added into the flask 5 is digitally displayed on the automatic brewer 2. The automatic computer 2 outputs this digital signal to the microcomputer 11. Further, a digital PH meter 13 is connected to the electrode 6. This digital PH meter 1
The potential at No. 3 is displayed on the digital PH meter 13 and is also input to the microcomputer 11 as a digital signal. With such a configuration, a titration method using the apparatus of this embodiment will be explained. First, at the start of titration, a predetermined titration liquid volume of 0.5 ml is added from automatic brewet 2 to the initial titration liquid volume ΔV _1.
and ΔV ₂ into flask 5. At this time, the microcomputer 11 determines the amount of titrant liquid ΔV ₃ to be dropped next from the potential E ₂ of the titrant liquid in the flask 5 . This determination method first calculates the absolute value S 2 of the change in the potential E 2 that occurs when the titrant volumes ΔV ₁ and ΔV ₂ are dropped, and the absolute value S ₂ of the change in the potential E ₂ that occurs when the titrant volumes ΔV ₁ and ΔV ₂ are dropped. The change ΔS ₂ between S ₂ and S ₁ is determined, and ΔV ₃ is determined using the following formula. A/S ₂ +ΔS ₂ +B=ΔV ₃ ...(1) (Here, A and B are constants, and the titration rate is 90
It is determined that the value of ΔV ₃ reliably decreases from about 0.5 ml to the minimum dripping amount of 0.06 ml in the range of ~99%. Further, S ₂ above represents a potential gradient, and ΔS ₂ is an increment of this potential gradient. ) When ΔV ₃ calculated by this formula (1) is 0.06ml≦ΔV ₃ ≦1ml, the next titration amount ΔV ₃ to be added is (1)
If the value of ΔV ₃ obtained by the formula (1) is 0<ΔV ₃ < _0.06ml , the next titrant volume ΔV ₃ to be dropped is the minimum titrant drop volume. If ΔV ₃ determined by equation (1) is ΔV ₃ > 1 ml or ΔV ₃ < 0, then the next titrant volume ΔV ₃ to be dropped is the preset maximum titrant volume. The microcomputer 11 controls the automatic brewet 2 so that the volume is 1 ml. Furthermore, the amount of titrant liquid ΔV ₄ to be dropped next to this amount of titrant liquid ΔV ₃ is determined in the same manner as the method for determining ΔV ₃ above. In this way, the amount of titrant liquid ΔV _o+1 to be dropped next to the nth titration liquid amount ΔV _o is determined by the absolute value S _o of the change in potential E _o that occurred when dropping ΔV _o , and this It is determined based on the above equation (1) based on the increment ΔS _o of the above S _o that occurs when ΔV _o is dropped. Continuing the titration, when the increment ΔS _o of S _o changes from positive to negative, that is, the inflection point P of the titration curve in Figure 2
When the time has passed, the microcomputer 11 controls the supply of titrant from the automatic bottle 2 to stop. Here, the meanings of constants A and B will be explained. The constant B is used to prevent only S _o and ΔS _o from directly affecting the calculation of the dropping amount in the above calculation formula. This is because the amount of potential change differs depending on the titrant and sample, so it is necessary to determine the optimum titration. For example, when the titrant is a strong base and the sample is a weak acid, the effect of the potential change due to the addition of a drop of the strong base titrant is reduced. It is for the purpose of The constant A is used to make ΔV _o+1 a unit of volume, and by introducing the constant A into the numerator of the above calculation formula, it becomes a unit of volume. This constant A is
When titrating a strong base with a weak acid, a small value is preferable, and when titrating a weak base with a strong acid, a large value is preferable for the constant A. The values of these constants A and B are determined by the content of the titration, but for inexperienced samples and titrants, it is important to know how many times the titrant has been dropped in advance and some ΔV,
We can take the data of S and ΔS, apply it to the formula A/S+ΔS+B=ΔV to create an equation, and determine A and B from the two formulas. For example, if 0.5ml is dropped, then S+ΔS=
If 0.3 ml of M is dropped and S+ΔS=N is obtained, the values of A and B can be determined using the following equations: A/M+B=0.5 A/N+B=0.3. Furthermore, when ΔV _o+1 <0 in terms of the calculation formula, when the constant B has a positive value, ΔS _o becomes negative, so in this case, the dropping is stopped as described above. When the constant B is a negative value, ΔV _o+1 < 0 in the calculation formula, but in this case, B < - (S _o + ΔS _o ), and in this case it is far from the inflection point. ,
As ΔV _o+1 , a titration amount of ΔV _MAX is dropped. FIG. 3 is a flowchart showing the above titration procedure of the apparatus of this embodiment. Further, Table 1 shows the titration value and the required titration time when 100 ml of the sulfamic acid solution was repeatedly titrated five times with a 0.1N potassium hydroxide solution using the apparatus of this example.

【table】

〔Effect of the invention〕

As described above, according to the present invention, the amount of the titrant to be dropped next is calculated and determined by a microcomputer from the potential gradient caused by dropping the titrant and the increment of the potential gradient, and the potential gradient By configuring the system so that the titration is stopped and the titration end point is determined when the increment of ) Since the time required for titration can be shortened, it is possible to titrate a large number of samples in a short time. (c) It is possible to titrate not only aqueous solutions but also samples in organic solvent systems. By shortening the time, the process waiting time caused by titration is shortened, which shortens the manufacturing period and increases productivity, which is economically advantageous. (e) The titration end point can be automatically determined, reducing individual differences in end point determination. It has an excellent effect of reducing

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a titration curve using this device. FIG. 3 is a flowchart showing the titration procedure of the apparatus of this embodiment. 1...Sample feeding device, 2...Automatic brewet,
3... Rotating table, 5... Flask, 6... Electrode, 7, 9... Pipe, 10... Titrant liquid tank, 11
...Microcomputer, 13...Digital PH
Total.

Claims (1)

[Scope of Claims] 1. A titration unit that stores a sample solution and drops a titrant into the sample solution; a billet that measures the titrant to be dropped into the titration unit; In an automatic titration apparatus, the automatic titration device is equipped with a potential detection section that detects E, and a burette control means that controls the titration amount to be dropped from the burette based on the detection output of the potential detection section, and the burette control means is configured to control the titration from the burette to the burette. When the amount of titrant liquid dropped into the titration section is ΔV _o , the next amount of titrant liquid to be dropped ΔV _o+1 is A/S _o +ΔS _o +B=ΔV _o+1 (However, S _o is the above ΔV _o It is the absolute value of the change in the potential E (E _o −E _o-1 ) that occurred when dropping,
ΔS _o is the change in S _o when the above ΔV _o is dropped (S _o -S _o-1 ), A and B are constants, and n is the number of drops of the titrant. ), and the titrant volume ΔV _o+1 is ΔV _nio ≦ΔV _o+1 ≦ΔV _nax (where ΔV _nio and ΔV _nax are the predetermined minimum and maximum titrant drop amounts, respectively). .)
A means for setting ΔV _o+1 = ΔV _o when this titration liquid volume ΔV _o+1 is 0 < ΔV _o+1 < ΔV _nio , a means for setting ΔV _o+1 = ΔV _nio , and this titration. When the liquid volume ΔV _o+1 is ΔV _o+1 > ΔV _nax or ΔV _o+1 < 0, there is a means for setting ΔV _o+1 = ΔV _nax , and further, when the above ΔS _o becomes negative, dropping is stopped. An automatic titration device comprising: means for stopping the titration. 2. The automatic titration apparatus according to claim 1, wherein the initial dripping amounts ΔV ₁ and ΔV ₂ of the titrant from the titration unit are predetermined constant amounts. 3. The automatic titration apparatus according to claim 1, wherein the brewet control means stops the dripping when ΔS _o becomes negative when it is detected that ΔS _o is negative twice.