JP2017151071A - Titration control method and automatic titrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titration control method and an automatic titrator capable of maintaining titration accuracy and reducing a titration time.SOLUTION: A titration control method is configured to: add a titrant to a sample; detect change of a chemical quantity as an output signal by a sensor; for every time of addition of the titrant, set a time point when the change of the output signal becomes maximum to a moment maximum change, when the output signal at a time point of addition of the titrant is reference in a period since the titrant is added, until the output signal is stabilized; set a waiting sensitivity according to the change quantity at the moment maximum change; and simultaneously, set a waiting time according to an addition amount of the titrant when a feedback control for setting an addition amount of the titrant according to a lapsed time until the change reaches the moment maximum change, and change of the output signal, is used.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a titration control method and an automatic titration apparatus using the titration control method of the present invention.

  The principle of titration is to use a titrant that reacts with a target substance at a known ratio in order to chemically measure a specific substance in a sample. Is detected as an output signal by a sensor, and based on the detected output signal, the amount of the target substance is derived from the amount of titrant necessary to reach the end point of the titration.

  In the above titration, an automatic titration apparatus that automatically performs titration of a titrant and determination of an end point has been put into practical use. Among them, in the conventional titration control method used in-house, when a small amount of titrant is added to the sample and the change in the output signal is measured, the titrant is added, and then the sample is added. There are setting items such as waiting time and waiting sensitivity as a reference for judging whether the reaction of the titrant is completed.

  This is because when the titrant is added dropwise, the change in the output signal is measured, and when the fluctuation range of the output signal is within the set waiting sensitivity range in the set waiting time range, the sample It is determined that the reaction of the titrant is completed and the output signal is stable, and the next titration is performed or the end of the titration is determined. When the fluctuation range exceeds the waiting sensitivity range within the waiting time range, the output signal is continuously waited for stability, and within the waiting time range, the output signal fluctuation width is within the waiting sensitivity range. This is a titration control method in which it is determined that the reaction between the sample and the titrant is completed (see, for example, Patent Document 1).

  By repeating the titration control, it is possible to add the next titrant solution when the output signal becomes stable, especially when the amount of change in the output signal becomes large near the end point of titration.

  FIG. 3 shows a flowchart for explaining the operation of the conventional titration control method.

JP 58-061456

  When determining the end point of titration with the above conventional titration control method, the time required for the chemical reaction differs depending on the type of titration and the concentration of the sample or titrant, and if the titration speed is increased, the end point may be detected incorrectly. On the other hand, if the titration speed is slowed down in order to surely detect the end point, it is a factor that impairs the speed.

  Accordingly, an object of the present invention is to provide a titration control method capable of maintaining the titration accuracy in the conventional titration control method and shortening the titration time, and an automatic titration apparatus using the titration control method of the present invention. That is.

  The purpose is to add a small amount of titrant that chemically reacts with a specific substance in a sample to a certain sample, detect a change in the chemical amount of the sample as an output signal by a sensor, and detect the detected output. This is a control method in titration for measuring a change in signal. For each titration of the titrant, the output at the time of titration of the titrant is from the time when the titrant is added until the output signal becomes stable. The point at which the change in the output signal is maximum when the signal is used as the reference is the instantaneous maximum change, depending on the amount of change at the maximum instantaneous change, the elapsed time to reach the maximum instantaneous change, and the change in the output signal Fluctuation of the output signal allowed when the output signal is detected the next time the titrant is added according to the titrant's titration amount when using the feedback control to set the titrant's titration amount Width and output signal from the sensor It is achieved by an automatic titrator using a titration method of controlling titration control method and the present invention according to the present invention which is characterized in that so as to control the magnitude of the waiting time for detection.

  According to the present invention, when the amount of change in the instantaneous maximum change of the output signal when the titrant is added is large, the output signal allowed when the output signal when the titrant is added next is detected. The fluctuation range is set large, and when the change amount at the instantaneous maximum change is small, the fluctuation range is set small.

  In addition, when the elapsed time until reaching the instantaneous maximum change of the output signal when adding the titrant is large, the waiting time for detecting the output signal when adding the titrant is added next. When the elapsed time until reaching the instantaneous maximum change is small, the waiting time is set small.

  At the same time, if the titration amount of the titrant is small when the feedback control is used, the waiting time for detecting the output signal when the titrant is added is set large, and the titration liquid drops When the amount of addition is large, the waiting time is set small.

  According to the present invention, the titration is a titration control method characterized by simultaneously controlling the fluctuation range of the output signal allowed when the output signal is detected and the waiting time for the detection of the output signal.

  According to the present invention, the titration mainly corresponds to precipitation titration for measuring the amount of chloride ions, the sensor used for the titration is a silver electrode, and the change in the output signal by the sensor is the electrical of the reagent. It is a change in the amount.

  In the present invention, when the titration liquid is added to the sample by the titration control method and the automatic titration apparatus and the change in the output signal is detected by the sensor, the instantaneous maximum change in the output signal when the titrant is added is detected. By setting the waiting sensitivity according to the amount of change, and simultaneously setting the waiting time according to the elapsed time until the instantaneous maximum change is reached and the amount of titrant added, the titrant As a result, the effect of maintaining the titration accuracy of the conventional titration control method and shortening the titration time can be obtained.

The schematic block diagram of the automatic titration apparatus for implementing the titration control method of this invention. The flowchart explaining operation | movement of the titration control method of this invention. The flowchart explaining operation | movement of the conventional titration control method.

  FIG. 1 shows an outline of an automatic titration apparatus for carrying out the present invention. The automatic titration apparatus is roughly classified into an operation switch (not shown) and a calculation control apparatus 1 (hereinafter referred to as a main body 1) having a function of displaying or printing a measurement result, a burette apparatus 13 operated by control of the main body, and a sample and titration. It comprises a stirrer device 10 for stirring the liquid and performing titration.

  The main body 1 includes a control unit 2 that performs output signal stability, determination of an end point, control of a titration amount of the titrant 18 in the feedback control, a detection unit 3 that receives output signals from the indicator electrode 7 and the comparison electrode 8, It comprises a display unit 4 and a recording unit 5 for displaying and recording changes in output signals and titration results.

  The burette device 13 includes a syringe 15 for discharging and sucking the titrant 18 by moving the piston 14 up and down, and a three-way cock 16 for switching the flow path. By linking the above-described units, the titrant 18 is sucked from the titrant 17 into the syringe 15 and the titrant is discharged from the syringe 15 into the titration nozzle 11.

  In this method, the titration control method of the present invention is described as being applied to precipitation titration with sodium nitrate of sodium chloride using a silver electrode as the indicator electrode 7 as a sensor.

  FIG. 2 shows a flowchart for explaining the operation of the titration control method of the present invention. Next, a case where titration is performed according to the control method of the present invention using the automatic titration apparatus having the above-described configuration will be described with reference to FIG.

  In FIG. 1, first, a 0.1N silver nitrate aqueous solution is put as a titrant 18 in a titrant container 17, the burette device 13 is operated, and the syringe 15, the titration nozzle 11 and the tube connecting each part are filled with the titrant.

  Next, the titration container 6 is placed on the stirrer 10 and the stirring bar 9 is placed in the container. In this method, 5 mL of 0.1N sodium chloride aqueous solution is accurately weighed with a whole pipette as a sample in the container, and about 5 mL of 1N nitric acid and about 50 mL of pure water are added. The stirrer 9 disposed in the container is rotated by the stirrer device 10 to sufficiently stir the sample and pure water. The stirrer is always rotated during the titration. The indicator electrode 7 and the comparison electrode 8 are connected to the main body 1, and the electrodes are immersed in a mixed solution of the sample and pure water (hereinafter referred to as a test solution 12) in the container, and titration is performed.

  In the above state, first, the output signal of the test solution 12, that is, the potential E1 in this method, is detected by the main body 1 from the signals from the electrodes 7 and 8, and this potential is stored (step 1).

After detecting the potential E1, a predetermined amount of titrant 18 is added into the titration vessel 16 by the burette device 13 (step 2). At this time, the time at which the change in potential becomes maximum when the potential at the time of dropping is used as a reference during the determination of potential stability from the time of dropping is referred to as the instantaneous maximum change. After adding the titrant 18, the potential P1 at the moment of maximum change and the elapsed time R1 from the point of addition to the moment of maximum change are stored (steps 3 and 4). It is determined from the preset waiting sensitivity S _INT and waiting time T _INT whether the reaction between the test solution 12 and the titrant 18 is completed, and the potential E2 at the time when the reaction is completed is detected and stored (step) 5, 6, 7).

  Further, as feedback control, a differential value (potential change amount with respect to titration droplet addition amount) is obtained from the potentials E1 and E2, and the next addition amount of the titrant 18 is automatically set from the obtained differential value. (Step 8). The value to be set varies depending on the conditions set in the main body 1 in advance. However, when the differential value is large, it is determined that the end point is close, and the titration amount of the titrant 18 is set small, and the differential value is small. In this case, it is determined that a large amount of titrant is necessary until the end point, and the titration amount of the titrant 18 is set to be large.

Next, by applying the absolute value Es of the maximum potential change range (the previously stored potential E1−the potential P1 at the moment of the maximum instantaneous change) to a preset waiting sensitivity control equation, the titrant 18 is then dropped. In addition, the waiting sensitivity S _INT for determining whether the reaction between the test solution 12 and the titrant 18 is completed is automatically reset (step 9).

In parallel with the step 9, the elapsed time R1 from the time of addition to the instant maximum change time and the next addition amount of the titrant 18 set in the step 8 are set in advance waiting time control. By applying to the equation, the titration solution 18 is then added dropwise, and the waiting time T _INT when determining whether the reaction between the test solution 12 and the titration solution 18 is completed is automatically reset ( Step 10).

  At this time, the end point of the titration is determined from the differential value of the potential change (step 11), and when the end point is determined, the titration operation is terminated. When it is determined that the end point is not reached, the process returns to step 2 and the titrant 18 is again added into the titration container 6 by the predetermined amount set in step 8 (step 2).

After adding the titrant 18, the potential P2 (not shown) at the moment of maximum change and the elapsed time R2 (not shown) from the moment of addition to the moment of maximum change are stored (step 3, 4). The waiting sensitivity S _INT and the waiting time T _INT are reset based on the above steps 9 and 10, and the reaction between the test solution 12 and the titrant 18 from the reset waiting sensitivity S _INT and waiting time T _INT. Is completed, and a potential E3 (not shown) at the time when the reaction is completed is detected and stored (steps 5, 6, and 7).

  A differential value of the potential change is obtained from the potentials E2 and E3, and the next addition amount of the titrant 18 is automatically set again from the obtained differential value (step 8).

Next, by applying the absolute value Es of the maximum potential change width (the previously stored potential E2−the potential P2 at the moment of the maximum instantaneous change) to a preset waiting sensitivity control equation, the titrant 18 is then added dropwise. Then, the waiting sensitivity S _INT for determining whether the reaction between the test solution 12 and the titrant 18 is completed is automatically set again (step 9). Further, in parallel with the above step 9, the elapsed time R2 from the time of dropping to the moment of maximum change and the next amount of addition of the titrant 18 set in step 8 are set in advance waiting time control. By applying to the equation, the titration liquid 18 is then added dropwise, and the waiting time T _INT when determining whether the reaction between the test solution 12 and the titration liquid 18 is completed is automatically set again ( Step 10).

  Subsequently, as in the previous time, the end point of the titration is determined, and the titration is finished, or the process returns to step 3 and the titration operation is continued according to the above procedure (step 11). The above procedure is repeated until the end point of the titration is determined or it is determined that the titration is abnormal from the conditions set in the main body 1 and the titration is completed.

By performing the above titration control, when the absolute value Es of the maximum change width of the potential is large, the waiting sensitivity S _INT is set large, and when the absolute value Es is small, the waiting sensitivity S _{INT is set.} Set to a smaller value. By the above control, by setting an appropriate waiting sensitivity according to the fluctuation range of the potential at the time of dropping, an end point detection error that may have occurred in the conventional titration control method, and a long titration time are required. The effect of preventing the conversion is obtained.

As for the waiting time, if the elapsed time R until the moment of maximum change is large, the reaction between the sample and the titrant is expected to take a long time, and the waiting time T _INT is set large. If the elapsed time R is small, The response time is predicted to be early and the waiting time _TINT is set small. Further, when the titration amount of the titrant is small, the test solution 12 and the titrant 18 are mixed, and it takes a long time for the electrodes 7 and 8 to detect the reaction between the sample and the titrant. And predicting that the time required for the electrodes 7 and 8 to detect the reaction between the sample and the titrant is short when the amount of titrant added is large. Set a small waiting time. By the above control, an appropriate waiting time is set according to the reaction rate of the sample and the titrant. By performing the titration with a short waiting time, the titration time can be shortened, and the end point of the titration can be reliably detected.

  Table 1 shows the titration value and titration time of the titrant in this method.

Further, as Comparative Example 1, titration using a conventional titration control method was performed with reference to FIG. For comparison, titration was performed using the same automatic titration apparatus, material and conditions as in this method except that the waiting time T _INT was fixed at 3 seconds and the waiting sensitivity S _INT was fixed at 3 mV.

The titration value and titration time of the titrant in Comparative Example 1 are shown in Table 1.

  From the results shown in Table 1, the titration control method based on the present invention and Comparative Example 1 which is a conventional titration control method have substantially the same titration droplet addition values, and also show fluctuations indicating repeatability. The coefficients were all 0.1% or less, and it was confirmed that the end point was detected accurately and accurately. Further, the titration time was 1 minute 29 seconds in this method, whereas it was 2 minutes 16 seconds in Comparative Example 1, and the titration control method of the present invention compared to the conventional control method. It was confirmed that the time can be shortened.

  From the above explanation, when the titration liquid is added to the sample by the titration control method of the present invention and the change in the output signal is detected by the sensor, the titration liquid is added every time the titration liquid is added. By setting the waiting sensitivity according to the amount of change at the momentary maximum change, and at the same time setting the waiting time according to the elapsed time until reaching the momentary maximum change point and the titration amount of the titrant, it is always appropriate The titration liquid can be added dropwise under various conditions, thereby maintaining the titration accuracy of the conventional titration control method in-house and achieving the effect of shortening the titration time. The titration control method of the present invention is not limited to this method.

1. Arithmetic control device (main unit)
2, control unit 3, detection unit 4, display unit 5, recording unit 6, titration vessel 7, indicator electrode (silver electrode)
8, reference electrode 9, stirrer 10, stirrer 11, titration nozzle 12, test solution 13, burette device 14, piston 15, syringe 16, three-way cock 17, titrant container 18, titrant

Claims (7)

  A titration control method in which a titration solution that chemically reacts with a specific substance in a sample is added to a sample in small amounts, and a change in the chemical amount of the sample is measured as an output signal to a sensor. Every time the titrant is added, the change in the output signal is maximized when the output signal at the time of the titrant addition is used as a reference between the time when the titrant is added and the time when the output signal stabilizes. Using the feedback control to set the titration liquid drop amount according to the change of the instantaneous maximum change, the amount of change at the moment maximum change, the elapsed time until reaching the moment maximum change, and the change of the output signal Depending on the titration amount of the titrant, the amount of fluctuation of the output signal allowed when detecting the output signal when the titrant is added next time, and the detection of the output signal by the sensor Controlling the amount of waiting time Titration control method characterized.   If the amount of change in the instantaneous maximum change of the output signal when adding the titrant is large based on a preset waiting sensitivity control equation, the output signal when the titrant is added next 2. The titration control method according to claim 1, wherein the fluctuation range of the output signal allowed at the time of detection is set to be large, and the fluctuation range is set to be small when the change amount at the instantaneous maximum change is small.   If the elapsed time until reaching the instantaneous maximum change of the output signal when adding the titrant is large based on a preset waiting time control equation, the next time the titrant is added 2. The titration control method according to claim 1, wherein a waiting time for detecting an output signal is set to be large, and the waiting time is set to be small when an elapsed time until the instantaneous maximum change is reached is small.   Based on a preset waiting time control equation, when the change in the output signal is large, the next titration amount of the titrant is reduced, and when the change is small, the next titration amount of the titrant is increased. When the amount of titrant added is small when the feedback control is used, the waiting time for detecting the output signal when the titrant is added is set large, and the titration of the titrant is added. 2. The titration control method according to claim 1, wherein when the amount is large, the waiting time is set small.   The titration control method according to claim 1, wherein the control according to claim 2, 3, and 4 is performed simultaneously.   The titration mainly corresponds to precipitation titration for measuring the amount of chloride ions, the sensor used for the titration is a silver electrode, and the change in the output signal by the sensor is the change in the electrical amount of the reagent. It is. The titration control method according to claim 1.   The point at which the change in the output signal is maximum when the output signal at the time of addition of the titrant is used as the reference is the instantaneous maximum change, and the amount of change in the instantaneous maximum change and the time until the instantaneous maximum change is reached The output signal when the titrant is added next according to the titration amount of the titrant when the feedback control is used to set the titration amount of the titrant according to the change in time and output signal. An automatic titration apparatus configured to control the fluctuation range of the output signal allowed at the time of detection and the waiting time for detection of the output signal by the sensor.

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