JP4526905B2 - Automatic titrator - Google Patents

Description

  The present invention relates to an automatic titration apparatus.

  Conventionally, in order to analyze various samples, a titration apparatus is used in which a titration reagent is dropped on a sample arranged in a titration cell to obtain an equivalence point. In such a titration apparatus, in order to detect the titration state of the test liquid, a sensor is inserted into the test liquid, and the titration state is grasped by an electric signal output from the sensor.

  In this type of titration apparatus, in order to perform various types of titration such as neutralization titration (oxidation-reduction titration), polarization titration, photometric titration, conductivity titration, etc., a composite glass electrode, photometric sensor, or Several sensors such as a conductivity sensor are prepared, and an appropriate sensor is selected and used according to the purpose of titration or the type and concentration of the test liquid (for example, see Patent Document 1).

  In addition, the titration performed in the titration apparatus is, for example, an automatic end point stop titration in which the number of equivalent points is set and the titration is stopped when a set number of equivalent points is found, or output from a sensor. Set a threshold value for the electrical signal to be detected, stop titration when the electrical signal output from the sensor reaches the threshold value, and continue titration until the titration reaches a preset titration value. The process is executed until an end condition such as total titration is satisfied.

  In recent years, an automatic titration apparatus that automatically performs titration by arbitrarily combining the various sensors described above and various titration end conditions has been developed and used.

  FIG. 7 shows an outline of a conventional automatic titration apparatus. For example, in the automatic titration apparatus 100 illustrated in FIG. 7, the burette unit 2 is connected to the main body 1. The burette unit 2 detects, for example, a titration nozzle 21, a burette drive unit 22 that supplies a titration reagent to the titration nozzle 21, a titration cell 23 in which the test solution S is stored, and a titration state of the test solution S 1. An electric signal output from the sensor 24 is amplified by an amplifier 3 provided in the main body 1 and converted into a digital signal by an A / D converter 4 before being constituted by a microcomputer, a memory, or the like. Is input to the control unit 5.

  The control unit 5 includes a titration control unit 51, a data management unit 52, and a calculation unit 53. The titration control means 51 operates the bullet drive unit 22 based on a program corresponding to a titration end condition (automatic end point stop titration, end point potential setting titration) designated in advance via the operation unit 6. Parameters for setting the titration conditions (sensor 24 type, initial titration, various set values for each titration end condition, amplifier gain, display unit (mV, pH, etc.), etc.) are input via the operation unit 6. The control unit 5, the amplifier 3, and the display means 8 are inputted.

As described above, when the output signal from the sensor 24 is digitized and the digitized value (hereinafter simply referred to as an output value) is input to the data management means 52 of the control unit 5, the data management means 52 The output value is stored in the storage unit 7 and output to the calculation unit 53. At this time, the calculation means 53 determines the next titration amount based on the output value and outputs it to the titration control means 51. The titration control means 51 operates the bullet drive unit 22 in accordance with the titration amount, and the calculation means 53 performs calculation for equivalent point detection. The data management means 52 displays the output value on the display means 8 provided in the main body 1 as necessary.
Japanese Patent Laid-Open No. 05-256843

  By the way, although it has become possible to automatically perform titration using various sensors by the automatic titration apparatus as described above, a user who does not use such an automatic titration apparatus can easily perform the measurement. Therefore, the above-mentioned optical titration (a titration for obtaining an equivalent point by coloration of an indicator mixed in a test solution) is widely used.

  A user who has used this optical titration introduces the above-mentioned automatic titration apparatus, for example, potentiometric titration (a titration for obtaining an equivalent point by a sensor that outputs a target ion concentration as a potential difference between electrodes, such as a pH sensor). When using titrations to detect other physical quantities or chemical quantities, it is possible to confirm whether or not the equivalence point of the optical titration used conventionally and the equivalence point of the potentiometric titration to be newly used are the same. Emphasized from the viewpoint of measurement traceability. Since such confirmation needs to be performed by obtaining statistical data such as measurement variations, it is preferable that confirmation can be performed continuously for a predetermined period or periodically, not just once.

  However, in order to compare data between titrations for obtaining equivalence points based on such different physical quantities or chemical quantities, the titration operations (titration of titration reagent, stirring of test solution, etc.) must be the same. It must be very laborious.

  For example, the titration data (titration curve) acquired by an automatic titration apparatus equipped with an optical titration sensor and the titration data obtained by an automatic titration apparatus equipped with a potentiometric sensor have the same output value from each sensor. Therefore, the titration amount of the titration reagent that varies depending on the output value from the sensor is not the same, and a simple comparison cannot be performed.

  Further, if the titration amount of the titration reagent is constant, it is possible to acquire titration data with the same titration amount of the titration reagent, but it takes an enormous amount of time for the confirmation. Although the time can be shortened by using two automatic titration apparatuses, it is not preferable because the cost becomes high.

  In the conventional automatic titration apparatus, the titration amount is controlled based on the output of a specific sensor, and necessary points such as an equivalence point are detected by the output of the same sensor.

  However, since a sensor that can obtain a titration curve suitable for titration control is different from a sensor that can obtain a titration curve suitable for obtaining an equivalence point, the above conventional method is used under optimum control. Thus, an optimal titration curve (a titration curve in which a necessary point such as an equivalence point is easily found) was not always obtained.

  FIG. 8 shows a titration curve in the case of potentiometric titration (pH sensor) and a titration curve in the case of photometric titration (optical sensor).

  As shown in FIG. 8 (a), in potentiometric titration, the pH changes greatly in the vicinity of the equivalence point, so that the titration amount can be controlled correspondingly, but the equivalence point itself is difficult to determine. A curve will be obtained.

  On the other hand, in photometric titration, since the change in the titration curve near the equivalent point is small, if titration control is performed based on the output of the photometric sensor, the titration does not decrease even immediately before the equivalence point. Therefore, the titration curve changes rapidly at the position exceeding the equivalence point as shown by the broken line in FIG. 8B (over titration), and high-precision measurement cannot be performed. On the other hand, when an appropriate titration curve is obtained, as shown by the solid line in FIG. 8 (b), the intersection of the straight line before coloring and the straight line after coloring may be set as the equivalent point. The equivalence point can be obtained accurately and accurately.

  The present invention has been proposed on the basis of the above-mentioned conventional circumstances, and it is possible to obtain an equivalence point using a sensor that is optimal for the test liquid, and for different physical quantities or the same test liquid. An object of the present invention is to provide an automatic titration apparatus capable of easily grasping the correspondence of titration data based on the chemical amount.

  The present invention employs the following means in order to achieve the above object. First, the present invention is premised on an automatic titration apparatus that titrates a titration reagent on a test liquid and obtains an equivalence point of the test liquid. And the automatic titration apparatus which concerns on this invention is provided with the several detection means which detects the titration state of the said test liquid by detecting a respectively different physical quantity or chemical quantity.

The automatic titration apparatus includes a calculation unit, a selection unit, a titration determination unit, and a titration control unit. That is, the calculation means outputs the output value of each detection means indicating the titration state of the test liquid to which the specified amount of titration reagent has been dropped, and the output of each detection means indicating the titration state of the test liquid before the dropping. Based on the value, the rate of change of the output value output from each detection means is calculated. The selection means is a priority when there is a change rate of the output value of each detection means calculated by the calculation means, a range of change rates preset for each detection means, and a plurality of calculated change rates belonging to the range. Based on the ranking, when at least one of the calculated rate of change of the output value belongs to the above range, a plurality of detection means determine the amount of titration reagent to be dropped into the test solution after the dropping. One detection means to be used is selected. The titration amount determination means is a titration that drops on the test liquid after the dropping that is the calculation target of the change rate based on the change rate of the output value calculated by the calculation means for the detection means selected by the selection means. Determine the amount of reagent . The titration control means determines whether or not a preset titration end condition is satisfied, and if the titration end condition is not satisfied, the titration determination amount of the titration reagent determined by the titration determination means is measured. Dripping into. Then, the equivalence point of the test solution is calculated based on the output value of another detection means different from the detection means used to determine the amount of titration reagent dropped onto the test solution at the equivalence point.

  According to the above configuration, the selection unit automatically selects the detection unit that best captures the change in the titration state of the test liquid from the plurality of detection units, and based on the rate of change in the output value of the detection unit. The next titration of the titration reagent can be determined. For this reason, it is possible to perform titration based on the output value of the detection means suitable for determination of the titration amount, and to obtain the equivalence point based on the output value of the detection means suitable for obtaining the equivalence point.

As the plurality of detection means, for example, a first detection means for detecting the pH value of the test solution and a second detection means for detecting the light transmittance of the test solution can be employed. Thereby, the titration curve indicated by the pH value of the test solution and the titration curve indicated by the color of the indicator mixed in the test solution can be obtained with a single titration for the same test solution. it can. Further, in both titration curves, the titration amounts of the titration reagent (or the elapsed time from the start of titration) are completely coincident with each other, so that the two titration curves can be easily compared .

  Further, if the automatic titration apparatus has a display means for displaying the detection values of the plurality of detection means in real time on one screen, the titration state of the test liquid detected by each detection means can be compared more. It can also be easily performed.

  According to the present invention, it is possible to automatically select an optimal sensor for detecting the titration state of the test liquid based on the output values of a plurality of detection means arranged in the same test liquid. . For this reason, it becomes possible to obtain an equivalence point for an unknown test solution in a shorter time than in the prior art.

  It is also possible to control the titration based on the output value of the detection means suitable for determining the titration amount, and to obtain the equivalence point based on the output value of the detection means suitable for obtaining the equivalence point.

  Furthermore, according to the present invention, since the titration state of the same test solution is detected based on different physical quantities or chemical quantities, it is possible to easily compare titration curves detected by different types of sensors, which has been difficult in the past. The effect that can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a configuration of an automatic titration apparatus 10 according to the present invention, and FIG. 2 is a flowchart showing processing performed by the automatic titration apparatus 10. In FIG. 1, the same reference numerals are given to parts that operate in the same manner as the conventional automatic titration apparatus 100.

  As shown in FIG. 1, in an automatic titration apparatus 10 according to the present invention, a bullet unit 2 is connected to a main body 1 in the same manner as a conventional automatic titration apparatus 100. The burette unit 2 includes a titration nozzle 21, a buret drive unit 22, a titration cell 23, and a plurality of detection means 24 (24 a and 24 b) that detect the titration state of the test liquid S in the titration cell 23.

  The detection means 24 may be any sensor that detects the titration state of the test solution S based on different physical quantities or chemical quantities, and the type and number thereof are not limited. For example, a composite glass electrode that outputs the concentration of specific ions (for example, hydrogen ion concentration) in the test solution S as a potential difference between the electrodes, and the coloration by the indicator mixed in the test solution indicates the light transmittance of the test solution. Sensor for detecting the change in the concentration, conductivity sensor for detecting the ion concentration in the test liquid as conductivity, ORP (Oxidation Reduction Potential) that outputs the redox potential of the test liquid as a potential difference between the electrodes Among sensors conventionally used such as sensors, two or more types of sensors can be employed depending on the purpose. One of the plurality of detection means 24 is preferably a pH sensor composed of a composite glass electrode for confirming and acquiring the pH value at the equivalence point. In FIG. 1, the structure provided with the pH sensor 24a which consists of a composite glass electrode, and the optical sensor 24b as the detection means 24 is shown.

  Further, the main body 1 is provided with a plurality of amplifiers 3 (3a, 3b) for amplifying the electric signals output from the detection means 24a, 24b according to the sensor type. The output of the amplifier 3 is converted into a digital signal by the A / D converter 4 and then input to the control unit 5.

  The control unit 5 of the automatic titration apparatus 10 according to the present invention includes a calculation unit 74 that calculates the change rate of each output value, and one detection unit among a plurality of detection units 24 based on the change rate of each output value. It differs from the control part 5 of the said conventional automatic titration apparatus by the point provided with the selection means 55 which selects 24. FIG.

  In the above configuration, the user first designates from the operation unit 6 which type of sensor is used as the detection means 24 and under which titration end condition, and the initial titration and titration end. Enter parameters that define the conditions.

  In the example shown in FIG. 1, it is assumed that a composite glass electrode and an optical sensor are designated as the detection means 24, and the total amount titration is selected as the titration end condition (S1 in FIG. 2). It is assumed that the test liquid S is mixed with an indicator that colors at the equivalent point.

  After the input of various parameters is completed, titration is started when the user presses a titration start button provided on the main body 1. At this time, the initial output signal of each detection means 24 is acquired, and the titration control means 51 starts titration using the initial titration as the titration (FIG. 2, S2 → S3).

  When the discharge of the titration reagent for titration is completed, the output signal of each detection means 24 is input to the data management means 52 via the amplifier 3 and the A / D converter. At this time, the data management means 52 stores the output value of the amplifier 3 corresponding to each detection means 24 in the storage means 7 together with the titration amount of the titration reagent obtained from the titration control means 51 and the identification code for identifying the type of the detection means 24. The output value is displayed on the display means 8 (S4 in FIG. 2).

  The data management unit 52 inputs the same data as the data stored in the storage unit 7 to the calculation unit 54 in parallel (or before and after) with the storage of the output value. The calculation means 54 is configured to hold the output value immediately before each detection means 24, the latest output value immediately before that, the latest output value of each input detection means 24, and the titration amount of the titration reagent. Based on the above, the change rate of each output value is calculated (S5 in FIG. 2). Needless to say, when the initial output value of each detecting means 24 is acquired, the above calculation is not executed. In the present embodiment, the calculation result of the calculation means 54 is also stored in the storage means 7 via the data management means 52.

  When the calculation of the change rate of each output value is completed, the calculation means 54 inputs the calculation result to the selection means 55. The selection means 55 is preset with a change rate threshold value for each type of the detection means 24, and the value of each change rate input from the calculation means 54 after the gain of the amplifier 3 is taken into consideration for the threshold value. Is evaluated. For example, for a detecting unit 24 in which the absolute value of the rate of change increases near the equivalent point, such as a pH sensor or an optical sensor, it is determined whether the absolute value of the rate of change exceeds the threshold value. Further, for the detection means 24 in which the absolute value of the change rate decreases near the equivalent point, such as a conductivity sensor, it is determined whether the absolute value of the change rate is smaller than the threshold value (S6 in FIG. 2).

  The selection means 55 selects the said detection means 24, when the detection means 24 which satisfy | fills the above-mentioned conditions exists (FIG. 2 S6 Yes-> S7). At this time, when there are a plurality of detection means 24 that satisfy the above-described conditions, for example, the detection means 24 is selected according to the priority order, or a plurality of thresholds having different levels are set for each detection means 24, and the higher One detection means 24 is selected by selecting the detection means 24 that satisfies the level condition.

  Next, the selection unit 55 inputs the type and change rate of the selected detection unit 24 to the titer determination unit 56. In the titer determination unit 56, a titer corresponding to the rate of change is set for each type of the detection unit 24, and the next titer is determined according to the rate of change input from the selection unit 55 (FIG. 2 S8). For example, for the detection means 24 in which the absolute value of the rate of change increases in the vicinity of the equivalence point, such as a pH sensor or an optical sensor, the titer is set smaller as the absolute value of the rate of change is larger. In addition, for the detection means 24 in which the absolute value of the rate of change decreases near the equivalent point, the titer is set smaller as the absolute value of the rate of change is smaller.

  When the next titration is determined by the titration determination means 56, the titration control means 51 confirms the titration end condition, and performs the next titration based on the titration determined only when the titration end condition is not satisfied. Perform (No in FIG. 2 S9).

  On the other hand, in the evaluation of the change rate, when there is no detection unit 24 that satisfies the above-described conditions, the selection unit 55 notifies the titration determination unit 56 to that effect. The titer determining unit 56 increases the titer by a predetermined amount set in advance (or without changing the titer), and instructs the titration controller 51 to perform the next titration (FIG. 2, S6 No → S8).

  Then, the above-described processing is repeated until the titration end condition is satisfied (FIG. 2, S9 Yes).

  Here, the situation in which the selection means 55 selects the detection means 24 will be described using specific examples. The curves shown in FIG. 3 are titration curves obtained when a strong acid and a strong base are used for the test solution S and the titration reagent in the configuration shown in FIG. In FIG. 3, a curve A indicated by a solid line is a titration curve (left axis) acquired by the pH sensor 24a, and a curve B indicated by a broken line is a titration curve (right axis) acquired by the optical sensor 24b.

  As shown in FIG. 3, the titration curve A acquired by the pH sensor 24a gradually increases as it approaches the equivalent point, and rapidly increases near the equivalent point. On the other hand, the titration curve B acquired by the optical sensor 24b hardly changes until it approaches the equivalent point, and rapidly decreases near the equivalent point.

  In this case, the selection means 55 of the automatic titration apparatus of the present invention selects the pH sensor 24a when the absolute value of the rate of change of the pH sensor 24a exceeds a preset threshold value, and outputs the output value of the pH sensor 24a. Titration is performed based on the rate of change. For this reason, the titration curve B by the optical sensor 24b can be easily acquired in a shorter time than in the past.

  That is, since the titration determined based on the output value of the pH sensor 24a is controlled to be smaller as the equivalence point is approached, the titration obtained based on the output value of the optical sensor 24b under the control of the titration amount. Of course, the curve B is also an appropriate curve. Therefore, in the titration curve A, instead of obtaining the equivalent point from the point where the rate of change is maximum, in the titration curve B, by obtaining the equivalent point from the intersection of the straight line before coloring and the straight line after coloring, The equivalence point can be obtained relatively easily. That is, according to the present invention, the titration amount is controlled based on the output value of the detection means suitable for titration control, and the equivalence point is determined based on the detection means suitable for finding a point such as the equivalence point. It can be sought.

  It should be noted that after exceeding the equivalence point, the selection means 55 may perform a titration based on the rate of change of the output value of the optical sensor 24b, but this is data after the equivalence point is detected. There is no problem.

  Moreover, the curve shown in FIG. 4 is a titration curve acquired when a weak acid and a weak base are used for the test solution S and the titration reagent, respectively. In FIG. 4, a curve C indicated by a solid line is a titration curve (left axis) obtained by a conductivity sensor provided in place of the optical sensor of FIG. 1 or in addition to the configuration of FIG. A curve D shown is a titration curve (right axis) acquired by the pH sensor 24a.

  In this case, the titration curve C acquired by the conductivity sensor decreases as it approaches the equivalence point, and becomes a minimum point at the equivalence point. On the other hand, the titration curve D acquired by the pH sensor 24a increases substantially constant until it approaches the equivalent point, and the rate of change slightly increases near the equivalent point.

  Also in this case, in the automatic titration apparatus 10 of the present invention, the selection means 55 selects the conductivity sensor when the absolute value of the change rate of the conductivity sensor falls below a preset threshold value, and the conductivity sensor Titration is performed based on the rate of change of the output value. That is, an optimal sensor for automatically detecting a change in titration state near the equivalent point is automatically selected.

  Furthermore, the curves shown in FIG. 5 are titration curves obtained when a weak base and a weak acid are used for the test solution S and the titration reagent, respectively. In FIG. 5, a curve E indicated by a solid line is a titration curve (left axis) obtained by an ORP sensor provided in place of the optical sensor of FIG. 1 or in addition to the configuration of FIG. F is a titration curve (right axis) acquired by the pH sensor 24a.

  As shown in FIG. 5, the titration curve E acquired by the ORP sensor gradually decreases as it approaches the equivalent point, and rapidly decreases near the equivalent point. On the other hand, the titration curve F acquired by the pH sensor 24a decreases almost constant until it approaches the equivalent point, and the absolute value of the rate of change slightly increases near the equivalent point.

  Also in this case, in the automatic titration apparatus 10 of the present invention, the selection means 55 selects the ORP sensor when the absolute value of the change rate of the ORP sensor exceeds a preset threshold value, and the output value of the ORP sensor Titration is performed based on the rate of change. That is, an optimal sensor for automatically detecting a change in titration state near the equivalent point is automatically selected.

  As described above, according to the automatic titration apparatus 10 of the present invention, it is possible to select an optimal detection means for detecting a change in titration state from a plurality of detection means 24 that detect different physical quantities or chemical quantities. it can. For this reason, it becomes possible to obtain an equivalence point in a short time even for a test solution whose equivalence point is unknown.

  By the way, the automatic titration apparatus of the present invention includes the display means 8 as described above, and displays the output values of the plurality of detection means 24 for detecting different physical quantities or chemical quantities on the display screen in real time on one screen. I have to. FIG. 6 is an example of a screen display in the automatic titration apparatus that is executing the titration of the example shown in FIG.

  As shown in FIG. 6, since the data obtained by detecting the titration state of the same test solution based on different physical quantities or chemical quantities is displayed, a comparison of titration curves detected by different sensors, which has been difficult in the past, can be seen at a glance. Can be done.

  In addition, from the viewpoint of comparing the titration curves acquired based on different physical quantities or chemical quantities, the selection means does not depend on the rate of change of the output value from each detection means, but is a detection means designated by the user in advance. You may make it the structure which selects.

  Moreover, the structure of the automatic titration apparatus described above shows a specific example, and does not limit the technical scope of the present invention. It is possible to design arbitrarily within the range where the effects of the present invention are exhibited.

  In the above description, the calculation for obtaining the equivalence point is not particularly mentioned, but the calculation may be performed by a known method based on the titration data acquired as described above.

  The present invention can complete titration in a short time compared to the prior art, and can easily and in real time compare the titration data of the same test liquid detected by different types of sensors. As very useful.

The schematic of the automatic titration apparatus of this invention. The flow chart of the titration of the present invention. The figure which shows an example of the titration of this invention. The figure which shows an example of the titration of this invention. The figure which shows an example of the titration of this invention. The figure which shows the example of a screen display of this invention. Schematic of the conventional automatic titration apparatus. The figure which shows an example of the conventional titration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main body 2 Bullet unit 5 Control part 10,100 Automatic titration apparatus 21 Titration nozzle 22 Bullet drive part 23 Titration cell 24 (24a, 24b) Detection means (sensor)
51 Titration control means 52 Data management means 53 Calculation means 54 Calculation means 55 Selection means 56 Titration amount determination means S Test liquid

Claims (3)

In the automatic titration device that drops the titration reagent on the test liquid and calculates the equivalence point of the test liquid,
A plurality of detection means arranged in the test liquid, each detecting a titration state of the test liquid by detecting different physical quantities or chemical quantities;
The output value of each detection means indicating the titration state of the test liquid to which the specified amount of the titration reagent has been dropped, and the output value of each detection means indicating the titration state of the test liquid before the dropping Based on the calculation means, the calculation means for calculating the rate of change of the output value of each detection means,
Priority when the rate of change of the output value of each detection means calculated by the calculation means, a range of change rates preset for each detection means, and a plurality of the calculated change rates belonging to the range are present Based on the above, when at least one of the calculated change rates of the output value belongs to the range, the amount of the titration reagent to be dropped into the test solution after the dropping from the plurality of detection means. Selection means for selecting one detection means to be used for determination;
Based on the change rate of the output value calculated by the calculation means for the detection means selected by the selection means , the amount of the titration reagent to be dropped into the test solution after the drop that is the calculation target of the change rate A titration determination means for determining
It is determined whether or not a preset titration end condition is satisfied, and when the titration end condition is not satisfied, an amount of the titration reagent determined by the titration determination unit is dropped onto the test solution. Titration control means,
Equipped with a,
The equivalence point of the test liquid is calculated based on the output value of another detection means different from the detection means used for determining the amount of the titration reagent dropped into the test liquid at the equivalence point. Automatic titrator. The automatic titration apparatus according to claim 1, wherein the plurality of detection means are a first detection means for detecting a pH value of the test liquid and a second detection means for detecting a light transmittance of the test liquid. The automatic titration apparatus according to claim 1 or 2, further comprising display means for displaying the output values of the plurality of detection means on a single screen in real time.

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