JP4589172B2 - Calibration method of pH meter - Google Patents

Description

The present invention relates to a calibration method of a pH meter that performs calibration by spraying a standard solution onto an electrode held in the air.

Conventionally, an industrial pH meter in which calibration with a standard solution is completely automated has been used. In such a pH meter with an automatic calibration function, it is necessary to bring the electrode into contact with the standard solution in a state where the sample solution is not mixed, and various methods are employed.
For example, a method of spraying a standard solution onto an electrode pulled up from a sample solution and held in the air to form a drop end of the standard solution at the tip of the electrode (see Patent Document 1), drawing the electrode into a calibration space, and a sample solution space (See Patent Document 2), a method in which the lower end of the electrode holder of the electrode pulled up from the sample solution is closed with a bottom cover, and a standard solution is supplied into the electrode holder (see Patent Document 3), a sample solution A method using a movable basket (see Patent Document 4) or the like is known so that the electrode pulled up from the container can be accommodated in a basket containing a standard solution.
Japanese Examined Patent Publication No. 56-38903 Japanese Patent No. 2964342 Japanese Patent No. 3064723 Japanese Patent No. 3502503

  In the method of Patent Document 1, standard solution calibration can be performed simply by pulling up the electrode from the sample solution, and the device structure and sequence operation can be made very simple. However, in this method, since the standard solution continues to flow at about 100 mL per minute until the glass film or the like responds and stabilizes to the pH value of each standard solution, the consumption of the standard solution is large. In particular, under adverse conditions such as low ambient temperature, it takes 3 minutes or more to stabilize, and 300 mL or more of standard solution is consumed for one calibration. Therefore, the standard solution must be replenished frequently, which increases the running cost and the maintenance.

On the other hand, in the methods of Patent Documents 2 to 4, since the standard solution is used in a state where it is stored in a basket or the like, the consumption of the standard solution can be reduced. However, in order to store the standard solution, movable members such as a lid and a basket are required, and the structure and sequence of the apparatus are complicated and the cost is high.
The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for calibrating a measuring instrument that can simplify the apparatus structure and sequence operation and consumes a small amount of standard solution. And

In order to achieve the above object, the present invention employs the following configuration.
[1] A composite electrode type pH electrode in which a glass film and a liquid junction are arranged on the lower end surface is held in the air, and a standard solution is sprayed on the electrode, and an output potential from the electrode is acquired as a calibration signal. A calibration method of a pH meter , wherein after the start of spraying of the standard solution , the standard solution is sprayed within a range in which the drop end of the standard solution is formed on the lower end surface of the electrode and the drop end is maintained. A calibration method for a pH meter , characterized in that a calibration signal is acquired after an interruption period is provided , and after the interruption period ends and spraying of a standard solution is started again .

  According to the calibration method of the present invention, the apparatus structure and sequence operation can be simplified, and the consumption of the standard solution can be reduced.

The calibration method of the present invention to explain. FIG. 1 shows a detection unit 1 of a pH meter for carrying out the measurement method of the present invention. The detection unit 1 includes an electrode holder 10, a pH electrode 20 that is inserted into the electrode holder 10 with the lower end exposed, and a protective cylinder that is fixed to the lower end side of the electrode holder 10 and protects the exposed portion of the pH electrode 20. 30, an air cylinder 40 for raising and lowering the electrode holder 10, and a cleaning calibration tank 50 arranged so as to surround the protective cylinder 30 when being raised by the air cylinder 40 (in the state indicated by a broken line in FIG. 1). And. Further, a lead wire 60 led out from the top of the electrode holder 10 is provided.
The pH meter for carrying out the measuring method of the present invention takes in the signal of the pH electrode 20 via the lead wire 60 of the detection unit 1 and performs predetermined data processing, and at the same time an instruction converter that controls the entire sequence ( (Not shown).

As shown in FIG. 2, the pH electrode 20 is arranged such that a glass film 22 of a glass electrode, liquid junctions 23 and 23 of a reference electrode, and a temperature compensation element 24 are exposed on a lower end surface 21 a of an electrode body 21. It becomes the composition.
The protective cylinder 30 is provided with a notch 31 in a substantially cylindrical member, and a standard solution or the like can be sprayed onto the pH electrode 20 through the notch 31.
The cleaning calibration tank 50 is cylindrical and has no bottom cover or the like, and the pH electrode 20 together with the protective cylinder 30 can be moved in and out only by vertical movement.

As shown in FIG. 1, the cleaning calibration tank 50 is fed with a joint 81 of a liquid feeding pipe 71 that feeds the standard liquid A, a joint 82 of a liquid feeding pipe 72 that feeds the standard liquid B, and cleaning water. A joint 83 of a liquid feeding pipe 73 and a joint 84 of a liquid feeding pipe 74 for feeding a chemical solution are attached.
The joint 81 and the joint 82 are attached adjacent to each other in the horizontal direction, and their attachment positions are substantially the same height as the exposed portion of the electrode body 21 when the electrode holder 10 is raised.
Further, the joint 83 and the joint 84 are attached adjacent to each other in the horizontal direction, and their attachment positions are substantially the same height as the lower end side of the protective cylinder 30 when the electrode holder 10 is raised.

As shown in FIG. 3, a nozzle N <b> 1 penetrating substantially horizontally is formed on the peripheral surfaces of the joint 81 and the cleaning calibration tank 50, and the standard solution A is ejected from the nozzle N <b> 1 toward the peripheral surface of the electrode body 21. It has come to be.
Similarly, a nozzle N2 that penetrates the joint 82 and the peripheral surface of the cleaning calibration tank 50 substantially horizontally is formed, and the standard solution B is ejected from the nozzle N2 toward the peripheral surface of the electrode body 21. ing.

Further, a nozzle N3 that obliquely penetrates the joint 83 and the peripheral surface of the cleaning calibration tank 50 is formed, and cleaning water is jetted from the nozzle N3 toward the lower end surface 21a of the electrode body 21. .
Similarly, a nozzle N4 that obliquely penetrates the joint 84 and the peripheral surface of the cleaning calibration tank 50 is formed, and a chemical solution is ejected from the nozzle N4 toward the lower end surface 21a of the electrode body 21. .

When measuring the pH of the sample liquid W with a pH meter provided with the detection unit 1, the electrode holder 10 is lowered by the air cylinder 40. As shown by a solid line in FIG. 1, the pH electrode 20 is immersed in the sample liquid W when descending, and an output potential corresponding to the pH of the sample liquid W is generated.
On the other hand, when performing calibration or cleaning, the electrode holder 10 is raised by the air cylinder 40. Then, as indicated by a broken line in FIG. 1, the pH electrode 20 is held in the air in the cleaning calibration tank 50.

Calibration is performed by spraying each standard solution toward the peripheral surface of the electrode main body 21 while the pH electrode 20 is held in the air, and the instruction converter acquires a calibration signal obtained from the pH electrode 20 at that time. Do.
In the calibration method of the present invention, an interruption period for interrupting the spraying of the standard solution is provided between the start of the spraying of the standard solution and the acquisition of the calibration signal.

  When the standard solution is sprayed toward the peripheral surface of the electrode body 21, the standard solution that has fallen along the electrode body 21 forms a droplet end D on the lower end surface 21 a of the electrode body 21 as shown in FIG. 3. As shown in FIG. 4, the droplet end D is in a state of covering all of the glass film 22, the liquid junctions 23 and 23, and the temperature compensation element 24 of the pH electrode 20. In other words, the glass film 22, the liquid junctions 23 and 23, and the temperature compensation element 24 of the pH electrode 20 are immersed in the droplet end D. Therefore, the pH electrode 20 can generate an output potential corresponding to the pH of the standard solution despite being held in the air.

This drop end D eventually falls and disappears. However, the present inventor has found that once the continuous spraying is interrupted, the formed droplet end D is maintained for a while. That is, even if the spraying of the standard solution is interrupted after the formation of the drop end D, the state in which the glass film 22, the liquid junctions 23 and 23, and the temperature compensation element 24 are immersed in the drop end D can be continued. Meanwhile, it is possible to advance the response of the electrode without consuming the standard solution.
The time until the formation of the droplet end D depends on the flow rate of the standard solution to be sprayed, the diameter of the electrode body 21, etc., but when a standard solution of about 100 mL per minute is sprayed on a standard electrode having a diameter of about 15 mm, 30 to Spraying for 60 seconds is sufficient. Moreover, it is preferable to set it as 30 to 60 seconds as a period which interrupts spraying. The interruption period may be one time or a plurality of times.

After the interruption period (in the case of multiple interruptions, after the final interruption), the standard solution is sprayed again to obtain a calibration signal, and calibration is performed. Specifically, the indicator converter obtains the output potential obtained from the pH electrode 20, and the relationship between the output potential and the pH of the standard solution is taken. In addition, the signal of the temperature compensation element 24 is acquired at the same time, and calibration is performed by correcting the influence of temperature.
The calibration signal may be acquired after the start of re-blowing and after the elapse of a predetermined time when the output potential is expected to be sufficiently stable, but the output potential is continuously monitored to automatically determine whether it is stable. It is preferable to perform stability determination. As a result, the calibration signal is acquired at an appropriate timing, and the spraying of the standard solution can be stopped immediately. Therefore, accurate calibration can be performed while avoiding unnecessary use of the standard solution.
As a result of the stability determination, when the stable state cannot be detected even after a long time, it is preferable to stop the spraying of the standard solution and perform an alarm output or the like.

There is no limitation on the types of standard solution A and standard solution B, but it is preferable to use standard solution A and standard solution B by combining a pH 7 standard solution defined in JISZ8802 and a pH 4 or pH 9 standard solution.
The standard solution calibration is preferably performed after washing. It is also preferable to perform simple cleaning between calibration with the standard solution A and calibration with the standard solution B.

The detection unit 1 is cleaned by spraying cleaning water and chemicals toward the lower end surface 21 a of the electrode body 21. As the washing water, tap water, industrial water, or the like can be used. The chemical solution is preferably an acid solution, particularly a hydrochloric acid solution.
The order and time of spraying the cleaning water and chemical solution may be set as appropriate in consideration of the degree of electrode contamination, etc.When using the chemical solution, after pre-washing with the cleaning water, spray the chemical solution and then again It is preferable to restore the unstable state caused by the chemical solution by spraying washing water. In this case, the pre-cleaning time is set within the range of 20 to 60 seconds, the chemical solution cleaning time is within the range of 30 to 90 seconds, and the cleaning time with the cleaning water after the chemical solution cleaning is appropriately set within the range of 30 to 600 seconds. Can do.
Note that the cleaning performed between the calibration with the standard solution A and the calibration with the standard solution B is usually sufficient only by performing the cleaning with the cleaning water for a short time.

The calibration method of the present invention is not limited to two-point calibration using two types of standard solutions A and B. For example, the calibration method is performed only with a standard solution close to the pH value of the sample solution (for example, a standard solution with pH 4). Calibration is also possible.
Moreover, the measuring instrument calibrated by the calibration method of the present invention is not limited to a pH meter, and may be, for example, an ion concentration meter.

Calibration of the pH meter having the detection unit 1 of FIG. 1 was performed according to the time chart of FIG. The flow rate of each standard solution spray was 100 mL / min. Moreover, the flow rate of chemical solution spraying was 100 mL / min, and the flow rate of cleaning water spraying was about 10 L / min. The meanings of the symbols in FIG. 5 are as follows.
w1: Cleaning process by spraying cleaning water (set to 20 seconds)
w2: Cleaning process by spraying chemical solution (5% hydrochloric acid) (set to 50 seconds)
w3: Re-cleaning process by spraying cleaning water (set to 120 seconds)
s1: pH 7 standard solution spraying process (set to 60 seconds)
s2: pH7 standard solution spray interruption process (set to 60 seconds)
s3: Re-spraying process of pH7 standard solution (finished after obtaining a calibration signal after stability determination)
w4: Cleaning step with cleaning water performed between s3 and s4 (set to 10 seconds)
s4: pH 4 standard solution spraying process (set to 60 seconds)
s5: pH 4 standard solution spray interruption process (set to 60 seconds)
s6: pH 4 standard solution re-blowing process (end after obtaining calibration signal after stability determination)
w5: Washing process with washing water after s6 (set to 10 seconds)

  In addition, the stability determination in each re-spraying process was performed by continuously detecting the pH output value, and assuming that the pH output value change per second became 0.003 pH or less, and obtaining a calibration signal. . In both steps s3 and s6, the time required for stability determination was less than 30 seconds. That is, both steps s3 and s6 were completed in less than 30 seconds.

  The process shown in FIG. 5 (first cleaning / calibration process) and the subsequent second cleaning / calibration process were performed, and then the standard solution stored in the beaker was measured. The pH output chart in all these steps is shown in FIG. In addition, although the temperature of the washing water, chemical | medical solution, and each standard solution in all the processes was about 15-17 degreeC, pH output value is converted into the value of 25 degreeC by temperature compensation.

6, the same steps as those shown in FIG. 5 are denoted by the same reference numerals as those in FIG. The meanings of the other symbols are as follows.
W-1: First wash (w1-w3)
pH 7-1: First calibration with pH 7 standard solution (s1 to s3)
pH4-1: First calibration with pH4 standard solution (s4 to s6)
W-2: Second wash (same process as w5 and w2-w3)
pH 7-2: Second calibration with pH 7 standard solution (same process as pH 7-1)
pH4-2: Second calibration with pH4 standard solution (same process as pH4-1)
pH 7-3: Measurement of pH 7 standard solution in beaker pH 4-3: Measurement of pH 4 standard solution in beaker The same process as w4 was performed between pH 7-2 and pH 4-2.

As shown in FIG. 6, the output pH at the time of calibration signal acquisition in the first and second calibrations was the same, and it was confirmed that high reproducibility was obtained by the calibration method of the present invention.
Moreover, when the standard solution of the beaker was measured after the second calibration, a measured value of 6.86 pH was obtained for the pH 7 standard solution. In addition, for the pH 4 standard solution, a measured value of 3.96 pH was obtained. Therefore, it was confirmed that accurate calibration was possible by the method of the present invention.
The total spraying time of each standard solution was about one and a half minutes (s1 + s3, s4 + s6). That is, the amount of the standard solution used per calibration with each standard solution is about 150 mL, which can be reduced to about half of the conventional amount (sprayed continuously for 3 minutes at a flow rate of 100 mL / min).

It is a detection part of the pH meter for enforcing the measuring method of the present invention. It is the perspective view which expanded the principal part of the detection part of FIG. It is a partially cutaway sectional view showing the state of spraying standard liquid. It is explanatory drawing of the drop end formed by standard liquid spraying. It is a time chart which concerns on the Example of this invention. It is a pH output chart which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Detection part, 10 ... Electrode holder, 20 ... pH electrode, 21 ... Electrode main body,
22 ... Glass film, 23 ... Liquid junction, 24 ... Temperature compensation element, 30 ... Protection cylinder,
40 ... Air cylinder, 50 ... Cleaning calibration tank, 60 ... Lead wire

Claims (1)

A pH meter that holds a composite electrode pH electrode in which a glass film and a liquid junction are arranged on the lower end surface in the air, and obtains an output potential from the electrode as a calibration signal while spraying a standard solution on the electrode The calibration method of
After starting sprayed the standard solution, provided the suspend interrupt period spraying the standard solution within the drip edge from drop end of the standard solution is formed is maintained at the lower end surface of the electrode, the interruption period The calibration method of the pH meter is characterized in that a calibration signal is acquired after the completion of the process and the spraying of the standard solution is started again .

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