JPH08313481A - Free chlorine measuring device - Google Patents

Abstract

PURPOSE: To provide a redox current measuring rotary electrode or vibration electrode type free chlorine measuring device capable of accurately measuring the concn. of free chlorine by excluding the effect of bound chlorine without performing complicated measuring work. CONSTITUTION: In a rotary electrode or vibration electrode type free chlorine measuring device, a detection electrode 12 is a platinum electrode and the opposed electrode 16 is a silver/silver chloride electrode and a measuring current at a time when free chlorine with a concn. of 2mg/l is measured by applying measuring voltage of 0.2 volt across both electrodes 12, 16 is 2μA or less, pref., 0.2-1.2μA. In this case, measuring voltage of 0-0.3 volt, pref., 0.15-0.3 volt is applied across both electrodes 12, 16 to perform measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a redox current measuring type free chlorine measuring device (rotating electrode type or vibration type) in which a sample liquid is brought into contact with a rotating or vibrating detection electrode to measure the concentration of free chlorine in the sample liquid. Electrode-type free chlorine measuring device).

[0002]

2. Description of the Related Art Residual chlorine includes free chlorine (free effective residual chlorine) and bound chlorine (bond effective residual chlorine). Free chlorine is chlorine that is not bound to nitrogen, specifically hypochlorous acid (HClO).
There are free chlorine acting as hypochlorite ion (ClO ⁻ ) and organic free chlorine. Bound chlorine is chlorine bound to nitrogen. The measurement of free chlorine in a sample solution requires elimination of interference by bound chlorine.

Conventionally, as a redox current measuring type free chlorine measuring device, a rotating electrode type free chlorine measuring device using a gold electrode as a detecting electrode and a silver / silver chloride electrode as a counter electrode has been widely used. The device had the drawback of being greatly affected by bound chlorine. That is, in a conventional rotary electrode type free chlorine measuring apparatus using a gold electrode as a detection electrode, a negative voltage (usually 0 to -0.2 volt) showing sensitivity to both free chlorine and combined chlorine is used as a measurement voltage. It was applied, and therefore the effect of combined chlorine was generated. However, if the measurement voltage was made positive in order to eliminate the influence of bound chlorine, the sensitivity to free chlorine was lost.

On the other hand, in order to reduce the influence of combined chlorine in the rotary electrode type free chlorine measuring device, the actual open flat surface 5
The invention described in Japanese Patent Publication No. 43064 has been proposed. In the free chlorine measuring apparatus described in claim 1 of the above-mentioned publication, the linearity of the calibration curve obtained when gold is used by configuring the material of the detection electrode with an alloy whose main components are gold and platinum. While maintaining it, the effect of combined chlorine is reduced to some extent. Further, in the free chlorine measuring apparatus according to the second aspect, the material of the detection electrode is made of platinum in order to further reduce the influence of the combined chlorine, but there is a problem that the linearity of the calibration curve cannot be obtained. This is avoided by providing a means for correcting the linearity. That is, claim 2
The device described in (1) has a problem that occurs when a platinum electrode is used as a detection electrode and the measurement voltage is set to a constant value (for example, 0.2 V).
Trying to solve it using the correction means (

See).

However, the free chlorine measuring apparatus described in claim 1 of Japanese Utility Model Laid-Open No. 5-43064 reduces the effect of bound chlorine to some extent as compared with the case where the material of the detection electrode is gold. However, the effect was not sufficient (see FIG. 5). The free chlorine measuring apparatus according to claim 2 further reduces the influence of bound chlorine, but the plateau region cannot be obtained (see Fig. 6) and the calibration curve does not become a straight line. Not only was the means for linearization complicated, but the measurement accuracy was inferior to that of alloys (

See).

The present invention has been made in view of the above circumstances, and an oxidation-reduction current measurement formula capable of correctly measuring the concentration of free chlorine by eliminating the influence of combined chlorine without performing a complicated measurement work. An object of the present invention is to provide a rotating electrode type or vibrating electrode type free chlorine measuring device.

[0007]

In order to achieve the above-mentioned object, the present invention comprises a redox current measuring type free chlorine measuring device having a detection electrode and a counter electrode for performing measurement while rotating or vibrating the detection electrode. The detection electrode is a platinum electrode, the counter electrode is a silver / silver chloride electrode, and a concentration of 2 mg is obtained by applying a measurement voltage of 0.2 V between the detection electrode and the counter electrode.
/ Μl of free chlorine is measured current is 2μ
Provided is a free chlorine measuring device characterized by being A or less.

The free chlorine measuring apparatus of the present invention can be constituted by a known rotating electrode type or oscillating electrode type free chlorine measuring apparatus in which the detection electrode is a platinum electrode and the counter electrode is a silver / silver chloride electrode. .

In the free chlorine measuring apparatus of the present invention, a concentration of 2 V is applied by applying a measuring voltage of 0.2 V between the detection electrode and the counter electrode.
The measurement current (electrode output) when measuring mg / l of free chlorine is 2 μA or less, preferably 0.2 to 1.
2 μA. When the measured current exceeds 2 μA, a good polarogram cannot be obtained and the iR drop (described later) becomes large.

The measurement current of the free chlorine measuring apparatus of the present invention becomes smaller as the surface area of the detection electrode becomes smaller, and becomes smaller as the rotation speed or vibration speed (linear velocity) of the detection electrode becomes smaller. Therefore, as a means for suppressing the measurement current when measuring 2 mg / liter of free chlorine at a measurement voltage of 0.2 V to 2 μA or less, the measurement current can be set by setting one or both of the surface area of the detection electrode and the linear velocity of the detection electrode. It is possible to employ means for suppressing the value of the above value within the above range.

The free chlorine measuring apparatus of the present invention measures the free chlorine by applying a measurement voltage of 0 to 0.3 V, particularly 0.15 to 0.3 V between the detection electrode and the counter electrode. Is desirable. If the measured voltage is on the negative side, the effect of bound chlorine may be large, and if it exceeds 0.3 V, the electrode output may be a negative value, which is not preferable for measurement.

[0012]

In the free chlorine measuring apparatus of the present invention, the sample current is brought into contact with the rotating or vibrating detecting electrode to obtain a measuring current (diffusion current) corresponding to the free chlorine concentration corresponding to the potential of the detecting electrode. Specifically, a potential that gives a substantially constant measurement current even if the potential of the detection electrode fluctuates slightly is applied as the measurement voltage, and the free chlorine concentration is determined from the measurement current at that time. Is.

Here, in the free chlorine measuring apparatus of the present invention,
A platinum electrode was used as the detection electrode, a silver / silver chloride electrode was used as the counter electrode, and a measurement voltage of 0.2 V was applied between the detection electrode and the counter electrode to measure the measurement current when the concentration of free chlorine of 2 mg / liter was measured. Since it is set to 2 μA or less, a polarogram excellent in linearity can be obtained in a region where there is no influence of bound chlorine, as shown in an experimental example described later.

Further, in the free chlorine measuring apparatus of the present invention, since the detected measurement current is set to a small value as described above, a sample liquid having a low conductivity such as pure water or a high concentration of free chlorine is used. Even in the case of the sample liquid in which the value of the included measurement current is large, it is possible to suppress the voltage drop (iR drop) due to the product of the liquid resistance and the measurement current and perform accurate measurement.

[0015]

EXAMPLES Next, the present invention will be illustrated concretely by examples, but the present invention is not limited to the following examples. FIG. 1 shows an embodiment of the free chlorine measuring apparatus of the present invention. In this apparatus, 2 is a flow cell, 4 is a sample solution inlet, 6 is a sample solution outlet, 8 is a sample solution introduced into the flow cell 2, 10 is a cylindrical detection electrode support whose lower part is immersed in the sample solution 8, 1
Reference numeral 2 is a circular detection electrode (platinum electrode) attached to the outer peripheral surface of the detection electrode support, 14 is a cylindrical counter electrode support whose lower part is immersed in the sample solution 8, and 16 is an outer peripheral surface of the counter electrode support 14. The attached counter electrode (silver / silver chloride electrode), 18 is a detection electrode rotating motor, 20 is a voltage applying circuit, and 22 is an ammeter.
The inside of the flow cell 2 is divided into a detection electrode chamber 26 and a counter electrode chamber 28 by a partition 24, and beads for cleaning the detection electrode (not shown) are put in the sample solution in the detection chamber 26.

When the free chlorine concentration in the sample solution is measured using the free chlorine measuring apparatus of this embodiment, the detection electrode support 10 is rotated by the operation of the motor 18, and the detection electrode 12 is thereby rotated. Then, the measuring voltage is applied between the detection electrode 12 and the counter electrode 16 by the applied voltage circuit 20, and the measurement current i flowing between the detection electrode 12 and the counter electrode 16 at this time is detected by the ammeter 22.

In this case, the apparatus of the present embodiment uses the detection electrode 12
When a measurement voltage of 0.2 V is applied between the counter electrode 16 and the counter electrode 16 to measure free chlorine having a concentration of 2 mg / liter, the measurement current i is set to be 2 μA or less. In addition, between the detection electrode 12 and the counter electrode 16, 0 to 0.3
Measurement is performed by applying a measurement voltage in the range of volts.

In this embodiment, the detection electrode is a rotating platinum electrode, the counter electrode is a silver / silver chloride electrode, and the measurement current when 2 mg / liter of free chlorine is measured at a measurement voltage of 0.2 V is 2 μA or less. As a result, the effect of bound chlorine can be eliminated, and a good polarogram excellent in linearity can be obtained.

Experimental Example In the free chlorine measuring apparatus shown in FIG. 1, various sample liquids were measured by using a circular detection electrode and changing the surface area of the detection electrode variously. In this case, the outer diameter of the detection electrode support is constant (1
2 mm) and the rotation speed was also constant (600 rpm). The voltage sweep rate ΔV was set to 100 mV / min. The results are shown in FIGS.

FIG. 2 is a polarogram showing the relationship between the measurement voltage and the measurement current when the measurement is carried out using a detection electrode having a diameter of 4 mm, and FIG. 3 is a calibration curve of free chlorine at that time, and FIG.
Is a polarogram showing the relationship between the measured voltage and the measured current when the measurement is performed using a detection electrode having a diameter of 3 mm, and FIG.
Is a calibration curve of free chlorine at that time, FIG. 6 is a polarogram showing the relationship between the measurement voltage and the measurement current when measurement is performed using a detection electrode having a diameter of 2 mm, and FIG. The calibration curve, FIG. 8 is a polarogram showing the relationship between the measurement voltage and the measurement current when the measurement is performed using the detection electrode having a diameter of 1 mm, and FIG. 9 is the calibration curve of free chlorine at that time.

In the polarograms of FIGS. 2, 4, 6 and 8, a is a sample liquid having a free chlorine concentration of zero and a combined chlorine concentration of zero, and b is a free chlorine concentration of zero and a combined chlorine concentration of 2 mg /
Liter of sample liquid, c is zero bound chlorine concentration, free chlorine concentration is 1 mg / liter sample liquid, d is zero bound chlorine concentration,
It is a result of a sample liquid having a free chlorine concentration of 2 mg / liter.
In the calibration curves of FIGS. 3, 5, 7, and 9, e is a measurement voltage of 0 V, f is a measurement voltage of 0.1 V, g is a measurement voltage of 0.2 V, h is a measurement voltage of 0.3 V, and i is Is a calibration curve when the measurement voltage is 0.4 V, and the points indicated by triangles are the indicated values of the sample liquid having a free chlorine concentration of zero and a combined chlorine concentration of 2 mg / liter.

As a result, 2 mg at a measuring voltage of 0.2 V
The measurement current when measuring 1 / liter of free chlorine is about 2 μA when the detection electrode has a diameter of 4 mm, about 1.13 μA when the diameter of the detection electrode is 3 mm, and about 0.46 μA when the diameter of 2 mm is 1 mm. Is about 0.21 μA
Met. Therefore, the detection electrode is a platinum electrode and the counter electrode is silver /
2 mg / with silver chloride electrode and measuring voltage 0.2 V
By setting the measurement current when measuring liters of free chlorine to 2 μA or less, preferably 0.2 to 1.2 μA,
It was confirmed that a polarogram with excellent linearity could be obtained in the region free from the influence of bound chlorine.

Further, as can be seen from the figure, the influence of the combined chlorine is smaller as the measurement voltage is set to the positive side. However, it is not preferable that the measured current has a negative value. In this respect,
Measuring voltage 0-0.3V, preferably 0.15-
It was confirmed that by setting the voltage to 0.3 V, the influence of bound chlorine was small, and measurement could be performed within a range in which the measurement current did not have a negative value.

[0024]

According to the free chlorine measuring apparatus of the present invention, the interference of bound chlorine can be eliminated by a simple measuring mechanism, and the free chlorine concentration in the sample solution can be accurately measured.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a free chlorine measuring device according to the present invention.

FIG. 2 is a polarogram showing a relationship between a measurement voltage and a measurement current when measurement is performed using a detection electrode having a diameter of 4 mm.

FIG. 3 is a calibration curve of free chlorine at that time.

FIG. 4 is a polarogram showing a relationship between a measurement voltage and a measurement current when measurement is performed using a detection electrode having a diameter of 3 mm.

FIG. 5 is a calibration curve of free chlorine at that time.

FIG. 6 is a polarogram showing the relationship between the measurement voltage and the measurement current when measurement is performed using a detection electrode having a diameter of 2 mm.

FIG. 7 is a calibration curve of free chlorine at that time.

FIG. 8 is a polarogram showing the relationship between the measured voltage and the measured current when measurement is performed using a detection electrode having a diameter of 1 mm.

FIG. 9 is a calibration curve of free chlorine at that time.

[Explanation of symbols]

 2 Flow cell 8 Sample liquid 10 Detection electrode support 12 Circular detection electrode (platinum electrode) 14 Counter electrode support 16 Counter electrode (silver / silver chloride electrode) 18 Detection electrode rotation motor 20 Applied voltage circuit 22 Ammeter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naomi Narasaki 4-13-14 Kitamachi Kichijoji Kitamachi, Musashino City, Tokyo Electrochemical Instruments Co., Ltd.

Claims (2)

[Claims] 1. An oxidation-reduction current measurement type free chlorine measuring apparatus comprising a detection electrode and a counter electrode, which performs measurement while rotating or vibrating the detection electrode, wherein the detection electrode is a platinum electrode,
The counter electrode is a silver / silver chloride electrode, and a measuring voltage of 0.2 V is applied between the detection electrode and the counter electrode to obtain a concentration of 2 m.
The measurement current when measuring g / l of free chlorine is 2
A free chlorine measuring device characterized by having a value of μA or less. 2. The free chlorine measuring device according to claim 1, wherein the measurement is performed by applying a measurement voltage of 0 to 0.3 V between the detection electrode and the counter electrode.