JPH0617895B2 - Coulometric analysis method - Google Patents

Description

The present invention quantifies the concentration of ions to be measured contained in test water in an electrolysis cell by measuring the current flowing between a plurality of electrodes provided in the electrolysis cell. The present invention relates to a coulometric analysis method.

Such a coulometric analysis method is called amperometry or coulometry, and if the electrode surface on which the electrode reaction takes place is contaminated by deposits or oxide film, it becomes impossible to perform accurate quantification. There is.

In one prior art for solving such a problem, the electrode surface is cleaned after the measurement operation is completed, thereby removing the deposits and oxide film from the electrode surface, but the work is troublesome. Therefore, a long time is required for measurement.

An object of the present invention is to provide a coulometric analysis method capable of omitting the work described above and performing accurate quantification.

Further, in such a prior art, for example, when measuring the cyan ion concentration, the sulfide ion is adversely affected, and when measuring the bromine ion concentration, the iodine ion is adversely affected, and an accurate analysis cannot be performed.

Another object of the present invention is to provide a coulometric analysis method capable of performing accurate coulometric analysis without being adversely affected by interfering components.

The present invention relates to a pair of electrodes 3 and 4 provided in the electrolysis cell 1.
In the coulometric analysis method, in which the concentration of ions to be measured contained in the sample water in the electrolysis cell 1 is quantified by measuring the current flowing therethrough, the electrodes 3 and 4 are cylindrical working electrodes 3 And a cylindrical counter electrode 4 coaxially arranged around the working electrode 3, and an insulating member 15 is provided in the gap between the electrodes 3 and 4,
In the flat surface 11 on which the electrode reaction in 4 is performed,
A rotor 13 formed by covering the entire outer peripheral surface of the cylindrical permanent magnet and both end surfaces in the axial direction with a wear-resistant material is provided, and the rotor 13 is provided with a magnetic stirrer 14 to prevent the working electrode 3 from moving. Between the reference electrode 5 and the working electrode 3, the DC component V1 predetermined in the limiting current region of the pre-discharged substance and the pulse between which the amplitude V2 increases with the passage of time are slidably rotated around the axis line. It is a coulometric analysis method characterized in that a rectangular wave voltage in which pulse rest periods are alternately repeated is applied.

An embodiment of the present invention will be described below with reference to the drawings. First
The figure is a cross-sectional view of an embodiment of an analytical device constructed in accordance with the present invention. This analyzer is used, for example, to measure the concentration of cyan ions contained in test water. The electrolysis cell 1 in this analyzer includes a cell body 2, a working electrode 3, a counter electrode 4, and a reference electrode 5. Cell body 2
Is composed of a bottomed cylindrical bottom portion 6 and an upper portion 8 including an inverted-pyramidal portion 7 which is formed in a tapered shape upward from the bottom portion 6 (upper side in FIG. 1). The bottom part 6 and the upper part 8 are hermetically integrated with each other, whereby an electrolytic chamber 9 is formed in the cell body 2. Cell body 2 configured in this way
Are formed of synthetic resin such as vinyl chloride resin.

The working electrode 3 is made of silver and is formed in a columnar shape. The counter electrode 4 is made of, for example, stainless steel and has a cylindrical shape. The working electrode 3 is loosely inserted into the counter electrode 4, and an insulating member 15 made of an electrically insulating substance such as alumina or a dispersed synthetic resin is provided in the gap between the working electrode 3 and the counter electrode 4 and the outer periphery of the counter electrode 4. . Thus, the insulating member 15
The working electrode 3 and the counter electrode 4 which are integrated via the airtightly penetrate the bottom plate 10 of the bottom portion 6 of the cell body 2 and are fixed to the cell body 2. Working electrode 3 facing the electrolysis chamber 9,
The end faces 11 at the upper ends of the counter electrode 4 and the insulating member 15 are formed flush with each other.

The reference electrode 5 has a tip 12 facing the electrolysis chamber 9 and a cell body 2
The upper part 8 is penetrated in an airtight manner, whereby the reference electrode 5 is fixed to the cell body 2. As the reference electrode 5, for example, a silver-silver chloride electrode is used.

Referring to FIG. 2 together, a cylindrical rotor 13 is mounted on the end surface 11. The rotor 13 is formed by covering the entire outer peripheral surface of the cylindrical permanent magnet and both end surfaces in the axial direction with a wear resistant material such as silicon carbide SiC. Below the bottom portion 6 of the electrolysis cell 1, a rotor 13 is provided.
The magnetic stirrer 14 is arranged in correspondence with. This magnetic stirrer 14 is provided with a plurality of permanent magnets or electromagnets arranged at equal intervals around the axis of the working electrode 3, and these permanent magnets or electromagnets are driven to rotate around the axis to rotate. The child 13 is rotatable around the axis. The length d1 of the rotor 13 is selected to be larger than the outer diameter d2 of the counter electrode 4.

In the analyzer configured in this way, the test water is introduced into the electrolysis chamber 9 through the flow path 20 formed in the bottom portion 6 of the cell body 2. In the electrolytic chamber 9, the cyan ion CN ⁻ contained in the test water causes an electrode reaction as shown in the first formula on the end surface 11 of the working electrode 3, that is, the electrode surface.

Ag + 2CN ⁻ → Ag (CN) ₂ ⁻ + e (1) The current flowing between the working electrode 3 and the counter electrode 4 based on the electron e emitted by the electrode reaction represented by the first formula is the working electrode 3, It is measured by a current measuring means 21 provided in association with the counter electrode 4 and the reference electrode 5. As a result, the concentration of cyan ions contained in the test water flowing in the electrolytic chamber 9 is quantified. The sample water after the concentration of cyan ions has been quantified in this way passes through the flow path 22 formed in the inverted conical portion 7 of the upper portion 8 of the electrolysis cell main body 2 to the electrolysis chamber 9
It is discharged outside.

As described above, the rotor 13 is rotated around the axis of the working electrode 3 by the magnetic stirrer during the quantification of the concentration of cyan ions contained in the test water, as indicated by the arrow 30 in the second illustration. . Therefore, the end faces 11 of the working electrode 3 and the counter electrode 4 are rubbed by the rotor 13. Therefore, even if contaminants contained in the test water adhere to the end surface 11, they are removed by the rubbing force of the rotor 13. Further, on the end surface 11 of the working electrode 3, silver oxide (Ag
O, Ag ₂ O) and the like may be formed, but these films are also removed by the rubbing force of the rotor 13 like the contaminants. Therefore, the end surfaces 11 of the working electrode 3 and the counter electrode 4, that is, the electrode surfaces on which the electrode reaction takes place are always kept clean, the current flowing between the electrodes 3 and 4 is accurately measured, and the concentration of cyanide ions in the test water is Accurately quantified.

Incidentally, in the conventional coulometric analysis method in which the concentration of the ions to be measured contained in the test water in the electrolysis cell is quantified by measuring the current flowing between the electrodes as described above, the inside of the electrolysis chamber 9 is It has been considered impossible to rotate the rotor 13 in the electrolysis chamber 9 because the current becomes a pulsating flow when the flowing test water becomes a turbulent flow. However, according to the experiments by the inventor of the present invention, when the number of rotations of the rotor is set to, for example, 300 rpm, the current flowing between the working electrode 3 and the counter electrode 4 becomes an alternating current of a constant cycle, and the alternating current is smoothed. As a result, the current corresponding to the concentration of the ions to be measured contained in the test water, that is, the cyan ions, could be obtained.

In the present invention, the voltage applied between the working electrode 3 and the reference electrode 5 is further changed as shown in FIG. In the waveform of this applied voltage, a DC component V0 is always applied, and a pulse wave in which a pulse whose amplitude increases as V1, V2, ... To be done. Such a measuring method is called a normal pulse method. By applying the voltage between the working electrode 3 and the reference electrode 5 by the above method, the value of the current flowing between the two electrodes can be accurately detected regardless of the mixture of the pre-discharge substance. , The content of the substance can be quantified from the integrated value of the current value.

For example, FIG. 4 is a graph showing the experimental results of the present invention, which is 2 × 10 ⁻⁴ MBr when silver is used for the working electrode.
^- recorded potential by normal pulse method in precipitation wave to (0.1MKNO ₃₎ of the electrode on the - shows the current curve. In the present embodiment, the limit voltage −0.05V of iodine ion I ^{− serving} as the pre-discharge material is used as V0 in FIG. 3 between the working electrode 3 and the reference electrode 5, and V1 = 0.15.
Bromine was used as an analyte when a rectangular wave voltage was applied in which V, V2 = 0.3 V, ... Ion Br ⁻ and iodine ion I
^If it contains a-, the waveform of l1 is given. l1
The current value in the range of W1 between the point l11 corresponding to V0 and the point l12 until the current sharply rises corresponds to the iodine ion I ⁻ , and the current of l1 becomes constant next to l13. The current value in the range of W2 between 114 and 114 corresponds to bromine ion Br ⁻ and iodine ion I ⁻ .
That is, when iodine ion I ⁻ and bromine ion Br ⁻ are included, A obtained by integrating 11 with W1 is the amount of I ⁻ ,
Since B obtained by integrating 11 over W2 is the amount of Br ⁻ + I ⁻ , Br ⁻ = BA. When this sample contains only bromide ions Br ⁻ , a waveform indicated by 12 is obtained. When iodine ion I ⁻ which is the pre-discharge substance is not contained, there is no interference by iodine ion I ^−, so that the period during W2 when the current becomes constant becomes clear. W from the waveform of l2
If the range of 2 is determined, it can be more accurate than the range of 11 to W2. Also, as indicated by l2, the voltage V0
The current will start to flow when it reaches. In the present invention, in addition to voltage V0 as the FIG. 3 always further peak value V1, V2 as time elapses, since the superimposing pulse having a ..., iodide ion I ^- bromine even thickness interference by The charge of the ion Br ⁻ can be measured.

FIG. 5 is a graph in which the diffusion current was measured while changing the concentration of the substance to be detected, that is, the interfering substance iodine ion mixed in the bromine ion, with the voltage V2 kept constant. l
3, l4, l5, l6 and l7 are iodine ion concentrations of 10 ⁻⁴ M, 2 × 10 ⁻⁴ M, 5 × 10 ⁻⁴ M and 10 respectively.
^-3 M, 2 * 10 ^-3 M.

As described above, according to the present invention, since the electrode surface 11 on which the electrode reaction is performed is rubbed by the rotor 13, the deposits and oxide film on the electrode surface 11 are removed and included in the test water. The concentration of the measured ion can be accurately quantified.

Further, between the reference electrode 5 and the working electrode 3, a direct current component V1 which is predetermined in the limiting current region of the pre-discharge substance, and a pulse pause period between the pulses in which the amplitude V2 increases with the passage of time are alternately repeated. Since a rectangular wave voltage is applied, it is possible to eliminate the error of the coulombic quantity due to the pre-discharged material and to perform accurate coulometric analysis of the material to be quantified.

Further, since the rotor 13 is rotationally driven by the magnetic stirrer 14, the electrode surface 1 can be easily driven by a simple mechanism.
1 polishing can be performed.

Further, since the rotor 13 is formed by covering the entire circumferential surface of the circular magnet and both end surfaces in the axial direction with a wear resistant material, the electrode surface 11 can be sufficiently polished.

Further, the working electrode 3 has a cylindrical shape, the counter electrode 4 is concentrically arranged, and the rotor 11 has an end face 11 perpendicular to the axial direction.
Since the polishing is performed by the method described above, the polishing of the electrode surface 11 can be performed uniformly and efficiently.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an embodiment of an analyzer constructed according to the present invention, FIG. 2 is a plan view of the vicinity of the rotor 13 shown in FIG. 1, and FIG. 3 shows a working electrode 3 and a reference electrode 5. Fig. 4 is a waveform diagram of the voltage applied between them, Fig. 4 is a potential-current curve when a normal pulse voltage is applied between the working electrode and the reference electrode, and Fig. 5 is a graph showing a diffusion current in the presence of a pre-discharge substance. is there. DESCRIPTION OF SYMBOLS 1 ... Electrolytic cell, 3 ... Working electrode, 4 ... Counter electrode, 5 ... Reference electrode, 13 ... Rotor, 14 ... Magnetic stirrer, 21
... Current measuring means

Claims (1)

[Claims] 1. A pair of electrodes 3, provided in an electrolysis cell 1.
By measuring the current flowing between the four electrolysis cells 1
In the coulometric analysis method for quantifying the concentration of ions to be measured contained in the sample water, the electrodes 3 and 4 are a cylindrical working electrode 3 and a cylindrical cylinder arranged coaxially around the working electrode 3. Counter electrode 4, and an insulating member 15 is provided in the gap between the electrodes 3 and 4,
In the flat surface 11 on which the electrode reaction in 4 is performed,
A rotor 13 formed by covering the entire outer peripheral surface of the cylindrical permanent magnet and both end surfaces in the axial direction with a wear-resistant material is provided, and the rotor 13 is rotated around the axis of the working electrode 3 by a magnetic stirrer 14. Pulses and pulses that are slidably rotated to a direct current component V0 predetermined between the reference electrode 5 and the working electrode 3 in the limiting current region of the pre-discharge substance, and the amplitude increases to V1, V2, ... With time. A coulometric analysis method comprising applying a rectangular wave voltage in which pulse rest periods are alternately repeated.