JPH073322Y2 - Coulometric detector - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a coulometric detector, and particularly to a coulometric detector capable of reducing background current noise and accurately measuring a minute current or an electric quantity. Regarding vessels.

[Conventional technology]

Coulometry, which is one of the electrolytic analysis methods
Has attracted attention as an absolute quantitative method that does not require a calibration curve. However, since this analysis method requires electrolysis for a long time, there is a problem in that analysis is lacking in speed.

In order to eliminate such a defect, an analysis method using a detector having a cell composed of a conductive porous body and having a structure in which a detection electrode and its counter electrode are laminated via a diaphragm is proposed ( The Chemical Society of Japan, 56th Annual Meeting, April 3, 1988; 55th Spring Meeting of the Electrochemical Society, April 5-7, 1988; see Japanese Patent Application No. 63-18696).

In this method, a detection electrode made of a conductive porous body is impregnated with a predetermined electrolytic solution to such an extent that the electrolytic solution does not flow in the detection electrode, and a sample containing a substance to be quantified is directly administered thereto, This is a method in which the whole is electrolyzed using counter electrodes, each of which is made of a conductive porous body and impregnated with a predetermined electrolytic solution, as an electrode, like the detection electrode.

The detector used in this method incorporates the cell having the above-mentioned structure. In that case, the conductive porous body is chemically stable to the electrolytic solution and also has conductivity. Therefore, a porous carbon body is usually used as a suitable material regardless of the shape such as cloth, felt or block. Also, a simple porous film can be used as the diaphragm, but in that case, the noise level of the electric signal such as the current, voltage, or electric quantity derived from the detector, or the background level becomes high, and the accuracy of analysis becomes high. Therefore, a conductive ion exchange membrane is usually used as a suitable material.

In this detector, lead wires are connected to the detection electrode and the counter electrode, respectively, to derive an electric signal at the time of electrolytic reaction in the detection electrode, which is caused by injecting the sample.
The lead wire may be a normal metal wire such as a steel wire or a copper wire if the electrolytic solution is not corrosive, but in the case of an electrolytic solution containing an acid or the like, it may be corrosive. Mainly platinum wire is used. The detection electrode and the lead wire are connected by embedding a metal net in the detection electrode and welding the metal net and the lead wire, for example.For the counter electrode, a collector plate is brought into contact with the counter electrode. The method of connecting the lead wire with is done.

In addition, the lead wire is not limited to a metal wire, but carbon fiber may be used because it has high corrosion resistance. In this case, the connection is made by simply mechanically contacting the carbon fiber with the detection electrode or the counter electrode.

[Problems to be solved by the device]

By the way, this detector has a compact structure,
Often carried and used. In the process, the lead wire receives an external force such as repeated bending motion and external vibration. Since the metal lead wire is generally weak in repeated bending motion and easily fatigued, there is a problem that the lead wire is disconnected in a relatively short time when the lead wire in this detector receives the external force as described above. Occur. Further, when the lead wire is made of carbon fiber, when the above-mentioned external force is applied to the lead wire, poor contact is likely to occur at the contact portion with the detection electrode, resulting in increased noise and a drastic increase or decrease in the background current density. However, the accuracy of analysis will be reduced. In addition, when the strength of the carbon fiber is excessively low, there is a problem that the carbon fiber itself is damaged due to vibration or bending motion during carrying, and eventually cut.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a coulometric analysis detector in which the background current is stable and the variation in the current value or the measured value of the electric quantity is small.

[Means for Solving the Problems]

To achieve the above object, the present invention provides a coulometric detector having a cell structure in which a flat plate-shaped detection electrode and a counter electrode each made of a porous conductor are laminated with a diaphragm interposed between 0.01 and 1.0 mm. A gold wire having a diameter is alternately passed in the plane direction and the cross-sectional direction of the detection electrode and the counter electrode, sewn so as to cover at least the central portion thereof, and the end portion thereof is led out of the cell to form a lead wire. Is characterized by.

[Action]

The detector for coulometric analysis of the present invention is configured such that the conductive porous body of the electrode is alternately passed through the thin gold wire in the plane and the cross-sectional direction, and is sewn so as to cover at least the central portion thereof, thereby forming the electrode and the current collector. The contact area with and the reaction is not unevenly distributed on the electrode, and as a result, the background current value is stabilized, the measurement current peak becomes sharp, and the measurement accuracy improves.

[Embodiment]

FIG. 1 is a sectional view showing one embodiment of the coulometric analysis detector of the present invention.

In the figure, a detection electrode 3 is provided above the counter electrode 1 through a diaphragm 2.
Are closely attached to each other and stacked to form a cell. And this cell is installed in the electrically insulating container 4. At this time, the electrolytic solution impregnated in the detection electrode 3 and the counter electrode 1
The peripheral edge of the diaphragm 2 is provided on the side wall 41 of the container 4 so that the electrode liquid impregnated into the side does not mix through the inner wall of the container 4.
It is sandwiched liquid-tightly.

Tubes 5a and 5b for inflowing / outflowing the respective electrolytic solutions to / from the counter electrode 1 and the detection electrode 3 are respectively provided in a portion 41a surrounding the counter electrode 1 and a portion 41a surrounding the detection electrode 3 of the side wall 41 of the container 4. , It is installed so as to reach each pole. A cap 6 having a sample injection port 6a in the center is provided on the upper surface of the container 4.

Gold wires 9 and 10 having a diameter of 0.01 to 1.0 mm alternately pass through the counter electrode 1 and the detection electrode 3 in the plane and cross-sectional direction of the porous carbon body 3 in a pattern as shown in FIGS. 2 and 3, for example. However, it is sewn so as to cover at least the central portion thereof. Covering the central part here means the second
As shown in FIGS. 3 and 4, it is sufficient that the gold wire is not locally unevenly distributed and is distributed including the central portion of the porous carbon body 3. The gold wire must be sewn through the porous carbon body in the cross-sectional direction as shown in FIG. As the sewing pattern, it is preferable to include a cross shape as shown in the drawing. This is because the sample is usually supplied to the central part of the electrode.

The lead wires 7a and 7b may be formed by drawing the gold wires 9 and 10 out of the cell as they are, but can be integrally joined with another gold wire or a copper wire if necessary. Lead wires 7a, 7b
The other end of is connected to a power source and an integrating unit 8.

Now, in the detector having such a structure, both the counter electrode 1 and the detection electrode 3 are made of a porous carbon body. The carbon body may be graphitic or carbonaceous. Also, the reason for making it porous is that when impregnated with an electrolytic solution,
This electrolyte can be retained in a uniformly dispersed state,
This is because when the sample liquid containing the substance to be quantified is injected into the detection electrode, the sample liquid can be uniformly diffused throughout the detection electrode.

As such a porous carbon body, a carbonaceous or graphitic cloth, felt, or block can be used.

The porosity of these carbon bodies is not particularly limited, but if it is excessively porous, the liquid retaining property of the electrolytic solution or the sample solution deteriorates, and if it is dense, the above-mentioned sample solution is uniformly dispersed. Therefore, the apparent specific gravity is 0.05 to 1.0 g / cm ³
It is also preferable that the porous body has a porosity of 40 to 98%.

In the case of current detection, for example, this detector operates as follows. That is, first, the power source and the integrator unit 8 are operated in a state where the counter electrode 1 and the detection electrode 3 are each impregnated with a predetermined electrolytic solution. A predetermined background current flows between both electrodes due to the set voltage of the power supply and the integrator unit 8.

In this state, the sample liquid is injected into the detection electrode 3. The sample solution is uniformly diffused in the detection electrode 3, and the substance to be determined therein reacts with the electrolytic solution or directly reacts with the electrode, whereby an electrolytic current is superposed and flows between both electrodes. And
The power supply and integrator unit 8 integrates this electrolytic current with respect to time. Since this integrated value (electrical quantity) is a function of the amount of the substance to be quantified, the quantitative analysis of the substance to be quantified becomes possible by calculating the integrated value.

〔Example〕

Example 1 A carbonaceous block having an apparent specific gravity of 0.45 g / cm ³ and a porosity of 73% was cut to obtain a porous carbon disk 2 having a diameter of 20 mm and a thickness of 3 mm.
I made a piece. A gold wire having a diameter of 0.1 mm is sewn into these discs in a pattern as shown in FIG. 2 to integrate the disc and the gold wire, and the end of the gold wire is taken out of the cell.
The detector of the present invention was assembled by using the lead wires and omitting the tubes 5a and 5b in FIG. That is, a disk sewn with the gold wire is attached as the counter electrode 1 to the inner bottom of the container 4 made of acrylic resin, and the gold wire is attached to the outside of the container 4 with the lead wire.
Withdrawn as 7a. Then, about 2 ml of an acetic acid-sodium acetate aqueous solution (pH: about 5) containing 0.1 M potassium ferrocyanide was impregnated into the counter electrode 1 as an electrolytic solution. Another disk is attached as a detection electrode 3 on the counter electrode 1 via a cation exchange membrane (diaphragm) 2, and the gold wire sewn on this disk at the same time is pulled out of the container as a lead wire 7b. It was The detection electrode 3 was impregnated with about 3 ml of an acetic acid-sodium acetate aqueous solution (pH: about 5) using 0.05 M potassium ferrocyanide as a redox mediator as an electrolytic solution. Then, the whole container was covered with a cap to form a detector of the present invention, and the lead wires 7a and 7b were connected to a power source and an integrator section (consisting of a constant voltage power source and a current integrator) 8.

Vitamin C (L-ascorbic acid) in mandarin orange was quantified using the above-mentioned detector. The stabilization waiting time from voltage application to measurement was about 3 minutes. The waveform of the current-time curve is shown in FIG. As a result of measuring 5 times, the average value is 35.2
mg / 100 ml, standard deviation 0.35 mg / 100 ml, coefficient of variation 1.01%. The quantitative value by the titration method value was 35.4 mg / 100 ml.

Comparative Example 1 A detector was assembled in the same manner as in Example 1 except that a platinum wire having the same diameter as a lead wire was inserted into the disk.

Using this detector, the same amount of vitamin C in the mandarin orange as above was quantified. The average value measured 5 times was 33.4 mg / 100 ml, the standard deviation was 1.75 mg / 100 ml, and the coefficient of variation was 5.2%. The waveform of the current-time curve at this time is shown in FIG. The stabilization wait time from voltage application to measurement was about 30 minutes, and data processing such as once shaping the signal waveform with a filter circuit was required.

As is clear from FIG. 4 and FIG. 5, the curve of the detector of the present invention stabilizes the background current and the measured current peak becomes sharp, but the curve of the detector of the comparative example is broad and the background current. There was a lot of noise, and the measured values varied greatly.

[Effect of device]

According to the present invention, the following excellent effects are achieved by sewing the porous conductor with the gold wire.

(1) Background current noise is, for example, 20-40 μA
To 0.2 to 0.4 μA, which makes it possible to measure minute currents or electric quantities.

(2) Since the contact area between the collecting wire and the electrode is improved, the resistance due to the collecting current is reduced, and the sewn gold wire eliminates the uneven distribution of the reaction at the electrode, and the measured current peak becomes sharp. Therefore, the load on the measuring electric circuit of the measuring instrument is reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the detector of the present invention,
2 and 3 are plan views, 4 and 5 of the porous conductor showing an example of a sewing pattern when a gold wire is sewn into the porous conductor (electrode) used in the present invention. Is
FIG. 4 shows the results of measurement using the detector of Example 1 and FIG. 5 shows the measurement results when the detector of Comparative Example 1 was used. 1 ... counter electrode, 2 ... diaphragm, 3 ... detection electrode, 4 ... container,
41 …… Container side wall, 5a, 5b …… Tube, 6a, sample inlet, 6 …… Cap, 7a, 7b …… Lead wire, 8 …… Integrator part, 9,10 …… Gold wire.

Claims (1)

[Scope of utility model registration request] 1. A coulometric detector having a cell structure in which a flat plate-shaped detection electrode and a counter electrode each made of a porous conductor are laminated with a diaphragm interposed therebetween, and a gold wire having a diameter of 0.01 to 1.0 mm is detected. For coulometric analysis, characterized in that the poles and counter electrodes are alternately passed in the plane direction and the cross-sectional direction, sewn so as to cover at least their central portions, and their ends are led out of the cell to form lead wires. Detector.