JP2526298B2 - Coulometric cell - Google Patents

Description

The present invention relates to a cell for coulometric analysis, and more particularly to a cell for coulometric analysis excellent in detection sensitivity and storage stability.

[Conventional technology]

Recently, the fields of application of electrochemical analysis methods have been expanded in so-called biosensors, liquid chromatographic detectors, and the like.

The conventional method for detecting an analyte in an electroanalytical method is to immerse an electrode, which is a detection part, in a sample solution (ion electrode, biocene electrode, etc.), or to force the sample solution to flow in the detection electrode (chromatography). Graph detectors, etc.), a method in which a sample is directly added to an electrolytic solution (eg, water content determination by the Karl Fischer method), and the like.

However, in the above-mentioned conventional technique, there is a drawback that the analysis time becomes long because it takes a long time to clean the electrode portion, and the analysis accuracy decreases when the cleaning is insufficient. Moreover, since the background level is high, it is not suitable for microanalysis, and it is difficult to reduce the detector capacity.

[Problems to be Solved by the Invention]

The present applicant has previously proposed that the analysis time is short, the electrical analysis method is highly accurate and has excellent operability, that is, the electrolyte solution does not flow out to the electrodes (detection electrode and counter electrode) made of a conductive porous body. We have proposed a method of impregnation, direct administration of a sample to the electrode, electrolysis, and quantitative determination (JP-A-1-195358), and a disposable type analytical cell based on this electroanalytical method, which is excellent in storage stability. (Japanese Patent Application No. 1-135050)
(Japanese Patent Laid-Open No. 2-311756).

However, the electrolyte to be impregnated into the counter electrode is usually a supporting electrolyte substance as its solute, and potassium ferricyanide, potassium ferrocyanide, sodium iodide, ethylenediaminetetracarbonate iron (iron edta), which can easily cause the counter electrode reaction. Therefore, the storage stability of the cell is limited because of the necessity of using the redox substance of 1), and the detection sensitivity is limited because of the residual current (background current) caused by the redox substance. This is also the case when the electrolytic solution with which the counter electrode is impregnated does not contain a supporting electrolyte but contains only a redox material.

The object of the present invention is to solve the above problems and to perform quantitative analysis without including a redox substance in an electrolytic solution (counter electrode solution) impregnated into a counter electrode, in detection sensitivity, long-term storage stability and productivity. It is to provide an excellent cell for coulometric analysis.

[Means for solving the problem]

The present invention is a coulometric analysis cell in which a detection station and a counter electrode made of a conductive porous body impregnated with an electrolytic solution are arranged on both sides of a diaphragm with a solute of the electrolytic solution impregnating the counter electrode being a supporting electrolyte only. The present invention relates to a cell for coulometric analysis comprising:

In the present invention, the supporting electrolyte dissolved in the counter electrode solution has no electrode reactivity, its function is to ensure the conductivity of the counter electrode solution, as a specific supporting electrolyte alkali phosphate compounds, alkali acetate System compounds and the like.

[Action]

In an electroanalytical reaction, it is usually necessary to make a counterelectrode liquid coexist with a sufficiently electrochemically active substance, for example, a redox substance, in order to avoid that the counterelectrode reaction becomes the rate-determining factor of the whole analytical reaction. In the present invention, since the conductive porous body having a large specific surface area is used as the detection electrode and the counter electrode, a counter electrode having a large electric double layer capacity (an electrode capable of taking a large capacitor current) can be used, and a sample to be supplied to the detection electrode. Since the amount of is very small, the reaction current at the detection electrode can be covered by the electric double layer capacity, and therefore, without the presence of an active substance such as a redox substance in the counter electrode liquid, only with the supporting electrolyte. Quantitative analysis can be performed. The electrolyte of the counter electrode can gradually return to the original electrical (neutral) condition due to the residual current of the electrolytic solution.

When the counter electrode is made of a porous carbon material, not only the double layer capacity but also the reaction of the functional groups on the carbon surface is large, which can contribute to the electrolysis current. The reaction of the functional group is, for example, a redox reaction between a carbonyl group and a hydroxy group.

Therefore, in the present invention, since the detection electrode and the electrolytic solution of the counter electrode can be made common, there is no need to use an expensive ion exchange membrane as a diaphragm as in the conventional case, and the cost can be reduced. Also, since it is not necessary to use a redox substance, the background current is greatly reduced,
The detection sensitivity can be improved, and the storage stability and productivity of the cell can be improved.

The electrode used in the present invention is a conductive porous body, and examples thereof include an aggregate of carbonaceous or graphitic carbon fibers and porous carbon.

The electrolytic solution used in the present invention is a solution containing a supporting electrolyte as described above, for example, phosphoric acid-sodium phosphate solution, acetic acid-sodium acetate solution, various pH buffer solutions such as lithium fluoride solution. Can be mentioned.

The diaphragm used in the present invention is not particularly limited as long as it is a porous membrane, and for example, cellulose-based filter paper, ion exchange membrane, etc. can be used.

FIG. 1 is a sectional view of a cell for coulometric analysis showing an embodiment of the present invention. This cell comprises a container 1 having detection terminal insertion holes 8 and 8A, a counter electrode 2 and a detection electrode 3 made of carbon felt impregnated with an electrolytic solution, a counter electrode 2 and a detection electrode 3
And a spacer 5 provided on the outer periphery of the detection electrode 3 for fixing the diaphragm 4 to the container 1, a seal 7 for sealing the detection terminal insertion holes 8 and 8A, The lid 6 of the container 1 and the detection liquid insertion hole 10 provided in the lid 6
And a seal 9 for sealing the detection liquid insertion hole 10.

The detection electrode 3 and the counter electrode 2 are housed in the container 1 via the diaphragm 4, and the thickness thereof is not particularly limited as long as the detection terminal can be inserted. The container 1 is provided with an annular step portion 11 between the accommodating portion of the detection electrode 3 and the accommodating portion of the counter electrode 2, and the circular diaphragm 4 is placed on the step portion 11. An annular spacer 5 is provided on the diaphragm 4 on the outer periphery of the detection electrode 3. The spacer 5 presses the diaphragm 4 against the stepped portion 11 of the container and prevents the electrolytic solution from leaking out of the container. Container 1
The material is not particularly limited as long as it can be processed and heat-sealed, and polyethylene, polypropylene or the like is used. The shape is not particularly limited, but a circular shape is preferable in terms of ease of molding.

The container 1 has a detection terminal insertion hole 8A that directly communicates with the counter electrode 2.
And a detection terminal insertion hole 8 communicating with the detection electrode 3 through the spacer 5, and the hole is sealed by a seal 7. The sealing method of the seal 7 is not particularly limited as long as the detection terminal can be easily inserted at the time of use and the electrolyte does not leak due to the terminal insertion. For example, silicone rubber is used as the sealing material. You can stop it.

The lid 6 has a detection liquid insertion hole 10 and is heat-sealed or mechanically adhered to the container 1. The detection liquid insertion hole 10 is sealed with a seal 9 when not in use. The sealing method of the seal 9 is not particularly limited as long as the detection liquid can be easily inserted during use. The detection liquid can be inserted by, for example, a method of inserting a detection liquid by inserting a pipette or a syringe into the seal, a method of inserting the detection liquid after removing the seal, and the like.

The above-mentioned electrolytic analysis cell is capable of easily quantifying a substance to be detected such as lipid peroxide, vitamin C, glucose, juice acidity, ozone, residual chlorine, and dissolved oxygen by inserting the detection terminal from the detection terminal hole at the time of use. You can

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to Examples.

Examples 1 and 2 Carbon felt was used as the detection electrode and the counter electrode, phosphoric acid-disodium hydrogen phosphate aqueous solution was used as the electrolyte of the detection electrode and the counter electrode, and filter paper No. 5 (Example 1) and the cation exchange membrane were used as the diaphragm 4. A cell for coulometric analysis was prepared by using each of (Example 2), and a background current when a voltage of 0.5 V was applied and 10 μl of a sample (a solution obtained by adding potassium iodide to ozone water) was added. The detection limit concentration of ozone was examined, and the results are shown in Table 1. A control measurement of the ozone concentration of the sample was performed with a flow-type ozone analyzer.

Comparative Examples 1 and 2 Carbon felt was used as the detection electrode and the counter electrode, phosphoric acid-disodium hydrogen phosphate aqueous solution was used as the detection electrode electrolyte, and 0.2 M potassium ferrocyanide phosphate-disodium hydrogen phosphate aqueous solution was used as the counter electrode electrolyte solution. A cell for coulometric analysis using a cation exchange membrane as the diaphragm 4,
The background currents when applying voltages of 35 V and 0.5 V and the detection limit concentrations similar to those in Example 1 were examined, and the results are shown in Table 1.

From Table 1, in the present embodiment, the background current can be greatly reduced, the detection sensitivity is improved,
It is shown that the detection limit concentration can be lowered.

Example 3 Using the cell prepared in Example 1, the amount of I ₂ liberated in the sample (KI added to 5.7 ppm ozone water) was quantified 5 times. The current-time curve at that time is shown in FIG. It was found that the electric quantities were 0.26, 0.28, 0.28, 0.26 and 0.26 millicoulombs, and stable measurement was possible. In addition, the electricity amount of 5.7 ppm ozone water by the conventional redox titration method is 0.23 millicoulomb.

〔The invention's effect〕

The cell for coulometric analysis of the present invention does not require the use of a redox material in the counter electrode liquid, can significantly reduce the background current, and has no portion in contact with air, and therefore has detection sensitivity and long-term storage stability. Can be improved. In addition, the coulometric analysis cell of the present invention can be commonly used for the electrolytic solution of the detection electrode and the counter electrode, and therefore is easy to manufacture, and can be put on a mass production line and mass-produced at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a cell for coulometric analysis according to an embodiment of the present invention, and FIG. 2 is a current-time curve diagram for 5.7 ppm ozone water analysis in Example 3. 1 ... container, 2 ... counter electrode, 3 ... detection electrode, 4 ... diaphragm,
5 ... Spacer, 6 ... Lid, 7 ... Seal, 8, 8A ...
… Detection terminal insertion hole, 9 …… Seal, 10 …… Test liquid insertion hole.

Claims (1)

(57) [Claims] 1. A coulometric cell in which a detection electrode and a counter electrode made of a conductive porous material impregnated with an electrolytic solution are arranged on both sides of a diaphragm, and the solute of the electrolytic solution with which the counter electrode is impregnated is a supporting electrolyte. A cell for coulometric analysis, characterized by comprising only