JPH0623730B2 - Coulometric method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a coulometric method, and more particularly to a solution static coulometric method capable of performing rapid and easy automatic quantification.

(Prior Art) Coulometric analysis is one of the analytical methods that can be used as a primary standard together with gravimetric analysis, and it is theoretically possible to quantify extremely minute amounts of components with high accuracy. That is, a standard substance such as a standard solution is prepared in the same manner as the gravimetric method in which the quantity of the precipitated product is weighed to determine the amount of electrolysis of the substance to be quantified whose number of electrons involved in oxidation or reduction is clear. Accurate quantitative values can be obtained without the need for comparison. In coulometric analysis, 1/100 coulomb to 1
It is possible to measure an electric quantity of about / 1000 coulomb with extremely high accuracy, and this value is 10 ^-7 〜 when converted to the number of moles.
This corresponds to a very small amount of 10 ^-8 mol.

(Problems to be Solved by the Invention) However, the coulometric analysis method, which is excellent in principle as described above, has not come into widespread use due to the following problems.

(1) The substance to be quantified may not be easily electrolyzed,
Even if it can be electrolyzed, the number of oxidation or reduction electrons may not be stable. In particular, when the number of electrolysis products is not one, but two or more, there are multiple electrolysis reactions.In such cases, slight changes in reaction conditions such as temperature and hydrogen ion concentration cause each of the substances to be quantified to change. Since the ratio of contribution to the electrolytic reaction changes, it is usually impossible to accurately grasp the number of oxidation or reduction electrons, and the analysis accuracy often deteriorates extremely.

(2) Like other electrochemical analysis methods such as voltammetry, in trace analysis, the S / N ratio (Sig
The nal / Noise ratio, in this case the electrolysis current / residual current) becomes small, which greatly affects the analysis accuracy. When the residual current is stable at a constant value, it is relatively easy to correct the residual current value and improve the analysis accuracy.
The problem is how to stabilize the residual current.

An object of the present invention is to provide a coulometric analysis method which eliminates the above-mentioned problems of the prior art, has a short electrolysis time, and can perform automatic quantification quickly and easily.

(Means for Solving Problems) The present inventor filled a porous electrode made of a liquid-permeable carbon felt in the electrode chamber of a coulometric cell, and a liquid containing a substance to be measured which communicates with the inside and outside of the electrode. The inner diameter of the inlet and outlet holes of
Below, preferably 3 mm or less, more preferably about 1 mm, and by electrolyzing the solution to be measured in a stationary state, a small amount of the solution can be electrolyzed almost simultaneously in the porous electrode, so that the electrolysis time is greatly shortened. It was found that the present invention has been achieved.

That is, the present invention is a coulometric analysis cell in which an electrode chamber is filled with a porous electrode made of a liquid permeable carbon felt, and the inner diameter of the inflow / outflow hole of the liquid containing the substance to be measured, which communicates with the inside and outside of the electrode chamber, is 5 mm or less. In addition, after the solution is supplied, electrolysis is performed in a stationary state, and the measured current is integrated to quantify the substance to be measured from the obtained electric quantity.

In the present invention, it is necessary that the liquid-permeable type porous electrode is completely filled in the electrode chamber as the working electrode chamber, and when the porous electrode is not filled in the electrode chamber, high efficiency is achieved in a short time. Electrolysis cannot be performed at. In the present invention, the carbon felt used as the porous electrode is a high density porous sheet obtained by filling the carbon fibers without weaving them so as not to separate them so as not to separate them. Further, when the inner diameter of the solution inlet / outlet hole exceeds 5 mm, the liquid diffuses (mixes) inside and outside the cell, which lowers the analysis accuracy. The hole length is preferably long to some extent, and for example, when the inner diameter of the solution inflow / outflow hole is 1 mm, it is preferable that the hole length is several mm.

With the above-mentioned configuration, the analysis time is shorter than that of the conventional apparatus using the solution stirring type (H-type cell) electrolytic cell or the porous electrode for the melt flow type electrolytic quantification method. ,
It enables quick measurement. Further, since the quantitative operation under the same condition can be repeatedly performed in a short cycle, there is almost no fluctuation in the residual current in one quantitative determination. Since highly accurate repetitive analysis is performed, the number of oxidation or reduction electrons is also kept constant throughout a series of quantifications, enabling extremely highly accurate quantitative analysis. Further, even in the case of a substance to be quantified having a low electrode reaction rate, stable quantification can be achieved in a short time.

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

FIG. 1 and FIG. 2 are explanatory views of a cell for coulometric analysis showing an embodiment adopting the method of the present invention.

In FIG. 1, this device is shown as an electrolyte 1 of a solution to be measured.
And a counter electrode chamber 2 provided with a diaphragm 3 therebetween, and solution inlets / outlets 4A, 4B and counter solution inlets / outlets 5A, 5B provided in the electrolytic chamber 1 and the counter electrode chamber 2, respectively.
The current collecting plates 6A and 6B provided on the side surfaces of the electrolytic chamber 1 and the counter electrode chamber 1, the lead wires 7A and 7B connected to the current collecting plate, and the electrolytic chamber 1 and the counter electrode chamber 2. It mainly comprises liquid feed pumps 8A and 8B and liquid feed lines 9A and 9B for feeding the solution to be measured and the counter electrode liquid, respectively. The electrolytic chamber 1 is filled with a porous chamber electrode 1A, and the inner diameters of the measured solution inflow / outflow holes 4A and 4B of the electrolytic chamber 1 are set to 5 mm or less. At the time of measurement, the pump 8A on the side of the measured solution electrolysis chamber 1 is operated to supply a predetermined amount of the measured solution into the electrolysis chamber 1, and then the pump 8A is stopped to perform electrolytic quantification by pouring into a stationary solution. . For the counter electrode liquid, the counter electrode liquid pump 8B is always operated to allow the counter electrode liquid to flow.

FIG. 1 shows the so-called two-electrode method electrolysis that is carried out at the same time as the counter electrode reaction to stabilize the electrode potential. However, when it is desired to measure the electrode potential of the measured solution electrolysis chamber side more accurately, Alternatively, electrolysis may be performed using a three-electrode method using a reference electrode. The electrolysis method in the present invention is a constant potential (constant voltage) or constant current coulometric analysis. Even if the electrolysis is not completely performed, the current or voltage within a certain period of the initial stage of electrolysis is measured, and extrapolation is thereby performed. The total amount of substance to be measured may be determined by a method or the like.

FIG. 2 shows another embodiment of the present invention, in which the feeding of the bipolar solutions of the solution to be measured in the electrolytic chamber 1 and the counter chamber 2 is stopped during the analysis time. The liquid feed pump 8 may be common to both electrodes, which has the advantage of simplifying the device.

(Effects of the Invention) According to the present invention, a porous electrode is filled in the electrode chamber, the inflow and outflow holes of the electrode solution are set to 5 mm or less, and electrolysis is performed in a static state, so that a small amount of the supply solution and high reproducibility are obtained. Enables rapid automatic quantification. Therefore, compared with the conventional solution stirring type or solution circulation type coulometric cell, the quantification time for one time is shortened, the operation becomes extremely simple, and troubles such as breakdown can be reduced. Further, compared with other analysis methods, such as optical analysis methods and analysis methods using electromagnetic waves, etc., the structure of the detector and the electric circuit etc. becomes simpler, so that it can be manufactured at a very low cost.

Hereinafter, specific examples of the present invention will be described.

(Examples) Examples 1 to 3 and Comparative Examples 1 and 2 In the electrolysis cells shown in FIG. 1, inner diameters of 7 mm (Comparative Example 1) and 5 mm (Comparative Example 1) were used as the measured solution inflow / outflow holes 4A and 4B of the electrolysis chamber, respectively. Example 1), 3 mm (Example 2), 1 mm
Using the vinyl chloride tube of (Example 3), four sets of electrolytic cells were prototyped under the following other conditions. The dimensions of the electrolysis chamber and the counter chamber of the electrolysis cell are 100 mm vertically and 10 mm horizontally,
It has a thickness of 3 mm. In addition to this, a polyvinyl chloride tube having an inner diameter of 1 mm is used as an inflow / outflow hole for the solution to be measured, but a cell (Comparative Example 2) in which the porous chamber electrode (carbon felt) is not filled in the electrolytic chamber 1 is used. I made a prototype.

Solution to be measured Electrolysis chamber filling electrode 1A: carbon felt (dimensions: vertical 100 mm, horizontal 10 mm, thickness 3 mm) collector plates 7A, 7B: phenol resin-bonded carbon plate (inner) + copper plate (outer) diaphragm 3: positive Ion-exchange membrane Solution to be measured: weak acidic phosphate iodine, potassium iodine aqueous solution Counter electrode: Same as solution to be measured.

The structure of the counter electrode chamber side was the same as that of the measured solution electrolytic chamber side.

In the above apparatus, first, the iodine ion standard solution was sent to each of the measured solution electrolysis chambers 1 of the five sets of cells, and the capacity thereof was measured. Then, electrolytic determination of iodine and iodine ions in each solution to be measured was performed by a constant potential method of ± 0.4V. Separately, the concentrations of iodine and iodide ions in the solution to be measured were measured by an aqueous sodium thiosulfate titration method or the like. The results are shown in Table 1.

Example 4 In the solution to be measured, constant voltage electrolysis (constant potential) and constant current electrolysis were performed using the same standard solution and solution to be measured as in Example 1 using the coulometric cell having the structure shown in FIG. Of iodine,
The iodine ion concentration was determined. The dimensions of the coulometric analysis cell are 100 mm vertically, 10 mm horizontally, 3 mm thick, and 100 mm vertically, 10 mm horizontally, and 10 mm thick in the counter electrode chamber.
Porous electrode in the electrolysis chamber is 100mm vertically and 10m horizontally
A carbon felt having a thickness of 3 mm and a thickness of 3 mm was used, and a silver mesh was used as an electrode in the counter electrode chamber. The results are shown in Table 2 and were sufficiently satisfactory.

Comparative Example 3 Iodine and iodine ions in the solutions to be measured in Examples 1 and 2 were quantified by a conventional platinum mesh electrode-containing H-type cell. The results are shown in Table 3.

As is apparent from Table 3, it is understood that the conventional coulometric analysis requires a measurement time and has a large variation in the measured values.

[Brief description of drawings]

1 and 2 are explanatory views of a coulometric analysis cell showing an embodiment of the present invention. 1 ... Measured solution electrolysis chamber, 1A ... Porous chamber electrode, 2 ...
Counter electrode chamber, 3 ... Diaphragm, 4A, 4B ... Measured solution inlet / outlet hole, 5A, 5B ... Counter electrode liquid inlet / outlet hole, 6A, 6B ... Current collecting plate, 7a, 7b ... Lead wire, 8 , 8a, 8
b ... liquid feed pump, 9a, 9b ... liquid feed line.

Claims (2)

[Claims] 1. A coulometric analysis cell in which a porous electrode made of a liquid-permeable carbon felt is filled in an electrode chamber, and an inner diameter of an inflow / outflow hole of a liquid containing a substance to be measured leading to the inside and outside of the electrode chamber is 5 mm or less. A coulometric analysis method, characterized in that after the solution is supplied, electrolysis is performed in a stationary state, and the measured current is integrated to determine the quantity of the substance to be measured from the obtained electric quantity. 2. The coulometric analysis method according to claim 1, wherein the electrolysis is performed by a constant current method or a constant potential method.