JPH0124260B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrode for selectively measuring the activities of nitrite ions, chloride ions, iodine ions, and perchlorate ions in an aqueous solution, and a method for manufacturing the same. The ionic activity in a solution is usually measured by the following method. That is, the reference electrode and the electrode for measuring ion activity are immersed in a solution to be measured, the potential difference between the two electrodes is measured, and the ion activity is determined from this. The following types of electrodes for measuring ion activity (hereinafter referred to as ion electrodes) are known.

[Table] Furthermore, an ion-selective coated wire electrode was recently developed by HENRYFREISER et al. This corresponds to replacing the liquid membrane electrode with a polymer containing an ion exchange membrane, which has a simpler structure, is extremely easy to produce, is less expensive, and is more compact than known ion electrodes. Moreover, since it does not have an internal standard liquid, it is easy to handle. The present inventors particularly conducted intensive research on nitrate ion-selective coated wire electrodes, and filed an application as Japanese Patent Application No. 1983-69571 (Japanese Patent Application Laid-open No. 166461/1983, Japanese Patent Publication No. 17179/1983). The present invention was completed by researching other anions. That is, the present invention uses a bisphenol A epoxy oligomer as a polymer and a quaternary ammonium salt containing an anion such as nitrite ion, chloride ion, iodine ion, or perchlorate ion as an ion exchanger. The electrode of the invention is a covered electrode made of a conductive metal covered with a cured product of a mixture thereof. This electrode is prepared by adding 0.1% of a quaternary ammonium salt to an organic solvent such as decanol, methylcyclohexanone, nitrobenzene or chloroform.
~6.0% by weight, and further add strong acid dissociated salts such as chloride, nitrite, iodide, and perchlorate to transform the quaternary ammonium salt into anionic chloride ions and submersible salts. nitrate ion,
Exchange with either iodine ions or perchlorate ions, then add bisphenol A epoxy oligomer and curing agent to the ion exchanged product to form a paste-like material. At this time, a solvent may also be added. Finally, the conductive wire metal is coated with the produced paste-like material, and the paste-like material is cured to complete the process. Examples of liquid ion exchangers include quaternary ammonium salts with high ion exchange ability, such as trioctylmethylammonium chloride (for example, Aliquot 336S, manufactured by General Mills), benzyldimethyltetradecylammonium salt (Zefiramine), and ceyltrimethylammonium salt ( CTMA), dodecyltrimethylammonium salt (DTMA), etc. are used. Bisphenol A epoxy oligomer, curing agent and methyl ethyl ketone as a solvent to be added to the product after ion exchange.
Tetrahydrofuran, methyl isobutyl ketone, etc. can be used. Further, as curing agents, commonly used triethylenetetramine and cyclohexane anhydride 1.2 dicarboxylic acid are available. Further, the conductive metal to be coated may be a wire or thin plate of copper, tin, silver, or the like. Note that it is convenient to use the electrode if a holder is attached to it if necessary. Next, the present invention will be explained in detail based on examples. Example 1 Decanol was added to trioctylmethylammonium chloride (Aliquot 336S) to a concentration of 40% by weight, 1 mol/liter of potassium chloride was added in approximately the same amount, shaking and centrifugation were repeated, and a chlorine ion exchange solution was added. Next, this liquid, bisphenol A type epoxy oligomer, and hardening agent triethylenetetramine were mixed in a weight ratio of 5:10:2 and left to stand, and when it had a suitable viscosity, A copper wire with a diameter of 0.5 mm was coated uniformly to a thickness of about 0.2 mm, and left at room temperature for one week to dry and harden, producing a chloride ion selective coated wire electrode. Next, this electrode was attached to the holder shown in FIG. 1 to prepare a measurement electrode, and the electrode potential was measured using the apparatus shown in FIG. In Figure 1, 1 and 3 are copper wires, 2 is solder,
4 is a coating, 5 is a protective tube, 6 is a plastic holder, and 7 is a polytetrafluoroethylene tube. In addition, in FIG. 2, P is an anion-selective coated wire electrode of the present invention shown in FIG. 1, 8 is a measurement solution, and 9 is
10 is an insulator, 10 is a stirrer, 11 is a reference electrode which is a saturated calomel electrode, 12 is a voltmeter, 13 is an insulating box, and 14 is a recorder. The measurement method is shown next. To do this, first take 250ml of pure water in a 300ml beaker and keep it in a constant temperature bath at a constant temperature of 25°C. Next, this was taken out, placed on a stirrer, and the electric potential in pure water was measured while stirring. Next, drop the specified amounts of 10 ^-2 M and 1.0 ^M Kcl solutions into 250 ml ^of pure water using a biuret.
Toa Denpa HE-20E was used as a potentiometer using a saturated calomel electrode as a reference electrode over the activity range of
The potential response was measured using a model digital PH meter. The response characteristic is shown by the line 21 in the third diagram. In the figure, the vertical axis is the potential difference, and the horizontal axis is the logarithm of the chloride ion activity. Next, use potassium nitrite, potassium iodide, and potassium perchlorate instead of Kcl, and use the same method to create a nitrite ion-selective coated wire electrode, an iodine ion-selective coated wire electrode, and a perchlorate ion-selective coated wire electrode. Electrodes were created and electrode potentials were measured in exactly the same manner. The results are shown in Figure 3, lines 22, 23, and 24.
Shown below. According to Figure 3, the lower limit of linear response for all electrodes is approximately 5 × 10 ^-5 M, and the response slope is also 60 _(nv/aid).
This is quite close to Nernst's theoretical value of 59.2 _(nv/aid) . Moreover, the upper limit of the linear response exceeds the measured maximum activity of 4×10 ⁻² M in all cases. Furthermore, the potential stability is ±0.5 mV at 1×10 ^-2 M, 1×
About ±2mV at 10 ^-4 M, and the response stability is 1×
At 10 ^-2 M, it takes less than 1 second, and at 1×10 ^-4 M, it takes a few seconds. Table 1 shows the linear response range and its slope for each ion. Comparative Example 1 A simple liquid membrane electrode containing the ion exchange solution of Example 1 in the outer container of a silver-silver chloride type double junction electrode was used, and the potential response was measured. Table 2 shows the results. In the table, the linear lower limit is about 5×10 ^-4 M,
It is clearly worse than Example 1.

【table】

[Table] Example 2 Next, an example of selectivity in the presence of interfering ions will be shown. Selectivity was measured as follows. That is, the activity of the measurement ion, i, is varied in a solution containing a constant concentration of interfering ions, j, and the potential is measured using the ion-selective coated electrode of the present invention, and the relationship between the potential and the activity is shown. Draw the curve as shown in Figure 4. When a disturbance appears, the potential response becomes constant and forms a horizontal line. The intercept activity a _x for the measured ion, i, is determined from the intersection point B of the extension of this horizontal line and the extension of the Nernst linear response. Interfering ions in solution
The selection constant K ^pot _ij can be found from the activity a _j of , using the following equation. K ^pot _ij = a _x /(a _j ) ^1/n (1) where n is the number of charges on the interfering ion. In order to obtain a _j at this time, a curve showing the relationship between μ and a _i was drawn, f was obtained, and a _j = fCj (2) was calculated. Here, μ is the ionic strength, f is the activity coefficient, and Cj is the concentration of interfering ions, μ=1/2ΣCZ ² (3), logf=AZ ² √ (4). In addition, Z is the charge number of the ion, and A is 0.511 at 25°C.
is a constant, and equation (4) is called the DEBYE−HU¨CKEL equation. The interfering ions measured were SO ^2- ₄ , Cl ^- , NO ^- ₂ ,
They were NO ^- ₃ , I ^- , and ClO4 ^- , and special grade reagents were used for each. The selection constant K ^pot _ij was calculated by measuring the concentration of interfering ions using a mixed solution method. The results are shown in Table 3.

[Table] From the table above, SO ^2- ₄ ＞Cl ^- ＞NO ^- ₂ ＞NO ^- ₃ ＞I ^- ＞ClO ₄ ^-
It can be seen that in this order, it is generally less susceptible to interference.
In other words, the value of K increases as you go down in the table above, indicating that you are subject to greater interference. However, there is no difference in selectivity from conventional liquid film electrodes, and there is no problem in practical use. Example 3 In Example 1, trioctylmethylammonium salt, which is a quaternary ammonium salt, was used as the liquid ion exchanger and decanol was used as the solvent.
Zephyramine, CTMA, as class ammonium salt
A chloride ion coated electrode was prepared in exactly the same manner as in Example 1 using DTMA and decanol as the solvent, and the response characteristics and selection constants K ^pot _Cl-,NO3- for nitrate ions were measured in the same manner as in Example 1. The result is the fifth
It is shown in the figure and Table 4.

[Table] In FIG. 5, 25 is an aliquot, 26 is zephyramine, 27 is CTMA, and 28 is DTMA. The linear response of any electrode used is 1×10 ^-4 ~
The temperature gradient is about 4×10 ⁻² M, the temperature gradient is about 60 mv/aid, and there is not much difference in response characteristics, and the K ^pot for chlorine ions is about 3.3 to 4.5, which is almost the same.

[Brief explanation of drawings]

FIG. 1 shows an ion-selective coated wire electrode of the present invention used in Examples, and FIG. 2 shows a potential measuring device incorporating the ion-selective coated electrode of the present invention used in Examples.
Figure 3 shows the potential difference versus activity curve showing the results of Example 1, and Figure 4 shows the activity a _x in the presence of interfering ions.
FIG. 5 is a potential difference versus activity curve showing the results of Example 3. In the figure, 1 and 3 are copper wires, 4 is a coating film, and 6 is a holder.

Claims (1)

[Claims] 1. Containing a bisphenol A epoxy oligomer and any one of anionic species such as chlorine ion, nitrite ion, iodide ion, and perchlorate ion 4
chloride ion, which consists of a conductive metal covered with a hardening substance mainly composed of a mixture with a class ammonium salt;
Anion-selective coated electrode for either nitrite, iodine, or perchlorate. 2. Add a quaternary ammonium salt to an organic solvent at a concentration of 0.1 to 60% by weight, and then add a strongly dissociated salt containing the ion to be measured, such as chloride, nitrite, iodide, or perchlorate. is added to exchange the quaternary ammonium salt with any of the anions chloride ion, nitrite ion, iodine ion, and perchlorate ion, and then the bisphenol A epoxy oligomer and the curing agent are exchanged after the ion exchange. A method for producing an ion-selective coated electrode, comprising: adding the paste to a product of the above to produce a paste-like substance, coating a conductive metal with the produced paste-like substance, and then curing the produced paste-like substance.