JPS635256A - Uranyl ion selective electrode - Google Patents

Abstract

PURPOSE:To obtain an electrode having a potential difference gradient larger than a Nernst gradient, excellent in ion selectively and concn. response and having good reproducibility, accuracy and durability, by using a specific ion exchange material in a membrane forming base material. CONSTITUTION:In an ion exchange liquid membrane type electrode having an internal comparing electrode and an uranyl ion internal liquid, as a film forming base material, a response membrane treated with an ion exchange material consisting of one or more of an uranyl ion complex of neutral phosphoric ester or neutral phosphoric ester, a diluent excellent in the compatibility with said ion exchange material and a solvent having the compatibility with the film forming base material is used. As the complexing agent forming the ion exchange material, for example, neutral phosphoric ester or neutral phosphorous ester such as trioctyl phosphate or tri-n-butyl phosphite is used. As the diluent, for example, neutral phosphoric ester such as triethyl phosphate is used and, as the compatible solvent, for example, a plasticizer such as phthalic ester is used.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention relates to a uranyl, ion selective electrode with excellent fineness.

<Prior Art> With the recent development of the atomic crab industry, practical research is underway on electrodes for uranyl and ion analysis, which are essential to the atomic crab industry. Various reports have already been made regarding ion-exchange membrane-type uranyl and ion-selective electrodes in which a reference electrode is placed inside and a constant concentration of uranyl is filled between this and the outer cylinder, an ion internal solution is filled.

For example, Dietrich (W. C. Dietrich
) is di-2-ethylhexyl phosphate (D2E
It was reported that a polyvinyl chloride (PVC) membrane containing a complex of HP) and uranyl ions is sensitive to uranyl ions (Technical Progress Report
rtNo, Y1174D, Y-12Developme
nt Division.

Aug, 0ct- (1971)). Manning et al.
1. ) investigated the properties of PVC-based sensitive membranes containing uranyl and ionic complexes of acidic phosphate esters using acidic and neutral phosphonic esters or phosphoric esters as diluents.
Several types of sensitive membranes were obtained, and the gradient of the potential difference with respect to the common logarithmic concentration (hereinafter referred to as the "potential gradient"), which is correlated with the concentration response.
It is called. ) is at most 26 mV/decade
The theoretical potential difference gradient for divalent ions according to the Nernst equation (hereinafter referred to as the "Nernst gradient").
It was smaller (Anal.

etal, ) is D2EHP, tributyl phosphate (T
Properties of PVC-based sensitive membranes of acidic or neutral phosphoric esters, phosphorous esters, or acidic phosphonic esters and uranyl, ionic complexes, using any of BP ) and various phosphonic esters as a diluent, Vol. 1.52 ．． No. 1
3. pp. 2105-2108 (1980)).

In the above reports, Manning et al. and Goldberg et al. did not mix a solvent-friendly agent for PVC.

<Problems to be solved by the invention> Generally, the larger the potential difference gradient of the electrode, the better the performance as a sensor. However, in the above report, a valve chamber position gradient larger than the bivalent Nernst gradient was not obtained;
As a practical uranyl ion selective electrode, it was still unsatisfactory.

As a result of intensive study in view of the current situation, the inventor of the present invention found that
A potential difference gradient larger than the Nernst gradient was realized, and the present invention was completed.

In an ion-exchange liquid membrane type electrode having an internal liquid,
The film forming base material is an ion exchanger made of one or more types of ion complexes such as uranyl of a neutral phosphate ester or a neutral phosphite, a diluent having excellent compatibility with the ion exchanger, and a membrane. Uranyl, characterized in that it uses a sensitive film treated with a solvent that has an affinity with the forming substrate;
This relates to an ion-selective electrode.

The present invention will be explained in detail below.

The uranyl ion selective electrode related to the present invention is an ion exchange liquid model. In other words, an internal comparison electrode inside! Then, a certain concentration of uranyl and ion internal solution are filled between this and the outer cylinder, and the test solution and the internal liquid are uranyl, which is part of the outer cylinder.
They are in contact with an ion exchange liquid membrane sandwiched between them.

In the present invention, a conventionally used general electrode is used as the internal comparison electrode. For example, a silver-silver chloride electrode, a calomel electrode, a mercurous mercurous sulfate electrode, etc. can be used.

If the electrode is fuzzy, a ready-made electrode can be used as appropriate, and the key point of the present invention lies in the uranyl and ion exchange liquid membrane. The performance required for this uranyl ion exchange membrane is the concentration responsiveness, reproducibility, and accuracy of the potential difference compared with an external reference electrode.
For example, it has excellent stability and response linearity), durability, and good ion selectivity.

The membrane-forming substrate used in the present invention is one that can form an ion-exchange liquid membrane. For example, polyvinyl acetate, silicone rubber, cellulose acetate, polyvinyl chloride, epoxy resin, etc. are preferably used. Among these, polyvinyl chloride is particularly preferred.

As the complexing agent for forming the ion exchanger, a neutral phosphoric acid ester or a neutral phosphorous acid ester is used. These esters have alcohol residues each having 2 to 1 carbon atoms.
2 alkyl groups or halogenated alkyl groups are preferably used. Examples of the alkyl group having 2 to 12 carbon atoms or the halogenated alkyl group include ethyl, propyl, butyl, hexyl, octyl, dodecyl, and halogen-substituted products thereof. Among these, an alkyl group having 3 to 8 carbon atoms or a halogenated alkyl group is preferred.

Specific examples include tri-n-butyl phosphite, trioctyl phosphate, tri-chloropropino phosphate, tri-2-chloroethyl phosphate, trichlorobutyl phosphate, and chlorooctyl phosphate. These can be used alone or in combination.

Next, as a diluent having excellent compatibility with the above-mentioned ion exchanger, a neutral phosphoric acid ester can be suitably used. These esters have alcohol residues each having 2 to 1 carbon atoms.
The alkyl group of 2 is preferred. Examples of alkyl groups having 2 to 12 carbon atoms include ethyl, propyl, butyl, hexyl,
Among these, an alkyl group having 3 to 8 carbon atoms is preferred, such as octyl and dodecyl.

Specifically, triethyl phosphate, tripropyl phosphate,
Trihexyl phosphate, trioctyl phosphate, dodecyl phosphate, etc., among which tributyl phosphate is preferably used.

In addition, plasticizers and the like are used as solvents that have affinity with the film-forming substrate (compatible solvents), such as phthalate esters,
Examples include adipic acid ester, sebacic acid ester, and other glycol derivatives. Preferred among these are phthalic acid ester, adipic acid ester and sebacic acid ester.The alcohol residue of these esters is preferably an alkyl group having 2 to 12 carbon atoms.

Examples of the alkyl group having 2 to 12 carbon atoms include ethyl, propyl, butyl, heptyl, isodecyl, and the like. Among these, an alkyl group having 3 to 8 carbon atoms is preferred.

Specifically, dioctyl phthalate (DOP), dioctyl adipate (DOA), dioctyl sepacate (D
O5), etc.

The complexing agent is used in a ratio of 2 to 3 moles, particularly preferably 2.0 to 2.5 moles, per mole of uranyl described later, uranyl nitrate for adjusting the ionic internal solution, and 1 mole of hexahydrate. The mixing ratio of the diluent and the compatible solvent is preferably 3/1 to 2/1 to 1/2 by weight, and the ion exchanger made from the complexing agent and uranyl nitrate has an affinity for the diluent. The mixture with the solvent is mixed in a weight ratio of 1/7 to 1/20, preferably 1/8 to 1/15, and the mixture of these complexing agents, diluents, and compatible solvents is mixed so that the film forming substrate is entirely 20 of
% to 50% by weight, preferably 25% to 35% by weight
It can be used as a film-forming base material by mixing it so that it has the following properties.

In the present invention, the membrane-forming substrate is made of an ion exchanger made of one or more of uranyl and ion complexes of a neutral phosphate ester or a neutral phosphite, and is compatible with the ion exchanger. Any method may be used to obtain a sensitive film prepared with an excellent diluent and a solvent having affinity with the film-forming substrate. For example, there is a method of directly mixing the film-forming base material with the complex, diluent, affinity solvent, etc., and then thermoforming. It can be obtained by dissolving the membrane-forming substrate in a good solvent, mixing it with the ion exchanger, diluent, and affinity solvent, or adding them one after another to make a uniform solution, and then evaporating the good solvent.

The thickness of the film is suitably adjusted to be in the order of 0.1 yan to 0.8 yen, and particularly preferably in the order of 0.2 yan to 0.6 yen.

Incidentally, uranyl and the ion internal solution are prepared from uranyl nitrate and the like by a conventional method.

Hereinafter, embodiments of the present invention will be clarified through Examples.

<Example> (Experimental method) A common experimental method from the production of a sensitive membrane prototype to potential difference measurement is described below.

(1) Preparation of PVC-ion exchanger sensitive membrane 1) Preparation of ion exchanger For 1.00 g of uranyl nitrate hexahydrate, the molar ratio of
Add phosphoric acid ester (or phosphorous ester) so that the amount becomes 3.

This is stirred and shaken well until the solid phase of uranyl nitrate disappears to form a complex. If an aqueous phase is generated in the lower layer at this time, the aqueous phase and oil phase are completely separated using a centrifuge, and then the aqueous phase is removed using a syringe-like device or the like. This is a complex with the remaining viscous sulfur, and 100 TNI of anhydrous sodium sulfate is added twice, centrifuging each time to remove water in the complex.

The ion exchanger (complex) is stored in a dry capped test tube.

2) Preparation of sensitive membrane Ion exchanger 45T! Pg and 400 η of the mixed solvent are weighed into a dry 50-100 g beaker and stirred well. The ratio of diluent and compatible solvent in the mixed solvent was 1:1. However, there are cases where no affinity solvent is used. In that case, of course, add 400 ml of diluent only. To this solution is added a solution 6i in which hard PVC (manufactured by Sumitomo Chemical 5X-DH viscosity average degree of polymerization 2620) 1.751 is dissolved in 60 m of tetrahydrofuran (THF) in advance and stirred well. This solution has a diameter of about 3011! Pour into a dry Petri dish I11, cover with 2-3 sheets of P paper on top,
Place the solvent T in a fume hood horizontally.
The HF is slowly evaporated to dryness. Drying time shall be at least 36 hours.

(2) After assembling and drying the electrode, cut out the PvC sensitive membrane into a disk shape with a diameter of 12 using a cork polar cutter, cutter, etc.
Glue to one end of a PvC tube of 30-40 pharyngeal length. The adhesive used was one in which 7 g of PVC was dissolved in 60 - THF. After the bonded area has sufficiently dried, before using it as an electrode film, the PVC sensitive film is conditioned by immersing it in a to-2M standard concentration solution of uranyl for at least 24 hours, preferably at least 72 hours.

Also, when removing the electrode membrane and storing it, soak it in this standard solution. To assemble the electrode, attach the above-mentioned PVC tube with a film adhered to the tip of the silver-silver chloride reference electrode and fix it with sealing tape so that it does not come off. Note that the space between this electrode film and the reference electrode is filled in advance with a 10 −2 M uranyl nitrate solution (pH=3.0) as an internal solution. Therefore, the structure of this electrode (indicator electrode) can be written as follows.

Ag/AgC4, KCt 11 UO2 (NO3)2.
10-2M (pH=3)i membrane! Internal reference electrode
Internal solution (3) Preparation of uranyl nitrate aqueous solution at standard concentration.
A N solution was prepared and used.

(4) Potential Difference Measurement Method A battery was assembled using the above-mentioned indicator electrode and the same electrode as its internal comparison electrode as an external comparison electrode, and the electromotive force (potential difference) was stirred with a pH/mV meter F- manufactured by Horiba. A heat insulating mat was placed between the beaker and stirrer to prevent the temperature of the liquid from rising. The point at which the potential change in 10 minutes was 1 mV or less was read as the confirmed potential at that concentration.

Comparative Example 1 An ion exchanger according to the above experimental method + 111) was prepared using twice the molar amount (versus uranyl, ion) of DBP and D2EHP, and an electrode used in the preparation of the sensitive membrane in 2) using only TBP in the mixed solvent. The electromotive force of the assembled battery was kept the same in all other respects, and the performance of the sensitive membrane using the diluent was measured. The results are shown in Table 1.

Table 1 From Table 1, Comparative Example 1 is a PVC using dibutyl phosphate (DBP) and D2EHP-uranyl, an ion complex as an ion exchanger and TBP as a diluent, as a representative example of the above literature.
These are the results of a tracing experiment using a sensitive film as a base material. uranyl,
When looking at the potential difference with respect to the ion concentration, a bivalent Nernst gradient may be obtained, and response linearity may also be established within a certain range. The potential difference is stable, shows a constant value within a short time, and does not fluctuate. The experiment was performed from top to bottom of the table.

In other words, measure from the lowest concentration to the highest concentration,
Then, the concentration was changed in the opposite direction and measured. The reproducibility seen from this concentration change is very poor in the case of D2EHP, and 10
It can be seen that uranyl, which is more dilute than 3M, is hardly sensitive to ion concentration.

Example 1 An affinity solvent using tri-n-butyl phosphite as a complexing agent is D
Sensitive membranes of OA or DO5 were prepared and their performance investigated. The results are shown in Table 2.

Table 2 Example 2 Sensitive membranes were prepared using trichloropropinophosphate as a complexing agent and DOP or DOA as an affinity solvent, and performance tests were conducted. The results are shown in Table 3.

Table 3 Example 3 DOP using trioctyl phosphate as a complexing agent.

A sensitive membrane using DOA or DOS as an affinity solvent was prepared and its performance was tested. The results are shown in Table 4.

The results in Tables 2 to 4 are summarized and explained below. Example 1
Figures 3 to 3 show the results of electrodes prepared by the method of the present invention, and correspond to cases where the ion exchangers are tri-n-butyl phosphite, tri-Q lolopropinola phosphate, and a complex of trioctyl phosphate and uranyl nitrate, respectively. T diluent for each
The results are shown using dioctyl phthalate (DOP), dioctyl adipate (DOA), and dioctyl sebacate (DOS) as solvents compatible with BP and PVC substrates. First, it can be seen that the potential difference gradient is clearly larger than in Table 1. The Nernst slope of monovalent ions is approximately 59-60
mV/decade, in the ion exchange liquid membrane according to the present invention, the uranyl ion has an intermediate charge between monovalent and divalent. In addition, response linearity was achieved in the main regions, and the reproducible concentration range was widened.

Comparative Example 2 A sensitive film in which DOP was added as an affinity solvent in Comparative Example 1 was prepared and evaluated. The results are shown in Table 5.

Table 5 Comparative Example 2 shows the results using the same ion exchange liquid membrane as Comparative Example 1 except that DOP as an affinity solvent for the PVC base material was mixed with TBP. 02
It can be seen that in the case of EHP, the reproducibility and response linearity were considerably improved. In the case of DBP, on the contrary, both became worse. What should be noted is the potential difference gradient; in this complex system, the divalent Nernst gradient was not significantly exceeded regardless of whether or not an affinity solvent was added.

Comparative Example 3 A membrane in which the use of an affinity solvent in the preparation of the ion exchange membrane of Example 1 was omitted was fabricated and evaluated.

The results are shown in Table 6.

Table 6 1 Experiment Number ) 12 Comparative Example 4 In the trial production of the ion exchange solution in Example 2, a membrane was prepared and evaluated in which the use of an affinity solvent was stopped.

The results are shown in Table 7.

Table 7 Comparative Example 5 An ion exchange membrane in which the addition of the affinity solvent was stopped in the preparation of the ion exchange membrane of Example 3 was manufactured and evaluated. The results are shown in Table 8.

Table 8 Comparative Example 6 In Examples 1 to 3, the total amount of each diluent was placed in each affinity solvent, and a round electrode was examined. Without exception, they created a sea-island structure by oscillating the potentiometer needle several times per second with an amplitude of several mV. Good films are generally transparent, while poor films are translucent to opaque as shown in Comparative Example 6. These facts suggest that the properties of the co-solvent are very important in order to fully exhibit the electrochemical properties of uranyl and ion complexes. However, the present invention is not limited by the above morphological observations.

ゞ1 ``4 Example 3 is Example 1, Comparative Example 4 is Example 2, and Comparative Example 5 is Example 3. Comparative Example 5 is the ion exchange solution membrane of Example 3 in which the entire amount of the affinity solvent was replaced with TBP as a diluent. These are the experimental results of the exchange liquid membrane.It is clear that the potential difference gradient is close to the divalent Nernst gradient.On the contrary, Comparative Example 6
The following describes the case where each diluent TBP in Examples 1 to 3 was replaced in its entirety with each compatible solvent. Without exception, each experimental membrane electrode in the example exhibits oscillations with an amplitude of several mV at a rate of several cycles per second of the potentiometer needle.

The plasticizers of DOP, DOA, and DO3 are uranyl.

Dissolve the ionic complex. (However, the dissolution rate is slow.)
Nevertheless, unless it is a mixed solvent, the performance as an electrode will be extremely poor.

In this way, we conducted observations using a laser probe analyzer, which allows us to determine which films have good performance and which have poor performance. Although it was not possible to point out any clear difference between the two by optical microscopy and SEM observation, it was found by EPMA observation that the dispersion of the uranyl complex was clearly superior in the good film compared to the poor film.

Example 4 An evaluation was conducted using a uranyl nitrate solution (pH 3) containing a certain amount of zirconyl nitrate in the test solution of Example 1 Experiment No. 3.

The results are shown in Table 9.

Table 9 Example 4 is for the purpose of examining the selectivity of the membrane of Example 1. It is data on the potential difference gradient of a test solution in which zirconyl nitrate was added to a uranyl nitrate solution.

It is shown that in a dilute solution of uranyl with an ion concentration of 10-3M or less, zirconyl is affected even with an ion concentration of 104M.

Example 5 Cerium nitrate (m) was added to the test solution of Example 1 Experiment No. 3.
An evaluation was conducted using a uranyl nitrate solution (pH 8) containing a fixed amount of uranyl nitrate.

The results are shown in Table 10.

Table 10 Example 5 is a sample of Example 1 with cerium nitrate (I
Zirconyl nitrate solution mixed with I[) and cerium ion are important ions both quantitatively and electrochemically active as a composition in nuclear fuel reprocessing waste liquid. The above-mentioned Goldbarb literature states that the selectivity coefficient for cerium (IV) may exceed 3, but the selectivity coefficient in the above example was about 0.01, which is lower than that of conventional membranes. You can see that it doesn't hold back.

Example 6 An experiment was conducted in which the pH of the test solution in Experiment No. 3 of Example 1 was varied. The results are shown in Table 11.

The most significant interfering ion is hydrogen ion. Example 6 shows the results of investigating the influence of hydrogen ion concentration on the membrane of Example 1. As can be seen in the above-mentioned document by Manning et al., control of the hydrogen ion concentration is essential for improving quantitative performance in this type of electrode.

Example 7 A durability test was conducted on the electrode of Experiment No. 3 of Example 1. The test was carried out by lifting an electrode immersed in a 102M solution of uranyl nitrate at pH 3.0 at a predetermined time and performing potential difference measurements as described in the experimental method. Table 12 shows the results.
Shown below. Only the results for the first and longest time are shown here. The test time refers to the time from electrode prototype production.

Table 12 Example 8 The electrode of Experiment No. 4 of Example 1 was subjected to a similar durability test. The results are shown in Table 13.

During a period of 20 days to 1 month, this kind of electrode usually experiences some drift, but it can be seen that there are no icy changes.

Table 13 Example 9 The radiation resistance of the electrode in Experiment No. 5 of Example 2 was investigated. Gamma rays from a Cono I Luto 60 radiation source were used in the radiation exposure experiments. 3 due to dose rate 265x 105R/hr
Irradiation continued for 8 hours.

At that time, the internal solution of the electrode was a 10-2M uranyl nitrate solution with a pH of 0, and the test solution was a 10
” A solution of M was used.

The results are shown in Table 14. The potential difference before and after irradiation is a tricky comparison.

Table 14 Example 10 The electrode of experiment number 8 of Example 3 was irradiated in the same manner as in Example 9. Table 15 shows the potential difference measurement results before and after irradiation.

Table 15 In Examples 9 and 10, the respective membrane properties shifted only within a calibratable range, and the potentiometer pointer did not vibrate.

<Effects of the Invention> The present invention provides a uranyl- and ion-selective electrode with excellent uranyl- and ion-selectivity and concentration responsiveness. This electrode has good reproducibility, accuracy, and durability, and can be said to provide a practical electrode in the atomic crab industry, especially as an electrode for uranyl ion analysis.

Claims (1)

[Claims] Internal reference electrode and uranyl. In an ion-exchange liquid membrane type electrode having an ion internal liquid, the membrane-forming substrate is a neutral phosphate ester or a neutral phosphite ester of uranyl.
It is characterized by using an ion exchanger made of one or more types of ion complexes, a sensitive membrane treated with a diluent having excellent compatibility with the ion exchanger, and a solvent having affinity with the membrane-forming substrate. Uranyl. Ion selective electrode.