JPH0629875B2 - Uranyl ion selective electrode - Google Patents

Description

TECHNICAL FIELD The present invention relates to a uranyl ion-selective electrode. More specifically, the present invention relates to a uranyl ion-selective electrode having a uranyl ion-exchange membrane, which is excellent in concentration responsiveness, reproducibility, accuracy, and durability.

<Prior Art> With the recent development of the nuclear industry, practical research on the uranyl-ion analysis electrode, which is indispensable for the nuclear industry, is underway. Already, various kinds of reports have been made on the ion-exchange liquid membrane type uranyl ion-selective electrode in which the reference electrode is placed inside and the inner solution of the uranyl ion is filled between the outer electrode and the reference electrode.

For example, WC Dietrich reported that a polyvinyl chloride (PVC) membrane containing a complex of di-2-ethylhexyl phosphate (D2EHP) and uranyl ion was sensitive to uranyl ion (Technical Progre
ss Report No.Y1174D, Y-12 Development Division, Aug.
-Oct. (1971)). Meanwhile, DL Manning, et a
l.) is uranyl, an acidic phosphoric acid ester with an acidic or neutral phosphonic acid ester or phosphoric acid ester as a diluent.
The properties of a PVC-based sensitive film containing an ionic complex were investigated, and several kinds of sensitive films were obtained. The gradient of the potential difference correlating with the concentration responsiveness to the common logarithmic concentration (hereinafter referred to as “potential difference gradient”) was obtained. Nernst at 26 mV / decade at best
st) is less than the theoretical potential difference gradient for divalent ions (hereinafter referred to as “Nernst gradient”) (Anal.Che.
m., Vol.40, No.8, pp.1116-1119 (1974)). Furthermore, Goldberg et al. (I. Goldberg et al.) Used D2EHP, tributyl phosphate (TBP), and various phosphonates as diluents, and prepared acidic or neutral phosphates, phosphites, or acidic phosphates. Phosphonate and uranyl
By investigating the properties of the ionic complex PVC-based sensitive membrane, a potential difference gradient close to the Nernst gradient was obtained by the phosphite-based sensitive membrane (Anal. Chem., Vol. 52, No. 13, pp. 2105- twenty one
08 (1980)).

In the above report, neither Manning et al. And Gouldberg et al. Mixed the affinity solvent 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 potential difference gradient larger than the divalent Nernst gradient was not obtained, and it was still unsatisfactory as a practical uranyl ion-selective electrode.

The present inventor, as a result of earnest studies in view of the current situation,
The present invention has been completed by realizing a potential difference gradient larger than the Nernst gradient.

<Means for Solving Problems> The present invention relates to an ion exchange liquid membrane type electrode having an internal reference electrode and a uranyl-ion internal liquid, in which the membrane-forming substrate is a neutral phosphate or a neutral phosphorus. Ion exchanger consisting of one or more uranyl ion complex of acid ester, and a sensitive membrane treated with a diluent excellent in compatibility with the ion exchanger and a solvent having an affinity for the membrane-forming substrate. The present invention relates to a uranyl ion-selective electrode, characterized in that

Hereinafter, the present invention will be specifically described.

The uranyl ion-selective electrode according to the present invention is an ion exchange liquid membrane type. That is, an internal reference electrode is placed inside, and a constant concentration of uranyl ion internal solution is filled between this and the outer tube, and the test solution and the inner solution are uranyl ion which is part of the outer tube.
The ion-exchange liquid membrane is sandwiched in contact.

In the present invention, as the internal reference electrode, a commonly used conventional electrode is used. For example, a silver / silver chloride electrode, a calomel electrode, or a mercury mercuric sulfate electrode can be used.

As the internal reference electrode, for example, in the use in the nuclear industry, an existing electrode can be appropriately used except for the use in a radioactive exposure environment, and the point of the present invention lies in the uranyl ion exchange liquid membrane. The performance required for this uranyl ion exchange liquid membrane is excellent in concentration responsiveness, reproducibility, accuracy (for example, stability and response linearity) of the potential difference due to comparison with an external reference electrode, and durability. It has good ion selectivity.

The membrane-forming substrate used in the present invention is capable of forming an ion exchange liquid membrane. For example, polyvinyl acetate, silicone rubber, cellulose acetate, polyvinyl chloride, epoxy resin and the like are preferably used. Of these, polyvinyl chloride is particularly preferable.

Neutral phosphoric acid ester or neutral phosphorous acid ester is used as a complexing agent forming an ion exchanger. These esters have alcohol residues of 2 to 1 carbon atoms, respectively.
Alkyl groups or halogenated alkyl groups of 2 are preferably used. The alkyl group having 2 to 12 carbon atoms or the halogenated alkyl group is ethyl, propyl, butyl, hexyl, octyl, dodecyl or a halogen substitution product thereof. Among these, an alkyl group having 3 to 8 carbon atoms or a halogenated alkyl group is preferable.

Specifically, tri-n-butyl phosphite, trioctyl phosphate, tri (chloropropyl) phosphate, tri-phosphate
2-chloroethyl, trichlorobutyl phosphate, chlorooctyl phosphate and the like can be mentioned. These can be used alone or in combination.

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

Specifically, triethyl phosphate, tripropyl phosphate,
Examples thereof include trihexyl phosphate, trioctyl phosphate, dodecyl phosphate and the like, of which tributyl phosphate is preferably used.

A plasticizer is used as the solvent having an affinity with the film-forming substrate (affinity solvent), and examples thereof include phthalic acid ester, adipic acid ester, sebacic acid ester, and other glycol derivatives. Among them, phthalic acid ester, adipic acid ester and sebacic acid ester are preferable. In these esters, the alcohol residue 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 and isodecyl. Among these, an alkyl group having 3 to 8 carbon atoms is preferable.

Specifically, dioctyl phthalate (DOP), dioctyl adipate (DOA), dioctyl sebacate (DO
S) and the like.

The complexing agent is uranyl nitrate for adjusting the internal solution of uranyl ion described below. It is used in a ratio of 2 mol to 3 mol, particularly preferably 2.0 mol to 2.5 mol, per 1 mol of hexahydrate. The mixing ratio of the diluent and the affinity solvent is 3/1 to 1/3 by weight, particularly preferably 2/1 to 1/2, and the ion exchanger made from the complexing agent and uranyl nitrate is a diluent. 1/7 to 1/20 by weight with a mixture of a solvent and an affinity solvent, preferably mixed at 1/8 to 1/15,
Further, the mixture of these complexing agents, diluents, and affinity solvents comprises 20% by weight to 50% by weight, preferably 2% by weight, of the whole film-forming substrate.
It is also used as a film-forming substrate by mixing so as to be 5% by weight to 35% by weight.

In the present invention, the membrane-forming substrate is an ion exchanger composed of one or more uranyl ion complexes of neutral phosphate or neutral phosphite, and is compatible with the ion exchanger. Any method may be used to obtain a sensitive film by treating with a solvent having an excellent diluent and a film-forming substrate. For example, there is a method in which a film-forming substrate is directly mixed with a complex, a diluent, an affinity solvent, etc., and then thermoforming, etc., but in general, a solvent having good volatile property such as tetrahydrofuran or cyclohexanone is used. It can be obtained by dissolving the membrane-forming substrate in a solvent, mixing it with the above-mentioned ion exchanger, diluent and affinity solvent, or sequentially adding it to obtain a uniform solution, and then evaporating the good solvent.

The thickness of the film is suitably 0.1 mm to 0.8 mm, particularly preferably 0.
Prepare to be 2 mm to 0.6 mm.

The uranyl ion internal solution is prepared from uranyl nitrate or the like by a general method.

The embodiments of the present invention will be more specifically described below with reference to the examples.

<Example> (Experimental method) A common experimental method from trial production of a sensitive film to measurement of a potential difference will be described below.

(1) Preparation of PVC-Ion Exchanger Sensitive Membrane 1) Preparation of Ion Exchanger To 1.00 g of uranyl nitrate hexahydrate, the molar ratio was 2-3.
The phosphoric acid ester (or phosphite ester) is added so that. This is well stirred and shaken until the solid phase of uranyl nitrate disappears to form a complex. At this time, if an aqueous phase is generated in the lower layer, the aqueous phase and the oil phase are completely separated by a centrifuge, and then the aqueous phase is removed using a syringe or the like. The remaining viscous yellow liquid (oil phase) is a complex of phosphoric acid ester (or phosphorous acid ester) and uranyl nitrate, to which 100 mg of anhydrous sodium sulfate is added twice, and centrifugation is performed each time. Then, the water content in the complex is removed. The ion exchanger (complex) is stored in a dry test tube with a cap.

2) Preparation of Sensitive Membrane Weigh out 45 mg of the ion exchanger and 400 mg of the mixed solvent in a dry 50 to 100 ml beaker so that the weight ratio of the ion exchanger and the mixed solvent is about 1: 9, and stir well.
The ratio of the diluent to the affinity solvent in the mixed solvent was 1: 1.
However, in some cases, no affinity solvent is used. In that case, of course, 400 mg of diluent alone is added. Hard PVC (SX-DH viscosity average degree of polymerization 262 manufactured by Sumitomo Chemical Co., Ltd.
0) Add 6 ml of a solution prepared by dissolving 1.75 g of tetrahydrofuran in 60 ml, and stir well. Pour this solution into a dry petri dish with a diameter of about 30 mm, and put a few papers on it.
Cover with a sheet and let it stand in the draft while keeping it horizontal, and gradually evaporate the solvent, THF, to dry it. The drying time is 36 hours or more.

(2) Assembling the electrode The PVC-sensitive film that has been dried is cut out into a disk shape with a diameter of 12 mm using a cork borer, a cutter, etc.
Glue to one end of a 30-40 mm long PVC tube. The adhesive used was a solution of 7 g of PVC dissolved in 60 ml of THF. After the adhered portion is sufficiently dried, it is soaked for 24 hours or more, preferably for 72 hours or more, so that both sides of the PVC sensitive membrane are in contact with 10 ⁻² M standard uranyl concentration solution before being used for the electrode membrane. Also, when removing and storing the electrode membrane, soak it in this standard solution. To assemble the electrode, attach the above-mentioned PVC tube with the membrane attached to the end of the silver-silver chloride reference electrode and secure it with a sealing tape so that it will not come off. A 10 ⁻² M uranyl nitrate solution (pH = pH) was used as an internal liquid between the electrode film and the reference electrode.
3.0) in advance. Therefore, the structure of this electrode (indicator electrode) can be written as follows.

Ag / AgCl, KCl‖UO ₂ (NO ₃ ) ₂ , 10 ^-2 M (pH = 3) ｜ Membrane ｜ Internal reference electrode Internal solution (3) Preparation of standard uranyl nitrate aqueous solution pH to 3. 0 so as 1N HNO ₃ or 1N KOH solution was adjusted with ^{10 -1, 10 -2, 10 -3} , 10 -4 M
The uranyl ion standard solution was prepared and used.

(4) Potential difference measurement method A battery was assembled using the above-mentioned indicator electrode and the same internal reference electrode as the external reference electrode, and the electromotive force (potential difference) was adjusted to 25 ± 2 ° C using a Horiba pH / mV meter F-8AT type. It was measured at. The beaker containing the sample solution is magnetic. Stir slowly with a stirrer. A heat insulating mat was sandwiched between the beaker and the stirrer to prevent the liquid temperature from rising. The point at which the electrical change within 10 minutes was 1 mV or less was read as the definite potential at that concentration.

Comparative Example 1 Double molar amount of DBP and D2EHP (vs. uranyl.
Ion) was used to prepare the ion exchanger of the above experimental method (1) 1), and only TBP was used as the mixed solvent in 2) The electromotive force of the battery assembled with the electrode used to prepare the sensitive membrane was exactly the same. Then, the performance of the sensitive film by the diluent was measured. The results are shown in Table 1.

Table 1 shows that Comparative Example 1 is a representative example of the literature, and is the result of a trace experiment of a PVC-based sensitive membrane using dibutyl phosphate (DBP) and D2EHP-uranyl ion complex as an ion exchanger and TBP as a diluent. Is. Looking at the potential difference with respect to the uranyl ion concentration, a divalent Nernst gradient may be obtained and the response linearity may 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 the top of the table to the bottom. That is, the concentration was once measured from a low concentration to a high concentration, and then the concentration was changed in the opposite direction. It can be seen that the reproducibility seen from this concentration change is very poor in the case of D2EHP, and that it is hardly sensitive to the uranyl ion concentration dilute below 10 ⁻³ M.

Example 1 The affinity solvent using tri-n-butyl phosphite as a complexing agent was DO.
A sensitive film which is A or DOS was prepared and the performance was examined. The results are shown in Table 2.

Example 2 Tri (chloropropyl) phosphate and complexing agent with DOP or DOA
A sensitive film was prepared by using as an affinity solvent and the performance was tested. The results are shown in Table 3.

Example 3 A sensitive film was prepared by using trioctyl phosphate as a complexing agent and DOP, DOA or DOS as an affinity solvent, and the performance was tested. The results are shown in Table 4.

The results of Tables 2 to 4 are summarized and described below. Example 1
3 to 3 are the results by the electrodes prepared by the method of the present invention, and correspond to the case where the ion exchanger is tri-n-butyl phosphite, tri (chloropropyl) phosphate, and a complex of trioctyl phosphate and uranyl nitrate. To do. Diluent in each
Dioctyl phthalate (DO
P), dioctyl adipate (DOA), and dioctyl sebacate (DOC) are shown. First, it can be seen that the potential difference gradient is obviously larger than that in Table 1. Since the Nernst gradient of monovalent ions is about 59 to 60 mV / decade, the ion exchange liquid membrane according to the present invention has uranyl ions having an intermediate charge between monovalent and divalent. In addition, there was response linearity in the main region, and the reproducible concentration range was widened.

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

Comparative Example 2 is the same result as the ion exchange liquid membrane of Comparative Example 1 except that DOP as an affinity solvent for the PVC base material is mixed with TBP. In the case of D2EHP, it can be seen that the reproducibility and response linearity are improved considerably. On the contrary, in the case of DBP, both were worse. Notable is the potential difference gradient, and this complex system did not significantly exceed the divalent Nernst gradient regardless of the addition of an affinity solvent.

Comparative Example 3 A membrane in which the use of the affinity solvent was stopped in the preparation of the ion exchange membrane of Example 1 was manufactured and evaluated. The results are shown in Table 6.

Comparative Example 4 In the trial production of the ion exchange membrane of Example 2, a membrane in which the use of the affinity solvent was stopped was prepared and evaluated. The results are shown in 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.

Comparative Example 6 An electrode in which the total amount of each diluent in Examples 1 to 3 was replaced with each affinity solvent was examined. Without exception, they show the oscillation of the potentiometer's needle a few mV at several cycles per second with an amplitude of a few mV. All of these films were opaque and the EPMA observation revealed that the uranyl complex was poorly dispersed and formed a sea-island structure. The good film is generally transparent, whereas the bad film is semitransparent to opaque as shown in Comparative Example 6. These facts are Uranil. It is suggested that the characteristics of coexisting solvent are very important to fully exert the electrochemical characteristics of ionic complex. However, the present invention is not limited by the above morphological observation.

Here, Comparative Example 3 is Example 1 and Comparative Example 4 is Example 2
Comparative Example 5 is an experimental result of the ion-exchange liquid membrane in which the affinity solvent was simply replaced with TBP as the diluent in the trial production of the ion-exchange liquid membrane of Example 3. It is clear that the potential difference gradient was close to the divalent Nernst gradient. On the contrary, Comparative Example 6 describes the case where the diluent TBPs in Examples 1 to 3 were all replaced with the respective affinity solvents. The electrodes of each experimental membrane in the examples without exception show the vibration of the potentiometer needle with several mV amplitude at several cycles per second, DO
The plasticizers for P, DOA and DOS are uranyl. Dissolve the ionic complex. (However, the dissolution rate is slow.) Nevertheless, unless it is a mixed solvent, the performance as an electrode is extremely poor.

For the purpose of investigating the reason why a film with good performance and a film with poor performance are formed, an optical microscope, an SEM (scanning electron microscope), and
Observation was performed by EPMA (electron beam microprobe analyzer). Although no clear difference could be pointed out by observation with an optical microscope and SEM, it was found by observation with EPMA that the good film was clearly superior to the bad film in the dispersion of the uranyl complex.

Example 4 Example 1 The test solution of Experiment No. 3 was evaluated using a uranyl nitrate solution (pH 3) containing a certain amount of zirconyl nitrate. The results are shown in Table 9.

Example 4 is the data of the potential difference gradient of the test solution in which zirconyl nitrate was added to the uranyl nitrate solution for the purpose of observing the selectivity of the membrane of Example 1. Uranyl. In a dilute solution with an ion concentration of 10 ⁻³ M or less, zirconyl. It shows that the ion concentration is also affected by 10 ⁻⁴ M.

Example 5 Example 1 Evaluation was carried out using a uranyl nitrate solution (pH 3) containing a certain amount of cerium (III) nitrate in the test solution of Experiment No. 3. The results are shown in Table 10.

In Example 5, the cerium nitrate (II
This is the case where the uranyl nitrate solution mixed with I) was used as the test solution. cerium. The ion is zirconyl. Less affected than ionic. Zirconyl. Ions are also cerium. Ions are also important in terms of composition and electrochemical activity in the composition of the nuclear fuel reprocessing waste liquid. The Goldberg document mentioned above describes that the selectivity coefficient of cerium (IV) may exceed 3 in some cases, but the selectivity coefficient in the above embodiment is 0.
It can be seen that at about 01, it is as good as the conventional film.

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

The most disturbing ion is the hydrogen ion. Example 6 is the result of examining the effect of hydrogen ion concentration on the film of Example 1. As seen in the above-mentioned Manning et al., Control of the hydrogen ion concentration is essential for enhancing quantitativeness 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 conducted by pulling up the electrode immersed in a uranyl nitrate 10 ^-2 M solution having a pH of 3.0 for a predetermined time period and applying the potentiometric measurement described in the experimental method. The results are shown in Table 12. Only the results for the first and the longest time are shown here. The test time is the time from the trial production of the electrode.

Example 8 The electrode of Experiment No. 4 of Example 1 was subjected to the same durability test. The results are shown in Table 13. It can be considered that there is essentially no change in the electrode of this type, which is usually accompanied by a slight forgive drift between 20 days and 1 month.

Example 9 The radiation resistance of the electrode of Experiment No. 5 of Example 2 was examined. Gamma rays with cobalt-60 as the radiation source were used for the exposure experiment. Irradiation was continued for 38 hours at a dose rate of 2.5 × 10 ⁵ R / hr. At that time, the pH of the internal solution of the electrode was 10
^-2 M uranyl nitrate solution, the same as the test solution,
However, a 10 ⁻³ M solution was used. The results are shown in Table 14
Shown in. The potential difference before and after irradiation is compared.

Example 10 The electrode of Experiment No. 8 of Example 3 was irradiated in the same manner as in Example 9. Table 15 shows the results of measuring the potential difference before and after irradiation.

In Examples 9 and 10, the respective film characteristics were shifted only within a calibratable range, and the pointer of the potentiometer did not vibrate.

<Effect of the Invention> According to the present invention, uranyl. Uranyl, which has excellent ion selectivity and concentration response. An ion selective electrode is provided. This electrode has good reproducibility, accuracy and durability, especially uranyl. It can be said that it provides a practical electrode in the nuclear industry as an electrode for ion analysis.

Claims (1)

[Claims] 1. An ion exchange liquid membrane electrode having an internal reference electrode and a uranyl ion internal liquid, wherein the membrane-forming substrate is a uranyl ion complex of neutral phosphate or neutral phosphite. Alternatively, uranyl, characterized by using an ion exchanger composed of two or more kinds, and a sensitive membrane treated with a diluent having excellent compatibility with the ion exchanger and a solvent having an affinity for the membrane-forming substrate. Ion-selective electrode.