JPH0557540B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a uranyl ion exchange liquid membrane type electrode. More specifically, the uranyl ion exchange membrane has excellent concentration response, and has a long lifespan with excellent reproducibility, accuracy, and durability.
This invention relates to an ion-exchange liquid membrane type electrode.

<Prior Art> With the recent development of the nuclear power industry, practical research is underway on electrodes for uranyl ion analysis, which are essential to the nuclear power industry. Various reports have already been made regarding ion-exchange membrane-type uranyl ion-selective electrodes in which a reference electrode is placed inside and an internal solution of launyl ions at a certain concentration is filled between this and the outer cylinder. For example, WCDietrich reported that polyvinyl chloride (PVC) membranes containing a complex of di-2-ethylhexyl phosphate (D2EHP) and uranyl ions were sensitive to uranyl ions (Technical
Progress Report No.Y1174D, Y-12
Development Division, Aug.-Oct. (1971)).
On the other hand, DL Manning et al. investigated the properties of a PVC-based reaction membrane of an acidic phosphate ester-uranyl ion complex using an acidic and neutral phosphonate or phosphate ester as a diluent.
Although several types of membranes with good sensitivity were obtained, the gradient of the potential difference correlated with the concentration response in the common logarithmic concentration (hereinafter simply referred to as the potential difference gradient) was at best
At 26 mV/decade, it was smaller than the theoretical potential difference gradient for divalent ions according to the Nernst equation (hereinafter simply referred to as the Nernst gradient) (Anal.Chem., Vol. 46,
No.．． 8, pp. 1116-1119 (1974)). Additionally, I. Golderg et al. used D2EHP, tributyl phosphate (TBP), and any of a variety of phosphonates as diluents to dilute acidic, neutral phosphates, phosphites, or Complex of acidic phosphonic acid ester and uranyl ion
We investigated the properties of the PVC-based sensitive membrane and obtained a potential difference gradient close to the Nernst gradient using a phosphite-based sensitive membrane (Anal.Chem., Vol.52, pp.2105-
2108 (1980)). Shiga et al. developed a uranyl ion-selective electrode with a large potential difference gradient using a sensitive membrane treated with a diluent that has excellent compatibility with the ion exchanger and a solvent that has affinity with the membrane-forming substrate. (Special Application No. 150559/1983). However, these documents do not include any reports regarding the lifespan of the electrodes, except for one example. In that example, the lifespan is two weeks, which is grossly inadequate.

<Problems to be Solved by the Invention> Generally, the longer the life of an electrode, the more practical it is as a sensor. However, in the above reports, there is almost no report on the lifespan of the electrodes, and it is doubtful whether the standards have been reached as industrial sensors. As shown in the Comparative Examples described below, the lifespan of these products could not be said to be sufficient according to the research conducted by the present inventors.

As a result of intensive studies in view of the current situation, the present inventor has realized an industrially usable uranyl ion electrode that has a lifespan of 5 months or more, and has completed the present invention.

<Means for Solving the Problems> The present invention provides an ion-exchange liquid membrane type electrode in which the membrane-forming substrate is made of one or two uranyl ion complexes of neutral phosphate or neutral phosphite. Using a sensitive membrane treated with three types of reagents: an ion exchanger consisting of more than one species, a diluent with excellent compatibility with the ion exchanger, and a solvent with affinity with the membrane-forming base, a sensitive membrane was used as an internal reference electrode. In a uranyl ion electrode using a silver-silver chloride electrode, LiCl, CsCl, KNO ₃ , Mg are used as internal liquids in contact with the sensitive membrane.
The present invention relates to a uranyl ion exchange liquid membrane electrode characterized in that at least one compound selected from (NO ₃ ) ₂ or Sr(NO ₃ ) ₂ coexists with uranyl ions.

The present invention will be specifically explained below.

The uranyl ion exchange liquid membrane type electrode according to the present invention is of the ion exchange liquid membrane type. That is, an independent internal comparison electrode with a juncture is placed inside;
A certain concentration of uranyl ion internal solution is filled between this and the outer cylinder, and the test solution and the internal liquid are in contact with each other through a launyl ion exchange liquid membrane that is part of the outer cylinder, or the internal comparison described above This is a structure in which the electrode is only the electrode element, and the internal liquid composition for the internal comparison electrode and the internal liquid composition for the uranyl ion electrode, that is, uranyl ions, coexist.

The internal comparison electrode in the present invention is a silver-silver chloride electrode. There is no particular restriction on its structure, and it may be of a single-junction type or a double-junction type. Alternatively, a type may be used in which the partition wall between the internal comparison electrode and the ion exchange membrane is removed, and the electrode element is immersed in the internal liquid as the internal comparison electrode. 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 phosphate ester or a neutral insinite is used. In these esters, each alcohol residue preferably has an alkyl group having 2 to 20 carbon atoms. Examples of alkyl groups having 2 to 20 carbon atoms include ethyl, propyl, butyl, hexyl, octyl, and dodecyl. Of course, the three alcohol residues do not have to be the same.

Specific examples include tri-n-butyl phosphite, trioctyl phosphate, dibutynedecyl phosphite, diethyldecyl phosphite, dibutyldecyl phosphate, diethyldecyl phosphate, and the like. these are,
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. In these esters, each alcohol residue is preferably an alkyl group having 2 to 20 carbon atoms.
As the alkyl group having 2 to 20 carbon atoms, ethyl,
Examples include propyl, butyl, hexyl, octyl, dodecyl, etc. Among them, alkyl groups having 3 to 8 carbon atoms are preferred.

Specifically, triethyl phosphate, tripropylene phosphate, trihexyl phosphate, trioctyl phosphate, tridecyl phosphate, etc. are used, among which tributyl phosphate is preferably used.

In addition, a plasticizer or the like is used as a solvent having affinity with the film forming base (compatible solvent), and examples thereof include phthalic acid ester, adipic acid ester, sebacic acid ester, and other glycol derivatives. Among them, phthalate esters, adipate esters and sebacate esters are preferred. In these esters, each alcohol residue is preferably an alkyl group having 2 to 20 carbon atoms.
As the alkyl group having 2 to 20 carbon atoms, ethyl,
Propyl, butyl, heptyl, dodecyl, etc. Among these, an alkyl group having 3 to 8 carbon atoms is preferred.

Specific examples include dioctyl phthalate (DOP), dioctyl adipate (DOA), dioctyl sebadate (DOS), and the like.

The complexing agent is used in a ratio of 2 mol to 3 mol, particularly preferably 2.0 mol to 2.5 mol, per 1 mol of uranyl nitrate hexahydrate for preparing the uranyl ion internal solution described later. The mixing ratio of the diluent and the compatible solvent is preferably 3/1 to 1/3 by weight,
The ion exchanger made from the complexing agent and uranyl nitrate preferably has a weight ratio of 1/7 to 1/20 to the mixture of the diluent and the compatible solvent.
The mixture of these ion exchangers, diluents, and affinity solvents contains 20% to 50%, preferably 25% by weight of the film-forming base material.
It is used as a film forming base material by mixing it to a concentration of ~35% by weight.

In the present invention, the film forming base material is a neutral phosphate ester or a neutral phosphite ester containing uranine.
Any method can be used to obtain a sensitive membrane by treating an ion exchanger consisting of one or more types of ion complexes, a diluent having excellent compatibility with the ion exchanger, and a solvent having affinity with the membrane-forming substrate. It may be a method. For example, there is a method of directly mixing the film-forming base and the complex, diluent, or compatible solvent and then thermoforming the mixture, but generally speaking, it is better to use a volatile good solvent such as tetrahydrofuran or cyclohexanone that has a dissolving power. It can be obtained by dissolving the membrane-forming base, mixing it with the ion exchanger, diluent, and affinity solvent, or adding them sequentially to form a homogeneous solution, and then evaporating the good solvent.

The thickness of the film is suitably adjusted to 0.1 mm to 0.8 mm, particularly preferably 0.2 mm to 0.6 mm.

The uranyl ion internal solution in contact with the ion exchange membrane, i.e. the internal solution as an indicator electrode, contains uranyl ions and LiCl, CsCl, _KNO3 or
At least one compound selected from Mg(NO ₃ ) ₂ or Sr(NO ₃ ) ₂ (hereinafter referred to as the selected compound) is dissolved. There are no particular restrictions on the concentration. The uranyl ion concentration is preferably close to the concentration of the liquid to be measured, and the selected compound concentration is preferably about 0.1 to 4M.

<Example> (Experimental method) A common experimental method from the production of a sensitive membrane prototype to potential difference measurement is described below. In the present invention, experiments were conducted based on these unless otherwise specified.

(1) Preparation of PVC-ion exchanger sensitive membrane (1) Preparation of ion exchanger Add phosphate ester (or phosphite ester) to 1.00 g of uranyl nitrate hexahydrate at a molar ratio of 2. Add. This is thoroughly stirred and shaken 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 by centrifugation, and then the aqueous phase is removed using a syringe or the like. The remaining viscous yellow liquid (oil phase) is a complex of phosphate ester (or phosphite) and uranyl nitrate, and 100 mg of anhydrous sodium sulfate is added twice to this, centrifuging each time. Separate to remove water in the complex. This ion exchanger (complex) is stored in a dry, capped test tube.

(2) Preparation of sensitive membrane Measure 45 mg of ion exchanger and 40 mg of mixed solvent into a dry 50-100 ml beaker so that the weight ratio of ion exchanger and mixed solvent is about 1:9, and stir well. The ratio of diluent and compatible solvent in the mixed solution was 1:1. However, there are cases where only one of the diluent and the compatible solvent is used. In that case, of course, use 400 mg of the solvent.
Add. In this solution, pre-rigid PVC
(Sumitomo Chemical SX-DH viscosity average degree of polymerization
Add 6 ml of a solution of 1.75 g of 2620) dissolved in 60 ml of tetrahydrofuran (THF) and stir well. Pour this solution into a dry shear dish with a diameter of about 30 mm, cover it with two or three sheets of paper, and leave it in a fume hood in a horizontal position to gradually evaporate the solvent THF and dry it. Drying time should be at least 36 hours.

(2) Electrode assembly Cut out the dried PVC sensitive membrane onto a disk with a diameter of 12 mm using a cork polarizer, cutter, etc., and attach it to one end of a PVC tube with an outer diameter of 12 mm and a length of 30 to 40 mm. 7g of PVC for adhesive
A solution dissolved in 60 ml of THF was used. After the adhesive part has sufficiently dried, before using it as an electrode membrane, soak the PVC sensitive membrane for at least 24 hours, preferably for at least 72 hours, so that both sides are in contact with a 10 ^-2 M uranyl standard concentration solution. Perform shioning. 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 the film adhered to the tip of the silver-silver chloride reference electrode and fix it on a sealing table so that it does not come off. A 10 ^-2 M uranyl nitrate solution (PH=
3.0) must be satisfied 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〓――――〓――――〓 Indicator electrode (3) Standard concentration of uranyl nitrate Preparation of aqueous solution Add 1N HNO ₃ to pH 3.0 before setting the potential difference.
or 10 ^-1 adjusted using 1N KOH solution,
Uranyl ion standard solutions of 10 ^-2 , 10 ^-3 and 10 ^-4 M were prepared and used.

(4) Potential difference measurement method Assemble a battery using the above indicator electrode and the same electrode as its internal comparison electrode as an external comparison electrode, and measure the electromotive force (potential difference) using Horiba's PH/mV system F-
Measurements were made at 25±2° C. by Model 8AT. The beaker containing the sample solution was gently stirred with a magnetic stirrer. An insulating mat was placed between the beaker and the stirrer to prevent the temperature of the liquid from rising. The point at which the potential change in 10 minutes became 1 mV or less was read as the confirmed potential at that concentration.

(5) Lifespan measurement method The indicator electrode, which has been measured using the potentiometric method described above, is lifted from the sample solution and then immersed in the storage solution. The storage solution was the same 10 ^-2 M uranyl standard concentration solution used for conditioning. After a predetermined period of time (approximately 10 days) has passed, measure the potential difference using method (4). Repeat this storage and measurement. Although the potential difference gradient hardly changes over time, the indicated potential begins to oscillate over time. If the amplitude exceeds 2 mV two or more times in a row, the first measurement point is determined to be the end point of the electrode life.

Comparative Example 1 An ion exchanger according to the above experimental method (1) was prepared using twice the molar amount (based on uranyl ions) of DBP or D2EHP, and only TBP was added to the mixed solvent (2).
The life of the electrode used to prepare the sensitive membrane was approximately 15 days.

Comparative Example 1 uses dibutyl phosphate (DBP) as a representative example of experiments by Deitrich and Manning et al.
Or, it is a life test of a PVC-based sensitive membrane using D2EHP-uranyl ion complex as an ion exchanger and TBP as a diluent. This result indicates that the lifetime of their prototype electrode is not sufficient for industrial use.

Comparative Example 2 A sensitive membrane was prepared using tri-n-butyl phosphite as a complexing agent, TBP as a diluent, and DOA or DOS as an affinity solvent, and its life was measured. As a result, we obtained a lifespan of approximately 30 days.

Comparative Example 2 is a representative example of Shiga et al.'s experiment, using tri-n-butyl-uranyl phosphite ion complex as an ion exchanger and TBP as a diluent.
This is a lifespan test of a PVC-based sensitive membrane using DOA or DOS as an affinity solvent. This result shows that although the life of their prototype electrode is better than Comparative Example 1, it is still not sufficient for industrial use.

Example 1 In Comparative Example 2, (2) When assembling the electrode, a 10 ^-2 M uranyl nitrate solution was used as an internal solution between the electrode membrane and the reference electrode so that the pH was 3 and LiCl was 3.33N. A solution prepared in 1 was used. As a result, we obtained a lifespan of over 150 days.

Example 2 In Example 1, instead of LiCl in the internal solution,
A solution containing 2.96M CsCl was used. In this case too
It had a lifespan of over 150 days.

Example 3 In Example 1, instead of LiCl in the internal solution,
Solutions containing the same concentration of KNO ₃ were used. In this case too
It had a lifespan of over 150 days.

Example 4 In Example 1, instead of LiCl in the internal solution,
A solution containing 1.17M Mg( _NO3 ) ₃ was used. In this case as well, the lifespan exceeded 150 days.

Example 5 In Example 1, instead of LiCl in the internal solution,
A solution containing 1.47M Sr(NO ₃ ) ₃ was used. In this case as well, the lifespan exceeded 150 days.

Example 6 In Example 1, an ion exchanger in which diethylindecyl phosphate was used as the complexing agent was used. In this case as well, the lifespan exceeded 150 days.

Example 7 In Example 6, instead of LiCl in the internal solution,
A solution containing 2.96M CsCl was used. In this case too
It had a lifespan of over 150 days.

Example 8 In Example 6, instead of LiCl in the internal solution,
A solution containing 3.33M _KNO3 was used. In this case too
It had a lifespan of over 150 days.

Example 9 In Example 6, the internal solution contained, instead of LiCl,
A solution containing 1.17M Mg( _NO3 ) ₃ was used. In this case as well, the lifespan exceeded 150 days.

Example 10 In Example 1, instead of LiCl in the internal solution,
A solution containing 1.41M Sr(NO ₃ ) ₃ was used. In this case as well, the lifespan exceeded 150 days.

Example 11 In Comparative Example 2, the outer cylinder of the silver-silver chloride internal electrode was removed, leaving only the electrode element, and it was replaced with Example 1.
The life of an indicator electrode immersed in a cylinder containing an ion exchange membrane and an internal solution was measured. As a result, all had a lifespan of more than 150 days.

Example 12 In Comparative Example 2, the outer cylinder of the silver-silver chloride internal electrode was removed, leaving only the electrode element, and the life of the indicator electrode was measured by immersing it in the cylinder containing the ion exchange membrane and internal liquid of Example 2. did. The results showed that all of them had a lifespan of more than 150 days.

Example 13 In Example 1, Sr(NO ₃ ) ₂ was further added to the internal solution.
A solution was used in which the solution was added to saturation. In this case too
It had a lifespan of over 150 days.

Example 14 In Example 6, Sr(NO ₃ ) ₂ was further added to the internal solution.
A solution was used in which the solution was added to saturation. In this case too
It had a lifespan of over 150 days.

Example 15 In Example 11, Sr(NO) ₂ was further added to the internal solution.
A solution was used in which the solution was added to saturation.

In this case as well, the lifespan exceeded 150 days.

Example 16 In Example 1, a solution was used in which CsSO ₄ was further added to the internal solution until it was saturated. In this case also 150
It had a life span of more than a day.

Example 17 In Example 6, a solution was used in which MgCl ₂ was further added to the internal solution until it was saturated. In this case also 150
It had a life span of more than a day.

Comparative Example 3 In Example 1, instead of LiCl in the internal solution,
With 3.33M _LiNO4 , 1.56M _{Li2SO4 , 1.43MCs2SO4 ,} 0.82M
with _CsNO3 , with 1.47M _MgCl2 and with _0.811M MgSO4 and
For each case using 1.05M _SrCl2 ,
We conducted a lifespan test. In either case, the lifespan was 30 days at most.

<Effects of the Invention> The present invention provides a uranyl ion exchange liquid membrane type electrode that has excellent uranyl ion selectivity and concentration responsiveness and has a long life. This electrode has excellent reproducibility,
It has good accuracy and durability, and can be said to provide a practical electrode in the nuclear power industry, especially as an electrode for launyl ion analysis.

Claims (1)

[Claims] 1. In an ion-exchange liquid membrane type electrode, the membrane-forming substrate is an ion exchanger made of one or more uranyl ion complexes of a neutral phosphate ester or a neutral phosphite, and an ion exchanger that is compatible with the ion exchanger. In a uranyl ion electrode that uses a silver-silver chloride electrode as an internal reference electrode, the sensitive membrane is LiCl, CsCl, KNO ₃ , Mg
A uranyl ion exchange liquid membrane electrode characterized in that at least one compound selected from (NO ₃ ) ₂ or Sr(NO ₃ ) ₂ coexists with uranyl ions.