JP2022169988A - Bicarbonate ion-sensitive membrane - Google Patents

Abstract

To provide a bicarbonate ion-sensitive membrane which features high bicarbonate ion selectivity, less interference by amine compounds, and high reproducibility during manufacture.SOLUTION: A bicarbonate ion-sensitive membrane is provided, containing molecules having cations and anions at a ratio of 1:1 in one molecule dispersed in a plasticizer, the cations being onium cations, and the like, such as ammonium cations and phosphonium cations, and anions being carboxylate anions, sulfonate anions, phosphate anions, or the like.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a bicarbonate ion-sensitive membrane useful in an ion-selective electrode for ion concentration measurement.

In recent years, many attempts have been made to quantify ions contained in biological fluids such as blood and urine by applying ion-selective electrodes for medical purposes. Based on the fact that the concentration of specific ions in biological fluids is closely related to metabolic reactions in the living body, this method diagnoses various diseases by measuring the concentration of the ions. Currently, ion-selective electrodes are applied to measure the concentrations of sodium ions, potassium ions, and chloride ions (hereinafter also referred to as chloride ions) in biological fluids, and these ion concentrations can be measured simply and quickly. there is In general, an ion-selective electrode is, as shown in FIG. 13 and an internal reference electrode 14 are provided.

FIG. 2 shows a representative structure of an ion measuring device for measuring the activity of ions in a solution using the ion-selective electrode. That is, the ion-selective electrode 21 is immersed in the sample solution 23 together with the salt bridge 22, and the other end of the salt bridge is immersed together with the reference electrode 24 in a solution 26 such as a saturated potassium chloride solution. The potential difference between both electrodes is read by an electrometer 25, and the ion activity of a specific ion species in the sample solution can be obtained from the potential difference. The performance of the ion-selective electrode used in such an ion measurement device is greatly influenced by the performance of the ion-sensitive membrane used therein. Therefore, various ion-sensitive membranes have been developed over many years.

As one of the important ions present in biological fluids, particularly blood, concentration measurement of chloride ions is commonly performed. However, for the measurement of bicarbonate ion, which has the second highest concentration of anions in blood after chloride ion, there is a quantitative method (enzymatic method) based on a color reaction in a solution using an enzyme, but it is not possible to measure it directly with a sensor. No way to measure. Therefore, at present, it is obtained from the partial pressure of carbon dioxide (PCO ₂ ) and pH by the following formula (blood gas measurement method).
pH=6.1+log{[HCO ₃ ⁻ ]/0.03·PCO ₂ }
The enzymatic method is a method in which a blood sample is added to a solution reagent and the amount of dye produced is measured with a spectrophotometer when the solution is maintained at a constant temperature, and it takes a long time of several minutes. The blood gas measurement method takes about 30 to 60 seconds for measurement. In addition, since it is necessary to apply a measurement method different from the sodium ion, potassium ion, and chloride ion selective electrodes described above, it was necessary to measure the bicarbonate ion concentration using a device with a different mechanism.

In general, ion-selective electrodes can shorten the time required for measurement to a few seconds. It is also possible to measure Because of these advantages, various anion-sensitive membranes have been proposed as anion-sensitive membranes for selectively detecting bicarbonate ions.

For example, (a) a polymer such as polyvinyl chloride is mixed with a fat-soluble cation salt such as a quaternary ammonium salt, a trifluoroacetophenone derivative such as trifluoroacetyl-p-alkylbenzene, and a plasticizer to form a film. (b) A polymer such as polyvinyl chloride is mixed with an organic tin compound such as trioctyltin chloride, a plasticizer, and optionally a trifluoroacetophenone derivative such as trifluoroacetyl-p-alkylbenzene. and (c) a film obtained by forming a composition containing an aromatic boronic acid diester compound and a fat-soluble cation.

Examples of the ion-selective electrode using the anion-sensitive membrane of type (a) include the electrode disclosed by Wise et al. (see Patent Document 1) and the electrode reported by Greenberg et al. is mentioned.

Examples of the ion-selective electrode using the anion-sensitive membrane of type (b) above include the electrode reported by Auch et al. (see Non-Patent Document 2) and the electrode disclosed by Ushizawa et al. be done.

As an ion-selective electrode using an anion-sensitive membrane of the type (c), there is an electrode disclosed by Idori (see Patent Documents 3 and 4).

U.S. Pat. No. 3,723,281 JP-A-4-204368 WO 2000/07004 JP-A-11-323155

J. Greenberget, et al. , Anal. Chim. Acta. , 1982, 141, p57-64 U.S.A. Oesch, et al. , J. Chem. Soc, Faraday Trans. 1986, 1, 82, p1179-1186

However, although these prior arts have been presented, it is used for an anion sensor for clinical tests that has sufficient selectivity, a fast response speed, practical durability, and manufacturing reproducibility. At present, there is no anion-sensitive membrane.

The ion-selective electrode using the anion-sensitive membrane of type (a) above has high selectivity for lipid-soluble ions such as nitrate ions and thiocyanate ions, and the selectivity for bicarbonate ions is not good. Are known. It is known that an ion-selective electrode using an anion-sensitive membrane of type (b) above has a higher selectivity for chloride ions than for bicarbonate ions because the membrane contains an organic tin compound. This is because the tin atom has an affinity for halogen ions, and therefore responds to chloride ions as well. Further, the ion-selective electrode using the anion-sensitive membrane of type (c) above has good selectivity for various ions, but an aromatic boronic acid diester compound is included in the measurement buffer solution. As a result, it is known that a sufficient potential response cannot be obtained for bicarbonate ions. Furthermore, in any type of anion-sensitive membrane, the ratio of multiple compounds added to selectively detect anions greatly affects ion selectivity, resulting in low reproducibility during production. As a result, it is not possible to stably supply the product to the market. Here, the addition ratio of the compound for selectively detecting anions is the ratio of the quaternary ammonium salt and the trifluoroacetophenone derivative in the case of type (a), and the organic tin in the case of type (b). In the case of the type (c), it means the ratio between the compound and the trifluoroacetophenone derivative, and in the case of the type (c), the ratio between the aromatic boronic acid diester and the fat-soluble cation. Furthermore, in general, an ion selective electrode is stored in an aqueous solution containing about 0 to 1 mol/L of an inorganic salt in order to maintain its potential stability. It is also known that sensitivity performance deteriorates during storage. This is because, in the types (a) and (c), fat-soluble cations are eluted into the aqueous solution, and the intramembrane concentration thereof is reduced. This is because, in the type (b), the organic tin compound contained in the anion sensitive film gradually decomposes upon contact with the aqueous solution. That is, the storage stability is poor.

That is, ion-selective electrodes using conventional anion-sensitive membranes have low selectivity for bicarbonate ions, interference with amine compounds contained in buffers and the like, low reproducibility of performance during production, In addition, poor storage stability in water has been a problem.

The present inventors have made intensive studies to develop a bicarbonate ion-sensitive membrane that can solve such problems. As a result, a bicarbonate ion-sensitive membrane characterized by containing a molecule having a cation and an anion in a ratio of 1:1 per molecule in a form dispersed in a plasticizer was obtained as an anion-sensitive membrane. The inventors have found that the above problems can be solved by using them, and have completed the present invention.

That is, the bicarbonate ion-sensitive membrane of the present invention is characterized by containing molecules having cations and anions at a ratio of 1:1 per molecule in a form dispersed in a plasticizer. membrane.

The bicarbonate ion-sensitive membrane of the present invention uses a molecule having cations and anions in a ratio of 1:1 per molecule as an ion-sensitive substance. As a result, the problem that the selectivity to bicarbonate ion is expressed by adding a plurality of compounds, which has been a problem in the prior art, but the ratio of them varies depending on the part of the membrane, is solved. It has the feature that the performance as a film does not vary from film to film.

Furthermore, the bicarbonate ion-sensitive membrane of the present invention also has a feature of high selectivity to bicarbonate ions. Although the response mechanism is not clear, it is presumed as follows. That is, since the cations and anions are close to each other in the molecule of the ion-sensitive substance, the anions in the measurement sample are subjected to electric attraction and electric repulsion at the same time. When a molecule having a cation and an anion in one molecule of the present invention is used, the sum of the electric attractive force and the electric repulsive force of the bicarbonate ion is locally applied to other ions, although the reason is not clear. It is presumed that this is because the attractive force is stronger than

Furthermore, the bicarbonate ion-sensitive membrane of the present invention has a low solubility of the ion-sensitive substance in water and does not decompose due to reaction with water, so that it has good storage stability when stored in water.

By using the bicarbonate ion-sensitive membrane of the present invention, the effect of interfering ions such as chloride ions and amines, which are problematic in the field of clinical testing, is small, and a large amount of samples can be measured in a short time. It is possible to provide an ion-selective electrode with high reproducibility of the sensitivity performance of each membrane.

Diagram showing an ion-selective electrode Diagram showing a typical structure of an ion measurement device

The present invention includes the following items.
Item 1. A bicarbonate ion-sensitive membrane characterized by containing molecules having cations and anions in a ratio of 1:1 per molecule in a form dispersed in a plasticizer.
Item 2. The bicarbonate ion sensitive membrane according to Item 1, wherein the cation is an onium cation.
Item 3. The bicarbonate ion-sensitive membrane according to Item 2, wherein the onium cation is an ammonium cation, a phosphonium cation, an imidazolium cation, or a pyridinium cation.
Item 4. The bicarbonate ion-sensitive membrane according to any one of Items 1 to 3, wherein the anion is a borate anion, a carboxylate anion, a sulfonate anion, a phosphate anion, or a phenoxide anion.
Item 5. The bicarbonate ion-sensitive membrane according to any one of Items 1 to 4, wherein the bicarbonate ion-sensitive membrane contains a polymer, and the polymer contains molecules dispersed in the plasticizer. film.

The details of the present invention are described below, but the present invention is not limited to these descriptions. Molecules having cations and anions in one molecule of the present invention are sometimes referred to herein as zwitterionic molecules. A cation in a zwitterionic molecule is sometimes called an intramolecular cation, and an anion is sometimes called an intramolecular anion. Although one atom has a charge, in the present invention, a unit containing this (a structurally united partial structure of an organic compound is called a unit) is defined as an intramolecular cation or an intramolecular anion. handle. Each is described in detail below.
(Intramolecular cation)
A suitable example of the intramolecular cation used in the present invention is onium cathin, but it is not limited thereto. An onium cation is a group containing a nitrogen group element (group 15 element) such as nitrogen, phosphorus, arsenic, etc., and having positively charged atoms such as nitrogen, phosphorus, arsenic, and the like.

General structures of onium cations include (1) a nitrogen group element such as a nitrogen atom or a phosphorus atom to which 1 to 4 hydrophobic organic groups are bonded, and (2) a nitrogen group element that is an aromatic constituent element. and the like, but are not limited to these. Here, the hydrophobic organic group is preferably a group having carbon and hydrogen as main constituents and imparting water-insolubility to the compound having this group. Specific examples of onium cations that are commonly used include ammonium cations, phosphonium cations, imidazolium cations and pyridinium cations.

As an example of the above (1), an ammonium cation, which is an onium cation having a nitrogen atom, will be described below. Preferred examples include compounds in which the hydrophobic organic group is an alkyl group or an alkylene group, and 1 to 3 alkyl groups are bonded to the nitrogen atom. An atom that bonds to an adjacent unit may be the nitrogen atom or an alkylene group bonded to the nitrogen atom. A hydrogen ion (H ⁺ ) is added to the remaining binding site to form an ammonium cation. An alkyl or alkylene group can be straight or branched. It may also be a cyclic saturated hydrocarbon such as a pyrrolidine ring. Furthermore, a group in which part of these alkyl or alkylene groups is replaced with a double bond or triple bond, or a part of the alkyl or alkylene group is modified with a functional group such as a hydroxyl group, a keto group, or an ester group. may be a group. Examples of commonly used structures are as follows.

（ここで、Ｒ_１はアルキル基を表し、Ｒ_２アルキレン基を表し、Ｒ_３は三価の炭化水素基を表す。また、Ｒ_４は炭素数４以上のアルキレン基、Ｒ_５は炭素数３以上のアルキレン基を、破線は隣接ユニットと結合することを表す。）

(Here, R ₁ represents an alkyl group, R ₂ represents an alkylene group, R ₃ represents a trivalent hydrocarbon group, R ₄ represents an alkylene group having 4 or more carbon atoms, R ₅ represents a A dashed line indicates that the above alkylene group is bound to an adjacent unit.)

Furthermore, the hydrophobic organic group may be a group containing an aromatic ring. A hydrophobic organic group may be a single aromatic ring. In addition, the hydrophobic organic group includes an alkyl group, and an aromatic ring may be included in the middle of the alkyl group, or one or more hydrogen atoms of the alkyl group may be substituted with an aromatic ring. Specific examples of aromatic rings include benzene, naphthalene, anthracene, and the like. Of course, these aromatic rings may contain alkyl groups, halogeno groups, nitro groups and the like.

Examples of the case where the hydrophobic organic group is a cyclic saturated hydrocarbon are further described below. That is, a non-aromatic 4-membered ring ammonium cation containing a nitrogen atom such as an azetidinium ion, a pyrrolidinium ion, a non-aromatic five-membered ring ammonium cation containing a nitrogen group element such as an oxazolinium cation, piperidinium cations, non-aromatic six-membered ring ammonium cations containing nitrogen atoms such as piperazinium cations, homopiperazinium ions, non-aromatic seven-membered ring ammonium cations containing nitrogen atoms such as homopiperazinium ions, azepanium ions, etc. Examples include:

A plurality of hydrophobic organic groups bonded to a nitrogen group element may have the same structure or different structures.

Preferable examples of the molecular cations of the present invention are as follows, since the raw materials thereof are readily available and synthesis is easy. That is, trimethylammonium cation, triethylammonium cation, tripropylammonium cation, tributylammonium cation, trioctylammonium, dimethyloctylammonium cation, dimethyldecylammonium cation, dimethyldodecylammonium cation, dimethyltetradecylammonium cation, dimethylhexadecylammonium cation, Examples include trialkylammonium cations such as dimethyloctadecylammonium cation. Particularly preferred examples are tripropylammonium cation, tributylammonium cation, trioctylammonium, dimethyloctylammonium cation, dimethyldecylammonium cation, dimethyldodecylammonium cation, dimethyltetradecylammonium cation, and dimethylhexamonium cation because of their high hydrophobicity. Decylammonium cations and dimethyloctadecylammonium cations can be mentioned.
(Intramolecular anion)
Any kind of intramolecular anion can be used without limitation as long as it can be incorporated into the molecule.

Non-limiting examples include borate anions, carboxylate anions, sulfonate anions, phosphate anions, phenoxide anions, imide anions, and sulfamoyl anions. Also, these ions may be bound to any organic group. Among these, borate anions, carboxylate anions, sulfonate anions, phosphate anions, and phenoxide anions are preferably used because they can exist stably. Phosphate anions and sulfonate anions are more preferably used because of their ease of synthesis and high chemical stability. In the zwitterionic molecule, the carboxylate anion (—COO ⁻ ), sulfonate anion (—SO ₃ ⁻ ), and phenoxide anion (—(C ₆ H ₄ )—O ⁻ ) have the structure It has upper constraints and needs to be located at the end of the molecule.

On the one hand the phosphate anion,

（式中の破線は隣接ユニットと結合することを表す）
ボレートアニオン、

(The dashed line in the formula indicates that it connects with the adjacent unit.)
borate anion,

（ここで、Ｒ_６、Ｒ_７、Ｒ_８、Ｒ_９、は、独立して疎水性有機基を表し、破線は隣接ユニットと結合することを表す。なお、分子内アニオンの疎水性有機基は、分子内カチオンの疎水性有機基と同義である）
イミドアニオン、

(Here, R ₆ , R ₇ , R ₈ , and R ₉ each independently represent a hydrophobic organic group, and the dashed line represents binding to the adjacent unit. The hydrophobic organic group of the intramolecular anion is , is synonymous with the hydrophobic organic group of the intramolecular cation)
imide anion,

（ここで、Ｒ_６、Ｒ_８は、独立して疎水性有機基を表し、破線は隣接ユニットと結合することを表す）
は、分子の構造の途中にも位置することができる。
（両性イオン分子）
本発明の両性イオン分子は、一分子中に、１：１でカチオンおよびアニオンを有する分子である。ここで、分子内カチオンと分子内アニオンの比率が１：１とは、０．９５：１．００から１．００：０．９５の範囲、好ましくは、０．９８：１．００から１．００：０．９８の範囲ということである。よって、疎水性カチオンと疎水性アニオンの塩を用いる従来技術で問題となっていた、不純物イオンの共存によりカチオンとアニオンの比率が膜の部位によって異なることを原因として、重炭酸選択性電極膜としての性能がばらつくことは無い、という特長を有する。

(Here, R ₆ and R ₈ independently represent a hydrophobic organic group, and the dashed line represents bonding with the adjacent unit)
can also be located in the middle of the structure of the molecule.
(zwitterionic molecule)
The zwitterionic molecule of the present invention is a molecule having a 1:1 ratio of cations and anions in one molecule. Here, the ratio of intramolecular cations to intramolecular anions of 1:1 means a range of 0.95:1.00 to 1.00:0.95, preferably 0.98:1.00 to 1.00:0.95. 00:0.98 range. Therefore, the ratio of cations and anions varies depending on the site of the membrane due to the coexistence of impurity ions, which has been a problem in the conventional technology using salts of hydrophobic cations and hydrophobic anions. It has the advantage that there is no variation in the performance of

An example of a general structure of a zwitterionic molecule of the invention is shown below.

X1 ⁺ - Y1 ^-

RA- X1 ⁺ - Y1 ^-

X1 ⁺ - Y2 ^{- -} RB

RA- X2 ⁺ - Y2 ^{- -} RB

X1 ⁺ - RE - Y2 ^{- -} RA

RA- X2 ⁺ - RE- Y2 ^{- -} RB

X1 ⁺ - Y2 ^- - X2 ⁺ - Y1 ^-

X1 ⁺ - RE- Y2 ^- - RF- X2 ⁺ - RG- Y1 ^-

RA - X2 ⁺ - RE - Y2 ^- - RF - X2 ⁺ - RG - Y2 ^- - RB

（Ｘ１^＋は一価の分子内カチオン、Ｘ２^＋は二価の分子内カチオン、Ｙ１^－は一価の分子内アニオン、Ｙ２^－は二価の分子内アニオン、ＲＡ、ＲＢ、ＲＣ、ＲＤは一価の有機基、ＲＥ、ＲＦ、ＲＧは二価の有機基、Ｒは四価の有機基を表す。ここで、有機基としては、一般的には炭素数１~２２のアルキル基またはアルキレン基が用いられる。該アルキル基またはアルキレン基は分岐していてもよいし、一部が２重結合に置き換わっていてもよいし、水素原子の一部がヒドロキシル基、ケト基、エステル基等により置換されていてもよい。また、途中に酸素原子によるエーテル結合を含んでもよい。場合によっては、該アルキル基またはアルキレン基の結合の途中に芳香環を含んでいてもよい。該芳香環はアルキル基、ハロゲノ基、ニトロ基等が好ましい。）

(X1 ⁺ is a monovalent intramolecular cation, X2 ⁺ is a divalent intramolecular cation, Y1 ^- is a monovalent intramolecular anion, Y2 ^- is a divalent intramolecular anion, RA, RB, RC, RD are single A valent organic group, RE, RF, and RG represent a divalent organic group, and R represents a tetravalent organic group, where the organic group is generally an alkyl group or an alkylene group having 1 to 22 carbon atoms. The alkyl group or alkylene group may be branched, a portion thereof may be replaced with a double bond, or a portion of the hydrogen atoms may be substituted with a hydroxyl group, a keto group, an ester group, or the like. In addition, an ether bond formed by an oxygen atom may be included in the middle.In some cases, an aromatic ring may be included in the bond of the alkyl group or the alkylene group.The aromatic ring is an alkyl group. , a halogeno group, a nitro group, etc. are preferred.)

As the zwitterionic molecule of the present invention, one having low solubility in water is preferably used. Specifically, when the solubility in water at 25° C. is in the range of 0 to 0.01 g/100 ml, the elution of zwitterion molecules from the bicarbonate ion sensitive membrane of the present invention is suppressed, resulting in stable potential response. It is suitable for giving

The zwitterionic molecule of the present invention is readily available and has a low solubility in water, so that it gives a stable potential as follows. The description in parentheses following the compound name is the solubility in water at 25° C. (unit: g/100 ml).

An example containing an ammonium cation and a carboxylate anion in one molecule is 2-[[2-(methacryloyloxy)ethyl]dimethylammonio]acetate (0.01), which contains an ammonium cation and a sulfonate anion in one molecule. Examples include dimethyl(n-octyl)(3-sulfopropyl)ammonium hydroxide (0.00), decyldimethyl(3-sulfopropyl)ammonium hydroxide (0.00), tetradecyldimethyl(3-sulfo propyl)ammonium hydroxide (0.00), octadecyldimethyl(3-sulfopropyl)ammonium hydroxide (0.00) and the like. Further, examples containing ammonium cation and phosphate anion in one molecule include 2-(methacryloyloxy)ethyl phosphate 2-(trimethylammonio)ethyl (0.00), 1,2-dipalmitoyl-glycero-3 -phosphocholine (0.00), 1,2-distearoyl-glycero-3-phosphocholine (0.00), 1,2-dilinoleoyl-glycero-3-phosphocholine (0.00), etc. are ammonium cations and imide anions (Methoxycarbonylsulfamoyl)triethylammonium hydroxide (0.00) is an example containing in one molecule.
(Plasticizer)
In the present invention, the plasticizer refers to a low-volatility organic solvent in which the zwitterionic molecule of the present invention can be dispersed. In general, those that act as plasticizers for polyvinyl chloride are preferably used.

Here, the low volatility means that the vapor pressure is 0.1 Pa or less at 25°C, preferably 0.05 Pa or less at 25°C. By using a low-volatility organic solvent, the plasticizer is less likely to decrease or disappear due to volatilization. Therefore, the bicarbonate ion-sensitive membrane of the present invention can be stored and used for a long period of time.

The bicarbonate ion-sensitive membrane of the present invention is measured while in contact with the solution to be measured. Since an aqueous solution is mainly used as an object to be measured, it is desirable that the plasticizer has low solubility in water so that the bicarbonate ion-sensitive membrane does not dissolve and disappear during measurement. Specifically, it is desirable that the weight of the soluble plasticizer is less than 0.01 g with respect to 100 g of water.

The amphoteric ion molecule is dispersed in the range of 0.001 mmol to 10 mol with respect to 100 ml of the plasticizer.

There is a minimum value for the concentration at which the amphoteric ion molecules are dispersed in the plasticizer, because the smaller the concentration, the lower the sensitivity when used as a bicarbonate ion-sensitive membrane and the larger the measurement error. Specific values vary depending on the plasticizer used and the type of zwitterionic molecule. A general value thereof is 0.5 mmol or more, preferably 1 mmol or more, more preferably 2 mmol or more per 100 ml of plasticizer. The upper limit of the concentration to be dispersed is not particularly limited as long as the plasticizer in which the amphoteric ion molecules are dispersed can maintain physical strength sufficient to form a film-like material.

Also, as described below, in the present invention, a polymer can be used to impart physical strength to the bicarbonate ion sensitive membrane. In that case, it is desirable that the plasticizer has an affinity with the polymer. Here, affinity means that the polymer can be dispersed in the plasticizer, or that the contact angle of the plasticizer on the polymer surface is less than 90 degrees.

Specific examples of plasticizers include organic esters and organic ethers.

Examples of organic esters include dibutyl adipate, dioctyl adipate, dibutyl sebacate, dioctyl sebacate (hereinafter sometimes abbreviated as DOS), dibutyl phthalate, diethylhexyl phthalate, dioctyl phthalate, and dioctyl phosphate. be done. Organic ethers include o-nitrophenyl octyl ether (hereinafter sometimes abbreviated as NPOE), p-nitrophenyl dodecyl ether, diphenyl ether and the like. Among them, dioctyl sebacate, ethylhexyl phthalate, dioctyl phthalate, Preferred examples include dioctyl phosphate, o-nitrophenyl octyl ether and p-nitrophenyl dodecyl ether. Among these, dioctyl sebacate and o-nitrophenyloctyl ether are particularly preferred because of their good ion selectivity when used as bicarbonate sensitive membranes.

The bicarbonate ion-sensitive membrane of the present invention is used as a planar membrane. One surface of the plasticizer in which the zwitterionic molecules of the present invention are dispersed is brought into contact with the sample solution to be measured, and the other surface is brought into contact with the internal electrolyte. The ion-selective electrode produced using the bicarbonate ion-sensitive membrane of the present invention is desirably capable of measuring a plurality of sample solutions from the viewpoint of economy. That is, one side of the bicarbonate ion-sensitive membrane of the present invention is immersed in the first sample solution, washed with water, and then immersed in the second sample solution. Therefore, deformation and detachment may occur due to water flow or the like. Therefore, from the viewpoint of durability, it is preferable to use a plasticizer with low solubility in water and high viscosity. From this point of view, butyl adipate, butyl sebacate, etc. are preferable as plasticizers having an alkyl group of 4 or more carbon atoms, and more preferably dioctyl adipate and sebacic acid as plasticizers having an alkyl group of 8 or more carbon atoms. Dioctyl, dioctyl phthalate, o-nitrophenyl octyl ether, dioctyl phosphate, p-nitrophenyl dodecyl ether and the like are used.
(Polymer)
In the present invention, a polymer may be used to impart physical strength to the bicarbonate ion-sensitive membrane.

In this case, the polymer is further dispersed in the plasticizer in which the amphoteric ion molecules are dispersed. The bicarbonate ion-sensitive membrane formed in such a state is less likely to be ruptured due to tensile stress and has improved durability, so that it is preferably used.

The concentration of the polymer in the plasticizer can be set arbitrarily without any particular limitation, but it is common to set the strength so that the bicarbonate ion-sensitive membrane of the present invention does not cause practical difficulties. . A general range of the mass ratio of plasticizer to polymer is 0.01:100 to 1000:100, and a preferred range is 10:100 to 500:100. As a specific example, when dioctyl phthalate is used as the plasticizer and polyvinyl chloride is used as the polymer, the mass ratio of dioctyl phthalate and polyvinyl chloride is 0.1:100 to 1000: A range of 100 is used. A preferred range is 10:100 to 500:100, and a more preferred range is 40:100 to 300:100.

If the ratio of the plasticizer is small, the amount of amphoteric ion molecules contained in the membrane is small, so that the sensitivity when used as a bicarbonate ion sensitive membrane is low. In addition, when the ratio of the plasticizer is large, the physical strength of the film is reduced, so that the life of the bicarbonate ion-sensitive film may be shortened due to deformation, tearing, and the like.

When the polymer is difficult to disperse in the plasticizer, the bicarbonate of the present invention can be obtained by forming a porous film of the polymer in advance and impregnating the porous film with a plasticizer in which zwitterion molecules are dispersed. An ion sensitive membrane can be made.

Examples of polymers that can be suitably used include generally known linear polymers. That is, to give specific examples, polymers obtained from a single monomer such as polystyrene, polymethyl methacrylate, polyethyl methacrylate, polyvinyl chloride, methyl methacrylate-styrene copolymer, ethylene-styrene Polymers obtained by copolymerizing multiple monomers such as copolymers, styrene-ethylene-styrene block copolymers, styrene-ethylene-butylene-styrene block copolymers, and styrene-ethylene-propylene-styrene block copolymers. Amalgamation can be mentioned.

The degree of polymerization of these polymers can be determined in consideration of the strength required for the film to be obtained and the dispersibility in the plasticizer. If the degree of polymerization is small, the strength of the film will be low, but it will be easier to disperse in the plasticizer. The higher the degree of polymerization, the higher the strength of the film, but the more difficult it is to disperse in the plasticizer. Therefore, the preferred range of the degree of polymerization varies depending on the combination of each polymer and plasticizer, so a specific preferred range cannot be indicated. In general, those having a degree of polymerization in the range of 100 to 1,000 are preferably used in many cases.
(Method for forming bicarbonate sensitive film)
As a method for incorporating amphoteric ion molecules in a plasticizer in the form of a bicarbonate-sensitive film in a dispersed form, known methods can be used without any limitation. A common method is to put amphoteric ion molecules into a plasticizer and stir them. When the speed of dispersing the amphoteric ion molecules in the plasticizer is slow, a method of dissolving or dispersing the amphoteric ion molecules and the plasticizer in an organic solvent and then removing the solvent by vacuum distillation or the like can also be used. .

A plasticizer in which amphoteric ion molecules are dispersed can be used as the bicarbonate ion sensitive membrane of the present invention by forming a liquid film in the hollow tube.

To give an example of its construction method, a hollow tube having an inner diameter of about 1 to 2 mm is brought into contact with a plasticizer in which amphoteric ionic molecules are dispersed, and the plasticizer is taken into the hollow tube by capillary action to form a liquid film.

When a polymer is used, the film-like material is generally obtained as follows. That is, the method involves dissolving or dispersing a polymer, a plasticizer, and zwitterion molecules in an organic solvent capable of dissolving a plasticizer, casting the solution in a container such as a petri dish, and volatilizing the solvent.

When a polymer is used and the polymer is difficult to disperse in the plasticizer, the plasticizer in which zwitterion molecules are dispersed is impregnated into the polymer formed as a porous membrane to obtain a film-like material. can also Polymers formed as porous membranes are commonly available as commercial membrane filters. Alternatively, the polymer can be formed and used as a porous membrane. A general method can be used as the method, and an example thereof is as follows.

A polymer is dispersed in a solvent to form a dispersion, and a second polymer, which is immiscible with the polymer in a solid state, is dispersed. When this solution is cast on a Petri dish or the like and the solvent is evaporated, the second polymer is phase-separated in the polymer to obtain a film-like material in which the second polymer is finely dispersed. When this film-like substance is washed with a solvent in which only the second polymer is dispersed, the polymer is obtained as a porous film. Specific examples of such a polymer and the second polymer include polyvinyl chloride as the polymer, polyethylene glycol as the second polymer, chloroform as a specific example of the solvent, and only the second polymer being dispersed. Water can be mentioned as a specific example of the solvent.
(Constitution method of ion-selective electrode for bicarbonate measurement)
An example of a method for constructing an ion-selective electrode using the bicarbonate ion-sensitive membrane of the present invention is as follows.

In the case of a liquid film that does not use a polymer, after the liquid film is formed in the hollow tube as described above, one end of the liquid film is brought into contact with the internal electrolytic solution. Furthermore, an internal reference electrode is inserted into the internal electrolyte to form an electrode.

In the case of a membrane using a polymer, a bicarbonate ion-sensitive membrane is adhered to one end of a cylindrical container (Fig. 1 11) with an adhesive or the like, the container is filled with an internal electrolyte, and an internal reference electrode is inserted. electrode.
(Method for quantifying bicarbonate ion and method for evaluating performance)
The method of measuring ion activity (concentration) using an ion-selective electrode is described above with reference to FIG. 2, but will now be described in more detail. In order to measure the concentration of a solution to be measured, it is necessary to measure a solution of known concentration in advance, obtain the relationship between the concentration and the potential difference, and create a calibration curve.

A calibration curve is given by the Nernst equation, and there is a linear relationship between the logarithm of the concentration and the potential difference (ΔE).
ΔE = (constant) + (Slope) x log (concentration)
Here, (constant) and (Slope) are constants and take different values for each electrode film. (Slope) is also a value representing the performance of the ion-selective electrode. The theoretical value of (Slope) is -59 (at 25°C). This theoretical value varies with temperature. That is, the absolute value of the theoretical value of (Slope) changes in proportion to the value of the absolute temperature. In addition, the absolute value may decrease due to the influence of interfering ions. In general, (Slope) takes a value close to 0 in the range where the concentration of ions in the sample to be measured is extremely low. When the ion concentration is measured using the ion-selective electrode, it is desirable that (Slope) has a large absolute value because the concentration can be measured with high accuracy. A preferred range is -59 to -20 (at 25°C), and a more preferred range is -59 to -30 (at 25°C). (constant) is a value specific to the electrode, and depends on the membrane used for the electrode, the internal electrolyte, the type of internal reference electrode, and the type of reference electrode. Always a constant value.

As a value representing the performance of the ion-selective electrode, there is a selectivity magnification. When an interfering ion of 1 mmol/L gives a potential difference corresponding to a bicarbonate ion concentration of 5 mmol/L, it is expressed as follows and called a selectivity magnification of 5 times. The closer the interfering ion selectivity magnification is to 0, the smaller the error in the measurement value caused by the interfering ions, so it can be said that the performance of the ion selective electrode is good.

K _{HCO3, X} = 5 (X represents an interfering ion)
For example, if the selectivity factor for chloride ions (sometimes referred to as the selectivity factor for bicarbonate ions to chloride ions) is 0.1, then _KHCO3,Cl = 0.1.
is written as

When the bicarbonate ion-sensitive membrane of the present invention is applied to clinical examinations, it is desirable that the interference of chloride ions present in serum at a concentration four times or more that of bicarbonate ions is small. Therefore, it is desirable that the selectivity ratio of bicarbonate ions to chloride ions be less than one.

Also, serum contains proteins whose surface amines can interfere with the electrode response. To assess the degree of interference, the response of the amine compound to aqueous solutions is generally assessed. As an example of the evaluation method, there is a method based on selectivity magnification when an aqueous solution of an amine compound is measured. As a specific example, when an aqueous solution of tris(hydroxymethyl)aminomethane is measured as the amine compound, the selectivity ratio is less than 100 times, more preferably less than 10 times.

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to these examples.

<Example 1>
(1) Preparation of ion-selective electrode decyldimethyl(3-sulfopropyl)ammonium hydroxide as a zwitterionic molecule and o-nitrooctylphenyl ether (NPOE) as a plasticizer were added in the amounts shown in Table 1, respectively. After the addition, they were dispersed by stirring. One end of a glass tube having an inner diameter of 1 mm and a length of 10 mm was inserted into this solution, and the solution was introduced into the one end of the glass tube by capillarity so that the length of the inside of the tube was about 1 mm. An ion-sensitive membrane was used. A 100 mmol/L aqueous solution of NaCl, which is an internal electrolytic solution, was filled from the opposite end using an injection needle so that the aqueous solution and the NPOE solution were in contact with each other. Further, an Ag wire having a diameter of 0.3 mm (AgCl was formed on the surface and functioned as an internal reference electrode) was inserted into the NaCl aqueous solution to form an ion-selective electrode.

(2) Performance evaluation of ion-selective electrode Using the above-described ion-selective electrode, the potential difference between the ion-selective electrode and the reference electrode was measured with an ion measuring apparatus having the configuration shown in FIG. As samples to be measured, 0.1 mmol/L, 1.0 mmol/L, 3.0 mmol/L, 10 mmol/L NaHCO ₃ aqueous solution, and 1.0 mmol/L NaCl aqueous solution were used and compared with the ion-selective electrode. Immediately after inserting the electrode into the sample to be measured, the potential difference was recorded 10 seconds later. Table 2 shows the measurement results. From the measurement results of the NaHCO ₃ aqueous solution, the relationship between the logarithm of the concentration and the potential difference was plotted to obtain a calibration curve for bicarbonate ions (HCO ₃ ions), and the slope (Slope) is shown in Table 2. When the value is taken, it can be said that there is sensitivity to the anion of interest.As shown in Table 2, the Slope is -33, which indicates that there is sensitivity to the anion bicarbonate ion, that is, the bicarbonate ion sensitive membrane In addition, the potential difference when measuring 1 mmol / L NaCl aqueous solution is applied to the above calibration curve, converted to bicarbonate concentration, and the selectivity factor for chloride ion (Cl ^- ion) was found to be 0.01, indicating that the bicarbonate ion-sensitive membrane of this example selectively responds to bicarbonate ions rather than chloride ions.

In addition, as an evaluation of the response interference of the amine compound, when the selectivity factor calculated using the potential difference when 1 mmol/L of tris(hydroxymethyl)aminomethane, which is an amine compound, is measured is less than 10, "○" , and when it is 10 or more, "x" is indicated in the table. It was shown that the ion-selective electrode membrane of the present invention has little interference with the response of amine compounds.

<Comparative example 1>
A membrane having the same composition as in Example 1 was prepared with the composition shown in Table 1, except that the zwitterion molecule was not used. . Table 2 shows the results. Slope was zero. No zwitterion molecule was shown to be unresponsive to bicarbonate ions.

<Example 2>
Decyldimethyl(3-sulfopropyl)ammonium hydroxide, which is a zwitterionic molecule, was added to o-nitrooctylphenyl ether, which is a plasticizer, in the amounts shown in Table 1, and then dispersed by stirring. A commercially available membrane filter (made of PTFE (polytetrafluoroethylene), pore size 0.45 μm) was impregnated with this solution to obtain the bicarbonate ion sensitive membrane of the present invention. The bicarbonate ion-sensitive membrane was adhered to one end of a polyvinyl chloride cylinder (outer diameter: 12 mm, inner diameter: 8 mm) with an adhesive. and the NPOE solution were in contact with each other. Further, an Ag wire having a diameter of 0.8 mm (AgCl was formed on the surface and functioned as an internal reference electrode) was inserted into the NaCl aqueous solution filled in the cylinder to form an ion-selective electrode.

After that, performance evaluation was performed by the method shown in Example 1 (2) Performance evaluation of ion-selective electrode. The results are shown in Table 2. As shown in Table 2, the Slope was -33, indicating that it functions as a bicarbonate ion-sensitive membrane. Further, when the selectivity factor was obtained, it was 0.01. That is, it was shown that the bicarbonate ion-sensitive membrane of this example selectively responded to bicarbonate ions rather than chloride ions.

<Example 3>
Tetradecyldimethyl(3-sulfopropyl)ammonium hydroxide, which is a zwitterionic molecule, was added to o-nitrooctylphenyl ether, which is a plasticizer, in the amounts shown in Table 3, and then dispersed by stirring. This solution was added to a tetrahydrofuran solution of polyvinyl chloride (polymer) having a concentration of 1% by weight and stirred to disperse. The resulting tetrahydrofuran solution was cast in a petri dish, and the tetrahydrofuran was evaporated at room temperature. The same operation was performed 10 times to obtain 10 bicarbonate ion sensitive membranes. The bicarbonate ion-sensitive membrane was adhered to one end of a polyvinyl chloride cylinder (outer diameter: 12 mm, inner diameter: 8 mm) with an adhesive. and the NPOE solution were in contact with each other. Further, an Ag wire having a diameter of 0.8 mm (AgCl was formed on the surface and functioned as an internal reference electrode) was inserted into the NaCl aqueous solution filled in the cylinder to form an ion-selective electrode.

After that, performance evaluation was performed by the method shown in Example 1 (2) Performance evaluation of ion-selective electrode. The results are shown in Table 5. The Slopes of the 10 bicarbonate ion-sensitive membranes were all in the range of -30 to -45, indicating that good sensitivity was obtained. Furthermore, it was found that the reproducibility of the sensitivity performance of each membrane was high when a plurality of membranes were manufactured. In addition, as an evaluation of the response interference of the amine compound, when the selectivity factor calculated using the potential difference when 1 mmol/L of tris(hydroxymethyl)aminomethane, which is an amine compound, is measured is less than 10, "○" , and when it is 10 or more, "x" is indicated in the table. It was also shown to be less susceptible to amine compounds.

<Comparative Example 2>
Tetradecyldimethyl(3-sulfopropyl)ammonium hydroxide in the amount shown in Table 3 was added to a polyvinyl chloride solution in tetrahydrofuran having a concentration of 1% by weight and stirred to disperse. A film-like material was obtained in the same manner as in Example 3 using the obtained tetrahydrofuran solution. In addition, the amount of each component was taken into consideration and determined so that the intramembrane concentration of amphoteric ions would be approximately the same. An ion-selective electrode was produced using this membrane-like material and its performance was evaluated. The results are shown in Table 5. The Slope was 0, indicating that the film does not function as a bicarbonate ion-sensitive film when no plasticizer is used.

<Comparative Example 3>
As a known bicarbonate ion-selective electrode described in Patent Document 4, a salt of tridodecylmethylammonium and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate was used at a concentration of 50 mmol/L. A membrane was produced in the amount shown in , and an ion-selective electrode was produced and performance evaluation was performed in the same manner as in Example 3. The results are shown in Table 5.

Slope varies in the range of 0 to -45, and the number of electrode films of -30 or less, which is considered practical, was four. When the electrode films were manufactured, it was shown that the performance varied from film to film, that is, the reproducibility of sensitivity from film to film was low.

In Examples 1 to 3, it was shown that a change in potential can be obtained depending on the concentration of bicarbonate ions. In addition, the potential response of chloride ions, which are most abundantly contained in serum and plasma samples to be measured in clinical laboratory tests, was smaller than that of bicarbonate ions. Moreover, when 10 films were manufactured, all the films showed potential response with practical sensitivity. On the other hand, in Comparative Examples 1 and 2, the potential change according to the concentration of bicarbonate ions was not obtained. In Comparative Example 3, less than half of the membranes that can respond to bicarbonate ions with a practical sensitivity, that is, the membranes with a Slope value of less than -30, show that the sensitivity reproducibility for each membrane is low when a plurality of membranes are manufactured. shown. Furthermore, it was shown that the degree of interference by the amine compound varied among the multiple films, and that some films were more susceptible to interference by the amine compound.

From these results, it was shown that the bicarbonate ion exchange membrane of the present invention selectively responds to bicarbonate ions and has high reproducibility of sensitivity for each membrane when a plurality of membranes are produced.

<Comparative Examples 4 and 5>
Assuming that the ratio of cations and anions in one molecule deviates from 1:1, a film-like material containing each compound dispersed in a plasticizer in the amount shown in Table 4 was prepared in the same manner as in Example 3. prepared by the method. An ion-selective electrode was produced using this membrane-like material and its performance was evaluated. The results are shown in Table 6.

Comparative Example 4 is a case where the ratio of anions is large, and N-(2-hydroxyethyl)ethylenediamine-N,N',N'-3 acetic acid dihydrochloride (ratio of cations and anions = 0.5) is used as a zwitterion molecule. 67:1) was used. At this time, Slope took a positive value, indicating that it is sensitive to cations. Therefore, it did not respond to chloride ions and bicarbonate ions, which are anions. On the other hand, Comparative Example 5 is a case where the ratio of cations is large, and bis(1,3-dibutylbarbituric acid) trimethine oxonol sodium salt (ratio of cations and anions=2:1) is used as a zwitterionic molecule. was used, but Slope took a negative value, indicating that it is sensitive to anions. However, the selectivity factor for chloride ions was very large, 12, and no selectivity for bicarbonate ions was demonstrated. From these results, no ion selectivity to bicarbonate was obtained when the cation to anion ratio was not 1:1.

<Examples 4 to 7>
Using the amphoteric ions, plasticizers and polymers shown in Table 7 in the amounts also shown in Table 7, bicarbonate ion-sensitive membranes of the present invention were produced in the following manner, and the performance was evaluated.
First, the amphoteric ion molecules were added to the plasticizer and dispersed by stirring. This solution was added to a tetrahydrofuran solution of the polymer having a concentration of 1% by weight and dispersed by stirring. The resulting tetrahydrofuran solution was cast in a petri dish, and the tetrahydrofuran was evaporated at room temperature. The membrane remaining in the petri dish was obtained as a bicarbonate ion-sensitive membrane. The bicarbonate ion-sensitive membrane was adhered to one end of a polyvinyl chloride cylinder (outer diameter: 12 mm, inner diameter: 8 mm) with an adhesive. and the NPOE solution were in contact with each other. Further, an Ag wire having a diameter of 0.8 mm (AgCl was formed on the surface and functioned as an internal reference electrode) was inserted into the NaCl aqueous solution filled in the cylinder to form an ion-selective electrode.

After that, performance evaluation was performed by the method shown in Example 1 (2) Performance evaluation of ion-selective electrode. The results are shown in Table 8.

Furthermore, as an evaluation of the response interference of the amine compound, if the selectivity factor calculated using the potential difference when 1 mmol/L of tris(hydroxymethyl)aminomethane, which is an amine compound, is measured is less than 10, "○" is indicated. , and when it is 10 or more, "X" is indicated in the table. The results are also shown in Table 8.

In any combination, Slope took a negative value, and the selectivity coefficient for chloride ions was less than 1. In addition, amine interference was low. Therefore, the ion-selective electrode using the bicarbonate ion-sensitive membrane of the present invention responds to bicarbonate ions, responds selectively to bicarbonate ions rather than chloride ions, is less affected by amine interference, and is clinically useful. It has been shown to perform well when used with test electrodes.
<Comparative Example 6>

According to Patent Document 3, 0.2 g (350 μmol) of tridodecylmethylammonium chloride as an organic onium salt (concentration 3.5 mmol/L) and 2-phenyl-4,4,5,5-tetramethyl- as an aromatic boronic acid diester. 100 μl of 1,3,2-dioxaborolane and 50 mg of polyvinyl chloride as a polymer were weighed and dispersed in 2.5 ml of tetrahydrofuran. . Performance evaluation was carried out in the same manner as in Example 4. The results are shown in Table 8. Although the electrode film of this comparative example is excellent in slope and chloride ion selectivity, it was shown that the amine compound interferes greatly.
<Example 8>

The ion-selective electrode prepared in Example 3 was immersed in a 100 mmol/L NaCl aqueous solution at 15 to 20° C. for one month. The Slope of the bicarbonate ion calibration curve before and after immersion was measured according to Example 1 (2) and shown in Table 10 as Example 8.
<Comparative Examples 7 to 9>
As shown in Table 9, a known bicarbonate ion-sensitive substance described in literature, etc., as a compound not within the scope of the present invention, was used as a bicarbonate ion-sensitive film, and the concentration in the plasticizer of Example 3 was and the filmy product was prepared in the same manner as in Example 3. An ion-selective electrode was produced using this. As in Example 8, it was immersed in a 100 mmol/L NaCl aqueous solution for one month. Table 10 shows the slope before and after immersion.

The ion-selective electrode produced using the electrode film of Example 8 showed no change in slope even after being immersed in an aqueous sodium chloride solution for one month. That is, it was found that analytical sensitivity was maintained. On the other hand, in the electrode films of Comparative Examples 7 and 9, tridodecylmethylammonium chloride (solubility in water: 0.00 g/100 mL), which is a bicarbonate ion-sensitive substance, was eluted into the aqueous sodium chloride solution, resulting in Slope value has decreased. In addition, in the electrode film of Comparative Example 8, the Slope value decreased due to the reaction of trioctyltine chloride, which is an ion-sensitive substance, with water and decomposition.

Therefore, it was shown that the bicarbonate ion-sensitive membrane of the present invention is excellent in storage stability.

11: Cylindrical container 12: Ion sensitive membrane 13: Internal electrolytic solution 14: Internal reference electrode 21: Ion selective electrode 22: Salt bridge 23: Sample solution 24: Reference electrode 25: Electrometer 26: Saturated potassium chloride solution

Claims (5)

1. A bicarbonate ion-sensitive membrane characterized by containing molecules having cations and anions in a ratio of 1:1 per molecule in a form dispersed in a plasticizer. 2. The bicarbonate ion sensitive membrane according to claim 1, wherein said cation is an onium cation. 3. The bicarbonate ion sensitive membrane according to claim 2, wherein the onium cation is an ammonium cation, a phosphonium cation, an imidazolium cation, or a pyridinium cation. The bicarbonate ion sensitive membrane according to any one of claims 1 to 3, wherein the anion is borate anion, carboxylate anion, sulfonate anion, phosphate anion or phenoxide anion. 5. The bicarbonate ion sensitive membrane according to claim 1, wherein the bicarbonate ion sensitive membrane contains a polymer, and the polymer contains molecules dispersed in the plasticizer. .

Images