TWI701433B - Ph measuring method - Google Patents

Abstract

A liquid membrane-type hydrogen ion selective electrode, which in combination with a reference electrode can be used to measure the pH of solutions containing hydrofluoric acid, and particularly strongly acidic solutions, incorporates a sensitive membrane formed from an organic material containing amine-based hydrogen ion selective molecules and an anion exclusion agent represented by formula (1). In formula (1), Z₁ to Z₄ represent substituted phenyl groups Z having a general formula represented by formula (1a), and may be the same or different. In formula (1a), each of R₁ to R₅ independently represents any one of a hydrogen atom, a fluorine atom, an alkyl group with a carbon number of 1 to 6, and a substituent group with a carbon number of 1 to 6 that contains a fluorine atom, wherein at least one of R₁ to R₅ includes a fluorine atom or a substituent group with a carbon number of 1 to 6 that contains a fluorine atom.

Description

pH measurement method

The present invention relates to a hydrogen ion selective electrode, a pH measurement method and a sensing membrane that can be used to measure the pH (hydrogen ion index) of a solution containing hydrofluoric acid, and especially relates to a strong acid solution that can be used to measure hydrofluoric acid The pH hydrogen ion selective electrode, pH measurement method and sensing membrane.

Typical pH measurement using electrodes is to use a hydrogen ion selective electrode, a reference electrode and a DC potentiometer. The hydrogen ion selective electrode and reference electrode are immersed in the solution of the measurement object at the same time. At this time, the DC potentiometer is used to measure between the two electrodes. The resulting potential difference (response potential). The hydrogen ion concentration [H ⁺ ] can be obtained from the potential difference, and then the pH can be calculated according to the following formula.

pH=-log ₁₀ [H ⁺ ]

Generally, a pair of a hydrogen ion selective electrode and a reference electrode is often called a pH sensor or a pH electrode, a hydrogen ion electrode, etc. In this specification, a pair of a hydrogen ion selective electrode and a reference electrode is referred to as a pH electrode.

The pH electrode can be used for laboratory use, pH management of various equipment, measurement of industrial wastewater and other environmental management purposes, and other wide-ranging purposes. The hydrogen ion selective electrode that has been widely used for these purposes in the past is a glass membrane type hydrogen ion selective electrode that uses a glass film as a sensing membrane. The glass membrane type hydrogen ion selective electrode is generally also called a glass electrode. The reason why glass electrodes are widely used is that glass electrodes have the advantages of 1) a wide range of pH response, 2) almost no influence of other ions, 3) little influence of redox substances, and 4) easy use.

However, since the undissociated hydrogen fluoride (HF) molecules will corrode the glass, the glass electrode cannot be applied to the solution containing hydrofluoric acid. Especially, in the acidic to strongly acidic solution, the dissociation equilibrium of hydrogen fluoride tends to the non-dissociation side, and the proportion of hydrogen fluoride molecules in the solution increases, so the degree of glass corrosion increases. In order to solve this problem, pH electrodes using special glass that is durable to hydrofluoric acid are commercially available, but the measurement range is limited to solutions above pH 2, and solutions containing hydrofluoric acid above 1000 mg/L can only be used The solution with pH 3 or higher can be measured, and the solution with hydrofluoric acid above 10000mg/L can only be measured with a solution with pH 4 or higher.

In addition, for materials other than glass, although antimony film-type hydrogen ion selective electrodes (also called antimony electrodes) using antimony are commercially available, antimony electrodes can only be used in solutions with pH 3 or higher, and in the presence of oxidants Department cannot be determined.

Japanese Patent Publication No. 5-48859 (Patent Document 1) has disclosed a liquid membrane type hydrogen ion selective electrode as a solution to the disadvantages of glass electrodes. The liquid membrane ion selective electrode is a type of electrode that encapsulates molecules that are selectively coordinated with specific ions into a polymer matrix and uses the polymer matrix as a sensing membrane. If necessary, ion scavengers, plasticizers, etc. may be added to the polymer matrix. In order to make it possible to measure the pH of a solution containing hydrofluoric acid, Patent Document 1 has disclosed a liquid membrane type hydrogen ion selective electrode with a sensing membrane that uses tri-n-octyl phosphine oxide (tri- n -octylphosphine oxide, referred to as TOPO) as the hydrogen ion selective molecule, using potassium tetrakis(4-chlorophenyl) borate (abbreviated as TCPB) as anion scavenger, using o-nitrophenyl Octyl ether ( o- nitrophenyl octyl ether, NPOE for short) is used as a plasticizer, and these are sealed in polyvinyl chloride as a polymer matrix.

【Prior Technical Literature】

【Patent Literature】

[Patent Document 1] Japanese Patent Publication No. 5-48859

【Non-Patent Literature】

[Non-Patent Document 1] JIS (Japanese Industrial Standards) K-0122 (General Rules of Ion Electrode Measurement Method)

However, the hydrogen ion selective electrode disclosed in Patent Document 1 disappeared in about half a month in the state of immersing the hydrogen ion selective electrode in a solution containing hydrofluoric acid, and thus had practical problems.

The present invention is designed to solve the problems of the above-mentioned conventional technology. That is, the purpose of the present invention is to provide a liquid membrane type hydrogen ion selective electrode that can measure the pH of a solution containing hydrofluoric acid and has a long life, and is especially ideal for measuring the pH of a strong acid solution.

Another object of the present invention is to provide a pH measurement method that can measure the pH of a solution containing hydrofluoric acid stably for a long time, especially for a strong acid solution.

Furthermore, another object of the present invention is to provide a sensing membrane used in the above-mentioned hydrogen ion selective electrode of the present invention.

The hydrogen ion selective electrode of the present invention has a sensing membrane containing an amine-based hydrogen ion selective molecule and an anion scavenger represented by the following formula (1). However, in formula (1), Z ₁ to Z ₄ are substituted phenyl Z which may be the same or different from at least 2 of Z ₁ to Z _4. The general formula of substituted phenyl Z is It is represented by the following formula (1a). In formula (1a), R ₁ to R ₅ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, and a fluorine atom-containing substituent group having 1 to 6 carbon atoms, R ₁ At least one of ~R ₅ contains a fluorine atom, or a fluorine atom-containing substituent with 1 to 6 carbon atoms.

The pH measurement method of the present invention is a method in which the hydrogen ion selective electrode and the reference electrode are immersed in a solution containing hydrofluoric acid, and the response potential generated between the hydrogen ion selective electrode and the reference electrode is measured to measure the pH of the solution. Its characteristics are To use a hydrogen ion selective electrode with a sensing membrane containing an amine-based hydrogen ion selective molecule and an anion scavenger represented by the above formula (1).

The induction membrane of the present invention is a hydrogen ion-sensitive induction membrane, which is characterized by containing amine-based hydrogen ion selective molecules and the anion scavenger represented by the above formula (1).

According to the present invention, in a hydrogen ion selective electrode having a sensing membrane containing an amine-based hydrogen ion selective molecule and an anion scavenger, by using the compound represented by the above formula (1) as an anion scavenger, it is implemented as follows It is clear from the examples that a hydrogen ion selective electrode can be obtained that can measure the pH of a solution containing hydrofluoric acid, has a long life, and is ideal for the pH measurement of a strong acid solution.

1: Hydrogen ion selective electrode

2: Reference electrode

10: DC potentiometer

20: solution

31, 41: Internal electrodes

32, 42: Internal liquid

33, 43: Outer cylinder

34: Induction film

35: Conductor

36: Lead

44: Liquid junction

[Fig. 1] A cross-sectional view illustrating the structure of a hydrogen ion selective electrode according to an embodiment of the present invention.

[Fig. 2] A cross-sectional view illustrating the structure of a hydrogen ion selective electrode according to another embodiment of the present invention.

[Figure 3] A diagram illustrating the principle of pH measurement.

[Fig. 4] A cross-sectional view illustrating an example of the structure of the reference electrode.

[Figure 5] is a graph showing the change of response potential E versus pH of each hydrogen ion selective electrode immersed in a solution containing 10000 mg/L of hydrofluoric acid in Example 1.

[Figure 6] is a graph showing the change of the potential gradient ΔE of each hydrogen ion selective electrode after immersing in a solution containing 10000 mg/L of hydrofluoric acid in Example 1 for a specified time.

[Fig. 7] It shows the use of Potassium Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate], referred to as TFPB in Example 1. A graph of the pH response characteristics of the hydrogen ion selective electrode of the anion scavenger.

[Fig. 8] A graph showing the change of the potential gradient ΔE of the hydrogen ion selective electrode of Example 1 and the comparative example after immersing in a solution containing 10000 mg/L of hydrofluoric acid for a specified time.

[Figure 9] A graph showing the change in response potential E of the hydrogen ion selective electrode of Example 2 immersed in a solution containing 10000 mg/L of hydrofluoric acid with pH.

[Figure 10] A graph showing the change of the potential gradient ΔE of the hydrogen ion selective electrode of Example 2 after immersing in a solution containing 10000 mg/L of hydrofluoric acid for a specified time.

[Figure 11] is a graph showing the pH response characteristics of the hydrogen ion selective electrode of Example 2.

[Figure 12] is a graph showing the change of the potential gradient ΔE of each hydrogen ion selective electrode after immersing in a solution containing 10000 mg/L of hydrofluoric acid for a specified time in Reference Example 1.

[Figure 13] is a graph showing the change of the potential gradient ΔE of the glass electrode after immersing in a solution containing 1000 mg/L of hydrofluoric acid for a specified time in Reference Example 2.

Next, embodiments of the present invention will be described with reference to the drawings.

Fig. 1 illustrates the structure of a hydrogen ion selective electrode according to an embodiment of the present invention. The configuration shown in FIG. 1 illustrates an example of the hydrogen ion selective electrode based on the present invention, and the hydrogen ion selective electrode based on the present invention is not limited to this.

The hydrogen ion selective electrode illustrated in FIG. 1 includes an internal electrode 31, an internal liquid 32, an outer cylinder 33, and a sensing membrane 34. The sensing film 34 is a film that selectively responds to hydrogen ions, and is a film formed by dispersing hydrogen ion selective molecules, anion scavengers, plasticizers, and the like in a polymer matrix and drying them. The sensing film 34 is fixed to the outer cylinder 33. The outer cylinder 33 is filled with an internal liquid 32, and the internal electrode 31 is immersed therein. The response potential from the hydrogen ion selective electrode is taken out from this internal electrode 31 via a lead wire or the like.

Fig. 2 illustrates another example of the structure of the hydrogen ion selective electrode based on the present invention. The hydrogen ion selective electrode of FIG. 2 includes a sensing film 34, a conductor 35, and a lead 36. The hydrogen ion selective electrode is in a form that does not use an internal liquid, and there is no outer cylinder. The sensing film 34 is arranged in contact with the conductor 35. The sensing film 34 is the same as the sensing film in the hydrogen ion selective electrode illustrated in FIG. 1. The conductor 35 of FIG. 2 often uses conductive polymers such as polypyrroles, polyanilines, polythiophenes, polyacetylenes, polyphenylene vinylenes, and polyphenylene sulfides. The response potential of the hydrogen ion selective electrode illustrated in FIG. 2 is taken out from the conductor 35 through the lead 36. Since the ion selective electrode of this form does not have a liquid part compared with the example shown in Fig. 1, it is called an all-solid ion selective electrode.

The sensing membrane 34 of the hydrogen ion selective electrode based on the present invention contains: an amine-based hydrogen ion selective molecule and an anion scavenger represented by the general formula (2). In the formula (2), Z ₁ to Z ₄ are substituted phenyl Z which may be the same or different from at least 2 of Z ₁ to Z _4. The general formula of the substituted phenyl Z is as follows (2a) said. In formula (2a), R ₁ to R ₅ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, and a fluorine atom-containing substituent group having 1 to 6 carbon atoms, R ₁ At least one of ~R ₅ contains a fluorine atom, or a fluorine atom-containing substituent with 1 to 6 carbon atoms.

The sensing film 34 is formed by dispersing the amine-based hydrogen ion selective molecules and anion scavenger together with a plasticizer and the like in a polymer matrix and drying it. Therefore, the hydrogen ion selective electrode based on the present invention is a liquid membrane type hydrogen ion selective electrode that uses a sensing membrane composed of an organic substance.

First, the amine-based hydrogen ion selective molecule used in the present invention will be explained.

The so-called amine-based hydrogen ion selective molecules are molecules with at least one primary or secondary or tertiary amine in the molecular structure. As we all know, the nitrogen atoms (N) of primary, secondary and tertiary amines have non-covalent electron pairs. Hydrogen ions (H ⁺ : that is, protons) are easy to coordinately bond to this non-covalent electron pair. Therefore, primary, secondary and tertiary amines can generally be used as carriers of protons in the sensing membrane of liquid membrane ion selective electrodes, and can be used as hydrogen ion selective molecules. Amine-based hydrogen ion selective molecules are commercially available, such as the Selectophore series of Sigma-Aldrich.

In order to prevent the hydrogen ion selective molecule from dissolving in a solution, etc., the amine-based hydrogen ion selective molecule used in the present invention preferably has a total of 10 or more carbon atoms in the molecule. The structure of the amine-based hydrogen ion selective molecule can be chain or cyclic.

As the compound suitable for the amine-based hydrogen ion selective molecule of the present invention, for example, a molecule having a structure represented by the general formula (3) can be exemplified. In the formula (3), R ₇ to R ₉ represent a hydrogen atom and/or an aliphatic residue and/or an aromatic residue, and R ₇ to R ₉ may be the same or different, and may contain heteroatoms. However, at least one of R ₇ to R ₉ is a group with 6 or more carbon atoms, and the total number of carbon atoms contained in the molecule is 10 or more. If there is no at least one carbon 6 or more group, the overall hydrophilicity of the molecule becomes higher, and the hydrogen ion selective molecule is easily eluted from the polymer matrix into the solution. In addition, if the total number of carbon atoms contained in the molecule is not more than 10, the hydrophilicity of the entire molecule becomes high, and hydrogen ion selective molecules are easily eluted from the polymer matrix into the solution. In addition, when R ₇ and R ₈ are aliphatic residues and/or aromatic residues, a ring may also be formed between R ₇ and R ₈ ; and, when R ₇ to R ₉ are aliphatic residues and/or Or in the case of an aromatic residue, a ring may be formed between R ₇ and R ₈ and R ₉ .

When R ₇ ~R ₉ are aliphatic residues, amine-based hydrogen ion selective molecules, for example, can be ideally used: tris(dodecyl)amine (R ₇ =R ₈ =R ₉ =-C ₁₂ H ₂₅ ), tris (tetradecyl) amine (R ₇ = R ₈ = R ₉ = -C ₁₄ H ₂₉ ), tris (hexadecyl) amine (R ₇ = R ₈ = R ₉ = -C ₁₆ H ₃₃ ), three (octadecyl) amine (R ₇ = R ₈ = R ₉ = -C ₁₈ H ₃₇ ), two (octadecyl) methylamine (R ₁ = R ₂ = -C ₁₈ H ₃₇ , R ₃ =-CH ₃ ), octadecyl dimethylamine (R ₇ =-C ₁₈ H ₃₇ , R ₈ =R ₉ =-CH ₃ ), etc.

In addition, when R ₇ to R ₉ are aromatic residues, amine-based hydrogen ion selective molecules, for example, tribenzylamine represented by formula (4) and dibenzylnaphthylamine represented by formula (5) can be ideally used Amine, dibenzylpyrenemethylamine represented by formula (6), etc.

As yet another example of aromatic residues, n-octadecylaniline represented by formula (7) and the like can also be preferably used.

As another example of the hydrogen ion selective molecule used in the present invention, a pyridine derivative represented by the general formula (8) can be used. In the formula (8), R ₁₁ to R ₁₅ represent a hydrogen atom and/or an aliphatic residue and/or an aromatic residue, and R ₁₁ to R ₁₅ may be the same or different, and may contain a hetero atom. However, at least one of R ₁₁ to R ₁₅ is a group with 6 or more carbon atoms. If at least one group with a carbon number of 6 or more is not present, the overall hydrophilicity of the molecule becomes higher, and hydrogen ion selective molecules are easily eluted from the polymer matrix into the solution. In addition, when any two or more groups of R ₁₁ to R ₁₅ are aliphatic residues and/or aromatic residues, a ring may be formed between these groups.

It is a hydrogen ion selective molecule of the amine system of a pyridine derivative, such as 4-nonadecylpyridine represented by formula (9) (R ₁₃ =-C ₁₉ H ₃₉ , R ₁₁ =R ₁₂ = R ₁₄ =R ₁₅ =H) is preferred. Also, for example, 1-(pyridin-4-yl)decane-1,3-dione (1-(pyridin-4-yl)decane-1,3-dione) represented by formula (10) can also be used The molecule acts as a hydrogen ion selective molecule with heteroatom-containing substituents.

Also, picolinic acid derivatives such as isonicotinic acid derivatives represented by general formula (11), nicotinic acid derivatives represented by general formula (12), picolinic acid derivatives represented by general formula (13), etc. can be used as the Other examples in which the substituent R contains a hetero atom.

Pyridinecarboxylic acid derivatives that can be used as amine-based hydrogen ion selective molecules, such as decyl isonicotinate (R ₁₆ = -C ₁₀ H ₂₁ ), dodecyl isonicotinate (R ₁₆ = -C ₁₂ H ₂₅ ), isonicotinic acid myristyl (R ₁₆ = -C ₁₄ H ₂₉ ), isonicotinic acid cetyl (R ₁₆ = -C ₁₆ H ₃₃ ), isonicotine Stearyl nicotinate (R ₁₆ =-C ₁₈ H ₃₇ ), Decyl nicotinate (R ₁₇ =-C ₁₀ H ₂₁ ), Lauryl nicotinate (R ₁₇ =-C ₁₂ H ₂₅ ), Myristyl Nicotinate (R ₁₇ =-C ₁₄ H ₂₉ ), Cetyl Nicotinate (R ₁₇ =-C ₁₆ H ₃₃ ), Stearyl Nicotinate (R ₁₇ =-C ₁₈ H ₃₇ ), decyl picolinate (R ₁₈ =-C ₁₀ H ₂₁ ), dodecyl picolinate (R ₁₈ =-C ₁₂ H ₂₅ ), tetradecyl picolinate (R ₁₈ =-C ₁₄ H ₂₉ ), hexadecyl picolinate (R ₁₈ =-C ₁₆ H ₃₃ ), stearyl picolinate (R ₁₈ =-C ₁₈ H ₃₇ ), etc. In particular, from the viewpoints of easy availability and high hydrophobicity, isonicotinic acid octadecyl ester represented by formula (14) is preferred.

啉衍生物。式(15)中，R₁₉表示脂肪族殘基及/或芳香族殘基，也可含雜原子。惟，R₁₉為碳數6以上之基。若不為碳數6以上，分子整體之親水性變高，氫離子選擇性分子會從高分子基質溶出至溶液中。尤以正十八烷基

啉(R₁₉=-C₁₈H₃₇)等較佳。 Furthermore, another compound of amine-based hydrogen ion selective molecule can be represented by general formula (15)

Morpholine derivatives. In formula (15), R ₁₉ represents an aliphatic residue and/or an aromatic residue, and may contain a hetero atom. However, R ₁₉ is a group with 6 or more carbon atoms. If the carbon number is not 6 or more, the hydrophilicity of the whole molecule becomes higher, and hydrogen ion selective molecules will be eluted from the polymer matrix into the solution. N-octadecyl

A morpholine (R ₁₉ =-C ₁₈ H ₃₇ ) and the like are preferable.

衍生物。式(16)中，R₂₁~R₂₂表示氫原子及/或脂肪族殘基及/或芳香族殘基，R₂₁~R₂₂可相同也可不同，又，也可含雜原子。惟，R₂₁~R₂₂中之至少一者為碳數6以上之基。若未存在至少一個碳數6以上之基，分子整體之親水性變高，氫離子選擇性分子容易從高分子基質溶出至溶液中。又，當R₂₁與R₂₂為脂肪族殘基及/或芳香族殘基時，亦可於R₂₁與R₂₂之間形成環。 Another compound of the amine-based hydrogen ion selective molecule can use the piperidine represented by the general formula (16)

derivative. In the formula (16), R ₂₁ to R ₂₂ represent a hydrogen atom and/or an aliphatic residue and/or an aromatic residue, and R ₂₁ to R ₂₂ may be the same or different, and may contain a hetero atom. However, at least one of R ₂₁ to R ₂₂ is a group with 6 or more carbon atoms. If at least one group with a carbon number of 6 or more is not present, the overall hydrophilicity of the molecule becomes higher, and hydrogen ion selective molecules are easily eluted from the polymer matrix into the solution. In addition, when R ₂₁ and R ₂₂ are aliphatic residues and/or aromatic residues, a ring may be formed between R ₂₁ and R ₂₂ .

衍生物之胺系之氫離子選擇性分子，例如可使用式(17)表示之1-十八醯基-4-甲基哌

(1-octadecanoyl-4-methylpiperazine)、式(18)表示之1-十八醯基-4-(2-吡啶基)-哌

(1-octadecanoyl-4-(2-pyridyl)-piperazine)等分子。式(18)之分子亦為式(8)表示之吡啶衍生物。 Piperazine

The hydrogen ion selective molecule of the derivative amine series, for example, 1-octadecanoyl-4-methylpiperidine represented by formula (17) can be used

(1-octadecanoyl-4-methylpiperazine), 1-octadecanoyl-4-(2-pyridyl)-piperazine represented by formula (18)

(1-octadecanoyl-4-(2-pyridyl)-piperazine) and other molecules. The molecule of formula (18) is also a pyridine derivative represented by formula (8).

As another compound of the hydrogen ion selective molecule, an aniline derivative represented by the general formula (19) can be used. R ₂₃ to R ₂₇ represent a hydrogen atom and/or an aliphatic residue and/or an aromatic residue, and R ₂₃ to R ₂₇ may be the same or different, and may contain heteroatoms. However, at least one of R ₂₃ to R ₂₇ is a group with 6 or more carbon atoms. If at least one group with a carbon number of 6 or more is not present, the overall hydrophilicity of the molecule becomes higher, and hydrogen ion selective molecules are easily eluted from the polymer matrix into the solution. In addition, when any two or more groups of R ₂₃ to R ₂₇ are aliphatic residues and/or aromatic residues, a ring may be formed between these groups. The molecule of 2-octadecyloxyaniline represented by formula (20) can also be used.

Next, the anion scavenger used in the present invention will be explained.

The anion scavenger used in the present invention prevents anions, especially fluoride ions (F-) from moving in the sensing membrane 34, and is represented by the above general formula (2) with substituted phenyl groups Z ₁ to Z ₄ Phenylboronic acid compound. The substituted phenyl groups Z ₁ to Z ₄ are represented by the above general formula (2b), and Z ₁ to Z ₄ may be the same group, or two or more of them may be different from each other. In formula (2b), R ₁ to R ₅ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, and a fluorine atom-containing substituent group having 1 to 6 carbon atoms, R ₁ At least one of ~R ₅ contains a fluorine atom or a fluorine atom-containing substituent with 1 to 6 carbon atoms. The alkyl group having 1 to 6 carbon atoms is a substituent represented by the general formula -C _n H _(2n+1) (but n=1 to 6). For example, methyl (-CH ₃ ) and ethyl (- CH ₂ CH ₃ ), propyl (-CH ₂ CH ₂ CH ₃ ), isopropyl (-CH(CH ₃ )CH ₃ ), etc.

An example of the anion scavenger represented by formula (2) is represented by formula (21). In formula (21), R ₆ is a substituent containing at least one fluorine atom, and preferably R ₆ is a substituent containing at least one trifluoromethyl group (-CF ₃ ).

The anion scavenger represented by the formula (21), especially from the viewpoint of easy availability, can ideally be used as R ₆ = -CF ₃ represented by the formula (22) [3,5-bis(trifluoromethyl)phenyl] Boric acid (tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), or R ₆ = -C(CF ₃ ) ₂ OCH ₃ represented by formula (23) [3,5-bis(1,1,1 ,3,3,3-hexafluoro-2-methoxy-2-propyl)phenyl]boronic acid (tetrakis[3,5-bis(1,1,1,3,3,3-hexafluoro-2- methoxy-2-propyl)phenyl]borate).

The central boron of the anion scavenger represented by the general formula (2) is an anion. The relative cation corresponding to this anion scavenger is preferably an alkali metal ion. For example, sodium, potassium, etc. can be used.

Furthermore, in addition to the compounds listed in formulas (22) and (23), those suitable as the anion scavenger of the present invention are represented by formula (24) (4-fluorophenyl) sodium borate dihydrate (sodium tetrakis (4-fluorophenyl)borate dihydrate), formula (25) represented by (pentafluorophenyl) lithium borate ethyl ether (lithium tetrakis (pentafluorophenyl) borate ethyl etherate), and formula (26) represented by (pentafluorophenyl) ) Sodium tetrakis (pentafluorophenyl) borate. The compound represented by formula (24) is obtained by setting R ₁ =R ₂ =R ₄ =R ₅ =-H and R ₃ =-F in formula (2), and the compounds represented by formulas (25) and (26) It is obtained by setting R ₁ =R ₂ =R ₃ =R ₄ =R ₅ =-F in formula (2).

As the plasticizer contained in the sensing film 34, well-known plasticizers such as phthalate, sebacate, adipate, phosphate, and phenyl ether can be used. From the viewpoint of ease of acquisition, 2-Nitrophenyl octyl ether (NPOE), bis(1-butylpentyl) adipate (Bis(1-butylpentyl)) can be ideally used. adipate (BBPA for short), Bis (2-ethylhexyl) sebacate (DOS for short), Tris (2-ethylhexyl) phosphate, Referred to as TEHP), 2-Fluorophenyl-2-nitrophenyl ether (2-Fluorophenyl-2-nitrophenyl ether), 2-nitrophenyl phenyl ether, dibutyl phthalate, etc.

The polymer matrix constituting the sensing membrane 34 is not particularly limited as long as it can hold hydrogen ion selective molecules, anion scavengers, plasticizers, etc., in a film form, but from the viewpoint of ease of acquisition, it is preferably Use polyvinyl chloride, polyaniline, polyurethane, cellulose triacetate, epoxy resin, silicone rubber, polyethylene, polypropylene, polyvinyl alcohol alone or mix them. In particular, from the viewpoint of durability, it is preferable to use polyvinyl chloride. It is also possible to mix polyvinyl chloride and epoxy resin.

Next, the preferable component ratio of each component in the sensitive film 34 is demonstrated.

The hydrogen ion selective molecule is preferably 0.1% by weight or more and 10% by weight or less with respect to all components in the sensing membrane 34. When the component ratio of hydrogen ion selective molecules is less than 0.1% by weight, there may be no response to hydrogen ions, and if it exceeds 10% by weight, the response potential may become unstable. The anion scavenger should preferably be 10% or more and less than 100% in terms of the amount of substance ratio (unit mole) relative to hydrogen ion selective molecules. When the anion scavenger is less than 10% relative to the hydrogen ion selective molecule, it is easily affected by the anions contained in the solution. If it is more than 100%, the response potential may become unstable. The plasticizer is preferably 30% by weight or more and 85% by weight or less with respect to all components in the induction film 34. If the plasticizer is less than 30% by weight, the sensing film 34 will be too hard and hinder the movement of hydrogen ions in the sensing film 34, so there may be no response; if it exceeds 85% by weight, the sensing film 34 will be too soft and may become impossible Maintain the condition of hydrogen ion selective molecules and anion scavengers. Usually, the remaining part is a polymer matrix.

The method of forming the sensing film 34 is not particularly limited. For example, add a specified amount of hydrogen ion selective molecules, anion scavengers, plasticizers, and polymer matrix to organic solvents such as tetrahydrofuran and dissolve them. After fully stirring, spread them on a glass plate, etc., It is dried at a temperature range of 60° C., thereby forming a film to be the sensing film 34. After that, the film is cut, and a solution obtained by dissolving a resin such as polyvinyl chloride in an organic solvent such as tetrahydrofuran is used as an adhesive, and the film is attached to the front end of the outer cylinder 33 or the like.

For the outer cylinder 33, for example, a resin such as polyvinyl chloride can be used as a constituent material.

The internal liquid 32 can use a well-known buffer, for example, a pH 2~3 buffer prepared by mixing acetic acid and sodium hydroxide, or a pH 5~3 prepared by mixing citric acid, sodium hydroxide and sodium chloride. 6 of buffer, etc. In addition, 0.01M to 1M hydrochloric acid can also be used for the inner liquid 32. In addition, those obtained by adding a gelling agent such as agar and an evaporation preventing agent such as glycerin to these buffer solutions are also suitable for use as the internal liquid 32.

The internal electrode 31 may be any electrode as long as it operates stably in the internal liquid 32, and for example, a silver-silver chloride electrode is suitable.

Next, the principle of measuring the concentration of hydrogen ions using a hydrogen ion selective electrode will be explained using FIG. 3.

The hydrogen ion concentration is measured by using a counter electrode consisting of a combination of the hydrogen ion selective electrode 1 and the reference electrode 2. Hydrogen ion selective electrode 1, as mentioned above, has a selective response to hydrogen ion induction The membrane 34, if the sensing membrane 34 contacts the hydrogen ions in the sample solution, a membrane potential corresponding to its concentration will be generated. The reference electrode 2 immersed in the solution 20 is used as the counter electrode of the hydrogen ion selective electrode 1 and connected to the DC potentiometer 10, and the potential difference between the two electrodes 1 and 2 is measured, thereby measuring the membrane potential. The relative potential measured by the DC potentiometer 10 at this time is referred to as the response potential E.

Between the response potential E and the hydrogen ion concentration [H ⁺ ] in the solution, the following equation generally holds.

This formula is called Nernst (Nernst) formula. In the formula, E ₀ is the standard electrode potential at 25℃, R is the gas constant, T is the absolute temperature, Z is the charge number of the ion to be measured (1 for hydrogen ion), F is the Faraday constant, log ₁₀ is the common logarithm. In the formula, [2.303RT/(ZF)] is called the Nernst constant, and the constant value when the ion concentration changes 10 times is called the theoretical response gradient or Nernst gradient. In the case of a monovalent hydrogen ion, the theoretical value of the Nernst gradient at 25°C is about 59 mV. The measurement method using an ion selective electrode is described in detail in, for example, JIS K-0122 (General Rules of Ion Electrode Measurement Method) (Non-Patent Document 1). It can be converted to pH by the formula described in the [Prior Art] column of this manual.

The reference electrode is an electrode that outputs a reference potential, and an example of its configuration is shown in FIG. 4. FIG. 4 is only an example of a user that can be paired with the hydrogen ion selective electrode based on the present invention, and it can also be used as a reference electrode other than the example shown here.

The reference electrode includes an internal electrode 41, an internal liquid 42, an outer tube 43, and a liquid junction 44. The liquid junction 44 is a member for electrically connecting the internal liquid 42 and the solution, and is usually made of a porous material. The liquid junction 44 is preferably made of ceramics such as silicon carbide or fluororesin, which is durable to hydrofluoric acid. This is because if the liquid junction part made of glass is used, the glass will be corroded by hydrofluoric acid and block the liquid junction part. For the internal electrode 41, for example, a silver/silver chloride electrode is preferably used. The outer cylinder 43 is filled with an internal liquid 42 and the internal electrode 41 is immersed therein. When a silver/silver chloride electrode is used as the internal electrode 41, the internal solution 42 generally uses a saturated potassium chloride aqueous solution. The outer cylinder 43 is preferably made of a material that is not suspected of being corroded by hydrofluoric acid, such as plastic. The response potential from this reference electrode is taken out from the internal electrode 41 via a lead or the like.

The DC potentiometer 10 only needs to have a circuit with high input impedance, and a circuit with low noise is particularly preferred. As the DC potentiometer 10, a commercially available potentiometer for ion selective electrodes can be used.

The hydrogen ion selective electrode of the present embodiment described above is capable of measuring the pH of a solution containing hydrofluoric acid stably for a long time, and is particularly capable of measuring the pH of a strongly acidic solution. The hydrogen ion selective electrode of this embodiment can be ideally used for, for example, the pH measurement of a solution containing hydrofluoric acid and a pH of 2 or less, or the pH measurement of a solution containing hydrofluoric acid of 1000 mg/L or more.

[Example]

Next, the present invention will be explained in more detail with examples.

[Production of hydrogen ion selective electrode]

A hydrogen ion selective electrode having the structure shown in FIG. 1 was fabricated.

The sensing membrane 34 is made by adding a specified amount of hydrogen ion selective molecules, anion scavengers, plasticizers, and polymer matrix to tetrahydrofuran and dissolving them at room temperature. After stirring for 10 minutes, they are flattened on a glass plate It is made by air-drying it all day and night. After that, a film with a diameter of 6 mm was cut out, and a tetrahydrofuran solution of 50 mg/mL of polyvinyl chloride was used as an adhesive, and the film was mounted on the outer cylinder 33. After that, the buffer solution (1M citric acid+2.73M NaOH+0.01M NaCl) as the internal solution 32 of pH 5.6 is injected into the outer cylinder 33, and the internal electrode 31 is inserted, thereby completing the hydrogen ion selective electrode. The outer cylinder 33 uses a commercially available ion electrode kit (manufactured by East Asia DKK), and the inner electrode 31 uses a silver/silver chloride electrode formed by electrodepositing silver chloride on a silver wire. The composition of the sensing film 34 is shown in Table 1. The polymer matrix used polyvinyl chloride (manufactured by Sigma-Aldrich Co., Ltd.). The hydrogen ion selective molecules, anion scavengers, and plasticizers used will be described later.

[Measurement System]

The response potential E is measured using a silver-silver chloride electrode (ELCP type electrode manufactured by Toa DKK) using a porous fluororesin as the liquid junction and saturated potassium chloride aqueous solution as the internal liquid as the reference electrode , Using an ion meter (manufactured by Toa DKK, IM-55G) as a DC potentiometer, and using a constant temperature bath to set the water temperature to 25°C.

[experiment method]

Test by measuring the pH of a solution containing hydrofluoric acid by using a hydrogen ion selective electrode that has been made. Separately prepare a mixture of hydrofluoric acid and hydrochloric acid with a pH in the range of 0.5 to 4 and prepare a large number of different solutions as the test sample solution. When preparing the solution, the pH value is calculated from the amount of mixed hydrofluoric acid and hydrochloric acid. The prepared hydrogen ion selective electrode and reference electrode are immersed in order from the sample solution of pH 4.0, and the response potential E is measured and recorded. After the test, keep immersed in the sample solution of pH 0.5, and place it until the next measurement time.

[Confirmation of pH response range]

For the produced hydrogen ion selective electrode, separate the test from the solution containing hydrofluoric acid, and use the solution without hydrofluoric acid to confirm the pH response range. To confirm the pH response range, prepare a 10mM Tris(hydroxymethyl)aminomethane (Tris)+10mM NaOH solution, soak the hydrogen ion selective electrode and reference electrode made, and record the response while adding hydrochloric acid. Changes in potential. The pH of the solution was measured with a commercially available pH glass electrode.

(Example 1)

In order to explore the differences in the characteristics of hydrogen ion selective electrodes caused by different types of anion scavengers, Octadecyl isonicotinate (manufactured by Sigma-Aldrich Co., Ltd.) was manufactured and used under the trade name Hydrogen. ionophore IV, referred to as Ionophore IV) as a hydrogen ion selective molecule, using Potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (Potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) ( Sigma-Aldrich Co., Ltd., referred to as TFPB), four [3,5-bis(1,1,1,3,3,3-hexafluoro-2-methoxy-2-propyl)phenyl] Sodium tetrakis[3,5-bis(1,1,1,3,3,3-hexafluoro-2-methoxy-2-propyl)phenyl]borate trihydrate (Sigma-Aldrich Co., Ltd.) HFPB), Potassium tetrakis(4-chlorophenyl)borate (manufactured by Sigma-Aldrich Co., Ltd., TCPB for short), and Potassium tetraphenylborate (By Sigma-Aldrich Co., Ltd., TPB for short) as an anion scavenger, using 2-Nitrophenyl octyl ether (NPOE for short) as a plasticizer Sensing membrane, and made into hydrogen ion selective electrode.

First, for each hydrogen ion selective electrode at the time of production, the response potential E to pH in a solution containing 10000 mg/L of hydrofluoric acid was determined. The results are shown in Figure 5. In addition, for comparison, the measurement results of a commercially available glass electrode (manufactured by Toa DKK, type ELP-040, abbreviated as glass) for hydrofluoric acid solution measurement are also shown in FIG. 5. No matter which electrode, in the strong acidic range of pH 0.5~4, a Nernst gradient with a potential change of -59mV for every pH difference 1 is obtained.

Next, place the electrodes while keeping them immersed in a solution of pH 0.5 containing 10000 mg/L of hydrofluoric acid, measure the pH response after a specified time, and obtain the potential gradient △ from the difference between the response potential of pH 1 and pH 2. E. The results are shown in Fig. 6. It can be clearly understood from Figure 6 that even a commercially available glass electrode used for measurement of hydrofluoric acid solution is immersed in a strong acid solution of pH 0.5 containing 10000 mg/L of high-concentration hydrofluoric acid. The response disappeared within 10 days. In addition, the hydrogen ion selective electrode using TCPB or TPB as the anion scavenger also disappeared within 10 to 20 days from the start of immersion. On the other hand, a TFPB or HFPB hydrogen ion selective electrode is used which is a compound represented by the above formula (21), and which corresponds to a compound in which the substituent R ₆ in formula (21) has a substituent containing at least one fluorine atom, After immersing in a solution of pH 0.5 containing hydrofluoric acid for 8 months, it still showed a pH response. From this, it can be clearly understood that the hydrogen ion selective electrode based on the present invention is effective for pH measurement of a solution containing hydrofluoric acid.

For the hydrogen ion selective electrode using TFPB as an anion scavenger, the pH response range was confirmed by measuring the pH of a solution containing no hydrofluoric acid. The result is shown in FIG. 7. It can be seen from Figure 7 that the hydrogen ion selective electrode, which uses Ionophore IV as the hydrogen ion selective molecule and TFPB as the anion scavenger, can be applied to the measurement of the pH range of 0.5 to 5 (strongly acidic to acidic range).

(Comparative example)

For comparison, with respect to the hydrogen ion selective electrode described in Patent Document 1, the change in characteristics after immersing in a solution containing hydrofluoric acid was investigated.

As a hydrogen ion selective electrode of a comparative example, a hydrogen ion selective electrode (referred to as TOPO- in the figure) was produced using TOPO as a hydrogen ion selective molecule, TCPB as an anion scavenger, and NPOE as a plasticizer. TCPB); and a hydrogen ion selective electrode (referred to as TOPO-TFPB in the figure) using TOPO as a hydrogen ion selective molecule, TFPB as an anion scavenger, and NPOE as a plasticizer.

The electrodes were placed in the state of being immersed in a solution of pH 0.5 containing 10000 mg/L of hydrofluoric acid. After a specified time, the pH response was measured, and the potential gradient ΔE was obtained from the difference between the response potentials of pH 1 and pH 2. The results are shown in Fig. 8. In Figure 8, for comparison, the hydrogen ion selective electrode shown in Example 1 using Ionophore IV as the hydrogen ion selective molecule, TFPB as the anion scavenger, and NPOE as the plasticizer is also shown. (Referred to as Ionophore IV-TFPB in the figure).

Although Patent Document 1 does not disclose information on the measurement example and its durability in a solution containing hydrofluoric acid, as is clear from FIG. 8, if the use of TOPO as hydrogen ion selectivity as disclosed in Patent Document 1 is adopted The hydrogen ion selective electrode which uses TCPB as an anion scavenger and is immersed in a solution containing 10000 mg/L of hydrofluoric acid with a pH of 0.5, the response disappears within 10 days from the start of the immersion. Even if TFPB contained in the category of the above formula (2) is used as an anion scavenger, when amine-based hydrogen ion selective molecules are not used as hydrogen ion selective molecules (TOPO-TFPB), the same 10 days from the start of soaking The answer disappears within. This shows that the combination of the amine-based hydrogen ion selective molecule and the anion scavenger represented by the above general formula (2) is effective.

(Example 2)

Use 4-Nonadecylpyridine (manufactured by Sigma-Aldrich. Trade name Hydrogen ionophore II, referred to as Ionophore II) as hydrogen ion selective molecule, TFPB as anion scavenger, and NPOE as plasticizer It is a hydrogen ion selective electrode.

For this hydrogen ion selective electrode when it was just manufactured, the response potential E to pH in a solution containing 10000 mg/L of hydrofluoric acid was obtained. The results are shown in Fig. 9. In the strong acid range of pH 1~4, a Nernst gradient with a potential change of -59mV for every pH difference 1 can be obtained.

Next, place the hydrogen ion selective electrode while keeping it immersed in a solution of pH 0.5 containing 10000 mg/L of hydrofluoric acid, and measure the pH response after a specified period of time, which is obtained from the difference in response potential between pH 1 and pH 2. Potential gradient △E. The results are shown in Fig. 10. It can be seen from Figure 10 that even if it is a hydrogen ion selective molecule that is different from that of the user in Example 1, as long as it is a hydrogen ion selective electrode using an amine-based hydrogen ion selective molecule, it still responds after 3 months. The present invention is effective.

For the hydrogen ion selective electrode of Example 2, the pH response range was confirmed by measuring the pH of the solution containing no hydrofluoric acid. The result is shown in FIG. 11. It can be seen from Figure 11 that this hydrogen ion selective electrode can be applied to the measurement of pH 1~10.

(Reference example 1)

In order to investigate the influence of the type of plasticizer contained in the sensing membrane, Ionophore IV was used as a hydrogen ion selective molecule, TFPB was used as an anion scavenger, and any of NPOE, BBPA, DOS and TEHP was used as a plasticizer. It is a hydrogen ion selective electrode.

First, for each hydrogen ion selective electrode at the time of production, the response potential E to pH in a solution containing 10000 mg/L of hydrofluoric acid was obtained. No matter which hydrogen ion selective electrode, in the strong acid range of pH 1~4, a Nernst gradient with a potential change of -59mV per pH difference 1 is obtained.

Next, place the electrodes while keeping them immersed in a solution containing 10000 mg/L of hydrofluoric acid at a pH of 0.5, and measure the pH response after a specified period of time, and obtain the potential gradient △ from the difference between the response potentials of pH 1 and pH 2. E. The results are shown in Fig. 12. Both electrodes show long-term stable response characteristics.

It can be seen from the above that the characteristics of the hydrogen ion selective electrode based on the present invention will not change greatly depending on the type of plasticizer.

(Reference example 2)

For a commercially available glass electrode (manufactured by Toa DKK, model ELP-040) for hydrofluoric acid solution measurement, the response potential E to pH in a solution containing hydrofluoric acid 1000 mg/L was determined. As a result, a Nernst gradient with a potential change of -59mV for every pH difference 1 in the strong acid range of pH 1~4 is obtained.

Secondly, the glass electrode was immersed and placed in a solution of pH 0.5 containing 1000 mg/L of hydrofluoric acid. After a specified time, the pH response was measured, and the potential gradient ΔE was obtained from the difference between the response potentials of pH 1 and pH 2. The results are shown in Fig. 13. It has been confirmed that when a glass electrode is used, the Nernst response disappears after 1 day in a solution containing 1000 mg/L of hydrofluoric acid at pH 0.5.

[Industrial use]

The hydrogen ion selective electrode based on the present invention can be used, for example, for pH measurement in the production step using hydrofluoric acid-containing solution, or the treatment step of hydrofluoric acid-containing waste liquid.

Claims (7)

A pH measurement method is to immerse a hydrogen ion selective electrode and a reference electrode in a solution containing hydrofluoric acid, and measure the response potential generated between the hydrogen ion selective electrode and the reference electrode to determine the pH of the solution. It is characterized in that: a hydrogen ion selective electrode with a sensing membrane is used. The sensing membrane contains hydrogen ion selective molecules of amine series and an anion scavenger represented by the following formula (3); the measured pH is above 0.5 and below 4 PH of the solution;

In formula (3), Z ₁ to Z ₄ are substituted phenyl Z which may be the same or different from at least 2 of Z ₁ to Z _4. The general formula of substituted phenyl Z is as follows (3a) means;

In formula (3a), R ₁ to R ₅ are each independently a hydrogen atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, and a fluorine atom-containing substituent group having 1 to 6 carbon atoms, R ₁ At least one of ~R ₅ contains a fluorine atom, or a fluorine atom-containing substituent with 1 to 6 carbon atoms. For example, the pH measurement method of item 1 in the scope of patent application, wherein the anion scavenger is a compound represented by the following formula (4);

In formula (4), R ₆ is a substituent containing at least one fluorine atom. Such as the pH measurement method of item 2 in the scope of the patent application, wherein the substituent R ₆ is a substituent having at least one trifluoromethyl group. Such as the pH measurement method of item 2 in the scope of the patent application, wherein the substituent R ₆ is -CF ₃ or -C(CF ₃ ) ₂ OCH ₃ . Such as the pH measurement method of any one of items 1 to 4 in the scope of the patent application, wherein the amine-based hydrogen ion selective molecule is a hydrogen ion selective molecule containing a pyridine derivative. For example, the pH measurement method of item 1 in the scope of the patent application is to measure the pH of a solution containing hydrofluoric acid and a pH of 2 or less. For example, the pH measurement method of item 1 in the scope of the patent application is to determine the pH of a solution containing hydrofluoric acid above 1000 mg/L.

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