JPH03137559A - Ph sensor - Google Patents

Abstract

PURPOSE:To obtain a stable pH sensor having chemical resistance, especially, hardly corroded by strong acid or strong alkali by using specific phosphine oxide being a proton responsive substance (neutral carrier). CONSTITUTION:As phosphine oxide being a neutral carrier having excellent selectively, there is phosphine oxide wherein the total number of carbon atoms contained therein is 18 or more and one carbon chain is composed of at least 6 or more carbon atoms. As a further pref. neutral carrier, there is phosphine oxide represented by general formula I (wherein R1 - R3 are an aliphatic residue and/or an aromatic residue and at least one of R1 - R3 is a 6 or more C group) and characterized by that the total number of carbon atoms contained therein is 18 or more and one carbon chain is composed of at least 6 or more carbon atoms.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a pH sensor, and particularly to a neutral carrier membrane type ion selective electrode type pH sensor.

[Prior art] pH sensors are used for experiments, pH control in various plants,
It is used for a wide range of purposes including environmental management such as measuring industrial wastewater.

Conventionally, what has been widely used for this purpose is a so-called glass electrode using a glass thin film as a response membrane.Glass electrodes have a wide pH response range and good ion selectivity, but have the following drawbacks.

1. The structure is complex because it consists of an outer wall with a glass membrane, an inner electrode made of silver electrodes, etc., and an internal salt bath liquid (KCI solution, etc.) that connects these, and impedance increases when miniaturized. Due to the high cost and difficulty of measurement, it is difficult to manufacture sensors that are smaller, larger, or of various shapes (needle-like, flat-plate, etc.) due to processing and manufacturing considerations.

2. Stable measurement is difficult because the glass thin film is gradually attacked in a highly alkaline solution, and there is also a problem that it is attacked by chemicals such as hydrofluoric acid.

3. Glass electrodes are brittle and susceptible to impact. Also, there is no flexibility.

In order to improve the above-mentioned drawbacks of glass electrodes, an ion-selective electrode type pH sensor using a binary carrier membrane has been developed.

1) ^nalytica Chimica Acta,
Vol. 13, p. 111 (1981) 2) Chimica
, Vol. 35, p. 178 (1981) Here, a so-called 221 tral carrier is used as a response membrane in a plasticized polymer membrane (a membrane made of a polymer compound such as polyvinyl chloride and a plasticizer such as sebacate ester). This is a pH sensor that uses a dissolved proton-sensitive substance as a response membrane, and as a neutral carrier, tri-n-dodecylamine is used in Reference 1), and 3-hydroxy-N-dodecylvicolinamide is used in Reference 2). . This pH sensor is
Although they are superior to glass electrodes in terms of manufacturing problems, chemical resistance, and impact resistance, they have a narrow pH response range and poor ion selectivity.

A film made of 3-hydroxy-N-dodecylpicolinamide, which is reported in literature 2) and is said to have excellent properties especially on the acidic side, also has p
It only responds up to around H1, and there are practical problems with fat-soluble acids such as perchloric acid and picric acid, as they are interfered with by perchlorate ions and picric acid ions.

[Problem to be solved by the invention] The objects of the present invention are as follows.

1. To provide a new pH sensor that is ultra-small, large-sized, or of various shapes without any problems in processing and manufacturing.

2. To provide a pH sensor that is strong against impact and has flexibility.

3. To provide a stable pH sensor that has chemical resistance, and is particularly resistant to corrosion by weak acids and strong alkalis.

4. To provide a pH sensor with a wide pH response range and excellent ion selectivity, especially a pH sensor that responds to the highly acidic side and is less susceptible to interference by fat-soluble ions.

[Means for Solving the Problems] The purpose of the present invention is to provide a neutral carrier in which a certain type of phosphine oxide has excellent selectivity (a proton-sensitive carrier sensitive to protons but not sensitive to other ions). This was achieved by developing a neutral carrier membrane ion-selective electrode type pH sensor using this phosphine oxide as a neutral carrier.

As the phosphine oxide, a phosphine oxide in which the total number of carbon atoms contained in the compound is 18 or more and the length of one carbon chain is at least 6 or more carbon atoms is a neutral carrier with excellent selectivity. As a more preferable neutral carrier, the following general formula (
I), and the total number of carbon atoms contained in the compound is 1
The phosphine oxide is 8 or more, and the length of one carbon chain is at least 6 or more carbon atoms.

In the general formula, R1, R2, and R3 represent aliphatic residues and/or aromatic residues, and RISR2 and R5 may be the same or different, and may contain a heteroatom. Furthermore, a ring may be formed between R3 and R2, and between R11R2 and R3. However, at least one of RISR2 and R3 represents a group having 6 or more carbon atoms.

Phosphine oxide exhibits excellent selectivity, especially on the acidic side. Examples of structural formulas of specific phosphine oxide compounds that serve as neutral carriers exhibiting excellent selectivity are shown below. It goes without saying that neutral carriers that are effective in the present invention are not limited to these specific examples.

C, Hl 1 C 婁Hs An example of the configuration of a neutral carrier exchange type ion selective electrode type pH sensor using the above phosphine oxide is shown in FIG. In the figure, 1 is a neutral carrier plasticized polymer film containing phosphine oxide, which contains copper, silver, gold, platinum, graphite, etc. coated with an insulator 3 such as Teflon.
It is closely fixed to the tip of an electrode 2 made of a conductive material such as flat carbon. Figure 1 shows a case in which a round bar-shaped electrode is used for the electrode 2, but since metal is used as the material for the electrode, it has good impact resistance and is easy to work with, so it is not limited to this. It can be used to collect objects with various shapes such as needles, plates, and spheres. Therefore, pH sensors of various shapes, such as ultra-small and large-sized ones, can be made.

Neutral carrier plasticized polymeric membranes are composed of a polymeric material, a plasticizer, and a neutral carrier, phosphine oxide. As the polymer material, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl butyral, silicone rubber, etc. are used, and polyvinyl chloride is the most preferred material. As the plasticizer, phthalic acid ester-based, sebacic acid ester-based, adipic ester-based, phosphoric ester-based, phenyl ether-based plasticizers, etc. are used. The polymeric material and plasticizer may be those that have good affinity with phosphine oxide and can exhibit good characteristics as a neutral carrier film together with phosphine oxide, and both are limited by the above examples. It's not a thing.

The composition of the membrane is, by weight, 25 to 45% polymer material (preferably around 33%) and 75 to 55% plasticizer (preferably 6%).
6%) and 0.1 to 1% phosphine oxide (preferably around 0.6%). Further, a trace amount (approximately 0.5%) of tetraphenylborate salt, divicrylamine salt, etc. may be added for the purpose of reducing the electrical resistance of the film. The electrical resistance of the resulting membrane can typically be much lower than that of glass membranes. The membrane can be formed by dissolving a polymer material, a plasticizer, and phosphine oxide in an organic solvent such as tetrahydrofuran (THF) or cyclohexanone, and applying this solution directly onto the electrode (or its tip) to make it adhere. Alternatively, this solution can be cast onto a glass plate to evaporate the organic solvent to form a film, and the film can be electrically conductively adhered to the electrode and fixed tightly, or the film can be placed on the tip of the electrode. It is also possible to cover and fix a chemical-resistant net such as Teflon net.

The pH sensor configuration shown in Fig. 1 is an electrode belonging to the so-called coated wire type electrode, but there are also other electrodes such as the Moody-Thomas type electrode [Surface, 24 volumes, N
o, page 3.12 (5) (1986), Figure 6] and FET
Type electrode [Patent application No. 63-219194. 63-2252
81. 63-288059].

FIG. 2 shows an example of a measurement system using the sensor of the present invention. In the figure, the PH sensor and the reference electrode are shown separately, but they can also be integrated and used as a single electrode. In FIG. 2, 4 represents the pH sensor of the present invention, and 5 represents the pH sensor of the present invention.
The reference electrodes are immersed in the test liquid 7 contained in the tank 8, and the potential difference generated is measured by the potentiometer 6.

[Example] (Example 1) 1. Objective An experiment was conducted to prove that a membrane using phosphine oxide exhibits an excellent pH response, especially on the acidic side.

2. Experiment a. The phosphine oxide used in the experiment for creating a neutral carrier film was tri-n-octylphosphine oxide shown in the structural formula No. 1 among the specific compounds shown above. Furthermore, polyvinyl chloride was used as the polymer material, and dioctyl sebacate was used as the plasticizer. Each material was weighed out and dissolved in tetrahydrofuran so that the film composition was 0.06% tri-n-octylphosphine oxide, 33.31% polyvinyl chloride, and 66.63% dioctyl sebacate by weight. After thorough mixing, this solution was spread evenly on the bottom of a glass Petri dish with a flat bottom, and the solvent tetrahydrofuran was evaporated at room temperature to form a neutral carrier film with a thickness of about 400 μm.

b. Creation of pH sensor A pH sensor having the shape shown in FIG. 1 was created.

As electrode 2 in the figure, a Francie carbon electrode with a diameter of 5 mm was used. The created neutral carrier film has a thickness of 3 mm.
A pH sensor was made by cutting out a circular shape, attaching it to the tip of the electrode as shown in Figure 1, and fixing it with Teflon net.

c. Assembling the pH measuring device The measuring device shown in Figure 2 was assembled.

The pH sensor 4 is contained in the test liquid 7 contained in the tank 8.
is immersed together with a silver-silver chloride electrode as a reference electrode 5. At this time, the pH sensor 4 and the reference electrode 5 are each connected to a potentiometer 6, and the potential difference (electromotive potential) of the pH sensor with respect to the reference electrode 5 is measured by the potentiometer 6.

d. pH measurement of test solution H, PO, 0,01M5H, Bo as test solutions.

0, OIMSCH, C00HO, 01MSKNOsO1
Universal buffer solution (pH 2~
12, adjusted with KoH) was used to measure the electromotive potential of the pH sensor for each pH. The pH of the test solution was tested using a glass electrode.

3. Results Figure 3 shows the relationship between the electromotive potential value and pH of the pH sensor of the present invention. The relationship between electromotive potential value and pH is 57 m per pH.
It shows a good linear relationship with a slope of V. Furthermore, the response time of the pH sensor of the present invention was within 3 seconds, which was good.

(Example 2) 1. Purpose The conventional neutral carrier prototype ion-selective electrode type pH sensor has the ability to interfere with fat-soluble ions such as perchlorate ions and picrate ions, especially on the acidic side. It is known that the correct value is not shown at a receiving pH of 2 or higher.

[Reference Chimica, Vol. 35, p. 178 (1981
) Therefore, an experiment was conducted to prove that the pH sensor of the present invention is not affected by such ion interference at a pH of slightly less than 1.

2. Experimental The configuration of the pH sensor and the configuration of the pH measuring device are the same as in (Example 1). A 0.2M H(10, solution) was used as the test solution.An appropriate amount of IM NaOH aqueous solution was added dropwise to this solution, and while the pH of the solution was gradually lowered, the electromotive potential of the pH sensor of the solution was measured at each time. The value was measured and at the same time the pH of the solution was verified using a glass electrode.

3. Results Figure 4 shows the relationship between electromotive potential value and pH in a 0.2M MCl1O solution.

The electromotive potential value of the pH sensor of the present invention is 0.2M HCl0
．． Even in solution, it shows a good linear relationship with pH up to pH 1 or less. This means that in the pH sensor of the present invention, C1
This shows that the presence of fat-soluble ions such as o4- does not interfere with pH measurement.

〔Effect of the invention〕

The pH sensor of the present invention exhibits excellent response characteristics even on the strongly acidic side, and is hardly susceptible to fat-soluble interference such as perchlorate ions and picrate ions. It is also possible to measure the pH of hydrofluoric acid solutions, which is impossible with glass membrane electrodes. Furthermore, since it has excellent impact resistance, pH can be monitored with good reproducibility. Furthermore, since it can be easily processed into various shapes, it can be used in a wide range of fields, from large industrial sensors to ultra-small medical sensors.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts showing an example of a pH sensor according to the present invention, FIG. 2 is a schematic diagram showing how the pH sensor of the present invention is used, and FIG. 3 is a diagram showing the origin of the pH sensor of the present invention in Example 1. Graph showing the relationship between potential value and pH. FIG. 4 is a graph showing the relationship between electromotive potential value and pH of the pH sensor of the present invention in Example 2. Figure procedural amendment December 22, 1999

Claims (1)

[Claims] 1. A phosphine oxide in which the total number of carbon atoms contained in the compound is 18 or more and the length of each carbon chain is at least 6 carbon atoms is used as a proton-sensitive substance (neutral carrier). Neutral carrier membrane type ion selective electrode type pH sensor. 2. The phosphine oxide has the following general formula (I)
The neutral carrier membrane ion selective electrode type pH sensor according to claim 1, which is a compound represented by: General formula▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) In the formula, R_1, R_2, R_3 are aliphatic residues or /
and represents an aromatic residue, and R_1, R_2, and R_3 may be the same or different, and may contain a heteroatom. Furthermore, between R_1 and R_2, and R_1
, R_2, and R_3 may form a ring, provided that at least one of R_1, R_2, and R_3 represents a group having 6 or more carbon atoms.