JPH0371039A - Ion measuring device - Google Patents

Abstract

PURPOSE:To miniaturize the sensor part and to facilitate the handling and measurement by forming the sensor part only by a piezoelectric element and an ion sensitive material. CONSTITUTION:The sensor part 1 is connected to an impedance measuring device 2 with the measuring frequency capable of being optionally set, and the measuring device 2 is connected to a computer 3 for arithmetic control. The sensor part 1 is fixed in a cell 7 so that only one side of the piezoelectric element 6 is brought into contact with a sample to be tested. The surface of the element 6 to be brought into contact with the sample is coated with an ion sensitive material 8. The resonance frequency and resonance resistance value of the element 6 are obtained by measuring the impedance by the impedance measuring device 2 in the vicinity of the resonance frequency of the element 6 and calculating the impedance by the computer 3. Consequently, since a standard sample need not be retained in the sensor, attention need not be paid to handling, and measurement is easily carried out without any special pretreatment.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to the fields of analyzing ion species and quantifying ions in solutions in the fields of analytical chemistry, electrochemistry, food industry, medicine, and pharmacy. is possible.

[Summary of the invention]

As shown in FIG. 2, the sensor section of the ion measuring device of the present invention has a structure in which a piezoelectric element is coated with an ion-sensitive substance. This ion measurement device is characterized by detecting changes in the weight and structure of the ion-sensitive material that occur when the ion-sensitive material captures ions, as changes in the resonance resistance value or resonance frequency of the piezoelectric element. By using an ion-sensitive material that selectively captures specific ions, specific ions can be quantified without analysis of ion species or special separation operations.

The present invention includes a sensor section and at least one of a resonant frequency measuring device or a resonant resistance measuring device.

[Conventional technology]

As shown in FIG. 3, a conventional ion measurement device has a membrane (ion-selective membrane 9) that selectively responds to target ions placed between a standard sample 10 and a test sample 11. However, a common method is to measure the potential difference generated across the membrane using two reference electrodes 12. Examples of the ion-selective membrane 9 include those using a glass thin membrane, a solid membrane of poorly soluble salt, and a membrane in which PVC (polyvinyl chloride) is impregnated with an ion-sensitive substance. Those using a glass thin film can emit hydrogen ions,
Sensors for sodium ions using poorly soluble salt solid membranes have been put into practical use as sensors for fluorine ions and chloride ions. Examples of sensors using PVC membranes include sensors for potassium ions impregnated with crown ether or palinomycin. In addition, there have also been reports of ions being quantified from changes in the resonance frequency of a crystal resonator, which occurs when the target ion is made into a poorly soluble salt and adhered to the crystal resonator.

[Problem to be solved by the invention]

Conventional ion measuring devices that use an ion-selective membrane in the sensor section have two
Two reference electrodes are required. This reference electrode includes a silver/silver chloride electrode and a saturated calomel electrode (SCE), but both have somewhat complex structures. In addition, this type of ion measurement device requires a standard sample and has a structure that holds liquid inside the sensor, making it difficult to miniaturize the sensor unit and requiring careful handling. There was a problem.

On the other hand, in an ion measuring device that measures the change in the resonant frequency of a crystal resonator when ions are made into a poorly soluble salt and attached to the crystal resonator, an operation to convert the target ion into a poorly soluble salt is required. The problem was that it required

(1) [Means for Solving the Problems] In the ion measuring device of the present invention, the sensor portion is composed only of a piezoelectric element and an ion-sensitive material, and measurement can be performed simply by immersing the sensor portion in a test sample.

Therefore, the structure of the sensor section is simple and miniaturization is easy. Furthermore, since there is no need to hold a standard sample inside the sensor, there is no need to pay special attention to handling, and measurements can be easily performed without special pretreatment.

[Effect]

A piezoelectric element is a device that utilizes the piezoelectric effect, and generates mechanical vibration by applying a voltage at a frequency near the resonance frequency. Although this vibration is extremely small,
When the substances are in contact with each other, they are subjected to resistance due to shear stress between the substance, the liquid, and the surface of the piezoelectric element. The resistance coefficient of this mechanical resistance can be considered to be equivalent to the electrical resistance when considering the correspondence between the mechanical vibration and the electrical vibration of the piezoelectric element. This resistance is called resonance resistance, and it changes depending on the viscoelasticity and density of the material with which the surface of the piezoelectric element is in contact.

It is also known that the resonance frequency changes due to the influence of viscosity, density G, and weight changes such as adsorption of substances onto the surface. On the other hand, ion-sensitive substances such as cyclic depsipeptides, cyclic peptides, cyclic lactones, and cyclic polyethers are known to include ions within one molecule or between multiple molecules. Palinomycin, a type of cyclic depsipeptide, has specificity for potassium ions, and crown ether, a type of cyclic polyether, has different selectivity for ions depending on the size of the crown ring.

Therefore, by coating a piezoelectric element with an ion-sensitive material that is selective to the target ions, changes in weight and structure when these ion-sensitive materials capture ions can be reflected in changes in the piezoelectric element's resonant frequency and resonance. This can be detected as a resistance change.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. FIG. 1 is a schematic diagram of the ion measuring device of the present invention. In FIG. 1, a sensor section 1 is connected to an impedance measuring device 2 whose measurement frequency can be arbitrarily set, and the impedance measuring device 2 is connected to a computer 3 for performing calculation and control.
The computer 3 has a printer 4. Display 5 is connected. The impedance measuring device 2 and the computer 3 can measure the resonant resistance value and the resonant frequency. FIG. 2 shows a schematic diagram of the sensor section of the ion measuring device of the present invention. Second
In the figure, the piezoelectric element 6 is fixed in the cell so that only one side is in contact with the test sample. The surface of the piezoelectric element 6 in contact with the test sample is coated with an ion-sensitive material 8.

The resonant frequency and resonant resistance value of the piezoelectric element 6 are
The impedance was determined by measuring the impedance near the resonance frequency.

Specifically, in impedance measurement, since there is a resonance frequency between the frequencies that give the maximum and minimum values of susceptance, which is the imaginary part of atomic sotance, the maximum and minimum values of susceptance are found by frequency sweeping, and the The susceptance of conductance was measured at equally spaced frequencies. As for the measured values, conductance and susceptance data were processed by the circular least squares method to determine the diameter of the circle, and the reciprocal of this was taken as the value of the resonant resistance. Further, the center of the circle was found, and a frequency on the circle having the same directness as the susceptance value at this center point was found from a polynomial approximation of the susceptance and the measurement frequency, and this was taken as the resonance frequency.

Such measurement and calculation processing can be automatically performed by a computer, and in the device of the present invention, 1
It was possible to perform multiple measurements within 3 seconds.

Crown ether having a structure as shown in FIG. 4 is used as the ion-sensitive material 8, and the piezoelectric element 6 has a resonance frequency of 9M.
As a result of measuring the concentration of potassium ions in the water'lB solution using a Hh AT-cut crystal oscillator, it was found that the resonance resistance and resonance frequency changed depending on potassium J and ion flow rate. became. This demonstrated that the ion measuring device of the present invention is capable of quantifying ions. Similar measurements were made using A'F cut or 8T with a resonance frequency of 1 to 40 M tlz as the piezoelectric element 6.
Cut crystal oscillator and resonance frequency is 10k, IIZ ~
It is also possible to measure using a ceramic piezoelectric body of 10 Mllz, and instead of the impedance measuring device 2, a resonance frequency measuring device consisting of an oscillation circuit and a frequency counter, or a resonant frequency measuring device consisting of an oscillation circuit and an oscillation amplitude measuring circuit can be used. It can also be measured using a resonant resistance measuring device.

〔Effect of the invention〕

By using the ion measuring device of the present invention, it has become possible to downsize the sensor section compared to conventional ion measuring devices. In addition, it was possible to simplify the handling of the sensor unit and the measurement method.

Figure 4 shows the ion-sensitive material (Dihenso 1) used in this example.
FIG. 8-Crown-6) is a diagram showing the structure.

■・・・Sensor part 6...Piezoelectric element 8...Ion sensitive substance that's all

Claims (5)

[Claims] (1) A piezoelectric element coated on at least one side with an ion-sensitive material is used in the sensor part, and the resonance resistance value of the piezoelectric element that occurs when ions in the solution are captured by the ion-sensitive material, or the resonance frequency change, An ion measuring device equipped with an ion sensor, which is characterized by determining ion species, ion concentration, and ion concentration. (2) The ion measuring device according to claim 1, comprising the sensor section and at least one of a resonant frequency measuring device or a resonant resistance value measuring device. (3) The piezoelectric element is an AT-cut crystal resonator or B
The ion measuring device according to claim 2, which is a T-cut crystal resonator. (4) The ion measuring device according to claim 2, wherein the piezoelectric element is a ceramic piezoelectric body. (5) The ion measuring device according to claim 3 or 4, wherein the ion-sensitive substance is any one of a cyclic depsipeptide, a cyclic peptide, a cyclic lactone, and a cyclic polyether.