JP2009174930A - Viscosity measuring device and viscosity measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a deviation amount of impedance at a high sensitivity, even for such a material as water, and the like, that intrinsically has low viscosity. <P>SOLUTION: A viscosity measuring device includes a reaction tank 12 which is communicated with a liquid introducing passage 18 and a liquid discharge passage 19 and a sensor in which a crystal resonator is resonated by ac signal supplied from a pair of electrodes on both surfaces of the crystal resonator set at the bottom part of the reaction tank. When a liquid of a measurement object is introduced into the reaction tank from the liquid introducing passage, the viscosity of the liquid is measured from the deviation amount of the impedance, at the resonance of the sensor then. The depth D of the reaction tank is set shallower than the degree of liquid infiltration, indicating the depth averaging the distances for the vibration of the crystal resonator at the liquid interface to infiltrate the liquid. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a viscosity measuring apparatus and a viscosity measuring method capable of measuring the viscosity in real time even if the amount of liquid to be measured is very small.

Conventionally, as a method for measuring the viscosity of a liquid, a measuring method using a viscosity capillary method or a quartz resonator is known. The viscosity capillary method is a method for obtaining the viscosity from the speed at which the liquid falls through the capillary. In addition, the measurement method using a crystal resonator is a method of measuring the impedance of the crystal resonator and then measuring the viscosity of the liquid.
The measurement method using a crystal resonator is capable of measuring even a very small amount of sample, and has an advantage that a change in mass adhering to the electrode surface of the crystal resonator can be simultaneously measured in real time.
Among the measurement methods using a crystal resonator, impedance measurement is performed using an impedance analyzer and a computer (see Patent Document 1), an oscillation circuit, a VF converter, a current-voltage conversion circuit, a peak. A measurement method using a device composed of a hold circuit (see Patent Document 2) is known.
Japanese Patent Laid-Open No. 4-151538 JP-A-6-109676

By the way, in the measuring method using the conventional crystal unit for measuring impedance, there is a problem that although a liquid having a high viscosity can be measured relatively easily, it is very difficult to measure a liquid having a low viscosity.
This is considered to be because when the impedance of the crystal resonator changes with a change in viscosity, the amount of change in impedance is too small for the liquid with low viscosity to measure the viscosity.

As a result of extensive research, the inventors have determined that the amount of change in impedance depends on the depth of the reaction vessel in which the frequency measurement sensor is accommodated, in other words, the amount of change in impedance is the depth of the reaction vessel. It has been found that the shallower the is, the larger it appears.
The present invention has been made in consideration of such circumstances, and its purpose is to provide a viscosity measuring device capable of measuring the amount of change in impedance with high sensitivity even with a liquid having a low viscosity such as water. It is to provide a viscosity measurement method.

In order to achieve the above object, the present invention provides the following means.
The viscosity measuring apparatus according to the present invention includes a reaction tank communicated with a liquid introduction path and a liquid discharge path, and an alternating current provided from a pair of electrodes on the front and back surfaces of the piezoelectric element provided at the bottom or top plate of the reaction tank. A sensor in which the piezoelectric element is resonated by a signal, and a liquid to be measured is introduced into the reaction tank from the liquid introduction path, and the impedance of the reference solution of the sensor at that time and the liquid to be measured A viscosity measuring device that measures the viscosity of the liquid from the amount of change from the impedance of the reactor, wherein the depth of the reaction tank is the average distance that the vibration penetrates into the liquid when the piezoelectric element vibrates at the liquid interface. It is characterized by being set shallower than the degree of liquid penetration.

  According to the viscosity measuring apparatus according to the present invention, the piezoelectric element causes mechanical vibration when an AC signal having a frequency near the resonance point is applied. This vibration of the piezoelectric element receives a shear resistance from the liquid flowing in the reaction tank. The resonance resistance value, that is, the impedance at this time varies depending on the viscosity of the liquid. Therefore, the viscosity of the liquid can be known by measuring the amount of change in impedance.

Here, when the vibration of the piezoelectric element receives shear resistance from the liquid in the reaction tank, the resonance resistance value varies greatly depending on the depth of the reaction tank.
In other words, when the depth of the reaction tank is deeper than the liquid penetration degree representing the average distance that the piezoelectric element vibrates at the liquid interface, the vibration of the piezoelectric element is received from the liquid in the reaction tank. Although the resonance resistance value is very small, if the depth of the reaction tank is shallower than the viscosity penetration, the resonance resistance value that the vibration of the piezoelectric element receives from the liquid in the reaction tank increases rapidly.

  In the present invention, since the depth of the reaction tank is set to be shallower than the viscosity penetration degree, the resonance resistance value of the vibration of the piezoelectric element, that is, the impedance itself is measured as a large value. Therefore, when the impedance changes under the influence of the viscosity of the liquid flowing in the reaction tank, the amount of change can be measured even when the impedance change rate is small. In other words, the amount of change in impedance can be measured with high sensitivity.

  The invention according to claim 2 of the present application is supplied from a reaction tank communicating with the liquid introduction path and the liquid discharge path, and a pair of electrodes on the front and back surfaces of the piezoelectric element provided at the bottom or top plate of the reaction tank. A sensor in which the piezoelectric element is resonated by an AC signal, and a liquid to be measured is introduced into the reaction tank from the liquid introduction path, and the impedance of the reference solution of the sensor at that time and the measurement target A viscosity measuring apparatus for measuring the viscosity of the liquid from the amount of change from the impedance of the liquid, wherein the depth of the reaction vessel is set to 20 μm to 200 μm.

  According to the present invention, since the depth of the reaction tank is set to 20 μm to 200 μm, even if the liquid to be measured is a liquid having a relatively low viscosity such as water, the depth of the reaction tank is set to be viscous. As a result, when the impedance changes under the influence of the viscosity of the liquid flowing in the reaction tank, the amount of change can be measured with high sensitivity.

The invention according to claim 3 of the present application is characterized in that a depth of the reaction vessel is set to 40 μm to 165 μm.
In this case, since the depth of the reaction tank is set shallower in a narrower range, the amount of change in impedance when the impedance changes can be measured with higher sensitivity.

In the invention according to claim 4 of the present application, when the liquid to be measured is introduced into the reaction tank from the liquid introduction path, the impedance of the reference solution of the sensor and the impedance of the liquid to be measured In addition to the amount of change, the amount of change in resonance frequency is also measured, and the viscosity of the liquid is evaluated.
In this case, the viscosity is evaluated by adding the amount of change in the resonance frequency in addition to the amount of change in the impedance of the reference solution and the impedance of the liquid to be measured. It is also possible to measure a minute change in weight due to the substance attached to the sensor. As a result, the properties of the liquid having a relatively low viscosity can be evaluated in more detail.

The invention according to claim 5 of the present application is characterized in that the liquid introduction path and the liquid discharge path are each formed by bending.
In this case, since the liquid introduction path and the liquid discharge path are formed by being bent, a large flow path resistance is added to these flow paths. As a result, a uniform flow with less drift is ensured in the reaction tank, and the viscosity of the liquid can be measured with high accuracy.

In the invention according to claim 6 of the present application, the liquid to be measured is circulated by the liquid introduction path and the liquid discharge path in the reaction tank set to a depth of 20 μm to 200 μm. The amount of change between the impedance of the reference solution of the piezoelectric element and the impedance of the liquid to be measured by applying an AC signal to a pair of electrodes provided on the front and back surfaces of the piezoelectric element provided on the bottom or top plate According to the present invention, the same effect as that of the invention according to claim 2 is obtained.

  According to the present invention, the depth of the reaction tank is set to be shallower than the degree of viscous penetration, and the resonance resistance value, that is, the impedance itself is measured as a large value. Therefore, the reaction tank is affected by the viscosity of the liquid flowing in the reaction tank. Thus, when the impedance changes, even if the impedance change rate is small, the change amount can be measured. That is, the amount of change in impedance can be measured with high sensitivity.

  Hereinafter, an embodiment of a viscosity measuring device according to the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram showing the overall configuration of the viscosity measuring device, FIG. 2 is a plan view of a microflow cell used in the viscosity measuring device, FIG. 3 is a sectional view of the microflow cell, and FIG. 4 is a block diagram of the viscosity measuring device. It is.

  As shown in FIG. 1, the viscosity measuring apparatus 100 of the present embodiment includes a sample container 1 in which a sample liquid to be measured is stored, a microflow cell 3 connected to the sample container 1 via a tube 2, A pump 5 having a suction side connected to the microflow cell 3 via a tube 4, a waste liquid container 7 connected to the discharge side of the pump 5 via a tube 6, and the microflow cell 3 being electrically connected to the microflow cell 3. On the basis of an output signal from a sensor 8 having a crystal resonator set in the microflow cell 3, a control unit 9 is provided for measuring a change in frequency and a change in impedance at the time of resonance of the sensor 8.

  As shown in FIGS. 2 and 3, the micro flow cell 3 is disposed at the center hold substrate 10, the resin plate 11 disposed above the hold substrate 10 in FIG. 3, and the hold substrate 10. The sensor 8 is provided and is configured by laminating them in three layers.

  The hold substrate 10 is a transparent substrate formed from an acrylic resin or the like, and has an outer shape formed like an SD memory card. In the hold substrate 10, a sample liquid is flowed from the upper surface side to the lower surface side in FIG. And a through hole to be a liquid discharge port 10b.

  Further, on the lower surface of the hold substrate 10, wiring pattern portions 13a and 13b are formed which are electrically connected to the detection electrode 8a and the counter electrode 8b of the sensor 8, respectively. The wiring pattern portions 13a and 13b function as external connection terminals. The wiring pattern portions 13a and 13b are formed by laminating one type of metal or different metals (for example, laminating titanium or chromium and gold in two layers).

  The resin plate 11 is formed in a plate shape with a transparent silicon resin. In the resin plate 11, an introduction groove 14 and a discharge groove 15 are respectively formed on the surface facing the hold substrate 10. Each of the introduction groove 14 and the discharge groove 15 communicates with the introduction through hole 16 and the discharge through hole 17 each having a diameter of about 1.5 mm, and the other end side has the same size as the liquid introduction port 10a and the liquid discharge port 10b. The recesses 14a and 15a have a diameter of about 0.5 mm. The resin plate 11 is bonded to the surface of the hold substrate 10 so that the recesses 14a and 15a communicate with the liquid inlet 10a and the liquid outlet 10b, respectively.

In the microflow cell 3 of this embodiment, the sample liquid is introduced into the reaction tank 12 through the liquid introduction path 18 including the introduction through hole 16, the introduction groove 14, and the liquid introduction port 10 a, and passes through the reaction tank 12. The sample liquid is discharged through a liquid discharge path 19 including the liquid discharge port 10 b, the discharge groove 15, and the discharge through hole 17.
Here, the liquid introduction path 18 and the liquid discharge path 19 are arranged so that the liquid introduction port 10a and the liquid discharge port 10b are not coaxial with the introduction through-hole 16 and the discharge through-hole 17, that is, respectively. Is bent as a whole.

The sensor 8 includes a crystal resonator 40 and a pair of electrodes provided on both surfaces of the crystal resonator 40 to resonate the crystal resonator 40 at a predetermined frequency, that is, a detection electrode 8a and a counter electrode 8b. QCM sensor (see FIG. 4).
The quartz oscillator 40 is, for example, an AT cut quartz plate, and is a transparent substrate formed in a square shape from an 8 mm square wafer. The detection electrode 8a and the counter electrode 8b are each formed by vapor deposition or sputtering so as to be positioned substantially at the center of the crystal resonator 40. That is, the detection electrode 8a and the counter electrode 8b are in a state of facing each other with the crystal resonator 40 interposed therebetween.

Further, on both surfaces of the crystal unit 40, lead electrodes 20a and 20b that are electrically connected to the detection electrode 8a and the counter electrode 8b, respectively, are formed. The detection electrode 8a, the counter electrode 8b, and the lead electrodes 20a and 20b are formed by laminating one kind of metal or different metals (for example, laminating titanium or chromium and gold in two layers) similarly to the wiring pattern portions 13a and 13b. ).
The detection electrode 8a has an impedance of 1 KΩ or less and a diameter of 3 mm that oscillates stably in the liquid. The counter electrode 8b has the same size.

  As shown in FIG. 3, the sensor 8 configured as described above is bonded to the back surface side of the hold substrate 10 with the ring-shaped packing 21 interposed therebetween. At this time, the sensor 8 is bonded so that the detection electrode 8 a faces the hold substrate 10.

  The reaction tank 12 is a space that surrounds the periphery of the detection electrode 8a, stores the sample liquid, and adsorbs or binds the specific substance contained in the sample liquid to the detection electrode 8a. As shown in FIG. 3, the depth D of the reaction tank 12 is set to be shallower than the liquid penetration degree representing the average distance that the vibration penetrates into the liquid when the piezoelectric element vibrates at the liquid interface. The liquid penetration degree will be described in detail later. The depth D of the reaction tank 12 is set to 20 μm to 200 μm, preferably 40 μm to 165 μm, when measuring a relatively low viscosity such as water.

The controller 9 is largely divided into two. One is a part for measuring the amount of change in impedance at the time of resonance indicated by 9A in FIG. 4, and the other part is a part for measuring the amount of change in resonance frequency indicated by 9B in FIG.
An oscillation circuit 41 is connected to the crystal resonator 40 that is a component of the sensor 8. A mixer 42 is connected to the oscillation circuit 41, and a signal serving as a reference for measurement is introduced from the reference clock 43 to the mixer 42. The mixer 42 is connected to a low-pass filter 44 that removes unnecessary noise. A frequency counter 45 is connected to the low-pass filter 44, and the frequency is counted here. The frequency counted here is sent to the frequency measuring unit 46. The frequency measurement unit 46 receives a reference signal also from the reference clock 43, and measures the frequency of the signal introduced from the oscillation circuit 41 with an accuracy of, for example, 1/100 hertz.

  On the other hand, an RMS / DC converter 47, an AD converter 48, and an impedance measuring unit 49 are sequentially connected to the oscillation circuit 41. The RMS / DC converter 47 converts the averaged AC signal into a DC signal, and the AD converter 48 converts the analog DC signal into a digital signal. Then, the impedance measurement unit 49 measures the resistance value when the crystal resonator 40 resonates, that is, the impedance.

Next, a method for measuring the viscosity of the liquid with the viscosity measuring apparatus configured as described above will be described.
Before starting the measurement, the sensor 8 is activated in advance, and an AC voltage is applied between the detection electrode 8a and the counter electrode 8b by an AC power source (not shown) to resonate the crystal unit 40. Then, the resonance frequency and impedance at that time are measured by the control unit 9 in advance.

  That is, an AC voltage is applied between the detection electrode 8a and the counter electrode 8b by an AC power source while periodically changing the frequency within a predetermined range. The current flowing through the crystal unit 40 becomes maximum at the resonance point. The value at this time is obtained as the resonance frequency. When a change in current flowing between the detection electrode 8a and the counter electrode 8b at the resonance point is converted into a voltage, a signal dependent on the resonance resistance of the crystal resonator 40 is obtained. The signal at this time is converted into a DC signal by the RMS / converter 47, and further converted from an analog DC signal to a digital signal by the AD converter 48, and finally an impedance which is a resistance value at the resonance point is obtained.

  Next, the pump 5 is operated to introduce the sample liquid (liquid to be measured) in the sample container 1 into the microflow cell 3 through the tube 2. At this time, the control unit 9 measures the amount of change in the impedance of the reference solution and the impedance of the sample solution and the amount of change in the resonance frequency when the crystal unit 40 vibrates.

When the sample liquid flows into the reaction vessel 12, the vibration of the crystal resonator 40 is subjected to shear resistance by the sample liquid. The resonance resistance value, that is, the impedance at this time varies depending on the viscosity of the liquid. Therefore, the viscosity of the liquid can be known by measuring the amount of change in impedance.
Here, the impedance of the reference solution is measured in advance and stored as data. As the reference solution, for example, water or a buffer solution is used. A buffer containing a salt is used so as not to change the pH. Specifically, PBS (physiological saline) or Tris buffer is used.

At this time, the resonance resistance value that the vibration of the crystal unit 40 receives from the liquid flowing in the reaction tank 12 varies greatly depending on the depth of the reaction tank 12.
In other words, when the piezoelectric element at the liquid (fluid) interface is vibrated, the degree of viscous penetration is expressed as the average depth (average distance) to which depth the vibration penetrates into the liquid (fluid). L. This degree of viscous penetration L is expressed by the following equation (1).

For example, when the liquid (fluid) is water, the viscosity penetration L is 165.6 μm, and when the fluid is air, the viscosity penetration L is 22.3 μm.
When the depth D of the reaction tank 12 is deeper than the viscosity penetration degree L, the resonance resistance value that the vibration of the crystal unit 40 receives from the liquid in the reaction tank 12 is very small, but the depth D of the reaction tank 12 Is less than the viscosity penetration L, the resonance resistance value that the vibration of the crystal unit 40 receives from the liquid in the reaction tank 12 increases rapidly.

  Here, in this embodiment, the depth D of the reaction tank 12 is set to a value shallower than the viscosity penetration degree L. For this reason, the resonance resistance value that the vibration of the piezoelectric element receives from the liquid in the reaction tank 12, that is, the impedance is a very large value. Therefore, when the impedance changes under the influence of the viscosity of the liquid flowing in the reaction vessel 12, even if the impedance change rate is very small, the impedance itself can be measured as a large value. can do. In other words, in this embodiment, the amount of change in impedance can be measured with high sensitivity.

FIG. 5 shows the relationship between the depth of the reaction tank and the resonance resistance value when the liquid introduced into the reaction tank is water having a relatively low viscosity.
Thus, in the case of water, when the depth D of the reaction vessel 12 becomes shallower than 165 μm, which is the value of the viscosity penetration L, the resonance resistance value increases rapidly. For this reason, as the depth D of the reaction vessel 12 is shallower than 165 μm, the resonance resistance value becomes larger and measurement becomes easier. However, if the resonance resistance value becomes too large, the signal intensity becomes weak accordingly, and this causes a decrease that makes measurement difficult. In measuring the resonance resistance value, that is, the amount of change in impedance, it is necessary to consider both the magnitude of the resonance resistance value itself and the signal strength. Considering both of these, the depth D of the reaction vessel 12 is preferably set to 20 μm to 200 μm, and more preferably set to 40 μm to 165 μm, which is about twice the minimum value of D.
Thus, when the depth of the reaction tank 12 is set, when the viscosity of the liquid of the measurement object is as low as water, the amount of change in impedance can be measured with high sensitivity, and the signal The strength is strong enough not to interfere with the measurement.

  The setting of the depth of the reaction tank 12 described above is an example in the case where the measurement target is a liquid having a low viscosity such as water, and when the viscosity of the liquid to be measured is different, the reaction tank is accordingly changed. What is necessary is just to change the depth of 12 suitably. That is, the depth D of the reaction tank 12 may be set deeper in the case of a liquid having a high viscosity, and the depth of the reaction tank 12 may be set shallower in the case of a liquid having a low viscosity. In short, it is sufficient to set the depth D of the reaction vessel 12 to be shallower than the viscosity penetration L while considering the signal strength.

  In parallel with the measurement of the change amount of the impedance, the change amount of the resonance frequency is also measured. A substance contained in the sample liquid introduced into the reaction vessel 12 may adhere to the crystal resonator 40. In this case, the resonance frequency changes. Therefore, by measuring the amount of change in the resonance frequency, information on the substance contained in the sample liquid can be obtained. That is, the properties of the sample liquid itself can be evaluated in more detail.

  In addition, in the present embodiment, the liquid introduction path 18 for introducing the liquid into the reaction tank 12 and the liquid discharge path 19 for discharging the liquid from the reaction tank 12 are formed by bending, whereby the flow paths 18, 19 are formed. Is given a large flow resistance. Therefore, a uniform flow with less drift is easily secured in the reaction tank 12, and as a result, the viscosity of the liquid can be measured with high accuracy.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of invention.
In the above embodiment, the crystal resonator 40 is used as an example of the piezoelectric element incorporated in the sensor 8, but the present invention is not limited to this, and other piezoelectric elements may be used.
Moreover, in the said embodiment, although the sensor 8 was provided in the bottom part of the reaction tank 12, you may provide the sensor 8 in the top-plate part (lower surface of the resin plate 11) of the reaction tank 12 instead.
Further, the reaction tank 12 is formed between the hold substrate 10 and the sensor 8, but the reaction tank 12 is not limited to be formed between the hold substrate 10 and the sensor 8, and two sheets are provided. It may be formed between the hold substrates. In this case, a sensor is assembled to any one of the hold substrates.

It is a simplified lineblock diagram of a viscosity measuring device showing one embodiment of the present invention. It is a top view of the micro flow cell used in a viscosity measuring apparatus. It is sectional drawing of the micro flow cell. It is a block diagram of the viscosity measuring apparatus of one Embodiment of this invention. In the reaction tank of the viscosity measuring apparatus shown in FIG. 1, it is a figure showing the relationship between the depth of a reaction tank, and a resonance resistance value.

Explanation of symbols

  1 Sample container 3 Micro flow cell 5 Pump 7 Waste liquid container 8 Sensor 9 Control unit 10 Hold substrate 11 Resin plate 12 Reaction tank 18 Liquid introduction path 19 Liquid discharge path 100 Viscosity measuring device.

Claims (6)

The piezoelectric element is resonated by an AC signal supplied from a reaction tank communicated with the liquid introduction path and the liquid discharge path and a pair of electrodes on the front and back surfaces of the piezoelectric element provided at the bottom or top plate of the reaction tank. A liquid to be measured is introduced into the reaction tank from the liquid introduction path, and the liquid is calculated based on the amount of change between the impedance of the reference solution of the sensor and the impedance of the liquid to be measured at that time. A viscosity measuring device for measuring the viscosity of
The viscosity measuring apparatus is characterized in that the depth of the reaction tank is set to be shallower than a liquid penetration degree representing an average distance that the vibration penetrates into the liquid when the piezoelectric element vibrates at the liquid interface. The piezoelectric element is resonated by an AC signal supplied from a reaction tank communicated with the liquid introduction path and the liquid discharge path and a pair of electrodes on the front and back surfaces of the piezoelectric element provided at the bottom or top plate of the reaction tank. A liquid to be measured is introduced into the reaction tank from the liquid introduction path, and the liquid is calculated based on the amount of change between the impedance of the reference solution of the sensor and the impedance of the liquid to be measured at that time. A viscosity measuring device for measuring the viscosity of
A viscosity measuring apparatus, wherein the depth of the reaction vessel is set to 20 μm to 200 μm.   The depth of the said reaction tank is set to 40 micrometers-165 micrometers instead of 20 micrometers-200 micrometers, The viscosity measuring apparatus of Claim 2 characterized by the above-mentioned.   When the liquid to be measured is introduced from the liquid introduction path into the reaction tank, the resonance frequency changes in addition to the amount of change between the impedance of the reference solution of the sensor and the impedance of the liquid to be measured. The viscosity measuring apparatus according to claim 1, wherein the viscosity of the liquid is evaluated by measuring the amount.   The viscosity measuring apparatus according to claim 1, wherein the liquid introduction path and the liquid discharge path are formed to be bent.   The liquid to be measured is circulated in the reaction tank set to a depth of 20 μm to 200 μm by the liquid introduction path and the liquid discharge path, and in this state, the piezoelectric element provided on the bottom or top plate of the reaction tank An AC signal is applied to a pair of electrodes provided on the front and back surfaces, and the viscosity of the liquid is measured from the amount of change between the impedance of the reference solution of the piezoelectric element and the impedance of the liquid to be measured. Viscosity measurement method.

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