JP2001317998A - Interference filter transmitted wavelength scan type photometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interference filter transmitted wavelength scan type photometer, capable of quantitatively determining a component under measure ment, without being influenced by interference components. SOLUTION: The inclination angle of the optical axis to the normal of an interference filter 3 is varied periodically to vary the wavelength in a narrow range, the center of the wavelength variation is set to a maximum absorption wavelength of a component under measurement, thus a modulated light passes through a simple, to generate a light the varying intensity of which is detected by an infrared detector 11 as an electrical signal, an a-c amplifier 14 amplifiers the a-c component of the detected electrical signal to obtain the zero-cross points of the rise and fall of the a-c signal, a microprocessor 16 obtains the times from one rise to the next rise, and from the rise to the next fall to calculate the value of (total period-2×half period)/total period, from the obtained total and half periods, and the density of the component under measurement is obtained from the variation of the obtained measured value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple and inexpensive analyzer for measuring a component to be measured in a sample containing a measurement interfering component by light absorption. More specifically, by using an interference filter that can periodically scan the maximum transmission wavelength, a change in the light transmission intensity of the sample in a narrow wavelength range is examined, and this is detected as an electric signal. The present invention relates to an apparatus for quantifying a component to be measured from a sample.

[0002]

2. Description of the Related Art Light is widely used to detect and quantify specific components in a sample. The simplest method is to measure a change in the amount of monochromatic light transmitted when a sample is irradiated with monochromatic light having an absorption wavelength of a specific component. As an apparatus for that purpose, for example, an ultraviolet absorption photometer for monitoring water quality is known. This is because the organic pollutants in the water are the mercury spectral lines 25
It utilizes the absorption of light having a wavelength of 3.7 nm and comprises a light source, a sample cell, a light receiver, an amplifier, and the like. In this method, called the single beam method, when there is a change in the light amount of the light source, the change is detected by the detector as it is, and the output fluctuation due to it is indistinguishable from the change due to the light absorption of the component, and the measurement error is reduced. Occurs.

As one means for solving the drawbacks of the single beam system, there is a double beam system. In this method, the light beam is divided into two, one is the measurement light beam, the other is the comparison light beam, and the difference or ratio of the intensity of each light beam is calculated. It seeks change. With this method, measurement can be performed without being affected by changes in the light source.

Another method which is not affected by a light source is a two-wavelength photometric method. This is a method in which light of two different wavelengths is alternately transmitted or reflected by a measurement sample, and the intensity of absorption by the measurement target component contained in the measurement sample is determined from the difference or ratio of the resulting light intensities. is there. One wavelength is selected as a wavelength that is not absorbed by the measurement sample, and the intensity of the light beam having the absorption wavelength of the target component is obtained based on the intensity of the light beam of this wavelength, so that the measurement can be performed without being affected by the light source.

Since the present invention aims at a system which is not affected by a change in light amount of a light source with a single light beam like a two-wavelength photometric system, the prior art of this system will be described in detail with reference to FIG. FIG. 1 is a drawing showing a filter correlation type infrared spectrometer.
1 passes through the sample cell 102 and travels to the rotary modulator 103 as transmitted infrared rays 122. The sample cell 102 is a cylindrical tube having infrared transmission windows on both end surfaces, and a sample gas inlet / outlet is provided near both end surfaces. The sample gas contains the gas to be measured, and the transmitted infrared rays 122 lose their intensity by the infrared absorption of the gas to be measured. The rotation modulator 103 is provided with a measurement filter 104 having a maximum transmittance at the absorption wavelength of the component gas to be measured and a reference filter 105 having a maximum transmittance at a wavelength at which the sample gas does not absorb the light. Periodically intersects with the transmitted infrared light 122 by the rotation of. This allows transmitted infrared 1
22 is modulated, and exits as a modulated infrared ray 123 that changes periodically in the order of transmission through the measurement filter 104, light blocking, transmission through the reference filter 105, and blocking. Modulated infrared 12
3 is condensed by an infrared condensing lens 107, and a detector 108
And is detected as an electric signal. The detected electric signal is amplified by a preamplifier 110 and enters a synchronous rectifier 111. On the other hand, the rotation period of the rotation modulator is determined by the synchronization signal detector 1.
At 06, the phase is adjusted to a phase suitable for synchronous rectification by the phase adjuster 109, and the phase enters the synchronous rectifier 111. Synchronous rectifier 11
In step 1, a signal depending on the concentration of the gas component to be measured is obtained from these input signals.

By the way, in a gas or liquid sample, many components coexist with the component to be measured in many cases. Among these coexisting components are, for example, water vapor when nitric oxide in flue gas is a measurement target component, electrolyte such as salt and water of a main component when measuring glucose in water as a measurement target component. There may be components that interfere with the measurement. As shown in FIG. 2, the absorption 1 of the component interfering with these measurements
52 is the maximum absorption wavelength 15 of the absorption 151 of the component to be measured.
It has no absorption extreme at the same wavelength as 3, but the absorption tails overlap. The tail of the absorption is a gradual change, but a high concentration has a fatal effect on the measurement. In the case of the above-described two-wavelength photometry method, the reference wavelength 154 is usually selected to be a wavelength close to the maximum absorption wavelength 153, but when there is a gradient in the absorption tail as shown in FIG. 2, the influence of the coexisting component cannot be avoided. There was a problem.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a spectroscopic measurement utilizing light absorption in which interfering components whose absorption skirt extends to the maximum absorption wavelength of the component to be measured coexist. It is an object of the present invention to provide an analyzer capable of quantifying a component to be measured in a sample while avoiding the influence of an interfering component. Another object of the present invention is to provide a simple and inexpensive analyzer that can measure nondestructively or noninvasively on a human body.

[0008]

According to the present invention, there is provided an apparatus for measuring a component to be measured in a sample containing a measurement interfering component by light absorption, wherein a light source and a maximum transmission wavelength are periodically measured. It consists of an interference filter with a means for scanning, an infrared detector, and a zero-cross detector,
The center of the wavelength of the scanning of the interference filter is determined so that the center of the wavelength change in a narrow range caused by the periodic scanning of the interference filter coincides with the maximum absorption wavelength of the measurement component, and the light from the light source interferes. After being transmitted or reflected by the filter and the sample placed in front of or behind the filter, it is put into an infrared detector and detected as an electric signal. (Interval between zero-cross points) is obtained by a zero-cross detector, and the component is quantified based on a change amount of a half cycle with respect to the entire cycle.

There are several known methods for scanning the maximum transmission wavelength using the interference filter. One method is to use a gas as a spacer layer between metal films and change the pressure of the gas to change the refractive index of the spacer layer.
A method of changing the thickness of the spacer layer is also known. In the present invention, a method of changing the inclination angle of the interference filter is suitable. That is, the most preferred embodiment of the present invention is to perform maximum transmission wavelength scanning by rotating an interference filter transmission wavelength scanning type photometer so that the angle between the normal line of the interference filter surface and the optical axis changes periodically. It is characterized by.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of the structure of an interference filter transmission wavelength scanning photometer of the present invention and the principle of a method for measuring a component to be measured using the same will be described below with reference to the accompanying drawings. In the present invention, the interference filter is rotated and oscillated at a single frequency so as to change the tilt angle with respect to the optical axis, and the short transmission wavelength 161 and the long transmission wavelength 162 around the maximum absorption wavelength 153 of the component to be measured in FIG. The extreme value of the wavelength transmitted through the interference filter is scanned between the narrow wavelengths as described above. It is known that the maximum transmission wavelength changes when the interference filter is tilted with respect to the optical axis. FIG. 3 shows the spectrum 17 of the interference filter obtained by changing the inclination angle between the normal line and the optical axis of the interference filter obtained by the experiment to 15, 20, and 25 degrees.
1, 172 and 173. The wavelengths of the respective peaks are 2289 nm, 2273 nm, and 2257 nm. (The horizontal axis of the spectrum in the figure is drawn as a linear wave number, and is non-linear with respect to the wavelength. The numerical values in the text are consistent with the discussion.) It is converted to a wavelength to maintain the property.)

When the inclination angle is 15 degrees, the maximum transmission wavelength of the interference filter becomes the long transmission wavelength 162 in FIG. When the gap is periodically vibrated, the transmittance of the light transmitted through the sample becomes high transmittance 163 and low transmittance 16.
It changes in the same cycle between four. Therefore, the light intensity also changes, and the electric signal detected by the detector changes in a sine wave like the signal 181 of the component that interferes with the measurement in FIG. In this case, the direction of the signal is such that the angle of the interference filter is 25 degrees,
That is, when the transmittance is high, the maximum value is on the positive side when the transmittance is 163, and when the transmittance is 15 degrees, that is, when the transmittance is low, the minimum value is on the negative side.

Next, it is assumed that the number of components to be measured in the sample increases, and the absorption 151 of the components to be measured increases accordingly. Due to the absorption 151 of the measured absorption component, the transmittance becomes the non-component transmittance 1 when the angle of the interference filter is about halfway between 15 degrees and 25 degrees.
From 65 the component transmittance 166 drops. As a result, FIG.
The signal 182 of the component to be measured, which is near the midpoint between the highest value and the lowest value of the signal 181 of the component that interferes with the measurement, that is, exhibits a negative extreme value at the zero crossing point, is increased. Therefore, the signal observed after the increase of the measurement target component is the measurement signal 183 obtained as the sum of the signal 181 of the component that interferes with the measurement and the signal 182 of the measurement target component. The amount we want to find here is
Signal 1 of the measurement target component caused by the increase of the measurement target component
82.

Next, a method for obtaining the amplitude of the signal 182 of the component to be measured, which is the quantity to be obtained, from the observed measurement signal 183 will be described. The signal 181 of the component that disturbs the measurement is a large signal. Assuming that the amplitude is A, the signal F is expressed as follows.

[0014]

## EQU1 ## where ω is an angular frequency and the period is T, ω = 2π / T
It is.

The signal 182 of the component to be measured is much smaller than the signal 181 of the component that interferes with the measurement.
81 is almost the same. However, focusing on the midpoint between the highest value and the lowest value of the signal, that is, the zero-crossing point, the increase in the signal 182 of the component to be measured is represented by the zero-crossing point of the signal 181 of the component that interferes with the measurement, assuming that the amplitude of the increase is ε. It serves to lower the nearby signal by (1/2) ε. Here, the signal 181 of the component that approximately disturbs the measurement is-(1 /
2) The time movement of the zero-cross point is determined assuming that the movement is parallel movement by ε. First, the gradient of the zero crossing point of the signal 181 of the component that disturbs the measurement can be obtained from the derivative of the signal F as in the following equation.

## EQU2 ## dF / dt = Aωcosωt

As a result, the gradient at ωt = π and 2π is
-Aω = -2πA / T and Aω = 2πA / T, respectively. When each point is translated by-(1/2) ε, the time required for the signal 181 to reach the zero-cross point is ω
At the point of t = π, it is accelerated by εT / 4πA, and at the point of ωt = 2π, it is delayed by εT / 4πA. In the measurement signal 183 in which the signal 182 of the component to be measured is added to the signal 181 of the component obstructing the measurement, the difference between the extended half cycle T2 and the shortened half cycle T1 is as follows by the above approximation.

[0017]

T2-T1 = εT / πA When the ratio to the period T is obtained, T2-T1 / T = ε / π
A, which is a value proportional to the amplitude ε of the signal 182 of the component to be measured. If one of the full cycle and half cycle is determined, the other half cycle is determined.Thus, by measuring the full cycle and one half cycle, the quantification of the component to be measured is not affected by coexisting components or principal components. Is possible.

Next, the structure of an interference filter transmission wavelength scanning type photometer of the present invention will be described with reference to FIG. 5 is largely divided into two parts, an optical system shown in a perspective view and an electronic circuit system shown in a block diagram.

In FIG. 5, the light emitted from the light source 1 is blocked by the short-wavelength light blocking filter 2 at the short-wavelength light portion, passes through the long-wavelength portion, and reaches the interference filter 3. The interference filter 3 is fixed to the drive coil 7 and is installed so as to rotate and vibrate around the shaft 4. S on both sides of the outermost drive coil 7 for applying a magnetic field to the winding portion
A pole 5 and an N pole 6 are provided. When an alternating current is passed through the drive coil 7, the interference filter 3 rotates and vibrates about the shaft 4. The initial angle is set near 20 degrees so that the angle between the normal line of the interference filter 3 and the optical axis is between 15 degrees and 25 degrees.

The light beam whose wavelength is modulated by the rotation vibration of the interference filter 3 is condensed by the lens 8 and enters the end face of the quartz rod 9. The quartz rod 9 guides the light beam to the vicinity of the sample 10 and irradiates the light beam toward the sample 10 from the other end face. The irradiated light is diffusely reflected on the surface of the sample 10, and a part of the reflected light reaches the infrared detector 11. The infrared detector 11 is modulated by a rotating interference filter,
A change in the amount of light received by diffusely reflecting the sample 10 is detected as an electric signal. The electric signal detected here is sent to the electronic circuit unit.

An oscillation circuit 1 for supplying an alternating current to a drive coil 7 for rotating and rotating the interference filter 3 is provided in the electronic circuit section.
2 is placed. Since the rotation vibration generated by the alternating current is a signal generation source, the stability of the rotation vibration is extremely important for measurement. For this reason, a detection coil is placed at the same position as the drive coil 7, the speed of the rotational vibration is detected, and feedback control is performed so that the energy of the rotational vibration is constant. Using the frequency of this rotational vibration as the fundamental frequency,
The electric signal generated in the optical system and detected by the infrared detector 11 is amplified by the preamplifier 13, and the AC amplifier 14 amplifies only the signal of the AC component, and then enters the zero-cross detector 15. The zero-cross detector 15 generates a signal when the AC signal becomes zero and rises and falls when the AC signal becomes zero, and functions to interrupt the microprocessor 16. The microprocessor 16 stores the rising and falling moments using a built-in timer. If the rise time is the beginning of the cycle, the time until the next rise is the whole cycle,
The time to fall is measured as a half cycle.

After repeating this measurement a predetermined number of times, twice the integrated value of the half cycle is subtracted from the integrated value of the entire cycle, and the value is divided by the integrated value of the entire cycle. If this value is defined as a distortion factor, the distortion factor becomes a measured amount. If the distortion factor and the concentration of the measurement target component (for example, a blood glucose level in the case of measuring the blood glucose concentration) are calibrated, a quantitative value of glucose is obtained from the measured amount, and the result is displayed and transmitted. The microprocessor 17 has a display 17 for displaying quantitative results and the like.
A key 18 for operating the apparatus and a communication port 19 for transmitting a result are provided.

[0023]

An example in which the present invention is applied to the determination of glucose in blood will be described.

Human lips have capillaries gathered near the epidermis and appear red to the naked eye. Using the diffuse reflection of the surface here, the measurement of the glucose concentration in blood was attempted by an interference filter transmission wavelength scanning photometer. FIG. 6 shows an optical sampling unit. A quartz rod 31 corresponds to 9 in FIG. Reference numeral 32 denotes a header which irradiates light from a quartz rod onto the surface of the lip 34 and determines and fixes the respective positions so that the diffusely reflected light from the lip 34 can be received by the infrared detector 33. The cavity between the surface of the lips 34 and the infrared detector 33 is pulled to a negative pressure by a suction pump 35 provided with a suction pressure adjuster 36 to improve the close contact between the surface of the lips 34 and the header 32.

FIG. 7 is a drawing showing spectra of main components of blood. FIG. 7 (A) is a spectrum of water, and FIG. 7 (B) is a spectrum of blood glue obtained by removing water from blood. FIG.
(C) is a difference spectrum of glucose obtained by subtracting the spectrum of water from the aqueous solution of glucose. In the present example, the glucose concentration was designed to be determined by using the change in the transmittance at a wavelength of 2273 nm (position 41). The change range of the maximum transmission wavelength of the interference filter is from 2289 nm (at position 42) to 2258 nm, centering on 2273 nm.
(Position 43).

Other design specifications are as follows. [Design Specifications] Rotational vibration frequency 150Hz Quartz rod 1.5mm outer diameter x 160mm length Frequency of cycle measurement timer 8MHz Measurement time 300sec Microprocessor clock 8MHz

Based on the above design specifications, a prototype of an interference filter transmission wavelength scanning photometer was manufactured, and the glucose concentration in blood was measured noninvasively. The measurement time was divided into ten, the distortion rate within the divided time was calculated, and the average of the median six points was taken as one measured value. The fasting blood glucose level of a healthy subject was measured with a commercially available blood glucose meter to obtain 89 mg / dL. In this state, the distortion rate of the subject's lips due to diffuse reflection was measured at five points using the transmission wavelength scanning photometer of the present invention. Next, the subject drank hot water in which 75 g of glucose was dissolved, and measured the three points of the distortion rate due to the diffuse reflection of the subject's lips from 40 minutes to 70 minutes later. After 60 minutes, the blood glucose level of the subject was measured to obtain 308 mg / dL.

The blood glucose level of the subject is assumed to be constant from 40 minutes to 70 minutes after drinking glucose, and the data are summarized in FIG. The correlation coefficient between the blood glucose level obtained with a commercially available blood glucose meter and the distortion factor measured with an interference filter transmission wavelength scanning photometer was 0.98, indicating a good correlation. From these results, it was proved that the measurement of the glucose concentration in blood was possible without invasion using the transmission wavelength scanning photometer of the present invention.

[0029]

The measurement utilizing the light absorption of a substance has desirable characteristics such as being non-destructive or noninvasive to the human body. However, in many cases, the absorption of the coexisting component overlaps the absorption wavelength of the target component, and it is difficult to measure only the light intensity of one wavelength. Therefore, multi-wavelength measurement, that is, spectrometry is used. This offers a considerable range of applications, but at the expense of equipment and cost.
Despite attention in such circumstances, it is not widely used as a general-purpose measuring instrument. For example, in the Japanese market for blood glucose meters, there has not yet been found any product using light absorption that uses only an electrode type and a colorimetric type.

In the present invention, performance equivalent to that of spectrometry is obtained with a simple structure for one component. Taking advantage of the advantages of optical measurement, it is possible to open the way to a cost-effective measuring instrument, and it is expected to contribute widely to the industrial field, environmental measuring field, and medical field, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a filter correlation type infrared spectrometer as an example of a conventional technique.

FIG. 2 is a diagram showing a relationship between a spectrum of a component to be measured and a coexisting component which hinders the measurement.

FIG. 3 is a drawing showing a measurement example of a spectrum obtained by inclining an interference filter with respect to an optical axis.

FIG. 4 is a diagram illustrating a relationship between a signal of a component to be measured and a signal of a coexisting component that interferes.

FIG. 5 is a drawing showing an example of a configuration of an interference filter transmission wavelength scanning type photometer of the present invention.

FIG. 6 is a diagram showing an optical sampling unit for extracting glucose concentration information from diffuse reflection of a human lip.

FIG. 7 is a drawing showing spectra of components taken as examples of the present invention.

FIG. 8 is a drawing showing the result of measuring the glucose concentration in blood using the transmission wavelength scanning photometer of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light source 2 short-wavelength light blocking filter 3 interference filter 4 axis 5 S pole 6 N pole 7 drive coil 8 lens 9 quartz rod 10 sample 11 infrared detector 12 oscillation circuit 13 preamplifier 14 AC amplifier 15 zero cross detector 16 microprocessor 17 Display 18 Key 19 Communication port 31 Quartz rod 32 Header 33 Infrared detector 34 Lip 35 Suction pump 36 Suction pressure adjuster 101 Infrared light source 102 Sample cell 103 Rotation modulator 104 Measurement filter 105 Reference filter 106 Synchronous signal adjuster 110 Front Amplifier 111 Synchronous rectifier 151 Absorption of measurement target component 152 Absorption of measurement interference component 161 Short transmission wavelength 162 Long transmission wavelength 163 High transmittance 164 Low transmittance 165 Non-component transmittance 166 Component transmittance 181 Signal of measurement interference component 82 measured components of the signal 183 measurement signal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G020 AA03 BA02 BA14 CA02 CA13 CB04 CB07 CC26 CC48 CC62 CD04 CD12 CD13 CD22 CD36 CD37 CD51 2G059 AA01 BB13 CC16 DD13 EE01 EE02 EE12 GG07 HH01 JJ02 JJ11 KK01 MM01 MM10 KL07 KM01 KX02 KY01 KY04

Claims (2)

[Claims] 1. An interference filter for measuring a component to be measured in a sample containing a measurement interference component by light absorption, the interference filter having a light source and a means for periodically scanning a maximum transmission wavelength, and a detector. And a zero-cross detector, and determine the center of the wavelength of the scanning of the interference filter so that the center of the wavelength change in a narrow range caused by the periodic scanning of the interference filter coincides with the maximum absorption wavelength by the measurement component. After transmitting or reflecting the light from the light source to the interference filter and the sample placed before or after it,
It is detected as an electric signal by entering the detector, and the full cycle and half cycle (time between each zero cross point) of the signal of the component that changes periodically are obtained by the zero cross detector. An interference filter transmission wavelength scanning type photometer, wherein the component is quantified. 2. The transmission wavelength of the interference filter according to claim 1, wherein the maximum transmission wavelength is scanned by rotating the interference filter so that the angle between the normal line of the interference filter surface and the optical axis changes periodically. Scanning photometer.