JP2001324446A - Apparatus for measuring isotope gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate apparatus for measuring isotope gases which utilizes a non-dispersive type infrared analyzer and is not affected due to the quantity change of light of a light source. SOLUTION: An infrared light source 18 is arranged inside a measurement cell 15, in which a sample gas is circulated. Band-pass filters 19, 21 and detectors 20, 22 for measuring absorption of 12CO2 and 13CO2 are set to both end faces of the cell 15. Lights, generated in both directions from the infrared light source 18 which drives to flicker by a predetermined cycle, are detected by the detectors 20 and 22. Since the same light source is utilized, effects due to the quantity change of light for a short time, even if present, can be offset. Moreover, since no mechanical chopper is used, variations in the quantity of light by a velocity change of the chopper can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the isotopes of
To¹²C and¹³Carbon dioxide containing C as a constituent element ¹²C
O₂as well as¹³CO₂Non-dispersive infrared absorption
By measuring using the collection method,¹²CO₂as well as¹³
CO₂Isotope gas measuring device for determining the concentration of
About the installation.

[0002]

2. Description of the Related Art Conventionally, a method called an isotope tracer method has been used to examine metabolism, accumulation, excretion and the like in a living body. In this method, a substance that behaves in a living body and exhibits the same behavior as the target element or substance to be tracked is labeled with an isotope to form a tracer, and the behavior of the target substance is examined by tracking the isotope.

[0003] As a specific application example, it is determined whether or not Helicobacter pylori (generally called "H. pylori", henceforth referred to as "H. pylori") is present in the stomach of a subject. There are tests to examine. H. pylori has the property of decomposing urea into carbon dioxide and ammonia. Therefore, urea labeled with ¹³ C, which is an isotope of ¹² C, is administered to a subject, and the urea is included in the breath of the subject.
The concentration of ¹³ CO ₂ (actually, ¹² CO ₂ and ¹³ CO ₂
Is measured). If H. pylori is present in the subject's stomach, the concentration of ¹³ CO ₂ should be higher than that of a normal person without H. pylori. Can be.

In general, isotope gas in a gas to be measured is generally
(For example,¹²CO₂as well as¹³CO ₂) Measures quality
Method using a mass spectrometer and simpler non-dispersive infrared
A method using an analyzer is known. Use mass spectrometer
Method has the advantage of allowing accurate measurements, but
However, the cost of equipment is high and requires skilled operators
I do. In contrast, a method using a non-dispersive infrared analyzer
Is cheaper and easier to handle.
Later, it is expected to spread widely.

[0005] An example of an isotope gas measurement device using a non-dispersive infrared spectrometer is described in Japanese Patent No. 2888587. FIG. 2 is a schematic configuration diagram of a main part of the conventional isotope gas measuring device. In FIG. 2, the cell 35 is
¹² CO and ₂ short measurement first sample cell ^{35a, 13} C
A long second sample cell 35b for measuring O ₂ . Cell 3
5 has a light source 31 which is a flat ceramic heater and first and second sample cells 35 from the light source 31.
The light source device 30 includes two waveguides 32 and 33 for irradiating infrared light to the light emitting devices a and 35b, respectively, and a rotary chopper 34 that intercepts and passes infrared light at a constant period. I have. On the other hand, at the opposite end of the cell 35,
First and second detectors 37 and 39 for detecting light passing through the cell 35 are disposed, and the first and second detectors 3 and 39 are provided.
Immediately before 7 and 39, the band-pass filter 36 that passes light corresponding to the absorption wavelength of ¹² CO ₂ (about 4280 nm) and the absorption wavelength of ¹³ CO ₂ (about 4412 n), respectively.
bandpass filter 38 that passes light corresponding to m)
Are provided.

Although a detailed description of the measurement procedure in this device is omitted, in the above device, the first
And the second sample cells 35a, 35b are filled with sample gas,
The infrared light emitted from the light source 31 and having passed through the first and second waveguides 32 and 33 passes through the sample gas. Then, the bandpass filters 36 and 38 control ¹² CO ₂ and ¹³ C
Only the wavelength light corresponding to O ₂ is extracted and detected by the first and second detectors 37 and 39. In addition, by rotating the chopper 34 at a predetermined cycle, the infrared light
The light is cut off, thereby removing the dark current of the detectors 37 and 39 and the influence of external light.

[0007]

However, the above-mentioned conventional apparatus has the following problems. In the above configuration, 1
From the light sources 31, the first and second sample cells 35a, 35
Two lines of light are extracted for b. Variations in the amounts of light of the two light beams are one factor in measurement errors.
Although the number of the light sources 31 is one, since the area is large, it is difficult to completely equalize the light emission amounts at the portions corresponding to the first and second waveguides 32 and 33. In addition, a change in the rotation speed of the chopper 34 due to a temperature change or the like may also be a cause of a change in the amount of light introduced into the cell 35.

[0008] The concentration of carbon dioxide in the breath, which is the measurement target of this device, varies among individuals, and differs even for the same individual depending on the state of the body. Therefore, the diagnostic index is the change in the abundance ratio of ¹² CO ₂ and ¹³ CO ₂ in the breath before and after the application of the reagent, and the diagnostic threshold is about 2.5 / mil. This value requires a high precision of two digits or more compared to the case of measuring carbon dioxide in the normal atmosphere. Therefore, although the measurement error due to the above-described factors is slight, it hinders such high-accuracy measurement. Of course, in a configuration in which different light sources are provided corresponding to the respective sample cells, it goes without saying that the variation in the light amount is further increased.

The present invention has been made in view of the above points, and an object of the present invention is to measure an isotope gas with extremely high accuracy without being affected by variations or fluctuations in the light amount of a light source. It is an object of the present invention to provide an isotope gas measuring device capable of performing the above.

[0010]

SUMMARY OF THE INVENTION An isotope gas measuring apparatus according to the present invention, which has been made to solve the above-mentioned problems, uses a non-dispersive infrared ray to measure a gas to be measured including carbon dioxide ¹² CO ₂ and carbon dioxide ¹³ CO _2. In an isotope gas measuring apparatus for measuring using an absorption method, a) a cylindrical sample cell through which the gas to be measured flows, and b) both ends of the sample cell which are installed inside the sample cell. A) a light source that emits infrared light toward
¹² ) first light detecting means for detecting infrared light having a wavelength corresponding to ¹² CO ₂ , d) carbon dioxide provided on the other end face of the sample cell,
Second light detecting means for detecting light having a wavelength corresponding to ¹³ CO ₂ , and e) each of carbon dioxide ¹² CO ₂ and ¹³ CO ₂ based on detection signals from the first and second light detecting means. And a calculation processing means for calculating the density of the two or the density ratio of the two.

According to this configuration, in the optical path from the light source to the first light detecting means, ¹² C
The absorption of infrared light corresponding to O ₂ is measured. On the other hand, the absorption of infrared light corresponding to ¹³ CO ₂ is measured in an optical path from the same light source to the second light detection means. That is, by using the same light source, there is no need to be affected by variations in the amount of emitted light.

Preferably, the apparatus further comprises driving means for driving the light source to blink on and off at a predetermined cycle, and the arithmetic processing means accumulates detection signals from the first and second light detecting means according to the predetermined cycle. It is good to

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a breath test apparatus which is an embodiment of the isotope gas measuring apparatus according to the present invention will be described. This breath test apparatus includes ¹² breaths included in a subject's breath.
The concentration ratio between CO ₂ and ¹³ CO ₂ (hereinafter referred to as “ ¹² CO ₂ and
The concentration ratio "of ¹³ CO ₂ is a device for measuring) of" concentration ratio of isotope gases ".

FIG. 1 is a schematic configuration diagram of the breath test apparatus. The gas flow path system of this device includes a sample gas introduction pipe 10,
The air introduction pipe 11, a carbon dioxide removal filter 12 provided on the air introduction pipe 11, a gas introduction pipe 14, and the sample gas introduction pipe 10 or the atmosphere introduction pipe 11 are selectively connected to the gas introduction pipe 14. It comprises a three-way valve 13, a measurement cell 15 to which a gas introduction pipe 14 and an exhaust pipe 16 are connected, and a pump 17 provided in the exhaust pipe 16.

The measuring cell 15 has a substantially cylindrical shape with an inner diameter of about 4 to 5 mm, and has a first band pass filter 19 and a first detector 20 for passing an absorption wavelength of ¹² CO ₂ on one end face. And a second bandpass filter 21 for passing the absorption wavelength of ¹³ CO ₂ on the opposite end face.
And a second detector 22 are provided. Pyroelectric detectors and PbSe detectors are generally used as the first and second detectors 20 and 22. In addition, a pneumatic detector having a detection sensitivity corresponding to the absorption wavelength of a target gas is used. (For details, see Shimadzu Review, Vol. 46, No. 1, p.
29-p. 36, 1989) is useful. When this pneumatic detector is used, the first and second bandpass filters 19 and 21 become unnecessary.

An infrared light source 18, which is a small light bulb, is disposed at a predetermined position in the measuring cell 15, and emits light to both sides when turned on. This infrared light source 18 is
4 is driven to blink at a predetermined cycle. This blinking cycle is extremely accurate determined by a quartz oscillator or the like, and the blinking frequency is preferably set to, for example, about 10 Hz. The inner wall surface of the measurement cell 15 is made of, for example, gold (Au).
It is desirable to make the mirror surface by a method such as coating. According to this, even if the light emitted from the infrared light source 18 hits the inner wall of the measurement cell 15, the absorption is small and the loss of the amount of light reaching the detectors 20 and 22 at both ends is small, so that the measurement error is reduced. Can be smaller.

The detection outputs of the first and second detectors 20 and 22 are both input to a signal processing unit 23, and the signal processing unit 23 calculates the concentration ratio of the isotope gas by performing arithmetic processing as described later. . The control unit 25 controls the operation of each of the above units based on an instruction from the operation unit 26, and causes the display unit 27 to display the measurement results and the like obtained by the signal processing unit 23.

In this example, the distance L1 from the first detector 20 to the infrared light source 18 is 30 mm, and the second detector 22
The distance L2 from the camera to the infrared light source 18 is set to 200 mm. Since the concentration of the target carbon dioxide is different, the influence of the light attenuation due to the absorption of the two is adjusted to the same degree, and the detectors 20 and 22 operate in a range where the linearity of the input versus output characteristics is good. It is to make it. However, in actual calculation, L2 is preferably longer, and the above value is adopted here in consideration of a trade-off between manufacturing convenience and miniaturization of the apparatus.

Next, a description will be given of a measurement using the breath test apparatus having the above configuration. (I) Measurement of reference gas First, measurement of a reference gas (zero gas) is performed. In this example, the atmosphere from which carbon dioxide has been removed is used as a reference gas. That is, under the control of the control unit 25, a flow path is set by the three-way valve 13 as shown by a dotted line in FIG.
The pump 17 is operated. Thereby, the air introduction pipe 11
The atmosphere is sucked through the CO2 removal filter 12
After the carbon dioxide has been removed in step (a), the gas is introduced into the measurement cell 15 via the gas introduction pipe 14. And the measuring cell 15
It diffuses and fills inside, and is discharged to the outside through the exhaust pipe 16.

The infrared light source 18 is driven to blink by a light source driving unit 24 at a predetermined cycle, and light emitted from the infrared light source 18 on both sides passes through the atmosphere filled with the measurement cell 15 and containing no carbon dioxide. After receiving the appropriate absorption, the light reaches the first and second band-pass filters 19 and 21. Then, only light near a predetermined wavelength is extracted by the first and second band-pass filters 19 and 21, respectively, and introduced into the first and second detectors 20 and 22. Since the infrared light source 18 is flickering, the first and second detectors 20 and 22 detect the light receiving signal corresponding to the intensity of the light receiving light at the time of lighting and the light receiving signal at the time of turning off the light (that is, a dark current signal or an external light). And a light receiving signal) are alternately output in accordance with the above-mentioned blinking cycle.

The signal processing unit 23 receives the detection signals from the first and second detectors 20 and 22, receives a timing signal synchronized with the blinking cycle from the control unit 25, and performs synchronous rectification for a predetermined period of time. Are integrated. At this time, the values (signal integrated values) measured corresponding to the first and second detectors 20 and 22 are represented by I ₀₁₂ and I _{0.
It is} assumed to be ₁₃ . This measured value is temporarily stored as a value for the reference gas.

(Ii) Measurement of sample gas (expiration) Next, measurement of a sample gas to be measured is performed. That is, under the control of the control unit 25, the three-way valve 13
The flow path is set as shown by a solid line therein, and the pump 17 is operated. As a result, the sample gas (expired gas) is sucked through the sample gas introduction tube 10 and introduced into the measurement cell 15 via the gas introduction tube 14. Then, it diffuses and fills the inside of the measuring cell 15 and is discharged to the outside through the exhaust pipe 17.

The infrared light source 18 is driven to blink in the same manner as in the above-described reference gas measurement. At this time, the signals detected by the first and second detectors 20 and 22 are integrated by the signal processing unit 23 in the same manner. Is done. When measuring the sample gas, the infrared light emitted from the infrared light source 18 is strongly absorbed by carbon dioxide contained in the sample gas. First bandpass filter 19
Since only the vicinity of the absorption wavelength by ¹² CO ₂ is extracted, the first detector 20 detects the infrared light affected by the absorption by only ¹² CO ₂ . On the other hand, since the second bandpass filter 21 extracts only the absorption wavelength of ¹³ CO ₂ , the second detector 22 detects the infrared light affected by the absorption of only ¹³ CO ₂ . At this time, the measured values corresponding to the first and second detectors 20 and 22 (the signal integrated value) to _{I 12} and I _13.

In the signal processing section 23, Lambert-Veil
Isotope abundance P is calculated based on the following equation using the law of
Will be issued. P = ｛− ln (I₁₃/ I₀₁₃) / (Α₁₃・ L '
2)｝ / ｛-ln (I₁₂/ I₀₁₂) / (Α₁₂・
L′ 1)｝ where α₁₂And α₁₃Is¹²CO₂as well as¹³CO₂of
The absorbances L'1 and L'2 are¹²CO₂as well as¹³CO₂To
It is the optical path length of the corresponding measurement infrared light. Measured as in this example
When the inner diameter of the cell 15 is small, the optical path length is
To the detectors 20 and 22
Therefore, L'1 and L'2 are L1 and L2 described above.
Can be That is, in the above equation, I₀₁₂ , I
₀₁₃ , I₁₂ And I₁₃ By applying
In the sample gas¹²CO₂When¹³CO ₂Abundance ratio, that is,
Is¹²C and¹³The abundance ratio with C is determined.

In this apparatus, if the measurement of the reference gas and the measurement of the sample gas are performed successively or without taking much time (in any order), the long-term fluctuation of the amount of light emitted from the infrared light source 18 can be obtained. (Eg, a decrease in the amount of light emission due to aging) can be offset. Also, even if there is variation in light emission amount in a shorter time, because it uses the same infrared source 18, the effect is ¹² CO
It appears in both ₂ and ¹³ CO ₂ , resulting in an offset.

In the above-described example, the infrared light source 18 is configured to be driven to blink. However, if the ratio between the light quantity at the time of lighting and the light quantity at the time of turning off, that is, the modulation rate is small, the effect of signal integration can be obtained too much. Error is caused by dark current, external light, and the like. Therefore, in such a case (for example, when the light source / light-off follow-up performance is not good), a mechanical chopper as conventionally used may be used instead of performing the blinking control.

[0027]

As described above, in the isotope gas measuring apparatus according to the present invention, the same light source is used when two isotope gases are measured at the same time. It is possible to perform extremely accurate measurement by removing the influence of the fluctuation of the measurement. Further, since the measuring cells are arranged on both sides of the light source with the light source at the center, the light source can be made smaller. When a large flat light source is used, the amount of emitted light tends to vary depending on the location of the light source. In the present invention, such a variation in the amount of emitted light can be avoided by reducing the size of the light source.

In the isotope gas measuring apparatus according to the present invention, if the light source is configured to be driven to blink, unlike a conventional mechanical chopper, since it does not have a movable portion, it is resistant to vibrations and can be mounted with a chopper. Therefore, there is no need to insert and separate a window material between the light source and the cell, and a chopper driving motor is not required, which is advantageous in cost.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a breath test apparatus which is an embodiment of an isotope gas measurement apparatus according to the present invention.

FIG. 2 is a configuration diagram of a main part of a conventional breath test apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Sample gas introduction pipe 11 ... Atmosphere introduction pipe 12 ... Carbon dioxide removal filter 13 ... Three-way valve 14 ... Gas introduction pipe 15 ... Measurement cell 16 ... Exhaust pipe 17 ... Pump 18 ... Infrared light source 19 ... 1st band pass filter 20 ... first detector 21 ... second band pass filter 22 ... second detector 23 ... signal processing unit 24 ... light source driving unit 25 ... control unit 26 ... operation unit 27 ... display unit

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Taisho Kinoshita 1 Nishinokyo Kuwaharacho, Nakagyo-ku, Kyoto Co., Ltd. Shimadzu Corporation (72) Inventor Hiroshi Nakano 1 Nishinokyo Kuwaharacho, Nakagyo-ku, Kyoto Co., Ltd. Shimadzu Corporation F term (reference) 2G045 AA25 AA35 CB21 CB22 DB01 FA25 FB07 GC30 JA01 JA07 2G059 AA01 BB12 CC04 DD12 EE01 FF08 GG07 HH01 JJ02 JJ24 KK03 KK09 LL02 LL04 MM01 MM15 NN01 NN08 PP04

Claims (1)

[Claims] 1. An isotope gas measuring device for measuring a gas to be measured containing carbon dioxide ¹² CO ₂ and ¹³ CO ₂ by using a non-dispersive infrared absorption method, wherein: a) the gas to be measured is circulated therein; A cylindrical sample cell, b) a light source installed inside the sample cell and emitting infrared light toward both ends of the sample cell, c) provided on one end surface of the sample cell, carbon dioxide
¹² ) first light detecting means for detecting infrared light having a wavelength corresponding to ¹² CO ₂ , d) carbon dioxide provided on the other end face of the sample cell,
Second light detecting means for detecting light having a wavelength corresponding to ¹³ CO ₂ , and e) each of carbon dioxide ¹² CO ₂ and ¹³ CO ₂ based on detection signals from the first and second light detecting means. And an arithmetic processing means for calculating the concentration of the two or the concentration ratio of the two.