JP4158314B2 - Isotope gas measuring device - Google Patents

Description

ここで、α_１２及びα_１３は^{1 ２}ＣＯ_２及び^{1 ３}ＣＯ_２の吸光度、Ｌ’1 及び Ｌ’2は^{1 ２}ＣＯ_２及び^{1 ３}ＣＯ_２に対応する測定赤外光の光路長である。本例のように測定セル１５の内径が小さい場合、光路長は赤外光源１８から各検出器２０、２２までの距離と看做すことができるから、Ｌ’1 及び Ｌ’2 は上述したＬ１及びＬ２とすることができる。すなわち、上記式に、Ｉ_０１２ 、Ｉ_０１３ 、Ｉ_１２ 及び Ｉ_１３ を適用することにより、試料ガス中の^{1 ２}ＣＯ_２と^{1 ３}ＣＯ_２との存在比、つまりは^{1 ２}Ｃと^{1 ３}Ｃとの存在比が求まる。
【００２５】
この装置では、参照ガスの測定と試料ガスの測定とを引き続いて、又はあまり時間をおかずに行うようにすれば（順序は問わない）、赤外光源１８の発光光量の長期的変動（例えば経時劣化による発光量の減少など）の影響を相殺することができる。また、より短い時間における発光光量の変動があった場合でも、同一の赤外光源１８を利用しているため、その影響は^{1 ２}ＣＯ_２と^{1 ３}ＣＯ_２の両方に現れ、結果的に相殺されることになる。
【００２６】
なお、上記例では、赤外光源１８を点滅駆動する構成としていたが、点灯時の光量と消灯時の光量との比、つまりは変調率が小さいと信号積算の効果があまり得られず、暗電流や外光などが誤差要因となる。そこで、このような場合（例えば、光源の点灯／消灯の追従性が良好でない場合など）には、点滅制御を行う代わりに、従来用いられているような機械的チョッパを利用してもよい。
【００２７】
【発明の効果】
以上説明したように、本発明に係る同位体ガス測定装置では、２つの同位体ガスを同時に測定する際に同一の光源を利用しているので、光源の発光光量の短時間の変動の影響を除去して、きわめて精度の高い測定を行うことができる。また、光源を中心に挟んで両側に測定セルを配置した構成であるので、光源を小さくすることができる。平板状の大きな光源を利用する場合、その光源の部位によって発光光量がばらつき易いが、本発明では光源を小さくすることによって、そのような発光光量のばらつきも回避することができる。
【００２８】
また、本発明に係る同位体ガス測定装置において光源を点滅駆動する構成とすれば、従来の機械的チョッパと異なり可動部を有していないので、振動に強く、しかも、チョッパを取り付けるために光源とセルとの間に窓材を挿入して分離する必要がなく、またチョッパ駆動用のモータも不要になるのでコスト的にも有利である。
【図面の簡単な説明】
【図１】 本発明に係る同位体ガス測定装置の一実施例である呼気検査装置のの概略構成図。
【図２】 従来の呼気検査装置の要部の構成図。
【符号の説明】
１０…試料ガス導入管
１１…大気導入管
１２…二酸化炭素除去フィルタ
１３…三方弁
１４…ガス導入管
１５…測定セル
１６…排気管
１７…ポンプ
１８…赤外光源
１９…第１バンドパスフィルタ
２０…第１検出器
２１…第２バンドパスフィルタ
２２…第２検出器
２３…信号処理部
２４…光源駆動部
２５…制御部
２６…操作部
２７…表示部[0001]
BACKGROUND OF THE INVENTION
The present invention is by measurement using nondispersive infrared absorption method the measurement gas containing the carbon dioxide ¹² CO ₂ and ¹³ CO ₂ of a constituent element ¹² C and ¹³ C which is an isotope with one ^{another, 12} The present invention relates to an isotope gas measurement device for obtaining the concentration of CO ₂ and ¹³ CO ₂ or the concentration ratio thereof.
[0002]
[Prior art]
Conventionally, a method called an isotope tracer method has been used to examine metabolism, accumulation, excretion, etc. in a living body. In this method, a substance that has the same behavior as the target element or substance to be traced in the living body is labeled with an isotope to form a tracer, and the behavior of the target substance is examined by tracing the isotope.
[0003]
As a specific application example, there is a test to check whether Helicobacter pylori (generally referred to as “H. pylori”), which is said to be the cause of stomach ulcer, etc., exists in the stomach of the subject. is there. H. pylori has the property of decomposing urea into carbon dioxide and ammonia. Therefore, urea labeled with ¹³ C, which is a ¹² C isotope, is administered to a subject, and the concentration of ¹³ CO ₂ contained in the breath of the subject (in reality, ¹² CO ₂ and ¹³ CO ₂ and Concentration ratio). If H. pylori is present in the stomach of the subject, the concentration of ¹³ CO ₂ should be higher than that of a normal person who does not have H. pylori. Can do.
[0004]
In general, a method using a mass spectrometer and a method using a simpler non-dispersive infrared analyzer are known for measuring isotope gases (for example, ¹² CO ₂ and ¹³ CO ₂ ) in a gas to be measured. It has been. Although the method using a mass spectrometer has an advantage that precise measurement can be performed, the price of the apparatus is high and a skilled operator is required. On the other hand, the method using a non-dispersive infrared analyzer is expected to become widely used in the future because the price of the apparatus is low and the handling is easy.
[0005]
An example of an isotope gas measurement apparatus using a non-dispersive infrared analyzer is described in Japanese Patent No. 2885687. FIG. 2 is a schematic configuration diagram of a main part of the conventional isotope gas measuring apparatus. In FIG. 2, the cell 35 includes a short first sample cell 35a for measuring ¹² CO ₂ and a long second sample cell 35b for measuring ¹³ CO ₂ . At one end of the cell 35, a light source 31 that is a flat ceramic heater and two waveguides for irradiating the first and second sample cells 35a and 35b with infrared light from the light source 31, respectively. A light source device 30 including 32 and 33 and a rotary chopper 34 that blocks and passes infrared light at a constant period are provided. On the other hand, the first and second detectors 37 and 39 for detecting the light passing through the cell 35 are arranged at the opposite end of the cell 35, and the first and second detectors 37 and 39 of the first and second detectors 37 and 39 are arranged. Immediately before, a band pass filter 36 that passes light corresponding to the absorption wavelength of ¹² CO ₂ (about 4280 nm) and a band pass filter 38 that passes light corresponding to the absorption wavelength of ¹³ CO ₂ (about 4412 nm) are provided. Is provided.
[0006]
Although a detailed description of the measurement procedure in this apparatus is omitted, in the apparatus described above, the first and second sample cells 35a and 35b communicating with each other are filled with the sample gas, emitted from the light source 31, and the first and second waveguides 32. , 33 is passed through the sample gas. Then, only the wavelength light corresponding to ¹² CO ₂ and ¹³ CO ₂ is extracted by the band pass filters 36 and 38, 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 is allowed to pass and cut off, thereby removing the influence of the dark current of the detectors 37 and 39, external light, and the like.
[0007]
[Problems to be solved by the invention]
However, the conventional apparatus has the following problems. In the above configuration, two light beams for the first and second sample cells 35 a and 35 b are extracted from one light source 31. The variation in the amount of light of these two systems is a cause of measurement error. Although the number of the light sources 31 itself is one, the area of the light source 31 is wide, so that it is difficult to completely match the light emission amounts at the portions corresponding to the first and second waveguides 32 and 33. Further, fluctuations in the rotation speed of the chopper 34 due to temperature fluctuations or the like can also be a cause for fluctuations in the amount of light introduced into the cell 35.
[0008]
The concentration of carbon dioxide in exhaled breath, which is a measurement target of this device, varies among individuals and varies depending on the physical condition of the same individual. Therefore, the diagnostic index is the change in the abundance ratio of ¹² CO ₂ and ¹³ CO ₂ in exhaled breath before and after application of the reagent, and the diagnostic threshold is about 2.5 / mil. This value requires a high accuracy of two orders of magnitude or more compared to the case of measuring carbon dioxide in a normal atmosphere. Therefore, although the measurement error due to the factors as described above is slight, it becomes a hindrance for such high-accuracy measurement. Of course, in the configuration in which different light sources are provided corresponding to the respective sample cells, it is needless to say that the variation in the amount of light further increases.
[0009]
The present invention has been made in view of these points, and the object of the present invention is to measure isotope gas with very high accuracy without being affected by variations or fluctuations in the light amount of the light source. An object of the present invention is to provide an isotope gas measuring device that can be used.
[0010]
[Means for Solving the Problems]
An isotope gas measuring apparatus according to the present invention, which has been made to solve the above problems, is an isotope for measuring a gas to be measured containing carbon dioxide ¹² CO ₂ and ¹³ CO ₂ using a non-dispersive infrared absorption method. In the gas measuring device,
a) a cylindrical sample cell through which the gas to be measured flows;
b) a light source installed inside the sample cell and emitting infrared light toward both ends of the sample cell;
c) a first light detecting means provided on one end face of the sample cell for detecting infrared light having a wavelength corresponding to carbon dioxide ¹² CO ₂ ;
d) a second light detecting means provided on the other end face of the sample cell for detecting light having a wavelength corresponding to carbon dioxide ¹³ CO ₂ ;
e) arithmetic processing means for calculating the respective concentrations of carbon dioxide ¹² CO ₂ and ¹³ CO ₂ or a concentration ratio thereof based on detection signals from the first and second light detection means;
It is characterized by having.
[0011]
According to this configuration, the absorption of infrared light corresponding to ¹² CO ₂ is measured in the optical path from the light source to the first light detection means. On the other hand, the absorption of infrared light corresponding to ¹³ CO ₂ is measured in the optical path from the same light source to the second light detection means. That is, by using the same light source, it is possible to avoid the influence of variations in the amount of emitted light.
[0012]
Preferably, the light source further includes a driving unit that blinks and drives the light source at a predetermined cycle, and the arithmetic processing unit is configured to integrate detection signals from the first and second light detection units according to the predetermined cycle. .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a breath test apparatus which is an embodiment of an isotope gas measurement apparatus according to the present invention will be described. In this breath test apparatus, a concentration ratio between ¹² CO ₂ and ¹³ CO ₂ contained in a subject's breath (hereinafter referred to as “concentration ratio between ¹² CO ₂ and ¹³ CO ₂ ” is referred to as “concentration ratio of isotope gas”). ).
[0014]
FIG. 1 is a schematic configuration diagram of the breath test apparatus. The gas flow path system of this apparatus includes a sample gas introduction pipe 10, an atmosphere introduction pipe 11, a carbon dioxide removal filter 12 provided on the atmosphere introduction pipe 11, a gas introduction pipe 14, and a sample gas introduction pipe 10. Alternatively, it includes a three-way valve 13 that selectively connects the air introduction pipe 11 to the gas introduction pipe 14, a measurement cell 15 that is connected to the gas introduction pipe 14 and the exhaust pipe 16, and a pump 17 that is provided in the exhaust pipe 16. Is done.
[0015]
The measurement cell 15 has a substantially cylindrical shape with an inner diameter of about 4 to 5 mm, and a first band pass filter 19 and a first detector 20 that allow an absorption wavelength by ¹² CO ₂ to pass therethrough are disposed on one end face. A second band-pass filter 21 and a second detector 22 that allow the absorption wavelength of ^{1 3} CO ₂ to pass through are disposed on the end face. As the first and second detectors 20 and 22, a pyroelectric detector, a PbSe detector, and the like are common, but in addition, a pneumatic detector having a detection sensitivity according to the absorption wavelength of the target gas. (For details, see, for example, Shimadzu review, Vol. 46, No. 1, p. 29-p. 36, 1989). When this pneumatic detector is used, the first and second band pass filters 19 and 21 are unnecessary.
[0016]
An infrared light source 18, which is a small light bulb, is disposed at a predetermined position in the measurement cell 15, and emits light to both sides when lit. The infrared light source 18 is driven to blink by a light source driving unit 24 with a predetermined period. This blinking cycle is a very accurate one determined by a crystal resonator or the like, and the blinking frequency is preferably about 10 Hz, for example. The inner wall surface of the measurement cell 15 is preferably a mirror surface by a method such as gold (Au) coating. According to this, even when 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 light amount reaching the detectors 20 and 22 at both ends is small. Can be small.
[0017]
The detection outputs of the first and second detectors 20 and 22 are both input to the 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 unit based on an instruction from the operation unit 26 and causes the display unit 27 to display measurement results obtained by the signal processing unit 23.
[0018]
In this example, the distance L1 from the first detector 20 to the infrared light source 18 is 30 mm, and the distance L2 from the second detector 22 to the infrared light source 18 is 200 mm. This is because the concentration of the target carbon dioxide is different, so that the effects of attenuation of light due to the absorption of both of them are matched to the same level, and the linearity of the input-to-output characteristics of the detectors 20 and 22 operates within a good range. This is to make it happen. However, in actual calculation, it is preferable that L2 is longer. Here, the above value is adopted in consideration of the trade-off between the manufacturing convenience and the downsizing of the apparatus.
[0019]
Next, measurement using the breath test apparatus configured as described above will be described.
(I) Measurement of reference gas First, measurement of a reference gas (zero gas) is performed. In this example, air from which carbon dioxide has been removed is used as a reference gas. That is, under the control of the control unit 25, the flow path is set by the three-way valve 13 as shown by a dotted line in FIG. 1, and the pump 17 is operated. As a result, the atmosphere is sucked through the atmosphere introduction pipe 11, carbon dioxide is removed by the carbon dioxide removal filter 12, and then introduced into the measurement cell 15 through the gas introduction pipe 14. Then, it diffuses and fills the inside of the measurement cell 15 and is discharged to the outside through the exhaust pipe 16.
[0020]
The infrared light source 18 is driven to blink at a predetermined period by the light source driving unit 24, and light emitted from both sides of the infrared light source 18 passes through the atmosphere filled with the inside of the measurement cell 15 and does not contain carbon dioxide. The first and second band-pass filters 19 and 21 are received upon absorption of. Then, only the light in the vicinity of the 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 blinking, the first and second detectors 20 and 22 receive the light reception signal according to the intensity of the received light at the time of lighting and the light reception signal at the time of turning off (that is, by a dark current signal or external light). Light reception signal) are alternately output according to the blinking cycle.
[0021]
The signal processing unit 23 receives the detection signals from the first and second detectors 20 and 22 and receives a timing signal synchronized with the blinking cycle from the control unit 25, and detects each detection signal for a predetermined time by synchronous rectification. Is accumulated. At this time, values (signal integrated values) measured corresponding to the first and second detectors 20 and 22 are defined as I ₀₁₂ and I ₀₁₃ . This measured value is temporarily stored as a value for the reference gas.
[0022]
(Ii) Measurement of sample gas (exhalation) Next, measurement of the sample gas which is a measurement object is executed. That is, under the control of the control unit 25, the flow path is set by the three-way valve 13 as shown by the solid line in FIG. 1, and the pump 17 is operated. As a result, the sample gas (expired air) is sucked through the sample gas introduction tube 10 and introduced into the measurement cell 15 through 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.
[0023]
The infrared light source 18 is driven to blink in the same manner as in the reference gas measurement, and the signals detected by the first and second detectors 20 and 22 at this time are similarly integrated in the signal processing unit 23. At the time of 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. Since the first band-pass filter 19 extracts only the vicinity of the absorption wavelength due to ^{1 2} CO ₂ , the first detector 20 detects infrared light affected by the absorption due to only ^{1 2} CO ₂ . On the other hand, since the second band pass filter 21 extracts only the absorption wavelength due to ^{1 3} CO ₂ , the second detector 22 detects infrared light affected by the absorption due to only ^{1 3} CO ₂ . At this time, values (signal integrated values) measured corresponding to the first and second detectors 20 and 22 are defined as I ₁₂ and I ₁₃ .
[0024]
In the signal processing unit 23, the abundance ratio P of the isotope is calculated based on the following equation using the Lambert-Beer law.

Here, α ₁₂ and α ₁₃ are absorbances of ^{1 2} CO ₂ and ^{1 3} CO ₂ , and L ′ 1 and L ′ 2 are optical path lengths of the measurement infrared light corresponding to ^{1 2} CO ₂ and ^{1 3} CO _2. . When the inner diameter of the measurement cell 15 is small as in this example, the optical path length can be regarded as the distance from the infrared light source 18 to each of the detectors 20 and 22, so L′ 1 and L′ 2 are as described above. L1 and L2. That is, by applying I ₀₁₂ , I ₀₁₃ , I ₁₂ and I ₁₃ to the above formula, the abundance ratio of ^{1 2} CO ₂ and ^{1 3} CO ₂ in the sample gas, that is, ^{1 2} C and ^{1 3} C The abundance ratio is obtained.
[0025]
In this apparatus, if the measurement of the reference gas and the measurement of the sample gas are performed continuously or without taking much time (the order does not matter), long-term fluctuations in the amount of light emitted from the infrared light source 18 (for example, over time) The effect of a decrease in the amount of light emission due to deterioration) can be offset. Even if there is a fluctuation in the amount of light emitted in a shorter time, since the same infrared light source 18 is used, the influence appears in both ^{1 2} CO ₂ and ^{1 3} CO ₂ , and as a result, cancels out. Will be.
[0026]
In the above example, the infrared light source 18 is driven to blink. However, if the ratio of the light amount when turned on and the light amount when turned off, that is, the modulation rate is small, the effect of signal integration is not obtained so much. Current, external light, and the like are error factors. Therefore, in such a case (for example, when the followability of turning on / off of the light source is not good), a mechanical chopper as conventionally used may be used instead of performing blinking control.
[0027]
【The invention's effect】
As described above, in the isotope gas measurement device according to the present invention, the same light source is used when measuring two isotope gases at the same time. It can be removed to make extremely accurate measurements. In addition, since the measurement cells are arranged on both sides with the light source in the center, the light source can be reduced. When a large flat light source is used, the amount of emitted light is likely to vary depending on the portion of the light source. However, in the present invention, such variation in the amount of emitted light can be avoided by reducing the light source.
[0028]
In addition, if the light source is driven to blink in the isotope gas measurement device according to the present invention, unlike the conventional mechanical chopper, it does not have a movable part, so that it is resistant to vibrations, and further, the light source for attaching the chopper. There is no need to insert and separate a window material between the cell and the cell, and a motor for driving the chopper is unnecessary, which is advantageous in terms of 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 ... Atmospheric 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 ... First band pass filter 20 ... 1st detector 21 ... 2nd band pass filter 22 ... 2nd detector 23 ... Signal processing part 24 ... Light source drive part 25 ... Control part 26 ... Operation part 27 ... Display part

Claims (1)

In an isotope gas measurement apparatus for measuring a measurement gas containing carbon dioxide ¹² CO ₂ and ¹³ CO ₂ using a non-dispersive infrared absorption method,
a) a cylindrical sample cell through which the gas to be measured flows;
b) a light source installed inside the sample cell and emitting infrared light toward both ends of the sample cell;
c) a first light detecting means provided on one end face of the sample cell for detecting infrared light having a wavelength corresponding to carbon dioxide ¹² CO ₂ ;
d) a second light detecting means provided on the other end face of the sample cell for detecting light having a wavelength corresponding to carbon dioxide ¹³ CO ₂ ;
e) arithmetic processing means for calculating the respective concentrations of carbon dioxide ¹² CO ₂ and ¹³ CO ₂ or a concentration ratio thereof based on detection signals from the first and second light detection means;
An isotope gas measuring device comprising:

Images