JPH0331218B2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field Various stable isotopes, such as ² H, ¹⁵ N, ¹⁸ O,
¹³ C and the like are used as labels, and the use of these tracers is widely used as an analysis tool in fields such as agriculture and medicine.

In the present invention, a compound labeled with ¹³ C among these isotopes is administered to a sample, and the target product obtained from these is a gas of ¹³ CO _2. Based on the difference in light absorption between ¹² CO ₂ and ¹³ CO ₂ , The present invention relates to an apparatus for analyzing various samples.

For example, after administering a compound labeled with a carbon isotope to a living body, the labeled carbon dioxide in exhaled breath carbon dioxide, which is the final metabolite, is measured, or blood, etc. is burned and this combustion gas is measured. It is used in a variety of fields, including the analysis of the characteristics of photosynthesis in plants, and the analysis of ¹³ C taken up by plants by adding carbon isotope-labeled chemical components to soil.

Conventional technology Compounds labeled with the radioactive isotope ¹⁴ C were administered to the sample and tracer measurements were performed using a scintillation counter, but there were difficulties in handling the radioactive isotope, and stable isotope ¹³ C was used. A measurement method using a tracer was desired.

Therefore, a method has been developed in which a compound labeled with the stable isotope ¹³ C is administered to a sample, the target product obtained from this is ¹³ CO ₂ , and the ratio of ¹² CO ₂ and ¹³ CO ₂ is determined using a mass spectrometer. Ta.

However, the measurement method using a mass spectrometer requires a vacuum system, is difficult to handle and maintain, is complex to analyze the analysis results, and is expensive, so it is not easy to use. There was a problem that I couldn't solve.

To solve this problem, stable isotopes
Invented a measurement method based on the difference in light absorption between ¹³ CO ₂ and ¹² CO ₂ , and filed patent application No. 11563, 1983,
The application was filed as No. 116564.

In patent application No. 11563/1983, ¹³ CO ₂ and
¹² To measure the ratio of CO ₂ ,
The wavenumber at which the amount of infrared absorption becomes equal at the abundance ratio of ¹³ CO ₂ and ¹² CO ₂ ( ¹² CO ₂ is 2390 mm ^-1 , ¹³ CO ₂ is 2270 cm
^-1 ) discloses a method for measuring the absorption intensity of both. In addition, in Japanese Patent Application No. 116564/1983, two long and short cells were installed so that the amount of infrared absorption was equal to the abundance ratio of ¹³ CO ₂ and ¹² CO ₂ in the natural world, and changes in ¹³ CO ₂ were measured. A method is disclosed.

The natural abundance of ¹³ C is about 1% of ¹² C.
The infrared absorption of ¹³ CO ₂ causes an isotopic shift of 70 cm ^-1 compared to ¹² CO ₂ , and the absorption amount is also extremely small compared _to ¹² CO ₂ ^.
12 Measuring the infrared absorption ratio of CO ₂ with high sensitivity is a very important technology.

By the way, a major problem that limits this sensitivity is the presence of air in the optical path from the light source to the detector.
Absorption occurs due to CO ₂ and energy loss occurs in the light source, significantly worsening the S/N ratio. Therefore, by placing the optical system in the red box and creating a vacuum inside the box to remove the CO ₂ gas in the box, absorption by CO ₂ existing in the optical path other than the cell is eliminated, resulting in a good S/N ratio. We can expect accurate measurements.

However, in order to prevent vacuum leaks in the box (spectroscope) and to reduce the pressure inside the spectrometer to prevent distortion of the spectrometer, an extremely sturdy case is required, and the adjustment of the optical system is extremely difficult. It's going to be difficult. Furthermore, the position of the optical element shifts due to changes in temperature, resulting in baseline or span drift between ¹² CO ₂ and ¹³ CO ₂ , which limits the ability to increase sensitivity.

OBJECTS OF THE INVENTION An object of the present invention is to provide a carbon isotope gas analyzer that can measure ¹³ CO ₂ and ¹² CO ₂ with high sensitivity, and has stable and good performance.

Structure of the Invention The optical carbon isotope gas analyzer introduces ¹³ CO ₂ as a measurement sample and ¹² CO ₂ as a reference sample, and
It has a sample cell and a reference cell for measuring the absorption of light from a light source, and uses two reflective mirror optical elements.
The light from the light source is divided into two optical paths and transmitted through the sample cell and reference cell, and a sector mirror alternately guides the light from the sample cell side and the light from the reference cell side to the same traveling optical path.
The light is input to a spectrometer, and the light that has passed through the sample cell and the reference cell is separated into different wavelengths such that the absorption in the infrared region is equal, and the light is emitted through separate output slits corresponding to each wavelength. The emitted light is irradiated onto one detector using an optical element, and ¹² CO ₂ and
¹³ The measurement principle is established by measuring the ratio of absorption of CO ₂ by adopting an automatic gain control method so that the output signal transmitted through the reference cell is constant, and in order to achieve the above purpose, The light source, measurement cell, reference cell, optical element, spectroscopic means, detector, and other elements are housed in a sealed case box (spectrometer), and this sealed case and the column container containing ^{the 12} CO ₂ absorbent are circulated. By connecting the pump with a pipe and circulating the air in the sealed case between the case and the column container, the air in the sealed case is removed.
¹² Configured to remove _CO2 .

Embodiments Preferred embodiments of the present invention will be described in more detail below with reference to the drawings.

As shown in Figure 1, the infrared absorption of CO ₂ is 2350 cm ^-1
It is located nearby and consists of P-branch and R-branch. ¹² CO ₂ goes from 2390cm ^-1 to 2290cm ^-1
13 CO ₂ is absorbed from 2320cm ^-1 to 2290cm ^-1 at 70cm
^-1 isotopic shift occurs. This is an optical carbon isotope gas analyzer that measures the ratio of the infrared absorption of this ¹³ CO ₂ isotope to the infrared absorption of ¹² CO ₂ .

FIG. 2 is a configuration diagram of an isotope gas analyzer according to the present invention.

11 is a box (spectroscope). 12 is an absorbent column. 13 is a constant temperature bath, 14 is a light source, 15,1
6 is a valve, and 17 is a circulation pump.

The air inside the spectrometer 11 is taken out from one end and fed into the spectrometer from the other end by a circulation pump 17. A tower 12 containing an absorbent (soder lime) is installed in the middle of the tower to absorb CO ₂ in the air and circulate the air from which CO ₂ has been removed. Furthermore, the column 12 containing the absorbent is placed in a constant temperature bath 13 to keep the temperature of the circulating air constant.

FIG. 3 shows an overall diagram of the optical system and electrical system of the present invention.

21 is a light source, 22 and 23 are concave mirrors, 24 is a power source for the light source, 25 is a sample cell, 26 is a reference cell, 27
is a tipper motor that rotates 29 sector mirrors and 43 tippers in synchronization. 30 and 31 are mirrors that keep the optical path constant after alternately switching the light from both cells with sector mirrors; 211 is a concave mirror 34 and 36, and a diffraction grating 35, which slits 38 the light at different wavelengths; It is designed to emit light at It is an optical system in which plane mirrors 41 and 42 are focused by plane mirrors 41 and 42 and concave mirrors 44 and 45 so that the emitted light is incident on a detector 46 by plane mirrors 39 and 40, respectively. The light reflected from the plane mirrors 39 and 40 is configured to be chopped at a chopper 43 in the middle of the optical path in synchronization with the sector mirror 29.

Reference numeral 212 is a sealed case that houses each element, and corresponds to box 11 (spectroscope) in FIG. In FIG. 3, the absorbent column 12, constant temperature bath 13, and piping shown in FIG. 2 are omitted.

The output of the detector 46 is amplified by a preamplifier and an amplifier, and automatic gain control is applied to the amplifier 48 so that the signal output of the reference light always remains at a constant value. As a result, the signal output of the sample light shows a change proportional to the temporal change in infrared absorption. 49 is a sample hold circuit that performs automatic gain control, the output of which is amplified by logarithmic amplifiers 50 and 51, recorded on two pen recorders, and the same signal is processed by a data processor. . Reference numeral 54 denotes a combustion device for generating ¹³ CO ₂ from the sample, and the gas of ¹³ CO ₂ flows into the sample cell 25 .

Effects of the invention By removing 300 ppm of natural carbon dioxide that exists in the box (case) containing the optical system,
When carbon dioxide containing 4% ¹³ CO ₂ is introduced into the sample cell using the conventional method of reducing the pressure inside the case to vacuum, which is a method of eliminating carbon dioxide absorption in the optical path other than the reference cell near 2300 ^cm -1. Figure 4 shows the output recorded to check for drift.

Similarly, FIG. 5 shows the recorded output of the drift investigation according to the present invention. The horizontal axis shows time, and the vertical axis shows output value. Compared to the baseline variation coefficient of 0.3% in the conventional method, it is 0.03% in the device using the present invention, and the stability is approximately 1%.
It's getting much better.

This is because when the box (case) containing the optical system is evacuated, the case becomes distorted and the drift becomes large. Furthermore, if there is a temperature change in the case environment, the distortion caused by the temperature change will increase the drift, so it was necessary that the temperature change be small. In the device of the present invention, the inside of the case is at normal pressure, so no distortion occurs in the case, and the tower containing the absorbent is placed in a constant temperature bath, so that the air from which carbon dioxide has been removed flows inside the case at a constant temperature. Because it circulates, it can withstand indoor temperature changes, making it a device that can be put to practical use.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the absorption spectrum of carbon dioxide when ¹³ CO ₂ and ¹² CO ₂ exist in the natural abundance ratio, and FIG. 2 is a schematic diagram for implementing the present invention. Fig. 3 shows an example of the optical system and electrical system of the present invention, Fig. 4 shows the output fluctuation when the inside of the case is reduced to vacuum, and Fig. 5 shows the case where the present invention is used. FIG. 3 is a diagram showing output fluctuations.

Claims (1)

[Claims] 1. ¹³ CO ₂ which is a measurement sample and a reference sample
¹² It has a sample cell and a reference cell for measuring the absorption of light from the light source by introducing CO ₂ , and an optical element divides the light from the light source into two optical paths and transmits the sample cell and the reference cell. The light transmitted by another optical element is guided to the same traveling optical path, and the light transmitted through the sample cell and the reference cell on the same traveling optical path is separated into different wavelengths by a spectroscopic means so that the absorption in the infrared wavelength region is equal. In a carbon isotope gas analyzer that detects the separated light with a detector and measures the absorption ratio of ¹² CO ₂ and ¹³ CO ₂ , the above-mentioned light source, measurement cell, reference cell, optical element, spectrometer are used. Each element such as the means and the detector is housed in a sealed case, and the sealed case and the column container containing _{the CO 2} ^absorbent are combined.
An optical carbon isotope characterized in that ¹² CO ₂ is removed from the air in the sealed case by connecting it to a circulation pump with a pipe and circulating the air in the sealed case between the case and the column container. Body gas analyzer. 2. The optical carbon isotope gas analyzer according to claim 1, wherein the column containing a carbon dioxide absorbent is placed in a constant temperature bath to maintain a constant temperature.