JP2903448B2 - Fourier transform infrared spectrophotometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Fourier transform infrared spectrophotometer (hereinafter, referred to as FTIR).

[0002]

2. Description of the Related Art When analyzing a gas component based on an infrared absorption spectrum obtained by FTIR, a gas to be measured is usually introduced into a cell, but in practice, an optical path other than the cell is used. Infrared light is also absorbed by gas components present therein, usually water vapor and carbon dioxide present in the atmosphere. Therefore, when performing quantitative analysis of low-concentration water vapor or carbon dioxide in a measurement sample, etc., in order to obtain highly accurate analysis results, lower the background water vapor or carbon dioxide concentration and stabilize it at a certain level. Need to be done.

Also, when analyzing a gas component whose main infrared absorption region overlaps water vapor or carbon dioxide, for example, nitrogen dioxide, it is necessary to lower the concentration of water vapor or carbon dioxide in the optical path other than the cell. desirable. Therefore, conventionally, an optical system such as a light source and an interferometer is housed in an airtight room, and the optical system is evacuated or purged with, for example, N ₂ gas having no absorption in an infrared region. I have.

[0004]

However, when performing vacuum evacuation, it is necessary to prepare a vacuum pump or take measures against vibration. When the N ₂ purge is constantly performed, the use amount of the N ₂ gas increases, the running cost increases, and the gas near the interferometer is disturbed, so that the output becomes unstable. . Also,
Even if the N ₂ purge is performed manually before analysis start, not must perform opening and closing of the valve each time, with a very troublesome, after purging ends, the stabilization time and temperature of the optical system according For this reason, there is a problem that a considerable waiting time (loss time) occurs.

Further, when the cell is detachable, or when the detector is an MCT (mercury cadmium tellurium) detector which requires cooling with liquid nitrogen, the airtightness of the optical system is hardly improved, and backing is not possible with a temporary purge. There is also a problem that the ground fluctuates easily.

The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to make it possible to easily purify an optical system and to always perform analysis in a stable state. An object of the present invention is to provide a Fourier transform infrared spectrophotometer which can be used.

[0007]

In order to achieve the above object, according to the present invention, a set of an optical system such as a light source and an interferometer and a set of a cell and a detector are housed in an airtight room which is partitioned. A Fourier transform infrared spectrophotometer in which a purge gas supply path is connected to each of the chambers, wherein the opening and closing of an on-off valve provided in each of the purge gas supply paths is controlled on a computer, and the purging of each of the chambers is automatically performed. In addition, the automatic supply of the purge gas is always performed in the chamber accommodating the cell and the detector, while the automatic supply of the purge gas is performed in the chamber accommodating the optical system by the start of analysis. and the chamber housing the detector, before
The above cell and other components for supplying liquid nitrogen to the detector, etc.
Immediately after opening the door of the
Immediately after the start, the system is configured to automatically supply a temporarily higher purge gas flow rate.

[0008]

The purge of the two chambers is controlled by a computer via an on-off valve so that both of the two compartments are always in a stable state. The purging of two chambers is performed unattended. In other words, the optical system such as the light source and the interferometer is easily airtight, so that the optical system can be stabilized only by supplying the purge gas before the start of analysis . Therefore, the purging of the optical system can be easily performed. On the other hand, since the airtightness of the cell and the detector is hard to increase, the purge gas is constantly supplied to maintain the room in a stable state. In particular, the airtightness is lost immediately after opening the door of the chamber to supply liquid nitrogen to the detector, etc. Will be able to analyze. As described above, highly accurate analysis can always be performed in a state where the concentration of background water vapor or carbon dioxide is low. Further, since there is no waiting time, the analysis efficiency is improved.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 schematically shows the structure of an analysis section of an FTIR according to the present invention. In this figure, reference numeral 1 denotes a housing of the analysis section, and the inside thereof is divided into two chambers 3 and 4 by a partition 2. I have. Each of the chambers 3 and 4 is configured to be airtight. The first chamber 3 contains a purge gas PG
Check valves 5 and 6 for introducing (described later) are provided. An optical system 9 including a light source 7 that emits infrared light and an interferometer 8 is provided in the first chamber 3. The interferometer 8 includes a beam splitter 10, a fixed mirror 11, a movable mirror 12, and the like. Reference numeral 13 denotes a mirror for adjusting an optical path.

The second chamber 4 contains a purge gas (to be described later).
An inlet 14 and an outlet 15 for introducing the gas are provided. A cell 16 for accommodating a measurement sample or a comparison sample having a transmission window (not shown) made of an infrared transmitting material at both ends on the optical path side is provided inside the second chamber 4.
Is provided, and a detector 17 composed of, for example, an MCT detector is provided. Reference numeral 18 denotes an optical path adjusting mirror.

A transmission window 19 made of an infrared transmitting material is formed in a portion of the partition 2 facing the optical path.
Reference numeral 20 denotes a computer which performs a Fourier transform on the interferogram output from the detector 17 at high speed,
Further, the concentration of the component to be analyzed is calculated based on the absorption spectrum obtained as the Fourier transform output, and the on-off valves 22, 23, 29, 38, and 4 described later are performed.
It is configured to issue a command to the pumps 1 and 44 and the pump 30 (see FIG. 2). That is, the computer 20 has a function of controlling a sampling system, a purge system, and the like, in addition to an arithmetic operation for analysis and storage of data.

Next, the configuration of a sampling system and a purge system for the analyzing section having the above configuration will be described with reference to FIG.

In FIG. 2, reference numeral 21 denotes a gas supply passage for supplying a measurement sample (sample gas) SG or a comparison sample (reference gas) RG (for example, N ₂ gas) to the cell 16, and an upstream side thereof. Valves, such as solenoid valves and solenoid valves 2
A sample gas supply path 24 and a reference gas supply path 25 respectively provided with 2 and 23 are connected in parallel with each other. 26 is a flow control valve such as a needle valve. Also,
27 is a flow control valve 28, an on-off valve 29, a suction pump 30,
This is a gas discharge path provided with a flow meter 31 and the like.

Reference numeral 32 denotes a purge gas PG (for example, N ₂ gas)
The regulator 33 and the pressure sensor 34
At the downstream side of the pressure sensor 34.
Two purge gas supply paths 35 and 36 (hereinafter, referred to as a first purge gas supply path 35 and a second purge gas supply path 36)
Has branched to. The pressure sensor 34 detects that a predetermined pressure is not applied to the purge gas supply path 32 (that is, the purge gas is not purged) and issues an alarm.

The first purge gas supply passage 35 is connected to the optical system 9.
It supplies N ₂ gas as a purge gas to the first chamber 3 containing a gas, and includes a flow regulating valve 37 such as a needle valve, an on-off valve 38 such as an electromagnetic valve, and a flow meter 39.
In addition, the second purge gas supply path 36 supplies N 2 as a purge gas to the second chamber 4 containing the cell 16 and the detector 17.
_It supplies _two gases and includes a flow control valve 40 such as a needle valve, an on-off valve 41 such as an electromagnetic valve, and a flow meter 42. And, in the second purge gas supply path 36,
A branch flow path 44 having a flow control valve 43 such as a needle valve and an on-off valve 44 such as an electromagnetic valve is provided so as to straddle the flow control valve 40 and the on-off valve 41.

In the Fourier transform infrared spectrophotometer configured as described above, the first purge gas supply passage 35 is used when the analysis is not performed using the timer in the computer 20.
Is opened only for a predetermined time. Thereby, the purge gas PG of, for example, 101 / min is stored in the first chamber 3 in which the optical system 9 such as the light source 7 and the interferometer 8 is housed.
(N ₂ gas) is supplied for about 10 minutes, and the inside of the first chamber 3 is replaced with N ₂ gas. Then, when the gas pressure in the first chamber 3 decreases to a preset pressure, the check valve 6 closes, so that the N ₂ gas can be automatically sealed in the first chamber 3. This operation may be performed once a day, for example.

By supplying the purge gas PG, the optical system 9 is purged unattended before the start of analysis, and the optical system 9 is purged.
Can be kept stable, and the optical system 9 can be easily purged. In order to prevent the purge from starting during the analysis, a certain period of time (for example, 30
Minutes) before the alarm is issued or the computer 2
Purging may not be started during the acquisition of the interferogram by 0 or during the operation of the sampling system.

The on / off valve 41 of the second purge gas supply passage 36 is normally opened in accordance with a command from the computer 20, so that the detector 1 requiring maintenance is required.
A purge gas PG (N ₂ gas) of, for example, 0.51 / min is constantly supplied to the second chamber 4 in which the chamber 7 and the cell 16 are housed. As a result, the inside of the second chamber 4 is constantly purged. In addition, immediately after opening the door of the second chamber 4 or the like immediately after the opening of the second chamber 4 to supply liquid nitrogen to the detector 17 or the like, the on-off valve 44 is also opened to temporarily increase the flow rate. For example, N ₂ gas is supplied at 101 / min for 10 minutes. Thereby, the replacement of the gas in the second chamber 5 is accelerated, and the analysis in a more stable state becomes possible.

The on / off valves 22 and 23 are appropriately turned on / off in accordance with a command from the computer 20 so that the measurement sample SG or the comparison sample R
G is supplied and a predetermined analysis is performed.

The present invention is not limited to the above-described embodiment. For example, on-off valves 22, 23, 29, 38, 41,
44 may be an air control valve. When a detector that does not require replenishment of liquid nitrogen (for example, a TGS (glycine trisulfide) detector) other than the MCT detector is used as the detector 17, the airtightness of the second chamber 4 is improved. Furthermore, the sample to be analyzed is not limited to a gas, but may be a liquid or a solid.

[0022]

As described above, according to the present invention,
Until the start of the analysis, the purging of the chamber accommodating the optical system such as the light source and the interferometer and the chamber accommodating the cell and the detector are performed unattended. That is, since the optical system such as the light source and the interferometer is easily airtight, the optical system can be stabilized by merely supplying the purge gas before the start of the analysis . Therefore, the analysis can be always performed in a state where the concentration of the background water vapor or carbon dioxide is low, the measurement accuracy can be improved, and there is no waiting time, so that the analysis efficiency is improved. In addition, by increasing the airtightness of the chamber that houses the optical system, the time required for purging and the amount of purge gas used can be significantly reduced, making it extremely economical and improving the purging efficiency, and always keeping the background stable. It can be analyzed in a state where it is done.

Further, since cells and detectors requiring maintenance are hardly airtight, a similar effect can be obtained by constantly supplying a purge gas. Furthermore, immediately after opening the chamber door for replenishing the detector with liquid nitrogen, etc., the airtightness is lost, but in this case, the purge gas with a temporarily higher flow rate is automatically supplied and stable as soon as possible. Analysis in the state becomes possible. Since these controls are performed by a computer, the operation is simple.

In particular, in a gas analyzer, when N ₂ gas is used as a purge gas, this N ₂ gas is often used as a comparative sample, so that the supply source can be shared and a dedicated vacuum pump is used. , The entire apparatus can be made more compact. Furthermore, even when an unknown gas other than water vapor or carbon dioxide leaks into the atmosphere, the effect can be eliminated.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an FTIR analysis unit according to the present invention.

FIG. 2 is a diagram schematically showing a configuration of a sampling system and a purge system for the analysis unit.

[Explanation of symbols]

3, 4 two chambers, 7 light source, 8 interferometer, 9 optical system, 16 cell, 17 detector, 20 computer
35, 36 ... purge gas supply path, 38, 41, 44 ... open / close valve.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01J 3/45 G01J 3/02

Claims (1)

(57) [Claims] 1. A Fourier transform infrared system in which a set of an optical system such as a light source and an interferometer and a set of a cell and a detector are housed in partitioned airtight chambers, and a purge gas supply path is connected to each of the chambers. In a spectrophotometer, the opening and closing of an on-off valve provided in each of the purge gas supply paths is controlled on a computer so that purging in each of the chambers can be automatically performed. while performing in the chamber for accommodating the cell and detector always in the chamber for accommodating the optical system configured to perform the time of start of the analysis, moreover the chamber accommodating the cell and the detector, the detector
The cell and detection for replenishing liquid nitrogen to the vessel
Immediately after opening the door of the chamber that houses the container or immediately after purging starts
To temporarily Fourier transform infrared spectrophotometer, characterized by being configured to automatically provide a greater flow rate of the purge gas.