JPS6033039A - Method for measuring continuously stable isotope by using device for detecting gas by microwave absorption method - Google Patents

Abstract

PURPOSE:To measure quickly an isotope component with high sensitivity by transforming respectively the components contg. the separated stable isotope to the compd. having the structure suitable for microwave spectrometry and feeding continuously a specific amt. of the same or resembling compd. as or to said compd. together with the transformed compd. CONSTITUTION:Nitrobenzene of <14>N and nitrobenzene of <15>N are separated from a sample contg. nitrobenzene having, for example, <14>N and <15>N as nitro group and are respectively transformed to <14>NH3 and <15>NH3 by reduction. A fixed amt. of NH3 together with the respective gases is fed to the sensor of a device for detecting and measuring gas by a microwave absorption method. The NH3 is passed continuously in the measuring system at the fixed amount exceeding the adsorption equil. condition therein. Then even if the <14>NH3 and <15>NH3 to be measured are trace, both attain quickly a specified concn. without being adsorbed to the measuring system and the <14>NH3 and <15>NH3 are respectively exactly separated and are measured with high accuracy. The isotopes of S compd. carbohydrate, etc. are also measured in the same way by transforming the same to SO2, CO2 and H2O.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring stable isotopes using a microwave absorption type gas detection device (hereinafter abbreviated as microwave gas sensor). Conventional microwave spectrometers had drawbacks such as large and expensive equipment and troublesome operation, but a spectrometer was developed that uses a cavity resonator as a sample cell and a solid-state microwave oscillation element. However, due to its miniaturization, high sensitivity, and improved economic efficiency, it is being considered as a practical gas sensor, but the drawbacks described below have not been overcome, so expectations for its use have been delayed. I can't say that.

The present inventors conducted studies to overcome these drawbacks, and as a result, they discovered and completed the present invention.

A microwave gas sensor measures polar molecules that have vapor pressure. For example, as a nitrogen compound, N
H3, N20, NO2, 80 as a sulfur compound
2. CH3SH, CO8,7 Rudehi)”f, n TehaH
Cl40.

a(3a(0) and other typical polar gases to be measured, such as H2o.

These molecules have the property of being adsorbed on the surface of the microwave gas sensor body and the attached gas line.

This adsorption phenomenon delays the response to changes in the concentration of the analyte. This leads to a substantial decrease in sensitivity as the amount of sample required for quantification is large.

In order to improve the responsiveness of a microwave gas sensor to changes in concentration, it is generally expected that methods such as selecting a material with low adsorption properties and reducing the gas contact area are effective. Furthermore, it is predicted that improvements in the characteristics can be expected by maintaining adsorption equilibrium conditions within the measurement system, but it is extremely difficult to realize each of these general predictions, and it is difficult to realize improvements in these general predictions. There is no known example of implementation that takes full advantage of the characteristics.

In particular, new problems arise when stable isotopes flowing out from a device that continuously separates samples, such as a gas chromatograph or a liquid chromatograph, are continuously measured. In other words, for example, in a method of converting the chemical form into an appropriate chemical form using a processing device and continuously supplying it to a microwave gas sensor for measurement, the previously supplied analyte is used to measure the analyte that is supplied later. This is because accurate measurements are impossible. In Figure 1a, the frequency of the microwave gas sensor is set to around 23870Δ4Hz +J. Benzene and 15N-nitrobenzene are pretreated with Ni-catalyzed hydrogenolysis to produce NH3
This shows an example of conversion into 15NH3 and measurement.

As is clear from the figure, 14NN (3) was detected for the first injection of 14N-nitrobenzene, and the same amount was detected for the second injection of 14N-nitrobenzene. In this limit 9, there is a significant tailing of the detected waveform, but it seems that the measurement is being carried out, but when 15N-nitrobenzene was injected in the 5th time, the detected waveform normally did not occur. However, as shown in the figure, !5 1'tH3 was detected, and the following 15N
-A similar phenomenon occurs with each person injected with nitrobenzene. In addition, Figure 1 shows the frequency of the microwave gas sensor as 22789.
■This shows the results when a similar experiment was conducted with the setting near Iz! When 715N-nitrobenzene is injected, 15 6 is similarly detected, but when 14N-nitrobenzene is subsequently injected, 15NH3 is detected again, and thereafter, 15]'IIT is detected for each injection of 14N-nitrobenzene. −
13 detections occur.

An object of the present invention is to provide a rapid, simple, highly sensitive, and economical stable isotope tracer method using a microwave gas sensor with good response to the rapid concentration of a measurement target. The above object of the present invention is to continuously flow a compound that is the same as or similar to the object to be measured at a constant concentration into the airflow to be measured, and perform measurement under the condition that the concentration in the measurement system is higher than the adsorption saturation condition. was achieved.

Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 2 is a schematic diagram of an apparatus for carrying out the method according to the present invention, including a sample pretreatment apparatus 10, a carrier gas inlet 21,
Microwave gas sensor 60, sample inlet 20
A sample separation device 1 is connected to.

The sample pretreatment device 10 transfers the sample to the microwave gas sensor 6.
21 is for converting into a compound having a chemical form to be measured at a constant concentration of the same or similar compound, such as "NH3," N
In the case of H3 measurement, it is an inlet for NH6 or methylamine (hereinafter abbreviated as ear gas flow).

A sample substance is converted into a target substance by the pretreatment device 10 mainly through oxidative decomposition or hydrogenolysis. The above reaction continuously converts a sample into a target product in the presence of a catalyst.

A reaction example is shown below.

Ni Compound water containing nitrogen ff1 ((support) solution μH, +CH4+
---t Oxygen-containing compound ykHIS'l! j 2”” ” ”
” - The sample separation device 1 may be a gas chromatograph device, a liquid chromatograph device, etc., but if the sample is volatile, a gas chromatograph device is mainly used, and if the sample needs to be separated in a solution state, a liquid chromatograph device is used. The microwave gas sensor 60 measures the microwave absorption spectra of not only different compounds, but also molecules of the same compound composed of different isotopes at completely different frequencies. Here, a cavity resonator is used as a sample cell, and a microwave gas sensor using a solid-state microwave oscillator is used to generate 14Nl (3,"I
'113 will be explained as an example.

Microwave Gas Sensor Co., Ltd. as described in the specification of JP-A-53-100887 (referred to as a transmission cavity type), or as the first embodiment in the specification of JP-A-57-197455. (referred to as double modulation reflective cavity type d type)
can be used. FIG. 3 shows a transmission cavity type sensor, including a rectangular digital talc cavity resonator 61, a microwave oscillator 62, an accompanying power source 66, a modulator 64, a lock-in amplifier 65, and a termination member. It consists of a recording diode 66, a recording diode 57, and a detection diode 58, and its operation is well known.

If 15N is to be measured using a transmission cavity type sensor as shown in FIG. 3, in the 41N configuration shown in FIG. The terminal member 66 of the rectangular digital talc cavity resonator 61 is converted into 15NI (3) and this monitor is connected to the termination member 66 of the rectangular digital talc cavity resonator 61 so as to continuously monitor the peak value of the absorption line of 22789 MHz. 15Nl13 may be similarly measured continuously using a double modulation cavity type sensor as shown in Fig. 4.

Dual modulation reflective cavity type sensor W: Geetalck cavity resonator 61', microwave source 62', microwave bridge 59, automatic frequency controller (AFC) 40, double modulator 64', lock-in amplifier 35 ．． )! J Agar Road 41,
The operation of the amplifier 4 and recorder 57 is well known.

In the example shown in FIG. 3 or 454, only 1'IN or 15N of the distillate component from the sample separation device 1 is continuously measured. In the present invention, after converting a series of stable isotope traces into a single substance, for example 1,5N, NH3 in the case of 14N, this substance, Continuously measures NH3 using a microwave gas sensor with excellent selectivity and isotope discrimination ability, and uses a carrier gas flow to improve the time response of the microwave gas sensor to rapid concentration changes of the measurement target. 0 Fig. 5 (a) (b) u In the configuration shown in Fig. 2 in which a gas chromatograph is used as the sample separation device 1 and Ni is used as a hydrogenolysis catalyst in the sample pretreatment device 10, the sample and L
This figure shows the output of the gas chromatograph device and the output pattern of the microwave gas sensor when measuring N-nitrobenzene and 15N-nitrobenzene while flowing a carrier gas containing dark from 21.

Figure 5 (Al) After measuring 15N-nitrobenzene at a sufficiently high concentration, 15NH3 was not detected even when 14N-nitrobenzene was used, indicating that NH3 in the measurement system was replaced or exchanged. Furthermore, as shown in Fig. 5(b), Wb t is relatively negligible.
h9) When 1015N-nitrobenzene is used as a sample, by substitution or conversion, 6. ”N) (Produces a small number of 3.

In this case, immediately after the output of ``N1 (3), an output of the same magnitude in the opposite direction is generated, and such a pseudo signal can be distinguished from the true 141'11 (of the output of 3) by the existence of this reverse direction output. In addition, it is possible to correct this phenomenon by using a sample with a known 15N content and creating a calibration curve for ``Nl-13,15NF (,'' depending on the required accuracy. You can use this.

As shown in Figures 5(a) and (b), when measurements are carried out while continuously flowing NH6 as a carrier at, for example, 2000 ppm, 14NH3 or "N" derived from the sample is
1-13 is diluted and the probability of adsorption in the system decreases; furthermore, even once adsorbed, it is easily displaced and desorbed by a large amount of carrier; the probability that desorbed molecules will be adsorbed again is small; Adsorption into the system can be virtually ignored due to the return.

Generally, it is difficult to supply a carrier containing a very small amount of NI"13 at a stable concentration. In the present invention, for example, a cylinder is filled with a gas containing 10,000 ppm OHe-based NI"13, and this is controlled by flow rate control. The concentration stability is improved by flowing 115% of the total gas flow rate, and the stability is calculated from the output of the microwave gas sensor, resulting in fluctuations of no more than 1 to 2 ppm.

In general, microwave gas sensors can obtain high-resolution spectra of any vaporizable polar molecule, but since the absorption frequency differs extremely from compound to compound, for example, the gas chromatograph If the gas sensor is directly connected to a microwave gas sensor, the measurement will be performed at a predetermined frequency of the target component. For this reason, the components that can be detected are limited to a single component. Therefore, in this case, it is effective in that the target substance can be distinguished even when the chromatographic peak of that component overlaps with other components and it is impossible to separate the target substance. Since the sensor becomes completely insensitive, the overall performance of the device can only be achieved by adding an auxiliary detector for detecting a single component to a gas chromatograph detector. Furthermore, it is completely impossible to continuously detect isotopes in each component that is distilled out one after another as in the present invention. It cannot be said that the conventional method, that is, an apparatus in which a microwave gas sensor is directly connected to a gas chromatograph, takes full advantage of the features of the microwave gas sensor. This is because if you want to take advantage of the high resolution of microwave gas sensors, that is, the fact that they are not affected by coexisting components, there is no need to perform separation using a gas chromatograph, and if you use a gas chromatograph, you can add detection of a single component. This is because there are many cases where it is practically meaningless to do something. In this way, a device that directly connects a gas chromatograph and a microwave gas sensor and the present invention may look similar due to the structure of the device, but there is a chemical structure between the gas chromatograph and the microwave gas sensor. As will be explained below, the present invention is completely different in character from the present invention, which is provided with a pretreatment device for nodule and further provided with a carrier gas inlet. In other words, the feature of the present invention is that isotopes of specific atoms, for example, 14N:5N
in separate detection. Therefore, the target atoms contained in each chromatographic fraction that are distilled out one after another are converted into NH3, which is expected to have the highest sensitivity for a microwave gas sensor, for example, no matter what kind of molecule the chromatographic fraction is. The method utilizes the high selectivity and excellent isotope discrimination ability that the method has. Therefore the special '1' on the device
．． Firstly, a microwave gas sensor with high isotope discrimination ability was used as a detector for stable isotope tracers, and secondly, microwave absorption signals of isotopes were detected with high sensitivity and for a wide range of compounds. It is equipped with a preprocessing device that can interrogate any sample to a common specific molecule in order to obtain it. The third feature is that by continuously flowing the same or similar compound as the measurement target through the carrier inlet, the response of the microwave gas sensor to rapid concentration changes is improved, and as a result, the amount of sample required for measurement can be reduced. In addition, in the case of samples such as animal and plant tissues for which ordinary separation equipment cannot be used, the sample is decomposed before being introduced into the separation equipment.
The decomposed gas can be introduced into a gas chromatograph device, separated and quantified continuously, and further introduced into a sample pretreatment device, where the chemical form can be converted if there is 8 narrower, and then measured by a microwave gas sensor. is the same as above. Furthermore, in the method according to the present invention, it is possible to determine the quantitative balance without creating a calibration curve for each substance in order to unify the chemical forms using the sample pretreatment device.

Next, taking as an example a tracer experiment using a 15N-labeled compound, the case where "NI(6" and "NH6") are simultaneously measured will be explained using the sensor shown in FIG.

The example in Figure 6 shows the chromatographic distillate components 15NH and NH3.
In this example, a transmission cavity type sensor shown in Fig. 3 is used to measure 141 cm, 13 cm, 25 cm, etc.
Settings are made to continuously measure the peak value of the absorption line at 870 MHz. As a sensor for the 15N measurement system, a double modulation reflective cavity type sensor shown in Fig. 4 is used, for example, as described above (
22789Mf (15NH using z's IM Km
Continuously monitor 3. The transmission cavity type sensor shown in Fig. 3 is used in the measurement system shown in Fig. 6.
The dual modulation reflective cavity sensor shown in the figure can also be used. The sample separated into each component by the sample separation device 1 is sent to a reaction tube, which is a sample pretreatment device 10, filled with a N1 catalyst, where it undergoes hydrogenolysis while being mixed with hydrogen.
It becomes 5NH3. Here, the decomposed gas enters the two microwave gas sensors 60 and 915N and ``N'' (3) are detected respectively. At this time, the response delay due to the adsorption of ``NH'' and ``NH3'' into the system is prevented by mixing carriers. As mentioned above, the improvement can be made by The detection limit for a transmission cavity type microwave gas sensor is 0.08.
pg (8ha to 1), and the double modulation reflective cavity type has a detection sensitivity of about 10 ppb since the sensitivity is further improved by several tens of times. The internal volume of these microwave cavity sample cells is approximately 60 m1, and if the sample pressure is approximately 5 mmHg and the actual weight of N in the sample cell is calculated, the detection limit is 10 mmHg.
~10 g, making it an extremely sensitive analytical method.

[Brief explanation of drawings]

Figures 1(a) and 1(b) are diagrams showing the measurement characteristics of a conventional microwave gas sensor in the measurement of N horses.
The figure is a schematic diagram of an apparatus for implementing the method of the present invention, Figures 3 and 4 are diagrams showing an example of the configuration of a microwave gas sensor, and Figures 5 (a) and 5 (b) are Fig. 6 shows an example of measurement of 14N)I, ``Nl(,'' when a carrier is used.
The figure is a schematic diagram showing an example of a sensor for simultaneously measuring two isotopes. 1... Sample separation device 10... Sample pretreatment device 20
...-Sample introduction port 60...Microwave gas sensor 31...Cavity resonator 62...Microwave oscillation? )
;3...Power source 34...Modulator 65...Lock-in amplifier 36...Terminal member 67...Recorder 68...Detection diode 69...Microwave bridge 40...AFC41 ...Trigger circuit 46...Amplifier patent applicant @35 @Figure 5 (C1) 〈-brocade←eye procedure correction! (Voluntary) May 23, 1981 Kazuo Wakasugi, Director-General of the I-Revision Agency 1,, Il' 1 Indication 1981 Patent Application No. 140618 21. Title of the invention: Method for continuous measurement of stable isotopes using a microwave absorption type gas detection device 3゜Relationship with small r/I= Patent applicant 5, Contents of amendment (1) Specification No. 5 of the present application Correct "concentration" in line 9 to "change in degree". (2) "Isotope identification" on page 14, line 10 is corrected to "isotope identification." (3) Insert "21...Carrier gas 24 population" next to "20...Sample introduction port" on page 18, line 5. that's all

Claims (1)

[Claims] A sample separation device separates the sample, continuously converts each of the separated components including stable isotopes into a compound having a chemical form suitable for microwave spectroscopy, and converts the sample into a chemical form that is the same or similar to the above compound. characterized in that the compound is introduced into the microwave gas sensor and detected while continuously supplying a certain amount of the compound having the following properties and exceeding at least an adsorption equilibrium condition within the measurement system into the measurement system, Continuous measurement method for stable isotopes.