JPH034113B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a nuclear magnetic resonance apparatus (NMR apparatus), and in particular to an NMR apparatus that can remove spinning side bands caused by rotation axis deviation of a sample tube, etc.
Regarding equipment.

[Prior Art] In a high-resolution NMR apparatus, a sample (sample tube) is rotated in a static magnetic field to average out the non-uniformity of the static magnetic field. However, in the case described below, modulation is added to the NMR signal, so
Peaks called spinning sidebands occur at positions separated by an integral multiple of the rotational frequency of the sample from each peak on the NMR spectrum, which is extremely inconvenient for spectrum analysis.

a When an excessive amount of inhomogeneous components of the static magnetic field asymmetrical with respect to the rotation axis of the sample remain b High-frequency magnetic field (pulse) irradiated during measurement
When the intensity of is spatially non-uniform c When the axis of rotation of the sample tube does not coincide with the center of the sample due to poor precision of the sample tube Among these, spinning sidebands caused by a and b occur during the use stage of the device. Although it can be removed by adjustment, those caused by c cannot be removed by electromagnetic adjustment, and the only way to deal with it is to improve the precision in manufacturing the device and the precision of the sample tubes used.

[Object of the invention] The present invention has been made in view of this point,
It is an object of the present invention to provide a nuclear magnetic resonance apparatus that can effectively remove spinning sidebands caused by the above c.

[Structure of the Invention] The present invention is a nuclear magnetism system in which a high-frequency pulse is irradiated to a sample while rotating a sample tube containing the sample in a DC magnetic field, and a free induction decay signal from the sample is detected after irradiation. The resonance device is provided with a means for detecting the rotational position of the sample tube and a means for integrating the free induction attenuation signal, and based on the detection signal from the detection means, the timing at which a specific part of the sample tube is at a specific position, and the corresponding The high-frequency pulse irradiation is performed at two timings when the specific region is at a position half a rotation away from the specified location, and the two types of free induction attenuation signals obtained by the high-frequency pulse irradiation at the two timings are collected by the integrating means. The feature is that it is integrated by . Hereinafter, the present invention will be explained in detail using the drawings.

[Explanation of the principle of the invention] First, the basic idea of the invention will be explained using FIG. In the figure, 1 is a sample tube containing a sample 2, and 3 is a saddle-shaped detection coil. If the rotation center O of the sample tube 1 is shifted from the sample center O',
As can be seen from the fact that the sample tube comes to the position shown by the broken line after half a rotation, the distance between the sample and the coil changes, and the detection coil 3 receives signals from the sample 2.
The NMR signal undergoes amplitude modulation synchronized with rotation.
Furthermore, in such a case, if the dielectric constant of the sample is large, the movement of the sample within the coil 3 will lead to a change in the stray capacitance of the coil 3. Since the coil 3 constitutes a part of the high-frequency tuning circuit for reception, its tuning frequency shifts in synchronization with the rotation of the sample, and the NMR signal extracted from the detection coil undergoes the above-mentioned amplitude modulation. In addition, it also receives phase modulation synchronized with rotation. Spinning sidebands are generated by the modulation received in this way.

Here, the rotation of the sample tube is represented by a sine wave S1 corresponding to the rotation angle of a specific part A of the sample tube as shown in Fig. 2a, and for ease of understanding, the amplitude modulation is shown in Fig. 2b. It is assumed that the processing is performed using a sine waveform S2 synchronized with the above. Now, we will conduct two observation sequences of around 1 second each, consisting of irradiation with high-frequency pulse P1 and subsequent sampling of free induction decay (FID) signals, as shown in Figure 3.
As shown in Figure c, the first observation was made at time T0, that is, when the rotation angle of the sample tube was 0° (the timing indicated by the solid line in Figure 1), when the high-frequency pulse P
The next observation was performed by irradiating high-frequency pulse P at time T1, that is, when the rotation angle of the sample tube was 180° (the timing indicated by the broken line in Figure 1).
Let us consider the FID signals obtained in each observation when irradiating 1.

The correct FID signal without amplitude modulation is shown in Figure 4a.
If the FID signal is in the form of , the FID signal obtained in the first observation starting from time T0 is subjected to amplitude modulation by the sine waveform shown in FIG. 2b, and is obtained as shown in FIG. 4b, for example.

Obtained in the second observation starting from time T1
The FID signal is obtained, for example, as shown in FIG. 4c.

Now, when comparing these two FID signals, the timing of the start of observation for both is determined by the rotation angle of the sample tube.
Since they are in an anti-phase relationship at 0° and 180°, the amplitude modulations received by the two FID signals are also in an anti-phase relationship. Therefore, by adding these two signals, their modulations cancel each other out, and as a result, it is possible to obtain the FID signal shown in FIG. 4a, which is not modulated. In this way, by performing observations at the timing of the sample tube rotation angle of 0° and 180° and adding them together, the first-order spinning sideband can be removed, but by adding the timings of 90° and 270°, the four types of If you add the FID signals,
Secondary spinning sidebands can be removed. It goes without saying that even higher-order spinning sidebands can be removed by adding FID signals obtained by observing at 30° intervals. Although only amplitude modulation has been discussed above for ease of understanding, it goes without saying that phase modulation can also be removed at the same time.

[Embodiment] FIG. 5 is a block diagram showing the configuration of an embodiment of the present invention based on the above-mentioned basic idea. In the figure, 4 is a magnet that generates a DC magnetic field, and an NMR probe 5 is placed inside the magnet 4. The NMR
A sample tube rotation mechanism 8 for rotating the sample tube 7 by blowing pressurized air from the compressor 6 and a rotation angle detection mechanism built into the rotation mechanism are attached to the upper part of the probe 5. Reference numeral 9 denotes a high-frequency oscillator, and the high-frequency wave having the resonant frequency of the observation nucleus generated from the oscillator is transmitted as a high-frequency pulse through a gate 11 controlled by an observation control circuit 10.
It is sent to the NMR probe and irradiated onto the sample via the irradiation coil. The FID signal generated from the sample in conjunction with the high-frequency pulse irradiation is detected by a detection coil in the NMR probe, and is sent to the demodulation circuit 12 and A- controlled by the observation control circuit 10.
It is sent to the data processing device 14 via the D converter 13. 15 is a recorder for recording the NMR spectrum obtained by Fourier transform processing by the data processing device.

FIG. 6 is a diagram for explaining the structure of the rotation angle detection mechanism incorporated in the sample rotation mechanism 8. In the figure, reference numeral 16 denotes a rotor attached to the upper part of the sample tube 7, and on its outer periphery, twelve markers 17 made of light reflectors or light absorbers are attached at intervals of, for example, 30 degrees. 18 is a light emitting element that generates a light spot projected onto the marker 17, and 19 is a photodetector for detecting a change in the amount of light that occurs when the marker passes the light spot position. The detection signal obtained from the photodetector 19 is sent to the observation control circuit 10 via a waveform shaping circuit 20.

In the above-described configuration, the amount of light incident on the photodetector 19 changes each time the marker 17 passes through the light spot, so the waveform shaping circuit 20 detects the sample tube 7 as shown in FIG. 7a. One clock pulse is obtained every time the sample tube rotates by 30 degrees, and the rotation angle of the sample tube 7 can be detected in units of 30 degrees.

The observation control circuit 10 starts the first observation by applying a high frequency pulse P1 as shown in FIG. 7B at the timing when the clock pulse CP1 is generated, that is, at the timing when the rotation angle is 0°.
The FID signal (0°) obtained through this observation is stored in the memory 14M within the data processing device 14.

Next, the observation control circuit 10 starts the second observation by irradiating the high frequency pulse P1 at the timing when the clock pulse CP2 is generated, that is, at the rotation angle of 30 degrees, as shown in FIG. 7B. FID signal F obtained from this observation
(30°) is added to F(0°) obtained in the first observation in the memory 14M.

The third observation was made at a rotation angle of 60 degrees, the fourth observation was made at a rotation angle of 90 degrees, and the fifth observation was made at a rotation angle of 120 degrees.
..., the 12th observation was started at a timing of 330°, and the FID signal F (60°) obtained in each observation was
F (90°), F (120°), ..., F (330°) are memory 1
4
It is integrated within M. As a result, the composite stored in memory 14M at the end of the 12th observation
The FID signal is F (0°) + F (30°) + F (60°) + F (90
゜)＋
…+F(300°)+F(330°). As explained above, F (0°) and F (180°), F (30°) and F
(210°), F (60°) and F (240°), F (90°) and F
(270°), F (120°) and F (300°), F (150°) and F
(330°) removes undesirable modulations that are in an anti-phase relationship with each other, so the resulting composite FID signal has undesirable modulations removed to a high order, and the S/N ratio improves by integration. The NMR spectrum obtained by Fourier transforming the spectrum has spinning sidebands removed to a high order and has an improved signal-to-noise ratio.

In the above-described embodiment, the 12th measurement was performed, but it goes without saying that only the second measurement is sufficient if only the primary sideband is to be removed.

Furthermore, in the above-mentioned embodiment, the timing was shifted sequentially from 0° → 30° → 60° →..., but the results do not change no matter what order the observations are made.

[Brief explanation of drawings]

Figure 1 is a diagram showing the rotational deviation of the sample tube, Figures 2 and 4 are waveform diagrams to explain the idea of the present invention, Figure 3 is a diagram to explain the sequence, and Figure 5 is a diagram of the present invention. FIG. 6 is a block diagram showing the configuration of an embodiment of the invention, FIG. 6 is a diagram for explaining the structure of the rotation angle detection mechanism, and FIG. 7 is a diagram for explaining its operation. 4: Magnet, 5: NMR probe, 7: Sample tube,
8: Sample tube rotation mechanism, 9: High frequency oscillator, 10:
observation control circuit, 11: gate, 13: A-D converter, 14: data processing device, 16: rotor, 1
7: marker, 18: light emitting element, 19: photodetector,
20: Waveform shaping circuit.

Claims (1)

[Claims] 1. In a nuclear magnetic resonance apparatus, a sample tube containing a sample is rotated in a DC magnetic field and a high-frequency pulse is irradiated to the sample, and a free induction decay signal from the sample is detected after irradiation. A means for detecting a rotational position and a means for integrating a free induction attenuation signal are provided, and based on the detection signal from the detection means, the timing at which a specific part of the sample tube is at a specific position and the timing at which the specific part has rotated half a rotation from then are determined. The high-frequency pulse irradiation is performed at two different timings, and the integrating means integrates two types of free induction attenuation signals obtained by the high-frequency pulse irradiation at the two timings. A nuclear magnetic resonance device featuring: