JPS6316705B2 - - Google Patents

Description

[Detailed description of the invention] The present invention is a pulsed nuclear magnetic resonance apparatus (NMR apparatus)
Regarding the nuclear magnetic resonance measurement method using a single high-frequency oscillation source, in particular, a nucleus that can perform the so-called homodecoupling method to obtain information on spin coupling with only a single high-frequency oscillation source and the so-called saturation method to saturate a specific spectral peak. Related to magnetic resonance measurement method.

In the homodecoupling method in NMR, a high frequency, for example ₁ , corresponding to the split spectral peak as shown in Figure 1a, generated by spin-spin coupling (homocoupling) between homogeneous nuclei, is used as the observational high frequency. is created using a separate oscillator and irradiated onto the sample. If you do this, the cut-off ring will be cut off (de-katsu ring).
Therefore, it is possible to transform the split peak into one sharp peak as shown in FIG. 1b.

Furthermore, for example, hydrogen nuclei (H
When observing H nuclei in water, as shown in Figure 2a, a spectral peak due to H nuclei contained in water appears with an extremely high intensity compared to the spectral peak of the sample to be observed. Since the dynamic range is limited by the high-intensity peak, the peak of the sample to be observed cannot be detected with high sensitivity. Therefore, in such cases, before irradiating the sample with observational high-frequency pulses, a saturation method is used in which a high-frequency wave with a frequency corresponding to the spectral peak due to H nuclei contained in water, for example ₂ , is irradiated to saturate the peak. . In this way, the high-intensity peak disappears due to saturation as shown in FIG. 2b, so that the peak of the sample to be observed can be detected with high sensitivity.

As mentioned above, when implementing the conventional homodecoupling method and saturation method, two oscillators are used: one for generating the high frequency for observation, and the other for generating the high frequency for homodecoupling or saturation. A equipped NMR device was required.

The present invention has been made in view of this point,
The object of the present invention is to provide a nuclear magnetic resonance measurement method that can perform both methods using an NMR apparatus equipped with a single oscillation frequency variable oscillator. The present invention will be explained in detail below using the drawings.

Figure 3 is a QD type NMR showing one embodiment of the present invention.
This is a configuration diagram of the apparatus, and in the figure, 1 is an NMR probe placed in a DC magnetic field. A high frequency generated from a single high frequency oscillator 2 is supplied to the NMR probe 1 via a gate circuit 3 and a drive circuit 4, but its level is switched by a switching circuit 5 and an attenuator 6 is inserted into the circuit. It can be changed in two stages by

A detection signal obtained from the NMR probe 1 due to high frequency irradiation is sent to two phase sensitive detectors (PSD) 8 and 9 via an amplifier 7. The PSD8,
9 is the same frequency as the high frequency irradiated to the sample.
Two high frequencies having a phase difference of 90° are supplied from the oscillator 2 as reference signals, and the PSD 8,
The two FID signals obtained from 9 are sent to A-D converter 1.
0,11 to the computer 12 for storage. The computer 12 performs Fourier transform based on the two FID signals to obtain an NMR spectrum. The obtained NMR spectrum is appropriately displayed on the display means 13. Incidentally, the computer 12 controls the gate circuit 3 and the switching circuit 5 according to a predetermined program.

In the above-described configuration, the case where the homodecoupling method is performed will first be described.

The operator first uses the usual measurement method to detect homocoupling, such as the one shown in Figure 1a.
Measure the NMR spectrum. That is, the frequency of the oscillator 2 is set to an appropriate value, for example ₀ , the switching circuit 5 is set to the _Q1 side, and the gate circuit 3 is set to the fourth
It is opened by a gate signal as shown in Figure a, and a high frequency pulse for observation of an appropriate width as shown in Figure 4b is applied to the sample. Then, detection is performed by the PSDs 8 and 9 for an appropriate period after the irradiation of the high-frequency pulse until the next irradiation. By performing Fourier transformation based on the obtained FID signal, an NMR spectrum as shown in FIG. 1a can be obtained.

Next, the operator determines the frequency corresponding to the spectral peak to be decoupled, for example ₁ in FIG. 1a, based on the obtained NMR spectrum. If you keep in mind that in a QD NMR device, NMR spectra are obtained on both sides (on the positive side and negative side) with the frequency ₀ of the observation high frequency irradiated on the sample as the center (OH ₂ ), it is easy to obtain ₁ . Can be done.

Then the operator sets the frequency of oscillator 2 _{to 1}
, and perform the measurement again. That is, gate circuit 3
is intermittently opened and closed during periods other than the observation high-frequency pulse irradiation period according to a gate signal as shown in FIG. 4c. Furthermore, since the switching circuit 5 is switched in accordance with the switching signal shown in FIG. 4f, the gate circuit 3
As shown in FIG. 4d, the high frequency supplied to the oscilloscope is at a high level during the observation high frequency pulse irradiation period, and at a low level suitable for homodecoupling during other periods. Therefore, the high frequency taken out from the gate circuit ₃ becomes as shown in FIG. The high frequency pulse P ₂ will be intermittently irradiated. Therefore, during that period, ₁ in Figure 1a
The bond corresponding to is cleaved, and the resulting NMR spectrum has one sharp peak, as shown in Figure 1b. However, strictly speaking, the spectrum obtained at this time is slightly different from that shown in FIG. 1b, and it goes without saying that the center frequency of the spectrum is ₁ .

Next, the case of implementing the saturation method will be described.

The operator first obtains an NMR spectrum as shown in FIG. 2a, in which a strong peak due to, for example, water contained in the sample appears, using a normal measurement method, just as in the homodecoupling method described above.

Then, frequency ₂ corresponding to the next strongest peak
Find , set the oscillator frequency to ₂ , and measure again. That is, the gate circuit 3 is opened and closed according to a gate signal as shown in FIG. 4g. Also, switching circuit 5
is switched in accordance with the switching signal shown in FIG. 4f, so the high frequency supplied to the gate circuit 3 is at a high level during the observation high frequency pulse irradiation period, as shown in FIG. 4d, and during other periods. is a level suitable for saturating strong peaks. Therefore, the high frequency wave taken out from the gate circuit 3 becomes as shown in Fig. 4h, and the high frequency pulse for observation is applied to the sample.
For a predetermined period before the irradiation of P ₁ , a low level saturation high frequency P ₃ is irradiated at the same frequency. In this way, measurement is performed by irradiating the observation high-frequency pulse after saturating the H nuclei contained in water with the saturation high-frequency wave, so the obtained NMR spectrum is as shown in Figure 2b. The strong peak disappears. However, strictly speaking, the spectrum obtained at this time is slightly different from that shown in FIG. 2b, and it goes without saying that the center frequency of the spectrum is ₂ .

As described in detail above, according to the present invention, a nuclear magnetic resonance measurement method is realized in which a homodecoupling method and a saturation method can be performed using an NMR apparatus equipped with a single oscillation frequency variable oscillator.

[Brief explanation of the drawing]

Figure 1 is a spectrum diagram for explaining the homodecoupling method, Figure 2 is a spectrum diagram for explaining the saturation method, and Figure 3 is a configuration diagram of a QD type NMR apparatus showing an embodiment of the present invention. , 4th
The figure is a waveform diagram for explaining the operation. 2: High frequency oscillator, 3: Gate circuit, 5: Switching circuit, 6: Attenuator, 8, 9: PSD, 1
2: Computer.

Claims (1)

[Claims] 1. A variable oscillation frequency oscillator, a gate circuit for extracting the high frequency generated from the oscillator in a pulsed manner and irradiating the sample as a high frequency pulse for observation;
and level changing means for reducing the level of high frequency waves generated from the oscillator, and configured to be able to irradiate the sample with the high frequency waves whose level has been reduced by the level changing means during a period other than the observation high frequency pulse irradiation period. A nuclear magnetic resonance measurement method using a nuclear magnetic resonance apparatus, which includes a first step of determining a frequency corresponding to a spectral peak to be decoupled, and setting the oscillation frequency of the oscillator to the frequency determined in the first step. In a second step, the high frequency wave generated from the oscillator is taken out in a pulsed manner through the gate circuit and irradiated onto the sample as a high frequency pulse for observation, and the high frequency wave whose level has been decreased by the level changing means is applied to the high frequency pulse. A nuclear magnetic resonance measurement method comprising: a third step of irradiating the sample as a decoupling high frequency wave during a period other than the irradiation period to perform nuclear magnetic resonance measurement.