JP5166711B2 - High resolution NMR probe - Google Patents

Description

  The present invention relates to a high-resolution NMR probe, and more particularly to a high-resolution NMR probe that can compensate for magnetic field distortion caused by a solvent in a sample tube.

  FIG. 1 shows a main part of a conventional NMR apparatus. In the measurement by the multiple resonance NMR apparatus 200, the sample tube 1 containing the sample 30 is set in the static magnetic field of the magnet 2 whose magnetic field distortion is corrected by the room temperature shim 3 controlled by the magnetic field correction apparatus 6. 30 is irradiated with an RF pulse having a frequency corresponding to the strength of the static magnetic field to cause an NMR phenomenon.

In that case, as the RF pulse, a pulse signal from the oscillator 14 is selected from a plurality of frequency bands (in the illustrated example, 3 bands; hereinafter, described as 3 bands) according to the nuclide to be observed in the sample 30. The multiple resonance NMR probe 4 is amplified by a power amplifier 13 corresponding to the frequency f ₁ , a power amplifier 15 corresponding to the frequency f ₂ , and a power amplifier 16 corresponding to the frequency f ₃ , and the duplexer 9 for switching input / output. , The sample 30 in the sample tube 1 is irradiated from the multiple resonance NMR probe 4.

  Then, because the sample 30 outputs an NMR signal having a resonance frequency specific to the nuclide due to the NMR phenomenon, the NMR signal is captured by the multiple resonance NMR probe 4.

  At that time, when it is necessary to measure the sample 30 at a predetermined temperature, the temperature around the sample tube 1 in the NMR probe 4 for multiple resonance is variably controlled by the temperature variable device 5 controlled by the computer 7. It has become.

  Then, the NMR signal captured by the multiple resonance NMR probe 4 is sent to the amplifier 10 via the duplexer 9 and amplified, and then converted to an audio frequency by the demodulation detector 11, and further, an A / D converter (ADC). 12 to convert to a digital signal.

  In this way, the digital signal is taken into the computer 7 and the computer 7 analyzes the signal, whereby the sample 30 is analyzed, the analysis result is displayed on the display 8, and the structure of the substance is examined by the multiple resonance NMR apparatus. It is done.

  FIG. 2 (A) shows a conventional high-resolution NMR sample tube used in combination with a high-resolution NMR probe. In the figure, 20 is a sample tube. The opening at the upper end of the sample tube 20 is covered with a cap 21 so that the sample does not leak outside. In addition, a rotor 22 is attached to the upper portion of the sample tube 20 in order to rotate the sample tube 20 during measurement of NMR. The rotor 22 receives the force of air blown from the stator 23 provided in the NMR probe, and rotates the sample tube 20 at a speed of several to several tens of Hz. The measurement sample 24 is disposed on the central axis of the sample coil 25 that generates a high-frequency magnetic field in a direction orthogonal to the static magnetic field direction.

  As shown in FIG. 2 (B), the high-resolution NMR sample tube is characterized by a glass containing a substance having substantially the same magnetic susceptibility as that of the sample 24 above and below the sample filling portion, for example, arsenic, bismuth, lead and the like. 26, thereby compensating for the static magnetic field distortion caused by the magnetic susceptibility caused by the magnetic susceptibility of the sample 24 being different from the surrounding magnetic susceptibility. By such a method, the static magnetic field distortion derived from the magnetic susceptibility of the sample 24 is relaxed, the decrease in measurement resolution caused by the non-uniform static magnetic field is avoided, and the high resolution state at the time of measurement is maintained. (Patent Document 3).

There are various methods for setting the glass that compensates for the static magnetic field distortion in the vicinity of the sample. Usually, as shown in FIG. 2C, the sample tube 20 is composed of the outer tube 27 and the inner tube. 2, a susceptibility compensation glass 26 is provided at the bottom of the outer tube 27, a susceptibility compensation glass 26 ^′ is provided at the tip of the inner tube 28, and the inner tube 28 is inserted into the outer tube 27 containing the sample. The sample 24 is sandwiched between the glasses 26 and 26 ^' as shown in FIG.

JP-A 63-128244 Japanese Unexamined Patent Publication No. 63-228051 Japanese Unexamined Patent Publication No. 1-227051 Japanese Patent Laid-Open No. 1-227052 JP-A-7-84023

  The problem with such a high resolution NMR sample tube is that it is difficult to prepare a good quality susceptibility compensation glass. Normally, heavy metals such as arsenic, bismuth, and lead are mixed in molten glass, and a mass with the desired magnetic susceptibility is made while stirring well. Then, a part of the formed mass is taken to inspect the magnetic susceptibility, and a magnetic susceptibility compensation glass tube is made from a small piece near the target magnetic susceptibility.

  Since the metal particles are dispersed in the amorphous material by such a method, the metal particles are hardly mixed uniformly, and even if they are mixed, the metal particles are likely to be localized due to aging. For this reason, even if the basic magnetic susceptibility control is performed in bulk, the magnetic susceptibility of copper can only be driven to several tens to several tens of percent. From the reality that the level of susceptibility control around the sample coil and its surroundings realized by recent NMR detectors has reached almost zero susceptibility from several percent of the susceptibility of copper, the level of susceptibility compensation glass Is at an inferior level. Therefore, such a magnetic susceptibility compensation glass can only be used for measurement of a sample system having a wide line width.

  In addition, the distribution of metal particles in the glass tends to show a sparse and dense uneven distribution state. As a result, a local magnetic susceptibility abnormality occurs, and a magnetic field correction by shims may not be effective.

  Moreover, when inspecting as a product, there is only a method of inspecting using an NMR apparatus. For this reason, it takes time and cost.

  Further, in such a high-resolution NMR sample tube, bubbles are likely to be generated in the sample, and the generated bubbles may cause new susceptibility distortion.

  Furthermore, it cannot be said that the use of toxic heavy metals such as arsenic, bismuth, and lead is a globally friendly technology recommended recently.

  An object of the present invention is to provide a high-resolution NMR probe capable of performing high-resolution measurement without relying on a conventional high-resolution NMR sample tube in view of the above points.

In order to achieve this object, a high-resolution NMR probe according to the present invention comprises:
In a high-resolution NMR probe that is arranged and used in a static magnetic field and has a sample coil in which a sample tube is inserted from above and generates a high-frequency magnetic field in a direction orthogonal to the static magnetic field direction,
A susceptibility compensation stick having a compensation member made of a substance having substantially the same magnetic susceptibility as the sample is held at the tip, and the compensation member at the tip is disposed close to the bottom of the sample tube inserted into the sample coil. An introduction mechanism that replaceably introduces the magnetic susceptibility compensation stick into the high resolution NMR probe from below the sample coil. The introduction mechanism causes the magnetic susceptibility compensation stick to enter the high resolution NMR probe. When introduced, the compensation member is arranged on an extension line of the axis of the sample tube .

  The compensation member is used in a pair with another compensation member having the same magnetic susceptibility arranged in the sample tube.

  Further, the compensation member is a resin molded body having substantially the same magnetic susceptibility as the sample solvent or a container in which a solvent having substantially the same magnetic susceptibility as the sample solvent is enclosed.

Further, the compensation member is configured to be removable from the magnetic susceptibility compensation stick and exchanged in accordance with the type of the sample solvent in the sample tube.

  Further, the compensation member is shielded from a high frequency used in NMR measurement by an electromagnetic field shield.

Further, the length of the compensation member in the sample tube axial direction is at least one time longer than the effective measurement length of the sample coil, including the two compensation members placed above and below the sample. It is a feature.

Also, sample tube axial length of the compensation member, the effective measuring length of the sample coil relative to its 1 together two compensating member placed above and below the sample. It is characterized by a length of 6 times or more.

  In addition, the length of the compensation member in the sample tube axial direction is at least 0.5 times the length of the compensation member placed below the sample tube with respect to the effective measurement length of the sample coil. It is a feature.

  Further, the length of the compensation member in the sample tube axial direction is 0.8 times or more of the compensation member placed below the sample tube with respect to the effective measurement length of the sample coil. It is said.

According to the high resolution NMR probe of the present invention,
In a high-resolution NMR probe that is arranged and used in a static magnetic field and has a sample coil in which a sample tube is inserted from above and generates a high-frequency magnetic field in a direction orthogonal to the static magnetic field direction,
A susceptibility compensation stick having a compensation member made of a substance having substantially the same magnetic susceptibility as the sample is held at the tip, and the compensation member at the tip is disposed close to the bottom of the sample tube inserted into the sample coil. An introduction mechanism that replaceably introduces the magnetic susceptibility compensation stick into the high resolution NMR probe from below the sample coil. The introduction mechanism causes the magnetic susceptibility compensation stick to enter the high resolution NMR probe. When introduced, because the compensation member is arranged on the extension line of the axis of the sample tube ,
It has become possible to provide a high-resolution NMR probe that can perform high-resolution measurements without relying on conventional high-resolution NMR sample tubes.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a conceptual diagram of a high resolution NMR probe according to the present invention. In the present invention, a cylindrical container filled with the same solvent as the solvent in which the sample in the NMR sample tube is dissolved, and having the same thickness as the NMR sample tube, Attach to. At that time, the NMR sample tube side may have a flat bottom or a round one as shown in FIG.

  FIG. 5 is a schematic diagram of the simplest tuning circuit on the NMR probe side. In the tuning circuit of the NMR probe, a high frequency pulse input from an RF terminal is tuned and matched by a matching capacitor C1 and a tuning capacitor C2 and applied to a sample coil. A high frequency magnetic field generated in the sample coil induces an NMR phenomenon in the sample. An NMR signal generated from the sample is detected by a sample coil and taken out from the RF terminal.

  FIG. 6 shows the structure on the NMR probe side when operating the present invention. In the present invention, the sample coil is connected to a lead wire (the ground potential side is called a cold lead and the non-ground side is called a hot lead) at a position corresponding to a predetermined node, and is connected to a tuning circuit.

  FIG. 7 to FIG. 10 explain this principle by enlarging this part. In the present invention, a cylindrical container filled with the same solvent as the solvent in which the sample in the NMR sample tube is dissolved, and having the same thickness as the NMR sample tube, As already described above, this will be referred to as a resolution compensation stick. In place of a cylindrical container containing the same solvent as the solvent in which the sample in the NMR sample tube is dissolved, a cylindrical resin molded body made of a resin having substantially the same magnetic susceptibility as the sample solvent can be substituted. Also good.

  As shown in FIG. 7, the resolution compensation stick is fixed in such a manner that it is inserted into a hole formed in the bottom of the body side base flange of the NMR probe. In order to facilitate the fixation of the resolution compensation stick, as shown in FIG. 8, the cell unit filled with the solvent is fixed with a male screw around the periphery by fastening with a cell fixing pin (screw), pressure contact, ratchet mechanism, or the like. It is attached to the upper end of the cut holder. The male screw on the holder side is screwed into the female screw carved in the hole formed in the bottom of the body side base flange of the NMR probe, so that the resolution compensation stick is arranged and fixed in the immediate vicinity of the NMR sample tube. A stopper provided on the screw portion is used for positioning the resolution compensation stick.

The guide tube for guiding the cell unit is made of a diamagnetic material (copper, brass, glass, resin, ceramic), a paramagnetic material (aluminum, ceramic, resin), or a combination thereof, as shown in FIG. Yes. When made of a material other than metal, the guide tube is surrounded by an electromagnetic field shield. For the electromagnetic field shield, a metal film having a thickness of about 23 times the skin depth at the RF frequency used in NMR measurement is employed. As a result, an attenuation effect of 100 dB or more can be obtained with respect to the high frequency that is about to enter the cell unit. For example, if the high frequency of 400 MHz used in ¹ H-NMR measurement is used, the skin depth is 4 μm as shown in FIG. 10 when aluminum is used as the material for the electromagnetic field shield, so the thickness of the electromagnetic field shield is about 92 μm. It is good to set to. By shielding the high frequency, the background signal of NMR derived from the cell unit can be prevented.

  As shown in FIG. 9, the electromagnetic field shield may cover only the outer surface of the guide tube, or may cover both the outer surface and the inner surface of the guide tube. Since it is desirable that the electromagnetic field shield does not cause static magnetic field distortion, a non-magnetic metal film with zero magnetic susceptibility, in which multiple layers of paramagnetic or diamagnetic metals such as copper, gold, platinum, palladium, etc. are stacked in addition to aluminum. Etc. can also be used. The high-frequency current flowing on the surface of the metal film due to the skin effect may be consumed internally as thermal energy by electrical resistance, or may be grounded to the ground of the NMR probe body and released to the ground.

  FIG. 11 shows a cell unit lineup. Since the role of the cell unit is to compensate for the static magnetic field distortion derived from the magnetic susceptibility of the NMR sample, the solvent has almost the same magnetic susceptibility as the solvent dissolving the NMR sample, preferably dissolving the NMR sample. It is desirable to enclose the same solvent as the solvent. As a solvent for dissolving the NMR sample, a deuterium substituted solvent such as deuterated chloroform, deuterated acetone, deuterated benzene and deuterated water is used. However, deuterium substitution is not necessarily required for susceptibility compensation. Therefore, the cell unit for heavy chloroform solution sample is filled with ordinary chloroform, the cell unit for heavy acetone solution sample is filled with ordinary acetone, the cell unit for heavy benzene solution sample is filled with ordinary benzene, The cell unit for the heavy aqueous solution sample is filled with ordinary distilled water to reduce the cost. Of course, if it is not necessary to consider the cost, the heavy solvent itself may be used. Since the cell unit is shielded from the high frequency by the electromagnetic field shield stretched on the guide tube, there is no fear of generating an NMR background signal. These cell units may be exchanged according to the heavy solvent in which the NMR sample is dissolved and used properly.

  The cell unit group may be prepared as a disk unit outside the probe main body or the probe, and may be configured to be exchanged automatically or by remote control operation by a cell selection mechanism.

  It has already been described that the cell unit can be replaced with a resin molded body made of a resin having substantially the same magnetic susceptibility as the solvent, instead of the container in which the solvent is sealed. In terms of cost, the resin molded body is lower in cost and has higher mechanical strength.

  The present invention can be modified. FIG. 12 shows an example in which the cell unit is provided not only below the NMR observation region but also above the NMR observation region. When cell units are placed above and below the NMR observation region, it is desirable that their shapes be vertically symmetric. When the cell unit is provided in the NMR sample tube, as shown in FIG. 13, the NMR sample tube has a double structure, a resolution compensation solvent is introduced from the opening of the inner tube, and the measurement sample is placed in the gap between the inner tube and the outer tube. Put in. And the cell unit of an inner tube is arrange | positioned so that the liquid level of a measurement sample may be contact | connected.

  In addition to the flat bottom shape, the bottom shape of the NMR sample tube may be round bottom. In the case of a round bottom, as shown in FIG. 14, it is desirable that the guide tube constituting the resolution compensation stick and the surface of the cell unit facing the NMR sample tube be formed into a spherical recess.

  The relationship between the NMR effective sample length b (≈sample coil length a), the length c of the lower cell unit in the sample tube axis direction, and the length d of the upper cell unit in the sample tube axis direction is as follows.

c + b + d ≧ 2.6 × b or c + a + d ≧ 2.6 × a
For example, in an experiment using a 5 mmφ NMR sample tube, if the coil length a = 15 mm, a homogeneous near magnetic field space that is almost theoretically obtained can be obtained if there is approximately 39 to 40 mm or more of homogeneous sample filling in the axial direction. I know. In other words, when the axial length filled with the sample is a finite value, magnetic field distortion is caused by the sample itself, so in order to perform measurement in the region with the highest magnetic field uniformity (= the region with the best resolution) It can be said that the amount of the sample liquid is 2.6 times or more the detection area (= coil length). However, at the expense of some resolution, even if it is about twice the detection area (= coil length), it is within a practical range. In that case,
c + b + d ≧ 2 × b or c + a + d ≧ 2 × a
It is sufficient to satisfy the relational expression. Since it is desirable that the lengths of c and d are substantially the same length,
c≈d ≧ 0.5b to 0.8b or c≈d ≧ 0.5a to 0.8a
It turns out that. In a specific numerical model, when a = 15 mm and b = 15 mm, c = 7.5 to 12 mm and d = 7.5 to 12 mm.

  If there is only the lower cell unit and there is no upper cell unit, the shortage corresponding to the length d of the upper cell unit may be compensated by increasing the sample solution in the NMR sample tube.

  According to the present invention, the sensitivity increase is about 3 times that when no compensation of magnetic field distortion is performed, and about 1.6 times that when magnetic field distortion is compensated by a conventional glass high-resolution NMR sample tube. confirmed.

  Also, assuming that the sensitivity when the cell units are arranged at the top and bottom is 100 (maximum sensitivity), the sensitivity is about 75% when only the lower cell unit is arranged, and about 34% when the cell unit is not arranged above and below. became.

  Can be widely used for NMR probes.

It is a figure which shows the conventional multiple resonance NMR apparatus. It is a figure which shows the conventional conventional high-resolution NMR sample tube. It is a conceptual diagram of the high resolution NMR probe concerning this invention. It is a figure which shows the example of the NMR sample tube used for this invention. It is a figure which shows an example of the tuning circuit of a NMR probe. It is a figure which shows one Example of the structure of the high resolution NMR probe concerning this invention. It is a figure which shows one Example of how to attach the stick for resolution compensation concerning this invention. It is a figure which shows one Example of how to attach the stick for resolution compensation concerning this invention. It is a figure which shows one Example of the guide tube concerning this invention. It is a figure which shows the skin thickness and electromagnetic shielding effect of a high frequency. It is a figure which shows the lineup of the cell unit concerning this invention. It is a figure which shows another Example of the stick for resolution compensation concerning this invention. It is a figure which shows the example of the NMR sample tube used for this invention. It is a figure which shows another Example of the stick for resolution compensation concerning this invention.

Explanation of symbols

1: Sample tube, 2: Magnet, 3: Room temperature shim, 4: NMR probe, 5: Temperature variable device, 6: Magnetic field correction device, 7: Computer, 8: Display, 9: Duplexer, 10: Amplifier, 11: Demodulator, 12: ADC, 13: power amplifier, 14: oscillator, 15: power amplifier, 16: power amplifier, 21: cap, 22: rotor, 23: stator, 24: sample, 25: sample coil, 26: Magnetic susceptibility compensation glass, 26 ^' : Magnetic susceptibility compensation glass, 27: Sample tube outer tube, 28: Sample tube inner tube, 30: Sample, 200: Multiple resonance NMR apparatus

Claims (9)

In a high-resolution NMR probe equipped with a sample coil that is used in a static magnetic field and generates a high-frequency magnetic field in a direction orthogonal to the static magnetic field direction inside,
A compensation member made of a material having substantially the same magnetic susceptibility as the sample is attached to the bottom of the high-resolution NMR probe so as to be close to the lower side of the sample tube inserted into the sample coil, and the compensation member in the sample tube is attached by the compensation member. A high-resolution NMR probe that compensates for static magnetic field distortion generated by a sample. The high-resolution NMR probe according to claim 1, wherein the compensation member is used in a pair with another compensation member having an equivalent magnetic susceptibility arranged in a sample tube. 3. The high resolution according to claim 1, wherein the compensation member is a resin molded body having substantially the same magnetic susceptibility as the sample solvent or a container in which a solvent having substantially the same magnetic susceptibility as the sample solvent is enclosed. NMR probe. The high-resolution NMR probe according to any one of claims 1 to 3, wherein the compensation member is configured to be exchanged according to a type of a sample solvent in the sample tube. 5. The high-resolution NMR probe according to claim 1, wherein the compensation member is shielded from a high frequency used in NMR measurement by an electromagnetic field shield. The length of the compensation member in the direction of the sample tube axis is at least one time longer than the effective compensation length of the sample coil, including the two compensation members placed above and below the sample. The high-resolution NMR probe according to any one of claims 2 to 5. Sample tube axial length of the compensation member, the effective measuring length of the sample coil relative to its 1 together two compensating member placed above and below the sample. The high-resolution NMR probe according to claim 6, wherein the length is 6 times or more. The length of the compensation member in the sample tube axis direction is at least 0.5 times the length of the compensation member placed below the sample tube with respect to the effective measurement length of the sample coil. The high-resolution NMR probe according to any one of claims 1 to 7. The length of the compensation member in the sample tube axial direction is 0.8 times or more of the compensation member placed below the sample tube with respect to the effective measurement length of the sample coil. The high resolution NMR probe according to claim 8.

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