EP2791693A1

EP2791693A1 - Nmr method and device with magic-angle spinning at a very low temperature

Info

Publication number: EP2791693A1
Application number: EP12806404.5A
Authority: EP
Inventors: Eric BOULEAU; Gaël DE PAËPE
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2011-12-13
Filing date: 2012-12-11
Publication date: 2014-10-22
Also published as: US20150177341A1; FR2983959B1; WO2013087626A1; FR2983959A1; US9995802B2

Abstract

The invention relates to a method for the NMR analysis of a solid sample arranged in a sample holder (21), characterized in that it includes the following steps: generating a plurality of high-pressure gas streams (2, 3, 4) from at least a first high-pressure gas source (1); cooling the gas streams (2, 3, 4) in at least one heat exchanger (12) using cooling gas from a second gas source (11); spinning the sample holder (21) using a first high-pressure cooled gas stream (2) and cooling the sample holder (21) using a second high-pressure cooled gas stream (3).

Description

METHOD AND NMR DEVICE WITH ROTATION AT MAGIC ANGLE A

VERY LOW TEMPERATURE

The invention relates to a method and a device for nuclear magnetic resonance (NMR), particularly suitable for the analysis of a sample in the solid state.

An NMR device comprises a sample holder rotated in a static magnetic field and exposed to a second magnetic field perpendicular to the first and created by a radio frequency coil, which receives back a signal which is analyzed to derive information on a solid sample placed in the sample holder. According to an embodiment of the state of the art, three gaseous streams coming from the same source, a standard container such as a helium bottle mounted under pressure, are directed towards the probe of the device which comprises the sample holder. The first flow has the function of rotating this sample holder, by acting on the blades or vanes of a turbine driving a rotor which comprises the sample holder. The second flow has the function of bringing the sample to a certain temperature, and the third flow creates an aerostatic bearing of lift of the rotor in the stator.

The search for the best performance of solid state sample analysis by NMR uses a rotation of the sample along a particular axis called the "magic angle". It is important to achieve a high speed of rotation. On the other hand, the increase in the intensity of magnetic fields, which currently reaches about 20 Tesla, has improved the sensitivity of NMR detection. However, it is very difficult today to increase this intensity. Existing solutions remain imperfect and insufficient and there is therefore a general need for improved detection and NMR analysis of a solid sample. More specifically, a first object of the invention is to allow the resolution and the sensitivity of the detection by NMR to be increased.

A second object of the invention is to implement NMR analysis at the lowest cost.

A third object of the invention is an NMR solution that ensures the safety of the responders and which respects the environment. For this purpose, the invention is based on a method of NMR analysis of a solid sample placed in a sample holder, characterized in that it comprises the following steps:

generating a plurality of high pressure gas streams from at least a first source of a high pressure gas;

cooling the gas flows in at least one heat exchanger from the circulation of a refrigerant fluid from at least a second source;

- Rotating the sample holder by a first cooled high pressure gas stream and cooling the sample holder by a second cooled high pressure gas stream.

The NMR analysis method may comprise a step of adjusting the speed of rotation of the sample holder by varying the pressure and / or the flow rate of the at least one first source of high pressure gas. The first high pressure gas stream may cause the sample holder to rotate by its action on fins or blades of a device connected to the sample holder to cause its rotation. The first high pressure gas stream can reach a flow rate so as to cause the sample carrier to rotate at a rotation frequency of 20 KHz or greater, or greater than or equal to 30 KHz.

The NMR analysis method may include a step of controlling the temperature of the high pressure gas stream by varying the pressure and / or the flow rate of at least a second source of refrigerant gas.

The temperature of the high pressure gas stream arriving at the probe comprising the sample holder can be regulated at a temperature of less than or equal to 10K.

The temperature of the high pressure gas stream arriving at the probe comprising the sample holder can be adjustable in a range from 4.2 to 300 K inclusive.

The first high pressure gas stream for rotating the sample holder and the second high pressure gas stream for cooling the sample holder can have temperatures substantially equal to the level of the probe comprising the sample holder.

The NMR analysis method can generate a third gas stream from the first source of a high pressure gas for sustentation of the sample holder. The NMR analysis method may comprise a step of setting temperature and rotation speed instructions of the sample holder, and may comprise a step of regulating the temperature and the flow rate of the high pressure gas flows at these instructions by modifying the pressure and / or the flow rate of the two gas sources.

The invention also relates to a computer program comprising a code means adapted to performing the steps of an NMR analysis method as described above when the computer program is executed on a computer.

The invention also relates to an NMR analysis device, comprising a sample holder, capable of receiving a solid sample to be analyzed, and at least a first source of a high-pressure gas for generating gas flows intended to rotating and cooling the sample holder, characterized in that it comprises at least a second source of a refrigerant gas for cooling the high pressure gas streams from the at least one first source in at least one circulating heat exchanger refrigerant.

The NMR analysis device may comprise a central unit which implements an NMR analysis method as described above. The at least one exchanger may be a countercurrent exchanger between the high pressure gas stream and the at least one refrigerant gas.

The NMR analysis device may comprise at least one countercurrent fluid / fluid exchanger comprising tubes for the circulation of high pressure gas stream inserted in a tube in which a refrigerant gas is circulated.

The NMR analysis device may comprise at least one exchanger for heating the temperature of the gases leaving the device and / or may comprise a gas recovery device leaving the device.

The at least one first source of a high pressure gas and / or the second source of a refrigerant gas may be a helium or nitrogen cylinder.

These objects, features and advantages of the present invention will be set forth in detail in the following description of a particular embodiment made in a non-limiting manner in relation to the appended figures among which:

Figure 1 shows schematically an NMR device according to one embodiment of the invention. Figure 2 schematically shows a section of an exchanger of the embodiment of the invention.

FIG. 3 is a diagrammatic side view of the heat exchanges within an exchanger of the embodiment of the invention.

FIG. 4 schematically represents an NMR device according to a variant of the embodiment of the invention.

Figure 5 schematically shows a side view of an NMR device according to the embodiment of the invention. According to the approach adopted, the embodiment of the invention proposes to carry out the NMR detection from a temperature which can go down very low, up to about 5 K, for example, to reach a high sensitivity. The attainment of a very low temperature requires the cooling of the sample but also the compensation of unavoidable heat input at the probe because of the friction caused by the very fast rotation of the sample holder. Indeed, it is also expected to achieve high rotation speeds of the sample to be analyzed, of the order of 30 kHz for example.

Figure 1 shows the architecture of an NMR device according to one embodiment. This device comprises at least a first high-pressure source 1 for generating three distinct high-pressure gas streams 2, 3, 4. In a variant, it is of course possible to use several sources each dedicated to one or more streams. This source 1 may for example consist of a bottle of compressed gas at 200 bar and at room temperature. Its pressure is controlled by flowmeters coupled to control valves. The high pressure gas of this first source 1 may be nitrogen or helium. The three gas streams from this first source 1 pass through a cryostat 10, in which they are cooled in one or more heat exchangers 12, before reaching the NMR probe 20 comprising the sample holder 21. The latter is positioned inclined with an adjustable angle between the parallel and perpendicular axes of the static magnetic field. The radiofrequency components forming a transmitter / receiver, designed to receive a signal coming from the sample to be analyzed, are also exposed to the cooling gas flow and subjected to the same temperature as the sample holder 21. In order to be able to reach very low temperatures, the heat exchangers 12 are supplied with a low-pressure cryogenic fluid, at a low temperature below the temperature of the gas of the first source 1, which serves as a refrigerant 15, originating from one or more second (s) source (s) 1 1, distinct (s) of the first source 1 high pressure. This cooling fluid can also be nitrogen or helium.

Figures 2 and 3 show more particularly a heat exchanger 12 of the cryostat 10 according to the embodiment of the invention. It comprises three high-pressure tubes 14 for the circulation in a first direction of respectively the three high-pressure gas streams 2, 3, 4. These three tubes are positioned inside a larger low pressure tube 13 in which the refrigerant gas 15 circulates in a second reverse direction. The tubes are formed in a material suitable for cryogenics, for example in a so-called low carbon austenitic stainless steel grade. Thus, the heat exchanger 12 is of the fluid / tubular fluid type against the current. It allows a transfer of heat between the two fluids, inducing a cooling of the gas streams 2, 3, 4 high pressure. This heat exchange between the two fluids is obtained by forced convection between the gas streams 2, 3, 4 and the wall of their respective high-pressure tubes 14, then by conduction through this wall, before a new forced convection between the outer surface. of this wall of the high pressure tubes 14 and the refrigerant 15. The symmetrical distribution of the three high pressure tubes 14 within the refrigerant flow ensures the same outlet temperature for the three gas streams 2, 3, 4. At their ends, the tubes of this exchanger 12 may be equipped with a bellows, to facilitate their connections with the tubes of another exchanger or with tubes out of the cryostat. These bellows also allow adaptation to variations in dimensions components of the device, such as tubes, because of significant temperature variations. The assembly is further coiled to reduce the overall size of the exchanger 12. One or more exchangers 12, identical or not, can be arranged in series in the cryostat, in a modular manner, to allow the addition and removal easy to modules, according to the needs. In the embodiment shown, two exchangers 12 are installed. Of course, the cryostat may include any other number and type of heat exchanger than that described. However, the refrigerant circulation exchanger allows a dynamic treatment of heat exchange, to reach very low temperatures.

The cryostat 10 is in the form of a vacuum chamber closed by a removable plate which allows access to its inner part. On this plate are arranged input and output connectors, to allow the passage of fluids mentioned above as well as for data communication devices, for example from pressure sensors, temperature, rotor frequency, of electrical power ... A dynamic vacuum of around 10 ^"5 mbar is maintained in the vacuum chamber of the cryostat to minimize heat loss by convection and gas conduction All the elements inside the cryostat are fixed mechanically by parts made of a material with a very low thermal conductivity, which limits thermal leakage by thermal conduction, these components are furthermore protected from the ambient radiation emitted by the internal surface of the vacuum enclosure, at approximately 300 K, by a screen thermal circulation maintained at low temperature by a circulation 18 of refrigerated fluid.This circulation is obtained by collecting output of the NMR probe, all the gas streams 2, 3, 4 that have been used, which form a global flux sufficiently powerful to carry the heat shield of the cryostat to an intermediate temperature between the ambient temperature of the vacuum chamber and the coldest temperature of the cryostat. This arrangement further allows to optimize the use of the fluid from the first source 1 high pressure. The vacuum chamber is made of a weakly magnetic material, and its heat shield in a metal material very good thermal conductor. The insulation of the enclosure can be obtained by a first cover of a super insulator, such as MLI based for the English name of "Multi Layer Insulation", while a second similar cover directly covers the exchangers 12 .

Then, at the outlet of the cryostat 10, the three gas streams 2, 3, 4 reach the NMR probe 20, advantageously cooled to the same temperature, and fulfill the three functions mentioned above. Alternatively, the temperatures may differ, but are preferably equal to each other to 100%. The first high pressure stream 2 rotates the sample, the second high pressure stream 3 cools the sample, and the third high pressure stream 4 allows the sample holder to be sustent. FIG. 4 represents an alternative embodiment of the NMR device in which the two exchangers 12, 12 'of the cryostat 10 are fed by two separate sources 11, 11' of refrigerant gas. This solution makes it possible, for example, to use nitrogen as a cold source of a first stage formed by the first exchanger 12, operating in the temperature range of 90 to 300 K, and then of helium as a cold source of a second exchanger stage 12 ', covering the temperature range up to 5 K.

Naturally, other variants are conceivable for generating one or more cooling streams and for cooling the high pressure gas streams. On the other hand, three gas streams 2, 3, 4 high pressure are used, but alternatively, any other solution is possible with at least the first two gas streams 2, 3 mentioned above. Finally, the NMR device according to the embodiment is equipped at the output of a system for heating and recovering fluids. The refrigerant gases are heated in exchangers 23 at the outlet of the cryostat 10. Similarly, the high-pressure gas streams 2, 3, 4 are redirected at the output of the NMR probe to an exchanger 24. These exchangers 23, 24 provided at the outlet of the The device makes it possible to raise the temperature of the gases used by the device, preferably at room temperature, or close to room temperature. This warming ensures the safety of the personnel and avoiding their burns in contact with very cold parts, avoiding falls by slipping due to the melting of the condensates, or their electrification. It also reduces the risk of damage to the equipment by short circuits or oxidation of metal parts. Then, at least the most expensive fluids, such as helium, can be recovered by a recovery device 25 for reuse. Figure 5 shows a side view of the NMR device according to the embodiment. A rigid cryogenic line 16 makes it possible to conduct the cooled high-pressure gas streams 2, 3, 4 from the cryostat outlet 10 to the NMR probe 20. This line is short, of the order of one meter in length, isolated , pumped in secondary vacuum and equipped with a heat shield. The NMR probe 20 comprises a sample holder 21 movable in rotation, placed in a device 26 to form the static magnetic field of the NMR measurement.

This solution has the following advantages: The flow rate of the gas streams 2, 3, 4 from the first high pressure source is chosen by acting on the pressure of this first source, which finally makes it possible to choose the speed of rotation of the sample holder which depends on this flow rate; The temperature of the streams 2, 3, 4 is determined by at least one separate cooler refrigerant from an independent source January 1. The variation of the pressure of this independent source makes it possible to regulate the flow rate of the refrigerant gas stream and thus finally to choose the temperature of the gas streams 2, 3, 4 at the outlet of the cryostat 10.

This solution thus dissociates the cooling function of the streams 2, 3, 4 arriving in the NMR probe of the high-pressure generating function of these streams intended for cooling the sample, the rotation of the sample, and to the levitation of the sample, which is not the case in the solutions of the state of the art. By this means, it is possible to choose the temperature in a range of 300 to 4.2 K, independently of the speed of rotation of the sample, which can also be set at a value greater than or equal to 20 kHz, even 30 kHz.

The device further comprises a central unit, not shown, which comprises at least one computer and hardware (hardware) and software (software) to implement the steps of the NMR detection method which will be detailed later. This management unit comprises a human machine interface which makes it possible to set temperature and rotation speed instructions of the sample holder. The device implements a step of regulating the pressures of sources 1, 1 1 of high and low pressure gas, in order to reach and respect these setpoint values. For this, it acts on actuators of gas sources, sending commands by communication. In return, it receives measurement values of these pressures, measured by sensors and transmitted by the communication devices. The device comprises several sensors for measuring its operating conditions, and transmitting the measured values to the central unit. For example, temperature probes based on Cernox ™ and platinum resistors are used in particular in the heart of the cryostat, in addition to pressure sensors, to monitor the evolution of energy phenomena and to enable the regulation of the device.

The method of detection and NMR analysis of a solid sample disposed in a sample holder 21 of an NMR device as described above thus comprises the following steps:

generating a plurality of high-pressure gas streams 2, 3, 4 from a first source 1 of a high-pressure gas;

cooling the gas streams in at least one heat exchanger 12 from a refrigerant gas from a second source of gas, which is colder and preferably low-pressure;

- Rotating the sample holder by a first high pressure gas stream and cooling the sample holder by a second high pressure gas stream.

The NMR detection method comprises a step of adjusting the speed of rotation of the sample holder 21 by varying the pressure of the first source 1 of high pressure gas and thus the flow rate of the first resulting gas stream 2 intended to act on fins or blades connected to the sample holder 21. This pressure is advantageously set at a level sufficient to reach a rotation frequency greater than or equal to 20kHz, or greater than or equal to 30kHz, of the sample holder. In Alternatively, the flow rate can be determined by another setting than the pressure of the first source.

The NMR detection method further comprises a step of controlling the temperature of the high pressure gas stream by varying the pressure and / or the flow rate of the second source of refrigerant gas. The latter is chosen to reach a temperature of the high pressure gas stream arriving at the level of the sample holder less than or equal to 10K, which can go down to 4.2K inclusive, and / or be variable (in particular adjustable) in a range of 4. , 2 to 300 K included.

Claims

claims

1. Method of NMR analysis of a solid sample placed in a sample holder (21), characterized in that it comprises the following steps:

- generating a plurality of high pressure gas streams (2, 3, 4) from at least a first source (1) of a high pressure gas;

- cooling the gas streams (2, 3, 4) in at least one heat exchanger (12) circulating a refrigerant gas (15) from at least a second source (1 1) of gas;

- Rotating the sample holder (21) by a first cooled high pressure gas stream (2) and cooling the sample holder by a second cooled high pressure gas stream (3).

2. NMR analysis method according to the preceding claim, characterized in that it comprises a step of adjusting the speed of rotation of the sample holder (21) by the variation of the pressure and / or the flow rate of the minus a first source (1) of high pressure gas.

3. NMR analysis method according to one of the preceding claims, characterized in that the first high pressure gas stream (2) causes the rotation of the sample holder (21) by its action on fins or blades of a device connected to the sample holder (21) for rotating it.

4. NMR analysis method according to the preceding claim, characterized in that the first high pressure gas stream (2) reaches a flow rate so as to cause the rotation of the sample holder (21) at a rotation frequency greater than or equal to at 20 kHz, or greater than or equal to 30 kHz.

5. NMR analysis method according to one of the preceding claims, characterized in that it comprises a step of adjusting the temperature of the gas stream (2, 3, 4) high pressure by the variation of the pressure and / or the flow rate of at least a second source (1 1) of refrigerant gas (15).

6. NMR analysis method according to the preceding claim, characterized in that the temperature of the gas stream (2, 3, 4) high pressure arriving at a probe (20) comprising the sample holder (21) is regulated at a temperature less than or equal to 10K.

7. NMR analysis method according to claim 5 or 6, characterized in that the temperature of the gas stream (2, 3, 4) high pressure arriving at the probe (20) comprising the sample holder is adjustable in range from 4.2 to 300 K included.

8. NMR analysis method according to one of the preceding claims, characterized in that the first high pressure gas stream (2) for the rotation of the sample holder (21) and the second gas stream (3) high pressure for cooling the sample holder (21) have equal temperatures at a probe (20) comprising the sample holder (21).

9. NMR analysis method according to one of the preceding claims, characterized in that it generates a third gas stream (4) from the first source (1) of a high pressure gas for the levitation sample holder (21).

10. NMR analysis method according to one of the preceding claims, characterized in that it comprises a step of setting temperature and speed of rotation of the sample holder (21), and in that it comprises a step of regulating the temperature and the flow rate of the high pressure gas streams (2, 3, 4) at these instructions by modifying the pressure and / or the flow rate of the two gas sources (1, 1 1).

1 1. Computer program comprising a code means adapted to perform the steps of an NMR analysis method according to one of the preceding claims when the computer program is executed on a computer.

An NMR analysis device, comprising a sample holder (21), adapted to receive a solid sample to be analyzed, and at least a first source (1) of a high pressure gas for generating gas streams (2, 3, 4) for rotating and cooling the sample holder, characterized in that it comprises at least a second source (1 1) of a refrigerant gas (15) for cooling the high pressure gas streams from the at least one first source (1) in at least one refrigerant circulation heat exchanger (12).

13. NMR analysis device according to the preceding claim, characterized in that it comprises a central unit which implements an NMR analysis method according to one of claims 1 to 10.

14. An NMR analysis device according to claim 12 or 13, characterized in that the at least one exchanger (12) is a countercurrent exchanger between the high pressure gas streams (2, 3, 4) and the at least one a refrigerant gas (15).

15. NMR analysis device according to one of claims 12 to 14, characterized in that it comprises at least one exchanger (12) fluid / fluid against the current comprising tubes (14) for the circulation of gas flows (2, 3, 4) high pressure inserted into a tube (13) in which a refrigerant gas (15) is circulated.

16. NMR analysis device according to one of claims 12 to 15, characterized in that it comprises at least one exchanger (23, 24) for heating the temperature of the gas leaving the device and / or in that it comprises a device (25) for recovering the gases leaving the device.

17. NMR analysis device according to one of claims 12 to 16, characterized in that the at least one first source (1) of a high pressure gas and / or the second source of a refrigerant gas (15). ) consists of a bottle of helium or nitrogen.