Nuclear magnetic resonance double spinning system

Abstract

There is provided a solid-state nuclear magnetic resonance, NMR, probe (10). The probe (10) comprises: a cylindrical stator (103), the cylindrical stator (103) configured to receive a cylindrical sample rotor (107); a single gas input (111), configured to provide gas to the cylindrical stator (103); wherein the single gas input (111) is configured to be orientated to direct the gas along an inner surface of the cylindrical stator (103) thereby to cause a double rotation of the cylindrical sample rotor (107).

Description

[0001] NUCLEAR MAGNETIC RESONANCE DOUBLE SPINNING SYSTEM

[0002] Field

[0003] The present invention relates to a solid-state NMR probe and methods of using said probe. More specifically, it relates to a solid-state NMR probe that is capable of causing a double rotation of a sample rotor, and a method of using the probe to perform said double rotation.

[0004] Background

[0005] Nuclear Magnetic Resonance (NMR) experiments performed on solid state samples typically involve spinning the sample orientated at the magic angle (i.e. 57.4° with respect to the static Bo magnetic field). This averages out a majority of spin - spin interactions dramatically increasing the resolution of the acquired spectra. For homogenous broadening, it has been demonstrated by Sternberg et al (Journal of Magnetic Resonance 291 (2018) 32-39) and Levitt et al (J. Chem. Phys., 92 (1990), pp.

[0006] 6347-6364) that for an NMR experiment on a rotating (i.e. spinning) sample around the magic angle the homogenous broadening of the NMR signal decreases linearly and / or quadratically with the spinning speed. Therefore, the quest for higher resolution in solid state NMR experiments lead to development of ever smaller rotors. There is inevitably a trade-off - with a decrease in size of rotor leads to decrease in sample volume and therefore a decrease in signal from the sample meaning a longer experimental time required.

[0007] Rotation of solids is achieved by packing the sample in a cylindrical rotor with a turbine cap. Two gas supplies are provided to ensure the spinning. Bearing compressed air reduces the friction while drive compressed air is guided to rotate the turbine cap. The designs of magic angle spinning (MAS) equipment involve a stator with a diameter slightly larger than the diameter of the rotor. Up to date no MAS design can overpass the speed of sound at the rotor circumference, attempts to spin faster result in a rotor crash.

[0008] MAS spinning at a single angle reduces the quadrupolar broadening experienced. To further reduce the quadrupolar broadening experienced common techniques include traditional double rotation (DOR) and dynamic angle spinning (DAS). In a DOR experiment a smaller rotor containing the sample is placed within a larger rotor. The outer rotor is oriented at the magic angle, with the inner rotor orientated at 30.56°, with both spun at these angles. DAS experiments involve spinning at least two different angles over time by a reorientation. Bearing and drive gas supplies are both required in these experiments to produce these spinning. With two bearing gasses and two drive gasses for traditional DOR.

[0009] It is desirable to reduce the broadening in MAS experiments further. In addition, DAS and DOR experiments involve complicated set ups that are not easy to carry out. It would be desirable to alleviate these drawbacks.

[0010] Summary of Invention

[0011] According to an aspect of the invention there is provided a solid-state nuclear magnetic resonance, NMR, probe comprising: a cylindrical stator, the cylindrical stator configured to receive a cylindrical sample rotor; a single gas input, configured to provide gas to the cylindrical stator; wherein the single gas input is configured to be orientated to direct the gas along an inner surface of the cylindrical stator thereby to cause a double rotation of the cylindrical sample rotor.

[0012] In this way, the single gas input incident on the inner surface of the cylindrical stator causes the single rotor to perform a double rotation (i.e. two different simultaneous rotations with the same single rotor). Advantageously, this helps to remove homonuclear and heteronuclear dipolar couplings resulting in an improvement in resolution of NMR spectra. In addition, such a set-up having only a single gas input is less complex than traditional rotation experiments which require two gas inputs both bearing and drive, or traditional double rotation experiments which requires four gas inputs, two bearings and two drives. Thus, it is a cheap and robust alternative to conventional MAS. Further advantageously, this method can provide enhanced motional averaging with reduced centrifugal forces which can be beneficial for delicate organic tissue samples. Directing the single gas input along the inner surface of the cylindrical stator creates a turbulent gas flow which results in the rotor rotating (i.e. spinning) about two axis (the double rotation) simultaneously. The inner surface may be an inner side surface of the stator.

[0013] The single gas input is the sole source of gas causing the double rotation of the cylindrical sample rotor. The double rotation may alternatively be referred to as double spinning and the two terms may be used interchangeably.

[0014] Preferably, a longitudinal length of the cylindrical stator defines a first axis, and a longitudinal length of the cylindrical sample rotor defines a second axis, wherein the single gas input is configured to be orientated to direct gas along an inner surface of the cylindrical stator thereby to induce a rotation of the cylindrical sample rotor about the first axis and a rotation of the cylindrical sample rotor about the second axis simultaneously thereby causing the double rotation of the cylindrical sample rotor. The longitudinal length (i.e. the longest length) of the cylindrical stator defines a first axis about which the rotor rotates - the first rotation of the double rotation. The longitudinal length (i.e. the longest length) of the cylindrical sample rotor defines a second axis about which the rotor rotates - the second rotation of the double rotation. The first rotation and second rotation are performed simultaneously resulting in the double rotation. The first axis defined by the longitudinal length of the stator may otherwise be referred to as the stator symmetry axis, and the second axis defined by the longitudinal length of the rotor may otherwise be referred to as the rotor symmetry axis.

[0015] Preferably, the NMR probe contains a coil, the coil configured to receive an electric current to thereby generate a magnetic field (Bl). The coil is used for both excitation and detection. More specifically, the magnetic field generated by the coil is configured to excite the spins in the sample being analysed. The coil is further configured to detect a signal from the excited spins in the sample being analysed. The coil may be composed of an inductor, or inductive elements, and a set of capacitive elements.

[0016] The single gas input may comprise a fluid conduit. The fluid conduit may comprise a pipe for transporting the gas, and a nozzle for outputting the gas from the pipe into the stator, wherein the nozzle is orientated to direct the gas along an inner surface of the cylindrical stator.

[0017] Preferably, one end of the pipe may be connected to a gas source. The other end of the pipe may be connected to the nozzle. The nozzle may have a circular cross section, in other arrangements the nozzle may have a tapered end. The nozzle and / or pipe may have attachment means for securing to the body of the NMR probe. The single gas input may comprise a connector attachment for connecting between the pipe for transporting gas and an external pipe that attaches to the external gas source. In other arrangements, the pipe may be connected directly to the gas source. The nozzle may have a diameter of less than D / 5, where D is the diameter of the cylindrical stator. D may be the inner diameter of the stator. In some arrangements, the nozzle may have a diameter of less than 2mm.

[0018] Preferably, a longitudinal length of the cylindrical stator defines a first axis, and wherein the single gas input may be configured to be orientated to direct the gas along an inner surface of the cylindrical stator and orientated at an angle to the first axis between 10° and 120°.

[0019] Preferably, the cylindrical stator may be made from glass or plastic. The material that the stator is made from can have an effect on the double rotation achieved. In particular, the material from which the inner surface of the cylindrical stator is made. The gas speed at the interface with the stator will be smaller for a plastic stator compared to a glass stator. Therefore, the ratio of the inner rotation frequency (i.e. that around the longitudinal axis of the rotor) to the outer rotation frequency (i.e. that around the longitudinal axis of the stator) will be higher for a plastic stator than for a glass stator.

[0020] The probe has a long axis and the stator may be configured to be orientated at 54.7° with respect to the long axis. The probe has a body that has a long axis. The probe comprises a cylindrical portion. The cylindrical portion is configured to be inserted into the bore of an NMR magnet. The stator is housed within the body and configured to be orientated at 54.7° with respect to the long axis such that it is at 54.7° with respect to Bo magnetic field generated by the NMR magnet when the probe is received in the bore of the NMR magnet. The angle 54.7° is known as the magic angle. In other arrangements, the stator may be orientated at a different angle to 54.7°.

[0021] Preferably, the cylindrical rotor has a diameter d, and the cylindrical stator has a diameter D, and the cylindrical stator may have a diameter that is greater than 1.1 times the diameter of the cylindrical rotor (D > 1. Id). In this way, the cylindrical rotor has enough space within the stator to perform the double rotation.

[0022] Preferably, the inner surface of the cylindrical stator is an inner side surface of the stator and the cylindrical stator may be curved between the inner side surface of the cylindrical stator and a bottom surface of the cylindrical stator. In this way, there may be a smooth transition between the inner surface of the cylindrical stator (i.e. the side of the cylinder) and the bottom surface of the cylindrical stator. This may advantageously, improve the double rotation achieved. Specifically, the inner side surface may not be parallel to the axis along its whole longitudinal length. The inner side surface may have a curved region at the end nearest the bottom surface of the cylindrical stator which transitions from being parallel to the first axis to being perpendicular to the first axis thereby to transition into the bottom surface.

[0023] According to a further aspect there is provided a system comprising the solid-state NMR probe of the above aspect, and a cylindrical sample rotor.

[0024] Preferably, the cylindrical sample rotor may comprise a turbine cap. The turbine cap acts to cause the rotor to rotate (i.e. spin) in response to the single gas input. The rotor may be a cylindrical rotor of the type commonly used in conventional MAS experiments. The rotor may be made of Zirconia. In other arrangements, it may be made of any other suitable type of material. The turbine cap may be made from Polychlorotrifluoroethylene (Kel-F®), polyimide-based plastics (such as Vespel®), Zirconia, PEEK or any other material. Advantageously, by using double spinning a lower centrifugal force will be exerted on the rotor when spinning than with conventional MAS experiments. Therefore, materials that would not traditionally be used with conventional MAS experiments can be used - for instance using PEEK rotors rather than Zirconia. According to a further aspect there is provided a method of performing a solid state nuclear magnetic resonance, NMR, experiment, the method comprising: inserting a cylindrical sample rotor into a cylindrical stator of a solid state NMR probe; inserting the probe into a bore of an NMR magnet; connecting a single gas input to the cylindrical stator, such that it is orientated to direct the gas along an inner surface of the cylindrical stator; supplying gas from the single gas input into the cylindrical stator along an inner surface of the cylindrical stator thereby to cause a double rotation of the cylindrical sample rotor; and exciting a sample contained in the rotating sample rotor with an RF field and acquiring the NMR signal.

[0025] The above method steps are not necessarily performed in the order claimed. For instance, the connecting step may be before or after either or both of the inserting steps. Likewise, the supplying gas step might be prior to inserting the probe into the bore of the magnet. Although the steps can be performed in the order stated above, the scope is not limited to such.

[0026] The method may be performed using the probe of the above aspect.

[0027] Description of Figures

[0028] Figure 1 shows a cross sectional side view of a portion of an NMR probe, including a cylindrical stator containing a sample rotor, and a gas input according to an aspect of the present invention;

[0029] Figure 2 shows the NMR probe, containing the portion shown in Figure 1;

[0030] Figure 3 shows a system for performing an NMR experiment according to the present invention including the NMR probe of Figure 2, an NMR spectrometer, a NMR magnet, and a gas source;

[0031] Figure 4 shows the cross-sectional side view of a portion of an NMR probe as shown in Figure 1 showing the gas flow from the gas input, and two axis of rotation that the sample rotor undergoes; Figure 5 shows a cross sectional side view of a portion of an NMR probe, including a cylindrical stator containing a sample rotor, as shown in Figure 1, showing parameters associated with the set up;

[0032] Figure 6A to 6C show a graph showing the spinning profile of the rotor during a double spinning experiment according to the present invention at various values of angle a and P;

[0033] Figure 7 shows a graph showing the spinning profile of the rotor during a double spinning experiment according to the present invention;

[0034] Figure 8 shows85Rb spectra of RbCl obtained using a double spinning solid-state NMR experiment according to present invention showing different spectra at a range of different spinning speeds of the rotor; and

[0035] Figure 9 shows a method of performing a solid-state NMR, experiment according to an aspect of the present invention.

[0036] Detailed Description

[0037] The present invention relates to a solid state nuclear magnetic resonance (NMR) probe for use in a solid-state NMR experiment, and a new method of performing such an experiment.

[0038] Figure 1 shows a cross sectional side view of a portion 101 of an NMR probe. Figure 2 shows NMR probe 10 also showing the portion 101 shown in Figure 1.

[0039] As can be seen in Figure 1, the probe 10, specifically the portion of the probe 101, contains a stator 103. The stator 103 has a cylindrical shape. The cylindrical stator 103 is housed within an outer stator housing 105. In Figure 1 the outer housing 105 has a cuboid shape but in other arrangements the outer housing 105 may have any type of shape that is suitable for holding the cylindrical stator 103.

[0040] The stator 103 is hollow in that it defines a space 109 for holding a cylindrical sample rotor 107 during an NMR experiment. A single gas input 111 is attached to a first (i.e. top) end 113 of the stator 103. The second (i.e. bottom) end 115 of the stator 103 is a closed end. The first end 113 of the stator 103 in the arrangement shown in Figure 1 is an open end. However, it would be understood that in other arrangements the first end 113 of the stator 103 may be closed, such as with a lid or cap, with a hole or aperture configured to receive the single gas input 111.

[0041] The stator 103 includes only a single gas input 111, as can be seen from Figure 1. Conventional NMR experiments contains at least two gas inputs - bearing and drive, to aid the rotation of the sample rotor. However, the arrangement of the present invention requires only a single gas input 111 (i.e. a single gas flow into the probe) to perform the NMR experiment.

[0042] The single gas input 111 includes a pipe 117 with a nozzle 119 at a first proximal end 121 of the pipe 117. The second distal end of the pipe 123 is connected (either directly or indirectly) to a gas source (as will be described in more detail below). The first end 121 of the pipe 117 is positioned so that the nozzle 119 is received in the first end 113 of the stator 103. The pipe 111 is formed of plastic material that is sufficient to support gas under high pressure.

[0043] A cylindrical sample rotor 107 is shown in the stator 105. The sample rotor 107 is removable from the stator 103 through the first end 113 of the stator 103. The sample rotor has a cylindrical body 124 which is hollow. It has a closed first end 127 and an open second end 129 into which the sample to be analysed may be placed. A turbine cap 131, having a plurality of fins, is positioned on the second end 129 to provide a sealed rotor 107 thereby sealing the sample in the interior hollow region of the rotor 107.

[0044] Moving on to look at Figure 2, Figure 2 shows the probe 10. The probe 10 has a cylindrical body 13 which is shown in cross section in Figure 2 showing the portion 101 as described above, including stator 103, housed within the cylindrical body 13. The stator 103 is orientated at an angle of 54.7° to an axis defined by the longitudinal length of the cylindrical body 13 such that when the probe 10 is inserted into an NMR magnet the stator 103 is orientated at the magic angle with respect to the static Bo field. The cylindrical body 13 is preferably a metal casing that houses the portion 101 along with the electronics of the probe, and RF coil. The cylindrical body 13 of the probe 10 has a first end 15 through which the rotor 107 can be inserted into the stator 103. The cylindrical body 13 has a second end 17, distal to the first end 15, having a housing 19. The housing 19 is not shown in cross-section in Figure 2 and instead shows the fronton view. The housing 19 includes the attachments for attaching the probe 10 to the NMR spectrometer and the gas supply. Specifically, the housing 19 has a RF input attachment 21 which provides the RF signal for exciting the spins in the sample from the spectrometer to the probe 10, and for receiving the RF signal generated by the sample when detected. Probe 10 can simultaneously excite and detect multiple nuclei, having 1, 2, 3, 4 or more RF channels. The housing 19 further has gas attachment 23. The gas attachment 23 has a fitting that can receive a mating fitting from an external gas supply to provide the gas supply to the probe from an external source. The gas attachment 23 is in fluid communication with pipe 111 via a further pipe 125 via fluid connector fixing 128. In other arrangements, pipe 111 may be directly connected to gas attachment 23 without the need for fluid connector fixing 128 or further pipe 125.

[0045] Figure 3 shows a system 1 for performing an NMR experiment according to the present invention including the NMR probe 10 of Figure 2, an NMR spectrometer 3 and NMR magnet 33, and a gas source 30. NMR probe 10 is shown connected to spectrometer 3 via cable 9. Cable 9 is preferably a 50 Ohm transmission line cable suitable for providing the NMR RF field from the spectrometer 3 (and / or amplifier thereof) to the probe 10. It is also responsible for returning the detected signal back from the probe 10 to the spectrometer 3. Cable 9 is attached to the probe via RF input attachment 21 as outlined above. In case multiple channels are used each RF channel will have its own cable to connect the probe with the spectrometer.

[0046] Spectrometer 3 includes a series of buttons 5 and screens 7 to aid its use. It may be connected to a computer system (not shown) that is responsible for controlling the spectrometer 3.

[0047] The probe 10 is attached through gas attachment 23, via pipe 32, to external gas supply 30 to provide the gas supply to the probe 10 from the external source. The external gas supply 30 has an attachment 31 to which the pipe 32 connects. The external gas supply 30 may be a portable gas canister. In other arrangements, the external gas supply may be a wall mounted gas supply that is connected to a static refillable gas canister, or compressors. The gas from the gas supply is preferably compressed air. However, other gases may instead be used. For instance, the sample under experiment may be air sensitive so it may be beneficial to use a gas other than air. For instance, the gas may be compressed nitrogen from boil off liquid nitrogen dewar.

[0048] NMR magnet 33 is also shown. NMR magnet provides the static Bo field. The magnet is typically a superconducting magnet. The magnet has three legs 35 which support the magnet from the ground on which it is housed. A bore of the magnet 37 acts as a receiving portion for the probe 10. More specifically, the cylindrical body 13 of the probe 10 is pushed upwards so that cylindrical body 13 of the probe is fully received in the bore 37 with the housing 19 protruding from the bore. This allows the sample to be positioned within the magnet 10, and therefore the Bo field, whilst also having the housing 19 with the attachments 21, 23, outside of the magnet 10 for easy access.

[0049] The NMR magnet may have a size of from a few tesla (T) to many tesla (T). For instance, it may be 2T or in excess of 20T.

[0050] Although the NMR probe 10 is shown attached to the NMR spectrometer 3 and gas supply 30 prior to inserting it into the NMR magnet 33 this is not necessarily the case. The probe 10 may be inserted into the magnet 33 and then the attachment to the spectrometer 3 and / or gas supply 30 may then be done once the probe 10 is inside of the magnet 33.

[0051] The specifics of the double rotation experiment, according to the present invention, achieved using the NMR probe 10 and system 1 shown in Figures 1 to 3 will now be described in detail. Figure 4 shows the cross-sectional side view of a portion 101 of an NMR probe 10 as shown in Figure 1 showing the gas flow from the gas input 111, and two axis of rotation that the sample rotor 107 undergoes during such an experiment.

[0052] As can be seen from Figure 4, the gas passes along single gas input 111, through pipe 117 and exits through nozzle 119 into stator 103. The nozzle 119 is positioned such that the gas is directed along the surface of the interior wall 140 (i.e. inner side surface) of the stator 103 following its exit from the nozzle 119. This can be seen in region A of Figure 4 where it can be seen that the gas flow 142 follows the wall 140 of the stator. The gas continues to follow the wall and the curvature of the stator when it reaches the second end 115 of the stator 103 before it curves in region B along the bottom end 115 of the rotor upwards the opposite side of the rotor i.e. the part of the wall opposite to the part of the wall it was initially following, towards the rotor 107 (this is due to The Coanda effect). The manner in which the interior wall 140 meets the bottom end 115 of the stator is such that there is a gradual transition between the side wall 140 and the bottom end 115 of the stator 103 aiding the gas flow (as opposed to a hard 90° transition between the side and bottom which could negatively affect the gas flow). Gas flow acting in this way causes a double spinning. By the gas following the curvature of the inner portion of the stator 103 the initial laminar flow turns turbulent as the direction of the flow changes. Such a turbulent flow produces a vortex around the symmetry axis of the stator 103. This will drive a double spinning of the rotor 107 with an inner rotation coin around the rotor symmetry axis 151, and an outer rotation coOut around the stator symmetry axis 153. The stator symmetry axis 153 is defined by the longitudinal length of the stator - the longitudinal length defined between a first end 113 and the second end 115. The rotor symmetry axis 151 is defined by the longitudinal length of the rotor - the longitudinal length defined between a first end 127 and the second end 129 of the rotor 107.

[0053] By analogy, such an inner rotation and outer rotation can be considered comparable to the movement of the planets around the sun whilst also rotating about their own axis. Such movement involves orbital motion (coOut) of the rotor 107 around the stator symmetry axis 153 whilst an inner rotation (coin) around the rotor symmetry axis 151. Such a double rotation can provide a reduction in heteronuclear and homonuclear dipolar interactions thereby providing a reduction in broadening due to the heteronuclear and homonuclear dipolar interaction. It also helps lead to a reduction in first order quadrupolar interaction thereby providing a reduction in broadening due to the first order quadrupolar interaction. This is advantageous when performing solid-state NMR experiments in which it is desirable to have narrower line widths due to reduction of these interactions.

[0054] Conventional MAS experiments have a drive gas moving faster than speed of sound and bearing gas moving slower than speed of sound (i.e. two gas inputs). A disadvantage of this is that it can cause shockwaves and peak overpressure. In the present described double spinning experiment there is only a single gas flow which can move faster than speed of sound. Thus, the shockwaves may be pushed outside the stator (where faster than speed of sound gas meets slower gas) which can potentially result in faster spinning without a rotor crash than conventional MAS. Even if faster than the speed of sound spinning is not utilised with the present double spinning experiment the combined effect of both rotations (which add up together) can result in an effective spinning speed that is equivalent to spinning at faster than the speed of sound.

[0055] It has been found that the material that the stator 103 is made from can have an effect on the double rotation achieved. In particular, the material from which the inner wall (i.e. inner side surface) 140 of the cylindrical stator 103 is made. In some arrangements the stator 103 may be made of glass. In other arrangements the stator 103 may be made from plastic. The gas speed at the interface with the stator 103 will be smaller for a plastic stator compared to a glass stator. Therefore, the ratio of the inner rotation frequency (coin) (i.e. that around the longitudinal axis 151 of the rotor 107) to the outer rotation frequency (coOut) (i.e. that around the longitudinal axis 153 of the stator 103) will be higher for a plastic stator 103 than for a glass stator 103.

[0056] Figure 5 shows a cross sectional side view of a portion of an NMR probe, including a cylindrical stator 103 containing a sample rotor 107, as shown in Figure 1, showing parameters associated with the set up. The external magnetic field Bo is shown with the stator 103 orientated at 54.7° to the Bo field (i.e. at the magic angle).

[0057] The rotor has a diameter of d, and a length 1. The stator has a diameter of D, and length L.

[0058] Cartesian axis x, y and z are shown in Figure 5 to help demonstrate the direction of gas input 111 with respect to the stator 103. The x-axis lies along the longitudinal length of rotor, i.e. parallel to axis 153 shown in Figure 4. Angle a defines the angle between the direction 501 of the gas input (e.g. the direction that gas exits nozzle 119 as shown in Figure 4) and the z-axis. Angle defines the angle between the direction 501 of the gas input and the y-axis. The distance between the direction 501 of the gas input and the x-axis is defined by f. It has been found that within these constraints double rotation can be achieved:

[0059] D > 1.1 x d

[0060] L > 1.5 x I

[0061] < 120 0° < < 180°

[0062] 0 < f < 0.5 x D

[0063] p < D / 5

[0064] Where p is the diameter of the input gas nozzle 119 (as can be seen in Figure 4). Specifically, it was found that double rotation was achieved with a gas flow rate larger than 10 1 / min through a nozzle with a diameter less than 2mm. For a fixed orientation of the input gas the rotation speeds (inner and outer) increase with increased gas flow. By optimising a, P, f, and p, for various d and D the maximum rotation speeds can be determined for that particular rotor and stator. Of course, the specific parameter values selected within the ranges above to achieve double rotation are selected ensuring that the single air input is directed along the surface of the cylindrical stator to achieve said double rotation. An example of such parameters are described in relation to Figure 6A to 6C below.

[0065] Figure 6A to 6C show a graph showing a faster Fourier transform (FFT) of the sound produced by the spinning of the rotor during a double spinning experiment according to the present invention at various values of angle a and . The specific values of each experiment are also described.

[0066] Figure 6A shows spinning profile of a rotor using a flow rate of 6 1 / min; D=9 mm; L=49 mm; d=3.2 mm; 1=17 mm; p = 0.7 mm; f= 1 mm; a =70°; p =45°. This produces a double spinning with: outer rotation = 235 Hz (and its harmonics at 470 Hz, 705 Hz, 940 Hz, 1175 Hz, 1410 Hz) and inner rotation = 528 Hz; (and its harmonics at 1058).

[0067] Figure 6B shows spinning profile of a rotor using a flow rate of 6 1 / min; D=9 mm; L=49 mm; d=3.2 mm; 1=17 mm; p = 0.7 mm; f= 1 mm; a =45°; p =20°. This produces a double spinning with: outer rotation = 208 Hz (and its harmonics at 416 Hz, 624 Hz, 832 Hz, 1040 Hz, 1248 Hz) and inner rotation = 534 Hz (and harmonics at 1068 Hz).

[0068] Figure 6C shows spinning profile of a rotor using a flow rate of 6 1 / min; D=9 mm; L=49 mm; d=3.2 mm; 1=17 mm; p = 0.7 mm; f= 1 mm; a =25°; p =60°. This produces a double spinning with: outer rotation =175 Hz (and its harmonics at 350 Hz and 525 Hz, 700 Hz, 875 Hz 1050 Hz) and inner rotation =499 Hz (and harmonics at 998 Hz). Figure 7 shows a graph 300 showing the spinning profile of the rotor 107 during a double spinning experiment according to the present invention. It is shown with an outer rotation (coOut) 301 having frequency of 380 Hz (and two harmonics at 2x 303 and 3x 305 the outer rotation frequency) and an inner rotation (coin) 301 having frequency of 2700 Hz giving a ratio of inner to outer spinning of 7.1. The frequency of the inner and outer rotations can be measured by recording the sound of the spinning. This may be through using an acoustic detector and computer which processes the sound to provide the Fourier transformed graph 300 as shown in Figure 7. Figure 7 was measured for d = 3.2 mm diameter rotor 107 undergoing double spinning in a glass stator 103 with D = 9 mm inner diameter. Similar double spinning was obtained for rotor diameters of d = 1.3 mm, 1.6 mm, 4 mm spinning inside glass tubes with D = 5 mm, 9 mm or 21 mm, as well as for larger diameter cylinder of d = 7 mm in a D = 9 mm or 21 mm tube.

[0069] Figure 8 shows85Rb solid state NMR spectra 400 of RbCl obtained using a double spinning experiment according to present invention at a range of different spinning speeds of the rotor 103. The spectra 400 were measured on a 20 T Bruker NEO NMR spectrometer. Spectrum 401 is a spectrum from a static sample (i.e. inner and outer rotations = 0) (linewidth FWHM = 440ppm). Spectrum 403 is from a sample with an outer rotation = 160 Hz (linewidth FWHM = 126ppm). Spectrum 405 is from a sample with an outer rotation = 290 Hz (linewidth FWHM = 85ppm). Spectrum 407 is from a sample with an outer rotation = 350 Hz) (linewidth FWHM = 68ppm). As can be seen with increase in outer spinning speed a decrease in line width is achieved. These linewidths are narrower than that achieved with conventional MAS at higher spinning speeds. These results were acquired using compressed air with a pressure of approximately 4 bar and a flow of 20 1 / min through a 2 mm diameter nozzle resulting in a speed of the air exiting the nozzle of 106m / s.

[0070] Figure 9 shows a method 800 of performing a solid-state NMR, experiment according to an aspect of the present invention.

[0071] At step 801 a cylindrical sample rotor is inserted into a cylindrical stator of a solid-state NMR probe. The solid-state NMR probe may be probe 10 shown in Figure 2.

[0072] At step 803 the probe is inserted into a bore of an NMR magnet. In this way, the sample contained in the sample rotor is placed within the Bo static magnetic field. At step 805 a single gas input is connected to the cylindrical stator, such that it is orientated to direct the gas along an inner surface of the cylindrical stator.

[0073] At step 807 gas is supplied from the single gas input into the cylindrical stator along an inner surface of the cylindrical stator thereby to cause a double rotation of the cylindrical sample rotor.

[0074] At step 809 the sample contained in the rotating sample rotor is excited with an RF field and the NMR signal acquired.

[0075] Method 800 may be performed by the system of Figure 3 as described above. The steps may be carried out in the order specified in Figure 9 or any other order that would make sense. For instance, step 803 may be carried out before steps 801 and 805.

[0076] While the disclosure has been described in terms of various embodiments, the person skilled in the art will recognise that the disclosure can be practiced with modification within the spirit and scope of the claims.

[0077] Although the single gas input 111 is shown as having a nozzle 119 in the figures in other arrangements, there may be no nozzle. The first distal end 121 of the pipe 111 may be received directly in the first end 113 of the stator 103.

[0078] Although a particular NMR probe arrangement is shown in Figure 2, the present invention is not limited to such an arrangement. The portion 101 could be included within other designs of probes. For instance, it was stated that the sample may be inserted through a first end of the cylindrical body 13 of the probe 10. However, it would be understood that in other arrangements the end of the probe may not be open and the cylindrical body 13 may instead be fully removed to insert the sample. Other probe 10 arrangements may equally be implemented within the scope of the invention.

Claims

CLAIMS1. A solid-state nuclear magnetic resonance, NMR, probe comprising:a cylindrical stator, the cylindrical stator configured to receive a cylindrical sample rotor;a single gas input, configured to provide gas to the cylindrical stator; wherein the single gas input is configured to be orientated to direct the gas along an inner surface of the cylindrical stator thereby to cause a double rotation of the cylindrical sample rotor.

2. The solid-state NMR probe of claim 1, wherein a longitudinal length of the cylindrical stator defines a first axis, and a longitudinal length of the cylindrical sample rotor defines a second axis, wherein the single gas input is configured to be orientated to direct gas along an inner surface of the cylindrical stator thereby to induce a rotation of the cylindrical sample rotor about the first axis and a rotation of the cylindrical sample rotor about the second axis simultaneously thereby causing the double rotation of the cylindrical sample rotor.

3. The solid-state NMR probe of any preceding claim, wherein the NMR probe contains a coil, the coil configured to receive an electric current to thereby generate a magnetic field (Bl).

4. The solid-state NMR probe of any preceding claim, wherein the single gas input comprises a fluid conduit.

5. The solid-state NMR probe of claim 4, wherein the fluid conduit comprises a pipe for transporting the gas, and a nozzle for outputting the gas from the pipe into the stator, wherein the nozzle is orientated to direct the gas along an inner surface of the cylindrical stator.

6. The solid-state NMR probe of claim 5, wherein the cylindrical stator has a diameter D, and the nozzle has a diameter of less than D / 5.

7. The solid-state NMR probe of any preceding claim, wherein a longitudinal length of the cylindrical stator defines a first axis, and wherein the single gas input is configured to be orientated to direct the gas along an inner surface of the cylindrical stator and orientated at an angle to the first axis between 10° and 120°.

8. The solid-state NMR probe of any preceding claim, wherein the cylindrical stator is made from glass or plastic.

9. The solid-state NMR probe of any preceding claim, wherein the probe has a long axis and the stator is configured to be orientated at 54.7° with respect to the long axis.

10. The solid-state NMR probe of any preceding claim, wherein the inner surface of the cylindrical stator is an inner side surface of the stator and the cylindrical stator is curved between the inner side surface of the cylindrical stator and a bottom surface of the cylindrical stator.

11. A system comprising the solid state NMR probe of any of claims 1 to 10, and a cylindrical sample rotor.

12. The system of claim 11, wherein the cylindrical sample rotor comprises a turbine cap.

13. The system of claim 11 or 12, wherein the cylindrical rotor has a diameter d, and the cylindrical stator has a diameter D, and the cylindrical stator has a diameter that is greater than 1.1 times the diameter of the cylindrical rotor (D > 1. Id).

14. A method of performing a solid state nuclear magnetic resonance, NMR, experiment, the method comprising:inserting a cylindrical sample rotor into a cylindrical stator of a solid state NMR probe;inserting the probe into a bore of an NMR magnet;connecting a single gas input to the cylindrical stator, such that it is orientated to direct the gas along an inner surface of the cylindrical stator;supplying gas from the single gas input into the cylindrical stator along an inner surface of the cylindrical stator thereby to cause a double rotation of the cylindrical sample rotor; andexciting a sample contained in the rotating sample rotor with an RF field and acquiring the NMR signal.

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