SAMPLE EXTENSION ON THE SAMPLING HEAD SIDE TO REDUCE THE B0 FIELD DISTURBANCE AT THE END OF THE SAMPLE TUBE

Abstract

An NMR apparatus having a magnet system for generating a homogeneous static magnetic field B.sub.0 along a z direction, with a sampling head (1) comprising an RF transmitting and receiving coil system (2) and an opening (3) extending in the z direction for receiving a sample tube (4) containing a sample substance to be analyzed by means of NMR measurement, a compensation element (5) being present which at least partially compensates for disturbances in the homogeneous magnetic field B.sub.0 due to the sample substance and the material of the sample tube at the sample end of the sample tube that protrudes farthest into the sampling head during measuring operation, is characterized in that the compensation element is arranged outside the sample tube protruding into the sampling head during measuring operation of the NMR apparatus and in the z direction below the sample end, and is mounted so as to be movable, in particular displaceable, in the z direction. Thus, the compensation element can nestle against the sample tube during operation without problem. In this way, the susceptibility jump and the resulting B.sub.0 field disturbance in the lower region of the NMR-active sample liquid caused by the lower end of the sample tube are effectively minimizable with particularly uncomplicated technical means.

Claims

1-14. (canceled)

15. A sampling head for an NMR apparatus comprising: an RF transmission and reception coil system; an opening extending in a z direction for receiving a sample tube containing a sample substance to be analyzed by means of NMR measurement; and a compensation element which at least partially compensates for disturbances of a homogeneous magnetic field B.sub.0 due to the sample substance and a material of the sample tube at a sampling end of the sample tube protruding into the sampling head during a measuring operation, the compensation element being arranged outside the sample tube and protruding into the sampling head during the measuring operation and in the z direction below the sampling end, and being movably mounted in the z direction on a spring device acting in the direction of the z axis or on an air cushion formed by a flow of temperature control gas in the sampling head.

16. The sampling head according to claim 15, wherein the compensation element is mounted so as to be freely rotatable about the z axis and is able to rotate with the sample tube during the measuring operation.

17. The sampling head according to claim 15, wherein the compensation element is hollow and is protected against uncontrolled removal from the sampling head by being firmly attached via a retaining element to the sampling head.

18. The sampling head according to claim 15, wherein an upper stop for the compensation element is provided in the sampling head in the z direction.

19. The sampling head according to claim 15, wherein the compensation element has gas passages on its outside in the form of longitudinal grooves parallel to the z direction and/or on the z axis in the form of an axial through-hole.

20. The sampling head according to claim 15, wherein the compensation element has a susceptibility χ which is between an average susceptibility of the sample tube and a typical susceptibility of the sample substance.

21. The sampling head according to claim 15, wherein the compensation element has a susceptibility χ and is configured to be exchangeable for another compensation element with a different susceptibility χ′.

22. An NMR apparatus having a magnet system for generating homogeneous static magnetic field B.sub.0 along a z direction, and comprising a sampling head according to claim 15.

23. The NMR apparatus according to claim 22, wherein the compensation element is configured to continue the cross-sectional geometry of the sample tube in the z direction.

24. The NMR apparatus according to claim 22, wherein the compensation element has a contour that clings to a contour of the sample tube at the sampling end, wherein the sampling end of the sampling tube has a hemispherical shape and a portion of the compensation element opposite the sample tube is shaped like a hemispherical shell.

25. The NMR apparatus according to claim 22, wherein the compensation element is formed from or coated with a material which minimizes a frictional resistance between the compensation element and the sample tube resting against it during the measuring operation, the material having an average susceptibility χ between 0.4 cgs and 0.8 cgs.

26. The NMR apparatus according to claim 22, wherein the compensation element is configured to allow a fluid flow of temperature control gas from the compensation element into an annular gap between an outer shell of the sample tube protruding into the sampling head during the measuring operation and a wall element surrounding the sample tube, which carries the RF transmitting and receiving coil system.

Description

DETAILED DESCRIPTION OF THE INVENTION AND THE DRAWINGS

[0051] The invention is illustrated in the drawings and is explained in more detail with reference to exemplary embodiments.

[0052] In the drawings:

[0053] FIG. 1 is a schematic vertical sectional view of a first embodiment of the sampling head for an NMR apparatus according to the invention having a compensation element that is movably mounted on a spring device acting in the direction of the z axis;

[0054] FIG. 2 shows an NMR sampling head as in FIG. 1, but in a simpler embodiment, with a rigid compensation element acting as a stop for the sample tube in the direction of the z axis and integrated into the sampling head;

[0055] FIG. 3a is a very schematic vertical section through an embodiment of the compensation element provided according to the invention with gas passages parallel to the z direction;

[0056] FIG. 3b is a schematic horizontal section through an embodiment of the compensation element according to FIG. 3a with fine longitudinal grooves on the outside parallel to the z direction and with an axial through-hole;

[0057] FIG. 3c is a schematic horizontal section through an embodiment of the compensation element similar to that shown in FIG. 3b, but with coarser longitudinal grooves;

[0058] FIG. 4a is a schematic vertical section through an embodiment of the compensation element provided according to the invention with a retaining element firmly connected to the sampling head and engaging in the compensation element in a central z-position; and

[0059] FIG. 4b shows the compensation element from FIG. 4a, but with the retaining element in a z position just in front of the stop.

[0060] FIGS. 1 to 4b of the drawing each show, in schematic views with different details, preferred embodiments of the NMR apparatus according to the invention in the region of the sampling head.

[0061] Such an NMR apparatus with a magnet system, not specifically shown in the drawing for reasons of clarity, for generating a homogeneous static magnetic field B.sub.0 along a z direction comprises a sampling head 1; 1′, which has an RF transmitting and receiving coil system 2 and an opening 3 extending in the z direction for receiving a sample tube 4, which, during operation, contains a sample substance to be examined by means of NMR measurement, a compensation element 5; 5′; 5″; 5′″ being present which at least partially compensates for disturbances of the homogeneous magnetic field B.sub.0 due to the sample substance and the material of the sample tube 4 at the axial sample end of the sample tube 4 protruding farthest into the sampling head 1 during measuring operation.

[0062] The NMR apparatus according to the invention is distinguished from the known arrangements according to the prior art in that the compensation element 5; 5′; 5″; 5′″ is arranged outside of the sample tube 4 protruding into the sampling head 1; 1′ in the measuring operation of the NMR apparatus and in the z direction below the sample end.

[0063] In FIG. 1 a preferred embodiment of the sampling head 1 is arranged within the NMR apparatus according to the invention. The sampling head comprises a compensation element 5 which is designed in such a way that it continues the cross-sectional geometry of the sample tube 4 in the z direction, its contour nestling against the contour of the sample tube 4 at the sample end. At its axial end, the sample tube 4 is spherical and the compensation element 5 in its portion opposite the sample tube 4 is designed as a spherical cap, in particular as a hemispherical shell.

[0064] The outer radius of the spherical end of the sample tube is advantageously smaller than the inner radius of the spherical cap of the compensation element. In this way, a punctiform contact between the compensation element and the sample tube is achievable. When the sample tube rotates within the sampling head, the friction with respect to the compensation element is reduced, the contours of the sample tube and compensation element still nestling against one another. This design is particularly well-suited for a compensation element that is rigidly integrated into parts of the sampling head.

[0065] Furthermore, the compensation element 5 is designed in such a way that a fluid flow, for example a temperature control gas flow, from the compensation element 5 into an annular gap 6 between the outer shell of the sample tube 4 protruding into the sampling head 1 during measuring operation and a wall element 7 of the sampling head 1 surrounding the sample tube 4 in this position, which in particular carries the RF transmitting and receiving coil system 2, is hindered as little as possible.

[0066] The compensation element 5 is movable, in particular displaceable, in the z direction, and is mounted on a spring device 8 acting in the direction of the z axis. Contrary to the drawing, the compensation element is to be pressed against the sample tube by the spring device in order to leave as small a gap as possible here. The compensation element is rotatably mounted with the spring device 8 in order to impede a rotation of the sample tube as little as possible during an NMR measurement. In addition, it is designed to be exchangeable for another compensation element having a different susceptibility.

[0067] Another, particularly simple embodiment of the invention is shown schematically in FIG. 2. The sampling head 1′ shown there is similar in most features to the sampling head 1 shown in FIG. 1, but it differs therefrom by the different design of its compensation element 5′:

[0068] In this embodiment, namely, the compensation element 5′ is rigidly integrated into parts of the sampling head 1′ in the relevant lower axial region and is simply not movably supported. However, in this case the sample tube 4 is mountable on an air cushion above the compensation element 5′, which is preferably formed by a flow of temperature control gas in the sampling head 1.

[0069] FIGS. 3a to 3c show exemplary embodiments in greater detail in which the compensation element 5″ has fluid passages, namely in particular on its outside in the form of longitudinal grooves 10; 10′ parallel to the z direction and on the z axis in the form of an axial through-hole 11. FIG. 3b shows the cross section of a compensation element perpendicular to the z direction with finer longitudinal grooves 10 on the outside that are parallel to the z direction, while somewhat coarser longitudinal grooves 10′ are present in the exemplary embodiment according to FIG. 3c.

[0070] Finally, FIGS. 4a and 4b show an embodiment of a compensation element 5′″ arranged according to the invention in the NMR sampling head axially below the sample tube 4, which compensation element is hollow and protected against uncontrolled removal from the sampling head by a retaining element 9 firmly connected to the sampling head 5′″ and engaging in the compensation element. As a result, there is also an upper stop in the z direction for the compensation element 5′″. The compensation element is advantageously pressed in the direction of the sample tube by a spring or the fluid flow of a temperature control gas.

[0071] In order to compensate even better for the magnetic field distortion due to the jump in susceptibility at the lower end of the sample tube 4, it is possible in the case of a hollow compensation element 5′″, as a rule after the mounting element 9 has been installed, to also insert a plug 5a made of the same material as the compensation element 5′″ into the opening facing the sample tube 4.

[0072] While in the schematic vertical section according to FIG. 4a the compensation element 5′″ axially movable in the z direction is shown in a central z position relative to the retaining element 9, which is firmly connected to the sampling head and engages in the hollow compensation element 5′″, FIG. 4b shows the compensation element 5′″ relative to the retaining element 9 in a z position just in front of the axial stop in order to minimize the friction with the retaining element firmly connected to the sampling head when the sample tube 4 rotates.

[0073] The features of all the above-described embodiments of the invention may also be combined with one another at least in most cases.

LIST OF REFERENCE SIGNS

[0074] z z axis of the arrangement [0075] 1; 1′ NMR sampling head [0076] 2 RF transmission and reception coil system [0077] 3 opening extending in the z direction [0078] 4 sample tube [0079] 5; 5′; 5″; 5′″ compensation element [0080] 5a plug [0081] 6 annular gap [0082] 7 surrounding wall element [0083] 8 spring device [0084] 9 retaining element [0085] 10; 10′ longitudinal grooves [0086] 11 axial through-hole

LIST OF REFERENCES

[0087] Documents taken into consideration for the assessment of patentability [0088] [1] U.S. Pat. No. 4,365,199 A [0089] [2] U.S. Pat. No. 9,500,726 B2≈DE 10 2013 204 131 B3 [0090] [3] U.S. Pat. No. 6,563,317 B2≈EP 1 239 296 B1≈DE 101 11 672 C2 [0091] [4] http://www.wilmad-labglass.com [0092] [5] U.S. Pat. No. 5,545,994 A [0093] [6] U.S. Pat. No. 5,684,401 A [0094] [7] U.S. Pat. No. 7,514,922 B2≈EP 1 909 111 B1≈DE 10 2006 046 888 B4