This application claims Paris Convention priority of DE 10 2007 004 227.4 filed Jan. 27, 2007 the complete disclosure of which is hereby incorporated by reference.
The invention concerns a cap for an NMR sample tube, with an inner bore for receiving an open end of an NMR sample tube, wherein the inner bore has a narrowing for sealing an NMR sample tube, received by the cap, along the outer periphery of the NMR sample tube.
A cap of this type is disclosed in DE 103 43 405 A1.
Nuclear magnetic resonance (NMR) spectroscopy is a powerful method for analyzing the structure of chemical compounds. Samples to be investigated are exposed to electromagnetic pulses in a strong, static magnetic field. The electromagnetic response of the sample is measured.
In some measuring methods, the samples are filled into sample tubes, wherein the sample comprises the actual measuring substance and a solvent (NMR solvent). The sample tubes are generally round glass or plastic tubes which are open on one end and have an outer diameter of 3 to 5 mm. Handling, in particular filling, of the sample tubes can be facilitated by using caps which comprise e.g. a funnel-shaped access channel. A cap (closing cap) is usually disposed onto a sample tube during the NMR measurement in order to prevent leakage of the sample, in particular, when the sample is quickly rotated during the NMR measurement.
The sample tubes are conventionally closed by a pin-like plug which is inserted into the sample tube. The plug introduces tensile forces into the wall of the sample tube, which could easily damage the sample tube, in particular, when the sample tube is made from glass.
The cap for an NMR sample tube, which is disclosed in DE 103 43 405, is pushed over the open end of a sample tube. The cap, which is produced from plastic material, has a press fit on an inner bore in which the NMR sample tube is disposed. The press fit comprises a contact surface which has the shape of a circular cylindrical surface and has a slightly smaller inner diameter than the outer diameter of the NMR sample tube in the relaxed state. The press fit typically has an axial extension of a few millimeters. When the sample tube is held, the cap is elastically stretched on the press fit and the entire contact surface abuts the outer periphery of the sample tube, thereby sealing the sample tube with respect to the cap in a gas-tight and liquid-tight fashion.
This conventional method is disadvantageous in that the contact surface and the outer wall of the sample tube must be produced with very close tolerances and must be matched to each other in order to achieve good sealing. Since the press fit abuts the sample tube over a large surface, the force acting on the sample tube can be relatively large, so that it can easily break.
One possibility to reduce the force input into the sample tube and increase the production tolerances consists in using a cap material that has a relatively soft elasticity, such as polypropylene. However, soft cap materials are generally less resistant to many NMR solvents, which limits the range of application.
It is therefore the underlying purpose of the present invention to provide a cap for an NMR sample tube, which provides good sealing between the cap and the NMR sample tube and which can be produced from a plurality of materials, in particular, materials having good chemical resistance to NMR solvents.
This object is achieved by a cap of the above-mentioned type which is characterized in that the narrowing is formed as an interior sealing lip.
The inner contour of the inventive cap is designed, such that at least one sealing lip forms one defined narrowing which can tightly surround an inserted sample tube, and which fixes the cap on the outer periphery of the sample tube with sufficient pressure. The sealing lip ensures that the cap and the sample tube are sealed with respect to each other in a liquid-tight and gas-tight fashion.
The sealing lip limits the sealing pressure on a defined zone in the cap material (usually plastic material), wherein the zone is much smaller than in prior art. The overall force acting on the sample tube is reduced. This facilitates sufficient elasticity even when materials having a relatively hard elasticity are used, e.g. to compensate for production tolerances when limited forces act on the sample tube. The mechanical load on the sample tube, which is generally made from glass, as well as the danger of breakage are reduced.
Due to the invention, the cap material is no longer restricted to relatively soft plastic materials. Relatively hard plastic materials, in particular, those having good chemical resistance to NMR solvents, can also be used as cap materials.
The inventive sealing lip is typically designed such that its cross-section tapers towards the interior of the inner bore (i.e. radially to the inside). The contact area between the cap and the sample tube is thereby reduced in a simple fashion. The sealing lip is designed such that, when a sample tube is clamped, the sealing lip (or the cap in the area and in the surroundings of the sealing lip) is deformed within an elastic range. In the clamped state, the sealing lip typically abuts the NMR sample tube in an axial direction over 0.5 mm or less, preferably 0.3 mm or less.
In one particularly preferred embodiment of the inventive cap, the sealing lip has a rounded cross-section on the side facing radially inwardly in the relaxed state. The rounded cross-section facilitates insertion of the NMR sample tube, produces little wear, and provides a small contact surface (in particular with small extension in the axial direction) between the cap and the sample tube.
In an alternative preferred embodiment, the sealing lip has a tapering cross-section on the side facing radially inwardly in the relaxed state. This also produces a small contact surface (in particular with a small extension in the axial direction) between the cap and the sample tube.
In a further particularly preferred embodiment, the cap has a uniform, constant wall thickness in the relaxed state in the area of the sealing lip and in the surroundings of the sealing lip. This produces a type of wave shape of the cap wall at locations, similar to a bellows. This geometry facilitates elastic deformation of the cap wall in the area of the sealing lip and thereby reduces the force input into a held sample tube. When radial forces act onto the sealing lip towards the outside (spreading of the sealing lip), the material of the sealing lip can easily deviate radially towards the outside, thereby also elastically axially displacing wall material. The force is thus partially deflected in the material. The extension forces are substantially limited to the spatial extension of the sealing lip itself. The above-mentioned geometry also facilitates the production of the cap through injection molding, which requires forced de-molding.
In one particularly preferred embodiment of the inventive cap, the inner bore comprises a contact ring for holding the NMR sample tube on its outer periphery, wherein the contact ring is different from the sealing lip. The contact ring is designed to fix a held sample tube in addition to the sealing lip and secure it against tilting relative to the cap. The contact ring may thereby define single contact elements, which abut at points or sections, or also a circumferential annular contact area with the sample tube.
In one preferred further development of this embodiment, the contact ring is disposed closer to an insertion opening for the NMR sample tube than the sealing lip. The upper area of the inner bore, which is limited by the sealing lip and in which gas is compressed when the sample tube is inserted and when a closing cap is provided, is particularly small in this case, and the counter force during insertion is correspondingly small.
In another further development of the above-mentioned embodiment, the contact ring is formed by several separate segments. Each segment individually abuts the sample tube. A cap of this type is particularly easy to mount.
In an alternative further development, the contact ring is designed as a further sealing lip which is disposed inside. This increases the sealing tightness and yields a clean two-point abutment which has particularly good mechanical stability.
In another preferred embodiment of the inventive cap, the cap has a groove on its outer periphery for engagement of a sample gripper, which advantageously facilitates handling of the cap, in particular, by an automatic sample gripper. The groove is preferably circumferential, which is however, not absolutely necessary. Several grooves may be provided to reduce weight or for engagement on several planes.
In a further development of this embodiment, the groove is designed such that at least three, in particular four, gripping fingers of the sample gripper can engage the groove, such that the gripping fingers can exert pressure on two outer edges of the groove. The sample gripper can, in particular, be designed as a gripping device of an NMR spectrometer as is described in DE 103 43 405 A1. In this case, the cap is particularly well suited for handling by a sample gripper having gripping fingers.
In another preferred embodiment, the inner bore is substantially circular cylindrical, in particular, wherein the cap has a substantially rotationally symmetrical design. NMR sample tubes having a circular cross-section are widely used and have proven to be useful. The rotational symmetry of the cap facilitates orientation of the cap including sample tube for sample management and for loading an NMR spectrometer.
In another preferred embodiment, the cap has an access channel to the inner bore, which opens into the inner bore in an upper area beyond the sealing lip facing away from an insertion opening for the NMR sample tube. A sample can be filled into a held sample tube via the access channel, e.g. using an injection needle.
In another preferred alternative embodiment, the cap completely closes the inner bore in an upper area beyond the sealing lip facing away from an insertion opening for the NMR sample tube. A closing cap of this type is generally required for closing a sample tube during an NMR measurement, in particular, when the sample tube rotates during the measurement, e.g. during magic angle spinning (MAS) measurements.
In one particularly preferred embodiment, the cap is produced from plastic material. Plastic materials are preferred, which have a relatively hard elasticity and a high chemical resistance to common NMR solvents, in particular chloroform. One particularly preferred plastic material type having a relatively hard elasticity is ORGALLOY LE 6000.
The invention also concerns an NMR sample configuration, comprising a cap and an NMR sample tube, onto which the cap can be disposed, characterized in that the cap is designed as described above in accordance with the invention. The sealing lip yields liquid-tight and gas-tight mutual sealing.
Further advantages of the invention can be extracted from the description and the drawings. The features mentioned above and below may be used individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but have exemplary character for describing the invention.
The invention is shown and explained in more detail in the drawing.
The inner bore 3 has a narrowing, i.e. a circumferential sealing lip 4. The sealing lip 4 is rounded in its radially innermost area (i.e. the area disposed most closely to the axis of rotation A). The sealing lip 4 thereby tapers in a radially inward direction (in the direction of arrow R).
The inner bore 3 has a further narrowing, i.e. a contact ring 5. The contact ring 5 is formed by several separate segments 6 which project radially inwardly, thereby tapering to the inside, similar to the sealing lip 4.
A sample tube (not shown, see
The cap 1 also has an access channel 8 through which the open end of a held sample tube can be accessed and thereby also the interior of the sample tube, e.g. for filling-in the sample. In an alternative fashion, the cap 1 may also be designed as a closing cap which tightly seals an upper area 9 of the inner bore 3 which is disposed beyond the sealing lip 4 facing away from the insertion opening 2. In this case, the access channel 8 is omitted and replaced by the solid material of the cap.
Several circumferential grooves 10, 11, 12 are furthermore formed on the outer contour of the cap 1. The outer grooves 10 and 12 reduce weight, whereas the central groove 11, at the bottom of which the sealing lip 4 is formed, is provided for engagement with gripper fingers (see
The inner contour of the sealing lip 4 is approximately symmetrical and two flanks 33 thereof extend at an inclination to the axial direction A′ in each case, however, approximately in a straight line. At the narrowest region 34, the inner contour of the sealing lip 4 is rounded.
In an alternative embodiment (shown in
The sample tube 52 is only clamped by a sealing lip 4, wherein the sealing lip 4 is slightly elastically spread. The outer diameter of the sample tube 52 is thereby slightly larger than the smallest inner diameter of the sealing lip 4 in the relaxed state. Typical outer diameters of sample tubes 52 within the scope of the present invention are 1 mm to 5 mm, in particular 3 mm, 4 mm, or 5 mm. The cap 51 or its sealing lip 4 is matched thereto.
Gripping fingers 55 engage a groove 11, extending on the outer periphery of the cap 51, and abut two outer edges 56 of the groove 11, thus providing secure handling, in particular, transport of the sample configuration 50 with an automatic sample gripper to which the gripping fingers 55 belong.
Number | Date | Country | Kind |
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10 2007 004 227.4 | Jan 2007 | DE | national |
20 2007 001 251.9 | Jan 2007 | DE | national |