Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2002-03-04
2003-05-13
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S309000
Reexamination Certificate
active
06563317
ABSTRACT:
This application claims Paris Convention priority of DE 101 11 672.1 filed Mar. 9, 2001 the complete disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention concerns a device for centering an elongated sample tube, filled with a measuring substance, relative to the vertical axis of a nuclear magnetic resonance (=NMR) receiver coil system which is rigidly mounted in a support device.
A device of this type is known from the company leaflet “High Resolution NMR, Probeheads” of the Bruker group from 1995.
In NMR spectroscopy, the exact centering of a sample tube relative to the transmitter and receiver coil is an important precondition to obtain optimum sensitivity of the spectrometer. In particular, the radial centering must be especially accurate since the separation between the receiver coil and the sample tube should be as small as possible to obtain an optimum fill factor. For sample tubes with decreasing sizes, the separation between receiver coil and sample tube must decrease linearly to maintain the same fill factor. Therefore, the requirements for the radial positioning accuracy also increase linearly. In the limiting case, the sample tube consists of a so-called measuring capillary and the requirements for the accuracy of the radial centering are particularly high. These measuring capillaries are preferably used for measuring substances which are only present in very small amounts.
Centering devices are known which can be divided into different accuracy levels, depending on the design:
The accuracy level 1 represents the lowest level of centering accuracy. The above-cited company leaflet of Bruker AG e.g. discloses an arrangement (as shown in
FIG. 1
) with which the sample tube
8
is inserted into the rotor
7
a
of an air turbine (=spinner) and this spinner is axially and radially centered on the conical guiding surface of the stator
2
a
of the air turbine located above the receiver coil
9
. The stator has a conical guiding surface and is not directly mechanically connected to the receiver coil but is indirectly connected to the upper and lower mounting
11
,
12
of the support tube
10
of the receiver coil
9
via the lower support part
3
, the lower part of the probe head
4
, and finally via the upper part
5
of the probe head. The position of the sample tube relative to the receiver coil therefore depends on a plurality of individual parts having different mechanical tolerances which, in the worst case, could add thereby deteriorating the accuracy and reproducibility of the centering.
In particular, it should be noted that the separation between the conical guiding surface and the receiver coil is relatively large. Consequently, even the smallest angular errors in the alignment of the axis of the conical guiding surface have a large influence on the position of the sample tube at the location of the receiver coil. This influence increases, the larger the separation between the conical guiding surface and receiver coil.
FIG. 2
shows a device with the next higher accuracy level 2. It permits more accurate centering of the sample tube compared to the device of FIG.
1
. The sample tube is also located in a spinner
7
a
which is positioned in an axial and radial direction by the conical guiding surface of the stator
2
b
of an air turbine which is located above the receiver coil
9
. In contrast to the arrangement of
FIG. 1
, the conical guiding surface of the stator is directly mounted to the upper part
5
of the probe head. Therefore, connecting the conical guiding surface to the receiver coil requires fewer intermediate parts which decreases the possible addition of mechanical tolerances. The separation between the conical guiding surface and the receiver coil is still as large as in FIG.
1
and angular errors in the alignment of the conical guiding surface could also produce large positioning errors in this case.
The unpublished German patent application with the official file number 100 06 324.1-33 describes a device with an even higher accuracy level 3. The sample tube is also located in a spinner which is positioned in an axial and radial direction by the conical guiding surface of the stator of an air turbine which is located above the receiver coil. The conical guiding surface is not directly connected to the upper part of the probe head (similar to
FIG. 1
) but via various support parts. An important additional feature of this device is a second radial centering which is mounted directly below the receiver coil. This permits nearly complete compensation of the influence of the angular error of the conical guiding surface despite the fact that the separation between the conical guiding surface and receiver coil is similar to the arrangements of
FIGS. 1 and 2
.
Departing from this prior art, it is the object of the present invention to further increase the centering accuracy compared to the above-described known devices using as simple technical means as possible to achieve optimum results even for measuring capillary sample tubes which require the most accurate centering.
SUMMARY OF THE INVENTION
This object is achieved in accordance with the invention in a surprisingly simple and also effective manner in that at least two centering means are provided which are separated from each other in the axial direction of the receiver coil axis and act only in the radial direction on the sample tube, one of which is disposed above and the other below the receiver coil, and at least one positioning means which acts only in the axial direction on the sample tube, which can be located either below or above the NMR receiver coil, wherein the centering means which act only in the radial direction are rigidly connected to the support device for mounting the receiver coil.
The two axially separated and only radially acting centering means ensure optimum radial centering of the sample tube even if same has the very small diameter of conventional measuring capillaries used for examination of very small substance amounts. The inventive rigid mechanical connection between the two radially acting centering means and a support device to which the NMR receiver coil system is rigidly connected ensures that the sample tube is necessarily radially centered relative to the NMR receiver coil system. Additional and independent axial centering is also provided which ensures very high overall centering accuracy. Moreover, separation of the individual centering functions provides for a particularly high number of degrees of freedom for the geometric design of the overall centering device such that centering can be effected as geometrically close to the receiver coil system as possible.
One particularly simple embodiment of the inventive device is characterized in that the positioning means which acts on the sample tube in the axial direction only is disposed below the NMR receiver coil system and comprises a stop part on which the sample tube is supported in the operating position. Axial centering of the sample tube is therefore technically straightforward but nevertheless precise.
In a further preferred embodiment of the inventive device, the positioning means which acts on the sample tube in the axial direction only, is alternatively disposed above the NMR receiver coil system and comprises a mounting sleeve which is disposed radially around the sample tube like a collar in such a manner that it cannot slip and which, in the operating position of the sample tube, abuts smoothly with a horizontal end face on a horizontal stop surface disposed above the NMR receiver coil system. This embodiment is technically more demanding than that described above, but considerably facilitates handling of the system during operation.
In a particularly advantageous further development of this embodiment, the stop surface for the mounting sleeve is provided in the bottom region on the inside of a rotor which is part of an air turbine for positioning and optionally for rotation of the sample tube and comprises a central axial inner bore
Marek Daniel
Seydoux Roberto
Warden Michael
Bruker BioSpin AG
Lefkowitz Edward
Shrivastav Brij B.
Vincent Paul
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