Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2002-06-05
2004-05-25
Gutierrez, Diego (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S318000
Reexamination Certificate
active
06741079
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a sample holder for use in an NMR spectrometer with liquid microsamples, comprising a rotationally symmetric rotor with a central bore for receiving, centering and holding a hollow cylindrical sample tube of glass or quartz with one closed and one open end which can be temporarily closed and which has an outer diameter of 5 mm or less in the region of its closed end. The invention also concerns a method for filling such a sample holder.
Such a sample holder for microsamples, i.e. liquid samples in a range of less than one microliter to a maximum of several milliliters is conventional equipment for NMR spectrometers manufactured by Bruker BioSpin GmbH (see also U.S. Pat. No. 5,517,856). In conventional sample holders, a glass tube having an outer diameter of approximately 1.0 mm to 2.5 mm and drawn to a length of approximately 100 mm is used as sample tube. A liquid microsample is filled into this tube using i.a. a pipette or injection needle.
The filled tube is subsequently inserted into the central bore of a hollow screw having a clamping and a sealing surface, the screw having an inner diameter which is slightly larger than the outer diameter of the tube to thereby center the tube. Different screws are provided for the different tube diameters, the screws having identical outer dimensions but matched hollow bores. The tube is fixed by the screw in a 10 mm plunger and simultaneously sealed. The sample tube fixed in this fashion is subsequently introduced, together with the 10 mm plunger, into a so-called NMR rotor having a coaxial bore of 10 mm. The rotor primarily comprises coaxial cylinders having a common central bore but different outer diameters, the two cylinders being joined via a conical section. The rotor and the sample tube are lowered vertically from the top in opposition to a gas flow and into the room temperature bore of the cryostat containing the superconducting NMR spectrometer magnet such that the conical part of the rotor is either supported on a corresponding part of a stator disposed in the probe head of the spectrometer or, in response to a gas flow, rotates directly thereabove on a gas cushion about its axis which then coincides with the magnet axis. In this rotor position, the filled part of the sample tube is precisely in the central region of the magnet coil and is closely surrounded by a radio frequency coil for exciting and detecting NMR sample signals. The sample itself should have as elongated a cylindrical shape as possible with both of its ends projecting past the sensitivity region of the RF coil to prevent excessive disturbance on the homogeneity of the magnetic field by the intrinsic susceptibility of the sample. Moreover, it should fill as large a portion of the RF coil sensitive volume as possible in order to maximize the signal-to-noise ratio. For this reason, the above-mentioned sample holders have also been used for microsamples. Alternatively, 5 mm tubes having an end tapering to 2.5 mm have been used instead of a standard sample holder having a tube without tapering. They can also be used in automatic or semi-automatic spectrometer operation, i.e. with automatic sample changer, robot gripping arm and with lowering and ejection via computer-controlled gas flow. The materials used in the sample holder must, of course, meet certain criteria which are absolutely necessary for NMR spectrometer operation. They should have as small a magnetic susceptibility as possible to prevent disturbance of the field homogeneity in the measuring volume, have little electrical conductivity, or produce little dielectric RF losses and, depending on the type of nucleus examined, they must be free from compounds which could produce NMR disturbance signals, i.e. free from protons and C
13
. Frequently used materials are glass, quartz, and Teflon®. Sample tubes of the above-mentioned type which are drawn to a thickness of 2.5 mm are described e.g. in the catalogue No. 851 (1985), page 28, of the Wilmad Glas Company Inc., New Jersey, USA and are distributed as type 520-1.
Sample tubes from glass with small, uniform cross-sections have also been used for microsamples having openings which are welded closed after filling-in the sample. These tubes have then been manually installed into the probe head of an NMR spectrometer and manually removed after the measurement. Automatic or reasonably user-friendly sample change was not possible.
Patents Abstracts of Japan, Sect. E, Vol. 3 (1979) No. 96 (E-130) discloses a sample holder for an NMR spectrometer having a sample tube of constant diameter which is inserted into the central bore of a rotor and is fixed by means of a pressure body pressed onto its open end. The lower end of a bent sample tube containing the sample is disposed on the axis by means of a guiding body and fixed through tightening a chuck, pressing the pressure body such that the sample tube remains fixed even after the guiding body is removed. This is intended to prevent the measuring sample from being outside of the NMR spectrometer measuring volume during the measurement, even when the sample tube is bent.
Other conventional techniques are also used outside the field of analytic spectrometers for e.g. clamping of round materials, e.g. in the heavy machinery industry, e.g. for clamping jaws of lathes or in other fields of application such as e.g. fixing lead pencil refills in writing instruments.
The above-mentioned sample holder for microsamples still has defects which were partly discussed above. The use of a screw for centering the sample tube inevitably transfers the coaxial asymmetry of the thread to the sample tube. Although optimization in production largely eliminates this defect it is, however, still present to some extent. Centering is fundamentally worse than with a central, precision bore. Spinning, i.e. rotating at high speed to improve the homogeneity was not possibly in many cases. Time-consuming shimming is then unavoidable in order to guarantee a sufficiently homogeneous field throughout the measuring region. Assembly and exchange of the sample tube is difficult since the entire plunger together with the mounted sample tube must always be removed from the spinner. The thin walls of the tubes used are very likely to break. For automatic filling of the sample tubes, it would be advantageous to use tubes shorter than the conventional 220 mm tubes having inner diameters in excess of 2.5 mm. Filling of 100 mm tubes is easier and produces less bubbles than in a 220 mm tube, in particular for the small inner diameters used for micro or milliliter tubes.
Disadvantageously, the probability that wall thicknesses in the narrowed region are not constant also increases with length. All these defects have a direct and very often fatal effect on the field homogeneity and therefore on the resolution of the spectrometer.
There is therefore a need for an NMR sample holder of the above-mentioned type which permits automatic spectrometer operation providing simpler and therefore safer and improved handling, and which is less susceptible to centering errors, wherein the amount of evaporated liquid sample is to be reduced e.g. compared to the conventional 5 mm sample tubes, as well as for a method for filling, releasing or fixing the sample tube of such a sample holder by which nearly no sample liquid is lost.
SUMMARY OF THE INVENTION
For a sample holder, this object is achieved by an NMR sample holder for liquid microsamples in an NMR spectrometer with the following components: 1) a rotationally symmetric rotor with a central bore; 2) a substantially cylindrical plunger with a thicker and a thinner region which can be inserted from one side into the central bore of the rotor and which is or can be connected therewith, wherein the plunger has a mounting means at its inserted end; 3) a hollow-cylindrical sample tube of glass or quartz with a closed and an open end which has a constant outer diameter of less than 11 mm across its entire length; 4) a clamp whose cylindrical part fits into the central bore of
Braumann Ernst Ulrich
Hofmann Martin
Bruker Biospin GmbH
Fetzner Tiffany A.
Gutierrez Diego
Vincent Paul
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