Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2001-01-22
2002-08-20
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S322000, C324S300000
Reexamination Certificate
active
06437570
ABSTRACT:
This application claims Paris Convention priority of DE 100 06 323.3 filed Feb. 12, 2000 the complete disclosure of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The invention concerns an NMR (=nuclear magnetic resonance) probe head comprising an RF (=radio frequency) receiver coil system, which can be cooled down to cryogenic temperatures, and a room temperature pipe extending in a z direction for receiving a sample tube containing a sample substance to be examined through NMR measurements.
A cooled NMR probe head of this type is e.g. known from U.S. Pat. No. 5,247,256.
The probe head is installed in a magnet, for generating a highly homogeneous static B
0
field, and comprises RF receiver coils disposed about a z axis which are cooled down during operation to temperatures of approximately 10 to 25 K by means of suitable heat exchangers and heat conducting elements to improve the signal-to-noise-ratio of the received NMR signal during the measurement. The RF receiver coils are in an evacuated region for heat insulation reasons which is formed essentially by a usually metallic casing of the probe head which is penetrated by a room temperature pipe disposed cylindrically about the z axis for receiving a sample tube. To permit passage of the RF signals from the sample to the RF receiver coils, the otherwise metallic room temperature pipe is replaced in the axial region of the coils by an RF permeable inner pipe, in most cases a glass pipe, which is connected to the metallic parts of the room temperature pipe in a vacuum-tight fashion.
After insertion of the sample tube into the room temperature pipe from the bottom, it is substantially maintained at a desired temperature (usually approximately 300K) using warm air flowing from below through the room temperature pipe to control the temperature of the sample substance. This, however, causes the associated problem that the measuring sample “feels” the considerably cooler surroundings of the NMR resonator, cooled down to 10 to 25 K, and radially radiates heat in this direction. This lost heat must be continuously replenished by the surging warm tempering air flow to ensure that the measuring sample remains essentially at the desired temperature. In consequence, an axial and radial temperature gradient is produced in the measuring sample which strongly impairs the NMR measurement.
It is therefore the underlying purpose of the present invention to provide a cooled NMR probe head comprising the above-mentioned features wherein the temperature gradient in the z direction occurring during operation is considerably reduced without thereby impairing the NMR measurement.
SUMMARY OF THE INVENTION
This object is achieved in accordance with the present invention in a both surprisingly simple and effective manner by providing a tempering means between the RF receiver coil system and the sample tube which extends in the z direction and radially surrounds the sample tube and is almost completely transparent to RF fields, or at least has an absorption for RF fields of <5%, preferably <1%.
In addition to exchangeable sample tubes, the NMR probe heads in accordance with the invention also include so-called flow-through heads wherein the sample tube remains fixedly installed and the fluid to be examined is introduced through a thin conduit on the one side (bottom) and is guided out on the other side (top). Probe heads of this type may be used in continuous passage and also in a flow and stop mode (for an extended measuring period). These probe heads are used for rapid introduction of the sample as well as for an important analysis step following a liquid chromatography separating cell. The former are called flow-through probe heads, the latter LC-NMR coupling. Probe heads of this type are also referred to as LC heads (liquid chromatography, in particular also HPLC High Pressure Liquid Chromatography). Probe heads of this type can particularly profit from cryotechnology and also from the modifications in accordance with the invention.
These inventive modifications prevent dissipation of heat from the measuring sample and thus uneven cooling without significantly impairing the received NMR signals. The principal advantage of such a tempering means compared to a conventional heated air flow for the sample tube is the fact that the thermal efficiency can act uniformly through the entire axial length of the sample tube. The central area is thus as well tempered as the edge areas thereby effectively preventing axial temperature gradients.
The heating means in accordance with the invention can be used individually and also in combination with an air flow tempering means. A combination of both heating types is particularly advantageous for optimum suppression of the residual temperature gradients.
In contrast thereto, a conventionally heated air flow, without the heating means in accordance with the invention, usually enters into the room temperature pipe at the lower end of the sample tube, starts to heat up the sample tube at this location and continues to cool down while rising in the axial direction. The temperature of the heated air flow in the upper region of the sample tube will therefore always be less than in the lower area thereby inevitably reducing the tempering performance in the upper region of the sample tube. As a result, there will always be an axial temperature gradient which can be somewhat reduced by increasing the amount of air per unit time, however cannot be prevented in principle. Moreover, the corresponding countermeasures are highly limited since, if the amount of air per unit time is too large, vibration free positioning or proper rotation of the sample tube can no longer be guaranteed.
Through corresponding selection of the tempering means with respect to its absorption behavior of RF fields, one tries to obtain an almost complete transparency to the RF fields to allow as free a passage as possible of the measuring signal from the sample to the RF receiver coil system.
The tempering means of the inventive NMR probe head can be realized in technically completely different ways, e.g. through heating with electric current but also heating through radiation or thermal conduction in the region about the sample tube.
A particularly preferred embodiment of the inventive NMR probe head is characterized in that the tempering means comprises a layer radially surrounding the sample tube in the axial region of the RF receiver coil system having a radial thickness of <1 mm, preferably <50 &mgr;m and which is made from a material which at least partially absorbs radiation in a wavelength range of 100 nm≦&lgr;≦100 &mgr;m and which is transparent to radiation in a wavelength range of &lgr;>100 mm. Absorption of thermal radiation in the layer permits temperature control of the sample tube in the corresponding axial region.
The NMR probe head in accordance with the invention preferably comprises a heating means for uniformly heating the layer, which can be designed with different technical means.
A preferred further development is characterized in that the heating means comprises a device for irradiating the layer with radiation in a wavelength range of 100 nm≦&lgr;≦100 &mgr;m, in particular with thermal radiation thereby providing contact-free and uniform heating of the layer.
The device for irradiating the layer is preferably disposed on the side of the room temperature bore facing the RF receiver coil system. Since the receiver coil system is generally accommodated in an evacuated region, the thermal radiation can pass through the vacuum to the heating layer without obstruction.
One further development is particularly space-saving with which the layer is disposed on the side of the room temperature pipe facing the RF receiver coil system.
Many materials which can be used to construct the room temperature pipe already absorb in the desired wavelength range such that heating up using radiation does not require a special radiation-absorbing layer.
The radiation absorbing heating lay
Bruker BioSpin AG
Lefkowitz Edward
Shrivastav Brij B.
Vincent Paul
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