Abstract:
There is disclosed an NMR detector permitting NMR measurements to be performed well by making use of the merit of a meander coil if a trace amount of solution sample is investigated. Furthermore, an NMR spectrometer equipped with this detector is offered. The NMR detector comprises a planar sample cell and a planar detection coil disposed close to the sample cell. The sample cell has parallel, elongated sample spaces in connection with each other. The detection coil consists of a continuous elongated conductor repeatedly bent into segments which are substantially parallel to the sample spaces. Each of the segments has a major axis in the longitudinal direction of each of the sample spaces.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an NMR detector used in an NMR spectrometer and to an NMR spectrometer equipped with the NMR detector. 
     2. Description of Related Art 
     An NMR spectrometer is an apparatus for gaining an NMR spectrum by placing a sample under investigation within a static magnetic field, irradiating the sample with an RF pulse, and then detecting a feeble RF signal (NMR signal) emanating from the sample. The molecular structure can be analyzed by extracting molecular structural information contained in the spectrum. 
       FIG. 1  schematically shows the structure of an NMR spectrometer having an RF oscillator  1  emitting an RF pulse. The phase and amplitude of the RF pulse are controlled by a phase controller  2  and an amplitude controller  3  and sent to a power amplifier  4 . 
     The RF pulse is amplified to a power necessary to excite an NMR signal by the power amplifier  4  and then sent to an NMR probe  6  via a duplexer  5 . The pulse is directed at a sample under investigation (not shown) placed within the NMR probe  6 . After the RF irradiation, a feeble NMR signal emanating from the sample is sent to a preamplifier  7  again via the duplexer  5  and amplified up to a signal intensity permitting reception. 
     A receiver  8  converts the frequency of the RF NMR signal amplified by the preamplifier  7  into an audio frequency that can be converted into a digital signal. The audio frequency of the NMR signal converted by the receiver  8  is converted into a digital signal by an analog-to-digital (A/D) converter  9  and sent to a control computer  10 . 
     The computer  10  controls the phase controller  2  and amplitude controller  3  and Fourier-transforms the NMR signal accepted in the time domain. The computer automatically corrects the phase of the Fourier-transformed NMR signal. Then, the signal is displayed as an NMR spectrum. 
       FIG. 2  shows the structure of the prior art NMR detector. The NMR probe has the detector  11  in which a detection coil  13  is mounted to emit an RF pulse for exciting a sample  12  to be investigated and to detect an NMR signal emanating from the sample  12 . The detection coil  13  cooperates with a tuning and matching circuit  14  to constitute an RF resonant circuit. This RF resonant circuit sends and receives RF pulses and NMR signals to and from the sample  12  contained in an NMR cell  15  placed within the probe  11 . Where the sample contained in the cylindrical NMR cell is in the form of a solution, high sensitivity can be obtained by this method of measurement. However, there is the problem that where the sample assumes a planar form, high sensitivity cannot be obtained. 
     In recent years, an NMR detector using a meander coil has been proposed to detect an NMR signal originated from a planar sample at high sensitivity (see U.S. Pat. No. 6,326,787).  FIGS. 3A–3C  show one example of an NMR detector using a meander coil.  FIG. 3A  is a plan view of the detector;  FIG. 3B  is a cross-sectional view taken in a lateral direction as indicated by the broken line in  FIG. 3A ; and  FIG. 3C  shows the direction of RF magnetic field around coil wires. In  FIGS. 3A–3C , a base plate or substrate  16  forms a sample cell. The base plate  16  is made of an insulator such as a glass plate of low dielectric loss to achieve high-sensitivity NMR measurements. 
     A meander coil  17  consisting of an elongated conductor repeatedly bent into comb teeth-like straight segments which are regularly spaced from each other and which are uniform in length is mounted on the surface of the base plate  16 . The segments at both ends of the meander coil  17  extend downward and are placed opposite to each other under the bent portions. A capacitor  18  made of a dielectric is bridged across the opposite ends. An LC resonant circuit is formed by the inductance L of the coil  17  and the capacitance C of the capacitor  18 . Thus, if radio waves are injected into the meander coil  17 , an RF magnetic field B 1  is produced across the meander coil as indicated by the arrow in  FIG. 3C . An RF magnetic field B 1  is applied to a planar sample  19  placed on the coil  17 . If a static magnetic field B 0  is previously applied parallel to the plane of the paper, an NMR signal from the sample  19  can be observed by interaction with the RF magnetic field B 1 . 
     In the prior art, the sample space extends planarity. In the sample space, in directions crossing the meander coil, the phase of the produced RF magnetic field is rotated. Therefore, there is the problem that if the sample diffuses in a direction crossing the meander coil, the intensity of the NMR signal decreases. Especially, in a case where the spacing between the adjacent segments of the bent conductor, or meander coil, is small, this effect is conspicuous. Therefore, samples making use of the feature of the meander coil, i.e., high sensitivity to trace amounts of sample, have been limited to solid samples. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an NMR detector which makes use of the merit of a meander coil and permits good NMR measurements of even trace amounts of solution samples. 
     This object is achieved by an NMR detector in accordance with the present invention, the detector comprising: a planar sample cell and a planar detection coil placed close to the sample cell which has a plurality of parallel and elongated sample spaces in connection with each other. The detection coil consists of a continuous elongated conductor repeatedly bent into segments each of which has a major axis in the longitudinal direction of each sample space and is substantially parallel to the sample space. 
     In one feature of the present invention, the sample spaces are filled with a solution sample. 
     In another feature of the present invention, each of the sample cells has a substantially straight elongated portion. 
     In a further feature of the present invention, the parallel elongated sample spaces are connected in series with each other. 
     In yet another feature of the present invention, the parallel elongated sample spaces are connected in parallel with each other. 
     The present invention also provides an NMR spectrometer equipped with an NMR detector comprising a planar sample cell and a planar detection coil placed close to the sample cell which has a plurality of parallel and elongated sample spaces in connection with each other. The detection coil consists of a continuous elongated conductor repeatedly bent into segments each of which has a major axis in the longitudinal direction of each sample space and is substantially parallel to the sample space. 
     In one feature of the present invention, the sample spaces are filled with a solution sample. 
     In another feature of the present invention, the elongated sample cells are substantially straight. 
     In a further feature of the present invention, the parallel elongated sample spaces are connected in series with each other. 
     In yet another feature of the present invention, the parallel elongated sample spaces are connected in parallel with each other. 
     In the NMR detector according to the present invention, the planar sample cell having the parallel elongated sample spaces and the planar detection coil are placed in proximity to each other. The sample spaces are in connection with each other. The coil consists of the continuous elongated conductor repeatedly bent into the segments substantially parallel to the sample spaces. Each segment has a major axis in the longitudinal direction of each sample space. Therefore, if the amount of the sample contained in the solution sample is quite small, an NMR measurement can be performed well. 
     The NMR spectrometer according to the present invention is equipped with the NMR detector comprising the planar sample cell and the planar detection coil placed close to the sample cell which has the plurality of parallel and elongated sample spaces in connection with each other. The detection coil consists of the continuous elongated conductor repeatedly bent into the segments each of which has a major axis in the longitudinal direction of each sample space and is substantially parallel to the sample space. Therefore, if the amount of the sample contained in the solution sample is quite small, an NMR measurement can be performed well. 
     Other objects and features of the present invention will appear in the course of the description thereof, which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of the prior art NMR spectrometer; 
         FIG. 2  is a schematic vertical cross section of the prior art NMR detector; 
         FIGS. 3A ,  3 B, and  3 C show the prior art meander coil; 
         FIGS. 4A ,  4 B,  4 C,  4 D, and  4 E show one NMR detector according to the present invention; 
         FIGS. 5A and 5B  show another NMR detector according to the present invention; 
         FIGS. 6A and 6B  show a further NMR detector according to the present invention; 
         FIGS. 7A ,  7 B,  7 C, and  7 D show yet another NMR detector according to the present invention; 
         FIGS. 8A and 8B  show still another NMR detector according to the present invention; 
         FIGS. 9A and 9B  show an additional NMR detector according to the present invention; and 
         FIGS. 10A and 10B  show a still further NMR detector according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Seven embodiments of the present invention are hereinafter described with reference to the accompanying drawings. 
     Embodiment 1 
       FIGS. 4A–4D  show one NMR detector according to the present invention. The sample cell is shown in  FIGS. 4A and 4B . The detection coil is shown in  FIGS. 4C and 4D . The direction of RF magnetic field around detection coil wires is shown in of  FIG. 4E .  FIG. 4A  is a plan view of the sample cell and  FIG. 4B  is a cross-sectional view taken in a lateral direction as indicated by the broken line of  FIG. 4A .  FIG. 4C  is a plan view of the detection coil.  FIG. 4D  is a cross-sectional view taken in a lateral direction as indicated by the broken line of  FIG. 4C .  FIG. 4E  is an expanded view of  FIG. 4D . 
     In  FIG. 4A , a base plate  20  forms a sample cell and is made of an insulator, such as a glass plate of low dielectric loss, to achieve high-sensitivity NMR measurements. As shown in  FIG. 4B , the base plate  20  consists of two glass plates  20   a  and  20   b  bonded together. The repeatedly bent comb teeth-like meandering grooves are formed as sample spaces  21  on one glass plate  20   a  by a chemical etching process of the glass plate  20   a . The grooves are regularly spaced from each other and uniform in length. The sample spaces  21  consist of the elongated grooves in connection with each other. The grooves are channels through which a solution sample flows. Sample ports  22  and  23  for introducing and expelling a liquid sample into and from the sample spaces  21  are formed on the other glass plate  20   b . The two glass plates  20   a  and  20   b  are melted and bonded together based on a microchip fabrication method, thus forming a planar sample cell (see Published Technical Disclosure 2004-502547 of Japan Institute of Invention and Innovation). 
     In  FIG. 4C , a base plate  24  forms the detection coil. The base plate  24  is made of an insulator, such as a glass plate of low dielectric loss, to achieve high-sensitivity NMR measurements. A planar meander coil  25  is formed on the surface of the base plate  24 . The coil  25  is made of a thin metal film fabricated by sputtering of a metal. The metal film forms a continuous elongated conductor that is repeatedly bent into comb teeth-like meandering segments that are regularly spaced from each other and are uniform in length. The meander coil  25  has both end portions extending downward and placed opposite to each other under the bent portions of the conductor. A capacitor  26  made of a dielectric is bridged across the opposite ends. Thus, a planar LC resonant circuit is formed by the inductance L of the meander coil  25  and the capacitance C of the capacitor  26 . 
       FIGS. 5A and 5B  show the manner in which the base plate  20  of the sample cell and the base plate  24  of the detection coil fabricated in this way are placed in proximity to each other. In  FIG. 5A  is a plan view of the resulting NMR detector and  FIG. 5B  is a cross-sectional view taken in a lateral direction as indicated by the broken line in  FIG. 5A . 
     The base plate  24  of the detection coil is firmly fixed within an NMR probe (not shown). On the other hand, the base plate  20  of the sample cell is inserted into the NMR probe (not shown) from outside it and placed close to the coil  25  within the NMR probe such that the meander coil  25  and sample spaces  21  are placed in a positional relationship as shown in  FIGS. 5A and 5B , using a retainer tool (not shown). 
     As can be seen from the figure, the spacing between the sample spaces  21  formed on the base plate  20  is equal to the spacing between the adjacent segments of the meander coil  25  formed on the base plate  24 . Therefore, the straight elongated portions of the sample spaces  21  are substantially parallel and exactly opposite to the straight segments of the meander coil  25 . Consequently, when radio-frequency waves are injected into the meander coil  25 , an RF magnetic field B 1  is produced across the coil as indicated by the arrow along the plane of the paper shown in of  FIG. 4E . The field B 1  is applied to the sample cells (base plate)  20  placed on the meander coil  25 . The sample spaces  21  are previously filled with a solution sample. Also, a static magnetic field B 0  is applied in a direction indicated by the arrow B 0  in of  FIG. 4A . Because of the interaction with the RF field B 1 , an NMR signal from the solution sample filled in the cells  20  can be observed. 
     At this time, the width W of the sample spaces taken in a direction crossing the meander coil is limited. Let B be the spacing between the adjacent segments of the meander coil in  FIG. 4B . A variation in the phase of a signal due to diffusion of the sample is less than 180°×W/B. Attenuation of the signal is suppressed. 
     In  FIG. 5B , if the distance A between the coil surface and the sample surface is set to approximately 0.8 times the spacing B between the adjacent segments of the coil, the same strength of RF magnetic field is applied also to the bends C of the sample channels. Hence, the bends act as areas detected under the same conditions (see U.S. Pat. No. 6,326,787). 
     The base plate  24  on which the meander coil  25  is carried can be removed from the NMR probe (not shown) according to the need. When an NMR measurement is performed in a different frequency band, the meander coil is appropriately replaced by another meander coil having frequency characteristics corresponding to the different frequency band. 
     Embodiment 2 
     In this embodiment, a sample cell having straight segments longer than the detection coil as shown in  FIGS. 6A and 6B  is used. This embodiment is characterized in that the bends C of the sample channels are not contained in the NMR detection area. 
     Accordingly, in this structure, in the areas located outside the detection area, no NMR signal can be detected. Where there is a difference between the magnetic susceptibility of the sample and the magnetic susceptibility of the glass forming the sample cell, the homogeneity of the static magnetic field in the detection area can be enhanced by intentionally separating the bends C of the channels from the detection area. As a result, the linewidth of the NMR spectrum can be narrowed. Hence, the resolution can be improved. 
     Embodiment 3 
     In this embodiment, plural independent sample spaces through which plural samples can flow are formed in one sample cell as shown in  FIGS. 7A ,  7 B,  7 C, and  7 D. This makes it possible to measure plural samples at the same time. Furthermore, plural samples can be detected in turn without the sample cell being removed from the NMR measurement portion. 
     This can be used in the following two ways: 
     (a) A first sample area  27  and a second sample area  28  are filled with different samples. Resulting NMR signals are measured at the same time. 
     (b) A first sample is loaded into the first sample area  27 . The resulting NMR signal is measured and then the first sample is extracted. Thereafter, the position of the sample cell is shifted. A second sample is loaded into the second sample area  28 . Then, the resulting NMR signal is measured. 
     Embodiment 4 
     In Embodiments 1 to 3, the straight elongated portions of the sample spaces  21  are exactly opposite to the straight segments of the detection coil  25 . Alternatively, the straight elongated portions of the sample spaces  21  may be staggered relative to the straight segments of the detection coil  25  as shown in  FIGS. 8A and 8B . 
     Embodiment 5 
     In Embodiments 1 to 4, the spacing B between the grooves in the sample spaces  21  is equal to the spacing C between the adjacent segments of the detection coil  25 . As shown in  FIGS. 9A and 9B , the spacing B between the grooves in the sample spaces  21  may be different from the spacing C between the adjacent segments of the detection coil  25 . In this case, the distance A between the sample space surface and the detection coil surface is set to approximately 0.8 times the spacing C between the segments of the detection coil  25 . Consequently, the same strength of RF magnetic field is applied to all the sample spaces  21 . It is possible that every sample space  21  acts as the same detection space. 
     Embodiment 6 
     In Embodiments 1 to 5, the plural elongated sample spaces  21  are connected in series. This meander sample cell is constructed as if one channel were repeatedly bent. The plural elongated sample spaces  21  may be connected in parallel with each other within the base plate  20  as shown in  FIGS. 10A and 10B . 
     Embodiment 7 
     By incorporating an NMR detector as shown in any one of Embodiments 1 to 6 into the existing NMR spectrometer, a novel type of NMR spectrometer capable of performing NMR measurements well if the amount of sample in the solution sample is quite small can be obtained. 
     NMR detectors according to the present invention can be widely used in NMR instruments. 
     Having thus described my invention with the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.