Microcoil

So we choose to use silicium microcoil. For example, the LETT [2] can realize 2 layer coils with 21 turns per layer, 7 pm wide by 3 pm thick track,... 

The size of sample required has been reduced by a number of technical developments including micro inverse probes and micro cells (references in Martin et al. 1998), and has been reduced even further using a newly developed 1.7-mm submicro inverse-detection gradient probe (Martin et al. 1998). The combined use of inverse detection probes with solenoid microcoils has also been developed to reduce sample volumes for NMR (Subramanian and Webb 1998). 

Subramanian R, AG Webb (1998) Design of solenoidal microcoils for high-resolution C NMR spectroscopy. Anal Chem 70 2454-2458. ... 

The development of microcoil techniques has been reviewed by Minard and Wind [24, 25] and by Webb [26]. In a more recent publication Seeber et al. reported the design and testing of solenoidal microcoils with dimensions of tens to hundreds of microns [27]. For the smallest receiver coils these workers achieved a sensitivity that was sufficient to observe proton NMR with an SNR of unity in a single scan of 10 pm3 (10 fL) of water, containing 7 x 1011 proton spins. Reducing the diameter of the coil from millimeters to hundreds of microns thus increases its sensitivity greatly, allowing analysis of pL to pL sample volumes. 

Although one can potentially attempt to cool the rf microcoil, which according to Eq. (2.5.2) would further improve the SNR by reducing the Rcoii term in the denominator, in the case of microcoils the sample is extremely close to the coil and if the sample has to be kept at room temperature, cooling the coil alone is extremely difficult. 

Fig. 2.5.6 Schematic of the experimental setup used to monitor reaction kinetics with a multiple microcoil system. Two syringes on the pump inject the reactants into two capillaries. The reactants are mixed rapidly with a Y-mixer. After mixin g, the solution flows through the...

Fig. 2.5.8 COSY spectra of 300 mM D-xylose plus 400 mM borate at pD = 10. The spectra were recorded at 300 MHz with a single NMR microcoil using the instrumentation shown in Figure 2.5.5. (a) Continuous-flow. Flow rate = 2 pL min-1, corresponding to a reaction time t 165 s. The on-flow COSY is highlighted by the presence of intense reactant peaks in the region of 3.0-3.5 ppm. (b) Stopped-flow. The spectrum shows very weak reactant cross...

K. R. Minard, R. A. Wind 2001, (Sole-noidal microcoil design - Part II Optimizing winding parameters for maximum signal-to-noise performance), Concepts Magn. Reson. 13, 190. 

A. G. Webb 1997, (Radiofrequency microcoils in magnetic resonance), Progr. Nucl. Magn. Reson. Spectrosc. 31, 1. 

D.L. Olson, T. L. Peck, A. G. Webb, R. L. Magin, J. V. Sweedler 1995, (High resolution microcoil H-NMR for mass limited nanoliter-volume samples), Science 270, 1967... 

M.E. Lacey, Z. J. Tan, A. G. Webb, J. V. Sweedler 2001, (Union of capillary high-performance liquid chromatography and microcoil nuclear magnetic resonance spectroscopy applied to the separation and identification of terpenoids), J. Chromatogr. A 922(1-2), 139. 

Fig. 2.6.10 Specialized experimental set-up for microfluidic flow dispersion measurements. Fluid is supplied from the top, flows via a capillary through the microfluidic device to be profiled and exits at the bottom. The whole apparatus is inserted into the bore of a superconducting magnet. Spatial information is encoded by MRI techniques, using rf and imaging gradient coils that surround the microfluidic device. They are symbolized by the hollow cylinder in the figure. After the fluid has exited the device, it is led through a capillary to a microcoil, which is used to read the encoded information in a time-resolved manner. The flow rate is controlled by a laboratory-built flow controller at the outlet [59, 60].

FIGURE 4.5 Schematic design of a microcoil NMR probe. (From Rehbein, J. et al., Characterization of Bixin by LC-MS and LC-NMR, John Wiley Sons Ltd., 2387, 2007. With permission.)... 

In summary, NMR spectroscopy is an extremely versatile tool useful that enables researchers to understand the structure of natural products such as carotenoids. For a full structural assignment, the compound of interest has to be separated from coeluents. Thus, it is a prerequisite to employ tailored stationary phases with high shape selectivity for the separation in the closed-loop on-line LC-NMR system. For the NMR detection, microcoils prove to be advantageous for small quantities of sample. Overall, the closed-loop system of HPLC and NMR detection is very advantageous for the structural elucidation of air- and UV-sensitive carotenoids. 

Krucker, M., Lienau, A., Putzbach, K., Grynbaum, M. D., Schuler, P., and Albert, K. 2004. Hyphenation of capillary HPLC to microcoil 11 NMR spectroscopy for the determination of tocopherol homologues. Anal. Chem. 76 2623-2628. 

Webb, A. G. 1997. Radio frequency microcoils in magnetic resonance. Prog. NMR Spec. 31 1-42. 

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