Solenoidal probe

The coil sensitivity of solenoidal probes is inversely related to the coil diameter [32], The S/N per unit volume for solenoidal coils with diameter greater than 100 pm is approximated by Eq. (2) [34] ... 

NMR instrumentation consists of three chief components a magnet, a spectrometer console, and a probe. While in the past much solid state NMR research was conducted on home-built equipment, the current trend is toward the acquisition of commercial systems. The magnets used for solid state NMR applications generally are superconducting solenoids with a cylindrical bore of 89-mm diameter. The most common field strengths available, 4.7, 7.0, 9.4, and 11.7 Tesla, correspond to proton resonance frequencies near 200, 300, 400, and 500 MHz, respectively. 

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). 

Figure 2.38 Diagram of an NMR probe. The solenoid coils on the pole faces of the magnet produce the variable magnetic field. The direction of the magnetic field through the sample is indicated by M.

FIGURE7.14 Instrumental setup for CE-NMR with online NMR detection using a solenoidal microcoil probe. 

Another important application of hyphenated NMR methods is to provide insights into processes that affect the separation. Eor example, online NMR detection of the water chemical shift was used to noninvasively probe intracapillary temperatures in CE separations with subsecond temporal resolution and spatial resolution on the order of 1 mm [111]. Lacey et al. [112] followed up this report with a second NMR study using a novel 2-turn vertical solenoidal coil to measure temperature increases of more than 50 C in a chromatographic frit of the type used in CEC. Insights into the mechanisms underlying cITP have also been investigated utilizing online NMR... 

One of the disadvantages concerns the fact that in axial magnets it is rather difficult to use probes with solenoid RF coils. The difficulties are related to sample insertion/removal complications and to numerous spatial constraints, exacerbated by the presence of a glass dewar for sample-temperature control (see Section VI). This is unfortunate because the alternative saddle coils are substantially less efficient, especially at the relatively low excitation/detection frequencies used in FFC NMR. 

An alternative to a saddle coil would be a solenoid coil which, however, would have to be oriented perpendicularly to the magnet bore and thus to the physical axis of the probe assembly. Due to spatial constraints, such an arrangement complicates considerably sample insertion, especially when the sample temperature has to be controlled and the assembly has to include an enveloping dewar for temperature control of the sample. ... 

Figure 6.45 Microbore LC-NMR layout. A Microbore HPLC system with a 0.5 mm X 150 mm C18 column is interfaced to a solenoidal microcoil probe. The transfer capfllary is connected to the NMR flow cell with a polyamide resin. Reproduced from [85] with permission. Copyright 1999 American Chemical Society.

Figure 8.2.2 (a) Schematic of the four-coil probehead introduced in Reference [12]. The four individual solenoidal coils are represented by an inductance (L), series resistance (R), and inter-turn capacitance (Q. The entire circuit was impedance-matched to 50 it at a frequency of 300 MHz by using the variable capacitors Ct and Cm. (b) Photograph of the four-coil assembly. Reprinted from MacNamara, E., Hou. T., Fisher, G., Wilhams, S. and Raftery, D., Multiplex Sample NMR an approach to high-throughput NMR using a parallel coil probe , Anal. Chem. Acta, 397, 9-16, copyright (1999), with permission of Elsevier Science... 

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