Cryogenic NMR probes applications

Applications of Small-Volume High-Sensitivity and Cryogenic NMR Probes 31... 

APPLICATIONS OF SMALL-VOLUME HIGH-SENSITIVITY AND CRYOGENIC NMR PROBES... 

Martin, G. E. Applications of cryogenic NMR probe technology for the identification of low-level impurities in pharmaceuticals. Mod. Magn. Reson. 2 1187—1194, 2006. 

Exarchou, V. et al., LC-LTV-solid-phase extraction-NMR-MS combined with a cryogenic flow probe and its application to the identification of compounds present in Greek oregano. Anal. Chem., 75, 6288, 2003. 

The incredible natural abundance double quantum transfer experiment (INADEQUATE) was proposed by Ray Freeman in 1980.1 2 The acronym of this remarkable technique sat high among the many NMR acronyms since, at the time of its birth, it accurately described all its attributes. INADEQUATE was seen as an incredible experiment with vast potential its widespread applications are dwarfed only by its inadequate sensitivity. Depending on the equipment available, an ovemight-to-weekend INADEQUATE experiment on a medium-sized molecule would typically require hundreds of milligrams of sample. Only recently have such unfavourable requirements been addressed with advent of cryogenically cooled probes. Now, INADEQUATE experiments using samples of 5-10 mg have become realistic propositions. 

INADEQUATE in the field of high-resolution NMR is still mainly applied to the establishment of carbon-carbon connectivities, but its application to other nuclei continue to appear in the literature sporadically. Improvements in the sensitivity comparable to those offered by 1H- or 13C-optimised cryogenically cooled probes would undoubtedly increase the usage of INADEQUATE for non-carbon nuclei significantly. 

Probes usually have variable temperature control to run experiments at temperatures selected by the analyst. Cryogenically cooled probes can improve the resolution of a system, so that a 600 MHz spectrometer equipped with such a probe can provide resolution equivalent to a 700-800 MHz instrument. New probe designs with flow-through sample holders are commercially available, for use in coupled HPLC-NMR instruments and HPLC-NMR-MS instruments. These hyphenated instruments are discussed under applications later in the chapter. 

Another probe choice is that of the flow variety. These probes come in several formats however, they all have one thing in common. This conunon feature is that of a flow cell. There are many different varieties of flow cells customized to the types of analysis that need to be done. These differences vary from either the thickness of the flow cell (SFC-NMR) to the actual volume the cell holds (e.g., flow NMR, LC-NMR, LC-SPE-NMR, etc.). An additional element that has truly enhanced the world of LC-NMR is the introduction of the flow cell inserts for cryogenically cooled probes. This has really taken this application of NMR to a much more productive level. The NMR community refer to flow cell sizes based... 

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