General Principles, NMR as a Highly Sensitive Analytical Tool pg to ng Amounts

General Principles, NMR as a Highly Sensitive Analytical Tool (pg to ng Amounts) 

The identification and structural characterization of biological materials, obtained for example from plants, was traditionally carried out via the classical sequence involving extraction, separation, isolation and characterization, a sequence which requires large amounts of substance and a great deal of time. Industrial problems, for example the search for small amounts of contaminants in industrial products or in waste water, also require intensive analytical studies. 

A direct combination of separation and analysis techniques is thus invaluable. GLC-MS and HPLC-MS coupling are now routinely used. Because of the high sensitivity of modern NMR instruments the coupling of HPLC and NMR is now used in many NMR laboratories, and we shall discuss the principles and show some results below. 

The coupling of HPLC in tandem with NMR requires two separate systems  

A long capillary with a computer-controlled switching valve (the instruments must be separated by 2-3 metres because of the strong magnetic field) connects the exit from the HPLC with the probehead. The latter is completely different in its construction from conventional probeheads instead of the NMR tube there is a small flow cell, the volume of which is 40-100 pi. The transmitter and receiver coils are attached directly to the cell in order to maximize the sensitivity. 

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