Microcoil NMR

Microcoil NMR probes, made with solenoidal coils wrapped around 1 uL or smaller flow cells, have 20-50 times better mass limits of detection than conventional 5 mm tubes.  A severe limitation in their applicability is the need to transfer samples into the flow cell  (in the NMR magnet) through several meters of capillary tubing, which has a 10-50 uL dead volume.  A method of lossless transfer of samples as "plugs" in an immiscible carrier, zero-dispersion segmented flow analysis, has been implemented for microNMR by the Institute.  This SFA-microNMR technique offers a 4-fold lower LOD than a 3 mm cryoprobe.   1D spectra have been obtained from as little as 0.1 ug;  typically COSY and TOCSY spectra can be obtained from 1-3 ug.  In offline LC-NMR, 100 uL fractions collected from conventional LC are concentrated 30-fold; fractions of interest may be studied in detail without time constraints.  Fully automated operation can comprehensive analyze an entire separation for compounds with poor MS ionization or no UV chromophores.  

Figure 1.  Automated SFA-microNMR.   3 uL samples prepared in 96-well plates are loaded as 'plugs', separated by an immiscible carrier fluid.  Samples may be rapidly  changed by advancing the train of plugs.