The use of ¹⁹F observation using MLEV ¹H decoupling in LC/¹⁹F {¹H} NMR was investigated as an alternative to LC/¹H NMR for fluorine containing mixtures and in order to avoid the solvent background problems associated with LC/¹H NMR. P-fluorobenzoate derivatives of various alcohols were analyzed by both LC/¹⁹F {¹H} and LC/¹H NMR.

Another alternative exists in supercritical fluid chromatography. A delivery system was assembled and an NMR flow probe was developed and demonstrated practical for directly coupled SFC/¹H NM. The alkane substituents of a model fuel mixture were identified using SFC/¹H NMR in contrast to using the normal phase LC/¹H NMR approach.

The relaxation behavior and molecular motion of dilute solutions of benzene and acetonitrile in sub- and supercritical CO₂ were determined using stopped flow ¹H and ¹⁴N NM. The nuclear spin-lattice relaxation times (T₁) for ¹H and ¹⁴N were measured through inversion recovery and linewidth, respectively. Relaxation was found to be dominated by spin-rotation interactions with molecular correlation times (r_sr and _rc) being determined directly from the ¹H and ¹⁴N T₁ over a wide range of viscosities and temperatures. Line-narrowing improvements of ¹⁴N averaged 3-fold as a result of the increased molecular motion.

The increased molecular motion as a result of supercritical CO₂ resulted in improved signal enhancement using flow dynamic nuclear polarization. The observed enhancements were two times greater than that typically achieved for the same system and configuration using normal liquid solutions. Through observed NMR enhancements, relative microwave magnetic field values in the vicinity of the NMR coils were measured for typical flow and static DNP-NMR configurations. The advantages of the former were noted.