LC-NMR: An Overview of the Technique, Applications, and Limitations

Although LC-NMR was used as early as 1978, it has only become a viable technique in recent years with the introduction of higher field magnets and improved hardware and software. An overview of the LC-NMR technique and an outline of the considerations required in both the LC and the NMR operations will be presented. Specific examples will be given to illustrate some of the limitations. Two of the major problems are: (1) changes in the retention time can result in changes in the chemical shifts because of the variation in the solvent composition during gradient LC separations, and (2) sufficient amounts of compounds in selected LC peaks are difficult to deliver to the NMR probe. A recent development that helps to overcome these two problems will be discussed.