Other Analytical Separation Techniques Hyphenated with NMR

3 Other Analytical Separation Techniques Hyphenated with NMR 

Recently, other chromatographic techniques have been coupled on-line to NMR for additional applications in the pharmaceutical environment, such as 

There are many examples in the literature for applications of LC-NMR in the pharmaceutical industry. In the area of natural products, LC-NMR has been applied to screen plant constituents from crude extracts [54,57,67,68] and to analyze plant and marine alkaloids [69-72], flavonoids [73], sesquiterpene lactones [74,75], saponins [58,76], vitamin E homologues [77], and antifungal and bacterial constituents [56,78,79] as examples. In the field of drug metabolism, LC-NMR has been extensively applied for the identihcation of metabolites [42, 80-88] and even polar [89] or unstable metabolites [43]. And hnally, LC-NMR has been used for areas such degradation products [90-93], drug impurities [94-102], drug discovery [103,104], and food analysis [105-107]. 

The capability of analyzing a complex mixture in a chromatographic run by the hyphenation of several techniques, such as NMR and MS, to HPLC is becoming more popular in the pharmaceutical industry. NMR and MS data on the same analyte are crucial for structural elucidation. When different isolates such as metabolites are analyzed by NMR and MS, one cannot always be certain that the NMR and the MS data apply to the same analyte, especially when the analytes have been isolated using analytical columns and prep columns for the MS and NMR analysis, respectively. HPLC conditions are not always reproducible when analytical and prep-HPLC columns are used to isolate different amounts of the analytes of interest. To avoid this ambiguity, LC-MS and LC-NMR are combined. MS data should be obtained initially because with NMR, data collection in the stop-flow mode can take hours or days, depending on the complexity of the structure and the amount of sample. This is why it is preferable to designate this operation as LC-MS-NMR rather than LC-NMR-MS or LC-NMR/MS. 

For the last 4-5 years, the LC-NMR-MS system has been commercially available only for the Bruker NMR instruments. For the Varian NMR instruments, the system has recently become available. The work presented here has been carried out by the author using a custom design of the LC-MS-NMR system on a Varian NMR instrument as explained above. 

---