Application of solid‐phase extraction coupled to an NMR flow‐probe in the analysis of HPLC fractions

The design and use of a system consisting of a disposable solid‐phase extraction cartridge coupled to an NMR flow‐probe (SPE–NMR) is demonstrated. Fractions obtained from high‐performance liquid chromatography of an extract of Habanero pepper (Capsicum chinense) were analysed. The fractions were loaded on SPE cartridges and the compounds were eluted with deuterated methanol directly into the NMR flow‐probe. Good‐quality NMR spectra were acquired and the structure of the compounds could be determined. The main advantages with SPE–NMR are the simple handling of small amounts of samples, the removal of polar additives and solvents from the preceding separation step allowing optimal conditions for both the chromatography and the NMR spectroscopy and the possibility of automating the procedure. Hence the method can facilitate the structural characterization of small amounts of natural products in complex mixtures.