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Quantitative analysis of pyrrolizidine alkaloid mixtures from Senecio vulgaris by carbon‐13 nuclear magnetic resonance spectroscopy

A 13C NMR method has been developed for obtaining simultaneously structural and quantitative information on mixtures of pyrrolizidine alkaloids from Senecio vulgaris L. (Compositae). The samples contained seneciphylline, senecionine, retrorsine and the corresponding E geometrical isomers, spartioidine, integerrimine and usaramine. The spin‐lattice relaxation times were measured and, after establishing the instrumental requirements for quantitative 13C FT NMR, all the alkaloids of the mixture could be determined. Quantitative 1H and 13C FT NMR analyses were carried out, and the advantages and limitations of these methods are discussed.