Aconitum and Delphinium genera are important rich sources of toxic C19-diterpenoid alkaloids. The alkaloidal content of A. napellus and D. elatum seeds have been investigated in detail. After maceration, crude alkaloidal extracts were obtained and then purified by repeated column chromatography (over silica and alumina gels) to sample homogeneity yielding five known C19-diterpenoid alkaloids from A. napellus, aconitine, neoline, 14-O-acetyltalatisamine, 14-O-benzoylaconine, and taurenine, and two others from D. elatum, delpheline (also including its X-ray single crystal analysis) and methyllycaconitine (MLA). These examples showed that mass spectrometry hyphenated with HPLC or other chromatography can be used as a tool for rapid alkaloid content screening of different extracts. NMR spectroscopic (using a variety of techniques and nuclei) data are presented in support of the first report of iminodelsemine A/B as an imino-alkaloid artefact from D. elatum. A detailed chromatographic study across different pH ranges, and over different solid supports, of aconitine and its main degradation product, 14-O-benzoyl-8-O-methylaconine, together with its semi-synthesis and that of its deuterated analogue are reported within studies to minimize artefact formation during the storage or extraction of A. napellus norditerpenoid alkaloids. Likewise, from D. elatum seeds, as a model source of Delphinium alkaloids, we compared the alkaloid yield using different extraction techniques and conventional chromatographic separations. The structures were confirmed by NMR spectroscopy and mass spectrometry. An NMR spectroscopic approach for the pKa determination of some C19-diterpenoid alkaloids has been developed. A modified calculation method for fatty acid composition quantification has also been developed using 1H-NMR spectroscopic methods.