Application of diffusion-edited and solvent suppression 1H NMR to the direct analysis of markers in valerian-hop liquid herbal products

The rising trend to consume herbal products for the treatment and/or prevention of minor ailments together with their chemical and pharmacological complexity means there is an urgent need to develop new approaches to their quality and stability. This work looks at the application of one-dimensional diffusion-edited ¹H NMR spectroscopy (1D DOSY) and ¹H NMR with suppression of the ethanol and water signals to the characterization of quality and stability markers in multicomponent herbal medicines/food supplements. The experiments were performed with commercial tinctures of Valeriana officinalis L. (valerian), expired and non-expired, as well as its combination with Hummulus lupulus L. (hops), which is one of the most popular blends of relaxant herbs. These techniques did not require purification or evaporation of components for the qualitative analysis of the mixture, but only the addition of D2O and TSP. The best diagnostic signals were found at  7 ppm (H-11, valerenic acid),  4.2 ppm (H-1, hydroxyvalerenic acid) and  1.5-1.8 ppm (methyl groups in prenylated moieties, α-acids/prenylated flavones). This work concludes on the potential value of 1D DOSY ¹H NMR to provide additional assurance of quality in complex natural mixtures.