Simultaneous quantification of 19 diterpenoids in Isodon amethystoides by high-performance liquid chromatography–electrospray ionization tandem mass spectrometry

A high-performance liquid chromatography with electrospray tandem mass spectrometry (HPLC–ESI-MS/MS) method was developed to characterize and quantify 19 diterpenoid compounds in Isodon amethystoides simultaneously. By employing a Diamonsil C18 column, 19 constituents were separated within 15 min using a gradient elution consisted of methanol containing 0.1% formic acid and 0.1% aqueous formic acid. The precursor and product ions of the analytes were monitored on a hybrid quadrupole linear ion trap mass spectrometer equipped with a turbo ion spray interface in positive and negative mode in a single run and quantified by a multiple-reaction monitor (MRM). All standard calibration curves showed good linearity (r2 > 0.99) within the test ranges. The precision was evaluated by intra- and inter-day tests, which revealed relative standard deviation (RSD) values within the ranges of 1.06–3.25% and 1.56–3.84%. The recovery studies for the quantified compounds were between 95.82 and 108.3% with RSD values less than 1.86%. The results indicated that the method is simple, rapid, specific and reliable. This method was successfully applied for identification and quantification of 19 diterpenoids in 11 batches of I. amethystoides. The results showed that the contents of diterpenoids in I. amethystoides from different sources were widely varied.