The quantitative results highlight that compounds are present in concentration ranges of 0.42–20.02 mg/100 g. Globoidnan A (6) was characterized in the MS/MS spectrum by an intense peak - at m/z 311 due to the neutral loss of a caffeic acid unit. MS/MS fragmentation pattern of rosmarinic acid (5) originated a main fragment ion - at m/z 161, due to the loss of a caffeic acid unit and water molecule. Protocatechuic acid (2), p-hydroxybenzoic acid (3), and caffeic acid (4) showed a very simple fragmentation pattern where the base peak was produced by the neutral loss of 44 Da corresponding to the carboxylic group. For this reason, this transition was selected for MRM experiments. Allantoin (1) in the MS/MS spectrum was characterized by the loss of 60 Da corresponding to the urea unit, originating an intense peak at m/z 97. The amount (per mg/100 g of dried extract) of each selected compound and the MRM transition selected for each compound is shown. LC/ESI/triple quadrupole(QqQ)/MS using a very sensitive and selective mass tandem experiment such as Multiple Reaction Monitoring (MRM) is considered one of the most suitable techniques for quantification of metabolites ( Masullo et al., 2016). (B) In order to determine the amount of the main compounds occurring in the ethylacetate fraction of comfrey roots, a quantitative determination by LC-MS was carried out. Noteworthy, compounds 1–5 were previously isolated in comfrey roots ( Grabias and Swiatek, 1998 Trifan et al., 2018) while this is the first report of globoidnan A (6). In this way, allantoin (1), protocatechuic acid (2), p-hydroxybenzoic acid (3), caffeic acid (4), rosmarinic acid (5), and globoidnan A (6) were identified. The HPLC profile showed peaks corresponding to the main compounds which were collected and structurally elucidated by NMR spectroscopy. (A) The ethylacetate fraction of comfrey roots was analyzed by HPLC-UV. officinale root extract and quantification of its main compounds.

Comfrey symphytum officinale