Simultaneous analysis of furfural metabolites from Rehmanniae radix preparata by HPLC-DAD–ESI-MS

•Development of a new analytical method for the analysis of 5-HMF derivatives from Rehmanniae radix preparata.•Structure determination of a new 5-HMF derivative.•Quantitative analysis of 5-HMF derivatives from eighteen Rehmanniae radix preparata samples from Korea and China.•Monitoring of the amounts of 5-HMF derivatives during the processing of dried Rehmanniae radix samples. A method based on HPLC with diode array detector (DAD) and electrospray ionisation mass spectrometry (ESI-MS) was established for the simultaneous determination of 5-HMF and its derivatives, including a new 5-HMF derivative, in Rehmanniae radix preparata. Validation parameters, such as linearity, limit of detection, limit of quantification, recovery, accuracy, and precision, were successfully obtained. In addition, the efficiencies of diverse extraction methods were compared for the development of a standard analytical method. The verified method was successfully applied to the quantitative determination of four representative metabolites in eighteen R. radix preparata samples from Korea and China. Additionally, the increase in the amount of 5-HMF derivatives was monitored during the processing of three dried R. radix samples. The results showed that a newly isolated diglycosylated 5-HMF derivative, 5-(α-D-galactopyranosyl-(1→6)-α-D-galactopyranosyloxymethyl)-2-furancarboxaldehyde, appeared in concentrations comparable to that of 5-HMF, suggesting its potential to serve as a marker compound in R. radix preparata.