Quantification of natural compounds in medicinal plant extracts: a case study on the leaf extract of Punica granatum L.

The identification and quantification of natural products is laborious, due to the complexity of plant extracts and the limited availability of pure reference standards [1]. This study aims to evaluate the precision of plant metabolite quantification in high performance liquid chromatography (HPLC) coupled with different detectors (PDA and MS), focusing on semi-quantification which occurs when the reference standard is not available. As a case study, an extract from Punica granatum L. leaves was selected. Although these non-edible plant parts are usually discarded, they have been proven to be a valuable source of bioactive metabolites. Their traditional medicinal use is documented, and in vitro studies have demonstrated beneficial effects, including inhibition of Zika virus infection and HIV-1 reverse transcriptase and integrase [2,3,4]. In this work the performance of PDA and MS in different acquisition modes (SIM and SRM) is compared for the quantification of luteolin 4’-O-glucoside, a major compound of the extract [1,2]. Quantification precision was calculated as percentage relative error, comparing the results with the calibration curve generated with either the reference standard or a similar compound, i.e. kaempferol 3-O-glucoside. As expected, quantification with the reference standard is more accurate, while semi-quantification gives higher percentage relative errors, especially with MS, due to differences in compound responses. To address this issue, a correction method using a correction factor is proposed to compensate for the over-and underestimation in semi-quantification. This approach led to promising results.