Fast quantitative analysis of ginsenosides in Asian ginseng (Panax ginseng C. A. Mayer) by using solid-phase methylation coupled to direct analysis in real time.

Abstract

A fast quantitative method for ginsenosides is essential to minimize analysis time; direct analysis in real time mass spectrometry (DART-MS) has the potential to be used for this purpose. However, in order to produce ginsenosides, a derivatization such as methylation is required because the strong polarity of ginsenosides makes it difficult to desorp and ionize them in DART-MS. The main objectives of this study were to achieve fast detection and quantitative analysis of ginsenosides by using DART-MS; solid-phase methylation of ginsenosides has been accomplished in a reaction column; methylated products of ginsenosides Rb1, Rd, Re, Rf and Rg1 were analyzed by applying DART-MS where samples could be detected after methylation without the need for further purification. For quantitative analysis, deuterated methylated ginsenosides were prepared by using the solid-phase methylation method and used as internal standards to improve repeatability in DART-MS. Methylated ginsenosides produced protonated molecules [M+H](+) and fragment ions in DART-MS. Two pairs of ginsenoside isomers, Rd/Re (C48 H82 O18 , MW 946) and Rf/Rg1(C42 H72 O14 , MW 800), could be discriminated based on their characteristic fragments in tandem mass spectrometry. By using deuterated methylated ginsenosides as internal standards, fast quantitative analysis of ginsenosides Rb1, Re and Rg1 in Asian ginseng was achieved by DART-MS. DART-MS is a feasible technique for fast quantitative analysis of ginsenosides by assisted methylation and the deuterated internal standard technique. Copyright © 2016 John Wiley & Sons, Ltd.