###### Abstract  
_Panax vietnamensis_ (PV), a wild _Panax_ species discovered in Vietnam in 1973, has been increasingly overexploited due to its economic value and therapeutic uses. This resulted in the development of PV cultivation to meet the market demand. There is little information on the accumulation of saponins in PV during cultivation, but this information could serve as an indication of the appropriate harvest time. In this study we developed an HPLC-UV/ELSD method to simultaneously determine the content of 10 characteristic saponins in PV from 2-7 years old, including G-Rb1, G-Rd, G-Rg1, G-Re, N-R1, M-R1, M-R2, V-R2, V-R11, and p-RT4. The result indicated that from 2 to 5 years, the content of saponins in PV rhizome and radix increase 3.02 and 4.2 times, respectively, whereas from 5 to 7 years, no significant changes were observed. Hence, our study suggests that after 5 years of growth could be considered as an appropriate time for PV to be harvested. Among the analyzed saponins, G-Rg1, G-Rb1, G-Rd, and especially M-R2 were the major saponins that contributed to the change of PV's saponin content through the years. In addition, the developed and validated HPLC method was proven to be reliable and effective for quality control of PV. _Panax vietnamensis_; vietnamese ginseng; HPLC-UV/ELSD; accumulation of saponins +
Footnote †: journal: Nuclear Instruments  
0000-0001-5000-5000]J. H. H.  
possess a number of biological effects such as anti-oxidative [5], hepato-cytoprotective [6], anti-stress [7], and anti-cancer activities [8; 9]. Recently, occtillol-type saponins from PV were reported to exhibit nephoprotective effects against cisplatin toxicity [10] as well as anti-melanogenic activity [11]. Due to its economic value and therapeutic uses, wild PV has been increasingly overexploited, and thus its natural reserve is seriously in danger of extinction. Consequently, a lot of effort has been focused on the cultivation of PV not only to preserve the natural source but also to meet the growing demand in the market. In ginseng cultivation practice, the content of saponins in the underground parts plays an important role in determining the appropriate time for harvest. For example, [PERSON], et al. examined the change of saponin contents of _P. ginseng_ with growth, in China, from age 1 to 5 years and found a gradual increase of PPD and PPT-type saponin contents with growth year [12]. However, in a study by [PERSON], et al., the variation of ginseng contents in _P. ginseng_ grown in Korea was higher at the beginning of growth (1-3 years) [13]. As for _P. quinquefolius_, according to [PERSON], et al. [14], ginseng contents changed with age at different rates, G-Re increased gradually with the increase of age. In contrast, the change of G-Rb1 was slight from age 1 to 2 years and significant from age 2 to 5 years. However, up to now, there has been little information on the accumulation of saponins in different parts of PV during cultivation, thus prompting our study. When it comes to the quantitative assessment of the saponin content in _Panax_ species in general, a wide spectrum of analytical methods has been developed so far including HPTLC and HPLC  
Figure 1: Structures of characteristic saponins in _Panax vietnamensis_ (PV). coupled with various detectors such as ultraviolet (UV), diode array detector (DAD), evaporative light scattering detector (ELSD), charged aerosol detector (CAD), and mass spectrometry (MS). Among those, HPLC-DAD or -UV detected at low wavelengths (\(<\)205 nm) are frequently used for determination of saponins in _Panax_ species [15]. [PERSON], et al. also reported the detection and quantitative determination of M-R2, an OCT-type saponin with no double-bond in its structure, at the wavelength of 196 nm with good linearity [16]. In addition, ELSD is another choice for detection of ginsenosides in _P. ginseng_[17] and _P. notoginseng_[18].