Certification of a pure reference material for the ginsenoside Rg ₁

Abstract

A pure certified reference material (CRM) for the ginsenoside Rg ₁ was prepared from roots of Panax ginseng by extraction and separation of ginsenosides. The mass fraction of the main component (ginsenoside Rg ₁ ) in the reference material was determined and its uncertainty was assessed from various input quantities, such as organic impurities, residual moisture, residual solvent, ash, and insoluble matters. To measure these input quantities, HPLC/CAD, Karl Fischer (KF) coulometry, gravimetry, and GC/FID were used. Homogeneity and long-term stability of the reference material are discussed. The certified mass fraction of Rg ₁ in the reference material is 0.974 ± 0.006 (k = 2) with a shelf life of 1 year.

Appendix

Brief description of the measurement model

The measurement model equation, Eq. 1, was derived as described below.

We considered the CRM material to be composed of Rg ₁ , organic impurities, water, ash, solvent, and insoluble residues. m denotes mass, and ‘SUM, IMP’, W, A, S, and I denote the summation of organic impurities, water, ash, solvent, and insoluble residues, respectively:

$$ m_{\text{crm}} = m_{{{\text{R}}g {\it 1}}} + m_{\text{SUM, IMP}} + m_{W} + m_{A} + m_{S} + m_{I} $$

(9)

The purity, P, is defined as the mass fraction of Rg ₁ in the material:

$$ P = {\frac{{m_{{{\text{R}}g{\it 1}}} }}{{m_{\text{crm}} }}} $$

(10)

The corona-charged aerosol detector (CAD) is known as a universal detector [15]. Therefore, assuming that the CAD is equally sensitive to different compounds, the ratio P _LC can be calculated from the areas (A) of the various peaks observed (the baseline was set manually and the individual peak areas were summed up):

$$ P_{\text{LC}} = {\frac{{A_{{{\text{R}}g{\it 1}}} }}{{A_{{{\text{R}}g{\it 1}}} + A_{\text{SUM, IMP}} }}} $$

(11)

Assuming that the individual peak areas are equally proportional to the respective masses, this ratio can be called ‘mass fraction’:

$$ P_{\text{LC}} = {\frac{{m_{{{\text{R}}g{\it 1}}} }}{{m_{{{\text{R}}g{\it 1}}} + m_{\text{SUM, IMP}} }}} $$

(12)

Introducing Eq. 12 into the definition of P yields:

$$ P = {\frac{{P_{\text{LC}} (m_{{{\text{R}}g{\it 1}}} + m_{\text{SUM, IMP}} )}}{{m_{\text{crm}} }}} $$

(13)

Using Eq. 9 provides:

$$ m_{{{\text{R}}g{\it 1}}} + m_{\text{SUM,IMP}} = m_{\text{crm}} - m_{W} - m_{A} - m_{S} - m_{I} $$

(14)

The mass fractions, W, A, S, and I are measured by the methods described in “Apparatus and methods”.

$$ W = {\frac{{m_{W} }}{{m_{\text{crm}} }}} $$

(15)

$$ A = {\frac{{m_{A} }}{{m_{\text{crm}} }}} $$

(16)

$$ S = {\frac{{m_{S} }}{{m_{\text{crm}} }}} $$

(17)

$$ I = {\frac{{m_{I} }}{{m_{\text{crm}} }}} $$

(18)

Equations 14 to 18 are introduced into Eq. 13 to yield:

$$ P = {\frac{{P_{\text{LC}} (m_{\text{crm}} - m_{W} - m_{A} - m_{S} - m_{I} )}}{{m_{\text{crm}} }}} = P_{\text{LC}} (1 - W - A - S - I). $$

(19)