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B rown & Y u : J ournal of AOAC I nternational V ol . 96, N o . 1, 2013  13

Table 1. MDL a and LOQ calculated in the SLV for individual ginsenosides

SLV Method Performance

A complete description of the SLV study has been published by AOAC INTERNATIONAL. The results for the SLV are summarized below.

Analyte

MDL, µg/mL

LOQ, µg/mL

1.1 1.3

2.9 3.4

Rg 1

Re

System Suitability and Selectivity

2.2

5.9

Rb 1

Rc

1.2

3.3

The HPLC-UV system in the SLVwork passed comprehensive suitability testing of eight consecutive injections using a low concentration of a mixed ginsenoside standard working solution. The repeatability RSD (RSD r ) values of the peak areas were ≤5%. Each of the reference analytes was chromatographically resolved (R s ≥ 1.5), with peak tailing (T) ≤ 2. Linearity The coefficient of determination (r 2 ) values of the regression lines using a seven-point calibration standard curve were ≥99.5% for all ginsenoside standards throughout the SLV study. There were no significant deviations in the slopes of the calibration curves or the goodness of fit while the intercepts were not forced to zero.

Rb 2

1.3

3.4

Rd

1.7

4.6

a  MDL = Method detection limit.

materials and finished products was recently completed using AOAC INTERNATIONAL guidelines (15, 16). The method implemented a basic hydrolysis step subsequent to the extraction of ginsenosides and analysis by HPLC-UV absorbance detection. The application of the basic hydrolysis step was only applied to raw materials, as finished products were assumed to have undergone heat or chemical processing, making additional hydrolysis unnecessary (16). To further assess the soundness of the validated method, this study was carried out to demonstrate and establish the inter-reproducibility of the method for the determination of individual and total ginsenosides in P. ginseng and P. quinquefolius raw materials and finished products. A number of laboratories were recruited based on their experience in natural health products and/or dietary supplement analysis; each participating laboratory was given the validated method to be tested using AOAC guidelines for collaborative study (17). Laboratories were instructed to follow the method accurately, as the study was to test the method for its reproducibility, not the laboratories’ proficiency in conducting the analysis. Data from the laboratories were collected and subjected to statistical analysis as per AOAC guidelines for collaborative studies to assess the method’s performance (17).

Method Detection Limit and LOQ

The LOD was defined using the U.S. Environmental Protection Agency method detection limit (MDL; 18) using seven replicates of a stock standard solution containing a very low concentration of each of the analytes. The LOQ was defined as 10 times the sample SD of the results of the MDL (18). The calculated MDL and LOQ for each analyte are listed in Table 1.

Precision

The repeatability of the method was evaluated by analyzing

Figure 1. Elution order of the ginsenosides (1) Rg1, (2) Re, (3) Rb1, (4) Rc, (5) Rb2, (6) Rd based on the mixed reference standards.