Identification of Wild and Domesticated Houttuynia Cordata by ICP-MS with Chemometric Analysis

Twenty-five samples each of wild and domesticated Houttuynia cordata were collected. A portion of 0.500 0 g was taken from each of the samples and digested with 5.0 mL of HNO₃ and 2.0 mL of H₂O₂ in a microwave digestor under prescribed programme to prepare a sample solution of 25.0 mL. Twenty-two inorganic elements were determined in each of the sample solutions by ICP-MS. ⁴⁵Sc, ⁷²Ge, ¹⁰³Rh, ¹⁵⁹Tb, ¹⁷⁵Lu and ²⁰⁹Bi were chosen as internal standards. Standard curves were prepared by mixed standard solutions. Good linear relationships of standard curves of the 22 elements were obtained. Tests for recovery and precision were performed by addition of standards to a known sample, giving values of recovery in the range of 82.0% to 114% and RSDs (n=6) in the range of 0.20%-4.5%. It was shown by the results of statistical study of t-test, distinctive differences of contents of inorganic elements in the 2 kinds of Houttuynia cordata were due to the differences of geographical and growing environments, the cultivation techniques, and mankind activities. In further, the principal component analysis was applied to the study of matrixes (50×22) of variable data given by the 50 samples of the Houttuynia cordata and the 22 inorganic elements. As shown by the results obtained, relationships between the contents of the inorganic elements and the kinds (i.e. wild or domesticated) of the Houttuynia cordata were revealed, but a clear differentiation between the wild and domesticated Houttuynia cordata was still not attained. Then, the progressive discriminant analysis was applied to study the 50×22 elemental variable data, five variable elements (Na, K, Cr, Se, Cd) having significant effect were sieved, and models of typical discriminant function and linear discriminant function were established, attaining to complete and ultimate differentiation between the 2 kinds of Houttuynia cordata. To verify the reliability of the discriminant models, tests of back-substitution and cross-validation were applied, and rate of discriminant accuracy of 100% was obtained. It was considered that by applying ICP-MS in combination with chemometrical methods, identification of wild and domesticated Houttuynia cordata could be realized.