Finding the most appropriate IR technique for plant species identification

Abstract

Quality control of herbal medicinal products is of extreme importance. Procedures for identification of plant species, such as biochemical analysis or macroscopic and microscopic examination of morphological and anatomical properties are time consuming and expensive[1]. A good alternative is infrared spectroscopy since it is rapid, easy to use, nondestructive and low-cost. Identification of species from dried whole leaf samples of pharmaceutically important Epilobium and Hypericum genera were investigated. To determine which infrared spectroscopy mode gives most informative spectra for plant species identification different modes of infrared spectroscopy were applied. These were diffuse reflectance, attenuated total reflectance (ATR), direct transmission of whole leaves, and KBr tablet transmission with comminuted leaves. First the informative wavenumbers were chosen by one-way analysis of variance. Afterwards the colinearity was reduced with principal component analysis. At last the species identification was determined with discriminant analysis. Best results were obtained with ATR and KBr tablet transmission. Still there were important differences between genera. ATR proved to be appropriate for discrimination among Epilobium species (accuracy of plant species identification was 98%), Epilobium species differ in distribution and morphology of trichomes on the surface of the leaves[2]. While for Hypericum species KBr tablet transmission proved to give best results (accuracy of plant species identification was 97%). Hypericum species differ in secondary metabolites that are acumulated in the interior of the leaves[3,4]. Results show that morphological properties of plant material should be taken into consideration when developing an infrared spectroscopy based method for identification of plant species.