The major methods employed in the authentication of herbal materials are macroscopic and microscopic examination, and chromatography. In addition, some pharmacopoeial monographs include chemical identification tests.
Macroscopic examination involves the comparison of morphological characters that are visible with the naked eye or under low magnification with descriptions of the plant or botanical drug in floras or monographs. Characters such as size, shape and colour of leaves (or leaf fragments), flowers or fruits are commonly used in macroscopic identification.
Microscopic examination focuses on anatomical structures in the plant material that are visible only with the help of a microscope.
Features such as trichome (hair) shape and structure, the arrangement of stomata in the epidermis, the presence or absence of compounds such as mucilage, starch or lignin, or the presence of tissues with characteristic cells might be used in the microscopic identifications of herbal drugs.
Chromatography is the separation of chemical compounds in a mixture. A number of chromatograqphic techniques exist, but all are based on the same basic principles.
Thin-layer chromatography (TLC) is widely employed in herbal authentication, and the majority of pharmacopoeial monographs for herbs include a TLC identification test. TLC separates mixtures of compounds to leave a a 'fingerprint' of separated compounds on a plate coated with silica gel. This fingerprint can be compared with that of an authentic sample or pure reference compounds.
High-performance liquid chromatography (HPLC) is another type of chromatography widely used in the authentication and analysis of herbal substances. Yet another type, gas chromatography, is used in particular for essential oils and fatty acids.