ABSTRACT
Natural samples are usually highly complex mixtures containing compounds of different chemical structures and physicochemical properties. Except for neutral compounds, ionized and ionizable compounds occur very often in real botanical samples. Among natural compounds there are numerous acidic substances containing carboxylic groups or slightly ionized hydroxyl groups attached to an aromatic ring, for example, phenolic acids, some avonoids, and tannins or glucuronic acids. Also, ionizable bases can be encountered in the analysis of natural samples, for example, alkaloids or heterocyclic amines. The aforementioned substances are analyzed often not only because of their common occurrence in plant extracts but also because of their wide spectrum of pharmacological activities. For example, phenolic acids were proved to have biligenic, cholagogue, hypocholesteremic, hypolipidemic, antibacterial, or antifungal properties [1]. Alkaloids are among the most potent herbal drugs, and many of them exhibit poisonous properties. They are used, for example, as spasmolytic, antibacterial, hypotensic, diuretic, analeptic, antifungal, or anticancer drugs [2].
