The inability of high-performance liquid chromatography to detect substances which lack a strong chromophore poses several problems to phytochemists for the identification of these compounds in crude plant extracts. This is particularly true in the case of saponins, which generally occur together with phenolic glycosides and pigments in polar plant extracts, and whose detection is not straightforward.Usually, analysis is performed with HPLC using an ultraviolet (IV) detector at short wavelength (208 nm) (1) or after suitable derivatization (2). However, the identities of peaks can be confirmed only by their retention time. Application of mass spectrometry (MS) as a tool for definitive identification of peaks is therefore a useful alternative.The combination of HPLC and MS has been attempted since the early 1980s and systems with several types of interfaces for direct and indirect introduction of the column effluent have bemn developed (3). Due to its simplicity and its ability to handle a variety of difficult samples. the thermospray interface is now used in laboratories throughout the world. However, very few applications in the area of polar compounds have been published as yet.The thermospray technique involves ionization of molecules in a similar fashion to CI (chemical ionization). Thus, analysis of mono-, di- and even triglycosides is possible. Application of thermospray LC-MS is a suitable method for the analysis of saponins. It can provide information on the molecular weight, the nature of the sugars and their sequence.This technique has been used for the analysis of the molluscicidal saponins from the methanolic extract of fruits of Tetrapleura tetraptera (Leguminosae) (4). With post-column addition of 0.2 mi/mm 0.2 M ammonium acetate to provide the volatile buffer for ion evaporation ionization, the thermospray LC-MS total ion current (mass range 450 to 900 amu) corresponded well with the UV trace at 208 nm (Fig. 1).The thermospray spectrum acquired for each saponin (A—E) in the extract displayed strong FM + H1 quasimolecular peaks, together with adduct species such as FM + NH4I and FM + Na + 2 NH4], confirming the molecular weight. Fragmentation of the sugar moiety was observed and peaks corresponding to the loss of first one (mono- and diglycosides) and then two sugars (diglycosides) were shown in all spectra. In addition, an important peak [A ÷ H] for the aglycone was visible in these spectra.Other examples of the analysis of saponin- containing plant extracts will be shown in this communication. In particular, optimization of the experimental conditions of ionization (e.g. temperatures of the source and the vaporizer) in order to enable detection and identification of triglycosides in these extracts.The results confirm that thermospray LC-MS can be an important aid in the detection and on-line identification of saponins in crude plant extracts. As a part of our ongoing chemical studies on the family Gentianaceae (1, 2) a large effort has been devoted to the search for new xanthones with potential MAO inhibitory activity (3, 4). In order to get a very rapid and precise idea of the phenolic constituents, crude extracts of certain Gentinaceae species have been analyzed by HPLC, combining UV photodiode array with post-column derivatization and