J. of Supercritical Fluids 40 (2007) 368–375 Optimisation of SFE method on-line coupled to FT-IR spectroscopy for the real-time monitoring of the extraction of tagitinin C in T. diversifolia E. Ziemons a,∗ , N. Wandji Mbakop a , E. Rozet a , R. Lejeune a , L. Angenot b , L. Thunus a , Ph. Hubert a a Laboratory of Analytical Chemistry, Bioanalytical Chemistry Research Unit, Department of Pharmacy, University of Li` ege, Avenue de l’Hˆ opital 1, B 36, 4000 Li` ege, Belgium b Laboratory of Pharmacognosy, Department of Pharmacy, University of Li` ege, Avenue de l’Hˆ opital 1, B 36, B-4000 Li` ege, Belgium Received 10 April 2006; received in revised form 13 July 2006; accepted 14 July 2006 Abstract The monitoring in real time of dynamic extractions of tagitinin C from Tithonia diversifolia leaves was carried out with a home made high- pressure fiber optic cell which coupled a supercritical fluid extractor with carbon dioxide as the extraction medium and a FT-IR spectrometer equipped with a mercury cadmium telluride detector (MCT). The shape of extraction curves obtained during the monitoring was used to decide when to stop the supercritical fluid extraction (SFE). No significant density dependence of the molar absorption coefficient or wavenumber of the C O stretching vibration ( C O ) of tagitinin C at 1668 cm -1 was noticed. The physical characteristics of SCCO 2 governing the extraction yield of the active component from leaves were optimized by means of a central composite design (CCD). The studied variables were temperature (40, 60 and 80 ◦ C) and pressure (8.0, 14.0 and 20.0 MPa) of the supercritical fluid. The composition profile of T. diversifolia extracts obtained by SFE was investigated in the range from 3400 to 2600 cm -1 according to the pressure and temperature conditions of SCCO 2 . The qualitative approach of the extracts composition was accomplished through the CH stretching vibrations (ν CH ) of components. © 2006 Elsevier B.V. All rights reserved. Keywords: On-line monitoring; Supercritical fluid extraction; FT-IR spectroscopy; Tagitinin C; Tithonia diversifolia 1. Introduction During the last two decades, interest in natural compounds acting like medicines, food additives or pesticides has increased [1,2]. However, the active compounds in plants are enclosed in rather complex matrices and usually in low concentration, thus selective extraction methods for sufficient recovery of these compounds from the raw materials must be investigated. Supercritical fluid extraction (SFE) is one-extraction technique which most closely meets these requirements. Indeed, the solvent strength of the fluid can be easily tuned by changing its pressure and/or temperature allowing to reach a selectivity. Extractions with supercritical fluids can be carried out in off-line ∗ Corresponding author. Fax: +32 4 3664324. E-mail address: eziemons@ulg.ac.be (E. Ziemons). or in on-line mode. In off-line SFE, the extracted compounds are removed from the supercritical fluid by depressurizing it through a restrictor and are trapped either into a small volume of liquid solvent, or on an inert solid support or on an active solid sorbent [3]. On-line SFE methods avoid the use of trapping by directly connecting the extraction system to a detection instrument, thus minimizing the opportunity for the sample to become contaminated, volatilized or degraded. Among them, SFE/FT-IR interface using optical fibres allowed qualitative and quantitative information to be obtained from the extracts of samples such as caffeine in coffee or total petroleum hydrocar- bons in soil, respectively [4–6]. Carbon dioxide is the solvent of choice due to its non-flammable, non-explosive and non-toxic properties, which are very important when the extracts are dedicated to the food, cosmetic or pharmaceutical industries. In addition, CO 2 is cheap, easily available at high purity degree and its critical temperature (31 ◦ C) is sufficiently low to treat 0896-8446/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.supflu.2006.07.009