Journal of Chromatography A, 1143 (2007) 36–40 Comparison between the conventional method of extraction of essential oil of Laurus nobilis L. and a novel method which uses microwaves applied in situ, without resorting to an oven Guido Flamini a,∗ , Marianna Tebano a , Pier Luigi Cioni a , Lucia Ceccarini b , Andrea Simone Ricci c , Iginio Longo c a Dipartimento di Chimica Bioorganica e Biofarmacia, Universit` a di Pisa, Via Bonanno 33, 56126 Pisa, Italy b Dipartimento di Agronomia e Gestione dell’Agroecosistema, Universit` a di Pisa, Via S. Michele Degli Scalzi 2, 56124 Pisa, Italy c Istituto per i Processi Chimico-Fisici, IPCF, Area di Ricerca del CNR, Via G. Moruzzi, 1, 56124 Pisa, Italy Received 1 November 2006; received in revised form 9 January 2007; accepted 10 January 2007 Available online 13 January 2007 Abstract A novel microwave method has been applied to the hydrothermal extraction of essential oil from plants. An insulated microwave coaxial antenna was introduced inside a 1000 ml glass flask containing dry Laurus nobilis L. leaves and tap water. Microwave power up to 800 W at 2450 MHz was emitted in continuous wave regime (CW) or in pulsed regime (PR) at 8kW peak power. Stirring with a magnetic bar and a Clevenger refrigerator connected to the flask enabled to complete the extraction in 1 h. The results of the in situ microwave extraction were compared with those obtained by heating the same reactor with a conventional electric mantle by gas chromatography–mass spectrometry (GC–MS) analysis. Differences were observed both in the composition of the essential oil and from the energetic point of view. The essential oil obtained with microwave (MW) methods contained substantially higher amounts of oxygenated compounds and lower amounts of monoterpenes than conventional method. The in situ microwave heating is safe and versatile; it presents time and energy saving advantages, and therefore it can be considered useful also for industrial applications. © 2007 Elsevier B.V. All rights reserved. Keywords: Laurus nobilis L.; Bay; Microwave extraction; Innovative technologies; Microwave industrial applications; In situ microwave heating 1. Introduction Several techniques are currently available for the extrac- tion of essential oils from plants including supercritical fluid extraction, pressurized liquid extraction, pressurized hot water extraction, hydrothermal extraction, water vapour extrac- tion, solvent extraction, membrane-assisted solvent extraction, solid-phase microextraction, stir bar sorptive extraction and ultrasounds. Recently, microwave-assisted extraction (MAE) methods appeared to be particularly attractive due to fast heating of aqueous samples [1,2]. At the state of the art of MAE, the extraction of essential oils is obtained introducing the plant sample in a multi-mode microwave cavity. Consequently, the shape and the sizes of the ∗ Corresponding author. Tel.: +39 0502219686; fax: +39 0502219660. E-mail address: flamini@farm.unipi.it (G. Flamini). vessel are important. The reactor walls must be non-metallic and the use of metal sensors and other devices with metal parts is severely limited. The use of auxiliary devices or glassware components directly connected to the reactor, such as a reflux condenser, a stirring bar, a water cooling bath or a metal probe, is not straightforward, and in general they must be placed out- side the oven. Direct visual and manual access to the reactor is forbidden to the operator. Previous investigations have applied microwaves for the extraction of essential oils. Lucchesi et al. compared the classic hydrodistillation method for the extraction of the oils of Oci- mum basilicum L., Mentha crispa L. and Thymus vulgaris L. with a solventless microwave (MW) method. The essential oils obtained in 30 min with the latter system were comparable, both from a qualitative and from a quantitative point of view, to those obtained after a 4.5 h hydrodistillation. The MW method permit- ted a more efficient extraction of oxygenated compounds saving time and energy [3]. 0021-9673/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2007.01.031