Determination of volatile components of green, black, oolong and white tea by optimized ultrasound-assisted extraction-dispersive liquid-liquid microextraction coupled with gas chromatography

Ultrasound assisted extraction (UAE) followed by dispersive liquid-liquid microextraction (DLLME) was used for extraction and preconcentration of volatile constituents of six tea plants. The preconcentrated compounds were analyzed by gas chromatography-mass spectrometry (GC-MS). Totally, 42 compounds were identified and caffeine was quantitatively determined. The main parameters (factors) of the extraction process were optimized by using a central composite design (CCD). Methanol and chloroform were selected as the extraction solvent and preconcentration solvent, respectively.The optimal conditions were obtained as 21 min for sonication time; 32 degrees C for temperature; 27 mu L for volume of extraction solvent and 7.4% for salt concentration (NaCl/H2O). The determination coefficient (R-2) was 0.9988. The relative standard deviation (RSD %) was 4.8 (n=5), and the enhancement factors (EFs) were 4.0-42.6. (c) 2013 Elsevier B.V. All rights reserved.