Extraction of Norflurazon Residues in Cotton Seeds with Supercritical CO 2 F. M. Lanqas* / M. A. Barbirato / M. S. Galhiane Universidade de S~o Paulo, Instituto de Qufmica de S~o Carlos, Cx. Postal 369, 13560-970, S~o Carlos (SP), Brasil Key Words Supercritical fluid extraction Norflurazon residues Cotton seeds Solid phase extraction Summary A new method for the extraction of Norflurazon residues in cotton seeds using supercritical CO 2 as the extracting fluid is described. The supercritical fluid extraction results were compared with those of the classical procedure using liquid extraction. All SFE experiments were performed using a home-made system. The method presented, besides being faster and more economical than existing methods, showed better recovery, with higher selectivity for Norflurazon extraction. Introduction Norflurazon, 4-chloro-5-(methylamine)-2-(~, ~, o~-trif- luro-m-tolyl)-3-(2H)-pyridazinone, belongs to the pyri- dazine chemical family. It is a selective herbicide, absorbed by the roots. It reduces carotenoid biosynthe- sis which causes chlorophyll depletion and hence inhibition of photosynthesis. It is used in the pre- emergence control of annual grasses and broad-leaved weeds and some perennial grasses and sedges in cotton, nuts, soya beans, citrus, pome fruit, stone fruit, cranber- ries and hops [1]. The classical methods of Norflurazon residue extrac- tion and clean-up in cotton seeds involve several steps which make the analytical procedure very slow and increase the risk of contamination and loss of sample [2, 3]. Supercritical fluid extraction (SFE) became an analyti- cal tool in the 80's [4] and has been shown to be an attractive replacement for conventional extraction meth" ods due to the reduced consumption of organic solvent in the extraction and quicker extraction. In contrast to most of the literature data, our laboratO" ry has used a home-made SFE system [5, 6], with lower costs when compared to commercial SFE systems. In the present work we describe a new extractio~a method for Norflurazon residues in cotton seeds utilizing supercritical CO 2 as the extracting fluid, witla this procedure it was possible to reduce the extractiorl time and to eliminate the defatting step of the extraction required by the classical methods. Experimental Samples The cotton seeds utilized in this work were cultivated under controlled conditions in an experimental station. The cotton crops were treated with Zorial, where the concentration of active ingredient (Norflurazon) is 800 g/kg. The samples received a single application of Norflurazon at two dose levels (2.4 and 4.8 kg.a.i./ha.) and were harvested 140 days after application. The harvested samples were submitted to a quartering process and were stored at - 20 ~ in a freezer. Sample Preparation The cotton seeds were ground in a Tecnal mod. TE 306 micro grinder, for 3 minutes before extraction. Extraction and Clean-up Procedures The extracts analyzed in this work were obtained by two extraction procedures: Solid-Liquid ExtractioO (SLE) and Supercritical Fluid Extraction (SFE). Solid liquid extraction (SLE). 25 g of samples were mixed with 10 g of Celite 545 and 150 mL of acetone/ water solution (85 : 15) were added. The mixture was stirred for 30 minutes and then filtered through Btickner funnel. The extraction was repeated and the 432 0009-5893/95/04 0432-03 $ 3.00/0 Chromatographia Vol. 40, No. 7/8, April 1995 9 1995 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH Original