Ion-pair extraction cleanup for liquid chromatographic determination of bentazon in crops and soil
Akerblom, M.; Alex, G.
Journal - Association of Official Analytical Chemists 67(3): 653-655
1984
ISSN/ISBN: 0004-5756 PMID: 6746492 Document Number: 221187
A selective cleanup method was developed so that bentazone could be determined by a reversed/phase HPLC method, instead of by gas chromatography after alkylation. Crops are extracted with methanol; extracts of crops such as potatoes and cucumbers are concentrated to a few ml, that of wheat is evaporated to dryness. Wheat extract residue is dissolved in phosphate buffer pH 8 and extracted with hexane; the hexane phase is discarded. The aqueous phase of potato and cucumber extracts is extracted with ethyl acetate; the ethyl acetate phase is dried, evaporated and the residue dissolved in pH 8 buffer. Bentazone is extracted from 3 ml pH 8 buffer by adding 200 micro l 0.01 M tetrabutylammonium ion to form an ion pair which is then extracted into dichloromethane. The dichloromethane is then evaporated and the residue is dissolved in the HPLC eluent, acetonitrile 0.1 M acetic acid (50:50) for potatoes and methanol 0.1 M acetic acid (30:70) for other crops. A reversed-phase Nucleosil 5 C18 column with UV detection is used. Recoveries of bentazone from cucumber, potatoes and wheat were 77-94% for fortification at 0.05 mg/kg and 80-103% at 0.20 mg/kg. Limit of detection is 0.02 mg/kg. Selective extraction of bentazone as an ion pair with tetrabutylammonium ion into dichloromethane was used to clean up crop and soil samples for determination of bentazone by reverse phase liquid chromatography and UV detection. Recoveries were 77-103% and the detection limit 0.02 mg/kg.