Determination of methidathion in barley malt by a solid phase extraction method

Abstract

The use of pesticides in agriculture has brought many obvious benefits, but their inappropriate use can result in unacceptably high levels of these compounds in cereals. Pesticide residues can be found even when they are applied in accordance with good agricultural practices. A solid phase extraction (SPE) method has been developed for determination of methidathion in barley malt samples. The method involves a rapid extraction procedure with acetonitrile using salting out step. Non-polar coextractives are removed by passing a portion of the acetonitrile extract through an octadecyl (C18) solid phase extraction clean-up cartridge. An aliquot is taken and concentrated for second extract clean-up, which is done with a carbon cartridge coupled to an aminopropyl cartridge using acetonitrile: toluene 3:1 (v/v) as the elution solvent. Analysis is performed by gas chromatography, employing mass selective detection in the selected ion monitoring mode. The method rendered recoveries ranging between 91 and 96%, the associated relative standard deviations ranging between 1 and 3%. Limit of detection methidathion were less than or equal to 0.002 mg/kg. The applicability of the proposed method to detect and quantify pesticide residues has been demonstrated by the analysis of 20 genuine samples. The methidathion content in barley malt samples is not regulated by Serbian legislation (Official Gazette of RS, 28/11) and relevant EU regulation (Council Directive 90/642/EEC, 1990). The methidathion concentration found in barley malt samples were bellow the MAC value permitted by EU regulations and in accordance with the currently valid Serbian regulations for barley.