Determination of diflubenzuron and its main metabolites in forestry matrices by liquid chromatography with on-line diode-array and electrochemical detection Original Research Article

A liquid chromatography (LC) method with on-line diode-array (DAD) and electrochemical detection (ED) has been developed for the determination of the pesticide diflubenzuron (DFB) and its main metabolites: 2,6-diflurobenzamide (2,6-DFBA), 4-chlorophenylurea (4-CPU), 4-chloroacetanilide (4-CAA), 4-chloroaniline (4-CA) and N-methyl-4-chloroaniline (NM-4-CA) in forestry matrices. Liquid chromatography was performed on a Spherisorb C18 column 5 μm (4.1×150 mm), using acetonitrile/methanol/citrate-disodium hydrogenphosphate buffer (50:2:48) at pH 7 as mobile phase, pumped at a flow rate of 1 ml min−1. The electrochemical study of the compounds proves the oxidation processes of 4-CPU, 4-CA, NM-4-CA and DFB on a glassy carbon electrode, which allows to determine them by oxidative amperometric detection. The amperometric detector equipped with a glassy carbon working electrode was operated at +1350 mV vs Ag/AgCl. The DAD detector was set at 245 and 260 nm, where the compounds show secondary maxima of absorbance which do not interfere with the matrix. The detection limits were 2.0–25.2 μg l−1 for the DAD detection and 0.07–1.8 μg l−1 for the amperometric detection. The method was applied to the determination of the pesticide and these metabolites in pine-needles. Samples were extracted into acetonitrile and further cleaned-up by solid-phase extraction through aminopropyl cartridges. Recoveries of the compounds from supplied pine-needle samples were higher than 90% in most of the cases, with relative standard deviations lower than 3.7%.