Microwave assisted solvent extraction and reversed phase liquid chromatography with diode array detection for screening sulfonylurea herbicides in soil samples

Abstract

Sulfonylurea compounds are characterized by high herbicidal activity allowing low-dose rates for the control of many grasses and broadleaf weeds in the agriculture of crops. This feature means, however, that under persistent conditions (e.g. high pH of soil, little rainfall and poor microbial activity) remaining low concentrations of these analytes can still affect the growth of susceptible plants. Hence, in order to control carry-over from one growing ~ season to the next, productive sensitive and selective methods are required for the determination of residues of sulfonylurea herbicides In soil. A screening method has been developed for the determination of sulfonylurea in various types of soils. Methodology is based on the use of microwave assisted solvent extraction (MASE) for fast and efficient extraction of the analytes from the soils and reversed-phase liquid chromatography (LC) with UV detection at 230 nm for the instrumental analysis of uncleaned extracts. Four types of soils, including sand and clay with a range in organic matter content of 1.45-4.39% and seven sulfonylurea herbicides (nicosulfuron, tritosulfuron, tribenuron-methyl, prosulfuron, rimsulfuron, oxasulfuron, triasulfuron) were selected as matrices and analytes, respectively. The method developed included the selection of suitable MASE and LC—UV conditions. MASE. conditions were established providing efficient extraction without degradation of the analytes, furthermore selectivity can be enhanced by ~ limiting the coextraction of interferences. Selected MASE conditions, including mixture dichloromethane-acetonitrile as the extraction solvent, provided a complete extraction of the analytes from soil samples. Method validation was performed by analysing freshly spiked soil samples with sulfonylurea and samples with aged residues at levels between 20 and 50 mg/ kg. Depending on the spiked level and the type of spiked sample recoveries were obtained between 70—-100% with relative standard deviations between 5 and 10%. Evaluation of the data set with principal component analysis revealed that the parameters increase of organic matter content of the soil samples and aged residues negatively effect the recovery of the analytes. The benefits of MASE, shorter extraction times, reduction of solvent consumption, improved selectivity and the possibility of processing 24 samples simultaneously, make this technique a good alternative to conventional extraction procedures.