Continuous-flow microwave-assisted extraction coupled with online single drop microextraction prior to GC-MS for...

A rapid method based on continuous-flow microwave-assisted extraction and online single drop microextraction was first developed and applied to the determination of amide herbicides in rice. The present method has the advantages of both continuous-flow microwave-assisted extraction and online single drop microextraction, which combines extraction, separation, preconcentration, and sample introduction in one step. By continuous-flow microwave-assisted extraction, analytes were first extracted from the rice samples using 15% methanol-water, and then concentrated into single drop. The microdrop was retracted into microsyringe and directly analyzed by gas chromatography with mass spectrometry without any filtration or clean-up process. The method greatly simplifies the sample treatment procedure, reduces consumption of toxic organic solvent, and extends the application of single drop microextraction to complex solid samples. Several parameters were optimized by Box-Behnken design. Under optimal experimental conditions, good linearity was observed in the range of 2.0-500.0 μg/kg. The limits of detection and quantification were in the range of 0.3-1.5 and 1.1-5.1 μg/kg, respectively. The intra- and inter-day precisions were between 1.9 and 4.8%. The present method was used to the analysis of real rice samples, and the recoveries of analytes were between 80.3 and 102.3% with the relative standard deviations ranging from 1.1 to 6.9%.