Headspace ionic liquid-based microdrop liquid-phase microextraction followed by microdrop thermal desorption-gas chromatographic analysis

Headspace microdrop liquid-phase microextraction (LPME) using ionic liquids as extracting solvents, followed by gas chromatography–electron capture detection was successfully developed to determine organochlorine pesticides in soil samples. A feature of the developed procedure is the simple handling of the ionic liquid extract in a normal, unmodified gas chromatograph injection port such that no special provision was needed to ensure that the ionic liquid did not contaminate it. This was achieved by only exposing the ionic liquid extract in the injection port while it was still attached to the syringe needle tip (i.e. mirroring the extraction configuration) to permit volatilization of the analytes, instead of injecting the extract. In this way, the spent ionic liquid could be recovered from the injection port, obviating the need to clean the port. Four 1-butyl-3-methylimidazolium-based ionic liquids were investigated, and 1-butyl-3-methylimidazolium hexafluorophosphate was finally selected as the most suitable extracting solvent. Parameters that affect the extraction and determination of the organochlorine pesticides were studied. Under the optimal conditions, the proposed method produced good linearity over a concentration range of 5–250 ng/g. Limits of detection ranging from 0.25 to 0.5 ng/g were achieved.