Method of analysis of a selected group of pyrethroids in soil samples using off-line flow-through extraction and on-column direct large-volume injection in reversed phase high performance liquid chromatography

An analytical method using flow-through extraction of a soil sample filled in a short HPLC column with methanol or methanol-water mixtures and large-volume injection in RP-HPLC has been developed for the simultaneous determination of residues of three pyrethroids - kadethrin, cypermethrin, and permethrin - from soil samples. The developed RP-HPLC method enables separation of four diastereoisomers of cypermethrin into three peaks and resolution of two diastereoisomers of permethrin. The UV photometric detection limits of direct on-column large-volume injection of 1.00 mL, of extract were 30 ng/mL of kadethrin, 37 ng/mL of total content of cypermethrin, and 65 ng/mL of trans-permethrin, which corresponds to a pyrethroid soil content of around 0.3 mg/kg. Effects of extractant flow rate and optimal extractant volume on the percentage recovery of pyrethroids from Slovak soil samples were studied. Recovery studies were performed at 0.5 - 5.0 mu g/g fortification level of kadethrin and 1.0-2.5 mu g/g fortification level of cypermethrin and permethrin in a soil sample. Recoveries ranged from 83 to 90% for kadethrin, from 87 to 94% for total cypermethrin, and from 85 to 98% for trans-permethrin. This work comprises a basic study aimed at elaboration of an RP-HPLC method of direct analysis of pyrethroids in a soil matrix at low concentration levels achieved by a solid sample injection in HPLC - on-line interfacing of analyte extraction, extract cleanup, and analysis.