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 μg/g fortification level of kadethrin and 1.0–2.5 μg/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 clean‐up, and analysis.