Method of fast trace microanalysis of the chiral pesticides epoxiconazole and novaluron 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 combining off-line flow-through extraction of a soil micro-sample (mass around 100 mg, packed into a short HPLC glass column) and direct on-column large-volume injection (LVI up to 1.00 mL) of a methanol-water soil extract onto a conventional C18 RP HPLC column enabled fast (within 3.5 minutes) trace micro-analysis of the relatively new chiral pesticides epoxiconazole (E) and novaluron (N), respectively. Linear calibration curves were evaluated from UV detection (230 nm) data in the range from 0.1 to 5 mg/kg in three most abundant Slovak agricultural soils. LOD (confidence band) at the levels 0.08-0.11 mg/kg and LOQ 0.4-0.6 mg/kg and LOD (S/N = 3) at the levels 0.007-0.018 mg/kg and LOQ (S/N = 10) 0.024-0.060 mg/kg, respectively, of dry soil were achieved. Recovery of pesticides in the overall LVI method including flow-through 130-200 mg soil micro-sample extraction was: for epoxiconazole from 74 to 85% and from 56% to 90% for novaluron with reproducibility within +/- 6% RSD. This fast (30 min) and simple method consists of just three steps which are short column filling with a solid micro-sample; flow-through liquid extraction and direct large-volume injection RP HPLC DAD analysis. The method is prepared for automation and further analysis of enantiomers of both investigated pesticides by achiral-chiral column switching techniques.