Use of Doehlert design in the optimization of extraction conditions in the determination of organochlorine pesticides in bovine milk samples by HS-SPME

Abstract

In this study, the extraction of pesticides lindane, heptachlor, aldrin, dieldrin and endrin from milk samples by HS-SPME was investigated followed by separation/detection of these compounds by gas chromatography coupled to an electron capture detector (GC-ECD). Due to the high complexity of milk samples and the hydrophobicity of the studied organochlorine pesticides, the samples were diluted with saturated NaCl solution prior to optimization of the extraction conditions. Dilution tests indicated that a total sample volume of 2 mL (0.5 mL of milk and 1.5 mL of NaCl solution) provided the best chromatographic responses. The fiber coating DVB/Car/PDMS presented the best extraction efficiency towards the target compounds. Optimization was performed using a Doehlert design, and the best conditions were found to be an extraction temperature of 80 °C and an extraction time of 90 min. The HS-SPME mode was used for all extractions from the milk samples. A single fiber, selected during the optimization of fiber coating, was used throughout the study, and no damage on coating was observed. The analytical figures of merit were evaluated, and good results were obtained for the extraction of the target organochlorine pesticides. The percentages of recovery were higher than 75% and the limit of quantitation ranged from 0.5 to 1.2 μg L⁻¹ (for heptachlor and dieldrin, respectively).