A Simple HPLC Method for the Determination of Chlorpyrifos in Black Oil Sunflower Seeds

Abstract

Damage to ripening sunflowers by blackbirds is an important agricultural problem in the northern Great Plains. In an effort to reduce crop loss by non‐lethal means, several insecticidal formulations were evaluated for potential bird repellency. One formulation, Lorsban^®‐4E, was highly effective in feeding studies with caged blackbirds. Chlorpyrifos (an organophosphate pesticide) is a registered insecticide and acaricide commonly used to control insects on sunflower, and is the active ingredient in Lorsban^®‐4E. To support further evaluation of chlorpyrifos repellency in field trials, a rapid, simple, high performance liquid chromatographic (HPLC) analytical method was developed to assess residues in sunflower seeds, which had been aerially sprayed. Control black oil sunflower seeds were cryopulverized, fortified with chlorpyrifos at 0.50 µg · g⁻¹, 5.0 µg · g⁻¹, 50 µg · g⁻¹, and 500 µg · g⁻¹, and extracted in 90% acetonitrile/10% 1 mM phosphate buffer (pH 4.5). Extracts were filtered and analyzed by reverse phase HPLC with UV detection at 230 nm, with one elution method for samples ranging from 5.00 µg · g⁻¹ chlorpyrifos to 500 µg · g⁻¹ chlorpyrifos, and a second elution method for samples ranging from 0.500 µg · g⁻¹ chlorpyrifos to <5.00 µg · g⁻¹ chlorpyrifos. The methods were rugged and reliable, with chlorpyrifos recovery >95% for all fortified concentrations. The method limit of detection was 0.328 µg · g⁻¹ and 0.221 µg · g⁻¹ chlorpyrifos for Methods 1 and 2, respectively, and no chromatographic interferences were observed with either method.

Keywords:

• Sunflower
• Blackbirds
• Chlorpyrifos
• CAS# 2921‐88‐2
• Lorsban^®‐4e
• High performance liquid chromatography
• HPLC

Acknowledgment

The authors would like to thank Donald Wille of Archer Daniels Midland Company for his invaluable assistance in procuring true control sunflower seeds.