Separation of Bifenthrin Enantiomers by Chiral HPLC and Determination of Their Toxicity to Aquatic Organism

TZU-LING LIU, YEI-SHUNG WANG AND JUI-HUNG YEN*

Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan, R.O.C.

(Received: October 22, 2004; Accepted: June 10, 2005)

ABSTRACT

   In this study, we separate enantiomers of bifenthrin, a pyrethroid insecticide, by using high performance liquid chromatography with a chiral stationary phase (CPS) column. Toxicity tests of bifenthrin enantiomers were performed with Daphnia (water flea, Daphnia pulex), tilapia fish (Tilapia spp.) and carp fish (Cyprinus carpio). Two enantiomers of bifenthrin were separated successfully by injecting 20 μL of bifenthrin 1000 mg/L standard solution into a Sumichiral OA-2500-I column. The mobile phase solvent system was composed of n-hexane, isopropanol, and ethanol in a ratio of 99.8/0.06/0.14, and the flow rate was 1.0 mL/min. Both enantiomers were eluted within 20 min. Two separated enantiomers, (-)-bifenthrin and (+)-bifenthrin, were identified by gas chromatography with mass spectrometry detector (GC-MSD) and polarimeter. Each enantiomer of bifenthrin and the standard bifenthrin solution showed the same fragmentation pattern spectrum. The fragment ions were m/z 115, m/z 141, m/z 165, m/z 181, and m/z 422. The specific rotations [α]20 ₃₆₅ of (-)-bifenthrin and (+)-bifenthrin were -66.41° and +69.63°, respectively. In the toxicity study, the LC₅₀ (12 hr) of (-)-bifenthrin and (+)-bifenthrin for daphina were 2.1 μg/L and 28.9 μg/L, respectively. On the other hand, the result of fish toxicity indicated the LC₅₀ (96 hr) of (-)-bifenthrin and (+)-bifenthrin for carp (C.carpio) were 0.99 and 2.08 μg/L, respectively, and for tilapia (Tilapia spp.) were 0.19 and 0.80 μg/L, respectively. The study of biological activity showed that the toxicity of (-)-bifenthrin was 10-fold greater than (+)-bifenthrin for Daphnia, and 2-fold greater for fish. This study provided improved methods for separating enantiomers of bifenthrin and assessing hazard of individual enantiomers toward non-target aquatic fauna.

Key words: HPLC, bifenthrin, biological activity, enantiomers