title: Quantitation of Deltamethrin in Rat Liver and Muscle Homogenates Using Dispersive Solid-Phase Extraction with GC-NCI-MS.
abstract: An improved bioanalytical method to determine pyrethroids from small-volume (300 μL) rat liver and muscle homogenates was developed, validated, and applied to small-animal studies. The method used dispersive SPE (d-SPE) to clean the samples, and GC negative chemical ion MS (GC-NCI-MS) to analyze the samples. High-quality trace analysis of pyrethroids in biological samples was necessary to assess the health risk of environmentally encountered levels. Currently used highly sensitive methods to measure pyrethroids have focused on large-volume samples related to environmental exposure (water, soil, food products) or urine; however, there are no validated methods for quantifying this class of compounds in small-volume rat liver and muscle tissue homogenates. Individual rat tissue homogenate samples (300 μL) were prepared by protein precipitation using hexane-saturated acetonitrile. The samples were mixed on a vortex mixer and decanted into a d-SPE tube containing octadecylsilyl (C18) and primary secondary amine (PSA) sorbents and magnesium sulfate. The samples were centrifuged before evaporation to dryness. Pyrethroids were extracted and reconstituted from the residue using toluene in advance of injection into an Agilent Model 6890N gas chromatograph equipped with a Model 5973 quadrupole mass analyzer. Samples were ionized via electron capture in the negative ion mode using methane as a chemical ionization gas. Six qualifying ions were monitored using selected-ion monitoring for quantitation and verification of the analyte. Cis-permethrin was used as the internal standard. Method linearity was from 1 to 500 ng/mL for muscle and liver homogenates. The inter- and intraday precision and accuracy of the method were better than 20% at the lower LOQ and better than 15% over the remainder of the linear range. The method was used to elucidate tissue time-courses of deltamethrin (DLM) disposition following oral dosing of rats with 1 to 5 mg/kg in corn oil. DLM was monitored in rat tissue samples ≤24 h following dosing. Sample cleanup with d-SPE provided more selective chromatography than previous analytical methods.