Headspace single-drop microextraction and GC-ECD determination of chlorpyrifos-ethyl in rat liver.

The present work describes a headspace single-drop microextraction (HS-SDME) method in conjunction with gas chromatography electron capture detection (GC-ECD) for the determination of an organophosphate insecticide, chlorpyrifos-ethyl (CPF), in rat liver. Sample preparation included tissue homogenization with methanol in the presence of anhydrous sodium sulfate in order to isolate CPF from the matrix, followed by dilution with 10 mL of 0.1 M H(2)SO(4) and headspace microextraction to a 2-microL drop of 1-octanol. The main factors affecting extraction efficiency were optimized [temperature 90 degrees C, preheating and extraction times of eight and six minutes, respectively, 2 g of (NH(4))(2)SO(4), stirring rate of 1000 rpm, 200 microL of methanolic extract]. The method allows for the separation and quantitation of residue levels of CPF in the livers of rats exposed orally to that insecticide. Using internal standardization (with chlorpyrifos-methyl used as an internal standard), the linearity of the method was demonstrated in the range 10-2500 ng g(-1) with a correlation coefficient R > 0.996 and a satisfactory level of precision (RSD 3.85%, n = 6). Moreover, the results obtained with the new method do not differ from those obtained with the conventional residue method used in our laboratory. The feasibility of this HS-SDME approach as an equivalent analytical method for the determination of CPF in rat liver that possesses advantages such as low cost, low solvent consumption and high throughput was confirmed.