A simple and rapid method for detecting the pesticide fipronil on egg shells and in liquid eggs by Raman microscopy

The pesticide fipronil was recently involved in a "poisonous eggs" scandal which resulted in substantial economic losses and public health risks. We report a simple and rapid method which can be implemented to detect fipronil on egg shells and in liquid eggs by Raman spectrometry. Fipronil rapidly crystallizes when solubilized in water-acetone solution (1:6, V/V, acetone/water). This process can be visually observed by naked eyes, suggesting a possible rapid and instrument-free screening action. Then, fipronil crystals were concentrated and recovered on a gold-coated glass slide for further identification and quantification by Raman microscopic analyses. A standard curve was established to quantify fipronil within the range of 1-500 mg/L (r(2) >= 0.997), based on the unique fipronil Raman shift at 2256 cm(-1). Acetone based extraction recovered fipronil at three spiked levels of 5, 60 and 100 mg/kg on chicken egg shells and in liquid eggs from 59.91% to 81.72% and 85.97% to 152.46%, respectively. The limit of detection translated to the weight of liquid egg (0.32 mg/kg) and the surface area of an egg shell (0.065 mg/m(2)). In conclusion, this method has demonstrated a strong capacity for the rapid (<30 min) detection of fipronil on chicken egg shells and in liquid eggs.