A rapid and precise spectroscopic method for detecting fipronil insecticide on solid surfaces

Fipronil, an insecticide commonly used to rid livestock of fleas, lice and ticks, is banned from use in the food industry in the U.S. and European Union. The incident of poultry eggs tainted with fipronil in 2017 caused recall of millions of eggs affecting more than 40 countries. Since commercial application of fipronil is as a spray, its most immediate and most rapid detection is on surfaces. A partial least squares regression (PLSR) model was developed with infrared (IR) data (750–2000 cm −1 ). The relationship between the peak intensity and the fipronil concentration is linear. The method finds a correlation coefficient R 2 = 0.98 in the calibration set and R 2 = 0.96 in the validation set. The IR spectral assignments were made for 18 vibrational modes (750–2500 cm −1 ). Eighteen Raman vibrational modes in the pure fipronil have also been found (500–2500 cm −1 ). The molecular sites in vibrational modes for C–C and C–N stretching in both IR and Raman spectra (1250–1750 cm −1 ) are similar, yet the pattern of their relative intensities in both are different. Differences in the relative spectral intensity at wavenumbers 1319, 1423, 1506, and 1634 cm −1 could also be less affected by potential interferences from matrix and background signals. The dual modality IR and Raman measurements can provide a unique and highly specific fingerprint of fipronil identity.