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

Authors: Chao, Kuanglin - Kevin Chao; Schmidt, Walter; Qin, Jianwei - Tony Qin; Kim, Moon

Submitted to: Journal of Food Measurement and Characterization
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2022
Publication Date: 4/7/2022
Citation: Chao, K., Schmidt, W.F., Qin, J., Kim, M.S. 2022. A rapid and precise spectroscopic method for detecting fipronil insecticide on solid surfaces. Journal of Food Measurement and Characterization. https://doi.org/10.1007/s11694-022-01384-4.
DOI: https://doi.org/10.1007/s11694-022-01384-4

Interpretive Summary: Fipronil, a broad-spectrum 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. Eggs contaminated with fipronil were found in European and Asian markets in 2017. Since commercial application of fipronil is as a spray, its most immediate and most rapid detection is on surfaces. The infrared (IR) spectroscopic technique was used to detect fipronil on surfaces. Computational techniques were applied and validated for quantifying fipronil levels as low as a fraction of a milligram. The spectroscopic technique results in a fingerprint that can be used in verifying the compound identity. The peaks most intense in IR were found to be different from those most intense in a sister spectroscopic technique (Raman). Combining the data of two of the larger peaks in IR with two of the larger peaks in Raman together can provide clean and clear evidence of identity even at low fipronil concentrations. Dual modality, using the sets of larger peaks from two different techniques, enables a more sensitive and a more rigorous fingerprint of fipronil identification. Food industry and consumers benefit when misused and banned insecticides like fipronil can be rapidly and accurately detected and quantified by innovative technologies.

Technical Abstract: The incident of poultry eggs tainted with fipronil in 2017 caused recall of millions of eggs affecting more than 40 countries. To address this public food safety concern, spectrochemical methods are required that can rapidly detect even fractions of a mg of fipronil on contaminated surfaces. A five latent factor PLSR model was developed with IR data (750 – 2000 cm-1). The method finds a correlation coefficient (R2) = 0.98 and RMSEC = 0.22 ppm in the calibration set. The estimated fipronil concentration found is R2 = 0.96 and RMSEP = 0.51 ppm in the validation set. The IR spectral assignments were made for 18 vibrational modes (750 – 2500 cm-1) and compared with (and cross correlated with) the Raman 18 vibrational modes (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 the same, yet the pattern of their relative intensities in both are different. IR asymmetrical modes at 1634 and 1319 cm-1 are 2-3 times larger than the corresponding wavelength in the Raman; Raman symmetrical modes at 1423 and 1513 cm-1 are 4-8 times larger than the corresponding wavelength in the IR. Differences in the relative spectral intensity at these four wavenumbers can provide a unique and enhanced specificity in asserting fipronil identity and, together, about an order of magnitude greater sensitivity. In principle these dual modality measurements could also be less affected by potential complicating spectral interferences from within a complex and heterogeneous matrix background signal.