摘要： BACKGROUND: Acetamiprid, as a low toxicity pesticide, had already been extensively used to increase plant production and quality. Although fipronil had been prohibited, it was usually illicitly added to acetamiprid due to its particular insecticidal action and effect, so it was highly desirable to obtain a rapid and effective method to detect its concentration. Mid-Infrared spectroscopy (MIR) technique combined with two variable selection methods, interval combination optimization (ICO) and interval partial least squares (iPLS), were used to determinate the prohibited addition of fipronil. RESULTS: The full spectra for both ICO and iPLS were divided into forty equal-width intervals. Consequently, 45 and 135 characteristic variables were extracted from ICO and iPLS to establish the models. Compared with iPLS, the ICO model acquired a more suitable spectral region and as a result gained a higher prediction accuracy. Specifically, ICO method selected the characteristic wavelengths ascribed to C-F and C-N (in five-membered heterocyclics), iPLS chose the intervals associated with C-F and S=O. CONCLUSION: Results revealed that MIR combined with ICO could be efficiently used for rapid identification of illegal addition and had a great potential to provide on-site pesticide quality control.