Fighting counterfeit pesticides using mid-infrared spectroscopy and chemometrics

• FT-MIR spectroscopy combined with a three-step chemometric protocol is an effective, and reliable tool for qualitative screening of pesticide formulations. • The proposed methodology enables discrimination between authentic and counterfeit products and verification of formulation integrity. • The proposed methodology can be considered green as FT-MIR is solvent-free, non-destructive and requires minimal sample preparation. • The tool proposed is suitable for routine quality control and high-throughput screening. The use of pesticides, which are essential for agriculture and public health, poses risks when they are of out of specification or counterfeited, as they may be ineffective, toxic, or harmful to human and animal health, crops, and the environment. Traditionally, the characterisation and authentication of pesticide formulations have relied on chromatographic and mass spectrometric techniques, which provide high analytical accuracy but are often limited by their operational complexity, elevated costs and extensive sample preparation. These limitations have prompted growing interest in complementary analytical methodologies, as those based on vibrational spectroscopy. Among these, Fourier Transform Mid-Infrared (FT-MIR) spectroscopy has emerged as a powerful and versatile green analytical approach due to its high sensitivity, molecular specificity, non-use of reactive and non-destructive nature. The present study explores the application of FT-MIR as an effective analytical tool for combating pesticide counterfeiting. In this work, FT-MIR is combined with the development of an extensive spectral library and the implementation of a completed, hierarchical chemometric protocol. This methodology has been applied and validated in blind using a set of simulated counterfeit samples as well as with a real-world case with three samples supplied by a private pesticide manufacturer, thereby demonstrating its potential for routine quality control and regulatory surveillance of pesticide products.