Development of a Validated LC-MS/MS Multi-Residue Method for Pesticide Detection in Nigerian Herbal Drug Materials and Market Products

Pesticide residue contamination in Nigerian herbal medicines represents a critically underinvestigated threat to public health, particularly as agricultural intensification increases pesticide application on medicinal plant farms across all geopolitical zones. The absence of validated, sensitive, and regulatory-ready analytical methods for multi-residue pesticide screening in Nigerian herbal materials constitutes a major gap in the national herbal product quality assurance infrastructure. This PhD research develops and fully validates a liquid chromatography-tandem mass spectrometry (LC-MS/MS) multi-residue analytical method for the simultaneous detection and quantification of 68 commonly used pesticides in Nigerian herbal drug materials and finished market products. Method development employed QuEChERS extraction optimised for complex herbal matrices with dispersive SPE cleanup. Validation was conducted according to the SANTE/11813/2017 guideline, covering selectivity, linearity, matrix-matched calibration, accuracy (recovery), precision, limit of detection, limit of quantification, and matrix effects across 12 representative herbal matrices. The validated method was applied to 150 herbal samples collected from farms and markets in Lagos, Kano, Enugu, and Sokoto, representing South West, North West, South East, and North West zones. Recovery rates of 70-120% were achieved for 61 of 68 target pesticides across all matrices. Pesticide residues were detected in 68% of farm samples and 44% of market samples, with chlorpyrifos, cypermethrin, and dimethoate as the most frequently detected residues above MRLs. Regulatory submission of the validated method to NAFDAC is proposed. Keywords: pesticide residues, LC-MS/MS, herbal medicines, QuEChERS, NAFDAC