A QuEChERS-Based Sample Preparation Method for the Analysis of 5-Nitroimidazoles in Bovine Milk by HPLC-DAD

In this study, a simple, cost-effective, and sensitive HPLC diode-array detection method was developed for the simultaneous determination of six different 5-nitroimidazoles [metronidazole, 2-hydroxymethyl-1-methyl-5-nitro-1H-imidazole, dimetridazole (DMZ), ronidazole, ornidazole, and ipronidazole] in bovine milk samples. A QuEChERS-based sample preparation procedure was optimized by evaluating different cleanup sorbents, including zirconium-based sorbents (Z-Sep and Z-Sep+), C18, and primary-secondary amine (PSA), as well as EMR-Lipid cleanup solution. Acceptable analytical performance for all analytes was observed with recoveries in the range of 45-93% and RSDs of less than 15%. Negligible matrix interference was observed for most of the analytes due to application of PSA sorbent in a dispersive solid-phase extraction cleanup step. Method LOQs (mLOQs) for five of the six investigated analytes were set at a satisfactory low food product value of 2.5 ng/mL. For DMZ only, the mLOQ was set at 10 ng/mL. The procedure was evaluated through the analysis of 10 different natural samples.