High-performance liquid chromatography-diode array detection assay for the detection and quantification of the Beauveria metabolite oosporein from potato tubers

A high-performance liquid chromatography-diode array detection (HPLC-DAD) assay is described for the detection and quantification of the secreted Beauveria brongniartii metabolite oosporein from potato tubers. Analyte recovery was achieved with a Britton–Robinson buffer system at pH 5.5 diluted with methanol 3:7 (v/v) (BR5.5-MeOH). An internal standard protocol using 2-iodobenzoic acid was established to minimize analytical error. The resulting assay, using a binary solvent gradient with acidic modifiers and detecting the metabolite at 287 nm, showed a limit of detection (LOD) of 2.4 mg oosporein/kg potato tubers. The oosporein content of potato tuber samples obtained from a field trial using the biological pest control B. brongniartii formulation Melocont-Pilzgerste in up to five-fold higher doses (250 kg Melocont-Pilzgerste/ha) as recommended per year was found to be below the established LOD.