This work aimed to develop and validate a method to detect and quantify protodioscin in Brachiaria grasses using ultraperformance liquid chromatography (UPLC) coupled to high-resolution quadrupole time-of-flight mass spectrometry. Samples were extracted by acetonitrile–water 50:50 v/v mixture and ultrasonication. The mobile phase consisted of 5 mM ammonium acetate in water–methanol and acetonitrile containing 0.1% formic acid. The parameters used to validate the method for determining protodioscin comprised determination of the selectivity, ionization suppression/enhancement (matrix effect), linearity of the calibration curve, the limit of detection (LOD), the lower limit of quantitation (LLOQ), and the precision and accuracy of the method. The LLOQ of protodioscin was determined as 0.1 μg mL−1, and the LOD was 0.03 μg mL−1. The developed method was applied for determining protodioscin levels in B. decumbens collected from three pastures where sheep showed clinical signs of photosensitization. The obtained values ranged from 0.71% to 1.12%. Thus, the developed method for determining protodioscin in Brachiaria grasses by LC coupled to high-resolution quadrupole time-of-flight mass spectrometry showed high accuracy, precision, and sensitivity.
