This document describes a method for the determination of free gossypol, extractable by acidified acetonitrile/water, in cottonseed, cottonseed products and complete feed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). This document has been successfully validated in the range of 69 mg/kg to 5 950 mg/kg by collaborative trial in the following matrices: cottonseed, cottonseed products (cake/meal, hulls) and complete feed for bovine, porcine and poultry.