Thoroughly homogenize frozen laboratory sample in blender and weigh ca 10 g in duplicate, using balance accurate to 0.1 mg. Use desiccated, tared weighing dishes, preferably made of Ni, Al, stain-less steel or glass 60-80 mm diameter and 25 mm deep, with well fitting but easily removable lids. Place uncovered dish containing test sample, with lid, in convection dryivg oven at 103±2°c for 16 h. Replace lid and transfer to desiccator to cool. When cool, weigh as quickly as possible to 0.1 mg. Uncover and replace dish and lid on oven additional 2 h. Replace lid, cool in desiccator and reweigh. Repeat 2 h drying desiccation and weighing steps until decrease in mass between successive weighings dose not exceed 0.5 mg or until increase in mass is recorded.