The fertilizer laboratory of the Division of Regulatory Services at the University of Kentucky uses the Retsch ZM 200 ultra centrifugal mill for milling fertilizer samples.
The samples vary from ingredients to mixtures, water soluble to organic, with or without pesticide or other additives. Applying AOAC International methods requires proper sample reduction, proper mixing and sub-sampling in the laboratory.
The analysis of the prepared laboratory sample portion can only provide accurate results if it is representative of the larger sample taken in the field by the inspection staff. The size reduction of the sample particles is achieved by mechanical grinding using the ultra centrifugal mill ZM 200. Fineness is achieved by using a ring sieve with a 0.75 mm opening. Approximately 225 to 300 grams of material are prepared after gated riffling the original sample shipped to the lab. The use of a rotor with tungsten carbide coating enhances the lifetime of the components when grinding the hard fertilizer materials. Ammonium nitrate, urea, diammonium phosphate, monoammonium phosphate, triple superphosphate, potash and other materials providing minor elements must be handled by the mechanical components used in the grinding process. (...)