This part of ISO 8968 | IDF 20 specifies a method for the determination of the non-protein nitrogen content of liquid milk, whole or skimmed.
ISO 8968-4:2001 history
2016ISO 8968-4:2016 Milk and milk products - Determination of nitrogen content - Part 4: Determination of protein and non-protein nitrogen content and true protein content calculation (Reference method)
2011ISO 8968-4:2001/Cor 1:2011 Milk - Determination of nitrogen content - Part 4: Determination of non-protein-nitrogen content; Technical Corrigendum 1
2001ISO 8968-4:2001 Milk - Determination of nitrogen content - Part 4: Determination of non-protein-nitrogen content