Microbiological assay of nystatin in feeds
Platt, T.B.; Itkin, A.G.
Journal - Association of Official Analytical Chemists 57(3): 536-540
1974
ISSN/ISBN: 0004-5756 PMID: 4833389 Document Number: 76666
A modification of the official method for nystatin in feeds was collaboratively studied. Feed is extracted into methanol and a portion of the extract is converted to a feed blank by heating 20 min at 121°C. The remaining portion of the extract is assayed vs. the standard curve prepared in feed blank. Four commercial poultry laying mashes were studied; 2 were tested as formulated, 2 were tested in both crumble and powder form, and 1 of the ground feeds was diluted with cornmeal. Each sample was prepared to contain ca 50 and 100 g nystatin/ ton. Each of 9 collaborators analyzed, in duplicate, 3 different samples. The theoretical nystatin content was established by the collaborators' assay of the premix used to prepare the samples. Recoveries of activity averaged 97.6% for the lower concentration and 100.4% for the higher concentration. The method was adopted as official first action to replace the present official first action method for feeds containing ≥ 50 g nystatin/ton, 38.200-38.203.