Microbiological assay of oxytetracycline in feed: manual turbidimetric assay and plate assay
Ragheb, H.S.; Cummings, A.M.; Browning, B.M.
Journal - Association of Official Analytical Chemists 56(1): 23-30
1973
ISSN/ISBN: 0004-5756 PMID: 4592491 Document Number: 60442
The useful range for manual turbidimetric analysis of Oxytetracycline (OTC), using K. pneumoniae, was between 0.04 and 0.08 μg/ml in the assay tubes. Laboratory-prepared feeds containing 43.5 and 86.5 g OTC.HCl/ton gave 90–98% recovery by the turbidimetric method and 104–116% by the AOAC method, 38.211–38.213. The coefficients of variation were 9.2–13.0 and 10.2–12.8%, respectively. Feeds containing 50 and 100 g OTC.HCl and neomyein sulfate/ton gave 77% of theory when analyzed turbidimetrically and 95% of theory by the plate method. The coefficient of variation for the turbidimetric method was about 16%, indicating unsatisfactory precision. At 200 g/ton theoretical concentration of each antibiotic, both methods agreed. Commercial premixes and finished feed samples gave almost the same results by both methods. The main advantage of the turbidimetric method over the plate assay is that results can be obtained the same day of analysis.