High Pressure Liquid Chromatographic Determination of Sulfamethazine or Sulfathiazole and Colorimetric Determination of Sulfathiazole in Feeds: Collaborative Studies

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Abstract
A high pressure liquid chromatographic method for sulfamethazine or sulfathiazole in feeds was studied collaboratively. The sample is extracted in 50% methanol and filtered, and an aliquot is injected into a liquid chromatograph. The column is μBondapak C18, the eluting solvent is acetonitrile–water (20+80), and the detection wavelength is 280 nm. Nine collaborators analyzed 3 different synthetic samples and 2 commercial samples labeled to contain 0.011% sulfamethazine, plus procaine penicillin and chlortetracycline. Average recoveries for the synthetic samples were 102.2% at the 0.005% level, 100.2% at the 0.01% level, and 103.6% at the 0.02% level; per cent standard deviations were 12.7, 10.4, and 8.67, respectively. Average sulfamethazine content of the 2 commercial samples was 77.8 and 82.9% of label with per cent standard deviations of 8.56 and 9.16. The same 2 samples, analyzed according to the official colorimetric procedure by 6 analysts, had an average sulfamethazine content of 81.7 and 89.4% of label with per cent standard deviations of 3.69 and 6.66. Eight collaborators analyzed 3 different synthetic samples and 2 commercial samples labeled to contain 0.011% sulfathiazole, plus procaine penicillin and chlortetracycline. Average recoveries of the synthetic samples were 101.6% at the 0.005% level, 103.0% at the 0.01% level, and 100.4% at the 0.02% level; per cent standard deviations were 9.52, 7.00, and 6.54. Average sulfathiazole content found by 9 collaborators was 0.0103% or 93.4% of label for Sample 1 and 0.0100% or 91.1% of label for Sample 2, with per cent standard deviations of 14.1 and 12.2. Colorimetric assays for sulfathiazole were made according to method 42.172–42.174 for sulfamethazine. Two synthetic samples were analyzed by 7 collaborators. Average recovery was 97.6% at the 0.01% level and 99.8% at the 0.02% level with per cent standard deviations of 5.05 and 8.16. The same 2 commercial samples used for the HPLC study were analyzed by 9 collaborators. Average sulfathiazole found was 86.4 and 87.9% of label with per cent standard deviations of 7.41 and 6.15.