Determination of sulfamethazine in swine and cattle feed by reversed-phaseliquid chromatography with post-column derivatization: Pre-collaborative study

In-house validation of a liquid chromatographic method for determination of sulfamethazine in swine and cattle feed was performed to verify that the m ethod was ready for collaborative study under AOAC INTERNATIONAL guidelines . In this method, sulfamerazine is added during the extraction procedure an d is used as an internal standard to correct for variable recovery of sulfa methazine from a variety of swine and cattle feed matrixes. The determinati ve step involves the use of post-column derivatization with dimethylaminobe nzaldehyde which reacts with the primary amine group on the sulfonamides. D etection is at 450 nm, a wavelength at which most co-extracted matrix mater ials and other feed additives do not absorb light. The results indicate tha t the method recovery, precision, and ruggedness meet normal criteria to be ready for a collaborative study. Fortification experiments over a range of sulfamethazine concentrations from 0.006 to 0.26% showed an overall recove ry relative to the internal standard of 100 +/- 2%, These studies include b oth swine and cattle feed matrixes. The mean recovery in the analysis of 3 beef cattle experimental feeds was 98.9%. The method results agreed with th e AOAC INTERNATIONAL Official Method for colorimetric analysis of swine fee d, Method precision was excellent during in-house validation studies, with coefficients of variation (CVs) ranging from about 0.5 to 3%. The method ru ggedness was verified with an overall CV of 3.5%.