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

A liquid chromatographic (LC) method for the analysis of sulfamethazine (SM T) in complete swine and cattle feed was collaboratively studied. The metho d uses post-column derivatization with dimethylaminobenzaldehyde and detect ion at 450 nm. To 5 g finely ground feed, extractant (0.2N HCI + 1.5% dieth ylamine in 25% methanol), and internal standard solutions are added, and th e SMT is extracted by shaking for 1 h. Clarified extract (high-level sample extract diluted to a target concentration of ca 5.5 mu g/mL) is chromatogr aphed on a C-18 reversed-phase LC column with acetonitrile-2% acetic acid ( 17 + 83) mobile phase. Sulfamerazine is used as an internal, or surrogate s tandard to correct for variable recovery of sulfamethazine from a variety o f feed matrixes. Six Youden matched-pair samples were sent to 10 collaborat ors in Korea, Canada, and the United States. Label claims on the commercial feeds ranged from 0.0077 to 0.22% SMT. The SMT mean recovery as determined from the 5 samples with known analyte content was 99.8%, The within-labora tory relative standard deviation (repeatability) ranged from 0.28 to 4.72%. Among-laboratory (including within-laboratory) relative standard deviation (reproducibility) ranged from 1.26 to 4.87%. The authors recommend the met hod for AOAC INTERNATIONAL Official First Action status.