DETERMINATION OF TILMICOSIN IN BOVINE-MILK BY LIQUID-CHROMATOGRAPHY WITH ULTRAVIOLET DETECTION

A method is described for determining tilmicosin in bovine milk by liq uid chromatography with ultraviolet (UV) detection, Samples are defatt ed by centrifugation. The lower skim layer is cleaned on a C-18 solid- phase extraction cartridge. The extract is concentrated and analyzed w ith a reversed-phase phenyl column with UV detection at 280 nm. The me thod was validated with control milk fortified at 50, 100, and 200 ng/ mL. Average recoveries (and intralaboratory coefficients of variation) were 97% (9%), 98% (5%), and 101% (3%), respectively. The limit of qu antitation is approximately 20 ng/mL, and the limit of detection is ap proximately 13 ng/mL. The method was tested on milk from a cow dosed w ith tilmicosin.