Determination of decoquinate in animal feeds by liquid chromatography: collaborative study

The performance characteristics of a liquid chromatographic (LC) method for the analysis of decoquinate (DEC) in supplements, premixes, and complete animal feeds at medicating and trace levels were collaboratively studied. DEC is extracted from ground feed samples with 1% calcium chloride-methanol solution using mechanical agitation for 90 min. After centrifugation for 5 min and dilution (if necessary), an aliquot of the extract is diluted with water. The diluted extracts are filtered and analyzed by reversed-phase LC with fluorescence detection. Suspect positive trace-level samples are confirmed by using an alternate excitation wavelength. Fourteen test samples of medicated feeds, supplement, and medicated premix, along with 8 test samples for trace-level analysis, were sent to 13 collaborators (one in Canada, 4 in Europe, and 8 in the United States). Test samples were analyzed as blind duplicates. Acceptable results were received from 12 laboratories for the medicated test samples and from 13 laboratories for the trace-level samples. Repeatability relative standard deviation estimates ranged from 1.3 to 5.6%. Reproducibility relative standard deviations estimates ranged from 2.8 to 6.1%, and HorRat values ranged from 0.22 to 0.74.