High pressure liquid chromatographic determination of arprinocid in feed

Arprinocid [9 - (2 - chloro - 6 - fluorophenylmethyl)-9H-purin-6-amine] is determined in feed by high pressure liquid chromatography with a silica column and ultraviolet detection. The drug is extracted from the feed into chloroform in the presence of pH 7 phosphate buffer, transferred to 0.1N HCl, and separated from interfering substances by partitioning with hexane. The acidic solution is neutralized, and the analyte is extracted into chloroform for injection into the chromatograph. This procedure has been applied to feeds containing 0.0030--0.0090% arprinocid with a precision of less than 5% relative standard deviation at the 0.0060% formulated concentration level. The results of this chromatographic procedure also correlate with those from a colorimetric analysis.