In view of routine work, we search for the high petfonnance liquid chromatographic method to detect pyrimethamine in feed. It can obtain good resolution by ion pair reverse phase chromatography using methanol: Pie B8 (60:40) as mobile phase, ￡g-bondapak C18 as chromato graphic column and 280 nut as detection wavelength. Under these conditions, it shows good linear effect between five standard concentrations (1,2.5,5,7.5 , and 10 ppm) and absorption intensity. In addition, its relative standard enor ofpeak area is below 2.3°/b and the reproducibitv is 97.7%. All of these results reveal the system stability is very well.
We use three clean-up methods to compare their complexity and select one which obtains the least interference peak. The principle of the clean-up method is that the feed is extracted by acetonitrile. defatted by n-hexane and past through alumina column and Sep-Pak Cl8 cartridge. The recovei-y test is done by ion pair reverse phase chromatography as mentioned above. The recovery of feeds are 70% and 60% individually when spike 0.5 and 2.0 ppm pyrimethamine. The detection limit is 20 ng in this experiment.