In this study an isocratic high-performance liquid chromatographic method with diode array detection was developed for simultaneous determination of mesotrione and nicosulfuron active ingredients content in pesticide products formulated as oil dispersion (OD). For the analysis, LC system an Agilent Technologies 1100 was used. Good separation was achieved on a Zorbax SB-C18 column using a mobile phase consisting of 0.1% CH3COOH/acetonitrile (75:25), at a flow rate of 0.9 ml/minute and UV detection at 245 nm. Column temperature was 40 °C, injected volume was 1 µl. Retention times for nicosulfuron and mesotrione were 3.009 min and 4.363 min, respectively. Validation of the method was performed according to IAEA guidelines. The obtained results showed that the linear coefficients were 0.9999 for both analyzed herbicides in the mixture. The repeatability of the method expressed as relative standard deviations (%RSDr) was 0.33% for mesotrione and 0.18% for nicosulfuron. The accuracy of the proposed method was determined from recovery experiments. The obtained results for mesotrione and nicosulfuron were 100.5-102.9% and 99.3-103.9%, respectively, proved to be acceptable. Precision of the method expressed as %RSD was 0.38% for mesotrione and 0.99% for nicosulfuron and are lower than the values calculated by the Horwitz equation
