A method based on ultra high performance liquid chromatography coupled with tandem mass spectrometry (UPLC/MS/MS) as development for simple and rapid determination of the residues of tinopal CBS - X in rice products. The sample were extracted by 4 % phosphoric acid in acetonitrile and then analyzed in multiple reaction monitoring (MRM) mode. The mobile phase was composed of solvent A (water) and solvent B (acetonitrile). Gradient program was performed as follows: 0 - 0.5 min, 80% A
0.5 - 4.0 min, 20% A and at initial condition. Total run time is 8 min. The flow rate was settled at 0.3 ml/min with an injection volume of 10 μl. Under the optimized conditions, the linear range for tinopal CBS - X is 1.0 – 10 ng/g, the linear correlation coefficients are more than 0.99. The limits of quantification of tinopal CBS - X are 2.20 ng/g. The recoveries of tinopal CBS - X ranged from 93.50 % - 118.3 % with relative standard deviation (RSD) between 0.96 – 12.06 %. The method was validated according to the Directive 2002/657/EC and subsequently applied to 18 samples of rice products.