[Determination of biurea in flour and its products by liquid chromatography-tandem mass spectrometry].

A novel method was established for the determination and identification of biurea in flour and its products using liquid chromatography-tandem mass spectrometry( LC-MS /MS). The biurea was extracted with water and oxidized to azodicarbonamide by potassium permanganate. The azodicarbonamide was then derivatized using sodium p-toluene sulfinate solution. The separation was performed on a Shimpak XR-ODSⅡ column( 150 mm × 2. 0 mm,2. 2 μm) using the mobile phase composed of acetonitrile and 2 mmol/L ammonium acetate aqueous solution( containing 0. 2%( v /v) formic acid) with a gradient elution program. Tandem mass spectrometric detection was performed in multiple reaction monitoring( MRM) scan mode with a positive electrospray ionization( ESI +) source. The method used stable isotope internal standard quantitation. The calibration curve showed good linearity over the range of 1- 20 000 μg /kg( R2 = 0. 999 9). The limit of quantification was 5 μg /kg for biurea spiked in flour and its products. At the spiking levels of 5. 0,10. 0 and 50. 0 μg /kg in different matrices,the average recovery of biurea was 78. 3%- 108. 0% with the relative standard deviations( RSDs) ≤5. 73%. The method developed is novel,reliable and sensitive with wide linear range,and can be used to determine the biurea in flour and its products.