Effect of Cooking Process on the Residues of Three Carbamate Pesticides in Rice

A gas chromatography mass spectrometry with spike calibration curve method was used to quantify three carbamate pesticides residue in cooked white rice and to estimate the reduction percentage of the cooking process duration. The selected pesticides are three carbamate pesticides including carbaryl and pirimicarb that their MRL is issued by “The Institute of Standards of Iran” and propoxur which is used as a widely consumed pesticide in rice. The analytical method entailed the following steps: 1- Blending 15 g cooked sample with 120 mL acetonitrile for 1 min in solvent proof blender, 2- Adding 6 g NaCl and blending for 1 min, 3- Filtering upper layer through 25 g anhydrous Na2SO4, 4- Cleaning up with PSA and MgSO4, 5- Centrifuging for 7 min, 6- Evaporating about 0.3 mL and reconstituting in toluene till 1 mL, 7- Injecting 2 μL extract into GC/MS and analyzing by single quadruple selected ion monitoring GC/MS-SQ-SIM. The concentration of pesticides and the percentage of pesticides amounts after the cooking were determined by gas chromatography mass-spectrometry (GC/MS) using with interpolation of the relative peak areas for each pesticide to internal standard peak area in the sample on the spiked calibration curve. Calibration curve was linear over the range of 25 to 1000 ng/g, and LOQ was 25 ng/g for all three pesticides. The percent of loss for the three pesticides were 78%, 55% and 35% for carbaryl, propoxur and pirimicarb respectively. Different parameters such as vapor pressure, boiling point, and suspect ability of the compound to hydrolysis, could be responsible for the losing of pesticides during the cooking process.