Unsalted sweet butter was heated at 100,150, or 200 °C for 5 h. The headspace volatiles formed were collected during heating using a simultaneous purging and solvent extraction apparatus. Among 140 peaks on a gas chromatogram of the headspace sample from butter heated at 200 °C, 77 were positively identified by gas chromatography and gas chromatography/mass spectrometry. Major compounds identified were 21 aldehydes, 12fatty acids, 11 ketones, lOnitrogenand/or sulfur-containing compounds, 7 alkanes, 6 -lactones, and 4 furans, which constituted over 85% of total volatiles recovered. The number of volatiles formed in a headspace of butter heated at 100 or 150 °C was much less than that formed at 200 °C. However, all volatiles formed at 100 and 150 °C were found in a sample heated at 200 °C.

Polished rice grains were fortified with 500 p p b of chlorpyrifos. T h e fortified residues were analyzed by gas chromatography with a nitrogen-phosphorus detector or a Hall detector. Chlorpyrifos and its breakdown product 3,5,6-trichloro-2-pyridinol were recovered from fortified rice grains in the levels of 456 and 3.4 ppb, respectively. Washing rice grains with water removed approximately 60% of the chlorpyrifos residues. Fortified chlorpyrifos was found in cooked rice at a level of 130 ppb, which was approximately 30% of t h e original quantity. Acid treatment was required t o remove chlorpyrifos bound to proteins or carbohydrates in the cooked rice.Heavy use of pesticides on farm fields has begun to receive much attention because pesticide residues in food commodities may be hazardous to human health. Therefore, many researchers have studied how to remove pesticide residues from food products (Liska and Stadelman, 1969;Geisman, 1975;Kim et al., 1979).Rice is one of t h e most important food crops in the world. In particular, it is the major diet in the countries of Southeast Asia. However, there is still not sufficient information on t h e role of washing or cooking processes in removing pesticide residues from rice to assess the safety of consumers' health because of the lack of a satisfactory analytical method.In this study, an analytical method t o determine chlorpyrifos residues spiked in polished rice was developed, and then removal of chlorpyrifos from polished rice under various cooking conditions was investigated. Chlorpyrifos was chosen because i t is the active ingredient of a nonsystemic insecticide used widely on a variety of agricultural commodities including rice (Worthing, 1987). EXPERIMENTAL PROCEDURESMaterials. Authentic chlorypyrifos, 3,5,6-trichloro-2-pyridinol (TCP), and chlorpyrifos oxone were from Dow Chemical Co. (Midland, MI). Silylation reagent bis(trimethylsily1)acetamide (BSA) was from Aldrich Chemical Co. (Milwaukee, WI). All solvents were of analytical grade and used without further purification. Rice grains (medium-grain variety) were obtained from a local market.Fortification of Chlorpyrifos to Rice Grains. Polished rice grains (2 kg) were spread over a polyethylene film and then 40 mL of an aqueous chlorpyrifos solution, prepared from a Lorsban 4E formulation (Dow), was evenly sprayed over the rice. The calculated amount of chlorpyrifos fortified was 500 ppb. The fortified rice grains were wrapped with a polyethylene film and stored in a refrigerator at 5 "C for 12 h. They were then dried in an aluminum tray in the shade for 2 days and stored in a freezer at -25 O C until analysis.Sample Preparations. Experiment Z. Fortified rice (100 g) was extracted with 600 mL of ethyl acetate in a Soxhlet extractor with a 60 mm X 180 mm thimble at the extraction rate of 60 min/cycle for 24 h. The extract was dried through sodium sulfate placed in a funnel. After an aliquot (100 mL) of the filtrate was concentrated to 20 mL by using a rotary flash evaporator at 40 OC under reduced pressure,...