This technique is based on the use of a solvent or combination of solvents to extract organic pollutants at elevated pressure and temperature from environmental samples, increasing 
the kinetics of the extraction process. As a result, the extraction time and solvent consumption are significantly decreased. In the last years, ASE has been applied for the extraction of pesticides from different matrices: soils, fish, fruits, vegetables, etc. and it is used in the U. S. Envir onmental Protection Agency method 3545 for the analysis of organic compounds in solid matrices. However, it has never been reported on the possibility of extending this approach to acetanilide herbicide residue analysis in cereal crops. In trace analysis of organic compounds in complex matrices like foods, the cleanup procedure is as important as the extraction step.
Moreover, the presence of inter ferences could impair the LOD or even damage the chro matographic MEK Inhibitors system. Therefore, when the great extracting power of the solvents and the analytical metho dology are employed, the extract contains numerous inter fering substance, which makes the purification of this extract mandatory. Several approaches have been developed for obtaining accurate results in pesticide residues deter mination, such as liquid liquid partitioning and size exclusion chromatography. However, these methods are usually time consuming or expensive. Over the last decades, solid phase extraction has become an important clean up technique and is commonly used in the process of acetanilide herbicides determination.
Daniele and Aramendia have applied Florisil tube for eliminating matrix LY-411575 interference in the determination of acetanilide herbicide in wheat and olive oil, respectively. Now, in parallel with the development of new technologies, more and more adsorbents have been used in SPE tube, which largely expanded the application of SPE in pretreatment. The main objective of this work was to develop a simple method based on ASE and SPE purification for the simul taneous quantification of eight acetanilide herbicides, propyzamide, napropamide, acetochlor, alachlor, metola chlor, butachlor, pretiachlor and di ufenican, in cereal crops. During the ASE process, four factors, including temperature, static time, extraction solvent and the number of cycle, were considered.
In order to minimize the presence DNA Damage of interfering compounds in the GC system, extraction was followed in both cases by a clean up step with SPE, graphitic carbon black/primary secondary amine, GCB, Florisil and alumina N SPE tubes and compared. Finally, the ASE GCB/PSA was used for the extraction and clean up procedure while gas chromatography electron capture detector was employed for the determination of acetanilide herbicides in the puri fied extracts due to the high sensitivity and selectivity of ECD, different samples from China were determined using the developed method. 2. 1 Materials and reagents Analytical standards of propyzamide, di ufenican and 2,4,5,6 tetrachloro m xylene as internal stan dard were purchased from Dr. Ehrenstofer. Alachlor, acetochlor, pretiachlor, butachlor, metola chlor, propanil were all supplied by Agro Environment Protection and Monitor Ministry.
The stock standard solution was prepared in n hexane at 100 mg/mL. The calibration solutions were prepared by diluting the stock solution using blank samples. Concentrations were Neuronal Signaling 0. 01, 0. 02, 0. 05, 0. 1 and 0. 5 mg/mL for each acetanilide herbicide. All stock solutions and working standard solutions were stored at _18 and 1 41C, respectively. Ethyl acetate, n hexane and acetonitrile were of chro matographic grade obtained from Tedia Company. Toluene, acetone and sodium sulfate were of analytical grade supplied by China National Medicine. Na 2SO 4 was heated at 6501C for 4 h, and then was stored in a desiccator before use. Deionized water was used throughout.
The SPE tubes investigated for the clean up PARP procedure were GCB/PSA SPE tube, 6 mL, carbon GCB SPE tube, 12 mL, Florisil SPE tube 6 mL and alumina N SPE tube 3 mL. The column oven temperature program was used as follows: initial temperature 1201C, held for 1 min and increased to 1401C at a rate of 101C/min, and held for 5 min, and increased to 1721C at 51C/min, and held for 10 min, and then increased to 2601C at 101C/min, and eventually held for 5 min. The injector temperature was set to 2601C in splitless mode and ECD tempera ture was 3401C. The carrier helium with a ow rate of 1. 5 mL/min and the make up gas nitrogen with a ow rate of 60 mL/min were selected based on the instrument optimization results provided by the manufac turers identification of peaks and compared with the retention times of each compound with the standard solution. 2. 4 Sample preparation The dried samples of cereals were collected from different areas of China. These samples were ground into powder and sieved through a 40 mesh sieve, and then stored at room temperature in glass recipients in the dark before their analysis.