When GCB/PSA was used in the cleanup procedure, the chromatogram registered was cleaner than other sorbents. And the carbon GCB commercial cartridge, Florisil commercial cartridge and alumina N commercial cartridge gave dirtier chromatograms, especially for the carbon GCB commercial cartridge. Co extractions interfered with the detection of target compounds, which could not be sepa rated from the target compounds absolutely. This may result in unstable baseline and cover the sign of analyses as well as made low metolachlor, pretiachlor and very high recoveries for butachlor. Although some other co extractions could not interfere with the pesticide peaks, they will be present in the elutes and can damage the chromatographic systems.

The highest cleanup ability of GCB/PSA cartridge may be the result of the following: the GCB/PSA cartridge is a dual layer SPE tube that contains both GCB and PSA separated EKB-569 by a polyethylene frit. GCB layer can remove most of the visible plant pigment but do little to eliminate the fatty acid, however, PSA layer significantly retains fatty acids, organic acids, sugars and some polar pigments, the combi nation of GCB and PSA was found to provide the best clean up of total matrix compounds in this study and it was selected for the purification procedure. 3. 3 Validation of the method 3. 3. 1 Linearity, limits of detections, limits of quantifications and analytical recoveries In this experiment, linearity calibration curves for all pesticides over five calibration levels, from 0. 01 to 0. 5 mg/ kg, were constructed using TCMX as the IS.

The calibration curves were linear over the whole concentration tested for all the acetanilide herbicides with correlation coefficients ranging from 0. 9930 to 0. 9996. Table 1 shows calibration parameters, SNX-5422 analytical recov eries and RSD from spiked rice, wheat and maize samples and LODs, LOQs and MRLs of analytes established by EU and Japanese Positive list system. LOD and LOQ were calculated for 3 and 10 times the standard deviation above the blank signal. As can be seen from Table 1, LODs and LOQs were in the range of 0. 8 1. 7 and 3. 1 5. 3 mg/kg, respectively. The obtained recoveries and RSDs were 80. 3 and 115. 8%, and 2 8. 3 and 12. 9%, respectively. Due to the different matrix affection, differences in recoveries and RSDs in rice, wheat and maize sample were obtained.

And these obtained results show that the developed method satisfies the need of monitoring acetanilide herbicides in rice, wheat and maize samples. 3. 3. 2 Analysis of real samples In order to assess the applicability of the method to real samples, nine samples including three rice samples, three wheat samples and three maize samples obtained from different areas of HDAC-42 China were analyzed in triplicate in accordance with the developed method. In only one wheat sample and one maize sample, propyzamide, metolachlor and di ufenican were detected but all concentrations were found lower than MRLs established by EU and Japanese. For comparison, the samples were also analyzed by shake ask extraction. The results are shown in Table 2. It can be observed that no statistical differences were determined between residues extracted by ASE and shake ask.

Besides, statistical evaluation indicated no significant differences between the quantities of the pesticide residues 4 Concluding remarks A method for acetanilide herbicides in cereal crops based on ASE SPE GC/ECD analysis was developed. Four parameters affecting caspase the efficiency of the extraction were investigated: temperature, static time, number of cycles and solvent. The cleanup step was also compared by testing GCB/PSA with other three different common sorbents: GCB, Florisil and alumina N. The GCB/PSA commercial cartridge was selected for purification because this sorbent gives the best cleanup recoveries and the cleanest GC ECD chromatograms.

The whole method of analysis was validated by the study of the analytical recoveries at spiked level, LODs, LOQs, accuracy HSP precision and by comparison of the values obtained with those obtained by shake ask. Recoveries of pesticides from fortified rice, wheat and maize samples are 103. 1 and 88. 6 115. 8% for fortified 0. 05 mg/kg levels, respectively. The RSDs were generally 8. 3 and 12. 9%, respectively. The results obtained and the standard deviations were satisfactory. Compared with other reports, this method presented other advantages related to cost, analysis time, solvent consumption and automation. It was demonstrated that the developed method is suitable for the analysis of acetanilide herbicides in cereal productions. Alachlor acetanilide) is an efective pre emergence and postemergence chloroacetani lide herbicide that has been widely used to control annual grasses and broadleaf weeds in agricultural crops.