Mei-E Yue

A rapid, simple, and sensitive method has been developed for the analysis of pyrethroid herbicides in fruits by using headspace in-tube microextraction (HS-ITME) coupled with reverse-flow micellar electrokinetic capillary chromatography (RF-MECC). In the newly developed method, by placing a capillary filled with background electrolyte (BGE) of RF-MECC in the HS above the sample solution, the pyrethroid herbicides were extracted into the acceptor phase in the capillary. After extraction, electrophoresis of the extracts in the capillary was carried out. The influence of some essential BGE components such as sodium dodecyl sulfate (SDS) and organic modifiers concentrations was investigated. Extraction parameters were also systematically investigated, including the extraction temperature, extraction time, salt concentration, and volume of the sample solution. Under the optimized conditions, enrichment factors for three pyrethroids were 309, 133, and 288, respectively. The proposed method provided a good linearity, low limits of detection (below 1.00 ng/mL), and good repeatability of the extractions (relative standard deviations [RSDs] below 7.83%, n = 6). The fruit samples were analyzed by the proposed method, and the obtained results indicated that the proposed method provides acceptable recoveries and precisions.

A simple, reproducible and sensitive micellar electrokinetic chromatography method was developed for the separation and determination of dimethyl phthalate (DMP), diethyl phthalate (DEP), dibuthyl phthalate (DBP), dihexyl phthalate (DHP) and bis(2-ethylhexyl) phthalate (DEHP) in running water and milk. Field-enhanced sample injection with reverse migrating micelles was used for on-line preconcentration of the analytes. The buffer contained 50 mM H₃PO₄–NaOH, 160 mM sodium dodecyl sulfate (SDS), 15% acetonitrile and 20% 2-propanol, at the pH of 2.0. The sample solution was diluted with water containing 5 mM SDS and injected for 5 s with–20 kV after gravity injection of 5 s water plug at 20 cm high. Under the optimum conditions, the analytes were well separated and by optimizing the stacking conditions, about 51, 62, 57, 48 and 43 fold improvement in the detection sensitivities were obtained for DMP, DEP, DBP, DHP and DEHP, respectively. The instrument detection limits (S/N = 3) of DMP, DEP, DBP, DHP and DEHP were 0.1, 0.05, 0.05, 0.02 and 0.05 µg/mL, respectively. The recoveries of DMP, DEP, DBP, DHP and DEHP in water were 86.9–98.7, 88.9–105.2, 91.7–109.4, 93.0–108.2 and 91.0–99.2%, respectively. The phthalates were successfully determined in running water and milk with satisfactory repeatability and recovery. The contents of DEHP and DHP in the running water were 0.45 and 1.23 µg/mL, respectively. The other analytes were not detected in the analyzed running water and milk.