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Liu S.,Northwest Agriculture and Forestry University | Liu S.,State Key Laboratory of Crop Stress Biology in Arid Areas | Xie Q.,Northwest Agriculture and Forestry University | Chen J.,Northwest Agriculture and Forestry University | And 3 more authors.
Journal of Chromatography A | Year: 2013

In this study, two novel sample extraction methods for the analysis of bisphenol A (BPA) in edible oils were developed by using liquid-liquid extraction followed by a dispersive liquid-liquid microextraction (LLE-DLLME) and reversed-phase dispersive liquid-liquid microextraction (RP-DLLME). RP-DLLME showed a superior characteristic over LLE-DLLME and other previously reported procedures because of its easy operation, short extraction time, high sensitivity, low organic solvent consumption and waste generation. The optimized extraction conditions of RP-DLLME for 1.0g of edible oil diluted in 4mL of n-hexane were: extractant, 100μL 0.2M sodium hydroxide solution (80% methanol, v/v); extraction time, 1min; centrifugation, 3min. The determination of BPA was carried out by high performance liquid chromatography coupled with a DAD detector. The method offered excellent linearity over a range of 0.010-0.5μgg-1 with a correlation coefficient of r>0.997. Intra-day and inter-day repeatability values expressed as relative standard deviation were 1.9% and 5.9%, respectively. The quantitation limit and detection limit were 6.3 and 2.5ngg-1. The target analyte was detected in 5 out of 16 edible oil samples. The recovery rates in real samples ranged from 89.5 to 99.7%. © 2013 Elsevier B.V. Source


He H.,Northwest Agriculture and Forestry University | Liu S.,Northwest Agriculture and Forestry University | Liu S.,State Key Laboratory of Crop Stress Biology in Arid Areas | Meng Z.,Northwest Agriculture and Forestry University | Hu S.,Northwest Agriculture and Forestry University
Journal of Chromatography A | Year: 2014

The current routes to couple dispersive liquid-liquid microextraction (DLLME) with capillary electrophoresis (CE) are evaporation of water immiscible extractants and backextraction of analytes. The former is not applicable to extractants with high boiling points, the latter being effective only for acidic or basic analytes, both of which limit the further application of DLLME-CE. In this study, with 1-octanol as a model DLLME extractant and six phenols as model analytes, a novel method based on acetonitrile stacking and sweeping is proposed to accomplish large-volume injection of 1-octanol diluted with a solvent-saline mixture before micellar electrokinetic chromatography. Brij-35 and β-cyclodextrin were employed as pseudostationary phases for sweeping and also for improving the compatibility of sample zone and aqueous running buffer. A short solvent-saline plug was used to offset the adverse effect of the water immiscible extractant on focusing efficiency. The key parameters affecting separation and concentration were systematically optimized; the effect of Brij-35 and 1-octanol on focusing mechanism was discussed. Under the optimized conditions, with ~30-fold concentration enrichment by DLLME, the diluted extractant (8×) was then injected into the capillary with a length of 21. cm (42% of the total length), which yielded the overall improvements in sensitivity of 170-460. Limits of detection and qualification ranged from 0.2 to 1.0. ng/mL and 1.0 to 3.4. g/mL, respectively. Acceptable repeatability lower than 3.0% for migration time and 9.0% for peak areas were obtained. The developed method was successfully applied for analysis of the phenol pollutants in real water samples. © 2014 Elsevier B.V. Source


Cao J.,Northwest University, China | Liu S.,Northwest University, China | Liu S.,State Key Laboratory of Crop Stress Biology in Arid Areas | Bai W.,Northwest University, China | And 2 more authors.
Analytical Letters | Year: 2013

A novel method for the determination of the migration of bisphenol A (BPA) from polycarbonate water bottles has been developed by using dispersive liquid-liquid microextraction (DLLME) followed by high performance liquid chromatography for compliance with the regulatory specific migration limit. Experimental parameters, including the type and volume of extractants and dispersers, the sample solution pH, addition of salt, extraction time, and temperature, were examined and optimized. Under the optimum conditions, average recovery rates for the real samples varied from 82% to 98%, with relative standard deviation values less than 3.6%. The method offered excellent linearity over a range of 0.8-600 μg L-1 with a correlation coefficient of r = 0.9999. Intra-day and inter-day repeatability values expressed as relative standard deviation were 3.9% and 6.9%, respectively. The method quantitation limit and detection limit were 0.7 and 0.2 μg L-1, respectively. The developed method was successfully applied to the determination of the migration of bisphenol A from 26 polycarbonate water bottles collected locally. The findings indicated the migration from the used bottles was significantly higher than the new ones, and the migration amounts from one sample was very close to the regulatory specific migration limit, and the amounts from seven samples exceeded the daily intake limit for infants. © 2013 Copyright Taylor and Francis Group, LLC. Source


Chen J.,Northwest University, China | Sun J.,Northwest University, China | Liu S.,Northwest University, China | Liu S.,State Key Laboratory of Crop Stress Biology in Arid Areas
Analytical Letters | Year: 2013

A very simple, sensitive, and reliable method for the routine determination of riboflavin in cereal grains by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was established. Two on-line concentration techniques, namely, stacking in reverse migrating micelles (SRMM) and sweeping, were examined to enhance the detection signal. The optimum separation buffer consisted of 20 mM phosphoric acid and 140 mM sodium dodecyl sulfate (SDS), and a hydrodynamic injection of 30 s at 0.5 psi was confirmed for the introduction of a sample. In addition, it was found that salt in sample matrix influenced the performance of SRMM, showing the standard addition method was required for the quantitative analysis. The linearity of the method was good with a range of 0.5-500 ng/mL (r = 0.9990). The limit of detection (LOD) was 0.29 ng/mL at a signal-to-noise ratio of 3. This procedure presented was successfully applied to determine riboflavin in 18 samples of 9 types of cereal grains. The recovery rates varied from 94% to 98%, and the relative standard deviation (RSDs) was less than 4.1%. © 2013 Copyright Taylor and Francis Group, LLC. Source


Fan Y.,Northwest University, China | Liu S.,Northwest University, China | Liu S.,State Key Laboratory of Crop Stress Biology in Arid Areas | Xie Q.,Northwest University, China
Talanta | Year: 2014

A very simple, fast and environmentally friendly sample extraction method was proposed for the analysis of phthalate esters (PAEs, di-isobutyl phthalate (DIBP), dibutylphthalate (DBP), butylbenzylphthalate (BBP) and bis(2-ethylhexyl)phthalate (DEHP)) in alcoholic beverages by using conventional ionic liquid dispersive liquid-liquid microextraction. The samples were extracted by 160 μL 1-octyl-3-methylimidazolium hexafluorophosphate in the presence of appropriate amount of ethanol and 10% (w/v) sodium chloride solution; the enriched analytes in sedimented phases were analyzed by high performance liquid chromatography-diode array detector (HPLC-DAD). Under the optimum conditions, a satisfactory linearity (in the range of 0.02-1 μg mL-1 for white spirits and 0.01-0.5 μg mL-1 for red wines with the correlation coefficients (r) varying from 0.9983 to 1), acceptable recovery rates (88.5-103.5% for white spirits and 91.6-104.6% for red wines), good repeatability (RSD≤8.0%) and low detection limits (3.1-4.2 ng mL-1 for white spirits and 1.5-2.2 ng mL-1 for red wines) were obtained. The developed method was successfully applied for the determination of the four PAEs in 30 white spirits and 11 red wines collected locally, and the DBP content in 63% (19:30) white spirits exceeded the specific migration limit of 0.3 mg kg-1 established by international regulation. © 2013 Elsevier B.V. Source

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