PubMed Health⌕ Search

Biomedical subjects

Wenmin Liu

Publications and source records attributed to Wenmin Liu.

9 recordsLinked to original sources
PubMed2006

Chiral separation of synthetic vicinal diol compounds by capillary zone electrophoresis with borate buffer and beta-cyclodextrin as buffer additive.

The investigation on capillary electrophoretic enantioseparation of six synthetic compounds containing vicinal diol groups has been undertaken to acquire the optimum conditions using native beta-cyclodextrin (beta-CD) as chiral selector and borate as a background electrolyte. The separation was carried out in an uncoated capillary (58.5 cm x 75 microm i.d., effective length 48.5 cm) and the effects of several important factors were investigated in detail. The results showed that beta-CD as a chiral selector exhibited good enantioselectivity and that the enantioseparation was greatly influenced by the structure of the diols, the borate concentration and the buffer pH. The optimum performance was obtained for the chiral vicinal diols under the conditions of 200 mM borate buffer of pH 9.8 containing 1.7% beta-CD at an applied voltage of 15 kV and a capillary temperature of 20 degrees C. Under the conditions, four diols were baseline separated with fast analysis time and the good theoretical plate numbers (above 10 x 10(4)) and favorable migration-time reproducibilities (RSDs below 3.0%) were obtained. The separation results were satisfactory.

Borates↗
PubMed2006

[Determination of organophosphorous pesticide residues in red wine by solid phase microextraction-gas chromatography].

A method for the determination of 12 organophosphorus pesticide residues (OPs) in red wine by fiber solid phase microextraction (SPME) coupled with gas chromatography (GC) was developed and validated. The SPME phase was prepared by sol-gel technology of physical incorporation. The extraction conditions were optimized with the results of stirring rate of 1,250 r/min, NaCl mass concentration of 150 g/L, and extraction time of 30 min. With the sample volume of 25 mL, the relative standard deviations (RSD) of peak areas for most of OPs were below 5%, and the detection limits of OPs were in the range of 5 ng/L-0.38 microg/L. It can be seen from the results that this method has the potential to analyze OPs in other beverages and soft drinking materials.

Beverages↗
PubMed2005

Physically incorporated extraction phase of solid-phase microextraction by sol-gel technology.

A sol-gel method for the preparation of solid-phase microextraction (SPME) fiber was described and evaluated. The extraction phase of poly(dimethysiloxane) (PDMS) containing 3% vinyl group was physically incorporated into the sol-gel network without chemical bonding. The extraction phase itself is then partly crosslinked at 320 degrees C, forming an independent polymer network and can withstand desorption temperature of 290 degrees C. The headspace extraction of BTX by the fiber SPME was evaluated and the detection limit of o-xylene was down to 0.26 ng/l. Extraction and determination of organophosphorus pesticides (OPPs) in water, orange juice and red wine by the SPME-GC thermionic specified detector (TSD) was validated. Limits of detection of the method for OPPs were below 10 ng/l except methidathion. Relative standard deviations (RSDs) were in the range of 1-20% for pesticides being tested.

Chromatography, Gas↗
PubMed2005

Determination of organophosphorus pesticides in cucumber and potato by stir bar sorptive extraction.

Organophosphorus pesticides (OPPs) in vegetables were determined by stir bar sorptive extraction (SBSE) and capillary gas chromatography with thermionic specific detection (TSD). Hydroxy-terminated polydimethylsioxane (PDMS) prepared by sol-gel method was used as extraction phase. The effects of extraction temperature, salting out, extraction time on extraction efficiency were studied. The detection limits of OPPs in water were < or = 1.2 ng/l. This method was also applied to the analysis of OPPs in vegetable samples and matrix effect was studied. Linear ranges of OPPs in vegetable samples were 0.05-50 ng/g with detection limits < or =0.15 ng/g and the repeatability of the method was less than 20% relative standard deviation.

Chemical Fractionation↗
PubMed2004

Preparation of stir bars for sorptive extraction using sol-gel technology.

A sol-gel coating method for the preparation of extractive phase on bars used in sorptive microextraction is described. The extraction phase of poly(dimethylsiloxane) is partially crosslinked with the sol-gel network, and the most part is physically incorporated in the network. Three aging steps at different temperatures are applied to complete the crosslinking process. Thirty-micrometer-thick coating layer is obtained by one coating process. The improved coating shows good thermal stability up to 300 degrees C. Spiked aqueous samples containing n-alkanes, polycyclic aromatic hydrocarbons and organophosphorus pesticides were analyzed by using the sorptive bars and GC. The results demonstrate that it is suitable for both aploar and polar analytes. The detection limit for chrysene is 7.44 ng/L, 0.74 ng/L for C19 and 0.9 ng/L for phorate. The extraction equilibration can be reached in less than 15 min by supersonic extraction with the bars of 30 microm coating layer.

Chromatography↗
PubMed2004

[Analysis of group components in oils and aromatics in fuel oils].

On-line coupling of capillary liquid chromatography-capillary gas chromatography (CGC) technique for detailed group component analysis of aviation kerosene, diesel fuels, lubricating oils, extraction oils, and residuum, is described. Aromatics in fuel oils were separated according to their ring number and structures. Different eluents were stored in loops on interface, and introduced sequentially onto the CGC for detailed separation and quantitative anal- pre-column and the components of interest (aromatics plus heavier compounds) eluting from an analytical column were all directed to the same flame ionization detector, which performed quantitative analysis of aromatic hydrocarbons in oils by correction factor normalization method. Real oil samples were analyzed and the results showed that the reproducibility, accuracy and reliability of the method can fulfill the requirements of practical application.

Chromatography, Gas↗
PubMed2004

[Determination of partition coefficient of dissolved gases in transformer oil using phase ratio variation method and static headspace gas chromatography].

The partition coefficients of dissolved gases in transformer oil were determined using a phase ratio variation method and static headspace gas chromatography (GC). A pressure balancing and gas volume-metering device was connected to the vent of a sample loop on a six-port injection valve of the GC. The gas phase sample from the headspace vial of 25 mL was transferred to an 80 microL sample-loop through a fused silica capillary of 0.53 mm i.d., and then separated and determined quantitatively by GC. A 2 m x 1 mm i.d. GDX502 micro-packed column was used for the separation. Five different gas-liquid volume ratios in the headspace vials were measured at different equilibrium concentrations. The partition coefficients of hydrocarbon gases including methane, acetylene, ethylene, ethane and propane dissolved in transformer oil were determined by using linear regression analysis at 20 degrees C and 50 degrees C separately. The errors between the real values and regression values from experimental data were less than 4.14% except methane. Fundamental data for on-line measurement of dissolved gases in transformer oil are provided by GC.

Acetylene↗
PubMed2003

Determination of flavones in Crataegus pinnatifida by capillary zone electrophoresis.

A capillary electrophoretic method for the separation of four flavones in Crataegus pinnatifida is developed. The four flavones in Crataegus pinnatifida are separated on baseline within 15 min using 50mM borax buffer containing 15% acetonitrile and adjusted to pH 8.15 with phosphoric acid. The detection limits of vitexin-2"-rhamnoside, hyperside, rutin, and vitexin are 0.35, 0.30, 0.40 and, 0.29 microg/mL, respectively. The recovery of these flavones is as follows: vitexn-2"-rhamnoside 96.8%, hyperside 99.9%, rutin 97.1%, and vitexin 97.8%. The results are in accordance with those obtained in the high-performance liquid chromatography system. The content of flavones is higher in Crataegus pinnatifida leaves than in its fruits, and hyperside is not detected in either Crataegus pinnatifida fruits or flowers.

Buffers↗