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Biomedical subjects

Yafeng Guan

Publications and source records attributed to Yafeng Guan.

24 records · Page 2Linked to original sources
PubMed2004

[Analysis of volatile oil in Illicium verum fruit by on-line coupled packed capillary liquid chromatography/capillary gas chromatography].

Volatile oil in Illicillm Verum Fruit was analyzed by on-line coupled packed capillary high performance liquid chromatography/capillary gas chromatography (micro-HPLC-CGC). A micro-HPLC column of 250 mm x 0.32 mm i.d. packed with 5 microm cyano-bonded silica stationary phase was used for group separation. n-Hexane/acetonitrile/dichloromethane (80:8:12, v/v) was used as mobile phase at a flow rate of 1.8 microL/min. Five groups of eluents from the micro-HPLC were collected and stored in a multi-loop interface, which were then transferred to a capillary gas chromatograph sequentially for further analysis. A 10 m x 0.53 mm i.d. retention gap connected with a 30 m x 0.53 mm i.d. x 1.0 microm SE-54 analytical column was used for CGC analysis. In-column splitless injection mode was adopted for better quantitation and manipulation of chromatograms. Five chromatograms were obtained and compared with the result of direct CGC analysis of the same sample. It was found that there were at least 3 new compounds that were not found nor separated before by conventional capillary gas chromatography/mass spectrometry method.

Allylbenzene Derivatives↗
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↗
PubMed2004

[Design of laser-induced fluorescence detector for high performance liquid chromatography].

Based on confocal configuration, a laser-induced fluorescence detector (LIFD) for high performance liquid chromatography (HPLC) is described and evaluated. A diode double-pumped solid-state laser emitting at 473 nm is used as excitation source. A detection cell of 7 microL physical volume and 0.1 nL effective optical volume was designed for conventional HPLC-LIFD. The angle between entrance and outlet channels of the cell was 120 degrees, without any change of internal diameters or right-angles along the channels. These measures insured the elimination of bubble accumulation or formation inside the cell, and additional band broadening effect. Riboflavin standard was used as test sample to evaluate the performance of the HPLC-LIFD. The analyses of real samples containing riboflavin were demonstrated.

Chromatography, High Pressure Liquid↗
PubMed2003

A miniaturized fluorescence detector with a windowless flow cell using a light-emitting diode.

A miniaturized fluorescence detector using a high-brightness light-emitting diode as an excitation source was constructed and evaluated. A windowless flow cell based on a commercial four-port cross fitting was designed to reduce the stray-light level and to eliminate the optical alignment. The observed detection limit for fluorescein was 26 nM in the continuous-flow mode. The error in the reproducibility of the responses was evaluated by the FIA method, and was found to be within 2% RSD.

Journal Article↗
PubMed2002

Column switching-back flushing technique for the analysis of aromatic compounds in gasoline.

A simple method, based on the technique of capillary column switching-back flushing, has been developed for the detailed analysis of aromatic compounds in gasoline. The sample was first separated on a 30-m long OV-2330 polar precolumn and then backflushed onto a nonpolar analytical column. The early eluting components from the precolumn and the components of interest (aromatic compounds plus heavier compounds) eluting from the analytical column are all directed to the same flame ionization detection system through a T piece, which permits the quantitative analysis of aromatic hydrocarbons in gasoline by a normalization method using correcting factors. The switching time window of the method is +/-5 s, resulting in easier operation and higher reliability. The reproducibility of the quantitative analysis was < or = 3% RSD for real gasoline samples.

Benzene Derivatives↗