Biomedical subjects

You-zhao He

Publications and source records attributed to You-zhao He.

4 recordsLinked to original sources

PubMed2006

Funnelform single-drop microextraction for gas chromatography-electron-capture detection.

A funnelform single-drop microextraction was developed for gas chromatography-electron-capture detection. A solvent microdrop of 4 microL was formed at the tip of a microsyringe needle assembled with a small brass funnel in the microextraction. In the funnel, the restricted microdrop was shaken gently by circular motion in an aqueous sample solution. Eleven organochlorine and two pyrethroid pesticides were used as the model compounds for evaluating the microextraction. The parameters affecting the enrichment factor of the microextraction were investigated, including the funnel inner angle, solvent component, and microdrop volume, etc. With the optimized microextracting conditions, the enrichment factors of organochlorines and pyrethroids were 272-875 and 147-183, respectively. The detection limit was in the range of 1-12 ng/L (S/N = 3). The relative standard deviation (RSD) of peak height was less than 10.2% (n = 8). This proposed technique is simple, convenient, and efficient.

Chromatography, Gas↗

PubMed2005

Reversed-phase electrochromatography with a monolithic microcolumn prepared in a 2.2-mm-inner diameter fused-silica tube.

Capillary electrochromatography possesses advantages of high separation efficiency and velocity, but it also has its disadvantages due to its small inner diameter, such as poor detection sensitivity, low sample capacity, and some trouble in its column preparation. To overcome these shortcomings, a monolithic microcolumn with a surface area larger than 200 m2/g was prepared by sol-gel polycondensation of tetraethoxysilane-hydrochloric acid-poly(ethylene glycol) and filling with fine quartz sand in a 2.2-mm-i.d. fused-silica tube. The prepared microcolumn was used in the separation of aromatic compounds by reversed-phase electrochromatography. Some factors that affected electroosmotic flow were explored, such as electric field strength, buffer concentration, and buffer pH. Acetonitrile concentration in the mobile phase was investigated for phenol, benzene, and naphthalene separation. The separation results were satisfying with the electrochromatographic microcolumns. The detection limits of phenol, benzene, and naphthalene were 0.07, 0.26, and 0.04 mg/L, respectively.

Journal Article↗

PubMed2003

Electrochromatography with a 2.7 mm inner diameter monolithic column.

Monolithic columns of 2.7 mm I.D. have been prepared and used in electrochromatography (EC) separation. Although capillary electrochromatography (CEC) has higher separation efficiency, it displays some shortcomings, such as limited sample loadability and restricted concentration detectability etc. In this paper, we investigate the feasibility of EC separation with millimeter diameter monolithic columns. By using a designed preparation method of monolithic column packed with about 150 microm quartz sand, the effect of Joule heating can be reduced, and the processes of frit making and column packing can be avoided. The concentration detectability of the EC is improved comparing with that of CEC. Moreover, the separation efficiency of 52,000 plates/m was achieved with a 70 mm length and 2.7 mm I.D. monolithic column.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2002

[Separation of saccharides in tobacco by capillary zone electrophoresis].

A method for the separation of derivatized saccharides in tobacco with high performance capillary electrophoresis and ultraviolet spectrophotometry (HPCE-UV) is presented. Five saccharides in tobacco were derivatized with p-aminobenzonitrile, separated at pH 10.5 with 50 mmol/L borate buffer containing 5% (volume fraction, the same in the following percentage concentration) methanol, 5% acetonitrile, 2.5% ethyleneglycol, 2.5% 2-propanol and 1 mmol/L sodium dodecyl sulfate, and detected at 285 nm.

Electrophoresis, Capillary↗