Biomedical subjects

Yanqiao Xiang

Publications and source records attributed to Yanqiao Xiang.

6 recordsLinked to original sources

PubMed2006

Ultrahigh pressure liquid chromatography using elevated temperature.

Fast liquid chromatographic (LC) methods are important for a variety of applications. Reducing the particle diameter (d(p)) is the most effective way to achieve fast separations while preserving high efficiency. Since the pressure drop along a packed column is inversely proportional to the square of the particle size, when columns packed with small particles (<2 microm) are used, ultrahigh pressures (>689 bar) must be applied to overcome the resistance to mobile phase flow. Elevating the column temperature can significantly reduce the mobile phase viscosity, allowing operation at higher flow rate for the same pressure. It also leads to a decrease in retention factor. The advantage of using elevated temperatures in LC is the ability to significantly shorten separation time with minimal loss in column efficiency. Therefore, combining elevated temperature with ultrahigh pressure facilitates fast and efficient separations. In this study, C6-modified 1.0 microm nonporous silica particles were used to demonstrate fast separations using a temperature of 80 degrees C and a pressure of 2413 bar. Selected separations were completed in 30 s with efficiencies as high as 220,000 plates m(-1).

Chromatography, High Pressure Liquid↗

PubMed2006

Pseudolinear gradient ultrahigh-pressure liquid chromatography using an injection valve assembly.

The use of ultrahigh pressures in liquid chromatography (UHPLC) imposes stringent requirements on hardware such as pumps, valves, injectors, connecting tubing, and columns. One of the most difficult components of the UHPLC system to develop has been the sample injector. Static-split injection, which can be performed at pressures up to 6900 bar (100,000 psi), consumes a large sample volume and is very irreproducible. A pressure-balanced injection valve provided better reproducibility, shorter injection time, reduced sample consumption, and greater ease of use; however, it could only withstand pressures up to approximately 1000 bar (15,000 psi). In this study, a new injection valve assembly that can operate at pressures as high as 2070 bar (30,000 psi) was evaluated for UHPLC. This assembly contains six miniature electronically controlled needle valves to provide accurate and precise volumes for introduction into the capillary LC column. It was found that sample volumes as small as several tenths of a nanoliter can be injected, which are comparable to the results obtained from the static-split injector. The reproducibilities of retention time, efficiency, and peak area were investigated, and the results showed that the relative standard deviations of these parameters were small enough for quantitative analyses. Separation experiments using the UHPLC system with this new injection valve assembly showed that this new injector is suitable for both isocratic and gradient operation modes. A newly designed capillary connector was used at a pressure as high as 2070 bar (30,000 psi).

Journal Article↗

PubMed2003

Application of diaza-18-crown-6-capped beta-cyclodextrin bonded silica particles as chiral stationary phases for ultrahigh pressure capillary liquid chromatography.

Two bonded chiral stationary phases (CSPs), 8-aminoquinoline-2-ylmethyl- and 8-aminoquinoline-7-ylmethyl-diaza-18-crown-6-capped [3-(2-O-beta-cyclodextrin)-2-hydroxypropoxy]propylsilyl silica particles (non-porous, 1.5 microm), have been prepared and evaluated using capillary liquid chromatography at high pressures (> or = 8000 p.s.i.). High column efficiency (up to 400 000 plates m(-1)) was achieved for chiral separations. These CSPs with two recognition sites, i.e. substituted-diaza-18-crown-6 and beta-cyclodextrin combined with high chromatographic efficiency provide good resolution of a variety of enantiomers and positional isomers in relatively short times under reversed-phase conditions. After inclusion of a Ni (II) ion from the mobile phase, the positively charged crown ether-capped beta-cyclodextrin facilitates specific static, dipolar, and host-guest complexation interactions with solutes.

Aza Compounds↗

PubMed2003

Synthesis of micron diameter polybutadiene-encapsulated non-porous zirconia particles for ultrahigh pressure liquid chromatography.

In this study, 1-microm diameter polybutadiene-encapsulated non-porous zirconia particles were synthesized, slurry packed into 50-microm I.D. fused-silica capillary columns, and evaluated using ultrahigh pressure liquid chromatography. The dependencies of column efficiency and solute retention factor on pressure were investigated. Efficiencies as high as 280000 plates per meter were obtained for the separation of anti-inflammatory drugs at a pressure of 1351 MPa. Comparing the reversed-phase behavior of the polybutadiene-encapsulated non-porous zirconia with octadecylsilane bonded non-porous silica, greater selectivity was found using the zirconia-based material for the applications reported in this study. The encapsulated non-porous zirconia particles demonstrated excellent thermal stability in the separation of polycyclic aromatic hydrocarbons at a temperature of 100 degrees C and a pressure of 1351 MPa.

Anti-Inflammatory Agents↗

PubMed2003

Safety concerns in ultrahigh pressure capillary liquid chromatography using air-driven pumps.

Ultrahigh pressure liquid chromatography (UHPLC) is an emerging technique which utilizes pressures higher than 10,000 p.s.i. to overcome the flow resistance imposed when using very small particles as packing materials in fused-silica capillary columns (1 p.s.i.=6894.76 Pa). This technique has demonstrated exceptionally high separation speeds and chromatographic efficiencies. However, safety is a concern when extremely high pressures are used. In this study, the safety aspects of capillary column rupture during operation were identified and carefully evaluated. First, liquid jets may be formed as a result of blow-out of the on-column frits or from rupture of the capillary at or near the column inlet. Second, incorrect installation of the capillary at the injector, failure of the ferrule used in the capillary connection, or rupture of the capillary can produce high speed projectiles of silica particles or column fragments. Experiments were carried out in the laboratory to produce liquid (water) jets and capillary projectiles using a UHPLC system, and the power density, an important parameter describing water jets in industrial practice, was calculated. Experimental results were in accordance with theoretical calculations. Both indicated that water jets and capillary projectiles under ultrahigh pressures might lead to skin penetration under limited conditions. The use of a plexiglass shroud to cover an initial length of the installed capillary column can eliminate any safety-related concerns about liquid jets or capillary projectiles.

Air↗

PubMed2003

Elevated-temperature ultrahigh-pressure liquid chromatography using very small polybutadiene-coated nonporous zirconia particles.

Capillary columns packed with small diameter particles typically lead to low permeability and long separation times in high-performance liquid chromatography. Ultrahigh pressures (>10,000 p.s.i.; 1 p.s.i. is identical with 6,894.76 Pa) can be used to overcome the limitations that small particles impose. Ultrahigh-pressure liquid chromatography (UHPLC) has demonstrated great potential for high-speed and high-efficiency separations. Decreasing the viscosity of the mobile phase by elevating the temperature could additionally reduce the pressure drop and facilitate the use of longer columns or smaller particles to achieve even higher total plate numbers. For this reason, we investigated the use of elevated temperatures in UHPLC. Water-resistant, flexible heater tape covered with insulation was used to provide the desired heat to the column. Polybutadiene-coated 1 microm nonporous zirconia particles were used because of their chemical stability at elevated temperature. A column efficiency as high as 420,000 plates m(-1) was obtained. The effects of temperature and pressure on the separation of parabens were investigated. Separation of five herbicides was completed in 60 s using 26,000 p.s.i. and 90 degrees C.

Butadienes↗