Tiing Yu

Liquid-liquid extraction of lysozyme using a dye-modified ionic liquid

An affinity-dye, Cibacron Blue 3GA (CB), derivatized organic salt [BMIM]3[CB] was synthesized for lysozyme extraction. This compound was formed by mixing an ionic liquid (IL) [BMIM][Cl] and the silver salt of CB. Liquid-liquid extractions of lysozyme from the aqueous and [BMIM]3[CB] in [BMIM][PF6] solutions were examined in this study. The transfer of lysozyme from the aqueous phase to the IL phase decreased while the pH of the aqueous phase increased. An extraction higher than 90% was observed at pH 4. Under a high ionic strength, the lysozyme would transform back from the IL phase into the aqueous phase. Lysozyme molecules were almost quantitatively recovered from the IL phase to the aqueous solutions of 1M KCl under pH 9-11. It appeared that the extraction was specific for lysozyme in contrast to cytochrome c, ovalbumin, and bovine serum albumin. The extraction efficiency of the IL phase remained essentially the same after eight cycles of extraction.

Size-fractionation of silver nanoparticles using ion-pair extraction in a counter-current chromatograph

Size separation of silver nanoparticles was investigated in counter-current chromatography (CCC) based on a unique step-gradient extraction process. Carboxylate anions were modified on silver nanoparticles to produce water-dispersible nanoparticles. The aqueous nanoparticles were readily transferred to the organic phase (toluene/hexane=1:1, v/v) together with the phase transfer catalyst, tetraoctylammonium bromide (TOAB), owing to the ion-pair adduct formation between silver nanoparticle anions and tetraoctylammonium cations. Smaller nanoparticles were found to be more readily transferred to the organic phase compared to larger nanoparticles. Various concentrations of TOAB in the organic elution phase were used in the CCC extraction experiments. It appeared that a concentration of 0.02 mM of TOAB was adequate to achieve optimum separation and recovery for the aqueous Ag nanoparticle sample (1.5mg) in the CCC extraction experiments. Samples of 15.8+/-5.3 nm were separated; the distributions of four fractions collected were 13.7+/-1.9, 14.1+/-3.5, 19.2+/-4.3, and 22.2+/-4.9 nm. Compared with the stepwise extraction performed in this study, the step-gradient extractions using CCC provided much better size discrimination.

Counter-current chromatography using supercritical fluid carbon dioxide as mobile phase

Abstract Supercritical fluid carbon dioxide was employed in solar eccentric counter-current chromatography (SECCC) to replace the liquid mobile phase in the traditional arrangement. The fundamental difference from the conventional liquid-liquid system is the requirement for high-pressure operation. The experimental set-up is presented to illustrate the necessary modifications that accomodate operation with a supercritical fluid. Studies on the stationary phase retention due to various experimental conditions are discussed. A mixture of acetophenone and benzophenone was chromatographed using mixtures of water and methanol as the stationary solvent system to demonstrate the feasibility of this technique. At present the efficiency of the separation is not satisfactory owing to the phase separator inserted in the system to remove liquid droplets which contributed to considerable peak broadening.

Peak crossover in high-performance liquid chromatography elution monitored using whole-column detection.

A whole-column detection (WCD) system was fabricated using the parts from a typical A4 size optical scanner. Optimum layout of the fluorescence tube, beam condenser and photon transducers from the scanner made an effective devise to examine the dynamic chromatographic separation process. This system was applied in monitoring peak crossover in an ion-pair chromatographic elution. A stage-wise gradient was conducted in eluting a mixture of New Coccine and Carmoisine. Compound New Coccine lagging behind after sample injection moved passing Carmoisine at the column outlet. The complete on-column elution process could be observed directly using this detection system. This inexpensive and rugged WCD system provided a 0.3mm spatial resolution and a 3.6 ms temporal resolution and was proven to be an adequate device to directly monitor solute retention behavior in the liquid chromatography column.

Feasibility study of using refrigerant 1,1,1,2-tetrafluoroethane as the mobile phase in high-speed counter-current chromatography

Newly synthesized environmentally benign refrigerant 1,1,1,2-tetrafluoroethane (R134a) was used as the mobile phase in high-speed counter-current chromatography (HSCCC) in this study. R134a remains as a liquid under mild pressure and becomes a gas at atmospheric pressure. Accordingly, operation of HSCCC equipped with regular polytetrafluoroethylene tubing was satisfactory. Since R134a turned into gas at ambient temperature and pressure, further concentration for the collected fractions after elution was not required. A mixture of four standard components of Angelicae radix was separated to demonstrate the feasibility of using this new mobile phase in HSCCC.

Resolution studies on counter-current chromatography using supercritical fluid carbon dioxide

Counter-current chromatography (CCC) is a form of liquid-liquid partition chromatography. It requires two immiscible solvent phases; the stationary phase is retained in the separation column, generally by centrifugal force, while the mobile phase is eluted. We recently replaced the mobile phase with supercritical fluid carbon dioxide (SF CO ). Since the solvent 2 strength of SF CO can be varied by changing the temperature and pressure of the system, separation adjustments are thus 2 more versatile. We investigated the pressure and temperature effects on resolution using water and low-carbon alcohol mixtures as the stationary phases. It was demonstrated that these special properties of SF CO were indeed beneficial to the 2 optimization of separations. In addition, the phase retention ratio was examined in terms of separation resolution. The results appeared very similar to those obtained from conventional traditional CCC. This study should be helpful for the future development of SF applications in CCC.

Peak shape and dispersion behavior of solutes in counter-current chromatography with a single phase.

The dispersion behavior of solutes was investigated in a rotating flowing coiled tube. Potassium iodide, tartrazine, ascorbic acid, lysozyme, bovine serum albumin (BSA), and silver nanoparticle (AgNPs) samples were eluted in a coiled tube of counter-current chromatography (CCC) apparatus with a single phase. Apparent convection peaks of low-diffusivity solutes appeared in the static CCC tube, while Gaussian-like peaks showed up for the high-diffusivity solutes. When the rotation speed of the CCC apparatus was elevated, all solute peak widths became smaller, and the convection peaks of AgNPs and BSA were minimized and formed Gaussian-like peaks. The axial dispersions of all solutes were reduced owing to the higher radial mass transfer in the rotating CCC column. The same reasoning could also be used to rationalize other special band shapes encountered in two-phase CCC separations.

Examination of the temporal effect in a flow injection analysis system using multi-channel absorbance detection

In addition to the Poiseuille effect, a so-called temporal effect was proposed recently to elucidate the commonly observed tailing peak signals of flow injection analysis (FIA). A multi-channel absorbance detector was used in this study to obtain the FIA peaks on both the spatial and temporal coordinates. The temporal effect was analyzed by comparison of the profiles between the experimental and the corresponding Gaussian peaks, and by comparison of asymmetry factors between the spatial and the temporal peaks. The temporal effect appeared to be the major factor under flow rates ranging from 0.5 to 8 ml min (-1). This was despite the presence of a spatially frontal peak observed in the FIA tubing, which was found to result in a tailing peak on the temporal coordinate due to this discussed cause. In addition, the temporal effect became greater as the flow rate increased.