Mixed Carrier System Research Articles

Organic and nutrient removal during start-up period for domestic sewage treatment by an A/O mixed carrier system

This study combined biofilm method and A/O process reasonably to form the biological treatment system. This experiment focused on the performance of the system for domestic sewage according to the determination of CODCr, ammonia nitrogen, total nitrogen, and total phosphorus. The A/O-mixed carrier system had a good removal effect on organic pollutants for simulated domestic sewage. At the start-up period, the average removal rates of CODCr, ammonia nitrogen and total nitrogen were 92%, 90% and 55%, respectively. But the removal effect of total phosphorus was not ideal.

Phase behavior of rifampicin in cholesterol-based liquid crystals and polyethylene glycol

The phase behavior of rifampicin in cholesteryl-based carbonate esters (CCEs), cholesterol and polyethylene glycol4000 (PEG4000) was determined to evaluate their potential in the formulation of dry powder inhalation dosage forms. To guide the identification of the most suitable liquid crystalline system for the solubilization of rifampicin, the dielectric constants were evaluated. Thereafter, the phase behavior of various mixtures were characterized by polarized light microscope (PLM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Among the mixed-carrier systems, the cholesteryl cetyl carbonate (CCC) and PEG4000 system at 1:1mole ratios yielded a homogeneous mixture with relatively high rifampicin content. This result was consistent with the prediction based on the dielectric constants. The phase diagram contained a eutectic point at CCC:PEG4000 (1:1) and 50°C. Finally, the rifampicin drug was successfully incorporated into CCC and PEG system at a 1:6:6mole ratio. Such a system would be amenable for oral inhalation.

Simultaneous determination of eleven ingredients in ophthalmic solutions by cyclodextrin-modified micellar electrokinetic chromatography with tetrabutylammonium salt

Cyclodextrin-modified micellar electrokinetic chromatography was applied to determine simultaneously 11 active ingredients in ophthalmic solutions. All the ingredients were successfully separated by using the mixed carrier system containing sodium dodecyl sulfate with β-cyclodextrin and tetrabutylammonium phosphate. The effects of the cyclodextrin type on selectivity were also examined. Excellent separation of the all ingredients was obtained by the use of dimethyl-β-cyclodextrin. The established method was validated and confirmed to be applicable to the determination of the active ingredients in a commercial ophthalmic solution. These results suggest that capillary electrophoresis can be applied to the quantitative analysis as well as qualitative analysis in pharmaceuticals.

Control of migration time window and selectivity in electrokinetic chromatography with mixed polymeric pseudostationary phases

Control of migration time windows and the improvement of separation were achieved by utilizing mixed polymeric pseudostationary phases in electrokinetic chromatography (EKC) in water–organic solvent mixtures. Polyallylamine (PAA)- supported pseudostationary phases, one with hexadecyl groups (PAA-C 16) with the shorter migration times and the other with decyl groups (PAA-C 10) with the longer migration times, enabled the control of migration time windows when used as a mixture. PAA-C 16 provided better separation for a region with relatively small k′ values as in typical micellar EKC, while PAA-C 10 gave better separation for a region with relatively large k′ values as in reversed-phase liquid chromatography, the mixture of the two PAA derivatives resulting in better overall separations for a wide range of hydrophobic compounds. The migration time of a solute is determined by the relative contribution of each pseudostationary phase to the partition of the solute in a mixed carrier system. A theoretical explanation was provided by assuming the contribution of the two polymeric pseudostationary phases working independently. The migration time of the effective (imaginary) pseudostationary phase was shown to be in between the actual migration times of the two carriers, and can be different for each solute depending upon the relative contribution of the two pseudostationary phases to the solute partition.

Liquid membrane transport of alkali metal cations with mixed carrier systems composed of phosphoric acid-crown ether having a side arm

The liquid membrane transport of alkali metal cations (Li +, Na +, and K +) across a chloroform membrane was carried out using mixed carrier systems composed of bis(2-ethylhexyl)phosphoric acid (B2EHPA) and a series of crown ethers (dioxo-13-crown-4, 13-crown-4, benzo-14-crown-4, 15-crown-5, and benzo-18-crown-6 ethers) having (benzyloxy)methyl and (benzoyloxy)methyl groups. Substituted 15-crown-5 and benzo-18-crown-6 derivatives/B2EHPA mixed carriers showed significantly enhanced transport rates of Li + and Na + compared with those of 15-crown-5/B2EHPA and benzo-18-crown-6/B2EHPA. It was revealed that the introduction of a side arm such as the (benzoyloxy)methyl group to the crown ring easily modified the selectivities of the alkali metal cations in these mixed carrier systems.

Transport of alkali and alkaline earth cations by a crown ether-alkylphosphoric acid system

Abstract Competitive transport of alkali and alkaline earth cations has been carried out by using a mixed carrier system composed of dibenzo-14-crown-4 and bis(2-ethylhexyl)phosphoric acid. In the absence of crown ether, bis(2-ethylhexyl)phosphoric acid transported alkaline earth cations with high selectivity. The combination of dibenzo-14-crown-4 and bis(2-ethylhexyl)phosphoric acid showed a synergistic enhancement in lithium transport, and the enhancement effect was not apparent in transport of other cations. On the other hand, the mixed carrier systems consisting of dibenzo-14-crown-4 and dodecylbenzenesulfonic acid, and of dibenzo-14-crown-4 and 1-bromohexadecanoic acid exhibited the enhancement effects both in lithium transport and in sodium transport. The formation of the synergistic complex was analyzed by using fast atom bombardment mass spectrometry.

Determination of antihistamines in pharmaceuticals by capillary electrophoresis

Capillary electrophoresis with on-column UV detection at 214 nm was used to separate a group of nine antihistamines. All these compounds were satisfactorily separated within ca. 6 min using a mixed carrier system containing sodium dodecyl sulphate with β-cyclodextrin and tetrabutylammonium hydrogensulphate as modifiers. The application of the method to the determination of the amount of antihistamines present in commercial pharmaceutical samples was demonstrated. In addition, the migration behaviour of the antihistamines in the mixed carrier system was examined.

Extraction and transport of lithium ion by a crown ether-alkylphosphoric acid system [1

Mixed carrier systems composed of crown ethers and alkylphosphoric acids have been studied as lithium ionophores using a solvent extraction technique and in transport across liquid membranes. The combination of dibenzo-14-crown-4 and bis(2-ethylhexyl) phosphoric acid showed a synergistic enhancement on both lithium ion selectivity and transport rate. The synergistic effects depended strongly upon crown ether structure and the enhancement was observed only when the metal cation corresponded to the crown ether's cavity diameter. Complex formation in the organic phase was assessed by use of FAB-mass spectrometry.

Thermodynamic analysis for silicon contamination of VPE GaAs

A thermodynamic analysis for silicon contamination in VPE GaAs is described. The analysis is carried out for the inert gas-hydrogen mixed carrier system. It is shown that silicon contamination is related, among other things, to the temperature difference between the source and the substrate and the hydrogen mole fraction in the carrier gas. An explanation is given for the impurity decrease in the single flat temperature zone (SFT) method.

Thermodynamic Analysis of the Vapour Growth of GaAs: The Inert Gas-Hydrogen Mixed Carrier System

An equilibrium calculation for the vapour growth of GaAs in an inert gas-hydrogen mixed carrier system is described. The partial pressures of gaseous- and gallium containing-species in equilibrium with GaAs are calculated for temperatures, chlorine to carrier gas mole ratios and mole fractions of hydrogen relative to the inert gas. It is shown that the general feature of the equilibrium pressures of the reactants for the inert gas- and inert gas-hydrogen mixed-carrier systems is similar to that of a hydrogen carrier system, and that GaAs tends to vaporize into the gas phase with the increase of the mole fraction of the inert gas. An application of the analysis to the vapour growth of GaAs with H2 introduction is discussed.

Vapor growth kinetics of III–V compounds in a hydrogen-inert gas mixed carrier system

Vapor growth of GaAs, GaP, InAs and InP has been carried out in a hydrogen-inert gas mixed carrier system. The growth rate dependences on inert gas partial pressure, subsrtee temperature and reactant (AsCl3 or PCl3) mole fraction have been examined. The growth rate of GaAs decreases with increasing inert gas partial pressure in the whole substrate temperature range; not only in the region where the growth process operates under thermodynamic control, but also in the region of kinetic control. In the thermodynamic control region, the growth rate decrease depends on the kind of inert gas, but this is not true in the kinetic control region. The growth rate decrease in the thermodynamic control region can be explained by an equilibrium calculation based on a single chemical reaction process and the diffusion of reactants in the mixed carrier gas. In the kinetic control region, the hydrogen partial pressure influences the growth rate through the p1.0H2 relation. A model for the growth kinetics, including thehydrogen gas effect, is presented. The inert gas effect on GaP and InAs growth is the same as that on GaAs growth. For InP growth, however, inert gas not only reduces the growth rate, but also causes the source reaction to go out of equilibrium.