A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems

Vejrosta, J., Novák, J. and Jönsson, J.Å., 1982. A method for measuring infinite-dilution partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems. Fluid Phase Equilibria, 8: 25–35.A method has been developed for measuring the partition coefficients of volatile compounds between the gas and liquid phases of aqueous systems, based on the direct analysis of both phases. A gas mixture containing a known proportion of a volatile compound is drawn through the liquid (water) until equilibrium is established. A defined volume of the liquid phase is then withdrawn through a porous-polymer trap while maintaining the system at equilibrium. The residual water in the trap is then expelled by a stream of nitrogen gas, and the deposit remaining is thermally desorbed and analyzed by gas chromatography. This approach, together with an experimental technique for producing gas mixtures containing an accurately known concentration of hydrocarbon at low values, makes it possible to determine accurately the partition coefficients of low-solubility compounds, such as for hydrocarbons in aqueous systems, at very low solute concentrations in the system. The method has been verified by measuring the partition coefficient of hexane between the gas and liquid phases of an aqueous system at various concentrations and temperatures.     

Channel shape effects on the solution-flow characteristics and the liquid/liquid extraction efficiency in polymer microchannel chips.

A polymer microchannel chip with a symmetrical or unsymmetrical zigzag-side-walled structure was fabricated by an imprinting method, and applied to study shape effects on solution flow characteristics as well as on the liquid/liquid extraction efficiency of an aluminium(III) chelate complex (Al-DHAB: DHAB = o,o'-dihydroxyazobenzene) in a microchannel chip. In an unsymmetrical zigzag-side-walled channel chip (us-channel), an oil/water interface was sinusoidal, while that in a symmetrical zigzag-side-walled channel chip (s-channel) was flat as long as the observation was made under an optical microscope. It was demonstrated that the efficiency of the water-to-oil (1-butanol) extraction of Al-DHAB in the microchannel was governed by the contact time between the two phases. As the most important results, furthermore, the extraction efficiency was higher in the us-channel, as compared with that in the s-channel, owing to the sinusoidal liquid/liquid interfacial structure and, therefore, to the high interfacial area between the two phases.     

Chromatographic sample collection from two-phase (gas+liquid) flows

A particularly challenging sample presentation in analytical chemistry is a flowing stream that consists of both a gas and liquid phase, combined with the common situation in which a reliable analysis is needed for both phases, separately. In these cases, the vapor and liquid must be physically separated (without change to either), before the individual phases can be collected and analyzed. It is not possible to analyze two-phase flows otherwise. Although the two phases are at equilibrium, it is imperative that no liquid contaminate the vapor, and no vapor be entrained in the liquid at a given temperature and pressure. In this paper, we describe a simple on-line device that can individually separate and collect the vapor and liquid phases of a two-phase flow. The apparatus, which we call P(2)SC, uses an adaptation of the branch point separator, with vapor collection done downstream in a metal bellows. The liquid collection is done in a length of Teflon tube. The separated vapor and liquid phases are then easily transferred into any desired analytical instrument with a syringe, although any sample introduction method, such as a valve, could be used as well. We discuss the application of this device with a stream of thermally stressed rocket kerosene.     

Coexistence of liquid phases in the sodium polyphosphate-chromium nitrate-water system

The formation of coexisting liquid phases out of aqueous aluminum polyphosphate solutions was previously suggested as an essential step in aluminum polyphosphate nanoparticle formation. This hypothesis could not be directly verified because the separation of the two phases is very difficult, but a different situation was found in the case of chromium (III) polyphosphate. The phase diagram of the sodium polyphosphate-chromium nitrate-water system at 25 degrees C presents an extensive region with two coexisting liquid phases (L-L), together with a single liquid phase (L) and a solid-liquid (S-L) domain. Within the L-L region, admixture of the reagents produces initially a turbid liquid, out of which two transparent liquid phases separate in a short time, under gravity: one is dense, dark, and viscous while the other has a light color and a lower density. The amounts of the separated phases were determined, as well as their viscosities, densities, pH, UV-vis spectra, and relevant molalities: P (from polyphosphate), Cr(3+), NO(-)(3+), and Na(+). The two liquid phases undergo significant color, pH, and viscosity changes with time. The calculated phase diagrams display the major features of the experimental phase diagram.     

Saturated vapor pressure in the thallium-cadmium system

Component vapor pressures in the thallium-cadmium system determined by the method of boiling points (isothermal variant) and the flow method were used to calculate the thermodynamic characteristics of the vapor and condensed phases in the region of the existence of liquid solutions. The temperature-concentration dependences of the thermodynamic values were determined. The phase diagram was augmented by liquid-vapor phase transitions at atmospheric pressure and in a vacuum (100 and 10 Pa) with the determination of the boundaries for the coexistence region of the liquid and vapor phases.     

Reversed-phase chromatography

HPLC (high-performance liquid chromatography) is an analytical method of great versatility and sensitivity. The use of silica-bonded non-polar stationary phases in place of the traditional polar stationary phases has resulted in the technique of reversed-phase chromatography. This has proved a most useful analytical tool, particularly for the analysis of biological samples. Furthermore the technique has great potential as a means of measuring a number of physicochemical properties.     

The phase behavior, structure, and dynamics of rodlike mesogens with various flexibility using dissipative particle dynamics simulation

We present a systematic dissipative particle dynamics (DPD) study on the phase behavior, structure, and dynamics of rodlike mesogens. In addition to a rigid fused-bead-chain model with RATTLE constraint method, we also construct a semirigid model in which the flexibility is controlled by the bending constant of k(φ). Using this notation, the rigid model has an infinite bending constant of k(φ)=∞. Within the parameter space studied, both two kinds of models exhibit the nematic and smectic-A phases in addition to the isotropic and solid phases. All of the phase transitions are accompanied by the discontinuities in the thermodynamical, structural, and dynamical quantities and the hysteresis around the transition points, and are therefore first order. Note that the obtained solid state exhibits an in-layer tetragonal packing due to the high density. For the rigid model, the simulations show that the liquid crystal phases can be observed for mesogens with at least five beads and the nematic phase is the first one to appear. More importantly, the phase diagram of seven-bead-chain models is obtained as a function of k(φ) and temperature. It is found that decreasing the value of k(φ) reduces the anisotropy of molecular shape and the orientational ordering, and thereby shifts the liquid crystal phases to the lower temperature end of the phase diagram. Due to the different k(φ) dependence of phase transition temperatures, the nematic phase range exhibits a more marked narrowing than the smectic-A phase as k(φ) is reduced, implying that the flexibility has a destabilizing effect on the nematic and smectic-A phases. We also have investigated the anisotropic translational diffusion in liquid crystal phases and its temperature and flexibility dependence. In our study, we find that the phases formed, their statical and dynamic properties, as well as the transition properties are in close accord with those observations in real thermotropic liquid crystals. It is clear that both the rigid and semirigid models we used are valuable models with which to study the behavior of thermotropic liquid crystals using DPD algorithm.     

Support-free pulsed liquid–liquid chromatography

A simple technique of support-free liquid–liquid chromatography is suggested that operates without incorporation of a centrifuge. The pulsed chromatography apparatus consists of a stationary coiled tube and a pulsation device to produce reciprocating motion of liquid phases within each individual coil segment. This reciprocating motion generates a centrifugal force field varying in intensity and direction that leads to an improved mixing of the two liquid phases and retains the stationary phase in the coiled tubing. The intensity of the back and forth motion of liquid phases within each coil unit can be varied by varying the frequency and/or the amplitude of the pulsations generated by the pulsation device. As the magnitude of the stationary phase retention is of paramount importance for success of the technique, the retention of the stationary phase in the pulsed coil column was experimentally studied. A few experiments were conducted to test the chromatographic behavior of valeric (n-pentanoic) and caproic (n-hexanoic) acids. The results obtained demonstrate the potential of the new separation method for preparative purposes.     

Using the liquid nature of the stationary phase in countercurrent chromatography. IV. The cocurrent CCC method

The retention volumes of solutes in countercurrent chromatography (CCC) are directly proportional to their distribution coefficients, K(D) in the biphasic liquid system used as mobile and stationary phase in the CCC column. The cocurrent CCC method consists in putting the liquid "stationary" phase in slow motion in the same direction as the mobile phase. A mixture of five steroid compounds of widely differing polarities was used as a test mixture to evaluate the capabilities of the method with the biphasic liquid system made of water/methanol/ethyl acetate/heptane 6/5/6/5 (v/v) and a 53 mL CCC column of the coil planet centrifuge type. It is shown that the chromatographic resolution obtained in cocurrent CCC is very good because the solute band broadening is minimized as long as the solute is located inside the "stationary" phase. Pushing the method at its limits, it is demonstrated that the five steroids can still be (partly) separated when the flow rate of the two liquid phases is the same (2 mL/min). This is due to the higher volume of upper phase (72% of the column volume) contained inside the CCC column producing a lower linear speed compared to the aqueous lower phase linear speed. The capabilities of the cocurrent CCC method compare well with those of the gradient elution method in HPLC. Continuous detection is a problem due to the fact that two immiscible liquid phases elute from the column. It was partly solved using an evaporative light scattering detector.     

The plastic and liquid phases of CCl3Br studied by molecular dynamics simulations

We present a molecular dynamics study of the liquid and plastic crystalline phases of CCl(3)Br. We investigated the short-range orientational order using a recently developed classification method and we found that both phases behave in a very similar way. The only differences occur at very short molecular separations, which are shown to be very rare. The rotational dynamics was explored using time correlation functions of the molecular bonds. We found that the relaxation dynamics corresponds to an isotropic diffusive mode for the liquid phase but departs from this behavior as the temperature is decreased and the system transitions into the plastic phase.     

Retention in liquid chromatography with multicomponent mobile phases: Relationship with binary systems

Summary Using the concept of an effective concentration a method is proposed for predicting retention in liquid chromatography with multicomponent mobile phases based on experiments with corresponding binary ones. The method is verified for normal and reversed-phase systems with ternary mobile phases and agrees closely with experimental data.     

Evaluation of ionic liquid stationary phases for one dimensional gas chromatography-mass spectrometry and comprehensive two dimensional gas chromatographic analyses of fatty acids in marine biota

Ionic liquid stationary phases were tested for one dimensional gas chromatography-mass spectrometry (GC-MS) and comprehensive two dimensional gas chromatography (GC×GC) of fatty acid methyl esters from algae. In comparison with polyethylene glycol and cyanopropyl substituted polar stationary phases, ionic liquid stationary phases SLB-IL 82 and SLB-IL 100 showed comparable resolution, but lower column bleeding with MS detection, resulting in better sensitivity. The selectivity and polarity of the ionic liquid phases are similar to a highly polar biscyanopropyl-silicone phase (e.g. HP-88). In GC×GC, using an apolar polydimethyl siloxane×polar ionic liquid column combination, an excellent group-type separation of fatty acids with different carbon numbers and number of unsaturations was obtained, providing information that is complementary to GC-MS identification.     

Molecular design of flexible liquid crystal oligomers stabilising the chiral frustrated phases

ABSTRACT

Chirality induces structural frustration in liquid crystal systems, producing various kinds of chiral frustrated phases, for example, twist grain boundary (TGB) phases, blue phases (BPs) and dark conglomerate (DC) phases. Almost all molecules exhibiting these frustrated phases have a rigid shape. Especially, a bent–core unit is regarded as a key structure for BPs and DC phases. This paper describes that some flexible liquid crystal oligomers being far from a rigid bent–core molecule stabilise these phases. The LC oligomers have a supermolecular structure in which mesogenic units are connected via flexible spacers. By designing intermolecular interactions, they can exhibit various molecular packing structures in the liquid-crystalline phases as follows: chiral dimers inducing TGB phases, U-shaped and T-shaped oligomers stabilising BPs and achiral liquid crystal trimers exhibiting DC phases. I discuss how the designed liquid crystal oligomers produce the chiral frustrated phases.     

Fluorocarbon stationary phases for liquid chromatography applications

This article presents an overview on fluorocarbon stationary phases for liquid chromatography (LC) applications. Fluorocarbons developed as alternative reverse phases have revealed previously unknown separation mechanisms and special utilities. Solvophobicity and fluorophilicity of the fluorinated phases provide enhanced selectivity for organofluorine compounds. The dual normal- and reverse-phase characteristics make fluorinated phases suitable for analysis of polar pharmaceutical and biological samples such as proteins, peptides, nucleotides, steroids, and alkaloids. Fluorinated phases for other applications including supercritical fluid chromatography (SFC), micellar electrokinetic liquid chromatography (MEKC), ion chromatography (IC), open tubular electrochromatography (OTEC), and liquid chromatography-mass spectrometry (LC-MS) are also highlighted.     

Using the liquid nature of the stationary phase. VI. Theoretical study of multi-dual mode countercurrent chromatography

Countercurrent chromatography (CCC) is a separation technique using a biphasic liquid system and centrifugal forces to maintain a support-free liquid stationary phase. Either one of the two phases can be the liquid stationary phase. It is even possible to switch the phase role during the separation. The dual-mode method is revisited recalling its theoretical background. The multi-dual mode (MDM) CCC method was introduced to enhance the resolution power of a CCC column. The theoretical study of the MDM method is validated by modeling the separation of two solutes. The basic hypothesis is that the forward step (partial classical elution) is followed by a backward step that returns the less retained solute to the column head. The equations show that the most important parameter to maximize resolution is not the number of MDM steps but the total volume of liquid phases used to elute the solutes. The model is validated calculating correctly the peak position of previously published MDM experiments.     

离子对反相液相色谱同时测定家兔血浆中的外源性磷酸肌酸及其代谢产物肌酸

建立了离子对反相高效液相色谱法(IP-RP-HPLC)同时测定家兔血浆中外源性磷酸肌酸(PCr)及其代谢产物肌酸(Cr)的方法,用于研究外源性PCr在家兔体内的药代动力学。以含离子对试剂四丁基硫酸氢铵(TBA)的磷酸盐缓冲液-甲醇为流动相,在Kromasil-C18色谱柱上进行梯度洗脱。采用内标法定量、以基线扣除法计算外源性PCr和Cr的浓度。PCr和Cr的线性范围分别为10～7500 mg/L和10～1500 mg/L;日内和日间精密度均≤6.2%,准确度分别为99.7%~102.2%和96.5%~102.4%;萃取回收率均大于92%。静脉注射PCr后,血浆中PCr的消除为二室模型,消除半衰期为(20.4±2.7) min;表观分布容积为(0.179±0.037) L/kg;清除率为(0.019±0.002) L/(kg\5min);静脉注射PCr后血浆中迅即出现降解产物Cr,其达峰时间为30 min;消除半衰期为(43.7±4.5) min。本方法的专属性强,准确度和精密度高,能特异性地测定家兔血浆中的PCr和Cr。实际应用结果表明,该方法完全符合PCr药代动力学生物分析方法学的要求。     

Feasibility of enhancing high-performance liquid chromatography using microwave radiation

High-performance liquid chromatography (HPLC) is the most versatile of the chromatographic techniques because it is applicable to a wide variety of analytes. Unfortunately, liquid mobile phases have relatively low diffusivities. A novel approach is presented for increasing the diffusivity of a liquid mobile phase. The method advocated in this study is the first process that has been described by which it is possible to increase the diffusivity of a liquid while having essentially no effect on other physical properties of the liquid, such as the temperature or solvating power. It is demonstrated that it is possible to sharpen peaks, in an HPLC separation, by the application of microwave radiation.     

Selective transport of Ag(Ⅰ) ion across a bulk liquid and polymer membranes incorporated with di-N-benzylated O_3N_2 donor macrocycles

<正>The selective bulk liquid membrane and polymer membrane transports of Ag(Ⅰ) from an aqueous solution containing seven metal cations,Co(Ⅱ),Ni(Ⅱ),Cu(Ⅱ),Zn(Ⅱ),Ag(Ⅰ),Cd(Ⅱ) and Pb(Ⅱ),was studied.The source phases contained equimolar concentrations of the above-mentioned cations,with the source and receiving phases being buffered at pH 5.0 and 3.0,respectively. Ag(Ⅰ) ion transport occurred with a good efficiency from the aqueous source phases across the bulk liquid membrane and polymer membrane(derived from cellulose triacetate) containing ligand 1 as the ionophores,into the aqueous receiving phases.Clear transport selectivity for Ag(Ⅰ) was observed using ligand 1.There was no selectivity for the cations using ligand 2 in the both bulk liquid membrane and polymer membrane transports.     

Adjusting the chromatographic properties of poly(ionic liquid)‐modified stationary phases by substitution on the imidazolium cation

Poly(ionic liquid)‐modified stationary phases can have multiple interactions with solutes. However, in most stationary phases, separation selectivity is adjusted by changing the poly(ionic liquid) anions. In this work, two poly(ionic liquid)‐modified silica stationary phases were prepared by introducing the cyano or tetrazolyl group on the pendant imidazolium cation on the polymer chains. Various analytes were selected to investigate their mechanism of retention in the stationary phases using different mobile phases. Two poly(ionic liquid)‐modified stationary phases can provide various interactions toward solutes. Compared to the cyano‐functionalized poly(ionic liquid) stationary phase, the tetrazolyl‐functionalized poly(ionic liquid) stationary phase provides additional cation‐exchange and π‐π interactions, resulting in different separation selectivity toward analytes. Finally, applicability of the developed stationary phases was demonstrated by the efficient separation of nonsteroidal anti‐inflammatory drugs.     

分散液-液微萃取快速、直接测定有机化合物lgP值

用3-氯丙基三甲氧基硅烷对Fe₃O₄纳米球的表面进行改性, 制得表面疏水的Fe₃O₄/SiCH₂CH₃Cl纳米球. 将Fe₃O₄/SiCH₂CH₃Cl纳米球均匀预分散在正辛醇中, 利用分散液-液微萃取建立了快速、 直接测定有机化合物lgP值的新方法. 待测有机化合物可在3 min内在两相达到分配平衡, 通过磁铁吸引含有Fe₃O₄/SiCH₂CH₃Cl纳米球的正辛醇小液滴, 可实现两相快速完全分离. 在萃取过程中, 由于Fe₃O₄/SiCH₂CH₃Cl纳米球被正辛醇包围, 失去对待测化合物的吸附能力, 因此Fe₃O₄/SiCH₂CH₃Cl纳米球对测定有机化合物分配平衡的影响很小. 通过该方法测定了14种不同有机化合物的lgP值, 结果均与文献报道一致. 与其它直接测定方法相比, 该方法快速、 准确、 简单且样品消耗少.