A new method for computing surface tension using a drop of liquid

In the simulation of a liquid drop it is expensive to calculate the excess pressure and obtain the surface tension by the Laplace formula. We use the Kelvin formula which only requires the vapour density, or at most the virial pressure. Some results are given for a Lennard-Jones 12-6 fluid.     

毛细管电泳柱上安培检测装置的研制

介绍了一种新的毛细管电泳柱上安培检测装置。以碳纤维微电极为工作电极,在自组装的ACS－2000毛细管电泳仪上,测定了三种苯二酚的异构体：邻苯二酚、对苯二酚、间苯二酚,在20min内达到了基线分离。     

Pressure drop in liquid chromatography

Measurement of pressure drop is routinely performed during chromatographic runs. In many cases this information is only used for regulation of mobile phase flow rate to keep pressure drop below defined limit. However, pressure drop can provide additional important information about performance of chromatographic process. In this review different parameters affecting pressure drop such as compressibility of chromatographic media, nature of applied sample and mobile phase flow regime are discussed. Detailed analysis correlating organization of particle based chromatographic media and pressure drop is presented together with its extension to convective media such as membranes and monoliths but also novel 3D printed media. Finally, estimation of layer thickness formed by adsorbed molecules based on a pressure drop data is presented and its applicability is discussed.     

A specialized apparatus for the study of liquid crystals at high pressures

Abstract

A pressure system specially designed for the study of liquid crystal materials at high pressures up to 4kbar is presented. The pressure system is based on a hydrostatic screw injector and uses either oil or gas as the pressure transmitting medium. The type of measurements which can be performed with the instrument include polarized microscopy, optical spectroscopy, electrooptic and electrical measurements. The different measurements performed place specific constraints on the design of the apparatus and the pressure cells, and details are given. A preliminary study of the smectic A modification of the twist grain boundary phase (TGB_A) at high pressures is presented. The pressure versus temperature phase diagram shows (i) a negative gradient of the TGB_A/isotropic phase boundary line and (ii) that the TGB_A phase does not exist at pressures above about 250 bar. Following Lubensky's analogy between the TGB_A phase and type II superconductors, the disappearance of the TGB_A phase at high pressure may imply that the Landau-Ginsburg parameter K decreases with pressure.     

A new high-pressure vapour–liquid equilibrium apparatus

A new variable volume static type high-pressure VLE apparatus has been designed, constructed, and tested on a number of systems. The apparatus has an operating temperature range from 250 K to 393 K and pressure range from absolute vacuum up to 120 bar. The stainless steel equilibrium cell has sapphire viewing windows and a novel liquid sampling technique utilizing gas chromatographic sampling valves which permit phase sampling without disturbance to the equilibrium condition. The apparatus was tested by measuring VLE isotherms for some binary systems, viz., carbon dioxide + toluene at 283.25 K, 311.15 K, 353.15 K and 391.45 K; carbon dioxide + methanol at 263.15 K, 273.15 K, 313.15 K, 363.15 K and 373.15 K; and propane + 1-propanol at 323.15 K, 378.15 K and 393.15 K. Satisfactory modeling was obtained of the measured VLE data and thermodynamic consistency tests showed the data to be not inconsistent.     

Flow of liquid around the encapsulated drop of another liquid

The problem of the infinite uniform flow of liquid around the spherical drop coated with the porous layer is solved. External liquid permeates into the porous layer but is not mixed with the liquid located in the internal cavity of a capsule. The flow inside the porous layer is described by the Brinkman equation; moreover, the viscosity of the Brinkman medium is assumed to be different than the viscosity of pure liquid. The boundary condition of the jump of tangential stresses at the liquid-porous medium interface is used. Velocity and pressure distributions are found and the hydrodynamic force acting on the capsule is calculated. Different limiting cases are considered.     

Temperature drop of feed liquid during pervaporation

Heat transfer during pervaporation through a membrane module of silicone-rubber microtubes was studied for ammonia/water and ethanol/water feeds. The temperature drops of the feed mixture were measured as a function of flow rate, concentration and permeate side pressure. A model calculation with a vapor-phase driving force was compared with the data. The vapor permeability of the permeate components needed in the model were independently measured using an original measurement method with a differential transformer. The present simple model for heat and mass transfer during pervaporation proved to be applicable to the theoretical calculation for a membrane module of pervaporation to be used as a heat-transfer unit.     

Ionic liquid for single‐drop microextraction followed by high‐performance liquid chromatography‐ultraviolet detection to determine carbonyl compounds in environmental waters

A sensitive method based on ionic liquid for single‐drop liquid microextraction coupled with HPLC‐UV was developed for the determination of carbonyl compounds in environmental waters using 1‐octyl‐3‐methylimidazolium hexafluorophosphate [C₈min][PF₆] as extraction solvent and 2,4‐dinitrophenylhydrazine as derivatizing agent. The extraction parameters affecting the enrichment factors such as solvent volume, pH, extraction time and salt concentration were investigated. A homemade funnel form polytetrafluoroethylene sleeve was fixed at the tip of the syringe needle and this allowed the use of 10 μL drop of ionic liquid for direct immersion extraction. Under the optimal conditions, the remarkable enrichment factors up to 150‐fold were obtained depending on the target analytes. The method has been validated when rectilinear relationship was obtained between the concentrations of analytes and peak area in the range of 5–100 ng/mL, the correlation coefficients were from 0.995 to 0.998, and the limit of detection was in the range of 0.04–2.03 ng/mL. The method was applied to monitor the concentration of carbonyl compounds in environmental waters with spiked recovery in the range of 84.2–106.9%.     

An automated evolved gas detection apparatus

An automated evolved gas detection apparatus is described consisting of a furnace, furnace temperature programmer, automatic sample changer, thermistor thermal conductivity detector, and a two channel recorder. The samples are automatically introduced into the furnace chamber, pyrolyzed to a preselected temperature limit, and then removed. After the system has cooled to a preselected lower temperature limit, the cycle is repeated. Eight samples can be studied in a sequential manner.     

Prediction of measurement precision of apparatus using a chemometric tool in electrochemical detection of high-performance liquid chromatography

The relative standard deviation (RSD) of measurements in high-performance liquid chromatography with electrochemical detection (HPLC-ECD) was predicted by a chemometric tool based on the 1/f fluctuation model which is made up of white noise and a Markov process, called the Function of Mutual Information (FUMI) theory. FUMI theory can provide aprecise and reliable detection limit from a single measurement of noise and signal in HPLC-ECD. To obtain RSD (n = 5) for determination of (-)-epicatechin at five concentrations required 12.5 h, while the predicted RSD by FUMI theory required only 0.5 h (one measurement). Moreover, to trace the source of instrumental noise, power spectra of chromatographic baseline were used. Selection of a suitable apparatus in HPLC-ECD system, acquisition of RSD, and detection limits for determination of catechins by HPLC-ECD were simply and easily made by this chemometric tool within a very short time. The use of the FUMI theory for the prediction of measuring precision was more efficient and the optimization was less time-consuming to be suited for determination.     

Titrating apparatus for the detection of soft β-emitting isotopes

The measuring devices reported in the literature allow only radiometric titrations indicated by hard β or γ-radiating isotopes. The authors developed an apparatus also suitable for the detection of soft β-emitting isotopes. In the course of the analysis, the activities are measured in a scintillation system in which the great surface of a mass of anthracene crystals provides excellent contact with the active solution. In studies on the linearity of the scintillation system the sources of error and their elimination were also examined. The sensitivity of the scintillation system was determined with³H,¹⁴C,³⁵S,⁴⁵Ca,³⁶Cl and³²P isotopes, frequently applied in organic chemical practice. The method of adjusting the specific activities of reagent solutions prepared from the various isotopes is discussed. The apparatus makes it possible to extend the applications of radiometric titration in the analysis of organic compounds.     

Developing liquid crystal-based immunoassay for melamine detection

Research on Chemical Intermediates - We have developed a liquid crystal (LC)-based immunoassay for melamine detection by using direct, sandwich and competitive formats. The detection mechanism was...     

A transistorized drop counter for chromatographic use

A completely transistorized drop counter for use in chromatography is described. The instrument is compact and reliable, and offers high versatility.     

Voltammetric/amperometric detection for liquid chromatography

A voltammetric/amperometric detector based on a dual-electrode electrochemical detector is described for liquid chromatography. The detector combines the advantages of both voltammetric and amperometric detection. A three-dimensional data array of current response as a function of both time (chromatographic domain) and potential (electrochemical domain) is obtained. From the chromatographic point of view, this allows post-experimental choice of the optimal detection potential. Different detection potentials can even be chosen for each chromatographic peak. Having the voltammetric data as well as the chromatographic data provides ready identification of chromatographically unresolved compounds and the ability to resolve such co-eluting compounds voltammetrically. The voltammetric data also provide a second method of peak identification for greater certainty in peak assignments. Voltammetric detection limits of less than 10 pmol of material injected on the column were achieved with this detection method. From the electrochemical perspective, voltammetric/amperometric detection provides a technique for obtaining hydrodynamic voltammograms with small amounts or small volumes of sample. Voltammograms can also be obtained for the individual components of complex mixtures without the need for isolation steps.     

Electrophoretic mobility of a liquid drop in a salt-free medium

A theory is proposed for the electrophoretic mobility mu of dilute spherical liquid drops of radius a in salt-free media containing only counterions (e.g., nonaqueous media). As in the case of the electrophoretic mobility of rigid particle in salt-free media, there is a certain critical value of the drop surface charge separating two cases, that is, the low-surface-charge case and the high-surface-charge case. For the low-surface-charge case, mu coincides with that of a drop in an electrolyte solution in the limit of very low electrolyte concentrations kappaa-->0 (Hückel's limit), where kappa is the Debye-Hückel parameter. For the high-surface-charge case, however, mu becomes constant independent of the drop surface charge, since the counterion condensation takes place near the drop surface.