Phase separation of gas–liquid and liquid–liquid microflows in microchips

Phase separation of gas–liquid and liquid–liquid microflows in microchannels were examined and characterized by interfacial pressure balance. We considered the conditions of the phase separation, where the phase separation requires a single phase flow in each output of the microchannel. As the interfacial pressure, we considered the pressure difference between the two phases due to pressure loss in each phase and the Laplace pressure generated by the interfacial tension at the interface between the separated phases. When the pressure difference between the two phases is balanced by the Laplace pressure, the contact line between the two phases is static. Since the contact angle characterizing the Laplace pressure is restricted to values between the advancing and receding contact angles, the Laplace pressure has a limit. When the pressure difference between the two phases exceeds the limiting Laplace pressure, one of the phases leaks into the output channel of the other phase, and the phase separation fails. In order to experimentally verify this physical picture, microchips were used having a width of 215 μm and a depth of 34 μm for the liquid–liquid microflows, a width of 100 μm and a depth of 45 μm for the gas–liquid microflows. The experimental results of the liquid–liquid microflows agreed well with the model whilst that of the gas–liquid microflows did not agree with the model because of the compressive properties of the gas phase and evaporation of the liquid phase. The model is useful for general liquid–liquid microflows in continuous flow chemical processing.     

Automated apparatus for the rapid determination of liquid–liquid and solid–liquid phase transitions

An automated apparatus developed for the determination of liquid–liquid and solid–liquid equilibrium temperatures with a resolution of 1 mK and a traceable accuracy of 0.01 K is described. The amount of light transmitted through six sample cells placed in a computer controlled thermostat is recorded at heating or cooling rates from 0.075 to 15 K h⁻¹. The construction does not require expensive optic equipment like lasers, glass fibre optics or photomultipliers, but is based on light emitting diodes (LED) as light sources and light dependent resistors (LDR) or photodiodes as detectors. As shown by the discussed examples, the instrument has a wide range of possible applications from the investigation of simple one-component and binary systems to the study of the complicated phase behavior of surfactant solutions.     

Comparison of dispersive liquid–liquid microextraction and hollow fiber liquid–liquid–liquid microextraction for the determination of fentanyl,alfentanil, and sufentanil in water and biological fluids by high-performance liquid chromatography

Dispersive liquid–liquid microextraction (DLLME) and hollow fiber liquid–liquid–liquid microextraction (HF-LLLME) combined with HPLC–DAD have been applied for the determination of three narcotic drugs (alfentanil, fentanyl, and sufentanil) in biological samples (human plasma and urine). Different DLLME parameters influencing the extraction efficiency such as type and volume of the extraction solvent and the disperser solvent, concentration of NaOH, and salt addition were investigated. In the HF-LLLME, the effects of important parameters including organic solvent type, concentration of NaOH as donor solution, concentration of H₂SO₄ as acceptor phase, salt addition, stirring rate, temperature, and extraction time were investigated and optimized. The results showed that both extraction methods exhibited good linearity, precision, enrichment factor, and detection limit. Under optimal condition, the limits of detection ranged from 0.4 to 1.9 μg/L and from 1.1 to 2.3 μg/L for DLLME and HF-LLLME, respectively. For DLLME, the intra- and inter-day precisions were 1.7–6.4% and 14.2–15.9%, respectively; and for HF-LLLME were 0.7–5.2% and 3.3–10.1%, respectively. The enrichment factors were from 275 to 325 and 190 to 237 for DLLME and HF-LLLME, respectively. The applicability of the proposed methods was investigated by analyzing biological samples. For analysis of human plasma and urine samples, HF-LLLME showed higher precision, more effective sample clean-up, higher extraction efficiency, lower organic solvent consumption than DLLME.     

Determination of non-steroidal anti-inflammatory drugs in urine by the combination of stir membrane liquid–liquid–liquid microextraction and liquid chromatography

A stir membrane liquid phase microextraction procedure working under the three-phase mode is proposed for the first time for the determination of six anti-inflammatory drugs in human urine. The target compounds are isolated and preconcentrated using a special device that integrates the extractant and the stirring element. An alkaline aqueous solution is used as extractant phase while 1-octanol is selected as supported liquid membrane solvent. After the extraction, all the analytes are determined by liquid chromatography (LC) with ultraviolet detection (UV). The analytical method is optimized considering the main involved variables (e.g., pH of donor and acceptor phases, extraction time, stirring rate) and the results indicate that the determination of anti-inflammatory drugs at therapeutic and toxic levels is completely feasible. The limits of detection are in the range from 12.6 (indomethacin) to 30.7 μg/L (naproxen). The repeatability of the method, expressed as relative standard deviation (RSD, n = 5) varies between 3.4% (flurbiprofen) and 5.7% (ketoprofen), while the enrichment factors are in the range from 35.0 (naproxen) to 72.5 (indomethacin).     

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.     

Determination of ochratoxin A in pig tissues by liquid–liquid extraction and clean-up and high-performance liquid chromatography

A fast, simple, and sensitive HPLC–FD method is described for determination of ochratoxin A (OTA) in pig kidney and muscle; a small mass (<2.5 g) of sample and a relatively small volume (<15 mL) of a non-halogenated extraction solvent are required. Ochratoxin B, systematically absent from all the samples investigated, was used as internal standard. Liquid–liquid partition was used for sample clean-up. Recoveries at the 1 ng g^–1 level were 86±15% and 74±8% for kidney and muscle, respectively, and detection limits were 0.14 and 0.15 ng g^–1. Clean-up by solid-phase extraction (SPE) is required for pig liver. A survey of the OTA content of tissues of pigs slaughtered in southern Italy revealed that 52 out of 54 analysed samples were contaminated; the OTA concentration in kidney ranged between 0.26 and 3.05 ng g^–1. The effect of measurement precision on compliance with legal limits is also discussed.     

Preconcentration and determination of five antidepressants from human milk and urine samples by stir bar filled magnetic ionic liquids using liquid–liquid–liquid microextraction-high-performance liquid chromatography

A sensitive and straightforward liquid–liquid–liquid microextraction method was developed to preconcentrate and cleanup antidepressants, including mirtazapine, venlafaxine, escitalopram, fluoxetine, and fluvoxamine, from biological samples before analyzing with high-performance liquid chromatography. The essential novelty of this study is using magnetic ionic liquids as the extraction phase in the lumen of hollow fiber and preparing a liquid magnetic stir bar. In this method, polypropylene hollow fiber was utilized as the permeable membrane for the analyte extraction. Six magnetic ionic liquids consisting of the transition metal and rare earth compounds were synthesized and then hollow fiber lumen was injected as acceptor phase to extract the antidepressants. Besides, 3-pentanol as a water-immiscible solvent was impregnated in the hollow fiber wall pores. The effective factors in the method were optimized with the central composition design. The resultant calibration curves were linear over the concentration range of 0.8–400.0 ng mL⁻¹ (R² ≥ 0.996). The method displayed the proper detection limit (0.11–0.24 ng mL⁻¹), the reasonable limit of quantification (≤0.79 ng mL⁻¹), wide linear ranges, high preconcentration factors (≥294.3), and suitable relative standard deviation (2.31–5.47%) for measuring antidepressant medications. Analysis of human milk and urine samples showed acceptable recoveries of 96.5–103.8% with excellent relative standard deviations lower than 5.95%.     

Isobaric vapor–liquid–liquid equilibrium and vapor–liquid equilibrium for the system water–ethanol-1,4-dimethylbenzene at 101.3 kPa

An all-glass, dynamic recirculating still equipped with an ultrasonic homogenizer has been used to determine vapor–liquid (VLE) and vapor–liquid–liquid (VLLE) equilibria. Consistent data have been obtained for the ternary water + ethanol + p-xylene system at 101.3 kPa for temperatures in the range of 351.16–365.40 K. Experimental results have been used to check the accuracy of the UNIFAC, UNIQUAC and NRTL models in the liquid–liquid region of importance in the dehydration of ethanol by azeotropic distillation.     

Pesticide extraction from table grapes and plums using ionic liquid based dispersive liquid–liquid microextraction

Room temperature ionic liquids (RTILs) have been used as extraction solvents in dispersive liquid–liquid microextraction (DLLME) for the determination of eight multi-class pesticides (i.e. thiophanate-methyl, carbofuran, carbaryl, tebuconazole, iprodione, oxyfluorfen, hexythiazox, and fenazaquin) in table grapes and plums. The developed method involves the combination of DLLME and high-performance liquid chromatography with diode array detection. Samples were first homogenized and extracted with acetonitrile. After evaporation and reconstitution of the extract in water containing sodium chloride, a quick DLLME procedure that used the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]) and methanol was developed. The RTIL dissolved in a very small volume of acetonitrile was directed injected in the chromatographic system. The comparison between the calibration curves obtained from standards and from spiked sample extracts (matrix-matched calibration) showed the existence of a strong matrix effect for most of the analyzed pesticides. A recovery study was also developed with five consecutive extractions of the two types of fruits spiked at three concentration levels. Mean recovery values were in the range of 72–100% for table grapes and 66–105% for plum samples (except for thiophanate-methyl and carbofuran, which were 64–75% and 58–66%, respectively). Limits of detection (LODs) were in the range 0.651–5.44 μg/kg for table grapes and 0.902–6.33 μg/kg for plums, representing LODs below the maximum residue limits (MRLs) established by the European Union in these fruits. The potential of the method was demonstrated by analyzing 12 commercial fruit samples (six of each type).     

High-performance liquid chromatographic determination of diltiazem in human plasma after solid-phase and liquid–liquid extraction

A selective, sensitive, and accurate high-performance liquid chromatographic method for determination of diltiazem in plasma samples has been developed and validated. The effects of mobile phase composition, buffer concentration, mobile phase pH, and concentration of organic modifiers on retention of diltiazem and internal standard were investigated. Solid-phase and liquid–liquid extraction were examined and proposed for isolation of the drug and elimination of endogenous plasma interferences. A 5 m Lichrocart Lichrospher 60 RP-select B chromatographic column was used; the mobile phase was acetonitrile–0.025 mol L^–1 KH₂PO₄ (pH 5.5), 35:65 ( v / v) at a flow-rate of 1.5 mL min^–1. The detection wavelength was 215 nm. The calibration plots were linear in the concentration range 20.0–500.0 ng mL^–1. The method has been implemented to monitor diltiazem levels in patient samples.     

Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys

Thermodynamic and surface properties of Ge–Ga and Ge–Sb liquid alloys have been studied using statistical mechanical formulations based on complex formation and that based on the concept of layered structure near the interface. The study showed that low level of complex formation of the form Ge _{2 Sb} exists in Ge–Sb toward the Ge-rich end of the concentration range and the surface properties of Ge–Ga are almost equal to their corresponding bulk equivalent.     

Circulation microchannel for liquid–liquid microextraction

A new method has been developed for liquid–liquid microextraction utilizing a circulation microchannel. A glass microchemical chip having a circular shallow microchannel in contact with a surrounding deeper microchannel was fabricated by a two-step photolithographic wet-etching technique. Surface modification reagent was selectively introduced to the shallow channel by utilizing capillary force, and the surface of the shallow channel was selectively made hydrophobic. With the aid of the hydrophobic/hydrophilic surface patterning, it was possible to keep organic solvent in the circular channel while the aqueous sample solution was continuously flowing in the deep channel. As a result, concentration extraction from sample solution to stationary extractant with a nanoliter scale volume became possible. Concentration extraction has been difficult in a multiphase continuous flow. Function of the newly developed microextraction system was verified with methyl red as a test sample, and concentration extraction to reach equilibrium was successfully carried out. A novel surface modification method utilizing frozen liquid as a masking material was also developed as a reverse process to make the shallow channel hydrophilic and the deep channel hydrophobic. Visualization of circulation motion inside the circular shallow channel induced by flow in the deep channel was observed with a particle tracing method.     

Direct and indirect photoinduced gas–liquid phase transitions

The condensation of supersaturated vapors of various substances in air under UV irradiation in a cloud chamber has been studied. The irradiation and subsequent photodissociation greatly facilitate the condensation of vapors in comparison with unirradiated mixtures, wherein both a vapor that directly absorbs radiation (direct photoinduced phase transition) and, for example, water vapor in the presence of photodissociating impurities (indirect photoinduced transition) can be condensed.     

Ultrasound-enhanced surfactant-assisted dispersive liquid–liquid microextraction and high-performance liquid chromatography for determination of ketoconazole and econazole nitrate in human blood

A simple and efficient method, based on ultrasound-enhanced surfactant-assisted dispersive liquid–liquid microextraction (UESA-DLLME) followed by high-performance liquid chromatography (HPLC) has been developed for extraction and determination of ketoconazole and econazole nitrate in human blood samples. In this method, a common cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used as dispersant. Chloroform (40 μL) as extraction solvent was added rapidly to 5 mL blood containing 0.068 mg mL⁻¹ CTAB. The mixture was then sonicated for 2 min to disperse the organic chloroform phase. After the extraction procedure, the mixture was centrifuged to sediment the organic chloroform phase, which was collected for HPLC analysis. Several conditions, including type and volume of extraction solvent, type and concentration of the surfactant, ultrasound time, extraction temperature, pH, and ionic strength were studied and optimized. Under the optimum conditions, linear calibration curves were obtained in the ranges 4–5000 μg L⁻¹ for ketoconazole and 8–5000 μg L⁻¹ for econazole nitrate, with linear correlation coefficients for both >0.99. The limits of detection (LODs, S/N = 3) and enrichment factors (EFs) were 1.1 and 2.3 μg L⁻¹, and 129 and 140 for ketoconazole and econazole nitrate, respectively. Reproducibility and recovery were good. The method was successfully applied to the determination of ketoconazole and econazole nitrate in human blood samples.     

Bubble points of hydrogen chloride–water–isopropanol and hydrogen chloride–water–isopropanol–benzene systems and liquid–liquid equilibria of hydrogen chloride–water–benzene and hydrogen chloride–water–isopropanol–benzene systems

Bubble points of the HCl–water–isopropanol and the HCl–water–isopropanol–benzene systems and liquid–liquid equilibria (LLE) of the HCl–water–benzene and the HCl–water– isopropanol–benzene systems were measured at 25–85°C and 30–70°C, respectively. The electrolyte nonrandom two-liquid model proposed by Chen et al. [C.-C. Chen, H.I. Britt, J.F. Boston, L.B. Evans, AIChE J. 28 (1982) 588–596] can satisfactorily correlate bubble points and liquid–liquid equilibria of the present mixed-solvent electrolyte systems over the entire range of temperature and concentrations using only binary adjustable parameters.     

Temperatures of liquid–liquid separation and excess molar volumes of {N-methylpiperidine–water} and {2-methylpiperidine–water} systems

Partial miscibility in binary systems {N-methylpiperidine–water} and {2-methylpiperidine–water} was studied. The temperatures of liquid–liquid separation were determined as function of composition using both calorimetric technique and phase equilibrium cell. The densities of {amine–water} mixtures were determined in the domain of total miscibility at temperatures between 288 K and 338 K. Excess molar volumes were derived from experimental density data and fit to a Redlich–Kister polynomial.     

Studies on morphology of polyaniline films formed at liquid–liquid and solid–liquid interfaces at 25 and 5 °C,respectively, and effect of doping

It is well accepted that the morphology of the nanomaterials has great effect on the properties and hence their applications. Therefore, morphology of materials has become a focus of research in the scientific world. The present study shows that interfacial polymerization and subsequent self-assembly provides a control over the morphology, nanorod/nanosheet, of polyaniline (PANI) films synthesized by liquid–liquid interface reaction technique and solid–liquid interface reaction technique. The synthesized PANI films and its particulate structure are characterized by using various spectroscopic techniques such as UV–visible, ATR-IR, Raman and XPS. The study confirmed the formation, the structure, the size and shape of particles and morphology of PANI by using analytical techniques namely, SAED, SEM and TEM. An important observation is that doping with HCl significantly improves the nanorod formation at the interface. The doped PANI electrode exhibits a higher area with rectangular shape in CV cycle and better cycle stability when compared with the performance of undoped PANI films. We believe that the results of these studies can give valuable leads to manoeuvre formation of PANI films with desired morphology for various applications.

Symmetries and defects in liquid crystals: Arceau–tetrahedra–arceau

To honor Yves Bouligand, champion of new ideas, complexity and living systems, I give a brief overview of our recent discovery of a biaxial Bouligand arceau in achiral tetrahedratic banana liquid crystals.