A re-appraisal of modelling in a liquid surfactant membrane waste water clean up process

Two categories of model have been developed to describe the mass transfer process in emulsion liquid membrane extraction of phenols/amines from waste water. In the first the reaction between the transferred solutes and the trapping agent in the internal phase is assumed to be irreversible while in the second a reversible reaction is involved. Generally the various authors have tested the proposed models against their own experimental data. The present study is an attempt to investigate the efficacy of the reversible reaction model of Bunge and Noble, which is simpler to use and requires input of less parameters to predict the experimental data reported by different authors. It is shown that by introducing a shape factor into the model for the effective diffusivity of solute within the macrodrop, it is possible to use this model to simulate experimental data of other groups reasonably well.     

Critical flux of hard sphere suspensions in crossflow filtration: Hydrodynamic force bias Monte Carlo simulations

A Monte Carlo method is developed for crossflow membrane filtration to determine the critical flux of hard sphere suspensions. Brownian and shear-induced diffusion are incorporated into an effective hydrodynamic force exerted on the hard spheres in a concentrated shear flow. Effects of shear rate and particle size on the critical flux are investigated using hydrodynamic force bias Monte Carlo simulations, providing a baseline of the critical flux.     

Two-phase flow in microfluidic-chip design of hydrodynamic filtration for cell particle sorting

As one of the flow-based passive sorting, the hydrodynamic filtration using a microfluidic-chip has shown to effectively separate into different sizes of subpopulations from cell or particle suspensions. Its model framework involving two-phase Newtonian or generalized Newtonian fluid (GNF) was developed, by performing the complete analysis of laminar flow and complicated networks of main and multiple branch channels. To predict rigorously what occurs in flow fields, we estimated pressure drop, velocity profile, and the ratio of the flow fraction at each branch point, in which the analytical model was validated with numerical flow simulations. As a model fluid of the GNF, polysaccharide solution based on Carreau type was examined. The objective parameters aiming practical channel design include the number of the branches and the length of narrow section of each branch for arbitrary conditions. The flow fraction and the number of branches are distinctly affected by the viscosity ratio between feed and side flows. As the side flow becomes more viscous, the flow fraction increases but the number of branches decreases, which enables a compact chip designed with fewer branches being operated under the same throughput. Hence, our rational design analysis indicates the significance of constitutive properties of each stream.     

Incorporation of ionic liquid into porous polymer monoliths to enhance the separation of small molecules in reversed‐phase high‐performance liquid chromatography

An ionic liquid was incorporated into the porous polymer monoliths to afford stationary phases with enhanced chromatographic performance for small molecules in reversed‐phase high‐performance liquid chromatography. The effect of the ionic liquid in the polymerization mixture on the performance of the monoliths was studied in detail. While monoliths without ionic liquid exhibited poor resolution and low efficiency, the addition of ionic liquid to the polymerization mixture provides highly increased resolution and high efficiency. The chromatographic performances of the monoliths were demonstrated by the separations of various small molecules including aromatic hydrocarbons, isomers, and homologues using a binary polar mobile phase. The present column efficiency reached 27 000 plates/m, which showed that the ionic liquid monoliths are alternative stationary phases in the separation of small molecules by high‐performance liquid chromatography     

Use of a keeper to enhance the recovery of volatile polycyclic aromatic hydrocarbons in HPLC analysis

Summary The recorveries of volatile polycyclic aromatic hydrocarbons in HPLC analysis may be enhanced if a long-chain alcohol, e.g. 1-hexanol or 1-octanol, is used as keeper in the solvent-evaporation step. Even under the harsh conditions of the vacuum-concentrator centrifuge, recoveries of more than 90% were achieved for 14 of the 15 PAH tested. The use of liquid-liquid extraction (LLE) eliminates the problem of adsorption of highly condensed aromatics by the wall of the sampling bottle. The combination of LLE with vacuum-controlled rotary evaporation and use of a keeper yielded overall recoveries between 50 and 130%, for most substances close to 100%, from tap water spiked with trace concentrations. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Analysis of nucleotides,nucleosides, nucleobases in cells by ion-pair reversed-phase HPLC

Summary HPLC methods for the separation of nucleotides, nucleosides and nucleobases by ion-pair reversed-phase are reviewed. The advantages of these are discussed versus anion-exchange and reversed phase separations. Extraction procedures for nucleotide determinations from cells and tissues are pointed out in detail. Extracts from red blood cells, Ehrlich ascites tumour cells, hepatocytes, intestine are used for determination of nucleotide concentrations by the methods described.     

Characterization of complex hydrocarbon mixtures using on-line coupling of size-exclusion chromatography and normal-phase liquid chromatography to high-resolution gas chromatography

An on-line coupling of size-exclusion Chromatography (SEC), normal-phase liquid Chromatography (NPLC), and gas Chromatography (GC) for the characterization of complex hydrocarbon mixtures is described. The hyphenated system separates according to size, polarity, and boiling point. The use of size exclusion as the first separation step allows for the direct injection of complex (“dirty”) samples withont prior clean-up. SEC-NPLC coupling was realized using an on-line solvent evaporator based on fully concurrent solvent evaporation (FCSE) using a modified loop-type interface, vapor exit and co-solvent trapping. Complete reconcentration of the analytes was realized by the introduction of a cryogenic cold trap. For the subsequent hydrocarbon group-type separation an ammo-silica column with n-heptane as eluent was used. The NPLC-GC coupling was based on an on-column interface using partially concurrent solvent evaporation (PCSE) and an early vapor exit. Initial results obtained on the analysis of a residue from the atmospheric crude-oil distillation (a so-called long residue) are presented as an example of the enormous separation power of the SEC-NPLC-GC system. The application of the system for quantitative analysis has not yet been studied.     

Separation of casein micelles from whey proteins by high shear microfiltration of skim milk using rotating ceramic membranes and organic membranes in a rotating disk module

This paper investigates the microfiltration of skim milk in order to separate caseins micelles from two whey proteins, α-lactalbumin (α-La) and β-lactoglobulin (β-Lg), using a modified dynamic filtration pilot (MSD) consisting in 6 ceramic 9-cm diameter membrane disks of 0.2 μm pores, rotating around a shaft inside cylindrical housing. A comparison was made with another dynamic filtration module consisting in a disk rotating near a fixed PVDF 15.5 cm diameter membrane with 0.15 μm pores. Maximum permeate fluxes were 120 L h⁻¹ m⁻² with the MSD module at 1930 rpm and at 40 °C, and 210 L h⁻¹ m⁻² at 2500 rpm and 45 °C, with the rotating disk module. Casein rejection was around 99% at high speed for both membranes. α-La transmission decreased with increasing transmembrane pressure (TMP) from 75% to 60% for ceramic membranes and from 25% to 10% for the PVDF one. β-Lg transmissions were lower, ranging from 23% to 15% for ceramic membranes and from 20% to 5% for the PVDF one. In a concentration test with the PVDF membrane at 2000 rpm, the flux decayed from 200 L h⁻¹ m⁻² at initial concentration to 80 L h⁻¹ m⁻² at VRR = 3.2 and 22.1% of the initial α-La mass was recovered in the permeate, against 8.1% for β-Lg. Permeate fluxes in the mass transfer limited regime (J_lim) of the MSD and rotating disk module operated at various speeds were well correlated by the equation J_lim = 17.13 V_av where V_av denoted the disk azimuthal velocity averaged over the membrane area. Measurements of J_lim, taken from Ref. [G. Samuelsson, P. Dejlmek, G. Tragardh, M. Paulsson, Minimizing whey protein retention in crossflow microfiltration of skim milk. Int. Dairy J. 7 (1997) 237–242] during MF of skim milk using tubular ceramic membranes at velocities from 1.5 to 8 m s⁻¹ with permeate co-current recirculation were found to obey the same correlation.     

Use of Counterflow in Bidirectional Capillary Isotachophoresis

Electrochemical cell using counterflow in bidirectional capillary isotachophoresis is designed. With this cell, steady-state concentrations of several solutions in cationic and anionic capillary isotachophoresis are determined simultaneously. Transport numbers of ionic components are calculated and compared with literature data.     

多壁碳纳米管滤过型净化柱净化-超高效液相色谱/串联质谱法同时测定生姜中的涕灭威及其代谢物

建立了多壁碳纳米管滤过型净化柱净化-超高效液相色谱/串联质谱联用技术同时测定生姜中涕灭威及其代谢物的分析方法。生姜样品经乙腈提取后,用多壁碳纳米管滤过型净化柱进行2次反复抽提净化,净化液用氮气吹干,用乙腈-水（5：95,v/v）溶解,采用正离子多反应监测（MRM）模式进行分析,外标法定量。结果表明：涕灭威、涕灭威砜及涕灭威亚砜在0.5~200 μg/L浓度范围内呈线性,其相关系数（r²）均大于0.99;在2、20、200 μg/kg添加水平下,回收率为71.4%~89.8%,相对标准偏差范围为0.7%~13.2%;3种目标物的定量限为1.0~2.0 μg/kg。本方法操作简单,灵敏度、准确度和精密度均满足农药多残留检测技术的要求,适用于生姜中涕灭威及其代谢物残留的快速测定。     

The effect of make-up flow on detector time variance in micro column liquid chromatography

Summary Time variance is better suited than volume variance to compare performances of columns of different diameters but of same length and working at the same linear velocity of the mobile phase. When a make-up flow is used at the detector inlet, only column and detector time variances remain additive. Make-up flow enables reduction of the detector contribution to the total variance. However, in some practical cases, the dispersion effects of the detector inlet tubing or electronic time constant can prevail over that of the flow cell. Owing to their different flow dependence, the decrease in detector variance due to make-up is often much lower than expected. Theoretical equations and curves are given for a rapid evaluation of make-up flow.     

Derivatization of beta-dicarbonyl compound with 2,4-dinitrophenylhydrazine to enhance mass spectrometric detection: application in quantitative analysis of houttuynin in human plasma

Houttuynin (decanoyl acetaldehyde), a beta-dicarbonyl compound, is the major antibacterial constituent in the volatile oil of Houttuynina cordata Thunb. In the present work, detection of houttuynin in human plasma based on the chemical derivatization with 2,4-dinitrophenylhydrazine (DNPH) coupled with liquid chromatography/tandem mass spectrometry was described. The primary reaction products between the beta-dicarbonyl compound and DNPH in aqueous phase were identified as heterocyclic structures, of which the mass spectrometric ionization and fragmentation behavior were characterized with the aid of high-resolution multistage mass spectral analysis. For quantification, houttuynin and internal standard (IS, benzophenone) in plasma were firstly converted to their DNPH derivatives without sample purification, then extracted from human plasma with n-hexane and detected by liquid chromatography tandem mass spectrometry performed in selected reaction monitoring (SRM) mode. This method allowed for a lower limit of quantification (LLOQ) of 1.0 ng/ml using 100-microl plasma. The validation results showed high accuracy (%bias < 2.1) and precision (%CV < 7.2) at broad linear dynamic range (1.0-5000 ng/ml). The simple and quantitative derivatization coupled with tandem mass spectrometric analysis facilitates a sensitive and robust method for the determination of plasma houttuynin in pharmacokinetic studies.     

Comments on the separation efficiency of asymmetrical flow field-flow fractionation in channels of constant channel and crossflow velocities leading to constant separation efficiency

It is shown theoretically that a claim in the literature about the overall separation efficiency of asymmetrical flow FFF channels being improved by geometries that permit a uniform channel flow velocity throughout the channel length is untrue.     

The Use of Encoded Structural Data to Predict the Liquid Chromatographic Retention Behavior of Tetradentate Metal Complexes

Abstract

Retention data for tetradentate metal complexes of copper and nickel are reported for microparticulate silica and reversed phase columns. An attempt is made to relate structure and stability constant data to the retention volume by means of multiple linear regression. The results indicate that if the structure is encoded by means of dummy variables it may be possible to predict retention volumes of metal complexes. There is not a strong correlation between the value of the stability constants for the metal diamine and metal ketone complexes and the retention volume.     

Use of molecular connectivity indices to predict LC retention of dansylamides in six different eluent systems

Summary Molecular connectivity indices (x) through the sixth order were calculated and compared with measured reversed-phase liquid chromatographic retention data of sixteen dansyl derivatives of amines (dansylamides). Retention measurements were performed in the capacity factor, k′, range 1–30 with organic solvent-water eluents using acetone, acetonitrile, ethanol, methanol, 1-propanol and 2-propanol. Mainly valence level indices were selected to describe retention. Indices of different order were selected in the different eluents, suggesting that there are differences in the retention mechanism in these eluents. Retention can be predicted with great accuracy by the molecular connectivity indices, as the high correlations between the calculated and observed retention indicate. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Combined use of supported liquid membrane and solid-phase extraction to enhance selectivity and sensitivity in capillary electrophoresis for the determination of ochratoxin A in wine

This paper proposes a novel strategy to enhance selectivity and sensitivity in CE, using supported liquid membrane (SLM) and off-line SPE simultaneously. The determination of ochratoxin A (OA) in wine has been used to demonstrate the potential of this methodology. In the SLM step, the donor phase (either a 20 mL volume of a standard solution at pH 1 or a wine sample at pH 8) was placed in a vial, where a micromembrane extraction unit accommodating the acceptor phase (1 mL water, pH 11) in its lumen was immersed. The SLM was constructed by impregnating a porous Fluoropore Teflon (PTFE) membrane with a water-immiscible organic solvent (octanol). In the off-line SPE step, the nonpolar sorbent (C-18, 4 mg) selectively retained the target ochratoxin, enabling small volumes of acceptor phase (1 mL) to be introduced. The captured analytes were eluted in a small volume of methanol (0.1 mL). This procedure resulted in sample cleanup and concentration enhancement. The method was evaluated for accuracy and precision, and its RSD found to be 5%. The LODs for OA in the standard solutions and wine samples were 0.5 and 30 microg/L, respectively. The results obtained demonstrate that SLM combined with off-line is a good alternative to the use of immunoaffinity columns prior to CE analysis.     

Development and Validation of a Stability-Indicating LC Method to Quantify Hydrochlorothiazide in Oral Suspension for Pediatric Use

A stability-indicating reversed-phase high-performance liquid chromatography (LC) method was developed and validated for the determination of hydrochlorothiazide in an oral suspension. Isocratic chromatography was performed on a C₁₈ column with 0.1 M sodium phosphate buffer pH 3.0/acetonitrile (70:30 v/v) as mobile phase, at a flow rate of 1.3 mL min⁻¹, and UV detection at 254 nm. The method was linear (r ² = 0.9998), accurate (mean recovery = 100.3%), and precise (RSD <2%). It was also validated for specificity and robustness. The method was successfully applied for the quality control analysis of a new pharmaceutical formulation of HCTZ for pediatric use.