Approaches for on-line coupling of extraction and chromatography

This review provides an overview of the approaches available in order to perform on-line coupling of various extraction techniques with liquid and gas chromatography, for the analysis of semivolatile and nonvolatile analytes in liquid and solid samples. The main focus is on the instrumental set-up of these techniques. Selected real applications are described by way of illustration. The extraction methods suitable for on-line coupling covered in this review are: liquid-liquid extraction, solid-phase extraction, membrane-based techniques, pressurised liquid extraction, supercritical fluid extraction, and microwave- and sonication-assisted extractions. The following systems are not covered in this review: on-line coupled solid-phase extraction-liquid chromatography, purge-and-trap-GC, and membrane extraction with a sorbent interface-GC.Abbreviations DMAE Dynamic microwave-assisted extraction - DSAE Dynamic sonication-assisted extraction - FIA Flow injection analysis - FID Flame ionisation detection - GC Gas chromatography - HGAAS Hydride generation atomic absorption spectroscopy - IC Ion chromatography - IPLC Ion pair liquid chromatography - LC Column liquid chromatography - LLE Liquid-liquid extraction - LVI Large-volume injection - MAE Microwave-assisted extraction - MESI Membrane extraction with a sorbent interface - MMLLE Microporous membrane liquid-liquid extraction - MS Mass spectrometry - NP Normal-phase - OTT Open-tubular trapping - OTTTD Open-tubular trapping with thermal desorption - PAH Polycyclic aromatic hydrocarbon - PHWE Pressurised hot water extraction - PCB Polychlorinated biphenyl - PLE Pressurised liquid extraction - PTV Programmed-temperature vaporizer - RP Reversed-phase - RSD Relative standard deviation - SAE Sonication-assisted extraction - SFE Supercritical fluid extraction - SIM Selective ion monitoring - SLM Supported liquid membrane - SPE Solid-phase extraction - SPE-TD Solid-phase extraction-thermal desorption - SVE Solvent vapour exit - TD Thermal desorption     

Metal-hydride bond activation and metal-metal interaction in dinuclear iron complexes with linking dinitriles: a synthetic,electrochemical, and theoretical study

The dinuclear iron(II)-hydride complexes [[FeH(dppe)(2)](2)(mu-LL)][BF(4)](2) (LL = NCCH=CHCN (1a), NCC(6)H(4)CN (1b), NCCH(2)CH(2)CN (1c); dppe = Ph(2)PCH(2)CH(2)PPh(2)) and the corresponding mononuclear ones, trans-[FeH(LL)(dppe)(2)][BF(4)] (2a-c) were prepared by treatment of trans-[FeHCl(dppe)(2)], in tetrahydrofuran (thf) and in the presence of Tl[BF(4)], with the appropriate dinitrile (in molar deficiency or excess, respectively). Metal-metal interaction was detected by cyclic voltammetry for 1a, which, upon single-electron reversible oxidation, forms the mixed valent Fe(II)/Fe(III) 1a(+) complex. The latter either undergoes heterolytic Fe-H bond cleavage (loss of H(+)) or further oxidation, at a higher potential, also followed by hydride-proton evolution, according to ECECE or EECECEC mechanistic processes, respectively, which were established by digital simulation. Anodically induced Fe-H bond rupture was also observed for the other complexes and the detailed electrochemical behavior, as well as the metal-metal interaction (for 1a), were rationalized by ab initio calculations for model compounds and oxidized derivatives. These calculations were used to generate the structural parameters (full geometry optimization), the most stable isomeric forms, the ionization potentials, the effective atomic charges, and the molecular orbital diagrams, as well as to predict the nature of the other electron-transfer induced chemical steps, i.e. geometric isomerization and nucleophilic addition, by BF(4)(-), to the unsaturated iron center resulting from hydride-proton loss. From the values of the oxidation potential of the complexes, the electrochemical P(L) and E(L) ligand parameters were also estimated for the dinitrile ligands (LL) and for their mononuclear complexes 2 considered as ligands toward a second binding metal center.     

Separation of endo-polygalacturonase using aqueous two-phase partitioning

The partitioning of endo-polygalacturonase (endo-PG) in polyethylene glycol (PEG)-polyvinyl alcohol (PVA10000) and PEG-hydroxypropyl starch (Reppal PES100) aqueous two-phase systems was studied, and revealed the possibility of using aqueous two-phase extraction to purify and concentrate endo-PG from its clarified fermentation broth. For the PEG8000-PVA10000 system, endo-PG presented in the fermentation broth (at concentration that is more than 40% of total protein) mainly dominates in the top phase with a partitioning coefficient of 6, while total protein concentrates in the bottom phase. A separation scheme consisting of two consecutive aqueous two-phase extraction steps was proposed: a first extraction in polyethylene glycol (PEG8000)-polyvinyl alcohol system, followed by a second extraction in PEG8000-(NH4)2SO4 system. This allowed the separation of endo-PG from polymer and the recycling of PEG polymer, since endo-PG was very strongly partitioned into the bottom phase of the PEG8000-(NH4)2SO4 system. Laboratory-scale experiments were performed to test the efficiency of this scheme. It was found that enzyme recovery was up to 91% with a total purification factor of about 1.9 and a concentration factor of more than 5. About 90% of the total PEG added into the systems can be recovered, and no reduction was obtained in the purification factor using recycled PEG.     

1H NMR spectral analysis and conformational behavior of n‐alkanes in different chemical environments

Alkyl chains are common structural units, for example in lipids, and their ¹H NMR spectral parameters offer valuable information about their conformational behavior in solvent environment. Even the spectra of short n‐alkanes are complex, which is obviously a reason why their accurate spectral analyses have not been reported before. The present study reports the quantum mechanical analysis of ¹H NMR spectra of n‐butane, n‐pentane, n‐hexane, and n‐heptane. The spectral parameters were used to characterize the conformational behavior of n‐alkanes. The temperature dependence analysis of coupling constants suggests that the enthalpy difference between the gauche (g) and trans (t) conformations (ΔH_g) of n‐butane in chloroform is 2.55–2.85 kJ mol^?1. The difference between the trans–gauche (tg) and all‐trans (tt) conformers of n‐pentane (ΔH_tg) seems to be 0.1–0.2 kJ mol^?1 higher. The coupling constant information shows that the t_n conformations become more favored with longer chains, although not only for energetic reasons but also partly because the g⁺g^‐ arrangements become sterically unfavorable, which decreases the number of favorable g_n‐type conformations. The analysis of the ¹H NMR spectra of n‐pentane and n‐hexane in solvents representing different chemical environments indicates that polar and spherical dimethyl sulfoxide favors clearly the g conformations, whereas n‐hexane‐d₁₄ favors slightly the extended t_n conformation. In addition to the intrinsic scientific importance for NMR spectral parameter prediction and molecular modeling in solution, the results provide some insights to behavior of hydrocarbon chains and their spectra in different chemical environments. Copyright © 2012 John Wiley & Sons, Ltd.     

MnOx Nanoparticles Supported on a New Mesostructured Silicate with Textural Porosity

A two‐step synthesis of a novel mesostructured silicate, KIL‐2, and its manganese‐containing analogue, Mn/KIL‐2, has been developed. KIL‐2 possesses interparticle mesopores with pore dimensions between 5 and 60 nm and a surface area of 448 m². The mesopores are formed by the aggregation of silica nanoparticles, which creates a network with interparticle voids. The particle size and the pore diameters depend on the temperature of the ageing step (first step) and on the solvothermal treatment in ethanol (second step), respectively. Mn/KIL‐2 contains octahedrally coordinated Mn³⁺ (80 %) and tetrahedrally coordinated Mn²⁺ (20 %) ions. Mn³⁺ ions are present in the extra‐framework MnO_x nanoparticles with typical dimensions of 2 nm, which are homogeneously distributed throughout the material. Mn²⁺ ions occur as isolated manganese framework sites. The material is also able to retain its structure characteristics after the hydrothermal treatment in boiling water. Because of its non‐toxic nature and cost‐effective synthesis, Mn/KIL‐2 thus exhibits properties that are needed for an environment‐friendly catalyst.     

New method to determine the viscoelastic properties of admicelles around the stick-slip transition

We report on a new method by which, for the first time, the viscoelastic properties of an adsorbed surfactant layer on a solid surface are measured. It is based on an analysis of the amplitude and the phase angle of the pressure fluctuations induced by a pulsating flow of a Newtonian surfactant solution through cylindrical pores. This method is subsequently used to determine the viscoelastic properties of an admicelle, formed when flushing surfactant solutions through nanopores, around the stick-slip transition. We find that the admicelle responds elastically for flow strengths below the transition and beyond the viscous. This is in agreement with the hypothesis formulated earlier (Cheikh, C.; Koper, G. J. M. Phys. Rev. Lett. 2003, 91, 156102).     

Ultrasonic characterization of proteins and blood cells

Ultrasound changes its intensity and speed when propagating through a liquid or a suspension containing particles. In addition it generates a weak electric signal by altering the motion of ions and charged particles. Hence acoustic and electroacoustic measurements provide information about the properties of suspended particles and molecules. Here we present both acoustic and electroacoustic results on blood suspensions and protein solutions, relevant to life sciences. For blood cells a strong increase in acoustic attenuation with volume fraction is found, from which the speed of sound in an erythrocyte is found to be about 1900 m/s, assuming the attenuation is due to scattering only. A similar value of 1700 m/s is found from the increase in sound speed of the dispersion with concentration. Electroacoustic measurements on bovine serum albumin (BSA) yield a charge of about seven elementary charges per BSA molecule. These results show the power and usefulness of acoustic and electroacoustic measurement techniques for biological systems.     

Worldwide interlaboratory study on the determination of ochratoxin A in different wine type samples

Interlaboratory studies are decisive tools to help the validation of a specific analytical methodology or to assess the reproducibility of the use of different methods to analyze a given compound or compounds in certain sample matrices. In this work, homogeneous samples of two white wines (“White Wine” and “White Liqueur Wine”) and one red wine (“Red Fortified Wine”) from Portugal with different production techniques and characteristics, namely in alcohol strength (10.5%, 16.0% and 19.0% ethanolic content, respectively), were analyzed for their contents in ochratoxin A (OTA), a mycotoxin generated from fungal contamination. White Liqueur Wine was naturally contaminated, whereas the other two wine type were spiked with ethanolic OTA solutions. The participation of 24 laboratories from 17 countries of five continents was ensured for this study. Although with no restrictions in terms of analytical methodology to employ, 75% of the laboratories resorted to immunoaffinity columns clean-up followed by high performance liquid chromatography with fluorescence detection (HPLC-FD), most of them in accordance with the European Standard EN 14133. For White Wine samples, the general mean OTA concentration was 1.96 μg/l (two outliers) with interlaboratorial standard deviation (s_L) of 0.53 μg/l; for White Liqueur Wine, mean of 1.59 μg/l (one outlier), with s_L = 0.59 μg/l; and for Red Fortified Wine, mean of 2.73 μg/l (no outliers), with s_L = 0.96 μg/l. Outliers were determined by Cochran and Grubbs tests. The Horrat index, recommended by the Association of Official Analytical Chemists (AOAC) for the quality assurance of the collaborative study was, on average, 1.7. This study proved that OTA determination in wines is reproducible, regardless of the methodology employed.     

Electroviscous sphere-wall interactions

A theoretical analysis is presented to determine the forces of interaction between an electrically charged spherical particle and a charged plane wall when the particle translates parallel to the wall and rotates around its axis in a symmetric electrolyte solution at rest. The electroviscous effects, arising from the coupling between the electrical and hydrodynamic equations, are determined as a solution of three partial differential equations, derived from Cox's general theory [R.G. Cox, J. Fluid Mech. 338 (1997) 1], for electroviscous ion concentration, electroviscous potential and electroviscous flow field. It is a priori assumed that the double layer thickness surrounding each charged surfaces is much smaller than the particle size. Using the matched asymptotic expansion technique, the electroviscous forces experienced by the sphere are explicitly determined analytically for small particle-wall distances, but low and intermediate Peclet numbers.     

The base sequence dependent flexibility of linear single-stranded oligoribonucleotides correlates with the reactivity of the phosphodiester bond

The effect of base sequence on the structure and flexibility of linear single-stranded RNA molecules and the influence of the base sequence on phosphodiester bond reactivity have been studied. Molecular dynamics simulations of 2.1 ns were carried out for nine chimeric oligonucleotides containing only one unsubstituted ribo unit, all the rest of sugars being 2'-O-methylated. The base sequence has recently been reported to make a big contribution to the reactivity of these compounds. A detailed examination of the interaction energies between the base moieties shows that base stacking is strongly context-dependent and cooperative. The strength of stacking at the site susceptible to chain cleavage by intramolecular transesterification was observed to be dependent on both the flanking bases of the cleavage site and those further apart in the molecule. The interaction energies between the bases in the vicinity of the scissile linkage were found to correlate well with the experimental phosphodiester bond cleavage rates: the stronger the bases close to the cleavage site are stacked, the slower the cleavage rate is.