Solvent desorption of asphaltenes from solid surfaces

The main goal of this paper is to compare the ability of different organic solvents to desorb asphaltenes from stainless steel surfaces. The asphaltenes were extracted from a North Sea crude oil by precipitation. The organic solvents are characterized based on their Hansen solubility parameters (HSPs). The adsorption of asphaltenes was followed by means of a Quartz Crystal Microbalance with Dissipation (QCM-D). The asphaltene desorption efficiency of the solvents tested varied between 20% and 70%, with pyridine as the most efficient solvent. Carbon disulfide was found to be a poor desorption solvent, indicating the importance of solvent polarity. A simple model based on the HSPs seemed to give a good quantitative explanation of experimental desorption experiments.     

混合溶剂对可录型光盘中吲哚类菁染料薄膜性能的影响

本文采用紫外可见光谱、FT-IR及AFM等手段,研究了混合溶剂对光盘记录介质吲哚类菁染料薄膜光学性能、稳定性和表面结构的影响.发现在不同混合溶剂下涂出的相同膜厚的染料薄膜,其光学性能和表面形貌都有很大的差异.不同的混合溶剂都存在一个最佳混合体积比,染料在此体积比下旋涂出膜的光学性能和表面形貌均优于单一溶剂下涂出的膜.对比不同混合溶剂涂出的膜的光学性质及AFM的观测结果,发现二丙酮醇与氯仿在等体积比混合、四氟丙醇与氯仿在7:3体积下混合时效果最好,易得到反射率高,表面较平整的染料薄膜.     

Enhancement of ionization efficiency of mass spectrometric analysis from non-electrospray ionization friendly solvents with conventional and novel ionization techniques

Electrospray ionization mass spectrometry (ESI-MS) has significantly impacted the analysis of complex biological and petroleum samples. However ESI-MS has limited ionization efficiency for samples in low dielectric and low polarity solvents. Addition of a make-up solvent through a T union or electrospray solvent through continuous flow extractive desorption electrospray ionization (CF-EDESI) enable ionization of analytes in non-ESI friendly solvents. A conventional make-up solvent addition setup was used and a CF-EDESI source was built for ionization of nitrogen-containing standards in hexane or hexane/isopropanol. Factors affecting the performance of both sources have been investigated and optimized. Both the make-up solvent addition and CF-EDESI improve the ionization efficiency for heteroatom compounds in non-ESI friendly solvents. Make-up solvent addition provides higher ionization efficiency than CF-EDESI. Neither the make-up solvent addition nor the CF-EDESI eliminates ionization suppression of nitrogen-containing compounds caused by compounds of the same chemical class.     

Rapid analysis of trace organics in aqueous solutions by enrichment in uncoated capillary columns

Summary A novel technique has been developed for the analysis of trace organics in aqueous solutions. Concentration of organics is effected by passage of the solution being analysed through uncoated plastic or metal capillaries as reported. The concentrated organics are then desorbed from the capillary using an organic solvent, and the desorbed solution is subsequently analysed by gas chromatography. Organics trapped inside a variety of columns have been recovered by solvent desorption in this manner using a number of different solvents, mixed solvents, different solvent volumes, different solvent flow rates through the capillary column and at different desorption temperatures, and the effects of these variables on the efficiency of desorption are discussed.     

Programmed-Temperature Vaporizing (PTV) Liners to Introduce Chlorinated and Sulfur Compounds into a Capillary Gas Chromatograph

Introduction of a sample at a programmed temperature is an attractive approach both for dilute samples in large volumes and to prevent discrimination inside the syringe needle with this injection into a capillary gas Chromatograph. Quantitative data obtained with glass liners packed with trapping materials including glass wool, Tenax TA, Chromosorb 101 and Thermotrap-TA to analyze chlorinated and sulfur compounds are compared. To eliminate the solvent, these vapors were vented through the injection port cap, which provided greater efficiency than through the split line.     

Injector-internal thermal desorption from edible oils performed by programmed temperature vaporizing (PTV) injection

Injector-internal thermal desorption is a promising technique for the analysis of a wide range of food components (e.g., flavors) or food contaminants (e.g., solvent residues, pesticides, or migrants from packaging materials) in edible oils and fats or fatty food extracts. Separation from the fatty matrix occurs during injection. Using programmed temperature vaporizing (PTV) injection, the oily sample or sample extract was deposited on a small pack of glass wool from which the components of interest were evaporated and transferred into the column in splitless mode, leaving behind the bulk of the matrix. Towards the end of the analysis, the oil was removed by heating out the injector and backflushing the precolumn. The optimization dealt with the gas supply configuration enabling backflush, the injector temperature program (sample deposition, desorption, and heating out), separation of the sample liquid from the syringe needle and positioning it on a support, deactivation of the support surface, holding the plug of fused silica wool by a steel wire, and the analytical sequence maintaining adsorptivity at the desorption site low. It was performed for a mixture of poly(vinyl chloride) (PVC) plasticizers in oil or fatty food. Using MS in SIM, the detection limit was below 0.1 mg/kg for plasticizers forming single peaks and 1 mg/kg for mixtures like diisodecyl phthalate. For plasticizers, RSDs of the concentrations were below 10%; for the slip agents, oleamide and erucamide, it was 12%. The method of incorporating PTV injection was used for about one year for determining the migration from the gaskets of lids for glass jars into oily foods.     

Coupling protocol for thin layer chromatography/matrix-assisted laser desorption ionization

Summary This paper reports the investigation and optimization of the thin layer chromatography/matrix-assisted laser desorption/ionization (TLC-MALDI) coupling protocol. The fundamental coupling parameters which influence sensitivity and lateral analyte spreading are extraction solvent selection, extraction time, and pressure. Selection of the solvent is dependent upon its extraction efficiency, which has been correlated with extraction solventR _f value. Maximum extraction efficiency occurs after two minutes for the analyte/solvent system studied. High extraction efficiency solvents cause significant lateral spreading of analyte; up to a three-fold increase in initial analyte spot size. Analyte recovery was found to be limited by the silica gel inter-partice porosity and the solvent extraction efficiency. For maintaining chromatographic resolution and maximizing signal intensity, extraction solvents withR _f values between 0.4 to 0.6 are optimal. The upper analyte recovery limit, using extraction solvents within thisR _f range, is estimated at 22%. Dedicated to Professor Werner Haerdi on the occasion of his 70^th birthday.     

A study on the physical properties of low melting mixtures and their use as catalysts/solvent in the synthesis of barbiturates

In recent years, deep eutectic solvents have become attractive due to their interesting characteristics such as, physicochemical properties, low cost of components, easiness to prepare, low toxicity, bio-renewability, and biodegradability. In order to make the deep eutectic mixture more cost-effective and renewable, carbohydrate derivatives were linked with deep eutectic mixtures, since, carbohydrates are the most important and widespread renewable compounds on the earth. In this work, we have used low melting mixtures comprised of carbohydrates to create the reaction media for organic transformations. The physical properties such as density, viscosity, acidity, refractive index, surface tension, solubility, glass transition temperature, thermal stability, solvent polarity, and toxicity of the mixture were studied. Low melting mixtures were used as reaction media and catalysts for the effective synthesis of Barbiturates. The reaction between aldehydes and barbituric acid/thiobarbituric acid, and the reaction between aldehydes, barbituric acid/thiobarbituric acid, and malononitrile/dimedone were performed effectively with good to excellent yields. The recyclability of the catalyst/solvent was also established.     

Micellar transitions in solvent-annealed thin films of an amphiphilic block copolymer controlled with tunable surface fields

We investigated the response of symmetric poly(styrene-block-4vinylpyridine) P(S-b-4VP) diblock copolymer micelles to surface fields of variable strength at free surfaces and substrate interfaces when the micelles as spun were subjected to solvent annealing. Free surface interactions were controlled with solvent annealing in solvents of varied selectivity. On exposure to vapors of a solvent strongly selective for PS, the micelles retained their spherical shape but grew into cylindrical micelles or lamellar nanostructures via fusion on exposure to slightly selective or neutral solvent vapors. Giant 2D disks that completely wetted PS-grafted substrates resulted when spherical micelles were exposed to vapors of a highly selective solvent for P4VP. The interfacial interactions were controlled through subjecting them to UV/ozone (UVO) substrates initially coated with an end-grafted layer of short PS chains, with which the grafted PS chains became oxidized, degraded, or totally removed through UVO treatment for a controlled duration. When thin films were annealed in vapors of THF, the structural transition from spherical to cylindrical micelles depended on the interfacial field. On applying selective UVO exposure of optimal duration, we fabricated a substrate with two interfacial chemistries that promoted varied micellar species (spherical and cylindrical micelles) with a sharp boundary developed within thin films through solvent annealing for a controlled duration.     

Solvent control of optical resolution of 2-amino-1-phenylethanol using dehydroabietic acid

The optical resolution of 2-amino-1-phenylethanol (2-APE) by the solvent switch method was investigated using dehydroabietic acid (DAA), a natural chiral acid obtained as one of the main components of disproportionated rosin. The solvent dependency of optical rotation measurements of 2-APE, DAA and the diastereomeric salts suggested solvent control of optical resolution. Both (R)- and (S)-2-APE were resolved, as the first success for aminoalcohols, only by changing the resolving solvents: (S)-2-APE was obtained in high optical purity by a single crystallization operation with polar solvents (epsilon > 50), whereas the efficiency was lower for (R)-2-APE using less polar solvents (20 < epsilon < 40). The results were compared and discussed with reference to the crystal structures of the diastereomeric salts.     

Development of novel thin-film solid-phase microextraction materials based on deep eutectic solvents for preconcentration of trace amounts of parabens in surface waters

A green and sensitive thin-film solid-phase microextraction method based on deep eutectic solvent was developed that enables simultaneous isolation, preconcentration, and determination of parabens in surface waters. Six new deep eutectic solvents were synthesized and used directly to prepare thin-film coatings on a stainless steel mesh support. Among the compounds obtained, the highest efficiency in the extraction of parabens was found for a material consisting of trihexyltetradecylphosphonium chloride and n-docosanol in a molar ratio of 1:2. For the proposed method, parameters affecting the extraction efficiency of parabens, such as the coating material, the desorption solvent, the volume of the sample, the pH of the sample, the extraction and desorption time, and the salting-out effect, were optimized. Under optimal conditions, the proposed method allowed us to achieve good precision between 3.6 and 6.5% and recovery ranging from 68.1 to 91.4%. The limits of detection range from 0.018 to 0.055 ng/mL.     

Determination of airborne trialkyl and triaryl organophosphates originating from hydraulic fluids by gas chromatography-mass spectrometry. Development of methodology for combined aerosol and vapor sampling

Methodology for personal occupational exposure assessment of airborne trialkyl and triaryl organophosphates originating from hydraulic fluids by active combined aerosol and vapor sampling at 1.5L/min is presented. Determination of the organophosphates was performed by gas chromatography-mass spectrometry. Combinations of adsorbents (Anasorb 747, Anasorb CSC, Chromosorb 106, XAD-2 and silica gel) with an upstream cassette with glass fiber or PTFE filters and different desorption/extraction solvents (CS(2), CS(2)-dimethylformamide (50:1, v/v), toluene, dichloromethane, methyl-t-butyl ether and methanol) have been evaluated for optimized combined vapor and aerosol air sampling of the organophosphates tri-isobutyl, tri-n-butyl, triphenyl, tri-o-cresyl, tri-m-cresyl and tri-p-cresyl phosphates. The combination of Chromosorb 106 and 37 mm filter cassette with glass fiber filter and dichloromethane as desorption/extraction solvent was the best combination for mixed phase air sampling of the organophosphates originating from hydraulic fluids. The triaryl phosphates were recovered solely from the filter, while the trialkyl phosphates were recovered from both the filter and the adsorbent. The total sampling efficiency on the combined sampler was in the range 92-101% for the studied organophosphates based on spiking experiments followed by pulling air through the sampler. Recoveries after 28 days storage were 98-102% and 99-101% when stored at 5 and -20 degrees C, respectively. The methodology was further evaluated in an exposure chamber with generated oil aerosol atmospheres with both synthetic and mineral base oils with added organophosphates in various concentrations, yielding total sampling efficiencies in close comparison to the spiking experiments. The applicability of the method was demonstrated by exposure measurements in a mechanical workshop where system suitability tests are performed on different aircraft components in a test bench, displaying tricresyl phosphate air concentrations of 0.024 and 0.28 mg/m(3), as well as during aircraft maintenance displaying tri-n-butyl phosphate air concentrations of 0.061 and 0.072 mg/m(3).     

Viscometric Behavior of Polystyrene in Binary Solutions Used as Eluents in Adsorption Chromatography

Calculated and experimentally measured characteristic viscosities [η] of polystyrene in some binary solvents used as eluents in chromatographic experiments in a wide range of mixture compositions were compared. The values of [η] were measured in solvents of varied thermodynamic quality, including the theta solvent and mixtures of solvents of the following compositions: two good solvents; good solvent and theta solvent; good solvent and precipitant; poor solvent and theta solvent. An equation that relates the anomalies observed in the dependences of [η] on the composition of a solvent mixture to parameters of the Flory-Huggins thermodynamic interaction was suggested.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 997–1002.Original Russian Text Copyright © 2005 by Bel’nikevich, Litvinova, Budtov.     

Enrichment of phenols from water with in-situ derivatization by in-tube solid phase microextraction-solvent desorption prior to off-line gas chromatographic determination with large-volume injection

Sorption of phenols from water into the stationary phase of open tubular columns (named in-tube solid phase microextraction) as an enrichment method for gas chromatographic (GC) analysis of aqueous samples was studied. The effect of operating conditions (stationary phase polarity, swelling of the stationary phase by solvents, number of sampling cycles, salting-out effect, sampling velocity, flow rate of desorption solvent) on the process efficiency was evaluated. Real water samples were also used in this study. Swelling of the stationary phase by organic solvent enables the volume of the stationary phase to be increased and its properties to be modified. The use of toluene or tetrachloromethane for the purpose results in high extraction efficiencies for most phenols. The results demonstrated a direct relationship between the extracted amount of phenols and its initial concentration in the sample. The limit of detection in off-line analyses applying large-volume injection was lower than 0.04 μg L⁻¹.These results of the use of in-tube solid phase microextraction with solvent desorption as a non-exhaustive (equilibrium sorptive) enrichment method show a great potential for on-line chromatographic analysis of micropollutants in real water samples.     

Control of various morphological changes of poly(meth)acrylate microspheres and their swelling degrees by SPG emulsification

Crosslinked poly(meth)acrylate polymers with a variety of morphologies were synthesized with two steps. In the first step, a microporous glass membrane (Shirasu Porous Glass, SPG) was employed to prepare uniform emulsion droplets by applying an adequate pressure to the monomer phase, which was composed of the ADVN initiator, solvent of toluene or heptane or their mixture, and a mixture of (meth)acrylate monomers. The droplets were formed continuously through the membrane and suspended in the aqueous solution, which contained a PVA‐127 suspending agent, SLS emulsifier, and NaNO₂ inhibitor to suppress the nucleation of secondary particles. SPG pore sizes of 0.90, 5.25, and 9.25 μm were used. Then the emulsion droplets were polymerized at 343 K with a rotation rate 160 rpm for 24 h. The (meth)acrylate monomers 2‐ethylhexyl acrylate (2‐EHA), 2‐ethylhexyl methacrylate (2‐EHMA), cyclohexyl acrylate (CHA), methyl methacrylate (MMA), lauryl acrylate (LA), and lauryl methacrylate (LMA) were used in this research. The influences of the ratios of the monomer and crosslinking agent EGDMA, the amount of diluents, the monomer type on the polymer particle morphology, the swelling degree, and the polymer particle size were investigated. It was found that an increase in the concentrations of EGDMA and heptane resulted in higher coarse porous spheres and smaller polymer particle sizes. A coefficient with a variation close to 10%, or a standard deviation of about 4, was obtained. The capacity of these spheres as solvent absorption materials was examined. The highest swelling degrees of heptane and toluene were obtained when LA was employed as the monomer with 30% (by weight) of EGDMA and 70% (by weight) of heptane as an inert solvent. The highest capacity of the solvent absorption was obtained when using a polymer particle size of 4.81 μm, as prepared by SPG pore size 0.9 μm. The polymer particles were able to absorb aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, and a mix of aliphatic hydrocarbon solvents and aromatic hydrocarbon solvents, such as toluene and heptane. The capacity of solvent absorption for the aromatic hydrocarbon solvents was higher than for the aliphatic hydrocarbon solvents. In addition, the particles did not rupture or collapse after absorption in solvents. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4038–4056, 2000     

Enhanced detection of olefins using ambient ionization mass spectrometry: Ag<Superscript>+</Superscript> adducts of biologically relevant alkenes

Spray solvent doped with silver ions increases the ease of olefin detection by desorption electrospray ionization (DESI). Characteristic silver adducts were generated in up to 50 times greater abundance when compared to conventional DESI spray solvents for the biologically significant olefin, arachidonic acid, in the positive ion mode. In the analysis of 26 lipids, silver adduct formation was highly favorable for fatty acids, fatty acid esters and prostaglandins but not applicable to some other classes (e.g., polar lipids such as ceramide and its derivative cerebroside sulfate). An investigation exploring competitive Ag⁺ cationization with a mixture of components demonstrated that polyunsaturated compounds form Ag⁺ adducts most readily. Silver cationization allowed the distinction between three sets of isomers in the course of multiple-stage collision-induced dissociation, so providing insight into the location of the olefin bonds. A silver ion-doped solvent was used in DESI imaging of normal and tumor canine bladder tissue sections. The Ag⁺ fatty acid adducts permitted post facto differentiation between the normal and tumor regions. In addition, silver adduct formation in the course of DESI imaging of tissue sections revealed the presence of triacylglycerides, a class of compounds not previously identified through DESI imaging. A simple silver nitrate spray solvent has the potential to further improve DESI analysis of unsaturated biomolecules and other molecules containing π-bonds through selective silver cationization.     

Screening Metal–Organic Frameworks for Separation of Binary Solvent Mixtures by Compact NMR Relaxometry

Metal–organic frameworks (MOFs) have great potential as an efficient alternative to current separation and purification procedures of a large variety of solvent mixtures—a critical process in many applications. Due to the huge number of existing MOFs, it is of key importance to identify high-throughput analytical tools, which can be used for their screening and performance ranking. In this context, the present work introduces a simple, fast, and inexpensive approach by compact low-field proton nuclear magnetic resonance (NMR) relaxometry to investigate the efficiency of MOF materials for the separation of a binary solvent mixture. The mass proportions of two solvents within a particular solvent mixture can be quantified before and after separation with the help of a priori established correlation curves relating the effective transverse relaxation times T_2eff and the mass proportions of the two solvents. The new method is applied to test the separation efficiency of powdered UiO-66(Zr) for various solvent mixtures, including linear and cyclic alkanes and benzene derivate, under static conditions at room temperature. Its reliability is demonstrated by comparison with results from ¹H liquid-state NMR spectroscopy.     

Solvent‐Polarity‐Tuned Morphology and Inversion of Supramolecular Chirality in a Self‐Assembled Pyridylpyrazole‐Linked Glutamide Derivative: Nanofibers,Nanotwists, Nanotubes,and Microtubes

The self‐assembly of a low‐molecular‐weight organogelator into various hierarchical structures has been achieved for a pyridylpyrazole linked L ‐glutamide amphiphile in different solvents. Upon gel formation, supramolecular chirality was observed, which exhibited an obvious dependence on the polarity of the solvent. Positive supramolecular chirality was obtained in nonpolar solvents, whereas it was inverted into negative supramolecular chirality in polar solvents. Moreover, the gelator molecules self‐assembled into a diverse array of nanostructures over a wide scale range, from nanofibers to nanotubes and microtubes, depending on the solvent polarity. Such morphological changes could even occur for the xerogels in the solvent vapors. We found that the interactions between the pyridylpyrazole headgroups and the solvents could subtly change the stacking of the molecules and, hence, their self‐assembled nanostructures. This work exemplifies that organic solvents can significantly involve the gelation, as well as tune the structure and properties, of a gel.     

The influence of organic sample solvents on the separation efficiency of basic compounds under strong cation exchange mode

This study investigated the influence of organic sample solvents on separation efficiency of basic compounds under strong cation exchange (SCX) mode. The mixtures of acidic aqueous solution and organic solvent such as acetonitrile, ethanol, methanol and dimethyl sulfoxide (DMSO) were tested as sample solvents. For later-eluting analytes, the increase of sample solvent elution strength was responsible for the decrease of separation efficiency. Thus, sample solvents with weak elution strength could provide high separation efficiencies. For earlier-eluting analytes, the retention of organic sample solvents was the main factor affecting separation efficiency. Weakly retained solvents could provide high separation efficiency. In addition, an optimized approach was proposed to reduce the effect of organic sample solvent, in which low ionic solvent was employed as initial mobile phase in the gradient. At last, the analysis of impurities in hydrophobic drug berberine was performed. The results showed that using acidic aqueous methanol as sample solvents could provide high separation efficiency and good resolution (R > 1.5).     

Triethylborane-induced bromine atom-transfer radical addition in aqueous media: study of the solvent effect on radical addition reactions.

A mixture of ethyl bromoacetate and 1-octene was treated with triethylborane in water at ambient temperature to provide ethyl 4-bromodecanoate in good yield. The bromine atom-transfer radical addition in benzene was not satisfactory. The addition proceeded smoothly in polar solvents such as DMF and DMSO, protic solvents such as 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoro-2-propanol, and aqueous media. Ab initio calculations were conducted to reveal the origin of the solvent effect of water in the addition reaction. The polar effect of solvents, which is judged by the dielectric constant, on the transition states in the bromine atom-transfer and radical addition steps is moderately important. Calculations show that a polar solvent tends to lower the relative energies of the transition states. The coordination of a carbonyl group to a proton in a protic solvent, like a Lewis acid, would also increase the efficiency of the propagation.