HPLC determination of non-ionic surfactants used in tertiary oil recovery

Summary Having developed a chromatographic technique with a diol bonded phase for the study of the distribution versus ethylene oxide number (E.O.) for various non-ionic polyoxyethylated surfactants used in enhanced oil recovery (KL 6, ; KM 11, and KM 20, ) we report here the titration of one of these surfactants (KL 6) in the presence of an ionic surfactant (S 385, sulfonated petroleum fraction) and other non-ionic surfactants (KM 11 and/or KM 20) which are the conditions found in enhanced oil recovery. This work has been carried out in brine and in n-decane, as a model for the petroleum phase. Obviously in the case of aqueous phases it was necessary to carry out a thorough dehydration before the chromatographic analyses. We have shown that it is possible, under these conditions, to determine the KL 6 surfactant in the concentration range 500 to 6000 ppm with a precision of 70 ppm without experiencing interference from KM 11 or KM 20 non-ionic surfactants or S 385 ionic surfactant. Furthermore, from some of the samples studied which were in contact with the rock shale, we showed that strong adsorption of the KL 6 occurs. Chromatographic analyses show that this surfactant is only desorbed from the rock shale when employing a non-ionic surfactant such as KM 25 which is much more polar than the KL 6.     

Neutral amphiphilic polysaccharides: chemical structure and emulsifying properties

Dextran, a neutral bacterial polysaccharide, is chemically modified by reaction with an aromatic epoxide (phenylglycidylether). The reaction conditions are either homogeneous, using dimethylsulfoxide as a common solvent, or heterogeneous, dispersing the epoxide into an aqueous solution of dextran. The grafting yield is much higher in homogeneous conditions. The viscometric characteristics of the amphiphilic polysaccharides are examined in water and in dimethylsulfoxide. These properties clearly depend on both the degree of substitution and the reaction conditions at a given degree of substitution. Highly modified dextrans (with more than 30% hydroxyl substituted) exhibit characteristic solubility in organic liquids that are non-solvents for the unmodified dextran. Changing the degree of hydrophobic substitution of the amphiphilic polysaccharide, direct and inverse submicronic emulsions are prepared. The stability of direct and inverse emulsions is analysed by following the evolution of the droplet size. Ostwald ripening is the major ageing process for both emulsions.     

The cloud point extraction of copper(II) with monocarboxylic acids into non-ionic surfactant phase

The possibility to use monocarboxylic acids and their mixtures with amines for copper concentrating by the way of micellar extraction at cloud point temperature, and later atomic absorption spectrometry (AAS) determination was investigated. Under the optimum conditions, preconcentration of 100 ml of water sample in the presence of 1% non-ionic surfactant OP-10, 0.005 M capric acid and 0.01 M octylamine permitted the detection of 0.01 μg ml⁻¹ copper. The proposed method has been applied to the AAS determination of copper in water samples after cloud point extraction.     

α-环糊精与季铵盐型双子表面活性剂包结作用的研究

在293.15 K下用微量热法结合核磁共振波谱研究了α-环糊精与三种阳离子型双子表面活性剂((CnN)2Cl2, n=12, 14, 16) 在水溶液中的包结作用. 实验结果表明, 包结物都相当稳定, 且随着疏水链CnH2n+1中碳原子数目的增加, 主-客体包结物的化学计量比由2∶1为主变为6∶1为主, 最大化学计量比的主-客体包结物形成过程的标准焓变(ΔHӨ) 和标准熵变(ΔSӨ) 均为负值且绝对值逐渐增大. 包结物的形成均属焓驱动过程. 1H核磁共振数据表明, (C12H25N)2Cl2的存在使α-环糊精上各质子的化学位移向高场移动, 从微观上证明了包结作用的发生.     

In situ monitoring of gold-surface adsorption and acidic denaturation of human serum albumin by an isolation-capacitance-adopted electrochemical quartz crystal impedance system

Combined measurements of piezoelectric quartz crystal impedance (PQCI) and electrochemical impedance spectrum (EIS) using a suitable isolation capacitance is reported for the first time to monitor in situ adsorption and acidic denaturation of human serum albumin (HSA) on gold electrodes in Britton-Robinson (B-R) buffers. This method provides simultaneously mutual-interference-free and accurate parameters of EIS and PQCI. Effects of surface thiol-modification, electrode-potential and solution pH on HSA adsorption were examined and discussed. Comparative experiments of HSA adsorption in a B-R buffer of pH 6.42 on bare, cysteine- and 1-dodecanethiol-modified gold electrodes revealed that HSA adsorption is more significant on a hydrophobic (1-dodecanethiol-modified) surface. Insignificant electrode-potential effect implied minor electrostatic effects on HSA adsorption. The adsorption amount of HSA at pH 3.28 was found to be notably greater than those at pH 4.84 and 6.42. To characterize HSA adsorption, electrode standard rate constants (k_s) of the Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ couple were measured before and after HSA adsorption. The k_s-pH curves on an HSA-modified Au electrode revealed that k_s increased abruptly with the decrease of solution pH below pH ∼4. Moreover, pH-dependent responses of the resonant frequency, the motional resistance, the double-layer capacitance, the capacitance of adsorbed HSA layer and the peak absorbance of HSA solutions at 278 nm all exhibited an inflexion change at pH ∼4, and these findings have been explained on the basis of acidic denaturation of HSA and electrical charges carried by HSA molecules.     

Selective removal of interference signals for near-infrared spectra of biomedical samples by using region orthogonal signal correction

New approach for chemometrics algorithm named region orthogonal signal correction (ROSC) has been introduced to improve the predictive ability of PLS models for biomedical components in blood serum developed from their NIR spectra in the 1280-1849 nm region. Firstly, a moving window partial least squares regression (MWPLSR) method was employed to locate the region due to water as a region of interference signals and to find the informative regions of glucose, albumin, cholesterol and triglyceride from NIR spectra of bovine serum samples. Next, a novel chemometrics method named searching combination moving window partial least squares (SCMWPLS) was used to optimize those informative regions. Then, the specific regions that contained the information of water, glucose, albumin, cholesterol and triglyceride were obtained. When an interested component in the bovine serum solution, such as glucose, albumin, cholesterol or triglyceride is being an analyte, the other three interests and water are considered as the interference factors. Thus, new approach for ROSC has employed for each specific region of interference signal to calculate the orthogonal components to the concentrations of analyte that were removed specifically from the NIR spectra of bovine serum in the region of 1280-1849 nm and the highest interference signal for model of analyte will be revealed. The comparison of PLS results for glucose, albumin, cholesterol and triglyceride built by using the whole region of original spectra and those developed by using the optimized regions suggested by SCMWPLS of original spectra, spectra treated OSC for orthogonal components of 1-3 and spectra treated ROSC using selected removing the highest interference signals from the spectra for orthogonal components of 1-3 are reported. It has been found that new approach of ROSC to remove the highest interference signal located by SCMWPLS improves of the performance of PLS modeling, yielding the lower RMSECV and smaller number of PLS factors.     

Hydrophobic layered double hydroxides (LDHs): Selective adsorbents for liquid mixtures

 The external and internal surface area of the calcium aluminum double hydroxide [Ca₂Al(OH)₆] NO₃ ⋅ 2H₂O were hydrophobized by the anionic surfactants sodium dodecylsulfate and sodium dodecyl-benzene sulfonate. The adsorption behavior towards liquid mixtures (benzene/n-heptane and n-propanol/ toluene) was studied by determining the surface excess adsorption isotherms, the heats of immersion in these liquids, and the basal spacing, i.e. the expansion of the interlayer space. Both hydrophobic layered double hydroxides (LDHs) adsorbed n-hep-tane, benzene, toluene, and n-pro-panol between the layers with considerable increase of the basal spacing. Interlamellar swelling of the hydrophobizised LDHs in n-heptane was fundamentally different to the behavior of hydrophobized 2 : 1 clay minerals (smectites, vermiculites). The surface excess isotherms for benzene/ heptane mixtures were U-shaped and indicate preferential adsorption of benzene. Dodecylbenzene sulfonate double hydroxide preferentially adsorbed propanol from n-propanol/ toluene mixtures but the dodecyl-sulfate derivative adsorbed both compounds. Received: 23 January 1997 Accepted: 10 February 1997     

First kinetic determination of partition coefficients for organic compounds between the three microenvironments of AOT-based microemulsions.

Kinetic data for the hydrolysis of N-picolinoylimidazole (I) and 2,4-dinitrophenylpicolinate (II) in AOT [bis(2-ethylhexyl) sodium sulfosuccinate] microemulsions are used to determine for the first time the two partition constants for each substrate (i.e. K(wi) and K(oi), corresponding to the incorporation of substrate molecules from water microdroplets and the continuous medium, respectively, into the interface). Application of the pseudophase formalism to the partition constants allowed the rate constant in each phase to be determined. The rate of hydrolysis of II increased with decreasing polarity of the medium; as a result, the hydrolysis reaction took place largely at the interface. On the other hand, the rate of hydrolysis of acylimidazole I decreased with decreasing polarity, possibly as a result of changes in the resonance structures of the reagent causing the hydrolysis process to occur preferentially in water microdroplets.     

Near-infrared spectroscopic determination of human serum albumin, γ-globulin, and glucose in a control serum solution with searching combination moving window partial least squares

Near-infrared (NIR) spectra in the region of 5000-4000 cm⁻¹ with a chemometric method called searching combination moving window partial least squares (SCMWPLS) were employed to determine the concentrations of human serum albumin (HSA), γ-globulin, and glucose contained in the control serum IIB (CS IIB) solutions with various concentrations. SCMWPLS is proposed to search for the optimized combinations of informative regions, which are spectral intervals, considered containing useful information for building partial least squares (PLS) models. The informative regions can easily be found by moving window partial least squares regression (MWPLSR) method. PLS calibration models using the regions obtained by SCMWPLS were developed for HSA, γ-globulin, and glucose. These models showed good prediction with the smallest root mean square error of predictions (RMSEP), the relatively small number of PLS factors, and the highest correlation coefficients among the results achieved by using whole region and MWPLSR methods. The RMSEP values of HSA, γ-globulin, and glucose yielded by SCMWPLS were 0.0303, 0.0327, and 0.0195 g/dl, respectively. These results prove that SCMWPLS can be successfully applied to determine simultaneously the concentrations of HSA, γ-globulin, and glucose in complicated biological fluids such as CS IIB solutions by using NIR spectroscopy.     

Vapor pressure measurements on nonaqueous electrolyte solutions. Part 6. Some remarks on integral equations

Various combinations of the hypernetted chain (HNC) equation with the mean spherical approximation (MSA) and the Percus-Yevick (PY) equation are compared both for a well-known aqueous 2-2 electrolyte model solution and for real acetonitrile solutions. Belloni's self-consistency test shows that classical HNC calculations yield the best compressibility data for the two systems despite an apparently unrealistic g₊₊ maximum in the case of the aqueous solution. Effective concentration-dependent potentials making use of the dependence of the solution permittivity on electrolyte concentration are used for HNC calculations of osmotic coefficients for methanol solutions.