Solute-micelle association constants of some polynuclear aromatic hydrocarbons by micellar liquid chromatography with alcohol additives to mobile phase

Summary The interaction between some polynuclear aromatic hydrocarbons of environmental concern, and sodium dodecylsulphate and hexadecyltrimethylammonium bromide in the presence of methanol, 2-propanol and n-butanol has been evaluated by high-performance liquid chromatography using micellar mobile phases. Solute-micelle association constants have been determined for the compounds investigated. The results show that the addition of the alcohol to the mobile phase decreases the association constant values, methanol <2-propanol <n-butanol, relative to those in the absence of any additive.     

Role of the Na+ ion on phenol derivatives/hydroxypropyl-beta-cyclodextrin complex formation on porous graphitic carbon phase

The reversed-phase liquid chromatography retention of phenol derivatives was investigated over a concentration range of sodium chloride (0-10(-2) M) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) (0-35x10(-3) M) using a porous graphitic carbon (PGC) stationary phase and a methanol/water mixture (50:50 (v/v)) as the mobile phase. A theoretical treatment was developed to investigate the effect of the sodium chloride and hydroxypropyl-beta-cyclodextrin on the equilibrium between the solutes with the PGC surface and the aqueous medium, respectively. The thermodynamic parameter variations were calculated using van't Hoff plots. It was expected that the sodium ion acted on the solute-PGC association process by modifying the surface tension of both the bulk solvent and the PGC surface. The phenol derivative/HP-beta-cyclodextrin complexation was shown to be entropically controlled for all the solutes except for the one which contained the -NO2 group in its structure, i.e. the nitro phenol derivative. A comparison of the compensation temperature of the solute-PGC association process when sodium chloride and HP-beta-CD concentration changed in the mobile phase led to the conclusion that these two modifiers acted via a variation in the hydrophobic effect.     

Effects of Spacer Chain Length and Additives on Solution Properties of Cationic Gemini Surfactant

The critical micelle concentration (CMC) has been determined for the gemini surfactant trimethylene-1,3-bis(dodecyldimethyl ammonium bromide)12-s-12,2Br^?1 by means of electricity conductivity measurements. For the same number of carbon atoms in the hydrophobic chain per hydrophilic head group, geminis have CMC values well below those of conventional single-chain cationic surfactants. The CMC of 12-3-12 reduces with the addition of n-alcohol except ethanol and with the increase of n-alcohol chain length as well as increase of concentration of n-butanol and sodium chloride. Steady-state fluorescence quenching technology has been employed to study the aggregation number of micelle, which increases with increase in the length of n-alcohol. The Kraft temperature measurements also indicate that the stability of solid surfactant hydrate decreases along with the improvement of concentration of n-butanol and sodium chloride.     

Retention modelling in liquid chromatographic separation of simvastatin and six impurities using a microemulsion as eluent

A novel and unique approach was used for retention modelling in the separation of simvastatin and six impurities by liquid chromatographic using a microemulsion as mobile phase. A microemulsion is a modification of a micellar system where a lipophilic organic solvent is dissolved in the micelles; for that reason, microemulsions are usually treated as solvent-modified micellar solutions. When microemulsions are used as eluents in HPLC separations, solutes partition between the charged oil droplets and the aqueous buffer phase. The complexity of the composition of the microemulsion permits extensive manipulations to be made during method development in order to achieve acceptable resolution of such a complex mixture of substances. In order to avoid a laborious "trial and error" procedure, a 2(3) full factorial design was applied for choosing an optimal microemulsion composition to obtain good separation in a reasonable run time. Organic solvent, sodium dodecyl sulphate, and n-butanol content were varied within defined experimental domain. Optimal conditions for the separation of simvastatin and its six impurities were obtained using an X Terra 50 x 4.6 mm, 3.5 microm particle size column at 30 degrees C. The mobile phase consisted of 0.9% w/w of diisopropyl ether, 2.2% w/w of sodium dodecylsulphate (SDS), 7.0% w/w of co-surfactant such as n-butanol, and 89.9% w/w of aqueous 25 mM disodium phosphate pH 7.0.     

Determination of (dichloromethylene) diphosphonate in physiological fluids by ion-exchange chromatography with phosphorus-selective detection

The influence of mobile phase composition on the chromatographic behaviour of human platelets, granulocytes, lymphocytes and erythrocytes has been studied by using a bisoxirane-coupled polyethylene glycol 20M-Sepharose 6B column at pH 7.5. Lowering of the concentration of dextran T40 from 8 to 2% (w/w) produced the highest separation factor between platelets and granulocytes. Addition of 0.5% (w/w) of DEAE-dextran to a mobile phase containing 2% dextran T40 or T500 increased the retention of platelets, and discriminated the cells from erythrocytes. Addition of sodium chloride increased the retention volumes of lymphocytes, granulocytes and platelets. These blood cells were adsorbed to the column in isotonic phosphate-buffered eluent, whereas in imidazole-buffered eluent about 0.15-0.154 M sodium chloride improved their resolution.     

Retention study of some cation-type compounds using bile acid sodium salts as ion pairing agents in liquid chromatography

The possibility of forming ion-pairs between bile acids (sodium taurocholate, sodium taurodeoxycholate and sodium taurochenodeoxycholate) and different compounds (pralidoxime, obidoxime and pyridostigmine) having a cationic character has been studied in reversed-phase liquid chromatography (RP-LC). This study can be useful in understanding the role of bile acids in the transport of ionic species through hydrophobic membrane. The present study focused on the influence of mobile phase composition on the retention parameters of chosen compounds (percentage of acetonitrile, pH of aqueous component or ionic strength). For constant concentration of bile acids in aqueous component of mobile phase the functional dependencies between the logarithm of the retention factor (k) and the methanol content in the mobile phase followed a binomial pattern (U-shaped), with a minimum positioned within the interval 70-85% methanol.     

微乳液结构的研究

测定了十二烷基磺酸钠／正丁醇／２０％苯乙烯／水体系的相平衡，用冷冻刻蚀、ＥＳＲ、ＦＴ－ＩＲ研究了上述体系微乳液的结构，研究表明，苯乙烯含量恒定时，随着体系中水含量增加，电导确定的双连续结构的微乳液经历着从油包水到以连续再到水包油变化，ＦＴ－ＩＲ测定表明，Ｗ／Ｏ微乳兴较Ｏ／Ｗ微乳液的ＯＨ伸缩振动和弯曲振动频率有显著减小，说明Ｗ／Ｏ微乳兴中氢键缔合要比Ｏ／Ｗ强得多。ＥＳＲ测定表明Ｏ／Ｗ微乳液的旋转相关     

Degree of Complexation of Anticoagulant Rodenticides with Human Serum Albumin: Effect of Saccharose and Sodium

A theoretical treatment has been developed to describe association between rodenticides and human serum albumin (HSA). The degree of complexation n_c (the amount (%) of complexed guest) and the association constant (K) for rodenticide–HSA binding were determined. Enthalpy–entropy compensation was also investigated in relation to this mathematical model to confirm rodenticide binding behavior with HSA. The role of the sodium cation and saccharose in this association were also analyzed. As expected for a salting-out agent, addition of Na⁺ cation to the mobile phase led to enhancement of n_c and K values by increasing the hydrophobic effect. When saccharose was increased above a critical x_c value equal to 4 mM, a decrease of the association constant and the degree of complexation was observed, owing to reduction of the radius of curvature of the HSA cavity.     

Determination of the micelle-solute association constants of some benzene and naphthalene derivatives by micellar high performance liquid chromatograph

Summary The interaction of some benzene and naphthalene derivatives with sodium dodecyl sulphate, hexadecyltrimethylmmonium bromide and polyoxyethylene [23] dodecanol micelles has been evaluated by high operformance liquid chromatography using micellar mobile phases. The micelle-solute association constants have been obtained for the compounds investigated. Good correlation between free energy of transfer for water-micelles and for octanol-water has been observed.     

离子色谱法测定“地沟油”中钠离子和氯离子的含量及其比例关系

采用离子色谱法测定“地沟油”样品中钠离子和氯离子的含量,通过计算两者的比例关系确定样品中是否含有“地沟油”。使用去离子水提取“地沟油”样品中钠离子和氯离子。氯离子以20 nmol/L KOH溶液为淋洗液,AS19分离柱(250 mm×4 mm)分离,抑制器电流112 mA;钠离子以20 nmol/L甲基磺酸(MSA)为淋洗液,CS12分离柱(250 mm×4 mm)分离,抑制器电流59 mA;两者分离采用的其他相同色谱条件为: 柱温、检测器温度30 ℃,电导检测器检测,进样量25 μL,流量1 mL/min,峰面积定量。氯离子的检出限为0.005 mg/L,在0～5 mg/L范围内有良好的线性关系（r2=0.999988）;钠离子的检出限为0.001 mg/L,在0～5 mg/L范围内有良好的线性关系（r2=0.999926）。氯离子平均加标回收率为94.2%,相对标准偏差(RSD)为2.4%;钠离子平均加标回收率为92.5%, RSD为2.7%。经测定、计算,正常食用油中钠离子和氯离子的物质的量比约为1,而“地沟油”中钠离子与氯离子的物质的量比高于4。“地沟油”中钠离子和氯离子的含量及其比例关系可作为判断“地沟油”的重要依据。     

Purification of Solid-Phase Synthesized Peptides on the Coil Planet Centrifuge

Abstract

The analytical flow-through coil planet centrifuge, an instrument for countercurrent chromatography, performs the preparative purification of synthetic peptides. Various two-phase solvent systems have been tried with either phase mobile to purify many synthesized peptides. A series of N-terminal fragment peptides of cholecystokinin octapeptide (CCK 26–33) were synthesized by solid-phase techniques and purified on the coil planet centrifuge. The peptides were sulfated and chromatographed again. For hydrophobic peptides, purification is effected in solvent systems with a mobile aqueous phase. The n-butanol, acetic acid and water system (4:1:5 by volume) with the lower phase mobile was utilized. For sulfated peptides, the neutral system, 0.2 M ammonium acetate and n-butanol was generally applied.     

Shape Transition in Micelles of Undecylammonium Chloride in the Presence of Sodium Chloride and n-Butanol: A Study by Dynamic Light Scattering

Dynamic light scattering measurements have been performed on micellar solutions of undecylammonium chloride in the presence of 0 to 0.5 mol dm(-3) n-butanol and 0 to 0.2 mol dm(-3) sodium chloride. The results support opposing effects of these additives on micellar growth, with the n-butanol causing a reduction of micelle size. The dependence of the aggregation number on the hydrodynamic radius suggests a transition from sphere to prolate ellipsoid when the aggregation number approximates that predicted for the maximum aggregation number of a spherical micelle. Micelle dimensions calculated from the aggregation number, conformational considerations, and packing criteria of the monomers in the micelle are compared with those from dynamic light scattering data. Copyright 2001 Academic Press.     

Phase behaviour and microstructures of microemulsions(Ⅰ)

By the orthogonal design,the optimal formation conditions for the middle-phase microemulsions in the system dioctadeeyldimethylammornum chloride (DODMAC)/ sodium dodecyl sulfate (SDS)/n-butanol/n-hep-ane/brine were obtained as follows.Investigations have been made on the effects of the concentrations of NaCl and n-butanol(1.0%-14.0%),the rantos of W to Wshs and the kinds of alcohols (n-propanol,n-butanol,and n-pentanol) on the formation,the phase behavtour,the ultralow interfacial tensions,the optimal salinity (S*),and the length of salinity (S).Some rules and data were worked out about the formation and characteristics of the middle-phase microemulsions.The mi-crostruenres of the middle-phase microemulsions were also studied by using FT-IR,ESR,and freeze fracture electron microscopy techmques The results from the three methods show that the microstructures of the middle-phase mi-croemnlsions undergo the change from O/W to bicontinuous(B C.) and to W/O.The distribution rule of the orga-mzed molecule ass     

Ion Chromatographic Determination of Sodium Isethionate

Abstract

Single column anion chromatography with conductivity detection has been used for the determination of sodium isethionate. A mobile phase of aqueous phthalic acid - methanol (pH 2.5) allows for the separation of isethionate from chloride and alkyl isethionate ester surfactants. Commercially available samples of sodium isethionate and alkyl esters were analyzed by the described procedure.     

Simultaneous Determination of Dextromethorphan Hydrobromide, Pyrilamine Maleate and Sodium Benzoate in a Cough Cold Syrup by LC

A liquid chromatographic method for the simultaneous determination of dextromethorphan hydrobromide, pyrilamine maleate and sodium benzoate in cough cold syrup has been developed. The method was based on replacing heptane sulfonate by sodium chloride as ion pairing agent. The addition of sodium chloride to the mobile phase has changed the retention behaviour of the basic drugs. The separation of these compounds was achieved in less than 8 min with an isocratic mobile phase consisting of acetonitrile/0.1 M dihydrogenphosphate buffer containing 0.1 M sodium chloride (29:71 v/v) at pH 2.5 and using a Kromasil C18 column. The analysis was performed at a flow rate of 1 mL min^?1 and at a detection wavelength of 220 nm. The selectivity, linearity of calibration, accuracy, within and between days precision, limit of detection and quantification, recovery were examined as parts of the method validation. Calibration curves were linear in the range 1–140 μg mL^?1 with a regression coefficient (R ²) better than 0.999. The results of the method repeatability (intra-day) and reproducibility (inter-day) were all less than 2% (n = 6). The lowest detectable concentration of dextromethorphan hydrobromide and pyrilamine maleate varied between 0.10 and 0.12 μg mL^?1. The proposed liquid chromatographic method was satisfactorily applied for the routine quality control of dextromethorphan hydrobromide, pyrilamine maleate and sodium benzoate in cough cold syrup formulations.     

A unified analytical treatment of the acid-dissociation equilibria of weakly acidic linear polyelectrolytes and the conjugate acids of weakly basic linear polyelectrolytes

 The influence of added sodium chloride concentration levels on the acid-dissociation equilibria of a weakly acidic linear polyelectrolyte and a conjugate acid of weakly basic linear polyelectrolyte has been investigated potentiometrically by use of polyacrylic acid (PAA) and poly(N-vinylimidazole) (PVIm) as examples of polyelectrolytes. Both equilibria are strongly influenced by the degree of dissociation of the polyacids as well as the concentration levels of sodium chloride due to an electrostatic effect originating from the negatively or positively charged polymer surfaces. These have been analyzed in a unified manner by taking accounts of two-phase properties of the charged linear polyions. Distribution of counterions and coions between a polyelectrolyte phase formed around the polymer skeleton and a bulk solution phase has been rationalized by a Donnan’s relation. Introduction of a volume term for the polyelectrolyte phase permits definition of averaged concentrations of mobile ions in the vicinity of the polyion molecules, which enables us to define hypothetical intrinsic acid-dissociation constants in the polyion domain. The intrinsic constants estimated by extrapolation of apparent acid-dissociation constants at zero-charge state are in good agreement with the acid-dissociation constants of the monomer analogs of the polymers, i.e., acetic acid for PAA and imidazole for PVIm, respectively. The difference between the apparent and intrinsic acid-dissociation constants for PVIm was much higher than that for PAA at defined degree of dissociation of the polyacids, even though the separations of the functionalities fixed on the linear polymers are approximately equal to each other. Received: 4 February 1997 Accepted: 26 May 1997     

Kinetics of Phase Transfer Catalytic Preparation of Benzyl Benzoate

The kinetics is studied for the phase transfer catalytic preparation of benzyl benzoate from sodium benzoate and benzyl chloride with tetrabutylaramonium iodide as catalyst in a well stirred batch reactor. Benzyl chloride is dissolved in toluene as the organic phase and sodium benzoate is dissolved in water as the aqueous phase. The kinetics of the overall reaction is described by a first-order model based on the concentration of benzyl chloride in the organic phase at the later time of the batch reaction. The rate constant increases with an increase of the catalyst concentration while decreases slightly with an increase of the concentration of sodium benzoate under the experimental condition.     

High-performance liquid chromatography of amino acid peptides and proteins

Summary The retention behaviour of seven globular proteins ranging in molecular weight from 12,000 to 69,000 was investigated using Mono-Q anion-exchange resin as the stationary phase and sodium chloride as the displacer salt. In particular the influence of changes in ionic strength and mobile phase pH on the isocratic retention properties was assessed. Several proteins were found to have significant retention when the pH of the mobile phase was below the reported pl values of the proteins. This behaviour results from the non-uniform charge distribution on the protein surface, which allows interaction with the charged stationary phase even though the protein net charge is equal to or greater than zero. The influence of pH and ionic strength on experimentally observed bandwidths was also investigated. The dependence of the effective reduced plate height on solute capacity factor was found to vary significantly with the mobile phase pH, a behaviour consistent with the interplay of complex multisite binding kinetics. These results provide a basis for further detailed investigations into the mechanism of interaction of proteins not only with charged surfaces associated with adsorptive chromatographic media but also with other macromolecules. For Part LXXXII, see ref. [27].     

水溶性疏水缔合聚合物在高岭土/水界面的吸附

表面活性剂;水溶性疏水缔合聚合物在高岭土/水界面的吸附     

Spectroscopic study of water-NaCl-benzene mixtures at high temperatures and pressures

Near-infrared and ultraviolet spectra of water-NaCl-benzene mixtures have been measured in the 473-573 K and 100-400 bar range and 373-498 K and 50-300 bar range, respectively. Concentrations of water in the benzene-rich phase and benzene in the water-rich phase were estimated from integrated intensities of the absorption bands. It is found that addition of NaCl in the aqueous phase suppresses transfer of water into the benzene-rich phase, and the relative decrease in water solubility in benzene exhibits good correlation with an increase in density of the aqueous NaCl solution relative to that of neat water. The salting-out constant for the water-NaCl-benzene system, which is estimated from a relative decrease in benzene solubility in the aqueous phase by addition of sodium chloride, increases significantly with increasing temperature. It is suggested that the effect of sodium chloride on the water-benzene mutual solubilities can be explained by ion-induced electrostriction of the aqueous phase.