Cyclohexane Toluene Research Articles

Validated simultaneous high-performance thin-layer chromatography‒mass spectrometry method for analysis of citalopram prochlorperazine, midazolam, and chlorodiazepoxide in urine for forensic analysis

Drug breakthroughs and development have been a great blessing to mankind. Problem arises when these are used in non-medical context such as use for recreational purposes, using drugs outside the label directions, and use with malicious intent as found in homicidal cases. Young generations get trapped into vicious cycle of drug addiction that has deleterious effects on their mind and body. Drugs including psychomotor drugs, opioids, narcotics, inhalants, stimulants, and central nervous system depressants are easily accessible. Forensic science plays a crucial role in investigation pertaining to drug abuse and overdose. Complex biological and non-biological matrices are submitted to forensic science laboratories for analysis and interpretation of the effects of drugs/toxicants/poisons on human body and environment. The aim of this study was to develop a method for the determination of various prescription drugs in the urine using high-performance thin-layer chromatography‒mass spectrometry (HPTLC‒MS) technique. New combination of solvent systems was tried for the simultaneous detection of frequently used prescription drugs in urine. The method was developed and validated using HPTLC‒MS for the quantitative estimation of benzodiazepines, anti-depressants, and tranquilizers in urine using a common solvent system for all the drugs. Mobile phase cyclohexane‒toluene‒diethylamine (7:1.5:1.5, V/V) with one drop strong ammonia solution was used as mobile phase. Method validation was carried out according to the International Council of Harmonization guidelines. The present HPTLC‒MS method being simple, sensitive, precise, and accurate can be used for the detection and quantitative estimation of benzodiazepines, anti-depressants, and tranquilizers in biological specimens.

Study of the Dynamic Modes of the Operation of Flowsheets for the Extractive Distillation of a Benzene–Cyclohexane–Toluene Mixture

Study of the Dynamic Modes of the Operation of Flowsheets for the Extractive Distillation of a Benzene–Cyclohexane–Toluene Mixture

Enthalpic and Liquid-Phase Adsorption Study of Toluene-Cyclohexane and Toluene-Hexane Binary Systems on Modified Activated Carbons.

The liquid-phase adsorption of toluene in cyclohexane and hexane solutions on modified activated carbons was evaluated; the energy involved in the interaction between these solutions and the solids was determined by immersion enthalpies of pure solvents and their mixtures, and the contribution of the system constituents was calculated by differential enthalpies. The thermal treatment generated modifications that favored adsorption and interaction with the evaluated solutions, since it increased the textural parameters and the basic character of the samples. Cyclohexane could create greater competition with the adsorption sites compared to hexane, but it favored the increase in adsorption capacities (0.416 to 1.026 mmol g−1) and the interactions with the solid evaluated through the immersion enthalpies. The immersion enthalpies of pure solvents (−16.36 to −112.7 J g−1) and mixtures (−25.65 to −104.34 J g−1) had exothermic behaviors that were decreasing due to the possible displacement of solvent molecules when increasing the solute concentration in the mixtures. The differential enthalpies for toluene were negative (−18.63 to −2.14 J), mainly due to the π–π interaction with the solid, while those of the solvent–solid component tended to be positive values (−4.25 to 55.97 J) due to the displacement of the solvent molecules by those of toluene.

Zeolite catalyst containing metals.

Adsorption desulfurization is one of the most promising ways to reduce the sulfur content of gasoline at deeper level. In this work, thiophene (TP) adsorption capacity in cyclohexane onto [Cu3(BTC)2(H2O)3] (HKUST-1) was measured by batch method, and the effect of cyclohexene and toluene on sulfur capacity was investigated. Adsorption isotherms of TP, cyclohexene, and toluene in cyclohexane onto HKUST-1 were conducted at 298.15–313.15 K to explicate the different extent of influence by cyclohexene or toluene addition. The results showed that, compared with cyclohexene, the addition of toluene in model gasoline led to a moderate decline in sulfur capacity of HKUST-1. The isotherm data of TP adsorption were well-correlated using Langmuir equation, while those of cyclohexene or toluene adsorption fitted Freundlich model, indicating different adsorption mechanisms between TP and competitors. The adsorption capacities followed the order of toluene < cyclohexene ≪TP at the same equilibrium concentrations, implying the order of the adsorption affinities, which is in good agreement with the different extent of influence by cyclohexene and toluene. The excellent regeneration performance of HKUST-1 in TP adsorption benefits from the physical adsorption mechanism, which was hinted by the enthalpy of TP adsorption (−37.31 ± 2.04 kJ mol−1) and no detection of new sulfur species.

Diffusion Coefficients of a Highly Nonideal Ternary Liquid Mixture: Cyclohexane–Toluene–Methanol

To better understand diffusion phenomena in highly nonideal ternary liquid mixtures, cyclohexane–toluene–methanol is studied by equilibrium molecular dynamics (EMD) simulation. Intradiffusion and Maxwell–Stefan (MS) diffusion coefficients, being strictly kinetic properties, are predicted by EMD over the entire composition range at ambient conditions. The thermodynamic contribution to the Fick diffusion coefficients is studied with an excess Gibbs energy model. Predictive results from the combination of these two approaches are in convincing agreement with experimental Fick diffusion coefficient data. Different aspects determining the composition dependence of diffusion coefficients, such as their behavior at the binary limits, hydrogen bonding, and stability criteria, are discussed. While the intradiffusion coefficients exhibit only a weak composition dependence, the MS diffusion coefficients are strongly affected by the nonideality of the present mixture. Fick diffusion coefficients reveal pronounced dif...

Development and validation of a high-performance thin-layer chromatographic method for the simultaneous determination of levamisole and cocaine in seized cocaine sample

Cocaine is the second most illicit drug worldwide. Levamisole, an anthelminthic drug, has been identified as a cocaine adulterant in the United States since the last decade. Now, its presence has increasingly been discovered in street cocaine samples seized in India. Recently, it has been observed in many street cocaine samples seized by investigation agencies in India. Due to the incidence of toxicity caused by this contamination which has been increasing rapidly since 2002, it is important to understand the chemical separation, identification, and quantification of this drug. In the present study, an attempt has been made to develop a new high-performance thin-layer chromatographic (HPTLC) method for the simultaneous discrimination and quantification of levamisole in seized cocaine samples. Chromatography was performed using a pre-coated silica gel aluminum plate as the stationary phase, and the mobile phase cyclohexane—toluene—diethyl amine (75:15:10) was able to discriminate between cocaine hydrochloride and levamisole hydrochloride significantly. Densitometric analysis was performed in the absorbance mode at 230 nm. The linear regression analysis of data for the calibration curve showed good linearity over a concentration range of 100–1200 ng per band and 200–2400 ng per band with a regression value of 0.997 and 0.995 for levamisole hydrochloride and cocaine hydrochloride, respectively. The developed method is used to quantify cocaine content as well as to estimate the concentration of adulterant levamisole. The method was validated according to the International Conference on Harmonization (ICH) guidelines and can be used in the identification and quantification of levamisole and cocaine in seized cocaine samples. The present method is simple, reproducible, and repeatable, which can easily be performed in any laboratory.

Adsorption desulfurization of model gasoline by metal–organic framework Ni3(BTC)2

Abstract This work presented the synthesis of Ni-based metal-organic framework material with a paddle-wheel structure Ni3(BTC)2 (Ni-BTC) and its application in thiophene (TP) adsorption from gasoline distillate by batch method. Adsorption isotherms of TP, cyclohexene, and toluene in cyclohexane onto Ni-BTC were conducted at 298–308 K to interpret the different effect of cyclohexene and toluene on TP adsorption. The results showed that, compared with cyclohexene, toluene addition in model gasoline led to a more evident decline in sulfur capacity of Ni-BTC, which is opposite to isostructural HKUST-1. The adsorption isotherms of TP, cyclohexene and toluene fit Langmuir model, S-type model and Temkin model well, respectively, indicating that the adsorption mechanisms of TP and the two competitors are different from one another. The adsorption capacities on Ni-BTC followed the order of cyclohexene

Application of the partially thermally coupled distillation flowsheets for the extractive distillation of ternary azeotropic mixtures

An application is considered of the extractive distillation flowsheets with partially thermally coupled columns for the separation of ternary azeotropic mixtures with the different type of vapor–liquid equilibrium diagrams. The feasible extractive distillation flowsheets with such columns are identified for all types of the ternary azeotropic mixture vapor–liquid equilibrium diagrams. The manifold of flowsheets is the search space to identify the optimal arrangement for the separation of the individual mixture. An applicability analysis of all possible extractive distillation flowsheets for all types of vapor–liquid equilibrium diagram decreases the number of feasible configurations for the selection of the optimal extractive distillation sequence for the mixture with unique vapor–liquid equilibrium diagram separation. For example, in the case of benzene–cyclohexane–toluene mixture distillation with N-methylpyrrolidone as an entrainer, only 10 extractive distillation flowsheets instead of 22 potential ones must be analyzed, calculated and optimized for the identification of the best extractive distillation arrangement.

Thiophene adsorption onto metal–organic framework HKUST-1 in the presence of toluene and cyclohexene

Adsorption desulfurization is one of the most promising ways to reduce the sulfur content of gasoline at deeper level. In this work, thiophene (TP) adsorption capacity in cyclohexane onto [Cu3(BTC)2(H2O)3] (HKUST-1) was measured by batch method, and the effect of cyclohexene and toluene on sulfur capacity was investigated. Adsorption isotherms of TP, cyclohexene, and toluene in cyclohexane onto HKUST-1 were conducted at 298.15–313.15 K to explicate the different extent of influence by cyclohexene or toluene addition. The results showed that, compared with cyclohexene, the addition of toluene in model gasoline led to a moderate decline in sulfur capacity of HKUST-1. The isotherm data of TP adsorption were well-correlated using Langmuir equation, while those of cyclohexene or toluene adsorption fitted Freundlich model, indicating different adsorption mechanisms between TP and competitors. The adsorption capacities followed the order of toluene < cyclohexene ≪TP at the same equilibrium concentrations, implying the order of the adsorption affinities, which is in good agreement with the different extent of influence by cyclohexene and toluene. The excellent regeneration performance of HKUST-1 in TP adsorption benefits from the physical adsorption mechanism, which was hinted by the enthalpy of TP adsorption (−37.31 ± 2.04 kJ mol−1) and no detection of new sulfur species.

Towards automated characterisation of liquid–liquid equilibria

A highly automated 2-step method for measuring and correlating liquid–liquid equilibria (LLEs) is presented: In step 1, samples are prepared and measurements are performed; step 2 covers data extraction and correlation with thermodynamic models. The procedure has been optimised such that a sample volume of 1mL per LLE is sufficient for reliable measurements. The experimental setup consists of commercially available modules assembled such that the setup automatically prepares the sample mixtures, waits for equilibrium, takes samples, and analyses them. Gas chromatography (GC) is employed to maximise flexibility with respect to the mixtures that can be studied. For GC analysis, neither further dilution nor addition of an external standard is needed. In step 2, the gathered data are converted into concentration data and the gE-models UNIQUAC and NRTL are adjusted to the data. The automated 2-step method is validated for the ternary systems cyclohexane–toluene–methanol, isooctane–o-xylene–methanol, and 1-octanol–ethanol–water. Good agreement with literature data is achieved while experimental effort is reduced significantly.

Photochromic Reactions of 4-[bis(9,9-dimethylfluoren-2-yl)amino]azobenzene in Low Molecular-Mass Organogels

In order to gain information about the environment at the solution region within the low molecular-mass organogels, photochromic reactions of title compound were investigated in 12-hydroxystearic acid– and 1,2-(1S,2S)-bis(stearoylamino)cyclohexane–toluene gels in comparison with those in toluene solution. The results suggested that the environment at the solution region within these gels was essentially the same as that in toluene solution although a small fraction of gelator molecules did not embed in the gel network but existed in the solution region.

Vapor–liquid–liquid equilibrium and vapor–liquid equilibrium for the quaternary system water–ethanol–cyclohexane–toluene and the ternary system water–cyclohexane–toluene. Isobaric experimental determination at 101.3 kPa

Experimental isobaric vapor–liquid–liquid and vapor–liquid equilibrium data for the ternary system water (1)–cyclohexane (2)–toluene (3) and the quaternary system water (1)–ethanol (2)–cyclohexane (3)–toluene (4) were measured at 101.3 kPa. An all-glass, dynamic recirculating still equipped with an ultrasonic homogenizer was used to determine the VLLE. The results obtained show that the system does not present quaternary azeotropes. The point-by-point method by Wisniak for testing the thermodynamic consistency of isobaric measurements was used to test the equilibrium data.

A novel stationary phase based on amino derivatized nanotubes for HPLC separations: Theoretical and practical aspects

A novel column based on silica containing immobilized carbon nanotubes (CNTs) was developed and evaluated in terms of its binding efficiency and resolution. First, CNT functionalized with amino groups (CNT-NH(2)) were prepared via chemical modification of carboxylic groups introduced on the CNT surface. Secondly the covalent immobilization of CNT-NH(2) was carried out by using glutardialdehyde activating agent on aminopropyl (AP)-silica surface. This CNT stationary phase was applied to the HPLC separation of two molecule series, i.e. polychlorinated biphenyl (PCB) isomers with different degrees of substitution in the ortho-position (non-ortho to tetra-ortho substituted) and terpenes (linalool, geraniol, thymol, alpha-terpineol). The retention behavior of these solute molecules was measured under isocratic conditions with different mobile phase compositions, ranging from 0.05-0.70 v/v of toluene in cyclohexane. The retention factors of the solute molecule do not depend linearly on the toluene fraction but follow a quadratic relationship. This CNT stationary phase was a very useful column for the separation of PCB congeners and terpenes. It was demonstrated that a planar conformation of the solute molecule enhanced the solute retention on this CNT stationary phase. As well, a quantitative structure relationship derived, demonstrated the significant input to retention was due to the structurally selective dipole-dipole and charge transfer interactions with the solutes. These results were compared with those obtained on the AP stationary phase. The proposed CNT stationary phase for the separation possess distinctive and interesting retentive properties, and chemometric analysis of retention data of appropriate designed series of test solutes appears to be a convenient, objective and quantitative method to prove a new phase specificity.

A humic acid stationary phase for the high performance liquid chromatography separation of buckminsterfullerenes: Theoretical and practical aspects

The influence of the mobile phase composition and column temperature on the chromatographic separation of five buckminsterfullerenes (C60, C70, C76, C78, C84) on a stationary phase based on silica gel with chemically bonded humic acid (Bonded humic acid column (BHAC)) was studied. The retention behavior of the fullerenes was measured under isocratic conditions with different mobile phase compositions, ranging from 0.05–0.70 (v/v) of toluene in cyclohexane. The column temperature was analysed in the range 35–75 °C. The retention factors of the five fullerenes do not depend linearly on the toluene fraction but follow a quadratic relationship. The best chromatographic conditions for baseline separation of the five fullerenes were selected. The retention of the fullerenes on the HA stationary phase was strongly affected by temperature. Positive values of thermodynamic parameters (changes of enthalpy and entropy) were due to the abnormal solubility behaviour of fullerenes in toluene in the temperature range 35–75 °C. The information obtained in this work makes this BHAC very simple to prepare and low cost, useful for fullerene research applications.

Molecular Dynamics Simulation Studies of Benzene, Toluene, and p-Xylene in a Canonical Ensemble

We have presented the results of thermodynamic, structural and dynamic properties of liquid benzene, toluene, and p-xylene in canonical (NVT) ensemble at 293.15 K by molecular dynamics (MD) simulations. The molecular model adopted for these molecules is a combination of the rigid body treatment for the benzene ring and an atomistically detailed model for the methyl hydrogen atoms. The calculated pressures are too low in the NVT ensemble MD simulations. The various thermodynamic properties reflect that the intermolecular interactions become stronger as the number of methyl group attached into the benzene ring increases. The pronounced nearest neighbor peak in the center of mass g(r) of liquid benzene at 293.15 K, provides the interpretation that nearest neighbors tend to be perpendicular. Two self-diffusion coefficients of liquid benzene at 293.15 K calculated from MSD and VAC function are in excellent agreement with the experimental measures. The self-diffusion coefficients of liquid toluene also agree well with the experimental ones for toluene in benzene and for toluene in cyclohexane.

Dynamic study of excited state hydrogen-bonded complexes of harmane in cyclohexane-toluene mixtures.

Photoinduced proton transfer reactions of harmane or 1-methyl-9H-pyrido[3,4-b]indole (HN) in the presence of the proton donor hexafluoroisopropanol (HFIP) in cyclohexane-toluene mixtures (CY-TL; 10% vol/vol of TL) have been studied. Three excited state species have been identified: a 1:2 hydrogen-bonded proton transfer complex (PTC), between the pyridinic nitrogen of the substrate and the proton donor, a hydrogen-bonded cation-like exciplex (CL*) with a stoichiometry of at least 1:3 and a zwitterionic exciplex (Z*). Time-resolved fluorescence measurements evidence that upon excitation of ground state PTC, an excited state equilibrium is established between PTC* and the cationlike exciplex, CL*, lambdaem approximately/= 390 nm. This excited state reaction is assisted by another proton donor molecule. Further reaction of CL* with an additional HFIP molecule produces the zwitterionic species, Z*, lambda(em) approximately/= 500 nm. From the analysis of the multiexponential decays, measured at different emission wavelengths and as a function of HFIP concentration, the mechanism of these excited state reactions has been established. Thus, three rate constants and three reciprocal lifetimes have been determined. The simultaneous study of 1,9-dimethyl-9H-pyrido[3,4-b]indole (MHN) under the same experimental conditions has helped to understand the excited state kinetics of these processes.

Light scattering method of determining the second virial coefficient for simple molecules and oligomers

A procedure of determining the molecular weight and second virial coefficient for simple molecules and oligomers from light-scattering measurements on a binary solution is presented on the basis of the well-established theory of fluctuations in multicomponent systems. It consists of determining first total isotropic scattering from the solution and then the composition scattering by subtracting from the former the density scattering (the Einstein-Smoluchowski term), where the values at finite concentrations should be used for the density scattering and also for the refractive index and its increment appearing in the optical constant. The required value of the density scattering is obtained by multiplying its observed value for the pure solvent by the concentration correction factor that is evaluated from a proper relationship between the refractive index and density of the solution. From experimental results obtained for a solution of toluene in cyclohexane at 25.0 {degrees}C as an example, the Lorentz-Lorenz equation is recommended as such a relationship. It is demonstrated that the multiple scattering theory by Bullough, which has often been used, is erroneous. 35 refs., 5 figs., 1 tab.

A Fiber-Optic FT-NIR Evanescent Field Absorbance Sensor

A polymer-clad fiber optic is used as an evanescent field absorbance sensor for solvents that penetrate into the polymer cladding. The sensor is coupled to an FT-NIR spectrometer for spectral measurements from 1.0 to 2.2 μm. A 400- μm core fiber optic, 1.5 m in length, was coiled with a 1.5-cm radius on a Teflon® support. The coiled sensor was then immersed in various nonpolar organic liquids which partitioned into the hydrophobic polysiloxane cladding. The evanescent-field near-infrared spectra of pure hexane, chloroform, and carbon tetrachloride are shown along with ethanol in chloroform. Various amounts of chloroform in carbon tetrachloride and toluene in cyclohexane were used to test the quantitative response. This sensor data are compared with data from a conventional NIR spectrometer using principal component regression.

Density measurement by oscillating tube. Effects of viscosity, temperature, calibration and signal processing

A frequency counter and precision thermostat, designed to operate in conjunction with an Anton Paar DMA 602 oscillating tube densitometer, have been built. The apparatus is capable of rapid density determinations. It can detect density changes of less than 5 × 10–7 g cm–3 and allows densities of low viscosity materials to be determined to an accuracy of ±5 × 10–6 g cm–3 if a suitable calibration standard is available. The effect of the viscosity of the samples on the density readings has been found to be significant when the viscosity is greater than ca. 1 mPa s. A correction procedure has been devised for such liquids. Excess volumes of the cyclohexane–toluene system have been measued at 298.15 K and agree with literature data, thus confirming the suitability of the apparatus for the determination of density differences.

Quaternary liquid—liquid equilibrium for acetonitrile—cyclohexane—toluene—benzene

Liquid—liquid equilibrium data at 298.15 and 318.15 K are presented for the quaternary system, acetonitrile—cyclohexane—toluene—benzene. The experimental results are compared with those calculated by use of extended UNIQUAC equation with sufficient accuracy.