High performance liquid chromatography of raw sugars and polyols using bonded silica gels

Summary Bonded silica columns have been evaluated for their ability to separate carbohydrates and polyols. Mobile phases consisting of dichloromethane/methanol produced the best separations in comparison with the acetonitrile/water mixtures commonly used with amino columns. Of all the bonded phases tested, LiChrospher Diol silica provided the best separations, and selectivities were not very different from those obtained on the most popular system using an amino bonded phase and acetonitrile/water as eluent. In addition, diol columns with a dichloromethane/methanol eluent offer excellent stability with no Schiffs base formation of reducing sugars. Using an evaporative light scattering detector, low limit detection is obtainable (20 ng of glucose from a column) and gradient elution is quite feasible.     

Mixture design optimization of extraction and mobile phase media for fingerprint analysis of Bauhinia variegata L

Two statistical mixture designs were used to optimize the proportions of solvents used in both the extraction medium and the reversed liquid chromatographic mobile phase to improve the quality of chromatographic fingerprints of Bauhinia variegata L extracts. For modeling, the number of peaks was used as a measure of fingerprint information. Three mobile phases, each with a chromatographic strength of two, gave good results. A methanol/water (77:23 v/v) mixture resulted in 17 peaks in the chromatographic fingerprint whereas acetonitrile/water (64.5:35.5 v/v) and methanol/acetonitrile/water (35:35:30 v/v/v) mixtures resulted in 18 and 20 peaks, respectively. The corresponding optimum solvent compositions to extract chemical substances for these three mobile phases were ethanol/acetone (25:75 v/v/v) and dichloromethane/acetone (70:30 v/v) mixtures, and pure dichloromethane, respectively. The mixture designs are useful for understanding the influence of different solvents on the strengths of the extraction medium and the mobile phase.     

ASSESSMENT OF DIELECTRIC ENRICHMENT AROUND TWO FLUOROPHORES IN BINARY SOLVENTS

Abstract We investigated dielectric enrichment, or the preferential interaction between a probe and a polar solvent, using two different fluorophores in binary solvents that will not form strong hydrogen bonds with the probe. The first probe, 6-propionyl( N,N -dimethylamino)naphthalene (PRODAN), undergoes a large change in dipole moment in the excited state. We found that its emission energy varies linearly with the dielectric parameter f(D) [f(D) = 2(D - 1)/(2D + 1)] in acetone/benzene and acetonekyclohexane mixtures. The emission of the second probe, N-acetyl tryptophanamide (NATA), also varies linearly with f (D) in ethylether/acetonitrile solvents. This lack of preferential solvation was further investigated by studies of NATA in acetonitrile/methanol mixtures where hydrogen bonding is possible. We found that NATA-methanol interactions are not energetic enough to give rise to significant preferential solvation. Since preferential solvation does not occur even for weakly hydrogen bonding solvents it is thus highly unlikely that dielectric enrichment, which takes place in the absence of specific interactions, occurs with any frequency. We postulate that previous reports of dielectric enrichment were due to a lack of consideration of changes in f (D) of the solvent.     

Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile

We present results of the theoretical study and numerical calculation of the dynamics of molecular liquids based on the combination of the memory equation formalism and the reference interaction site model (RISM). Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first-order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density (pressure) dependence of translational diffusion coefficients D and orientational relaxation times tau for acetonitrile in water, methanol in water, and methanol in acetonitrile--all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the extended simple point charge model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and tau observed in real and computer experiments. In particular, anomalous behavior, i.e, the increase in mobility with density, is observed for D and tau of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.     

Continuum Model for Electronic Polarization Based on a Novel Dielectric Response Function

A generalized response function based on the use of dielectric spectra for dielectric relaxation process is derived. We apply the general response function to the special case in order to examine how special dielectric relaxation functions developed by other authors for solvent relaxation can be derived based on our formulations. Three typical solvents, water, methanol, and acetonitrile are used to investigate the electronic polarization processes of polar solvents. The solvent electronic polarization process is shown after a linear variation with the external electric field imposed on the solvent. The results show a conclusion that the electronic polarization of the solvents will accompany the electronic transition synchronously, without time lag.     

Interactions between Crown Ethers and Water,Methanol, Acetone,and Acetonitrile in Halogenated Solvents

The interactions between crown ethers and water, methanol, acetone, and acetonitrile molecules in halogenated solvents are studied by means of calorimetric measurements. The results reveal the formation of 1:1 complexes between crown ethers and water in chloroform. The hydrogen bonding and ion–dipole interactions are responsible for the complex formation between the water molecules and crown ethers. For a better understanding of the influence of chloroform upon the complexation between crown ethers and water, chloroform is replaced by dichloromethane, 1,2-dichloroethane, and carbon tetrachloride. Since the hydrogen bonds are responsible for the complex formation between crown ethers and water in the halogenated solvents, further investigations are performed with methanol, acetone and acetonitrile. The interactions, the ligand nature, the concentrations of polar solvents, and the nature of nonpolar solvents involved in complexation are analyzed and discussed.     

高效液相色谱柱后衍生法测定谷物中9种氨基甲酸酯类农药及3种代谢物残留量

研究了用ＷａｔｅｒｓＣａｒｂａｍａｔｅ分析系统柱后衍生化荧光检测器测定谷物中氨基甲酸酯类农药残留量的方法。用ＷａｔｅｒｓＣａｒｂａｍａｔｅＡｎａｌｙｓｉｓＣｏｌｕｍｎ对９种农药和３种代谢产物进行分离,碱液水解,ＯＰＡ柱后衍生,有很好的选择性、重现性和灵敏度,最低检出限为５μｇ／ｋｇ。     

超高效液相色谱法测定甘蔗和土壤中敌草隆残留

建立了一种测定甘蔗和土壤中敌草隆农药残留的超高效液相色谱(UPLC)方法.样品经水和甲醇提取,二氯甲烷液-液分配后,过中性氧化铝柱纯化,用石油醚:乙酸乙酯的混合液(体积比85:15)淋洗和洗脱,洗脱液经减压浓缩后用5 mL乙腈定容.采用UPLC分离,紫外检测器检测,外标法定量.敌草隆在0.02～5.0 mg/L范围线性...     

Quantification of astaxanthin in shrimp waste hydrolysate by HPLC

In the present study, a simple and rapid reversed-phase HPLC method for the determination of astaxanthin in shrimp waste hydrolysate has been developed and validated. The analytical procedure involves the direct extraction of astaxanthin from the lipid fraction with methanol. The analytical column, SS Exil ODS, was operated at 25C. The mobile phase consisted of a mixture of water:methanol:dichloromethane:acetonitrile (4.5:28:22:45.5 v/v/v/v) at a flow rate of 1.0 mL/min. Detection and identification were performed using a photodiode array detector (lambda(detection) = 476 nm). The proposed HPLC method showed adequate linearity, repeatability and accuracy.     

Evaluation of Extraction Procedures of Organochlorine Pesticides from Natural Waters and Sediments

Abstract

This study aims to evaluate different procedures for the extraction of organochlorine pesticides (OCP's) from natural waters and sediments. In the case of extraction from water, a C18 disk solid-phase extraction method was employed. Recovery experiments in the range of 40 to 200 ng/l with selected organochlorine compounds resulted in average recoveries between 80 and 100%. Four different solvents, hexane, ethyl acetate, acetonitrile and methanol, were tested as eluting agents. Best recoveries were obtained with ethyl acetate and hexane. A comparative study of OCP sediment extraction procedures was performed employing sonication, Soxhlet extraction and shake-flask methods. The capacity of these methods to recover OCP's from a sediment sample fortified at 50 ng/g was evaluated using hexane : acetone (1:1 v/v), hexane: acetone (8:2 v/v), acetonitrile and dichlorometane. The three extraction techniques gave similar results and dichloromethane was the most effective solvent. The optimised methods were applied in the analysis of waters and sediments from the “Aiguamolls de l'Empordà” Nature Park, Girona (Spain).     

Determination of sulfonamides in swine muscle after salting-out assisted liquid extraction with acetonitrile coupled with back-extraction by a water/acetonitrile/dichloromethane ternary component system prior to high-performance liquid chromatography

A salting-out assisted liquid extraction coupled with back-extraction by a water/acetonitrile/dichloromethane ternary component system combined with high-performance liquid chromatography with diode-array detection (HPLC–DAD) was developed for the extraction and determination of sulfonamides in solid tissue samples. After the homogenization of the swine muscle with acetonitrile and salt-promoted partitioning, an aliquot of 1 mL of the acetonitrile extract containing a small amount of dichloromethane (250–400 μL) was alkalinized with diethylamine. The clear organic extract obtained by centrifugation was used as a donor phase and then a small amount of water (40–55 μL) could be used as an acceptor phase to back-extract the analytes in the water/acetonitrile/dichloromethane ternary component system. In the back-extraction procedure, after mixing and centrifuging, the sedimented phase would be water and could be withdrawn easily into a microsyringe and directly injected into the HPLC system. Under the optimal conditions, recoveries were determined for swine muscle fortified at 10 ng/g and quantification was achieved by matrix-matched calibration. The calibration curves of five sulfonamides showed linearity with the coefficient of estimation above 0.998. Relative recoveries for the analytes were all from 96.5 to 109.2% with relative standard deviation of 2.7–4.0%. Preconcentration factors ranged from 16.8 to 30.6 for 1 mL of the acetonitrile extract. Limits of detection ranged from 0.2 to 1.0 ng/g.     

Analysis of oligosaccharides using aminobonded silica gel and a ternary eluent with evaporative light scattering detection

Using two commercial, amino bonded, silica gel columns, binary eluents (methanol/water, acetonitrile/methanol) and ternary eluents (acetonitrile/methanol/water) are evaluated for their ability to separate oligosaccharides in comparison with classical acetonitrile/water eluents. Chromatographic data on glucose, maltose, raffinose, stachyose and maltodextrin are reported. Mobile phases consisting of acetonitrile/water or acetonitrile/methanol/water produce the best separations. Phase hydrolysis is evaluated using an evaporative light scattering detector. The reduction of the water content in the eluent stabilizes the aminocolumns and the life time of the amino columns should be improved with the ternary eluent. Moreover, a better detection limit can be obtained. Capabilties to run gradient elution without baseline drift are clearly demonstrated.     

Theoretical study of temperature and solvent dependence of the free-energy surface of the intramolecular electron-transfer based on the RISM-SCF theory: application to the 1,3-dinitrobenzene radical anion in acetonitrile and methanol

The free-energy surfaces along the intramolecular electron-transfer reaction path of the 1,3-dinitrobenzene radical anion in acetonitrile and methanol are investigated with the reference interaction site model self-consistent field theory. Although acetonitrile and methanol have similar values of the dielectric constant, the free-energy profiles are quite different. In the methanol solution, the charge is strongly localized on one of the nitrile substituents due to a strong hydrogen bond between 1,3-dinitrobenzene and the solvent, while the polarization is not so large in the case of acetonitrile. The temperature dependence of the reorganization energy, the coupling strength, and the activation barrier is evaluated in both acetonitrile and methanol. The reorganization energy and the activation barrier decrease with increasing temperature for both cases. The electronic coupling strength also shows a similar tendency in the temperature dependence; it increases with increasing temperature in both solvents but with different rates. The behavior is explained in terms of the strong polarization induced by the hydrogen bond between the solute and solvent in the methanol solution.     

HPLC—UV determination of pesticide residues at 0.01 ppm in apple and pear pulp used for baby food

Two distinct methods are described for determination of residues of ethiofencarb and triforine, and of diflubenzuron, teflubenzuron, and triflumuron at the 0.01 ppm level in apple and pear pulp used for baby food;recoveries are above 50%. Diflubenzuron, teflubenzuron, and triflumuron are extracted with a 1:1 mixture of dichloromethane and acetone, and the extracts are cleaned by SPE using C₁₈ as stationary phase and methanol as mobile phase. Ethiofencarb and triforine are extracted with dichloromethane, and the extracts cleaned using the same stationary phase but a 1:1 mixture of acetonitrile and water as mobile phase. Analysis of both groups of pesticides is by isocratic HPLC—UV at 210 nm using an RP-18 column and acetonitrile-water as mobile phase.     

Thermochemistry of electrolyte solutions

The results of calorimetric investigations of electrolyte solutions in the mixtures of water, methanol, N,N-dimethylformamide, and acetonitrile with numerous organic cosolvents are discussed with regard to the intermolecular interactions that occur in the solution. Particular attention is given to answer the questions how and to what extent the properties of the systems examined are modified by the cosolvent added and how much the properties of the cosolvent are revealed in the mixtures with the solvents mentioned above. To this goal, the analysis of the electrolyte dissolution enthalpies, single ionic transfer enthalpies, and enthalpic pair interaction coefficients as well as the preferential solvation (PS) model are applied. The analysis performed shows that in the case of the dissolution enthalpies of simple inorganic electrolytes in water–organic solvent mixtures, the shape of the dependence of the standard dissolution enthalpy on the mixed solvent composition reflects to a large extent the hydrophobic properties of the organic cosolvent. In the mixtures of methanol with organic cosolvents, the ions are preferentially solvated either by methanol molecules or by molecules of the cosolvent, depending on the properties of the mixed solvent components. The behavior of inorganic salts in the mixtures containing N,N-dimethylformamide is mostly influenced by the DMF which is a relatively strongly ion solvating solvent, whereas in acetonitrile mixtures, the thermochemical behavior of electrolyte solutions is influenced to a large extent by the properties of the cosolvent particularly due to the PS of cation by the cosolvent molecules.     

An improved HPLC Method for the Separation of Fourteen Carotenoids,Including 15-/13- and 9-CIS-β-Carotene Isomers,Phytoene and Phytofluene

Abstract

The isocratic separation of 14 carotenoids, as well as retinol, retinyl acetate, retinyl palmitate, α-tocopherol and tocopherol acetate, is accomplished in 12 minutes, using a Spheri-5-ODS column and acetonitrile:dichloromethane:methanol (70:20:10) as mobile phase, with two-channel, programmable multiwavelength detection. The carotenoids separated are as follows: lutein/zeaxanthin, canthaxanthin, β-apo-8′ carotenal, β-cryptoxanthin, echinenone, lycopene, γ-carotene, α-carotene, β-carotene, 9-cis-β-carotene, 15-cis-/13-cis-β-carotene, phytoene and phytofluene. The separation of lutein and zeaxanthin is obtained simply by changing the mobile phase to acetonitrile:methanol (85:15).     

Theoretical study of solvent effects on the thermodynamics of iron(III) [tetrakis(pentafluorophenyl)]porphyrin chloride dissociation

A quasichemical method that combines ab initio treatment of explicit solvent with dielectric continuum models has been used to study the origin of a strong effect of methanol on the extent of iron(III) [tetrakis(pentafluorophenyl)]porphyrin chloride dissociation in acetonitrile-methanol solutions. It is shown that the dissociation is energetically more favorable in methanol than in acetonitrile primarily because of the strong specific interactions between the chloride anion and the solvent methanol molecules in its first solvation shell. These interactions are weaker in acetonitrile. The final estimate for the difference in the dissociation free energies in methanol and acetonitrile is -23 kJ/mol, in a good agreement with the experimental value of -21 kJ/mol. Energy decomposition analysis of chloride-solvent interactions suggests that stronger chloride-methanol binding is a result of the contribution of charge delocalization effects to the chloride-methanol interactions.     

反相离子对色谱中有机溶剂浓度和离子对试剂浓度对保留值的影响

我们测定了氨基苯磺酸和氨基萘磺酸在反相离子对色谱中不同乙腈/水, 甲醇/水配比和离子对试剂浓度下的保留值,并把两种冲洗剂下的保留值和关系式lnk'=a+C~c~b中的参数a,C作线性关联,得到很好的相关性,这表明有机溶剂乙腈和甲醇对选择性并无显著的影响,但乙腈有更大的冲洗强度.证明关系式lnk'=A+Blnc~p+C~c~ b能较好地描述有机溶剂和离子对试剂浓度对保留值的影响, 但当离子对试剂浓度较高时该关系式不成立.同时提出了有机溶剂浓度和离子对试剂浓度"等同效应" 的概念     

反相色谱多二元溶剂的选择性调整

从统计热力学方法推导的溶质保留规律及其相关参数与分子结构之间的关系式出发,探讨了１６种多环芳烃在甲醇／水、乙腈／水、异丙醇／乙腈３种二元溶剂体系下选择性的差异,为确立复杂化合物分离的溶剂选择原则奠定了基础。     

Selectivity of monomeric metaphosphate reactions with alcohols in polar aprotic solvents

Evidence is presented for selectivity in the reaction of metaphosphate, PO₃^?, with methanol in preference to t-butanol in acetonitrile solution. In dichloromethane solution there is also evidence for preferential nucleophilic solvation of reactant by methanol $\text{vs.}$ t-butanol.