离子液体-非极性溶剂微波提取法在人参化学成分研究中的应用

以离子液体作为微波吸收介质建立了离子液体-非极性溶剂微波提取法,对人参中的化学成分进行了提取,并将该法与固体微波吸收介质-非极性溶剂微波提取法、极性溶剂微波提取法以及混合溶剂微波提取法进行了对比.结果表明,极性溶剂提取的主要化学成分为极性化合物,而固体微波吸收介质-非极性溶剂微波提取法与离子液体-非极性溶剂微波提取法相比,提取所得的化学成分并无明显差别,说明离子液体是一种较好的微波吸收介质和能量传递材料.所建立的方法具有提取时间短、操作简单及绿色环保等优点,且对后期分析无明显影响,是快速提取化学成分的理想方法.     

Separation of potential flavoring compounds by high-performance liquid chromatography

High-performance liquid chromatography separated successively and quantitatively the food flavoring agents pyrimidines, purines and nucleosides, followed by nucleotides, then by polyphenols and finally by pyrazines with a reversed-phase octadecylsilica (μBondapak C₁₈) column and various proportions of methanol, water, acetic acid and tetrabutylammonium phosphate (PIC A). The polar solvent (solvent A) was water—acetic acid—PIC A (97.5:1.5:1.0) and the relatively non-polar solvent (solvent B) was methanol—acetic acid—PIC A (97.5:1.5:1.0). Purines, pyrimidines, and nucleosides were eluted with solvent A. Nucleotides were eluted with a mixture of solvents A and B (9:1). Polyphenols were separated with a gradient starting at 10% solvent B and finishing at 25% solvent B, and finally the pyrazines were removed successively from the column with a gradient starting at 25% solvent B and finishing at 45% solvent B. The resolution and reproducibility were excellent for more than 50 compounds. By this method beverages could be analyzed directly, without solvent extraction, for flavoring compounds.     

精氨酸的溶剂浮选分离技术及其分离机制

以表面活性剂十二烷基苯磺酸为捕收剂(DBSA),二(2-乙基己基)磷酸酯(P204)为萃取剂,正庚烷为有机溶剂,采用溶剂浮选法对水溶液中精氨酸进行分离富集,并与气浮络合萃取法、泡沫浮选法和溶剂萃取法进行了比较.结果表明,在常温下,0.09 g/L精氨酸水溶液250 mL、初始pH 7.0,DBSA浓度0.15 g/L,正庚烷体积10 mL, P204体积4.5 mL,气体流量200 mL/min,溶剂浮选法分离水溶液中精氨酸的富集比为16.2,回收率为97.2%.溶剂浮选法分离精氨酸的动力学实验结果表明,精氨酸的溶剂浮选过程阶段性明显,大致可分为3个阶段,第一阶段和第二阶段都符合一级动力学方程,第三阶段符合零级动力学方程,探索了溶剂浮选法分离精氨酸的分离机制.     

Determination of organochlorine pesticides in water using solvent cooling assisted dynamic hollow-fiber-supported headspace liquid-phase microextraction

The organic solvent film formed within a hollow fiber was used as an extraction interface in the headspace liquid-phase microextraction (HS-LPME) of organochlorine pesticides. Some common organic solvents with different vapor pressures (9.33-12,918.9 Pa) were studied as extractants. The results indicated that even the solvent with the highest vapor pressure (cyclohexane) can be used to carry out the extraction successfully. However, those compounds (analytes) with low vapor pressures could not be extracted successfully. In general, the large surface area of the hollow fiber can hasten the extraction speed, but it can increase the risk of solvent loss. Lowering the temperature of the extraction solvent could not only reduce solvent loss (by lowering its vapor pressure) but also extend the feasible extraction time to improve extraction efficiency. In this work, a solvent cooling assisted dynamic hollow-fiber-supported headspace liquid-phase microextraction (SC-DHF-HS-LPME) approach was developed. By lowering the temperature of the solvent, the evaporation can be decreased, the extraction time can be lengthened, and, on the contrary, the equilibrium constant between headspace phase and extraction solvent can be increased. In dynamic LPME, the extracting solvent is held within a hollow fiber, affixed to a syringe needle and placed in the headspace of the sample container. The extracting solvent within the fiber is moved to-and-fro by using a programmable syringe pump. The movement facilitates mass transfer of analyte(s) from the sample to the solvent. Analysis of the extract was carried out by gas chromatography-mass spectrometry (GC-MS). The effects of identity of extraction solvent, extraction temperature, sample agitation, extraction time, and salt concentration on extraction performance were also investigated. Good enrichments were achieved (65-211-fold) with this method. Good repeatabilities of extraction were obtained, with RSD values below 15.2%. Detection limits were 0.209 microg/l or lower.     

A simple method to optimize the HSCCC two-phase solvent system by predicting the partition coefficient for target compound

A simple method was developed to optimize the solvent ratio of the two-phase solvent system used in the high-speed counter-current chromatography (HSCCC) separation. Some mathematic equations, such as the exponential and the power equations, were established to describe the relationship between the solvent ratio and the partition coefficient. Using this new method, the two-phase solvent system was easily optimized to obtain a proper partition coefficient for the CCC separation of the target compound. Furthermore, this method was satisfactorily applied in determining the two-phase solvent system for the HSCCC preparation of pseudolaric acid B from the Chinese herb Pseudolarix kaempferi Gordon (Pinaceae). The two-phase solvent system of n-hexane/EtOAc/MeOH/H(2)O (5:5:5:5 by volume) was used with a good partition coefficient K = 1.08. As a result, 232.05 mg of pseudolaric acid B was yielded from 0.5 g of the crude extract with a purity of 97.26% by HPLC analysis.     

Purification of high-throughput organic synthesis libraries by counter-current chromatography

Experiments were performed to evaluate whether counter-current chromatography (CCC) could function as an alternative purification method to reversed-phase high-performance liquid chromatography (RP-HPLC) and normal-phase supercritical fluid chromatography (SFC). RP-HPLC and SFC are the routine methods currently used in our high-throughput purification (HTP) facility for the purification of high-throughput organic synthesis (HTOS) libraries and medicinal chemistry reaction mixtures. Pre-equilibration of the solvent mixture layers was not mandatory for effective chromatography when hexanes–ethyl acetate–methanol–water (HEMW) solvent mixtures were used. Key to the use of CCC for high-throughput applications is the ability to effectively select a solvent system appropriate to each library member. Pilot-scale CCC elution time was used to estimate a starting solvent ratio and RP-HPLC retention time was then used to adjust solvent ratios within a particular library. It was also found that dimethyl sulfoxide (DMSO) and DMSO–methanol were suitable as sample injection solvents when using the HEMW solvent systems.     

Study of the interactions of sodium thiocyanate, potassium thiocyanate and ammonium thiocyanate in water+N,N-dimethylformamide mixtures by Raman spectroscopy

Raman spectra of water+N,N-dimethylformamide (DMF) mixtures and their solutions with NaNCS, KNCS and NH(4)NCS were obtained. The bands of nu(CO) stretching, delta(OCN) bending, r(CH(3)) rocking and nu(N-CH)(3)) stretching of the DMF molecule with and without salts were studied. The dependence of the vibration frequencies and Raman intensities of the bands on the composition of the mixed solvent was discussed. The change of the band frequencies as a result of the presence of the salts and the solvation of the cations by the solvent molecules was examined. The stronger cation solvation by the aprotic solvent molecules instead of the water molecules in DMF concentrated solutions was discussed. The nu(CN) and nu(CS) vibrations of the SCN(-) ions were observed as a function of the cation present and the solvent composition. The presence of the SCN(-) ions as "free", contact ion pairs, or solvent separated pairs, was discussed.     

Fluorescence solvatochromism in lumichrome and excited-state tautomerization: a combined experimental and DFT study

Fluorescence solvatochromism of lumichrome (LC) was studied by steady-state and time-resolved fluorescence spectroscopy. The excited-state properties of LC do not show any correlation with solvent polarity, however, reasonably good correlation with solvent E(T)(30) parameter was observed. A quantitative estimation of contribution from different solvatochromic parameters, like solvent polarizability (π*), hydrogen bond donor (α), and hydrogen bond acceptor (β) ability of the solvent, was made using linear free energy relationship on the basis of Kamlet-Taft equation. The analysis reveals that hydrogen bond donating ability (acidity) of the solvent is the most important parameter that characterizes the excited-state behavior of lumichrome. Quantum mechanical calculations using density functional theory (DFT) were done to study the most stable structure and excited-state tautomerization process of LC toward the formation of isoalloxazines. Charge localization in the excited state and formation of hydrogen-bonded cluster through solvent hydrogen bond donation on the N10 atom of alloxazine moiety were predicted to be the key step toward this water-catalyzed tautomerization process.     

Tuning aggregation of microemulsion droplets and silica nanoparticles using solvent mixtures

The effect of solvent on stability of water-in-oil microemulsions has been studied with AOT (sodium bis(2-ethylhexyl)sulfosuccinate) and different solvent mixtures of n-heptane, toluene and dodecane. Dynamic light scattering DLS was used to monitor the apparent diffusion coefficient D(A) and effective microemulsion droplet diameter on changing composition of the solvent. Interdroplet attractive interactions, as indicated by variations in D(A), can be tuned by formulation of appropriate solvent mixtures using heptane, toluene, and dodecane. In extreme cases, solvent mixtures can be used to induce phase transitions in the microemulsions. Aggregation and stability of model AOT-stabilized silica nanoparticles in different solvents were also investigated to explore further these solvent effects. For both systems the state of aggregation can be correlated with the effective molecular volume of the solvent V(mol)(eff) mixture.     

高效液相色谱梯度洗脱中弱溶剂的在线净化

利用一个在线净化预柱减少了高压梯度洗脱中由于试剂纯度不够造成的基线噪音。预柱的位置在溶剂泵Ａ和流动相混合器之间,由一个六通阀来控制。在线净化结果良好,有效地除去了空白梯度色谱图中的杂质峰,提高了梯度洗脱的分离重现性。该方法对开展梯度洗脱有实用价值。     

混合溶剂作淋洗剂的体积排除色谱谱图中溶剂化高分子峰和溶剂峰之间内在关系的理论分析

根据体积排除色谱(SEC)研究高分子溶质优先溶剂化的基本原理,证明在SEC色谱图中被束缚溶剂产生的面积与自由溶剂产生的面积大小相等方向相反,在研究优先溶剂化时从高分子峰入手和从自由溶剂峰入手在理论上具有等价性.分析表明,通过对溶剂化高分子峰的研究,还可以得到另一个重要物理参数——恒化学位时高分子溶液的折光指数增量.     

在非水溶剂中聚甲基丙烯酸甲酯及其甲基丙烯酸共聚物与Rh6G的相互作用

本文用乙酸乙酯与不同比例乙醇配成混合溶剂, 考察在不同极性的介质中, Rh_6G对聚甲基丙烯酸甲酯及其与甲基丙烯酸共聚物分子形态的影响, 以及聚合物对Rh_6G荧光强度的影响, 发现Rh_6G与聚甲基丙烯酸甲酯没有特殊相互作用, 而与共聚物的相互作用受溶剂的极性影响很大, 随着极性增加, 从氢键作用过渡到静电作用。     

Analysis of organochlorine pesticides in wine by solvent bar microextraction coupled with gas chromatography with tandem mass spectrometry detection

A solvent bar microextraction (SBME) technique combined with gas chromatography/tandem mass spectrometry (GC/MS/MS), for the determination of selected organochlorine pesticides (OCPs) in wine samples, is described. In this work the OCPs were extracted and dissolved in a 2-microL aliquot of organic extraction solvent (n-tetradecane) confined within a 1.7-cm length of hollow fiber. Both ends of the hollow fiber (solvent bar) were sealed, and it was placed in an aqueous sample solution for extraction. The effects of solvent selection, sample agitation, extraction time, extraction temperature, and salt concentration on the SBME performance were optimized. The influence of aqueous sample/organic solvent phase ratio was further investigated in detail. High enrichments (1900-7100-fold) could be obtained at an aqueous sample/organic solvent volume ratio of 20 mL/2 microL in this study. Good extraction reproducibility was obtained with relative standard deviation (RSD) values below 12.6%. Comparisons of sensitivity and precision between SBME and dynamic hollow-fiber liquid-phase microextraction were also investigated.     

High‐density extraction solvent‐based solvent de‐emulsification dispersive liquid–liquid microextraction combined with MEKC for detection of chlorophenols in water samples

For the first time, the high‐density solvent‐based solvent de‐emulsification dispersive liquid–liquid microextraction (HSD‐DLLME) was developed for the fast, simple, and efficient determination of chlorophenols in water samples followed by field‐enhanced sample injection with reverse migrating micelles in CE. The extraction of chlorophenols in the aqueous sample solution was performed in the presence of extraction solvent (chloroform) and dispersive solvent (acetone). A de‐emulsification solvent (ACN) was then injected into the aqueous solution to break up the emulsion, the obtained emulsion cleared into two phases quickly. The lower layer (chloroform) was collected and analyzed by field‐enhanced sample injection with reverse migrating micelles in CE. Several important parameters influencing the extraction efficiency of HSD‐DLLME such as the type and volume of extraction solvent, disperser solvent and de‐emulsification solvent, sample pH, extraction time as well as salting‐out effects were optimized. Under the optimized conditions, the proposed method provided a good linearity in the range of 0.02–4 μg/mL, low LODs (4 ng/mL), and good repeatability of the extractions (RSDs below 9.3%, n = 5). And enrichment factors for three phenols were 684, 797, and 233, respectively. This method was then utilized to analyze two real environmental samples from wastewater and tap water and obtained satisfactory results. The obtained results indicated that the developed method is an excellent alternative for the routine analysis in the environmental field.     

Dissolution of cellulose in ethylene diamine/salt solvent systems

Investigation of the dissolution of cellulose in Ethylene Diamine (EDA)/Potassium thiocyanate (KSCN) solutions by infrared spectroscopy (FTIR) and thermal analysis (DSC) indicated that changes to the solvent during freeze thaw cycling of mixtures was consistent with increased interaction between cellulose and solvent. Thermal transitions in the system, however, occurred at temperatures outside the range used in thermal cycling to promote dissolution. Further exploration of the dissolution and mixing process indicated that mixing was the limiting step in solution formation. The dissolution of two types of cellulose with different molecular weights (Degree of Polymerization (DP)=210 and >1000) was studied using EDA/KSCN solution as the solvent. The solubility and the dissolution rate of cellulose depended on both the solvent composition and cellulose molecular weight. Cellulose could dissolve faster in the solvent with lower salt concentration but the highest cellulose concentration was obtained in the solvent with 30~35% KSCN. Rheological measurements showed that cellulose solutions exhibited viscous solution behavior at low KSCN concentration but primarily elastic behavior at high salt concentration.     

Raman anisotropic bandwidth study of C=O stretching vibration of methyl isobutyl ketone: role of van der Waals' volume of the interacting systems

The bandwidth (FWHM) of the anisotropic component (Gamma(aniso)) of methyl isobutyl ketone (MIBK) for different concentrations of solvents varying from 10 to 90% was measured and was plotted as a function of solvent concentrations. In lower solvent concentration, the graph shows a curvature with a discontinuity which occurs between 40 and 60% and in higher solvent concentration, the graph shows a straight line for most of the solvents. In order to interpret the complicated behaviour we have taken into accounts the van der Waals' volume (V(w)) of the sphere of influence in solute dissolved in all solvents. Considering the role of van der Waals' volume in these systems the parameter Gamma(omega)=ln(Gamma(aniso)/V(w)) was plotted at different solvent concentrations. The graph shows a straight line for the entire region. In order to study the influence of screening effect on the bandwidth, the capacitances of the liquid mixture at different solvent concentrations varying from 10 to 90% were measured for all the solvents. The plot of capacitance at different solvent concentrations for each solvent shows a discontinuity around 50% of solvent concentration.     

PVT properties of di-(2-ethyl hexyl) phosphoric acid

Di-(2-ethyl hexyl) phosphoric acid (hereafter referred as D2EHPA) is an important solvent for solvent extraction industry. It is also used in nuclear solvent extraction as a solvent for TALSPEAK and REVERSED TALSPEAK processes for actinide (III)–lanthanide (III) separation. Its PVT properties are not available in literature. In this work, group-contribution approach was used to predict its PVT properties as well as selected physical properties like normal boiling point.     

Applicability of 0.05 mol kg(-1) potassium hydrogen phthalate as reference value pH standard in water-organic solvent mixtures

The applicability of 0.05 mol kg(-1) potassium hydrogen phthalate (KHPh(S), S=the solvent under study) as reference value pH standard (RVS) was studied in water-organic solvent mixtures. Phthalic acid in various aqueous organic solvent mixtures was titrated potentiometrically with Bu(4)NOH (MeOH), using a pH-ISFET and a glass electrode as pH-sensors, and the buffer capacity of the HPh(-) solution was roughly estimated from the difference between the first and second half-neutralization potentials. The influence of potassium ion to the buffer capacity was also studied, titrating KHPh and Et(4)NHPh with CF(3)SO(3)H and Bu(4)NOH (MeOH) and comparing the titration curves. The KHPh solution loses its buffer capacity if the solvent mixture has an aprotic property. For aqueous mixtures of protophilic aprotic solvents (e.g. DMSO and DMF), it is unsuitable as RVS if the water content is less than ca. 40 (v/v)%. The necessity of selecting subsidiary pH standard(s) is suggested for the solvent systems in which KHPh is inapplicable.     

Intrinsic viscosity of polystyrene in mixed solvents

The intrinsic viscosity of a single sample of polystyrene was measured as a function of the composition of solvent in three mixed solvent pairs. The parameter Y introduced by Shultz and Flory was useful for prediction of trends, but severely overestimated the effect of solvent (1)–solvent (2) interaction on the expansion of polymer coils. The system polystyrene–cyclohexane–ethyl acetate was studied in detail for five samples of polystyrene. The analysis of the data provided strong experimental proof of a strict validity of the Mark–Houwink–Sakurada relation. The dependence of the Mark–Houwink–Sakurada exponent α on the composition of the solvent mixture was unexpectedly unsymmetrical. The unperturbed dimentions of the polystyrene chain are reduced by specific interaction of polystyrene with carbonyl groups in the solvent mixture.