气相色谱-质谱法测定环境水体中24种半挥发性有机物

采用液液萃取-气相色谱-质谱法同时测定环境水体中的24种半挥发性有机物。水样经二氯甲烷萃取,萃取液经浓缩定容后在DB-5MS毛细管色谱柱上分离,质谱中选择电子轰击离子源-选择离子监测模式,以菲-D10为内标物进行定量。24种化合物的质量浓度在一定范围内与其峰面积呈线性关系,检出限为0.03~0.28μg·L-1。加标回收率在70.1%~128%之间,测定值的相对标准偏差(n=6)小于6%。实际样品分析结果表明,某地地表水和化工区水样中均检出硝基苯类、氯代苯酚类、酞酸酯类等化合物。     

Activity coefficients and excess Gibbs’ energies of the binary mixtures formed by 2-cyanopyrazine with some chloroaliphatics at 95.5 kPa

Bubble points at a pressure of 95.5?kPa, over the entire composition range are measured for the binary mixtures formed by 2-cyanopyrazine with: 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, trichloroethylene and tetrachloroethylene making use of a Swietoslawski type ebulliometer. The liquid phase composition versus temperature measurements are found to be well represented by the Wilson model. Computed values of the activity coefficients and excess Gibbs’ energies are also presented along with the phase equilibrium data.     

Proton transfer rate‐equilibria in apolar aprotic solvents: a historical perspective

Low dielectric constant apolar aprotic solvents, although employed on a limited scale for studying proton transfer reactions as compared with commonly used polar protic or dipolar aprotic ones, offer some particular advantages, namely, specific solute–solvent interactions are virtually eliminated and proton transfer occurs directly in an apolar aprotic solvent. An intriguing feature of these reactions is their general acid‐catalyzed/base‐catalyzed kinetics with a time scale over microseconds to minutes. In fact, the true or intrinsic relative strengths of acids/bases when measured in such solvents come to the fore much more clearly than those obtained in other classes of solvents. Recently, a review documenting the post‐1980 developments relating to proton transfer reactions in apolar aprotic solvents has been published. The present article is a commentary of the pre‐1980 developments in this area since the 1920s Brønsted–Lowry's “proton cult” of acid–base theory. Copyright © 2016 John Wiley & Sons, Ltd.     

Molar excess free energy of mixing of 1-propanol or 2-propanol with cyclohexane at 298.15 and 308.15 K in terms of association model with a Flory contribution term

Excess molar Gibbs free energies of mixing for 1-propanol or 2-propanol + cyclohexane over the whole composition range at 298.15 and 308.15 K have been calculated from vapour pressure data measured by static method. The data have been analysed in terms of a Mecke-Kempter association model with a Flory contribution term.     

Fluid multiphase equilibria and critical phenomena in binary and ternary mixtures of carbon dioxide, certain n-alkanols and tetradecane

Experimental results of fluid multiphase equilibria occurring in ternary mixtures of near-critical carbon dioxide, certain n-alkanols and tetradecane are presented. The following n-alkanols were used in this investigation: decanol, octanol, heptanol, hexanol and pentanol. In the ternary systems with decanol, octanol or heptanol a closed loop liquid-vapor two-phase region in the three-phase surface liquid-liquid-vapor was found. As far as the ternary system with decanol is concerned, this phenomenon is in agreement with an earlier and unexpected finding of Patton et al. (1993). In addition, it was also found in this study that the phase diagrams of the ternary mixtures with hexanol or pentanol as the n-alkanol show further complications.     

HPLC-determination of nifedipine in plasma on normal phase

Summary For the determination of nifedipine in plasma a sensitive and selective method is required. The use of on-line pre-column enrichment, followed by reversed phase separation and UV-detection at 350 nm proved to be too susceptible. Therefore, detection was carried out after a post-column on-line reduction and photoreaction step using a fluorescence detector. Although this method proved to be extremely sensitive (limit of detection 0.1 ng/ml plasma) and selective, a number of problems cropped up caused by the reduction agent which finally prevented the procedure being used in routine analysis. As a consequence, the following method was developed. After liquid-liquid extraction of nifedipine a 1/3 of the extract was chromatographed on a normal phase (diOH) system and detected at 235 nm, because detection at 350 nm was not sensitive enough. This method has a limit of detection of 1 ng nifedipine/ml plasma and the calibration curve is linear up to 320 ng/ml. The recovery lies around 82% and the standard deviation for the range 6–320 ng/ml is less than 5%. So far about 2000 plasma samples have been analysed by this method.     

Multiphase equilibria for mixtures containing water, isopropanol, propionic acid, and isopropyl propionate

Vapor pressures of isopropyl propionate and isobaric vapor-liquid equilibrium (VLE) properties of isopropyl propionate + isopropanol and propionic acid + isopropyl propionate were measured. Isothermal vapor-liquid-liquid equilibrium (VLLE) data were also determined experimentally for water + isopropyl propionate and water + isopropyl propionate + isopropanol at temperatures from 323.24 K to 373.15 K. The binary VLE and VLLE data can be correlated well with the NRTL-HOC and the UNIQUAC-HOC models. The ternary VLLE data were used to test the validity of two versions of the UNIFAC model and the NRTL-HOC and the UNIQUAC-HOC models with the parameters determined from the phase equilibrium data of the constituent binaries. The ternary VLLE data were also correlated with the NRTL-HOC and the UNIQUAC-HOC models and the Soave-Redlich-Kwong equation of state with the Wong-Sandler mixing rule.     

Noncooperative stochastic games under a n-stage local contraction assumption

We consider a class of noncooperative stochastic games with general state and action spaces and with a state dependent discount factor. The expected time duration between any two stages of the game is not bounded away from zero, so that the usual N-stage contraction assumption, uniform over all admissible strategies, does not hold. We propose milder sufficient regularity conditions, allowing strategies that give rise with probability one to any number of simultaneous stages. We give sufficient conditions for the existence of equilibrium and ∈-equilibrium stationary strategies in the sense of Nash. In the two-player zero-sum case, when an equilibrium strategy exists, the value of the game is the unique fixed point of a specific functional operator and can be computed by dynamic programming.