Supercritical fluid extraction

Supercritical fluid extraction (SFE) provides for the first time a viable option to conventional and widely used Soxhlet extraction. The ability to change the solvating power of a single supercritical fluid by changing its density is an exceedingly attractive feature. An environmentally safe alternative such as supercritical carbon dioxide to organochlorine solvents which are widely used today in many government and industrial analytical laboratories for sample preparation is desirable. SFE may also constitute a viable alternative to other popular sample preparation techniques such as liquid-liquid extraction, solid phase extraction and purge/trap. Much research, however, must be done in order to understand, optimize and apply this technology. For example, (a) automation of extraction, (b) matrix effects, (c) new fluids/modifiers/additives, (d) trapping efficiency, (e) recovery of extracted analytes, and (f) extraction kinetics are some areas which need a greater understanding. This review is concerned with many of these topics as they relate to trace organic analysis wherein SFE is the primary sample preparation technique.     

微机控制动态配气装置的研究

按照ISO6145标准，设计，研制了微机控制动态配气装置，实现了微机对动态配气装置主要动态参数的实时监控，存储和结果处理，将该动态配气装置与静态容量法配气装置进行了比较，两种方法配制的标准气体的量值一致，对动态法配气的量值不确定度进行了评定。     

超声处理条件对水煤浆浆体各性质的影响

选择了大同，兖州，红会，八一及神木等五种煤样。系统的考察了超处理时间超声强度对各煤浆浆体的流变特性，静态稳定性以及成浆性的影响。实验结果表明，在一定的超声条件，随着超声处理时间和超声强度的增加，五种煤的浆体都由胀性行为向屈服假塑性方向转化，浆体静态稳定性的由几ｈ可以提高到一个月！另一方面，添加剂的浓度为１％时，超声处理导致各浆体表观粘度略有上升。     

Dynamic and static interactions between bitumen droplets in water

In the commercial bitumen extraction operation, dynamic and static interaction forces between bitumen drops in water determine the likelihood of desirable bitumen coalescence at different process stages. These dynamic and static forces were measured using colloidal particle scattering and hydrodynamic force balance techniques, respectively. In the former technique, dynamic interactions are studied through droplet-droplet collision trajectory measurement. In the latter technique, the static attractive forces between droplets are determined when a doublet is separated with a known and adjustable hydrodynamic force. The dynamic force measurement implies the presence of rigid chains on bitumen surfaces. The mean chain lengths for deasphalted bitumen at pH 7, whole bitumen at pH 7, and whole bitumen at pH 8.5 are 50, 78, and 41 nm, respectively. However, the static force measurement indicates much shorter mean chain lengths (<9 nm) in these three bitumen systems. Shorter chain length indicates weaker repulsive force. This finding of a much weaker repulsion between bitumen droplets under static conditions has important implications on the commercial bitumen extraction operation.     

Assembly properties of Triton X-100/phosphatidylcholine aggregates during liposome solubilization

The assembly properties of the nonionic surfactant Triton X-100 and phosphatidylcholine (PC) aggregates during the overall solubilization process of PC liposome were investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light scattered by liposome suspensions. A direct dependence was established between the bilayer/aqueous phase surfactant partition coefficients (K), the growth of vesicles and the leakage of entrapped CF in the initial interaction steps (surfactant to phospholipid molar ratioRe up to 0.2). These changes may be related to the increasing presence of surfactant molecules in the outer monolayer of vesicles. In theRe range 0.2–0.35 the coexistence of a low vesicle growth with a constant increase of CF release may be correlated with the decrease inK (increased rate of flip-flop of surfactant molecules). Furthermore, in theRe range between 0.64 and 2.0 (lytic levels) almost a linear dependence was detected between the composition of these aggregates (Re) and the decrease in both the surfactant-PC aggregate size and the static light scattered by the system. This dependence was not observed in the last solubilization steps (Re range 2.0–2.60) possibly due to the increased formation of mixed micelles in this interval. The fact that the free Triton X-100 concentration at sublytic and lytic levels showed respectively lower and similar values than its critical micelle concentration confirms that permeability alterations and solubilization were determined respectively by the action of surfactant monomer and by the formation of mixed micelles.Abbreviations PC phosphatidylcholine - PIPES piperazine-1,4 bis(2-ethanesulphonic acid) - T_X-100 Triton X-100 - CF 5(6)-carboxyflucrescein - Re enective surfactant/lipid molar ratio - Re _SAT effective surfactant/lipid molar ratio for bilayer saturation - Re _SOL enective surfactant/lipid molar ratio for bilayer solubilization - S _W surfanctant concentration in the aqueous medium - S _B surfactant concentration in the bilayers - S _T total surfactant concentration - K bilayer/aqueous phase surfactant partition coefficient - K _SAT bilayer/aqneous phase surfactant partition coefficient for bilayer saturation - K _SOL bilayer/aqueous phase surfactant partition coefficient for bilayer solubilization - PL phospholipid - TLC-FID thinlayer chromatography/flame ionization detection system - PI polydispersity index - CMC critical micellar concentration - r ² regression coefficient     

Determination of residual solvents and reagents in X-ray contrast media by automatic static headspace capillary gas chromatography

A specific, sensitive, and simple method for the quantitation of residual methanol, 2-propanol, 2-butanol, 2-methoxy-1-ethanol, 1-chloro-3-methoxy-2-propanol, 3-chloro-2-methoxy-1-propanol, and 1,3-dimethoxy-2-propanol in two non-ionic X-ray contrast media, has been developed. The headspace of a 25 % w/V aqueous solution of contrast media, obtained at 90–110°C in 15 min, was injected onto a capillary column coated with cyanopropyl, phenyl, dimethylpolysiloxane polymer. The internal standards used were 2-pentanol and 3-methoxy-1-butanol. The limits of detection were below 5 μg/g. The repeatability of the method at 50 μg/g of each solvent was below 5 %; and at 100 μg/g of the methoxypropanol compounds and 2-methoxy-1-ethanol, below 10 % (RSD, N = 5).     

Additivity of atomic static polarizabilities and dispersion coefficients

A new empirical method is proposed to evaluate the average molecular polarizabilities assuming the additivity of atomic static polarizability. Atomic static polarizability for each atom in a particular valence state is obtained. Calculated molecular polarizabilities of 94 non-halogenated compounds and of the bases in nucleic acids show the excellent agreement with experimental data.To check the further validity of this method, dispersion coefficients for CH₄, C₂H₆, C₃H₈,n–C₄H₁₀,n–C₅H₁₂,n–C₆H₁₄,n–C₇H₁₆,n–C₈H₁₈, H₂, H₂O and NH₃ are obtained from a sum of atomic terms using a London-type formula, and are compared with the accurate values of dipole oscillator strength distribution (DOSD) method. The results show the excellent agreement between theory and experiment.     

混合煤制浆对水煤浆性质的影响

实验选用三种性能较差，不适宜制浆的煤作为原料煤，选用成浆性、稳定性或流变性较好的三种煤作为配煤进行混合煤制备水煤浆。实验结果表明，在相同的制浆条件下，加入成浆性、稳定性较好的煤种，使得水煤浆性质较差的煤成浆性、稳定性均有不同程度的提高，浆体流变性得到改善，煤浆粘度明显降低。根据配煤加入量的不同，煤的成浆浓度可提高约2%～3%，浆体稳定性增加，产生软沉淀的时间由1 d提高到10 d。加入成浆性较差的褐煤，亦可明显提高难制浆煤种的稳定性和改善浆体的流变性，使得浆体由胀塑性流体变为假塑性流体。煤的表面性质分析表明，配入表面性质差异较大的煤种，有利于改善难制浆煤种的水煤浆性质。     

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate in dioxane-water mixtures

Dielectric properties of solutions of tetra-iso-pentylammonium nitrate, i-Pen ₄ NNO ₃ . in various dioxane-water mixtures have been studied using dielectric time domain spectroscopy (TDS). The static permittivity of the solutions _s increases for low concentrations of solute but levels off to asymptotic values at higher concentrations. The limiting sloped_s dc, and the asymptotic value depend on the static permittivity of the solvent mixture. The relaxation time due to the solute varies with solute concentration and depends on the solvent mixture. In the solvent mixtures of lowest permittivity the plots of relaxation time vs. concentration go through a maximum, while in the mixtures of highest permittivity the relaxation time initially decreases and then levels off to an asymptotic value. The concentration dependence of the dielectric parameters is discussed in relation to ion association.