Sampling of volatile components using a PTV in the solvent split mode

Several packing materials were evaluated for their sampling performance with a cold programmed temperature vaporizing injector operated in the solvent split (solvent elimination) mode. Evaluations were made by comparing accuracy and precision of the data for mixtures of n-alkanes, ethyl esters, n-alcohols, and carboxylic acids covering polarity and volatility ranges typical of compounds present in food samples. Tenax exhibits the most desirable retention characteristics. Careful selection of the experimental conditions lowers losses of volatile compounds by co-evaporation with the solvent and allows a reliably quantitative analysis. Coefficients of variation of relative (normalized) peak areas and absolute peak area ratios of each compound to the standard are generally less than 2%.     

Volumetric Properties of Tetra-n-butyl ammonium bromide in Aqueous Solutions of Magnesium sulphate in the Temperature Range 298.15 to 318.15K and under the Atmospheric Pressure

Density and sound speed measurements have been carried out for the ternary systems consisting of tetra-n-butyl ammonium bromide (TBAB) in 0.1 m aqueous magnesium sulphate heptahydrate (MgSO₄.7H₂O)-water over the full range of composition from T = 293.15 to 318.15 K by using volumetric method. Using this experimental data, various physical and thermodynamical parameters such as adiabatic compressibility, apparent molal compressibility, apparent molal volume, apparent and limiting partial molar volumes of the electrolytes and ions in these mixtures have been evaluated and split into respective ionic contributions. The results have been discussed in terms of ion–ion and ion–solvent interactions occurring between TBAB and aqueous MgSO₄ solutions. Further, structure making/breaking behaviour of MgSO4 has been reported in terms of sign of the partial molar expansibility at infinite dilution.     

Contracted Gaussian-type basis functions revisited. IV. Atoms Rb to Xe

We report minimal-type contracted Gaussian-type function (GTF) sets, #n=(n3333/n33/n3) with n=5 and 6, #7= (74333/743/74), and #8= (84333/843/75), for the fourth-row atoms from Rb to Xe. Test calculations are performed on the Ag₂ molecule. Spectroscopic constants given by split valence sets derived from #5 and #6 are a little contaminated by basis set superposition error. However, we find that the fully valence split #8 set, (8433111/84111/711111), yields essentially the same results as a large GTF set, (22s15p12d), with a general contraction, when p-, d-, and f-type polarization functions are augmented. The present #7 and #8 CGTF sets are recommended for ab initio molecular calculations including fourth-row atoms. Received: 15 January 2002 / Accepted: 16 April 2002 / Published online: 24 June 2002     

Growth kinetics for AgI nanoparticles in AOT reverse micelles: effect of molecular length of hydrocarbon solvents

The growth kinetics for AgI nanoparticles formed in the solutions of water/AOT reverse micelles in n-hexane, n-octane, n-decane, and n-dodecane were investigated. In small micelles, the rate of nanoparticles growth was found to be independent of the type of solvent, while in large micelles the growth rate grew with increasing length of solvent molecules. The effect was explained by a different amount of free water in the micelle pools of the same size.     

Shedding Light on the Interactions of Hydrocarbon Ester Substituents upon Formation of Dimeric Titanium(IV) Triscatecholates in DMSO Solution

The dissociation of hierarchically formed dimeric triple lithium bridged triscatecholate titanium(IV) helicates with hydrocarbyl esters as side groups is systematically investigated in DMSO. Primary alkyl, alkenyl, alkynyl as well as benzyl esters are studied in order to minimize steric effects close to the helicate core. The ¹H NMR dimerization constants for the monomer–dimer equilibrium show some solvent dependent influence of the side chains on the dimer stability. In the dimer, the ability of the hydrocarbyl ester groups to aggregate minimizes their contacts with the solvent molecules. Due to this, most solvophobic alkyl groups show the highest dimerization tendency followed by alkenyls, alkynyls and finally benzyls. Furthermore, trends within the different groups of compounds can be observed. For example, the dimer is destabilized by internal double or triple bonds due to π–π repulsion. A strong indication for solvent supported London dispersion interaction between the ester side groups is found by observation of an even/odd alternation of dimerization constants within the series of n-alkyls, n-Ω-alkenyls or n-Ω-alkynyls. This corresponds to the interaction of the parent hydrocarbons, as documented by an even/odd melting point alternation.     

On what terms and why the thermodynamic properties of polymer solutions depend on chain length up to the melt

Theoretical considerations based on chain connectivity and conformational variability of polymers have led to an uncomplicated relation for the dependence of the Flory–Huggins interaction parameter (χ) on the volume fraction of the polymer (?) and on its number of segments (N). The validity of this expression was tested extensively with vapor‐pressure measurements and inverse gas chromatography (complemented by osmotic and light scattering data from the literature) for solutions of poly(dimethylsiloxane) in thermodynamically vastly different solvents such as n‐octane (n‐C₈), toluene (TL), and methylethylketone (MEK) over the entire range of composition for at least six different molecular masses of the polymer. The new approach is capable of modeling the measured χ (?, N), regardless of the thermodynamic quality of the solvent, in contrast to traditional expressions, which are often restricted to good solvents but fail for bad mixtures and vice versa. At constant polymer concentration, the χ values were lowest for n‐C₈ (best solvent) and highest for MEK (Θ solvent); the data for TL fell between them. The influences of N depended strongly on the thermodynamic quality of the solvent and were not restricted to dilute solutions. For good solvents, χ increased with rising N. The effect was most pronounced for n‐C₈, where the different curves for χ (?) fanned out considerably. The influences of N were less distinct for TL, and for MEK they vanished at the (endothermal) θ temperature. For worse than θ conditions, the χ values of the long chains were less than that of the short ones. This change in the sign of N agreed with this concept of conformational relaxation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1601–1609, 2004     

Peculiarities of asphaltene precipitation in <Emphasis Type="Italic">n</Emphasis>-alkane-oil systems

n-Pentane-, n-hexane-, and n-heptane-insoluble asphaltenes obtained via a standard procedure by precipitating from oil solutions in n-pentane, n-hexane, and n-heptane, respectively, as well as n-pentane/n-hexane/n-heptane-insoluble and n-heptane/n-hexane/n-pentane-insoluble asphaltene constituents prepared through successive washing (fractional dissolution) of n-pentane-insoluble asphaltenes with n-hexane and n-heptane and n-heptane-insoluble asphaltenes with n-hexane and n-pentane, respectively, are studied. Asphaltenes and their constituents extracted from three oils distinguished by high contents of asphaltenes, resins, and paraffins, respectively, are investigated by ¹H NMR spectroscopy in carbon tetrachloride solutions. It is established that the mass fractions and the fragment compositions of asphaltenes and their constituents depend on both the type of oil and the procedure of their preparation; i.e., the precipitation from n-alkane-oil systems or the extraction through the successive washing with a series of n-alkanes. The obtained experimental data made it possible to formulate a hypothesis according to which the precipitation of asphaltenes from oils is controlled by not only the dissolving power of a solvent with respect to molecular components of initial oils, but also (and primarily) by the dissolving power of a solvent with respect to supramolecular structures of asphaltenes formed in n-alkane-oil systems.     

钐(II)类卡宾CH3SmCH2I与乙烯环丙烷化反应及溶剂化效应的理论研究

用密度泛函B3LYP方法研究了过渡金属钐类卡宾与乙烯的环丙烷化反应的机理. 对钐类卡宾试剂CH₃SmCH₂I和CH₂CH₂反应的反应物、中间体、过渡态和产物构型的全部结构几何参数进行了优化, 并计算了THF溶液的溶剂化效应, 用内禀反应坐标(IRC)计算和频率分析方法, 对过渡态进行了验证. 结果表明: CH₃SmCH₂I与CH₂CH₂环丙烷化反应按亚甲基转移机理(通道A)和卡宾金属化机理(通道B)都可以进行, 与锂类卡宾的反应机理相同, 通道A比通道B反应的势垒降低了14.65 kJ/mol. 溶剂化效应使通道B比通道A的反应势垒大幅度提高, 更有利于反应沿通道A进行, 而不利于通道B.     

The kinetics of the decarboxylation of n-butylmalonic acid in alkanols and amines

Rate constants and activation parameters are reported for the decarboxylation of n-butylmalonic acid in four normal alkanols (hexanol? 1, octanol? 1, decanol? 1, and dodecanol? 1) and in five amines (aniline, N-methylaniline, N-ethylaniline, N-n-propylaniline, and N-n-butylaniline). Both ΔH? and ΔS? of the reaction in both homologous series decrease regularly with increasing length of the hydrocarbon chain of solvent. If we compare data for the reaction in alkanol–amine pairs containing the same total number of carbon atoms in the molecule, we find that the ΔH? values are identical, but that the value of ΔS? is 0.8 eu/mole higher for the reaction in the amines as compared with the alcohol. The rate constant, at all temperatures, is 1.5 times as large in the amine as it is in the corresponding alcohol. Empirical equations are deduced relating the parameters ΔH? ΔS? ΔG? and k of the reaction to the parameters n and T, where n is the total number of carbon atoms in the solvent molecule and T is the absolute temperature. The results reported herein are compared with previously reported data for malonic acid.     

Quick method for separating target compounds from the bark of Maqian (Zanthoxylum myriacanthum var. pubescens) by high‐performance countercurrent chromatography

Choosing a suitable solvent system for a countercurrent chromatography separation presents a challenge for many researchers. In this study, we introduce a quick method of separating a target compound from the bark of Zanthoxylum myriacanthum var. pubescens by countercurrent chromatography. This method relies on the thin‐layer chromatography based generally useful estimation of solvent systems. This paper will present how to quickly choose a suitable solvent system with a thin‐layer chromatography based generally useful estimation of solvent systems working chart. O‐Methyltembamide ( 1 ) was enriched by countercurrent chromatography using n‐hexane/ethyl acetate/methanol/water (6:4:6:4) as the solvent system. Further purification was achieved by high‐performance liquid chromatography with purities of 98.2% from Z. myriacanthum var. pubescens bark.     

REGIOSELECTIVE BENZYLATION OF PENTITOLS,TETRITOLS, AND SOME HEXITOLS VIA THEIR STANNYL ETHER DERIVATIVES: VERSATILE SYNTHESIS OF MONOBENZYLALDITOLS

The xylitol, ribitol and D-arabinitol were transformed into their tributylstannyl ether derivatives by reaction with bis-tributyltin oxide [(nBu₃Sn)₂O I] and azeotropic removal of water. Subsequent benzyl etherification, using BnBr with solvent or under free solvent conditions, led regioselectively to primary mono-O-benzylalditol derivatives in satisfactory yields for a direct regioselective synthesis (～ 52%). This etherification when applied to tetritols and some hexitols exhibits similar behaviour. With pentitols, an analogous study carried out with the n-dibutyltin oxide [nBu₂SnO (II)] as the activating reagent showed contrasting results as regards regioselectivity.     

The kinetics of the decarboxylation of malonic acid in normal alkanols

Rate constants and activation parameters are reported for the decarboxylation of malonic acid in seven normal alkanols (butanol-l to decanol-l inclusive). It is found that the enthalpy of activation of the reaction is a linear function of the number of carbon atoms in the hydrocarbon chain of tthe solvent, expressed by the equation: ΔH^≠ = –600n + 30,000, where n is thenumber of carbon atoms in the chain. Also an equation is developed relatingthe rate constant for the decarboxylation of malonic acid in normal alkanols to n (the number of carbon atoms in the chain): log K = 10.854283 – 0.3212674n + (131.136876n – 6556.5438)/T + log T. With the aid of this equation rate constants may be calulated for the decarboxylationof malonic acid in any alcohol at any temperature which agree with experimental values to within the limit of error of the experiments. A comparison of the data obtained in the present research for the decarboxylation of malonic acid in normal alkanols with previously reported data for the reaction in amines indicates that for reaction taking place in alcohols the transition state probably contains two molecules of solvent but only one for the reaction in amines.     

Thermodynamic Aspects of Metal–Ion Complexation in the Structured Solvent, <Emphasis Type="Italic">N</Emphasis>-Methylformamide

Chloride complexation of cobalt(II), nickel(II) and zinc(II) ions has been studied by calorimetry and spectrophotometry in N-methylformamide (NMF) containing 1.0 mol-dm^{− 3} (n-C₄H₉)₄NClO₄ as an ionic medium at 298 K. A series of mononuclear complexes, MCl_n^{(2 -n) +} (M=Co, Ni and Zn) with n = 1, 3 and 4 for cobalt(II), n = 1 for nickel(II), and n = 1–4 for zinc(II), are formed and their formation constants, enthalpies and entropies were obtained. It revealed that complexation is suppressed significantly in NMF relative to that in N,N-dimethylformamide (DMF) in all metal systems examined. The suppressed complexation in NMF is mainly ascribed to the smaller formation entropies in NMF reflecting that the solvent–solvent interaction or solvent structure in the bulk NMF is much stronger than that in the bulk DMF. Formation entropies, Δ S₁^o, of the monochloro complex in DMF, dimethyl sulfoxide and NMF are well correlated with the Marcus’ solvent parameter, Δ Δ_v S^o/R, according to Δ S₁^o/R = aΔ Δ_v S^o/R+b. The a value is negative and similar in all metal systems examined, whereas the b value depends on the metal system. When a gaseous ion is introduced into a solvent, the ionic process of solvation is divided into two stages: the ion destroys the bulk solvent structure to isolate solvent molecules at the first stage and the ion then coordinates a part of isolated solvent molecules around it at the second stage. We propose that the a and b values may reflect the changes in the freedom of motion of solvent molecules at the first and second stages, respectively, of the ionic process of solvation.     

Simple and rapid determination of phthalates using microextraction by packed sorbent and gas chromatography with mass spectrometry quantification in cold drink and cosmetic samples

A simple and rapid method using microextraction by packed sorbent coupled with gas chromatography and mass spectrometry has been developed for the analysis of five phthalates, namely, diethyl phthalate, benzyl‐n‐butyl phthalate, dicyclohexyl phthalate, di‐n‐butyl phthalate, and di‐n‐propyl phthalate, in cold drink and cosmetic samples. The various parameters that influence the microextraction by packed sorbent performance such as extraction cycle (extract–discard), type and amount of solvent, washing solvent, and pH have been studied. The optimal conditions of microextraction using C₁₈ as the packed sorbent were 15 extraction cycles with water as washing solvent and 3 × 10 μL of ethyl acetate as the eluting solvent. Chromatographic separation was also optimized for injection temperature, flow rate, ion source, interface temperature, column temperature gradient and mass spectrometry was evaluated using the scan and selected ion monitoring data acquisition mode. Satisfactory results were obtained in terms of linearity with R² >0.9992 within the established concentration range. The limit of detection was 0.003–0.015 ng/mL, and the limit of quantification was 0.009–0.049 ng/mL. The recoveries were in the range of 92.35–98.90% for cold drink, 88.23–169.20% for perfume, and 88.90–184.40% for cream. Analysis by microextraction by packed sorbent promises to be a rapid method for the determination of these phthalates in cold drink and cosmetic samples, reducing the amount of sample, solvent, time and cost.     

Solvent effect on the size of platinum nanoparticle synthesized in microemulsion systems

In this research work, the effect of solvent on the size of paltinum nanoparticles synthesized by microemulsion method was investigated. Platinum nanoparticles have been prepared by the reduction of H₂PtCl₆ with hydrazine in water-in-oil (w/o) microemulsions consisting of sodium bis(2-ethylhexyl) sulfo-succinate (AOT) and solvents n-hexane, cyclohexane and n-nonane. The size of the platinum nanoparticles was measured using transmission electron microscopy (TEM). It was verified that, for reduction of H₂PtCl₆ by hydrazine in microemulsion with different organic solvents, the solvents are arranged by their influence on nanoparticle sizes as follows: n-nonane > cyclohexane > n-hexane.     

8-Molybdogermanate of rhodamine 6G and its use for the photometric determination of germanium

A procedure was developed for determining germanium as a Rhodamine 6G-8-molybdogermanic heteropoly acid ion-pair complex in solutions obtained after germanium separation by solvent extraction from the matrix of various Ge-containing samples. The procedure accuracy was evaluated by determining germanium in a reference standard sample of steel after preliminary separation by solvent extraction. For the certified content equal to 1.1 × 10^-4% the found content was 1.1 sx 10^-4% (n = 10, RSD = 3.0%, andP = 0.95)     

Construction of ternary phase diagrams in nonsolvent/solvent/PMMA systems

In this work, the ternary phase diagrams in three nonsolvent/solvent/PMMA systems (n-hexane/n-butyl acetate/PMMA, water/acetone/PMMA, and n-hexane/acetone/PMMA) were constructed by theoretical calculation and experimental measurement. Binodal curves were calculated by using the Flory–Huggins theory for three-component systems and measured by titrating the PMMA solution with nonsolvent until the onset of turbidity. By using concentration-dependent nonsolvent/solvent and solvent/PMMA interaction parameters and constant nonsolvent/PMMA interaction parameters, good agreement has been obtained between the calculation and the measurement. The values of nonsolvent/solvent interaction parameters were taken from the literature sources, and the values of solvent/PMMA and nonsolvent/PMMA interaction parameters were measured by vapor sorption and swelling equilibrium, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 607–615, 1998     

Investigation of solvatochromism in the low-lying singlet states of dithienyl polyenes

To understand the low-lying singlet states of dithienyl polyenes, we investigated the solvatochromism of a series of α,ω-di(2-dithienyl 3,4-butyl) polyenes having n=1–5 double bonds. Absorption and emission spectra were collected in a series of aprotic solvents. The absorption energy dispersion effect sensitivity increased smoothly with n, reaching asymptotic behavior as n approached 5. The emission energy had less solvent sensitivity. The trends gave evidence for the existence of a ¹B^*_u absorbing state and a ¹A^*_g emitting state. We observed sensitivity of the absorbing and emitting states to solute–solvent electrostatic interactions, suggesting the dithienyl polyenes had a polar ground state conformation.     

Separation of iron(III) and gold(III) by paper chromatography using mixed solvents containing diisopropyl ether

The separation of iron(III) and gold(III) by partition paper chromatography has been investigated employing a mixture of diisopropyl ether (IPE) and n-alcohol saturated with hydrochloric acid (initial acid concentration 5.0 M) as solvent. Methyl, ethyl, n-propyl, n-butyl, and n-pentyl alcohols were used as components of the solvent. The content of n-alcohol in the initial organic phase was varied. It was found that the R_f values for both of the metals increased with an increase in the carbon-to-oxygen ratio in the alcohol (except in the case or iron(III) and n-pentyl alcohol), and with an increase in the alcohol content in the initial organic phase (except in the case of iron(III) and n-propyl alcohol). The best separation results were obtained by using the systems: hydrochloric acid (5.0 M)-IPE-n-propyl alcohol (50:35:15) gDR_f = 0.56, hydrochloric acid (5.0 M)-IPE-ethyl alcohol (50:15:35) ΔR_f = 0.51, and hydrochloric acid (5.0 M)-IPE-n-pentyl alcohol (50:35:15) ΔR_f = 0.37.     

Large volume sample introduction using temperature programmable injectors: Implications of liner diameter

Temperature programmable injectors with liner diameters ranging from 1 to 3.5 mm are evaluated and compared for solvent split injection of large volumes in capillary gas chromatography. The liner dimensions determine whether a large sample volume can be introduced rapidly or has to be introduced in a speed controlled manner. The effect of the injection technique used on the recovery of n-alkanes is evaluated. Furthermore the influence of the liner diameter on the occurrence of thermal degradation during splitless transfer to the analytical column is studied. Guidelines are given for the selection of the PTV liner internal diameter best suited for specific applications.