Method development for fingerprinting of biodiesel blends by solid-phase extraction and gas chromatography-mass spectrometry

A method based on the combination of solid-phase extraction (SPE) with gas chromatography-mass spectrometry (GC/MS) for detailed chemical fingerprinting of biodiesel/petrodiesel blends was developed in the present study. Forensic identification, commonly referred to as chemical fingerprinting, is based on the relative distributions of individual aliphatic hydrocarbons, aromatic hydrocarbons, fatty acid alkyl esters, and free sterols. Fractionation of fuel samples is optimized for the separation of fatty acid esters and free sterols from petroleum hydrocarbons into four fractions: aliphatic, aromatic, fatty acid ester, and polar components. The final recoveries of aliphatic and aromatic hydrocarbons were determined to be in the range of 65-103%, 73-105% for FAMEs, and 78-103% for free sterols in the polar fraction. Excellent separation with negligible crossover of components with different polarities between fractions was observed. Quantitative analysis of blend levels and individual chemical distribution were achieved. The method has great potential for the identification of biodiesel in diesel fuel blends and could form the basis of a method for characterization of biodiesel-contaminated environmental samples.     

Solvation and Intermolecular Exploration of Drug Molecule Fragments

The paramagnetic contributions from dioxygen to solute proton spin-lattice relaxation rate constants are reported for a series of aromatic hydrocarbons and drug molecule fragments, in order to examine the energetic factors for intermolecular exploration in solution. The measurements provide differences in local oxygen concentration at different sites on the solute molecule. The relaxation rate differences caused by steric factors are taken into account using a lattice model calculation to normalize the relaxation rates for intermolecular contact. The measurements reveal small differences in oxygen accessibility for aromatic solutes in aqueous acetone and for aliphatic drug fragments in chloroform. Larger differences are observed for aliphatic protons in dimethyl sulfoxide; however, the differences are generally small compared with previous measurements on amino acids in water. Concentration ratios between local oxygen concentrations and the solvent references are all smaller than 2.2 and high local concentrations are favored by bulky adjacent groups such as alkane chains.     

燃料馏分油气－液相平衡常数的测定与关联

实沸点蒸馏原油获得燃料馏分油。采用拟静态法测定不同沸程的22种燃料馏分油在系列温度下的泡点蒸气压，用Antoine方程关联蒸气压与温度的关系。在泡点压力分别为10 kPa、30 kPa、50 kPa、80 kPa和101.325 kPa时，按虚拟组分处理法计算了燃料宽馏分油中各虚拟组分的气-液相平衡常数，关联了气-液相平衡常数与虚拟组分的沸点以及相平衡温度、压力的关系，得到的表达式可以计算常压沸点范围在348.15 K至623.15 K间燃料宽馏分油的气-液相平衡常数，经180个数据点回归检验，平均误差为4.5%。     

Spin amplification in solution magnetic resonance using radiation damping

The sensitive detection of dilute solute spins is critical to biomolecular NMR. In this work, a spin amplifier for detecting dilute solute magnetization is developed using the radiation damping interaction in solution magnetic resonance. The evolution of the solvent magnetization, initially placed along the unstable -z direction, is triggered by the radiation damping field generated by the dilute solute magnetization. As long as the radiation damping field generated by the solute is larger than the corresponding thermal noise field generated by the sample coil, the solute magnetization can effectively trigger the evolution of the water magnetization under radiation damping. The coupling between the solute and solvent magnetizations via the radiation damping field can be further improved through a novel bipolar gradient scheme, which allows solute spins with chemical shift differences much greater than the effective radiation damping field strength to affect the solvent magnetizations more efficiently. Experiments performed on an aqueous acetone solution indicate that solute concentrations on the order of 10(-5) that of the solvent concentration can be readily detected using this spin amplifier.     

Mutual selective exclusion of unlike polymers in dilute solution and its measurement by light scattering

The interaction of unlike polymer molecules (components 2 and 4) in a ternary solution can be regarded as selective exclusion or desorption of one polymer by another. A relation is derived between the coefficient of selective sorption and the interaction parameters A₂₄ and A₂₄₄ which are analogs of the second and third virial coefficients. The ratio between the apparent light-scattering molecular weight and the true value for a polymer solute in a ternary system with one component of a binary solvent polymeric is more involved than in a ternary system in which both solvent components are of low molecular weight. Under certain conditions, the introduction of polymer component 2 into a dilute solution of polymer component 4 may lead to a decrease in the total intensity of scattered light.     

Temperature dependence of the structure of a carbosilane dendrimer with terminal cyanobiphenyl groups: Molecular-dynamics simulation

The molecular-dynamics simulation of the structure and molecular mobility of an individual macromolecule of a fourth-generation carbosilane dendrimer with terminal cyanobiphenyl groups in a highly diluted chloroform solution in the range 213–323 K is performed. Upon a change in temperature, the dendrimer undergoes structural rearrangement that depends on the ability of terminal segments to penetrate into the dendrimer. At temperatures close to the boiling point of the solvent, aliphatic spacers of terminal segments can penetrate deep into the dendrimer. As temperature decreases, the terminal segments are grouped only on the surface of the molecule; this leads to a 45% increase in the number of solvent molecules in the treelike part of the macromolecule. These results make it possible to give a new interpretation of temperature effects previously observed in NMR experiments for dilute solutions of these macromolecules.     

Composition of the black crusts from the Saint Denis Basilica, France, as revealed by gas chromatography-mass spectrometry

The organic fraction of black crusts from Saint Denis Basilica, France, is composed of a complex mixture of aliphatic and aromatic compounds. These compounds were studied by two different analytical approaches: tetramethyl ammonium hydroxide (TMAH) thermochemolysis in combination with gas chromatography-mass spectrometry (GC-MS), and solvent extraction, fractionation by silica column, and identification of the fraction components by GC-MS. The first approach, feasible at the microscale level, is able to supply fairly general information on a wide range of compounds. Using the second approach, we were able to separate the complex mixture of compounds into four fractions, enabling a better identification of the extractable compounds. These compounds belong to different classes: aliphatic hydrocarbons (nalkanes, n-alkenes), aliphatic and aromatic carboxylic acids (n-fatty acids, alpha,omega-dicarboxylic acids, and benzenecarboxylic acids), polycyclic aromatic hydrocarbons (PAH), and molecular biomarkers (isoprenoid hydrocarbons, diterpenoids, and triterpenoids). With each approach, similar classes of compounds were identified, although TMAH thermochemolysis failed to identify compounds present at low concentrations in black crusts. The two proposed methodological approaches are complementary, particularly in the study of polar fractions.     

A very simple method for the preparation of symmetrical disulfides

A serendipitiously discovered, extremely simple, fast and previously unreported method for the preparation of symmetrical aliphatic, aromatic and heteroaromatic disulfides is reported. Addition of sulfuryl chloride to an alkyl- or arylthiol in a 1:2 ratio under solvent free conditions or in dichloromethane solution produces the corresponding disulfides in nearly quantitative yields with the concomitant elimination of gaseous SO₂ and 2 equiv of HCl. Thus, optimally the reaction needs no work-up at all leaving the disulfide as the sole product in excellent yield. In dichloromethane solution, the reaction is conveniently carried out in a rotary evaporator by mixing the solvent, thiol and SO₂Cl₂ in a round-bottomed flask followed by evaporation of the volatiles.     

FT-Raman and photoacoustic infrared spectroscopy of syncrude light gas oil distillation fractions

FT-Raman and photoacoustic (PA) infrared spectra of 12 distillation fractions derived from Syncrude light gas oil (LGO), which has a boiling range from 195 to 343 degrees C, were analyzed in detail in this study. In the fingerprint region (200-1800 cm(-1)) most of the information is obtained from the FT-Raman spectra, which display 36 bands that are assignable to various alkyl or aryl functional groups. Monocyclic, bicyclic and tricyclic aromatics in the 12 fractions were also characterized using Raman bands in this region. The corresponding section of the infrared spectra is much simpler, displaying a relatively small number of bands due to either aromatic or aliphatic CH(n) (n=1, 2 or 3) groups. The Cz.sbnd;H stretching region in both FT-Raman and PA infrared spectra of the LGO distillation fractions was curve-fitted according to procedures established in previous investigations of Syncrude samples with various boiling ranges. The PA spectra of the LGO fractions were also analyzed using an accepted integration strategy that requires no a priori assumptions with regard to the number of constituent bands or their shapes. The curve-fitting results show that the frequencies of the 11 Raman and eight infrared bands used to model the aliphatic ( approximately 2775-3000 cm(-1)) parts of the respective spectra decrease systematically as the median boiling points of the LGO fractions increase. These band positions are consistent with those determined in earlier studies of other distillation fractions. Both curve fitting and integration show that the abundance of CH(2) groups increases at the expense of CH(3) groups as the boiling points of the fractions increase within the LGO region.     

Abnormal broadening in triplet-to-triplet absorption spectra caused by aromatic solvents

The triplet-triplet absorption spectra of a number of aromatic molecules were shown to be broadened in low temperature matrices formed by aromatic solvents (toluene, 4-isopropylbiphenyl) as compared with those in aliphatic solvents (ethanol, methylcyclohexane, triethylamine). The effect is exponentially dependent on the energy of the upper triplet state of the solute molecule. The phenomenon is discussed in terms of a strong exchange-resonance interaction between the triplet states of solute and solvent.     

Solvent effect on NMR spectra of poly(methyl methacrylate)

The NMR spectra of stereoblock poly(methyl methacrylate) in several solvents were measured. It is concluded from the following experimental results that the solute–solvent complexes are formed in benzene solution: the chemical shifts measured in C₆H₆ go to a lower field than do those in CDCl₃, except those of the ester methyl group, which splits into three resonances, and the shifts in the aromatic solvents are so different from those in the aliphatic solvents that Buckingham's theory cannot be applied to the results. The analysis of the temperature dependence of the chemical shifts of PMMA in benzene solution gave the heat of formation of the complex: ΔH = 2.8 ± 0.5 kcal./mole.     

Chromatographic chemical characterization of solvent refined coal I and II liquids for toxicological testing

Summary High resolution gas chromatography and gas chromatography/mass spectrometry were employed to determine the components in samples of solvent refined coal (SRC) II naphtha, middle distillate, heavy distillate, and fuel oil blend and SRC-I light oil, wash solvent, and process solvent in concentrations higher than approximately 0.5%. Quantitation was based on the addition of n-alkane internal standards and peak area response of a flame ionization detector with the use of fused silica and glass capillary columns coated with SE-52 and SF-96. The major differences in the SRC-I and II materials were the molecular weight ranges and sizes of the chemical components found in the products, an effect of the differences in the nominal boiling ranges of the materials. Alkanes, alkenes, hydroxylated aromatics, hydrogenated and polycyclic aromatic hydrocarbon ring systems, and alkylated derivatives of the above were found in greatest concentration in the unfractionated materials. Sulfur and nitrogen heteroatomic species were in greates concentration in the higher nominal boiling range materials. A major purpose of these investigations was to develop a method to obtain data on the composition of these complex sample matrices for use in designing studies for toxicological evaluation of these materials.     

One-Pot Etherification of Ketones and Aldehydes with Organic Halides Using Sodium Hydride as a Reductant

One-pot etherification reaction of aromatic and some aliphatic carbonyl compounds with organic halides in the presence of sodium hydride as a reducing reagent proceeded smoothly in dioxane, a polar solvent with higher boiling point, to provide desired ethers in moderate to high yields.     

Structure-type separation of diesel fuels by solid phase extraction and identification of the two- and three-ring aromatics by capillary GC-mass spectrometry

A simple and effective solid phase extraction (SPE) method using silica gel micro glass columns has been developed for the separation of diesel fuel into groups of aliphatic, and mono-, di- and polyaromatic hydrocarbons. It is based on a stepwise gradient of dichloromethane in n-pentane. The resulting fractions were analyzed by capillary gas chromatography with a flame ionization detector and coupled gas chromatography-mass spectrometry. Commercially available standards, and retention indices and mass spectra were used for identification of individual aromatic compounds. The principal polycyclic aromatic hydrocarbons (PAHs) in diesel fuel are naphthalene, biphenyl, fluorene, phen-anthrene and their alkylated derivatives. Sulfur-containing PAHs are mainly represented by methyl-substituted dibenzo-thiophenes.     

H NMR spectrum simplification of phenyl compounds containing electronegative groups by intermolecular interactions

Resolutions of ¹HNMR spectra of aromatic protons have been greatly improved by using simple alcohols, aliphatic amines and aliphatic acids as solvent-induced shift reagents. The hydrogen-bonding between the solvent and the solute molecules, and the self-association characteristics of the solvents are responsible for the spectrum resolution enhancement.     

The influences of solid-phase organic constituents on the partition of aliphatic and aromatic organic contaminants

The influence of natural organic matter (NOM) constituents on contaminant distribution coefficients was evaluated by determining the Koc values of aromatic and aliphatic organic compounds (solutes) with clays modified with both aromatic- and aliphatic-rich organic constituents. The studied compounds consisted of naphthalene, phenanthrene, n-pentane, and 2,3,4-trimethylmethane; the solid samples comprised two clays with little organic content, kaolinite and Ca-montmorillonite. Two aliphatic surfactants and three aromatic dyes, sorbed to the clays, served as reference NOM constituents. For solutes of comparable water solubilities, the organic-carbon normalized distribution coefficients (Koc) of the aliphatic solutes between sorbed aliphatic organic matter and aqueous solution slightly exceed those of the aromatic solutes. By contrast, the aromatic solutes exhibited higher Koc values than did the aliphatic compounds with sorbed aromatic-rich organic matter. The difference in Koc values could be attributed to either comparable solubility parameters or the difference in the chemical structure between nonionic organic solutes and specific components of the simulated NOM. The much higher Koc values observed for the aromatic solutes indicate that the NOM composition is a major factor determining the NOC environmental distribution.     

Physico-chemical analysis of semi-crystalline PEEK in aliphatic and aromatic solvents

Polyether ether ketone (PEEK) is a semi-crystalline thermoplastic polymer having excellent mechanical and thermal properties. Exposure of this polymer to aliphatic and aromatic solvents can lead to degradation or swelling of the polymeric material. The present work described the plasticization and stability analysis of semi-crystalline PEEK under different aromatic and aliphatic solvent environment. A variety of solvents (acetone, benzene, benzyl alcohol, chloroform, methanol, and toluene), based on their Hildebrand’s Solubility Parameter, were chosen for investigation. The physico-chemical characteristics of virgin and treated polymeric samples were investigated using Gas Chromatography–Mass Spectrometry (GC–MS), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Fourier Transform Infrared Spectroscopy (FTIR) techniques. The results indicated that the solvent exposure did not significantly affect the thermal behavior and chemical structure of the polymer. However, it seems that certain components of the polymer were leached into the solvent phase as revealed by the GC–MS analysis. The present study identified PEEK as a potentially suitable polymer for the applications where high resistance to aliphatic and aromatic solvents is needed.     

Comparative chemical analysis of commercial creosotes and solvent refined coal-II materials by high resolution gas chromatography

The chemical composition of a commercially available creosote was compared to a direct coal liquefaction product, i.e., solvent refined coal-II fuel oil blend (SRC-II FOB) using high resolution gas chromatography (HRGC). In addition, hydrogenated products of these materials were studied. Samples were fractionated by chemical class on neutral alumina. Those fractions previously shown to be the most mutagenic and tumorigenic in laboratory bioassays of coal-derived materials were analyzed and compared by HRGC and gas chromatography/mass spectrometry (GC/MS). Individual components were tentatively identified and quantitated. Although similar chemical components were present in the creosote and SRC-II FOB fractions studied, the creosotes had higher concentrations of heavy molecular weight materials and a lower ratio of alkylated to parent polycyclic aromatic compounds than the coal liquefaction products. The creosote samples also had a significantly higher concentration of components which eluted in the polycyclic aromatic hydrocarbon (PAH) chemical class fraction. Amino-substituted PAH were present in both nonhydrogenated coal liquid and creosote materials. The creosote and SRC-II FOB crudes and nitrogen-containing polycyclic aromatic compound (NPAC) chemical class fractions expressed similar microbial mutagenicity. Based on chemical analysis data, the predicted tumorigenic potency of the creosote in laboratory bioassay systems would be equivalent to or greater than the SRC-II FOB.     

Retention characteristics of octadecylsilyl silica,trimethylsilyl silica and phenyldimethylsilyl silica in reversed-phase liquid chromatography

Summary The hydrophobic retention characteristics of stationary ligands for reversed-phase high-performance liquid chromatography have been evaluated from the slope (r-value) of the plots relating the capacity factors (log k) of selected aliphatic and aromatic compounds with the reciprocal of methanol concentration (log (1/[MeOH])) in aqueous mobile phase. Octadecylsilyl (ODS), trimethylsilyl (TMS) and phenyldimethylsilyl (phenyl) groups were selected as the stationary ligands bonded to silica support.On ODS or TMS silicas, unlike on phenyl silica, aliphatic compounds gave slightly larger r-values than aromatic compounds, indicating that the shape of the ligand recognizes the hydrophobic surfaces of aliphatic and aromatic solute molecules. On TMS and phenyl silicas, the degree of solute hydrophobicity contributing to its retention is about 90% and 85% of that on ODS silica, respectively. On the other hand, on TMS and phenyl silicas, the polar functional group on the solute molecule brought about a smaller decrease in retention than on ODS silica.     

Applicability of Raoult's law in nonideal mixed solvents

In general, the vapor-pressure change due to the addition of a solute to a solvent mixture does not follow Raoult's law. We have demonstrated thermodynamically that if one adds to a binary solvent mixture solute and solvents in such a way that the vapor-phase composition remains constant, then the decrease of total pressure follows Raoult's law; a supplementary term which vanishes for very dilute solute concentration is introduced as a consequence of the nonideality of the ternary solution. Precise vapor-pressure measurements of dilute solutions of electrolytes and nonelectrolytes in a 40.000 wt. % water-tetrahydrofuran mixture are used in order to illustrate the applicability of Raoult's law under the above conditions. These may be regarded as a particular case of what has been called endostatic conditions, i.e., addition of a solute under constant solvent activity ratio.