N-Alkanes in Air Particulates of the Eastern Province of Saudi Arabia

Abstract

Oil hydrocarbons represent a great proportion of organic compounds in the atmosphere. Information about these compounds in the atmosphere of the Eastern Province of Saudi Arabia is lacking. In this study, n-alkanes and polynuclear aromatic hydrocarbons in air particulates were determined. The highest median concentration levels of n-alkanes in three urban areas and three areas near oil production centers were 121 ng/m³ and 42.9 ng/m³, respectively. Polynuclear aromatic hydrocarbons were also detected, although they are present in too low concentration for reliable quantitative measurement by GC and GC/MS techniques. A positive correlation was found between the concentration levels of n-alkanes in air particulates and the total suspended particulates measured at most locations. The carbon preference index (CPI) and the presence of the unresolved complex envelope suggested an anthropogenic origin for the n-alkanes.     

Aliphatic and Aromatic Hydrocarbons in the Mediterranean Aerosol

Abstract

The atmospheric transport of organic pollutants over long distances and their effect on the biological cycles of the sea are two major questions of concern in environmental chemistry. These processes are of particular importance in the Mediterranean Sea because of its semi-enclosed characteristics, which determine the accumulation of the pollutants entering into the system.

In order to get some insight into these processes a project (PHYCEMED), was developed for the evaluation of the atmospheric budget of organic and inorganic substances in the Western Mediterranean and for the investigation of the exchange mechanisms of these materials across the air/sea interface.

A high volume air sampling system including a cascade impactor was placed on board of the R/V le Suroit for collecting the acrosols along several transects parallel to the French, Spanish and North-African coasts, facing areas of different population densities and industrial activities. The cruise was realised on October 1983 and the particulate material was fractionated into the following sizes: 7.2, 3.0, 1.5, 0.96, and 0.03 μm. Quantitative and qualitative analyses of the aliphatic and the aromatic hydrocarbons present in these fractions were performed by high resolution gas chromatography and gas chromatography-mass spectrometry.

Total non-aromatic hydrocarbon concentrations are in the range 30-57 ng/m³ (10-14ng/m³ for n-alkanes). The distribution of n-alkanes indicates that most of the aerosol mass is associated with small particles < 1 μm.Polycyclic aromatic hydrocarbons are identified from phenanthrene to benzo(ghi)perylene with fluoranthene and pyrene as dominant compounds. Concentrations for individual PAH vary in the range 4.1 pg/m³ for benzo(a)anthracene up to 100 pg/m³ for fluoranthene. The evaluation of different contributions such as land plant waxes or soil sources and various anthropogenic sources is discussed from n-alkanes and PAH distribution patterns.     

High Temperature Steam Extraction for the Determination of Aliphatic Hydrocarbons in Petroleum Source Rock

A simple method for the extraction of hydrocarbons from petroleum source rock by high temperature steam was investigated and the conditions for maximum yield were determined. The results showed that the temperature and kinetic rates have significant effects. The optimum temperature for the extraction of n-alkanes and isoprenoid hydrocarbons from sedimentary organic rocks was 250 °C. The optimum extraction time for lower and medium molecular weight n-alkanes was 20 min, while the higher molecular weight alkanes were exhaustively extracted after 50 min. The yields of the analytes were much higher with using the high temperature steam extraction than Soxhlet extraction. The recoveries of the n-alkanes for GC–MS analysis from the extractant water by SPME with a PDMS fibre ranged from 90 to 100% and most of the compounds were above 93%.

     

Calculation of Heats of Vaporization of Long Chain Molecules by Group Contribution Method

Abstract

Benson's additivity rule has been used to compute the heat of vaporization (ΔH ^o _v) of long chain molecules includes n-alkylcyclopentanes, and n-alkylcyclohexanes and n-alkylbenzenes. From the error analysis empirical equations have been obtained which accurately predicts the ΔH ^o _v of these substituted n-alkanes. For simple n-alkanes it is observed that no modification is necessary in Benson's method. The present simple and elegant empirical approach can be utilized to calculate other thermodynamic properties of long chain molecules where such data are generally scarce.     

Excess Molar Volumes of Binary Mixtures of Propyl Ethanoate with some n-Alkanes at 298.15 K and 308.15 K

Abstract

Excess molar volumes v^E have been measured for the binary liquid mixtures of propyl ethanoate with five n-alkanes (n-hexane, n-heptane, n-octane, n-nonane and n-decane) at 298.15 and 308.15 K, using an Anton Paar densimeter. All the mixtures studied present positive v^E values that increase with the length of the chain of the alkane and with the temperature. The experimental results are compared with the predictions of the Nitta—Chao model.     

Study of the physicochemical characteristics of dispersions of n-alkanes C23H48 and C28H58 in water: zeta potential and temperatures of phase transitions

The effect of pH on the zeta potential of dispersions of individual n-alkanes C₂₃H₄₈ and C₂₈H₅₈ with particle sizes of the order of 100 nm, which were prepared by ultrasonic dispersion without the addition of surfactants, was studied. It is shown that at pH ranged from 4 to 12, the investigated n-alkanes form stable dispersions in water. They are characterized by a high zeta potential varying from ?30 to ?50 mV. The phase transition temperatures (melting point, crystallization temperature, formation of rotator phases) were determined for the dispersions using an optical method.

     

Synthesis of Novel Fluorinated [sgrave]-Conjugated Silicon-Containing Polymers: Polysilynes and Polysilanes

Abstract

The synthesis of fluorinated polysilynes, a new class of silicon-silicon network materials, has been achieved by reductive coupling of fluorinated trichlorosilanes with molten sodium in a mixture of toluene and diglyme (4:1) as a new synthetic route. Homopolysilynes containing fluorinated organogroups were insoluble in organic solvents due to side reactions. To improve solubility, copolysilynes were synthesized by co-polymerization of fluorinated trichlorosilanes with cyclohexyltrichlorosi-lane. All spectroscopic data indicate that the structure of the resulting fluorinated copolysilynes is a rigid, irregular network of monoalkyl sp ³-hybridized silicon units which exhibit extensive Si-Si [sgrave]-delocalization. They are more thermally stable than unfluorinated polysilynes. Upon exposure to deep-UV radiation in air, they undergo photooxidative crosslinking to give insoluble glass-like materials. This photooxidation process is accompanied by a large decrease in refractive index from n = 1.61 to n = 1.485. These results suggest that their potential applications include photoresists and optical waveguides. In order to understand the mechanism of reductive coupling of fluorinated trichlorosilanes, fluorinated linear polysilanes were also prepared.     

Temperature dependence of the free energy of sorption ofn-alkanes and energy contribution of their methylene groups on columns with fullerene C60

The partial molar free energy, enthalpy, and entropy of sorption of C₁₁−C₂₃ n-alkanes were calculated on the basis of the GC data obtained on the glass capillary column coated with fullerene C₆₀ (Ful-60) as stationary phase. The thermodynamic parameters ofn-alkane sorption on a column with Ful-60 and a fused silica capillary column with polydimethylsiloxane OV-1 were determined and compared. The enthalpy-entropy compensation effect for the sorption ofn-alkanes on Ful-60 and OV-1 was found. A linear dependence of the partial molar free energy ofn-alkane sorption on the temperature of analysis and carbon chain length was found. The free energy contributions of the methylene groups were calculated, and their temperature dependences were studied. The differences in the temperature dependences of the energy contributions of methylene groups ofn-alkanes on Ful-60 and OV-1 were revealed. The entropy contribution is 68–82% of the enthalpy contribution which indicates a substantial role of the number of contacts with Ful-60 in retention ofn-alkanes. The ability of Ful-60 for dispersive interactions is similar to those of nonpolar liquid phases and substantially differs from that for carbon adsorbents. Fullerene columns were shown to be convenient for analysis of highly boiling organic substances in aqueous and organic solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1490–1495, August, 1999.     

Predicting Excess Enthalpies of Ether and/or Hydrocarbon Binary Mixtures

Previous applications of the Flory–Patterson theory in the analysis of the excess molar enthalpies at 25°C for some binary mixtures composed of ethers, n-alkanes, br-alknes, and cycloalkanes are reviewed. The possibility of correlating the Flory interaction parameters X _ij in terms of the acentric factors of the components is examined. For selected ether (1) + n-alkane(2) mixtures, a set of linear relations between X ₁₂ and the acentric factors of the n-alkanes are reported.Visiting Professor on sabbatical leave from the     

Optimization of the Microwave-Assisted Saponification and Extraction of Organic Pollutants from Marine Biota Using Experimental Design and Artificial Neural Networks

Several improvements in sample pretreatment for the determination of organic pollutants (i.e. n-alkanes, polycyclic aromatic hydrocarbons, PAHs) in marine biota (mussels) are presented. The use of liquid nitrogen and homogenization of the samples are shown to be an alternative to the time consuming liophilization step required for the analysis of biota samples. Microwave-assisted hydrolysis and extraction are combined to isolate organic pollutants (19 n-alkanes and 27 PAHs) from biota matrices. Experimental design (ED) and artificial neural networks (ANNs) were used to optimize the experimental conditions. NIST-CRM 2978 was used to test the validity of the developed method which shows a good agreement with certified values.     

Significance of Photosensitized Oxidation of Alkanes During the Photochemical Degradation of Petroleum Hydrocarbon Fractions in Seawater

Abstract

A crude oil hydrocarbon fraction was photooxidized as a surface film on seawater under simulated environmental conditions. After irradiation, gas chromatography and gas chromatography/mass spectrometry analyses allowed to demonstrate the presence of relatively high quantities of compounds deriving from the photosensitized oxidation of n-alkanes, pristane and phytane, being among the non-acidic photoproducts of this fraction. The results suggest that the photochemical degradation of alkanes should be considered in studies of the fate of petroleum crudes in the marine environment.     

High Temperature Steam Extraction for the Determination of Aliphatic Hydrocarbons in Petroleum Source Rock

A simple method for the extraction of hydrocarbons from petroleum source rock by high temperature steam was investigated and the conditions for maximum yield were determined. The results showed that the temperature and kinetic rates have significant effects. The optimum temperature for the extraction of n-alkanes and isoprenoid hydrocarbons from sedimentary organic rocks was 250 °C. The optimum extraction time for lower and medium molecular weight n-alkanes was 20 min, while the higher molecular weight alkanes were exhaustively extracted after 50 min. The yields of the analytes were much higher with using the high temperature steam extraction than Soxhlet extraction. The recoveries of the n-alkanes for GC–MS analysis from the extractant water by SPME with a PDMS fibre ranged from 90 to 100% and most of the compounds were above 93%.     

Application of urea adduction technique to polluted urban aerosols for the determination of hydrogen isotopic composition of n-alkanes

We examined an applicability of an improved urea adduction technique for the determination of hydrogen isotopic composition (δD) of homologous series of n-alkanes present in polluted urban aerosols using GC/TC/IRMS. Unresolved complex mixture (UCM) of hydrocarbons that interferes with accurate isotope measurements of n-alkanes was removed from n-alkane fraction by a urea adduction method. Recoveries of C₂₀ to C₃₀ n-alkanes during the urea adduction procedure were greater than 90% when the concentrations of total n-alkanes exceed 6.1?µg?mL^?1. Our compound-specific D/H ratios confirm the absence of significant hydrogen isotope fractionation in n-alkanes during urea adduction and recovery of the purified n-alkane fraction. We applied this technique to the urban aerosols that contain a large quantity of UCM to measure δD of C₂₀ to C₃₅ n-alkanes in urban aerosols from Tokyo and Sapporo with an accuracy less than 10‰. We found that the δD values widely ranged from ?38 to ?179‰. Based on the δD values of individual n-alkanes in aerosol samples, we can obtain further information on the sources of aerosol n-alkanes and their source regions, and the atmospheric processes such as long-range transport and atmospheric mixing of air masses of different origin.     

The Melting Point Alternation in the Short-Chain n-Alkanes: Single-Crystal X-Ray Analyses of Propane at 30 K and of n-Butane to n-Nonane at 90 K

A less dense packing is observed in the odd-numbered n-alkanes compared to the even-numbered members, which consequently lowers melting temperatures. The reason for this is that the even-numbered n-alkanes have optimal intermolecular interactions at both ends (see the picture on the left), while the odd-numbered ones possess these only at one end—at the other end the intermolecular distances are longer (right)     

A comparison of different retention index systems with unsaturated and aromatic hydrocarbons in capillary gas chromatography on PEG 20M

Summary The correction of the reproducibility of retention indices on polar capillary columns with different film thickness, using more polar reference standards instead ofn-alkanes, was investigated. It was found that the replacement ofn-alkanes by 1-alkenes, 3-alkynes and n-alkylbenzenes as standards significantly improves the reproducibility of retention indices and diminishes their temperature increments forn-alkanes,n-alkynes and arenes on PEG 20M columns.     

Optimisation of solid-state urea clathrate formation as a chemical separation method coupled to compound-specific stable carbon isotope analysis

Solid-state urea clathrate formation (SSUCF) as a chemical separation method prior to stable carbon isotope fingerprinting of diesel fuel contaminations was studied. The stable carbon isotope ratios (δ¹³C) of n-alkanes in diesel fuel can be used to trace the origin of a contamination. The accurate measurement of the stable isotopic composition of individual compounds requires baseline separation from any other co-eluting compounds. For this purpose silica gel column chromatography (SGCC) and SSUCF were applied. Detailed optimisation of SSUCF was performed: different activators, clathrate formation temperatures, activator volumes, clathrate formation times and sample capacity were investigated. The main benefits of the developed method are reduced clathrate formation time and increased recoveries for lower molecular weight n-alkanes. The recoveries of the developed SSUCF method ranged between 63 and 100% for C10–C24 n-alkanes with relative standard deviation no more than 7%. The precision of the gas chromatography-isotope ratio mass spectrometry measurement was acceptable with a standard deviation of the δ¹³C values ranging between 0.08 and 0.15‰. The absence of isotopic fractionation was also investigated.

The robustness of the method was tested within a model experiment. Nine different water samples including distilled water, tap water, river water, industrial wastewaters and groundwater samples were spiked with the same diesel fuel. The water samples were extracted with n-hexane and after purification with both SGCC and SSUCF n-alkanes were measured. The δ¹³C values of n-alkanes were found to be similar for all samples. The importance of sample purification prior to compound-specific isotope analysis (CSIA) was also demonstrated within this model experiment by analysing samples from different stages of the sample preparation.

Our results show that the proposed method can remarkably improve the precision of compound-specific stable carbon isotope analysis of n-alkanes originating from diesel contamination of the aquatic environment.     

The effects of microbial degradation on ignitable liquids

The identification of ignitable liquid residues in fire debris is a key finding for determining the cause and origin of a suspicious fire. However, the complex mixtures of organic compounds that comprise ignitable liquids are susceptible to microbiological attack following collection of the sample. Biodegradation can result in selective removal of many of the compounds required for identification of an ignitable liquid. Such degradation has been found to occur rapidly in substrates such as soil, rotting wood, or other organic matter. Furthermore, fire debris evidence must often be stored for extended periods at room temperature prior to analysis due to case backlogs and available evidence storage. Hence, extensive damage to ignitable liquid residues by microbes poses a significant threat to subsequent laboratory work. In this work, the effects of microbial degradation of ignitable liquids in soil have been evaluated as a function of time. Key findings include the loss of n-alkanes, particularly C₉–C₁₆, which showed the most dramatic decrease in gasoline as well as the petroleum distillates, while branched alkanes remained unchanged. Monosubstituted benzenes also showed the most dramatic loss in gasoline. In the heavy petroleum distillates, n-alkanes with even carbon numbers were degraded more than n-alkanes with odd carbon numbers. Figure A “fully involved” house fire in Indianapolis, IN

Horizontal and vertical distributions of Biogenic and Anthropogenic Organic compounds in the Ross Sea (Antarctica)

Horizontal and vertical distributions of organic compounds extractable with n-hexane were investigated at five sampling stations (Ross Sea) during the Italian Antarctic Expedition 1997/98. Samples were collected from seven depths under pack ice and from two or three depths at the other stations located at different distances from the coast. The lowest concentrations of biogenic and anthropogenic compounds were found at station Y3, the furthest from the coast, while the highest concentrations were observed under pack ice (B2-2 station) or in the Polynya zone (Y1 station). The levels of organic compounds in the particulate phase were higher than those in the dissolved phase for all the investigated samples. Concentrations of biogenic organic compounds (long-chain aldehydes and alcohols, fatty acid esters and n-alkanes) were well related to fluorescence intensity, which is usually reported as a biological activity index. The odd-to-even carbon-number ratio for n-alkanes was lower than 1 at stations B2-2, Y1, Y5 and Y6 (located less than 150?km far from the coast) with the predominance of n-C16, n-C24 and n-C28, indicative of autochthonous pelagic species. An odd-to-even ratio higher than unity and a different n-alkane profile were observed at station Y3 (about 300?km from the Ross Ice Shelf and 600?km from Terra Nova Bay). Low levels of pollutants (i.e. phthalates) were found, mainly in the particulate phase up to a depth of 50?m, confirming a local source of the phthalates found at significant concentrations during previous expeditions.     

Applications of liquid crystals in biosensing and organic light-emitting devices: future aspects

ABSTRACT

This article summarises recent advances made in our laboratory towards the development of new technological applications, such as biosensors and organic light-emitting diodes (OLEDs) based on liquid crystals (LCs) other than LC displays. The study of biomolecular interaction using LC material relies on the specific interaction between the LC and the biomolecule of interest at interfaces that permit the biomolecular events to be amplified into easily measured signals for various sensing applications. In the first part, we emphases recent studies in the design and modulation of LC-based interfaces based on robust colloidal LC gels for biological amplification, qualitative and quantitative understanding of important biomolecular interactions at LC–aqueous interfaces for diagnostic and laboratory applications and design of LC droplets that hold promise to act as a marker for cells and cell-based interactions. In the second part, we described design of organic materials for application in OLEDs on various discotic monomers, dimers and oligomers. These molecules have the ability to transport charges, holes and electrons. In addition, because of the high conductivity and π–π stacking, they are considered as the advanced materials for practical applications. The technological advances in our laboratory using discotic LCs will be briefly presented in this article.     

Low-frequency Raman spectra of odd α,ω-disubstituted n-alkanes

Low-Frequency Raman spectra of odd α,ω-dibromo- and α,ω-dihydroxy-n-alkanes were recorded. The longitudinal acoustic mode (LAM-1) frequencies were assigned by references to the published results for n-alkanes and even α,ω-disubstituted n-alkanes and also by taking account of the effects of end intermolecular forces and end-group masses by use of the chain model of Minoni and Zerbi.