Detailed Hydrocarbon Class Composition Analysis and Trace Level BTEX Estimation in Raffinate Column Bottom (RCB) Using GC×GC–TOFMS

A two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC–TOFMS) method was developed for the hydrocarbon class composition analysis and benzene, toluene, ethylbenzene, and xylene (BTEX) estimation of raffinate column bottom (RCB), which is generated as a by-product from linear alkyl benzene (LAB) plants. The molecular level characterization of RCB is important to generate value-added products for the petrochemical industry. GC×GC–TOFMS was found to be an excellent tool for estimation of hydrocarbon class composition (paraffins, naphthenes, monoaromatics, diaromatics, and polyaromatic hydrocarbons) and trace level BTEX in a single run. The hydrocarbon class composition was validated with the standard method based on HPLC (ASTM D6591) and good correlation was obtained. Finally, RCB is anticipated to be a useful nonhazardous safe by-product which could be used further for generating added value.     

An ionophore–Nafion modified bismuth electrode for the analysis of cadmium(II)

A novel ionophore–Nafion modified bismuth electrode is described for sensitive and selective anodic stripping analysis of cadmium(II). The electrode is prepared by coating the glassy carbon electrode with the cadmium ionophore N,N,N′,N′-tetrabutyl-3,6-dioxaoctanedi(thioamide) and Nafion composite. Bismuth is deposited in situ on the electrode surface by plating simultaneously with cadmium in sample solution. Numerous key variables affecting the current response of cadmium have been optimized. The electrode has a linear concentration range of 0.5–10 nM with a deposition time of 180 s. The detection limit is 1.3 × 10^?10 M and the relative standard deviations for 0.5 and 7 nM cadmium are 6.5% and 4.5%, respectively. The proposed electrode shows excellent selectivity over other heavy metals, such as copper, lead and indium. The attractive performance of such electrode offers a feasible way to monitor trace cadmium(II) rapidly and precisely in complex matrixes.     

New strategies to screen for endocrine-disrupting chemicals in the Portuguese marine environment utilizing large volume injection–capillary gas chromatography–mass spectrometry combined with retention time locking libraries (LVI–GC–MS–RTL)

A new analytical strategy to screen for endocrine-disrupting chemicals (EDCs) in environmental matrices is presented. The strategy uses solid-phase extraction followed by large volume injection and capillary gas chromatography coupled to mass spectrometry combined with retention time locking libraries (SPE-LVI-GC-MS-RTL). Characterization of the proposed methodology (SPE-LVI-GC-MS) for selected classes of EDCs enabled high reproducibility and robustness at the ultratrace level. The RTL databases used allowed hundreds of non-target semivolatiles (i.e., pesticides, polycyclic aromatic hydrocarbons, polychlorinated biphenyls and other classes of suspected EDCs from a great number of unknown environmental matrices) to be simultaneously screened for in an easy, fast and remarkable manner. The application of the proposed methodology to real environmental samples demonstrated its remarkable selectivity and sensitivity at the ultratrace level. Screening assessments performed on water and sediment matrices from eight Portuguese estuaries and coastal waters identified EDC "hotspots." These EDCs mainly come from agricultural and a wide variety of industrial sources, and include pesticides and pesticide metabolites, phenolic derivatives and polycyclic aromatic hydrocarbons, which are included in the lists of priority substances published by international environmental agencies. The estuaries that contained relatively high levels of pesticides were Guadiana, Sado and Mondego, while Minho, Douro and Formosa showed enhanced levels of phenolic derivatives. Dibutyltin and tributyltin, selected as target compounds to be monitored by SPE-LVI-GC-MS in the selected ion monitoring mode, were shown to be widespread contaminants at trace levels in almost all of the sediment matrices assessed. The reliability of the proposed methodology undoubtedly makes it a valuable tool that could replace other analytical strategies currently used to screen for EDCs present in the environment at ultratrace levels.     

Applications of Gas Chromatography–Mass Spectrometry (GC–MS): An Examination of Selected African Cases

As a result of the new economic order in Africa, scientists face enormous challenges due to an increase in socio and economic activities. Gas chromatography–mass spectrometry (GC–MS) will be expected to play a big role in providing some of the solutions to the challenges. Up to now, applications of GC–MS in Africa have focused on profiling natural products for their chemical composition as seen from the number of papers published between 2005 and 2011, i.e. at approximately 62 % of the total. In order to meet the new challenges, a paradigm shift is suggested in the design of research projects. Some economic activities envisaged to boom are food and beverage production for local consumption and for export to markets in the developed world. To meet the requirements of these markets, monitoring pesticides and metabolites of veterinary drugs and other toxins in food will become paramount. Africa also needs to put stringent environmental monitoring policies in place. This will aid remediation following accidental or intentional spillages of chemicals not benign to the environment.

     

An arbitrary Lagrangian–Eulerian model for studying the influences of corrosion product deposition on bimetallic corrosion

In this paper, a model is established to simulate the time-dependent deposition of corrosion product on the metal surface by considering mass transfer, electrochemical reactions and precipitation reaction. The model is also capable of tacking the movement of metal corrosion interface and the growing interface of the corrosion product deposits via arbitrary Lagrangian–Eulerian finite element method. The current model not only can be used to predict the time-dependent metal corrosion but also for investigating the influences of the deposits’ nature on metal corrosion. The numerical results of current density and corrosion rate are in good agreement with experiments. The presented model predicts that an exponential relationship exists between the maximum corrosion depth and the porosity of corrosion product deposits, and it is also predicted that the growth of the corrosion product layer is linear relative with the root of time, which is consistent with the existing theories.     

Analytical methods for determination of mycotoxins: An update (2009–2014)

Mycotoxins are a problematic and toxic group of small organic molecules that are produced as secondary metabolites by several fungal species that colonise crops. They lead to contamination at both the field and postharvest stages of food production with a considerable range of foodstuffs affected, from coffee and cereals, to dried fruit and spices. With wide ranging structural diversity of mycotoxins, severe toxic effects caused by these molecules and their high chemical stability the requirement for robust and effective detection methods is clear.     

Combination of chemical and electron-impact ionisation with GC×GC–qMS for characterization of fatty alcohol alkoxylate polymers in the low-molecular-weight range up to 700 Da

The class of fatty alcohol alkoxylates describes surfactants that are synthesised by reaction of fatty alcohols with alkoxides such as ethylene oxide or propylene oxide or a combination of both as copolymers. Such alkoxylates are used, for example, as nonionic surfactants in home and industrial cleaning and washing agents. Chemical characteristics of such alkoxylate copolymers, for example the degree of alkoxylation, the arrangement of building blocks (random or block polymerisation), the type of the starter, and endcapping, play an important role in application behaviour. The analysis of these characteristics is challenging because in many cases such copolymers have high polydispersity and a large number of constitutional isomers depending on the degree of alkoxylation. Furthermore, the alkoxylates often occur in a complex multicomponent matrix. Here we present a method for characterization of silylated fatty alcohol alkoxylates in the low-molecular-weight range by means of comprehensive two-dimensional gas chromatography–mass spectrometry with electron impact and chemical ionisation. This method also enables detailed analysis of the alkoxylates in a complex matrix such as modern detergents.     

A new model and extension of Wong–Sandler mixing rule for prediction of (vapour + liquid) equilibrium of polymer solutions using EOS/GE

The cubic equation of state (CEOS) is a powerful method for calculation of (vapour + liquid) equilibrium (VLE) in polymer solutions. Using CEOS for both the vapour and liquid phases allows one to calculate the non-ideality of polymer solutions based on a single EOS approach. However, the traditional mixing rules are not appropriate to extend the CEOS to non-ideal mixtures such as polymer solutions. Several authors have applied the EOS/G^E approach to predict (vapour + liquid) equilibria in polymer solutions, however, incorporating an appropriate excess Gibbs free energy for the new mixing rule is a major step. In this research, the NRTL-NRF model was extended in terms of volume fraction of polymer and solvent (instead of mole fraction), then equilibrium calculations were carried out using PRSV EOS and Wong–Sandler mixing rules. Using the adjustable parameters as a function of solution temperature, the NRTL-NRF model can be used as a predictive model. In comparison with NRTL model, the results of the new NRTL-NRF model show better accuracy.     

Investigation,by single photon ionisation (SPI)–time-of-flight mass spectrometry (TOFMS), of the effect of different cigarette-lighting devices on the chemical composition of the first cigarette puff

Soft single-photon ionisation (SPI)–time-of-flight mass spectrometry (TOFMS) has been used to investigate the effect of different cigarette-lighting devices on the chemical composition of the mainstream smoke from the first cigarette puff. Lighting devices examined were a Borgwaldt electric lighter, a propane/butane gas lighter, a match, a candle, and the burning zone of another cigarette. To eliminate the effects of the different masses of tobacco burnt by use of the different lighting methods a normalisation procedure was performed which enabled investigation of changes in the chemical patterns of the resulting smoke. When another cigarette was used as the lighting device, elevated levels of ammonia and other nitrogen-containing substances were observed. These are high in the sidestream smoke of the cigarette used for lighting and would be drawn into the mainstream smoke of the cigarette being lit. In contrast, smoke from the cigarette lit by the electric lighter contained slightly higher normalised amounts of isoprene. Lighting the cigarette by use of a candle resulted in larger amounts of substances, e.g. benzene, which most probably originated from thermal decomposition of wax. The composition of the first puff of smoke obtained by use of the three lighting methods with open flames (gas lighter, match, and candle) was usually similar whereas the composition of the smoke produced by use of the electric lighter and the cigarette as the lighter were more unique. The chemical patterns generated by the different lighting devices could, however, be separated by principal-component analyses. Two additional test series were also studied. In the first the cigarette was lit with an electric lighter, then extinguished, the ash was cut off, and the cigarette was re-lit. In the second the cigarette was heated in an oven to 80 °C for 5 min before being lit. These treatments did not result in changes in the chemical composition compared with cigarettes lit in the ordinary way. Figure Time-of-flight mass spectrometry (TOFMS) has been used to investigate the effect of different cigarette-lighting devices on the chemical composition of the mainstream smoke from the first cigarette puff     

High-resolution gas chromatography retention data as a basis for estimation of the octanol–water distribution coefficients (<Emphasis Type="Italic">K</Emphasis>ow) of PCB: the effect of experimental conditions

The semi-experimental approach to approximating physicochemical data relevant to environmental distribution (vapor pressure and gas–octanol distribution) by correlation with gas chromatography (GC) retention data has been extended to the determination of Kow values. We estimated Kow values >10⁴ for polychlorinated biphenyls (PCB), which are often derived by liquid chromatography, by correlation with gas chromatographic retention data. Selecting a set of reference compounds with known Kow values for relative retention time (RRT) correlation enables easy and accurate semi-empirical calculation of further Kow values for a given group of congeners. The RRT/log Kow correlation is validated in this paper with regard to the following gas chromatographic conditions: (1) isothermal versus temperature-programmed elution, (2) the possible effect of the polarity of the stationary phase, and (3) the effect of the format of the standardized GC retention data. The advantages of our Kow(GC) method can be summarized as follows: complex mixtures can be analyzed, only amounts in the nanogram-range or less are required, Kow values of isomers can be determined and the exact structure of compounds need not be known. Normalized GC retention data of persistent organic pollutants are readily available. The quality of the Kow values obtained by the GC method compares well with that for other Kow estimation methods. It depends mainly on the accuracy of the Kow data of the structurally correlated compounds used as standards for the correlation cohort. The Kow(GC) data for all 209 PCB congeners are given.Dedicated to the memory of Wilhelm Fresenius     

An adapted isotope dilution 1H–13C heteronuclear single-quantum correlation (ID-HSQC) for rapid and accurate quantification of endogenous and exogenous plasma glucose

Analytical and Bioanalytical Chemistry - A wide variety of methods, such as enzymatic methods, LC-MS, and LC-MS/MS, are currently available for the concentration determination of plasma glucose in...     

Phase analysis of the solidified KF–(LiF–NaF–UF4)–ZrF4 molten electrolytes for the electrowinning of uranium

The X-ray diffraction (XRD) phase analysis of different solidified uranium-based fluoride systems ((LiF–NaF)_eut–UF₄; (KF–LiF–NaF)_eut–UF₄; (LiF–NaF)_eut–UF₄–ZrF₄ and (KF–LiF–NaF)_eut–UF₄–ZrF₄) were examined in order to provide the basis for pyro-electrochemical extraction of uranium in molten fluorides. Several uranium-based species (Na₂UF₆, Na₃UF₇, K₂UF₆, K₃UF₇, UO₂, K₃UO₂F₅) were identified in the solidified melts. The role of oxygen in argon atmosphere was found to be critical in the formation of uranium species during the melting and solidification. In order to reduce the accumulated level of free oxygen traces in our experiments, zirconium (in the form of ZrF₄) was used inside the melt as an oxygen buffer. It was found that ZrF₄ can really stabilize the uranium species by complexation and protects them against the oxygenation. The results of this work highlight the importance of oxygen removal for obtaining pure deposit in the electrorefinning of uranium.     

An SPME–GC–MS method using an octadecyl silica fibre for the determination of the potential angiogenesis modulators 17β-estradiol and 2-methoxyestradiol in culture media

A simple and easily automable method based on solid-phase microextraction followed by gas chromatographic–mass spectrometric analysis was developed for the determination of two potential angiogenesis modulators 17β-estradiol (17-BE) and 2-methoxyestradiol (2-MEOE) in culture media. Trifluoroacetic anhydride was used as the derivatising agent. A homemade octadecyl silica coating, characterised by a coating thickness of 72 ± 10 μm and a good thermal stability until 250 °C, was prepared. Experimental design was used to optimise the extraction conditions in terms of derivatisation time, derivatisation temperature and time of extraction. As for method validation, lower limits of quantification of 0.17 and 0.015 μg/l for 17β-estradiol and 2-methoxyestradiol, respectively, were obtained. Finally, the capabilities of the developed fibres were evaluated for the analysis of the investigated analytes developed by granulosa cells in culture media maintained under normoxic, hypoxic and anoxic conditions, in order to better elucidate their possible role in the angiogenic process. An increase of the production of both 17-BE and 2-MEOE in hypoxic and anoxic conditions seems to be related to the effect of oxygen deprivation.     

An Advanced Intermediate for the Synthesis of (±)‐Pumiliotoxin C and Its Analogues

Abstract

Compound 1 as a versatile intermediate for the synthesis of (±)‐pumiliotoxin C and its analogues was prepared from commercially available cyclohexanone. The key step in the synthesis was the construction of octahydroquinoline ring by a stereoselective aminocyclization.     

Standardized GC–MS (EI) procedure for monitoring the detection and identification performance applied to herbal remedies

A procedure for monitoring the identification performance of GC–MS instrumentation as applied to herbal remedies was established, using eugenol (extracted from cloves) as a control compound. The following parameters were monitored: retention time (acceptable variability 0.5%); signal-to-noise ratio (at least 40% of the initial value); ion intensity ratio (acceptable variability 20%); and identity search result (reverse match, with minimum match value of 850 for quadrupole instruments and 800 for ion trap instrument). Other candidates for control compounds (pulegone, caffeine, and methoxsalen) as well as other parameters (relative retention time, second ion intensity ratio, peak area, and direct match) did not give any additional information concerning variability, observed trends, and sensitivity.     

Modified procedure for the sol–gel processing of indium–tin oxide (ITO) films

Dispersions of crystalline nanoscaled ITO and solutions of amorphous precursors were used for the preparation of transparent conductive films on glass both by large area dip-coating (30 × 30 cm²) and pad-printing. The advantages of both types of coating materials regarding single layer thickness and conductivity were combined by a coating-infiltration procedure. The resulting films showed a specific resistivity down to 1.77 10E−03 Ω cm after treatment in reducing atmosphere and an increased resistance to subsequent storage in air.     

Chitosan–silica nanoparticles catalyst (M@CS–SiO2) for the degradation of 1,1-dimethylhydrazine

Research on Chemical Intermediates - Hybrid materials of chitosan–silica (CS–SiO2) with nonprecious-metallic ions (Cu) immobilized on (Cu–M@CS–SiO2) were developed as green...