Compehensive two-dimensional gas chromatography (GC×GC) and its applicability to the characterization of complex (petrochemical) mixtures

In general, petrochemical products contain only a limited number of chemical classes of compounds (sample dimensionality). The enormous number of individual components within these classes, however, soon puts limitations upon a single chromatographic technique when it comes to adequate characterization of these products. Comprehensive two-dimensional gas chromatography (GC×GC) clearly opens the possibility of estimating the composition of hydrocarbon mixtures in a far more detailed fashion than hitherto possible. Although the emphasis of papers of GCxGC thus far almost exclusively applies to the unsurpassed peak-capacity, in the oil industry there is a need for characterization, rather than for analyzing all the individual compounds. In principle a GCxGC system can provide an almost perfect match between its intrinsic properties and the dimensionality of oil samples. To establish the applicability of GCxGC towards petrochemical analytical challenges, a commercially aavailable prototype instrument was subjected to an exhaustive characterization of a typical hydrocarbon precess stream and a fast characterization of a light gas oil. Although there are no fundamental limitations towards the quantitative aspects of a GCxGC system, this paper confines itself to qualitative results only. Quantitative aspects of GCxGC will be published in a forthcoming paper.     

Characterisation of core-shell latexes by flow field-flow fractionation with multi-angle light scattering detection

Flat channel asymmetrical flow field-flow fractionation with multi-angle light scattering (MALS) detection was used to study the swelling behaviour of core-shell particles with either carboxylated or hydroxylated shells as a function of pH and ionic strength. The equilibration time of the most heavily carboxylated core-shells appeared to be of the order of several hours. At low ionic strength (5 mM), the carboxylated core-shells showed a definite swelling response to a change in pH in the range from 5 to 10, ranging from a hydrodynamic radius increase of 24 to 118%, depending on the degree of carboxylation. A much milder response was found for the change of the root mean square (r.m.s.) radius as measured with MALS, indicating that the scattering plane is moving inwards during the swelling process due to a decreasing density of the shell. The hydroxylated core-shells appeared to be inert to a change in pH. Also the response of two expanded (pH 10) carboxylated core-shells on increasing ionic strength was studied. Comparison of the results of these ionic strength experiments with theoretical predictions based on Donnan equilibrium led us to the conclusion that a significant amount of counter-ion condensation may take place in the shells.     

The characterization and quantitation of sulfur-containing compounds in (heavy) middle distillates by LC-GC-FID-SCD

A modified sulfur chemiluniinescence detector (SCO) has been interfaced to a HPLC-HRGC hyphenated system. This combination enables the full characterization and quantitation of the sulfur containing compounds in (heavy) middle distillate oil fractions (boiling range 150–450°C). The system is suited to identify and determine the various groups of orgaiio-sulfur structures such as: thiols + sulfides + thiophencs, benzothiophenes, dibenzothiophenes and benzo-naphthothiophenes. Within these groups a separation according to boiling point is accomplished. Therefore it allows the separation, identification and quantitation of a number of individual species, especially those which are refractory to hydrodesulfu-rization (HDS), such as 3-methyl-benzothiophene, 4-methyl-dibenzothiophene and -J,6-dimethyl-dibenzothiophene. The analysis of these groups and specific compounds is the key in understanding the kinetics of the chemistry involved in HDS. The complete instrumental set-up is fully automated by computer control. To suppress possible interferences and quenching of the sulfur response of the SCL from (large amounts of) hydrocarbons, it is aligned above the adapted flame ionization detector (FID) of the GC. This renders a sensitivity of the SCO for sulfur of 2 pg. s^?1, which corresponds to a minimum detectable level for individual sulfur species in oil fractions for the complete system of 1 ppm (mg. kg^?1) sulfur. Its linear dynamic range exceeds 10⁵, which means that also untreated, high sulfur containing feedstocks can be analyzed directly. The selectivity of sulfur to carbon of the modified SCO exceeds 10⁶. A number of HDS feedstocks and desulfurized products of different desulfurization levels have been analyzed with the system. From the analysis results the behavior of the refractory compounds in HDS can now be followed closely.     

Balinski—Tucker simplex tableaus: Dimensions, degeneracy degrees, and interior points of optimal faces

This paper shows the relationship between degeneracy degrees and multiple solutions in linear programming (LP) models. The usual definition of degeneracy is restricted to vertices of a polyhedron. We introduce degeneracy for nonempty subsets of polyhedra and show that for LP-models for which the feasible region contains at least one vertex it holds that the dimension of the optimal face is equal to the degeneracy degree of the optimal face of the corresponding dual model. This result is obtained by means of the so-called Balinski—Tucker (B—T) Simplex Tableaus. Furthermore, we give a strong polynomial algorithm for constructing such a B—T Simplex Tableau when a solution in the relative interior of the optimal face is known. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.     

Electrically driven capillary size exclusion chromatography

Summary Electrically driven size exclusion chromatography (ED-SEC) of polystyrenes in packed capillaries using dimethylformamide as solvent is demonstrated. The efficiency and retention behaviour of polystyrenes under pressure and electro drive were investigated. Under pressure drive the plate height (H) increases steadily with increasing linear velocity (u) whereas under electro drive the H-u curves largely coincide and are very flat. At higher velocities the plate heights are about 50% smaller with electro drive than with pressure drive. Calculations show that with increasing ionic strength, the flow through the particles may increase causing a clear diminishing of the elution window.     

Synergistic Interaction of Photodynamic Treatment with the Sensitizer Aluminum Phthalocyanine and Hyperthermia on Loss of Clonogenicity of CHO Cells

Abstract— When CHO cells were exposed to hyperthermia and subsequently to photodynamic treatment, the combined effects were additive but in the reverse sequence the interaction was synergistic. The synergistic interaction comprised two quite different components: (1) photodynam-ically induced sensitization of cellular proteins and/or supramolecular structures for thermal inactivation and (2) a photodynamically induced inhibition of the cellular repair system for sublethal thermal damage. The first component of the synergistic interaction was reflected by a change of the Arrhenius parameters of thermal cell killing. A lowering of the activation energy of this process was responsible for the synergistic interactions, whereas a concomitant decrease of the frequency factor, opposing this effect, actually caused a much lower degree of synergism at higher temperatures. This component of the synergistic interaction did not respond to the insertion of an intermediate incubation period between the two treatments. The second component of the synergistic interaction, viz. the interference with the ability of cells to survive sublethal thermal damage, was reversible, as an intermediate incubation between photodynamic treatment and hyperthermia resulted in its repair. The photodynamically induced inhibition of the ability of cells to survive sublethal thermal damage was not related to ATP or glutathione depletion, inhibition of de novo protein synthesis or impairment of degradation of damaged protein molecules. Restoration of the repair system for sublethal damage depended on a metabolic process and required free intracellular Ca²⁺, suggesting that a cell signaling pathway may be involved. Thus, in a practical sense the magnitude of the synergistic interaction between photodynamic treatment and hyperthermia depends on the length of the interval between the two treatments and on the temperature and duration of the subsequent thermal treatment. This may have significant consequences for the development of clinical protocols.     

Packed-column hydrodynamic chromatography using 1-μm non-porous silica particles

150×3 mm I.D. columns, packed with 1-μm non-porous spherical silica particles, were used to separate soluble synthetic polymers by hydrodynamic chromatography. The columns exhibited a plate height of about 1.4 μm allowing very fast and efficient separations of polymers in the molecular mass range 10³−2·10⁶ g/mol. The migration behaviour of polymers could be well described by a simple theoretical model. The applicability of packed bed HDC for the fast separation of polymers was illustrated with separations of polystyrene and poly(methyl methacrylate) mixtures.     

Solving the Simple Plant Location Problem using a Data Correcting Approach

The Data Correcting Algorithm is a branch and bound type algorithm in which the data of a given problem instance is `corrected' at each branching in such a way that the new instance will be as close as possible to a polynomially solvable instance and the result satisfies an acceptable accuracy (the difference between optimal and current solution). In this paper the data correcting algorithm is applied to determining exact and approximate optimal solutions to the simple plant location problem. Implementations of the algorithm are based on a pseudo-Boolean representation of the goal function of this problem, and a new reduction rule. We study the efficiency of the data correcting approach using two different bounds, the Khachaturov-Minoux bound and the Erlenkotter bound. We present computational results on several benchmark instances, which confirm the efficiency of the data-correcting approach.     

Control of plasmon resonance of gold nanoparticles via excimer laser irradiation

A significant shift of the surface plasmon resonance absorption spectrum of gold nanoparticles was obtained by the oxidation of the nanoparticle surface via pulsed excimer laser irradiation. The high UV-light absorption of gold nanoparticles chemically produced by citrate reduction led to the important surface oxidation up to 26%. As a result of laser irradiation, the gold/gold oxide core-shell nanoparticles with little variation of the nanoparticle size were produced. After only 5 min of laser irradiation, a 12-nm blue shift in surface plasmon resonance was obtained. The possible mechanisms governing the modification in surface plasmon resonance by laser irradiation of gold nanoparticles were discussed.