Selective Detection of Volatile Organics in a Mixture Using a Photoionization Detector and Thermal Desorption from a Nanoporous Preconcentrator

The selective detection of individual hazardous volatile organic compounds (VOCs) within a mixture is of great importance in industrial contexts due to environmental and health concerns. Achieving this with inexpensive, portable detectors continues to be a significant challenge. Here, a novel thermal separator system coupled with a photoionization detector has been developed, and its ability to selectively detect the VOCs isopropanol and 1-octene from a mixture of the two has been studied. The system includes a nanoporous silica preconcentrator in conjunction with a commercially available photoionization detector (PID). The PID is a broadband total VOC sensor with little selectivity; however, when used in conjunction with our thermal desorption approach, selective VOC detection within a mixture can be achieved. VOCs are adsorbed in the nanoporous silica over a 5 min period at 5 °C before being desorbed by heating at a fixed rate to 70 °C and detected by the PID. Different VOCs desorb at different times/temperatures, and mathematical analysis of the set of PID responses over time enabled the contributions from isopropanol and 1-octene to be separated. The concentrations of each compound individually could be measured in a mixture with limits of detection less than 10 ppb_v and linearity errors less than 1%. Demonstration of a separation of a mixture of chemically similar compounds, benzene and o-xylene, is also provided.

α-Chitin Nanocrystals Prepared from Shrimp Shells and Their Specific Surface Area Measurement

Alpha-chitin was isolated from shrimp shells. The chitin was subjected to extensive treatments of acid hydrolysis and mechanical disruption to yield nanocrystals. The goal of this article is to characterize alpha-chitin nanocrystals produced from shrimp shells in regard to crystallite properties and the specific surface area of the chitin nanoparticles. X-ray diffraction data indicate an increase in chitin crystallinity after hydrolysis, as less-ordered chitin domains are digested. Line broadening data were used to measure crystallite size and particle size in the hydrolyzed chitin nanocrystals. Dye adsorption with Congo red was used to measure the specific surface area of the particles, indicating values near 350 m2/g. This value was supported with calculations derived from X-ray crystallite size measurements. Particle surface area measurements were compared with similarly prepared cellulose nanocrystals.

Effect of sulfate groups from sulfuric acid hydrolysis on the thermal degradation behavior of bacterial cellulose

When used as fillers in polymer composites, the thermostability of cellulose crystals is important. Sulfate groups, introduced during hydrolysis with sulfuric acid, are suspected to diminish the thermostability. To elucidate the relationship between the hydrolysis conditions, the number of sulfate groups introduced, and the thermal degradation behavior of cellulose crystals, bacterial cellulose was hydrolyzed with sulfuric acid under different hydrolysis conditions. The number of sulfate groups in the crystals was determined by potentiometric titration. The thermal degradation behavior was investigated by thermogravimetric analysis. The sulfate group content increased with acid concentration, acid-to-cellulose ratio, and hydrolysis time. Even at low levels, the sulfate groups caused a significant decrease in degradation temperatures and an increase in char fraction confirming that the sulfate groups act as flame retardants. Profile analysis of the derivative thermogravimetric curves indicated thermal separation of the degradation reactions by the sulfate groups into low- and high-temperature processes. The Broido method was used to determine activation energies for the degradation processes. The activation energies were lower at larger amounts of sulfate groups suggesting a catalytic effect on the degradation reactions. For high thermostability in the crystals, low acid concentrations, small acid-to-cellulose ratios, and short hydrolysis times should be used.

Effect of sulfate groups from sulfuric acid hydrolysis on the thermal degradation behavior of bacterial cellulose

When used as fillers in polymer composites, the thermostability of cellulose crystals is important. Sulfate groups, introduced during hydrolysis with sulfuric acid, are suspected to diminish the thermostability. To elucidate the relationship between the hydrolysis conditions, the number of sulfate groups introduced, and the thermal degradation behavior of cellulose crystals, bacterial cellulose was hydrolyzed with sulfuric acid under different hydrolysis conditions. The number of sulfate groups in the crystals was determined by potentiometric titration. The thermal degradation behavior was investigated by thermogravimetric analysis. The sulfate group content increased with acid concentration, acid-to-cellulose ratio, and hydrolysis time. Even at low levels, the sulfate groups caused a significant decrease in degradation temperatures and an increase in char fraction confirming that the sulfate groups act as flame retardants. Profile analysis of the derivative thermogravimetric curves indicated thermal separation of the degradation reactions by the sulfate groups into low- and high-temperature processes. The Broido method was used to determine activation energies for the degradation processes. The activation energies were lower at larger amounts of sulfate groups suggesting a catalytic effect on the degradation reactions. For high thermostability in the crystals, low acid concentrations, small acid-to-cellulose ratios, and short hydrolysis times should be used.

Determination of the 8B neutrino spectrum

We have measured the total energy of the alpha particles following the beta decay of 8B by implanting 8B into a planar silicon surface barrier detector. Calibration was performed using alpha particles following the beta decay of 20Na, similarly implanted. The alpha spectrum is used to infer the 8B neutrino spectrum which is an important input in the interpretation of experiments that detect energetic neutrinos from the Sun. The alpha spectrum reported here is in disagreement with the previous best measurement which used two detectors in coincidence.

The crystal and molecular structure of VH amylose by electron diffraction analysis

The crystal and molecular structures of VH amylose were determined by a constrained linked-atom least-squares refinement, utilizing intensities measured from electron diffraction patterns and stereochemical restraints. Hexagonal platelet single crystals were grown from dilute aqueous ethanol solution and their electron diffraction diagrams analysed. These data indicated that the amylose chains were crystallized in a hexagonal lattice with a = b = 13.65 A, c (chain axis) = 8.05 A and space group P6(5)22. The best model obtained using the base plane data coupled with a stereochemical refinement yielded R = 0.24 (R'' = 0.25). It corresponded to a system of left-handed 6-fold helices packed on an hexagonal net but with statistically random up/down chain disorder. A column of six water molecules was present within each helical repeat. Additionally, the gap between each pair of adjacent helices was bridged by two water molecules positioned so as to allow hydrogen bonding with chains of either sense. This proposed crystal structure differs somewhat from previous reports which invoked orthorhombic lattices and requires a regularly alternating arrangement of up and down chains to account for the intensity. Suggestions are made to account for these differences.

Solid-state 13C NMR and X-ray diffraction of dermatan sulfate

Dermatan sulfate in the solid state has been studied by 13C CP/MAS nmr and X-ray diffraction in order to establish the ring conformation of the L-iduronate moiety. The solid state nmr spectrum is similar to the solution spectrum obtained previously, indicating that a ring conformation at least approximating to 1C4 predominates in the solid state. X-ray powder diffraction data from the same sample indicate the presence of the 8-fold helix form previously observed by fiber diffraction, and interpreted in terms of a 4C1 ring form. A likely explanation of the results is that a distorted 1C4 L-iduronate ring conformation, not considered in the initial X-ray analysis, may emerge to provide a satisfactory interpretation of all available physical-chemical data.

Studies on some characteristics of hydrogen production by cell-free extracts of rumen anaerobic bacteria

Hydrogen production was studied in the following rumen anaerobes: Bacteroides clostridiiformis, Butyrivibrio fibrisolvens, Enbacterium limosum, Fusobacterium necrophorum, Megasphaera elsdenii, Ruminococcus albus, and Ruminococcus flavefaciens. Clostridium pasteurianum and Escherichia coli were included for comparative purposes. Hydrogen production from dithionite, dithionite-reduced methyl viologen, pyruvate, and formate was determined. All species tested produced hydrogen from dithionite-reduce methyl viologen, but only C. pasteurianum, B. clostridiiformis, E. limosum, and M. elsdenii produced hydrogen from dithionite. All species except E. coli produced hydrogen from pyruvate, but activity was low or absent in extracts of E. limosum, F. necrophorum, R. albus, and R. flavefaciens unless methyl viologen was added. Hydrogen was produced from formate only by E. coli, B. clostridiiformis, E. limosum, F. necrophorum, and R. flavefaciens. Extracts were subjected to ultracentrifugation in an effort to determine the solubility of hydrogenase. The hydrogenase of all species except E. coli appeared to be soluble, although variable amounts of hydrogenase activity were detected in the pellet. Treatment of extracts of the rumen microbial species with DEAE-cellulose resulted in loss ofhydrogen production from pyruvate. Activity was restored by the addition of methyl viologen. It is concluded that hydrogen production in these rumen microorganisms is similar to that in the saccharolytic clostridia.

Details of glycosaminoglycan conformations and intermolecular interactions

Among the mucopolysaccharides, similarities of chemical constitution are manifested in the similar molecular conformations that can be assumed by most of them. The differences, however, result in a preference for particular conformations. Small amounts of one glycosaminoglycan in a mixture can change the conformational preference of the major component. Advances in the techniques of fiber diffraction analysis allow us to visualize the roles of water and ions in some of these structures and to rationalize the strikingly different effects produced by Ca2+ and Na+ in hyaluronate systems, for example.